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fine grinding occur

grinding tips - baratza

grinding tips - baratza

We have done extensive testing on our grinders with the most popular brewing methods and have come up with some settings that we think are great starting points. The key is to get started with your grinder and then adjust to your own preferred taste.

In addition to our grinding tips, you could ask the Roaster of the beans you purchased, or your local Caf, to give you a grind sample for the brew method you plan to use, then reproduce this grind sample on your grinder. Fine tune as you taste what you prefer.

Our multipurpose grinders allow you to explore different ways to make coffee in the journey to your favorite cup. There are many sources available with information on how to make any type of coffee you care to brew. Coffee professionals around the world have varying viewpoints about the best grind for different brewing methods and it might be overwhelming. Check out www.brewmethods.com.au to learn about different recipes for each or find new brewing methods to explore.

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 Internationally US & Canada Espresso AeroPress Hario V60 Automatic Brewer Chemex French Press

Please adjust the grind setting either with the unit completely empty of coffee, or with the machine running. When adjusting to a finer grind setting, the burrs are drawing closer together. If there are beans in the burrs and the unit is off, the beans are resisting the movement of the burrs. We explain more in this blog.

When using cleaning tablets we recommend setting your conical (Encore, Virtuoso+) grinder around the setting of #20 and setting the flat burr grinders (Vario and Forte) at a setting of #5. Thats just around the middle of your grind range allowing for a solid cleaning as the pellets are ground to powder. At finer settings we have seen clogging occur and possible mechanical damage. Follow your cleaning cycle with 30-40 gram coffee bean to purge any cleaner left in the grinder.

grinding cylpebs

grinding cylpebs

Our automatic production line for the grinding cylpebs is the unique. With stable quality, high production efficiency, high hardness, wear-resistant, the volumetric hardness of the grinding cylpebs is between 60-63HRC,the breakage is less than 0.5%. The organization of the grinding cylpebs is compact, the hardness is constant from the inner to the surface. Now has extensively used in the cement industry, the wear rate is about 30g-60g per Ton cement.

Grinding Cylpebs are made from low-alloy chilled cast iron. The molten metal leaves the furnace at approximately 1500 C and is transferred to a continuous casting machine where the selected size Cylpebs are created; by changing the moulds the full range of cylindrical media can be manufactured via one simple process. The Cylpebs are demoulded while still red hot and placed in a cooling section for several hours to relieve internal stress. Solidification takes place in seconds and is formed from the external surface inward to the centre of the media. It has been claimed that this manufacturing process contributes to the cost effectiveness of the media, by being more efficient and requiring less energy than the conventional forging method.

Because of their cylindrical geometry, Cylpebs have greater surface area and higher bulk density compared with balls of similar mass and size. Cylpebs of equal diameter and length have 14.5% greater surface area than balls of the same mass, and 9% higher bulk density than steel balls, or 12% higher than cast balls. As a result, for a given charge volume, about 25% more grinding media surface area is available for size reduction when charged with Cylpebs, but the mill would also draw more power.

stump grinding vs removal - pros, cons, comparisons and costs

stump grinding vs removal - pros, cons, comparisons and costs

There are many reasons for choosing to eliminate tree stumps in your yard. Apart from improving the aesthetics and sanitation concerns, it also ensures the safety of family members and neighbors. However, the challenge is deciding which method to adopt. Stump removal and stump grinding are two common techniques, and yet they are quite different in terms of removal. We describe the two forms of eliminating stumps to help you decide which option is best for you.

Eliminating the stumps in your yard is one of the most important aspects of tree maintenance and should be executed carefully. If you have second thoughts about eliminating stumps, here are some advantages for carrying out this task:

Stump grinding is an intricate process that excavates the stump of the tree without removing the root. In this situation, a stump grinder is employed to mechanically grind out the stump, leaving fine sawdust as a residue. The advantage of tree stump grinding is that the stump is ground down to your desired height. The grinding can be just 1 inch below the soil level or as low as 12 inches underground.

Since the stump is ground, it eventually mixes with the soil. This levels the ground and eliminates the need for extra filling. If, however, the stump is infected with honey fungus, which can kill the roots of perennial plants, it is advisable to dispose of the mulch1 and the residual sawdust.

In essence, the process of stump grinding is preferred for many reasons. It is far easier to execute and uses efficient tools to get the job done. Unlike stump removal, which leaves the environment in a messy state, stump grinding provides a greater level of neatness and environmental friendliness.

On the other hand, stump removal eliminates both the root and stump. So, you are sure that theres no chance of regrowth or sprout. You should bear in mind, however, that the process of disposing of the stump and root is more extensive and expensive.

Factors such as the diameter of the stump, age of the tree, soil type, root system, and number of stumps determine the cost of stump excavation. Some tree removal services stipulate a minimum service charge for the process and often, there is a discount on additional stumps.

For stump removal, the price ranges between $370 and $675 per stump. Normally, a more difficult stump, which takes more time to remove, costs considerably more. The cost of disposing of the stump and root may cost an additional $25. However, some companies charge by the hour.

For stump grinding, the average price range is from $75 to $400 per stump. The price can exceed $600 if it takes more time to grind the stump due to the topology of the area, age of the tree, or root system.

One major difference between both processes is that tree stump removal removes the root as well as the stump. This is what creates the large hole after removal. However, with tree stump grinding, the stump is ground, and the root is left to decay.

If the process of replanting a tree on that spot appeals to you, the best option is to remove the stump and root completely. Tree removal clears the surface and ensures that subsequent plantings are free to grow.

glen mills powder mixing, milling, and particle reduction

glen mills powder mixing, milling, and particle reduction

The mixing basket can hold any form of container having a maximum volume of 2 liters. The containers are fastened in place by twisted rubber rings. The basket movement is driven by elastic drive belts and an eccentric drive gear. The speed can be varied by adjusting the position of the drive belts on its 5 step pulleys. The speed can also be adjusted optional frequency converter set up next to the machine.

The mixing basket can hold up to 66 pounds in a 17 liter container. Twisted rubber clamping rings allow the use of smaller containers up to a maximum diameter of 220 mm. The movement of the mixing basket is controlled by a silent pendulum chain drive. The speed can be varied by adjusting the position of the round drive belt on the 4-step pulley.

The mixing basket can hold up to 165 pounds in a 55 liter container. Special holders must be mounted for smaller containers. These inserts are custom designed to fit the dimensions of your mixing vessel. The movement of the mixing basket is controlled by a silent pendulum chain drive and the speed can be varied by adjusting the position of the V-belt on the 5-step pulley. An extra slow speed drive is used to bring the mixing basket into its loading position. A hand cart can be purchased to help with loading.

Model equipped for both high speed revolution and a wide radius gyration, supporting for the production of high quality materials. The timing by which the revolving speed of rotation increases is controlled to improve the mixing rate of powders and liquids and sustains the generation of lumps.

90 different revolution-rotation speed patterns are available by varying the ratio of revolution and rotation. A high function model for covering from research and development to small-scale production.

A model with a vacuum reduced pressure function suited for medium-scale production. The individual revolution and rotation speed control system and wide radius gyration generate centrifugal force even at low revolving speeds, sustaining material of thermal elevation and composition change.

A high function model with a vacuum reduced pressure function. The individual revolution and rotation speed control system and the shifted cup tray enhance mixing performance and provide effective degassing.

A jet mill grinds materials by using a high speed jet of compressed air or inert gas to impact particles into each other. Jet mills can be designed to output particles below a certain size, while continue milling particles above that size, resulting in a narrow size distribution of the resulting product. Particles leaving the mill can be separated from the gas stream by cyclonic separation.

With two sharp, robust blades and apowerful 1000 W motor, it is ideal for homogenizing substances with a high water, oil or fat content as well as for grinding dry, soft and medium-hard products. Awide selection of lids and containersallows for adaptation of the mill toindividual application requirements. The GRINDOMIX GM 200 meets andexceeds all special laboratory and analytical requirementsand is a professional device superior to any commercial household mixer.

The mixer mill MM 200 is a compact versatile benchtop unit, which has been developed specially for dry grinding of small amounts of sample. It can mix and homogenize powders in only a few seconds. It is also perfectly suitable for the disruption of biological cells as well as for DNA/RNA extraction.

You may also be interested in theHigh Energy Ball Mill Emax, an entirely new type of mill for high energy input. The unique combination of high friction and impact results in extremely fine particles within the shortest amount of time.

With itsadjustable speedof 3,000 to 10,000 rpm the rotor beater mill SR 300 is intended foruniversal use: from sample preparation in laboratories up to preparing sample batches in pilot plants or production facilities. The grinding chamber, the feed hopper and the material inlet are completely made fromhigh quality stainless steel.

The SM 100 is thebudget-priced basic model among the cutting mills. With its strong 1.5 kW drive and 1,500 rpm rotor speed the mill is particularlysuitable for routine applications. Cleaning is made particularly easy.

In combination with the wide choice of bottom sieves, hoppers and collecting vessels, the mill can be easily adapted to varying application requirements. The SM 100 can be bench-mounted; alternatively a convenient base frame on wheels is available.

Cutting mills are suitable for thegrinding of soft, medium-hard, elastic, fibrous, and heterogeneous mixes of products.The new cutting mill SM 200 is a powerful and easy-to-operate instrument for efficient primary and fine size reduction.Cleaning is made particularly easy.

Within the group of the cutting mills, it is the universal standard modelwhichcovers a vast range of applicationswith its strong 2.2 kW drive and 1,500 rpm rotor speed.When operated with theoptional cyclone-suction-combination, the SM 200 is also suitable for grinding light sample materials or smaller quantities. In combination with the wide choice of bottom sieves, hoppers and collecting vessels, the mill can be easily adapted to varying application requirements.

Cutting mills are suitable for thegrinding of soft, medium-hard, tough, elastic, fibrous, and heterogeneous mixes of products.The new Cutting Mill SM 300excels especially in the tough jobswhere other cutting mills fail.

Thehigh torqueof the new 3 kW drive withRES technology(additional flywheel mass) allows for an exceptionally effective preliminary size reduction of heterogeneous mixtures, such as waste or electronic components. Analytical fineness is often achieved in one working run.

The cutting mill is used successfully for a great variety of materials. The sample is only moderately warmed up during the grinding process so that the mill is perfectly suitable forgrinding temperature-sensitive materials.Another innovation is the wide, freelyselectable speed range from 100 to 3,000 min-1.

When operated with theoptional cyclone-suction-combination, the SM 300 is also suitable for grinding light sample materials or smaller quantities. In combination with the wide choice of bottom sieves, hoppers and collecting vessels, the mill can be easily adapted to varying application requirements.

Cutting mills are suitable for thegrinding of soft, medium-hard, tough, elastic, fibrous, and heterogeneous mixes of products.The Cutting Mill SM 400 is ideally suited for pre-cutting of large sample pieces but, depending on the application, may also achieve the required fineness in one step.

The cutting mill is used successfully for a great variety of materials. The sample is only moderately warmed up during the grinding process so that the mill is perfectlysuitable for grinding temperature-sensitive materials.Due to the large open surface of the 240 mm x 240 mm bottom sieve, it is possible to grind large sample quantities and to increase the throughput.

When operated with theoptional cyclone-suction-combination, the SM 400 is also suitable for grinding light sample materials. In combination with the wide choice of bottom sieves, hoppers and collecting vessels, the mill can be easily adapted to varying application requirements.

Analysis or quality control requires finely ground samples. Easy to change grinding attachments and sieves extend the range of any samples that can be processed. Simple handling, high user safety and efficient grinding results are just a few of the advantages of this mill.

The fluid bed dryer TG 200 is used in quality control, sample preparation and R&D departments. It permits thegentle dryingof organic, inorganic, chemical or pharmaceutical bulk materialswithout localized overheating.Suitable materials can be coarse, fine, crystalline, fibrous or leafy. The powerful fan of the fluid bed dryer ensuresoptimal air throughputso that the products to be dried are loosened up and thoroughly mixed resulting inshort drying times.With the interval operation the fluidized bed is mixed even better. Temperature, drying time and air volume can be set digitally and adjusted continuously.

The PP 35 features an individual pressure force regulation in the range of 0 to 35 t. The PP 35 combines the advantage of a small bench top model with high press forces, which are built automatically in up to three steps, ensuring that even difficult materials are pressed perfectly.

The ultrasonic bath range UR includes three sizes forcleaning test sieves and grinding tools quickly and easily.UR 1 is for test sieves up to 203 mm dia., UR 2 for test sieves up to 450 mm dia., and the UR 3 for the simultaneous cleaning of up to 5 test sieves 200/203 mm dia. The gentle yet thorough cleaning of test sieves in an ultrasonic bathincreases their working livesas damage which could occur during manual cleaning is avoided.

The vibratory feeder DR 100 is used for theuniform, continuous feeding and conveyance of pourable bulk materials and fine powders. The DR 100 feeds mills, sample dividers, and particle measuring devices, and it is also suitable for other feeding tasks. Its performance, adaptability and compact design makes this device suitable for agreat variety of applications.The DR 100 can also bedriven and controlled externallyvia the built-in interface. Vibratory feeders guarantee reproducibly exact resultsand maximize the efficiency of downstream laboratory and testing devices.

Afaultless and comparable analysis is closely linked to an accurate sample handling.Only a sample representative of the initial material can provide meaningful analysis results. Sample splittersensure the representativeness of a sample and thus the reproducibility of the analysis.

The RT 100 is equipped with a feed hopper with closed outlet. Thus,up to 30 l sample materialmay be evenly spread over the entire width of the hopper. The outlet is opened manually by moving a lever and the sample is splitted. The slots of the dividing head can be adjusted to a maximum width of 108 mm.

Solid, high-quality pellets are an important precondition for reliable and meaningful XRF analysis. The PP 25 is a compact benchtop unit with particularlysimple and safe operation.With apressure force of 25 tit is ideally suited for thepreparation of solid samples for XRF analysis.The pellets produced are ofhigh qualityand are characterized by theirhigh degree of stability.The piston pressure can be read off from the clearly visible manometer scale. The dies for the Pellet Press PP 25 are available in several diameters and can be evacuated completely.

The well-proven RETSCH sieves consist of a solid stainless steel sieve frame of high stability for reliable sieving results. Paying close attention to mesh-specific requirements, the sieve fabric is precisely joined into the frame and tautened. RETSCH test sieve provides a clear and accurate labeling with full traceability.

The sieves can be easily combined with all other sieve brands. Each sieve that leaves our company comes with a test report or, at your request, with a special inspection certificate in conformity withnational and international standards (PDF). RETSCH calibration certificates confirm a great number of precision measurements, thus ensuring an even higher statistical reliability for your quality control.

The well-proven RETSCH sieves consist of a solid stainless steel sieve frame of high stability for reliable sieving results. Paying close attention to mesh-specific requirements, the sieve fabric is precisely joined into the frame and tautened. The individual laser engraving of each RETSCH test sieve provides a clear and accurate labeling with full traceability.

The sieves can be easily combined with all other sieve brands. Each sieve that leaves the company comes with a test report or, at your request, with a special inspection certificate in conformity with national and international standards (PDF). RETSCH calibration certificates confirm a great number of precision measurements, thus ensuring an even higher statistical reliability for your quality control.

The vibratory sieve shakers of the series AS 200 are used in research & development, quality control of raw materials, interim and finished products as well as in production monitoring. The controllable electromagnetic drive offers an optimal adaption for every product. Sharp fractions are obtained even after short sieving times.

The analytical sieve shakers of the series AS 200 are used in research & development, quality control of raw materials, interim and finished products as well as in production monitoring. The controllable electromagnetic drive offers an optimal adaption for every product. Sharp fractions are obtained even after very short sieving times.

With its all-digital controls, up to 99 sieving programs and calibration certificate the sieve shaker AS 200 control is indispensable for all users who attach importance to precision and operational convenience and need to comply with the guidelines of the ISO 9001.

The analytical sieve shakers of the series AS 200 are used in research & development, quality control of raw materials, interim and finished products as well as in production monitoring. The controllable electromagnetic drive offers an optimal adaption for every product. Sharp fractions are obtained even after short sieving times.

The new Air Jet Sieve AS 200 jet is particularly suitable for sieve cuts of powdered materials which require efficient dispersion and deagglomeration. The option to store up to 10 SOPs and the automatic vacuum regulator (accessory) guarantees reproducible and meaningful results.

The analytical sieve shaker AS 200 tap is used in research & development, quality control of raw materials, interim and finished products as well as in production monitoring. Its tapping motion supports the sieve analysis of certain products such as activated carbon, abrasives, metal powder, spices and diamonds, as specified in the corresponding standards.

The analytical sieve shaker AS 300 control is used in research & development, quality control of raw materials, interim and finished products as well as in production monitoring. The controllable electromagnetic drive offers an optimal adaption for every product. Sharp fractions are obtained even after short sieving times.

The AS 300 control is particularly designed for test sieves with a diameter of 305 mm (12). Compared to sieves with a diameter of 200 mm, a 2.25 times higher sieving surface is available. Therefore, the average sieving times can be greatly reduced with the AS 300 control. With its all-digital controls and calibration certificate the sieve shaker AS 300 control is indispensable for all users who attach importance to precision and operational convenience and need to comply with the guidelines of the ISO 9001.

The AS 400 control is used for the sieving of dry goods with test sieves of a diameter up to 400 mm. In this, the uniform, horizontal circular motion ensures exact separation of fine and coarse-grained products.

With its all-digital controls and calibration certificate the AS 400 control is indispensable for all users who attach importance to precision and operational convenience and need to comply with the guidelines of the ISO 9001.

The AS 450 basic, is a budget-priced alternative to the AS 450 control sieve shaker. The new sieve shaker covers a size range from 25 m to 125 mm and accepts loads of up to 15 kg. Time and amplitude are digitally set, a memory function allows storage of one program. The AS 450 basic is suitable for dry and wet sieving. It is the economic solution for customers who need to sieve larger quantities of dry material with reliable results.

The analytical sieve shaker AS 450 control is used in research & development, quality control of raw materials, interim and finished products as well as in production monitoring. The controllable electromagnetic drive offers an optimal adaption for every product. Sharp fractions are obtainable even after very short sieving times.

With the sieve shaker AS 450 control RETSCH have designed their first sieve shaker for 400 mm and 450 mm sieves which operates with a three-dimensional sieving motion. It can be used for dry and wet sieving. The optimized electromagnetic drive technology allows for an amplitude up to 2.2 mm even with maximum loads up to 25 kg. This makes the AS 450 superior to all other known sieve shakers based on conventional electromagnetic or imbalance drives.

choosing the right grinding wheel |
 

 modern machine shop

choosing the right grinding wheel | modern machine shop

Grinding wheels are generally labeled with a maximum safe operating speed. Don't exceed this speed limit. The safest course is not even to mount a given wheel on any grinder fast enough to exceed this limit.

In a grinding wheel, the abrasive performs the same function as the teeth in a saw. But unlike a saw, which has teeth only on its edge, the grinding wheel has abrasive grains distributed throughout the wheel. Thousands of these hard, tough grains move against the workpiece to cut away tiny chips of material.

Abrasive suppliers offer a wide array of products for a wide array of grinding applications in metalworking. Choosing the wrong product can cost the shop time and money. This article presents some of the fundamentals of selecting the best grinding wheel for the job.

Grinding wheels and other bonded abrasives have two major components-the abrasive grains that do the actual cutting and the bond that holds the grains together and supports them while they cut. The percentages of grain and bond and their spacing in the wheel determine the wheel's structure.

The particular abrasive used in a wheel is chosen based on the way it will interact with the work material. The ideal abrasive has the ability to stay sharp with minimal point dulling. When dulling begins, the abrasive fractures, creating new cutting points.

Aluminum oxide is the most common abrasive used in grinding wheels. It is usually the abrasive chosen for grinding carbon steel, alloy steel, high speed steel, annealed malleable iron, wrought iron, and bronzes and similar metals. There are many different types of aluminum oxide abrasives, each specially made and blended for particular types of grinding jobs. Each abrasive type carries its own designation-usually a combination of a letter and a number. These designations vary by manufacturer.

Zirconia alumina is another family of abrasives, each one made from a different percentage of aluminum oxide and zirconium oxide. The combination results in a tough, durable abrasive that works well in rough grinding applications, such as cut-off operations, on a broad range of steels and steel alloys. As with aluminum oxide, there are several different types of zirconia alumina from which to choose.

Ceramic aluminum oxide is the newest major development in abrasives. This is a high-purity grain manufactured in a gel sintering process. The result is an abrasive with the ability to fracture at a controlled rate at the sub-micron level, constantly creating thousands of new cutting points. This abrasive is exceptionally hard and strong. It is primarily used for precision grinding in demanding applications on steels and alloys that are the most difficult to grind. The abrasive is normally blended in various percentages with other abrasives to optimize its performance for different applications and materials.

Once the grain is known, the next question relates to grit size. Every grinding wheel has a number designating this characteristic. Grit size is the size of individual abrasive grains in the wheel. It corresponds to the number of openings per linear inch in the final screen size used to size the grain. In other words, higher numbers translate to smaller openings in the screen the grains pass through. Lower numbers (such as 10, 16 or 24) denote a wheel with coarse grain. The coarser the grain, the larger the size of the material removed. Coarse grains are used for rapid stock removal where finish is not important. Higher numbers (such as 70, 100 and 180) are fine grit wheels. They are suitable for imparting fine finishes, for small areas of contact, and for use with hard, brittle materials.

To allow the abrasive in the wheel to cut efficiently, the wheel must contain the proper bond. The bond is the material that holds the abrasive grains together so they can cut effectively. The bond must also wear away as the abrasive grains wear and are expelled so new sharp grains are exposed.

There are three principal types of bonds used in conventional grinding wheels. Each type is capable of giving distinct characteristics to the grinding action of the wheel. The type of bond selected depends on such factors as the wheel operating speed, the type of grinding operation, the precision required and the material to be ground.

Most grinding wheels are made with vitrified bonds, which consist of a mixture of carefully selected clays. At the high temperatures produced in the kilns where grinding wheels are made, the clays and the abrasive grain fuse into a molten glass condition. During cooling, the glass forms a span that attaches each grain to its neighbor and supports the grains while they grind.

Grinding wheels made with vitrified bonds are very rigid, strong and porous. They remove stock material at high rates and grind to precise requirements. They are not affected by water, acid, oils or variations in temperature.

Some bonds are made of organic substances. These bonds soften under the heat of grinding. The most common organic bond type is the resinoid bond, which is made from synthetic resin. Wheels with resinoid bonds are good choices for applications that require rapid stock removal, as well as those where better finishes are needed. They are designed to operate at higher speeds, and they are often used for wheels in fabrication shops, foundries, billet shops, and for saw sharpening and gumming.

Another type of organic bond is rubber. Wheels made with rubber bonds offer a smooth grinding action. Rubber bonds are often found in wheels used where a high quality of finish is required, such as ball bearing and roller bearing races. They are also frequently used for cut-off wheels where burr and burn must be held to a minimum.

The strength of a bond is designated in the grade of the grinding wheel. The bond is said to have a hard grade if the spans between each abrasive grain are very strong and retain the grains well against the grinding forces tending to pry them loose. A wheel is said to have a soft grade if only a small force is needed to release the grains. It is the relative amount of bond in the wheel that determines its grade or hardness.

Hard grade wheels are used for longer wheel life, for jobs on high-horsepower machines, and for jobs with small or narrow areas of contact. Soft grade wheels are used for rapid stock removal, for jobs with large areas of contact, and for hard materials such as tool steels and carbides.

The wheel itself comes in a variety of shapes. The product typically pictured when one thinks of a grinding wheel is the straight wheel. The grinding facethe part of the wheel that addresses the workis on the periphery of a straight wheel. A common variation of the straight wheel design is the recessed wheel, so called because the center of the wheel is recessed to allow it to fit on a machine spindle flange assembly.

On some wheels, the cutting face is on the side of the wheel. These wheels are usually named for their distinctive shapes, as in cylinder wheels, cup wheels and dish wheels. Sometimes bonded abrasive sections of various shapes are assembled to form a continuous or intermittent side grinding wheel. These products are called segments. Wheels with cutting faces on their sides are often used to grind the teeth of cutting tools and other hard-to-reach surfaces.

Mounted wheels are small grinding wheels with special shapes, such as cones or plugs, that are permanently mounted on a steel mandrel. They are used for a variety of off-hand and precision internal grinding jobs.

A number of factors must be considered in order to select the best grinding wheel for the job at hand. The first consideration is the material to be ground. This determines the kind of abrasive you will need in the wheel. For example, aluminum oxide or zirconia alumina should be used for grinding steels and steel alloys. For grinding cast iron, non-ferrous metals and non-metallic materials, select a silicon carbide abrasive.

Hard, brittle materials generally require a wheel with a fine grit size and a softer grade. Hard materials resist the penetration of abrasive grains and cause them to dull quickly. Therefore, the combination of finer grit and softer grade lets abrasive grains break away as they become dull, exposing fresh, sharp cutting points. On the other hand, wheels with the coarse grit and hard grade should be chosen for materials that are soft, ductile and easily penetrated.

The amount of stock to be removed is also a consideration. Coarser grits give rapid stock removal since they are capable of greater penetration and heavier cuts. However, if the work material is hard to penetrate, a slightly finer grit wheel will cut faster since there are more cutting points to do the work.

Another factor that affects the choice of wheel bond is the wheel speed in operation. Usually vitrified wheels are used at speeds less than 6,500 surface feet per minute. At higher speeds, the vitrified bond may break. Organic bond wheels are generally the choice between 6,500 and 9,500 surface feet per minute. Working at higher speeds usually requires specially designed wheels for high speed grinding.

The next factor to consider is the area of grinding contact between the wheel and the workpiece. For a broad area of contact, use a wheel with coarser grit and softer grade. This ensures a free, cool cutting action under the heavier load imposed by the size of the surface to be ground. Smaller areas of grinding contact require wheels with finer grits and harder grades to withstand the greater unit pressure.

Next, consider the severity of the grinding action. This is defined as the pressure under which the grinding wheel and the workpiece are brought and held together. Some abrasives have been designed to withstand severe grinding conditions when grinding steel and steel alloys.

Grinding machine horsepower must also be considered. In general, harder grade wheels should be used on machines with higher horsepower. If horsepower is less than wheel diameter, a softer grade wheel should be used. If horsepower is greater than wheel diameter, choose a harder grade wheel.

They should always be stored so they are protected from banging and gouging. The storage room should not be subjected to extreme variations in temperature and humidity because these can damage the bonds in some wheels.

Wheels should be handled carefully to avoid dropping and bumping, since this may lead to damage or cracks. Wheels should be carried to the job, not rolled. If the wheel is too heavy to be carried safely by hand, use a hand truck, wagon or forklift truck with cushioning provided to avoid damage.

Before mounting a vitrified wheel, ring test it as explained in the American National Standards Institute's B7.1 Safety Code for the Use, Care and Protection of Grinding Wheels. The ring test is designed to detect any cracks in a wheel. Never use a cracked wheel.

Always use a wheel with a center hole size that fits snugly yet freely on the spindle without forcing it. Never attempt to alter the center hole. Use a matched pair of clean, recessed flanges at least one-third the diameter of the wheel. Flange bearing surfaces must be flat and free of any burrs or dirt buildup.

Tighten the spindle nut only enough to hold the wheel firmly without over-tightening. If mounting a directional wheel, look for the arrow marked on the wheel itself and be sure it points in the direction of spindle rotation.

Always make sure that all wheel and machine guards are in place, and that all covers are tightly closed before operating the machine. After the wheel is securely mounted and the guards are in place, turn on the machine, step back out of the way and let it run for at least one minute at operating speed before starting to grind.

Grind only on the face of a straight wheel. Grind only on the side of a cylinder, cup or segment wheel. Make grinding contact gently, without bumping or gouging. Never force grinding so that the motor slows noticeably or the work gets hot. The machine ampmeter can be a good indicator of correct performance.

If a wheel breaks during use, make a careful inspection of the machine to be sure that protective hoods and guards have not been damaged. Also, check the flanges, spindle and mounting nuts to be sure they are not bent, sprung or otherwise damaged.

The grinding wheel is one component in an engineered system consisting of wheel, machine tool, work material and operational factors. Each factor affects all the others. Accordingly, the shop that wants to optimize grinding performance will choose the grinding wheel best suited to all of these other components of the process.

Because carbides, high speed steels, PCD, PCBN, ceramics and some other materials used to make cutting tools can be nearly as hard as conventional abrasives, the job of sharpening them falls to a special class of abrasives-diamond and the CBN, the superabrasives.

These materials offer extreme hardness, but they are more expensive than conventional abrasives (silicon carbide and aluminum oxide). Therefore, superabrasive grinding wheels have a different construction than conventional abrasive wheels. Where a conventional abrasive product is made up of abrasive all the way through, superabrasive wheels have abrasive on the cutting edge of the wheel that is bonded to a core material, which forms the shape of the wheel and contributes to the grinding action.

Superabrasive wheels are supplied in the same standard grit range as conventional wheels (typically 46 through 2,000 grit). Like other types of wheels, they can be made in a range of grades and concentrations (the amount of diamond in the bond) to fit the operation.

There are four types of bond used in superabrasive wheels. Resinoid bond wheels are exceptionally fast and cool cutting. They are well-suited to sharpening multi-tooth cutters and reamers, and for all precision grinding operations. Resin is the "workhorse" bond, most commonly used and most forgiving. Vitrified bond wheels combine fast cutting with a resistance to wear. They are often used in high-volume production operations. Metal bond wheels are used for grinding and cutting non-metallic materials, such as stone, reinforced plastics and semiconductor materials that cannot be machined by other cutting tools. Single-layer plated wheels are used when the operation requires both fast stock removal and the generation of a complex form.

Wire EDM units that swivel a horizontally guided electrode wire in a CNC-controlled E axis give this shop the workpiece clearance and flexibility to produce complex, high-precision PCD-tipped cutting tools.

fine grinding - an overview | sciencedirect topics

fine grinding - an overview | sciencedirect topics

For very fine grinding (<10 m) of dry plant material, we use a device made up of a cylindrical rotor turning at 3,000 rev.mn1 in a stator with a slightly bigger diameter. Rotor and stator surfaces are equipped with parallel corrugations along the vertical axle. Fines are pulled toward the top.

Pin mills have two discs equipped with pins that are parallel to their axle. One disk is fixed and the other turns. The feed is located at the center of the fixed disc. Pins are set in circles alternating from one disk to another. Fragmentation is carried out by pulling out and shattering pieces. Fibrous products are shredded. This equipment is used for soft products with a hardness that is less than 3 Mohs (carbon, chalk, talc, dyes, drugs, pepper, sugar, resins, shellac).

The product could have high moisture. The peripheral speed of the turning disc could reach 120 m.s1. It is possible to achieve a fineness that is less than 5 m and flow could reach up to 5 tonne.h1. The mobile disc turns at an adjustable speed of between 700 and 4,500 rev.mn1. A high speed corresponds to high production, but the presence of fines could be significant. The product is removed at the periphery by centrifugal force. This equipment falls into the category of mills for ultrafines.

At the mill, fine grinding of coal involves producing coal particle sizes such that 70% or more are finer than 75 m (200-mesh) to ensure complete combustion and minimization of ash and carbon on the heat exchanger surfaces.

Pulverized fuel size distribution: reduction of fraction going through <75 m mesh screen by 0.35% for a 1% increase in throughput for low-speed mill; reduction by 0.9% for a 1% increase in throughput for medium-speed mill

Abrasive flow machining (AFM) is a fine grinding process with rather low material removal rates. AFM is mainly used for polishing, deburring, and defined edge rounding and, due to the fact that a viscous carrier for the abrasive media is used, can be used to machine difficult-to-access cavities, inner contours, and undercuts in a reproducible manner [52]. Today AFM has found many applications in different industries such as automotive, aerospace, and mold and die making.

The machining process consists basically of the steps schematically described in Figure6.53. Before processing, the abrasive medium is filled into the lower cylinder of the machine, after which the workpiece is placed into a specifically designed fixture and clamped between the upper and lower cylinder. The fixture has to fulfill several requirements: To clamp the workpiece safely in the media flow, to seal the system against leakage of the medium, and to ensure a controlled media flow in the closed system. Inside the closed system, the abrasive medium is first heated to working temperature and then pressed along the workpiece contours and cavities. Here, the design of the fixture plays an important role in controlling which parts of the workpieces are machined with what intensity. The machining process is repeated in an alternating up-and-down movement of the pistons until the machining time needed to obtain the desired result is reached.

The abrasive medium used in AFM usually consists of a polymeric carrier material and abrasive grains. Depending on the machining task, a carrier to abrasive grain ratio of between 1:1 and 1:2 is chosen. The carrier is characterized by high viscosity and strongly non-Newtonian behavior. The high general viscosity ensures that even large abrasive grains, with diameters up to 1mm, will stay evenly distributed throughout the medium under working conditions. The viscoelastic behavior of the carrier in AFM is used to ensure lower viscosity at low shear rates, which occur along flat surfaces and a high viscosity when higher shear rates are applied, such as in small cavities and around sharp corners. A higher viscosity will lead to higher material removal rates (MRR). The viscoelastic behavior and thus the local MRR can be adjusted with additives. A wide range of abrasive grains can be used in AFM, such as silicon carbides, boron carbides and diamonds. Grain sizes vary between 10m and 1mm, depending on the requirements of the workpieces and the size of their features.

This operation is also known as lap grinding, fine grinding, or flat honing. Fine grinding is usually used for superabrasives wheels while flat honing is more for conventional abrasives wheels. Grinding with lapping kinematics is helpful when the workpiece needs machined precision surfaces on a difficult-to-grind material such as hard ceramics [55]. It is recommended for use if a mirror finish is needed when it cannot be obtained with constant feed or by using wheels finer than JIS #10000 [23].

Lap grinding differs from regular grinding because it is considered a cool process with lower speed and no sparks. However, a flood of cooling fluid is necessary to control the temperature and to remove the swarf from the machined workpiece. If insufficient coolant is provided, wheel loading increases and surface finish will not be as expected, in addition to the possibility of thermal damage to the workpiece or the wheel. In the experiment, the proposed TRIM C270E, high-performance synthetic is initially used with a concentration of 5% with water. This coolant is provided from Master Chemical Corporation located in Perrysburg, Ohio. The TRIM C270E has a low ferrous corrosion inhibition with an electrical conductivity of 1.8 mS, refractometer factor of 3.3, and a pH of 9.09.3 (typically pH of 8.79.2) [56].

This process is often useful in parallelism and its use of two parallel grinding wheels. Nevertheless, this experiment contains one grinding wheel only. Usually, the stresses on the machined surface were easily relieved, and mirror surface finish can be achieved. The wheels of grinding with lapping kinematics are flat wheels made out of aluminum oxide (Al2O3) or silicon carbide (SiC). Aluminum oxide is cheaper but silicon carbide is better. Nonetheless, in some cases where the material to be machined is quite hard, such as in this experiment, a harder wheel is necessary, like cubic boron nitride (CBN) or diamond. These wheels become more expensive if the friability is higher, which will give new sharp grains faster. Friability is the ability of the grains to break down and expose new sharp edges, which will increase the material removal rate with more accurate tolerances [57].

Lap grinding also differs from conventional grinding because it has a constant pressure throughout the operation. The pressure of the wheel depends on the type of material machined. Harder workpieces require more pressure than softer ones. Lower than the recommended pressure is always better than going over the recommended pressure; it is only going to consume more time, whereas in overpressure cases, more heat can be generated, causing more damage to the wheel by pulling off grains, and indeed bad surface finish production [57].

The sand mill, or stirred ball mill, achieves fine grinding by continuously agitating the bed of grinding medium and charge by means of rotating bars which function as paddles. Because of its high density, zircon sand is frequently used as the grinding medium. A fluid medium, liquid or gas, is continuously passed through the bed to remove the fines, as shown in Figure 2.31. A very fine product can be obtained at a relatively low energy input, and the mill is used for fine grades of ceramic oxides and china clay, and in the preparation of coal slurries.

In cases where it is important that the product should not be contaminated with fine fragments of the grinding medium, autogenous grinding is used where coarse particles of the material are to be ground form the grinding medium.

To liberate minerals from sparsely distributed and depleting the ore bodies finer grinding than generally obtained by the conventional Rod Mill Ball Mill grinding circuits is needed. Longer grinding periods in the conventional milling processes prove too expensive mainly due to large power consumption. Stirrer mills have been tried in mineral industry with considerable success and have therefore been increasingly used. In this chapter, the theories involved in the design and operation of these mills, as established till now, are explained. Further theoretical studies and designs of the mills are still in progress for a better understanding and improved operation. Presently, the mills have been proved to be economically viable and the mineral of interest conducive to improved recovery and grade.

Granulator machines are designed with high speed, medium inertia, open rotor body for fine grinding, with two, three, or five hardened steel knives. Granulators can grind material down to 0.177mm (80 meshes) or up to 5cm in size. Generally, the resulting particles vary in size from 3 to 20mm. Interchangeable qualifying screens with various diameter holes determine the final reduction size. With decibel ratings of less than 65Db, these units are ideal for placement at individual workstations. Granulators are sized by the dimensions of the cutting chamber and range in size from 20 25 to 40 88cm. Motor sizes range from 5 to 40HP. Complete systems can include air discharge units or conveyors, and can easily be integrated with existing shredder or grinder systems. Granulators have a smaller footprint than a full-sized grinder, but can still handle high volumes of product in the granulation process (Fig. 3.13) [68]. Hammer mills accomplish size reduction by typically impacting at rates of 7000rpm and higher [16]. A solid rotor for grinding scrap Cu wires, PCBs, metals, and plastics is used. These granulators are used for the sizing of plastics, nonferrous metals, heterogeneous materials, and enable to reach controlled output size in the recycling process with the use of classifier screens starting from 2mm diameter. The size of the granulators ranges between (1060 1800) (1700 1800) (2000) mm; power from 8 to 90kW, and weight from 0.7 to 4.2 tons.

Dressable metal bond wheels also allow high wheel speeds. These wheels are mainly used for fine grinding of brittle and very hard materials using superabrasives. Such wheels are not necessarily used at high wheel speeds since accuracy may take precedence over removal rate. The modern way of dressing metal bond wheels is by ELID: a process introduced by Ohmori and Nakagawa (1990). An alternative process described by Suzuki and Uematsu (1997) is EDD.

Metal bond wheels used for ELID grinding are described more fully in Chapter 4. ELID grinding wheels are often used for super-finishing and nanogrinding applications. ELID grinding is a process that allows the successful grinding of ceramics and can be used to achieve extremely close tolerances. For such applications, extremely small abrasive grain sizes are employed. The abrasive grains are contained within a dense metal bond. A cutting surface is achieved by machining away the metal bond surrounding the abrasive asperities using ELID.

Flotation has progressed and developed over the years; recent trends to achieve better liberation by fine grinding have intensified the search for more advanced means of improving selectivity. This involves not only more selective flotation agents but also better flotation equipment. Since the froth product in conventional flotation machines contains entrained fine gangue, which is carried into the froth with feed water, the use of froth spraying was suggested in the late 1950s to eliminate this type of froth contamination. The flotation column patented in Canada in the early 1960s and marketed by the Column Flotation Company of Canada, Ltd., combines these ideas in the form of wash water supplied to the froth. The countercurrent wash water introduced at the top of a long column prevents the feed water and the slimes that it carries from entering an upper layer of the froth, thus enhancing selectivity.

The microbubble flotation column (Microcel) developed at Virginia Tech is based on the basic premise that the rate (k) at which fine particles collide with bubbles increases as the inverse cube of the bubble size (Db), i.e., k1/Db3. In the Microcel, small bubbles in the range of 100500m are generated by pumping a slurry through an in-line mixer while introducing air into the slurry at the front end of the mixer. The microbubbles generated as such are injected into the bottom of the column slightly above the section from which the slurry is with drawn for bubble generation. The microbubbles rise along the height of the column, pick up the coal particles along the way, and form a layer of froth at the top section of the column. Like most other columns, it utilizes wash water added to the froth phase to remove the entrained ash-forming minerals. Advantages of the Microcel are that the bubble generators are external to the column, allowing for easy maintenance, and that the bubble generators are nonplugging. An 8-ft diameter column uses four 4-in. in-line mixers to produce 56 tons of clean coal from a cyclone overflow containing 50% finer than 500 mesh.

Another interesting and quite different column was developed at Michigan Tech. It is referred to as a static tube flotation machine, and it incorporates a packed-bed column filled with a stack of corrugated plates. The packing elements arranged in blocks positioned at right angles to each other break bubbles into small sizes and obviate the need for a sparger. Wash water descends through the same flow passages as air (but countercurrently) and removes entrained particles from the froth product. It was shown in both the laboratory and the process demonstration unit that this device handles extremely well fine below 500-mesh material.

Another novel concept is the Air-Sparged Hydrocyclone developed at the University of Utah. In this device, the slurry fed tangentially through the cyclone header into the porous cylinder to develop a swirl flow pattern intersects with air sparged through the jacketed porous cylinder. The froth product is discharged through the overflow stream.

what is single & double side fine grinding?

what is single & double side fine grinding?

Fine Grinding generally follows the same kinematic principle as lapping. The fine grinding workpieces are held in carriers which are driven to describe a planetary motion covering the full surface of the Fine Grinding wheel. The drive mechanism consists of an inner and outer pin ring. The outer ring is generally fixed while the inner ring rotates in either the opposing or the same direction as the lower working wheel to create a series of epicyclic rotations.

Lapmaster fine grinding machines and systems offers a complete line of products for all fine grindingrequirements. We can offer fully integrated systems and machines for high volume fine grindingand industrial production applications and equipment for low volume job shop applications. Lapmaster also offers used fine grinding(rebuilt and refurbished) and upgrade services for existing fine grindingmachines. We provide our customers with fully engineered complete custom solutions and offer a full line of accessories and consumables in addition to comprehensive training and repair services.

Our extensive line of fine grindingmachines / systemsfor both medium to large-scale serial production as well as small batch production; these systems can be made to be manually operated or fully automated. With innovation and customer service as our main objectives, Lapmaster continuously researching and developing new technology and fine grindingmachinery. By consistently staying on top of the latest developments on the market, we ensure that our customers are provided with the most state-of-the-art production and control.

PRECISION SURFACING SOLUTIONS supports manufacturers in a wide variety of industries in which precision grinding, lapping, polishing, deburring and advanced materials processing equipment is commonly used. They all need high-quality, high-precision, stable and well-engineered machines to manufacture high-quality work pieces.

Founded in Chicago in 1948 as a manufacture of lapping and polishing machines for the mechanical seal market, Lapmaster has grown to a worldwide solution provider for more than 20 industries like precision optics and advanced materials.

Since 1907 Barnes has been considered a world leader in developing innovative honing and bore finishing technology and processes. The earliest Barnes honing machines were the first to make honing a practical and efficient means of finishing automotive cylinder bores in a production environment.

Since May 2020, the brand ISOG belongs to the globally active Precision Surfacing Solutions Group. With the addition of ISOG to the already existing strong brands within the Group, PSS further strengthens its position as a leading supplier of high quality, best in class technologies in the market of surface quality enhancement solutions.

ELB-Schliff Werkzeugmaschinen GmbH has been producing surface and profile grinding machines for over 60 years. The company was founded by Edmund Lang in the city of Babenhausen which led to the name "ELB-Schliff".

The aba company was founded in 1898 under the name "Messwerkzeugfabrik Alig & Baumgrtel Aschaffenburg", hence the initials aba. Today, the aba Grinding Technologies is exclusively focused on the advancement and production of precision surface and profile grinding machines.

Founded in 1934, KEHREN is a well-established designer and builder of high-precision grinding machine tools and systems under the following categories: vertical grinding centers, vertical grinding centers with portal design, surface grinders with rotary tables and horizontal spindles, and surface grinders with dual rotary tables and vertical spindles.

Produced in Germany since 2009, MICRON machines are compact and dynamically rigid grinding machines especially designed for Creep Feed and Profile grinding. MICRON is an industry leader in grinding of Hydraulic components like stators, rotors and van pumps.

Founded in Germany in 1804 by Mr. Peter Wolters, Peter Wolters has been producing lapping, polishing and fine grinding equipment since 1936. In 2019 Precision Surfacing Solutions acquired the division Wafer plant and service business for photovoltaic and special materials of Meyer Burger. Further Information can be found at www.precision-surface.ch

Founded in Chicago in 1948 as a manufacture of lapping and polishing machines for the mechanical seal market, Lapmaster has grown to a worldwide solution provider for more than 20 industries like precision optics and advanced materials.

energies | free full-text | grinding behaviour of microwave-irradiated mining waste | html

energies | free full-text | grinding behaviour of microwave-irradiated mining waste | html

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grinding crack generation and solution - information - more superhard products co., ltd

grinding crack generation and solution - information - more superhard products co., ltd

The causes of grinding cracks may be as follows: the surface stress of the workpiece exceeds the fracture limit, that is, the workpiece has residual mechanical stress and thermal stress in the surface part due to previous grinding or heat treatment. Because this part of the grinding just to maintain the balance of the stress, resulting in its residual stress over the strength of the workpiece, from some will produce a grinding crack.

Of all the causes, "grinding cracks" are at the heart of the problem. The biggest problem is the stress generated by grinding heat. Because of the grinding heat, the temperature of part of the workpiece surface rises rapidly, and this part will undergo tempering or other heat treatment. Due to the change of the internal structure and the shrinkage of the surface, cracks were formed under the action of tensile stress.

(1)the tensile stress with the increase of grinding wheel feeding force will gradually increase, slowly approaching the workpiece material tensile strength. Cracks occur when the tensile strength of the workpiece material is exceeded.

(2)The compressive stress will not change too much, because the scale and the experimental conditions are different, so it cannot be compared. However, what is almost unchanged is that when the back bite is 0.05mm, the residual tensile stress will be the largest, even if it is cut deeper, the residual tensile stress will not be too large. It is generally believed that this is due to the falling off of the abrasive grains.

(2)As a tensile stress, the residual stress on the surface can act on the vertical direction of the grinding direction in the form of pressure while acting on the grinding direction. And the deeper inside, the less stress there is.

(3)When acting along the grinding direction and the vertical direction, it first becomes the compressive stress and then suddenly becomes the tensile stress consistent with the grinding direction. When the maximum value is reached, it gradually decreases and eventually becomes a small compressive stress.

what is single & double side fine grinding machine?

what is single & double side fine grinding machine?

Fine Grinding generally follows the same kinematic principle as lapping. The workpieces are held in carriers which are driven to describe a planetary motion covering the full surface of the Fine Grinding wheel. The drive mechanism consists of an inner and outer pin ring. The outer ring is generally fixed while the inner ring rotates in either the opposing or the same direction as the lower working wheel to create a series of epicyclic rotations.

PRECISION SURFACING SOLUTIONS supports manufacturers in a wide variety of industries in which precision grinding, lapping, polishing, deburring and advanced materials processing equipment is commonly used. They all need high-quality, high-precision, stable and well-engineered machines to manufacture high-quality work pieces.

Founded in Chicago in 1948 as a manufacture of lapping and polishing machines for the mechanical seal market, Lapmaster has grown to a worldwide solution provider for more than 20 industries like precision optics and advanced materials.

Since 1907 Barnes has been considered a world leader in developing innovative honing and bore finishing technology and processes. The earliest Barnes honing machines were the first to make honing a practical and efficient means of finishing automotive cylinder bores in a production environment.

Since May 2020, the brand ISOG belongs to the globally active Precision Surfacing Solutions Group. With the addition of ISOG to the already existing strong brands within the Group, PSS further strengthens its position as a leading supplier of high quality, best in class technologies in the market of surface quality enhancement solutions.

ELB-Schliff Werkzeugmaschinen GmbH has been producing surface and profile grinding machines for over 60 years. The company was founded by Edmund Lang in the city of Babenhausen which led to the name "ELB-Schliff".

The aba company was founded in 1898 under the name "Messwerkzeugfabrik Alig & Baumgrtel Aschaffenburg", hence the initials aba. Today, the aba Grinding Technologies is exclusively focused on the advancement and production of precision surface and profile grinding machines.

Founded in 1934, KEHREN is a well-established designer and builder of high-precision grinding machine tools and systems under the following categories: vertical grinding centers, vertical grinding centers with portal design, surface grinders with rotary tables and horizontal spindles, and surface grinders with dual rotary tables and vertical spindles.

Produced in Germany since 2009, MICRON machines are compact and dynamically rigid grinding machines especially designed for Creep Feed and Profile grinding. MICRON is an industry leader in grinding of Hydraulic components like stators, rotors and van pumps.

Founded in Germany in 1804 by Mr. Peter Wolters, Peter Wolters has been producing lapping, polishing and fine grinding equipment since 1936. In 2019 Precision Surfacing Solutions acquired the division Wafer plant and service business for photovoltaic and special materials of Meyer Burger. Further Information can be found at www.precision-surface.ch

Founded in Germany in 1804 by Mr. Peter Wolters, Peter Wolters has been producing lapping, polishing and fine grinding equipment since 1936. In 2019 Precision Surfacing Solutions acquired the division Wafer plant and service business for photovoltaic and special materials of Meyer Burger. Further Information can be found at www.precision-surface.ch

grinding of metals: origin and cutting action | industries | metallurgy

grinding of metals: origin and cutting action | industries | metallurgy

In this article we will discuss about:- 1. Introduction to Grinding 2. Origin of Grinding 3. Cutting Action in Grinding 4. Mechanics of Cutting Action in Grinding 5. Temperature in Grinding 6. Self-Sharpening Characteristics of Grinding Wheel 7. Residual Stresses in Grinding 8. Causes of Wheels Wearing too Rapidly 9. Causes of Wheels Glazing 10. Operating Conditions and Other Details.

Grinding can also be considered as a machining process, i.e. process of removing metal, but comparatively in smaller volume. To grind means to abrade, to wear away by friction or to sharpen. In grinding, the material is removed by means of a rotating abrasive wheel. The action of grinding wheel is very similar to that of a milling cutter.

The wheel is made up of a large number of cutting tools constituted by projected abrasive particles in the grinding wheel. Definite elongated metal chips varying in size from 0.4 to 0.8 mm can be seen by examining the material removed under the microscope.

(i) To remove a very small amount of metal from the workpiece to bring its dimensions within very close tolerances after all the rough finishing and heat treatment operations have been carried out. It is thus basically a finishing process employed for producing close dimensional and geometrical accuracies.

(i) It is very suitable for cutting hardened steels etc. Parts requiring hard surfaces are first machined to shape in annealed condition, only a small amount being left for grinding depending upon the size, shape and tendency of material to warp during heat-treating operation.

(vi) Very little pressure is required in this process, thus permitting its use on very light work that would otherwise tend to spring away from the tool. This characteristic permits the use of magnetic chunk for holding the work in many grinding operations.

(vii) Abrasives have very high hardness; are less sensitive to heat compared to other materials and can sustain high temperatures. Thus these can be worked at higher cutting speeds. Grinding wheels have self-sharpening properties due to releasing of dulled grains and exposing new sharp ones.

In the early stages, chisel was thought of as the most convenient tool for removing metal. In chisel there is only one cutting edge and more material can be removed by it but with very poor finish. For getting better finish on the materials man started using file. In file, there are multi cutting edges.

With it the material removed is less, but better finish can be obtained. With the advancement of technology, chisel was replaced by a single point cutting tool in order to have controlled removal of metal and the operation of metal removal is carried out on various machine tools like lathes, shapers, milling machines etc.

Similarly, in order to control the metal removal and obtain better finish by multi-cutting edge tool, grinding is used. The grinding process results in an improvement in geometric accuracy of a component ( 0.02 mm) and an improvement of surface finish (0.1 m Ra).

It will be observed from Fig. 20.1 that a grinding wheel consists of abrasive particles, bonding material and voids. The projecting abrasive particles act like cutting tool tips and remove metal. A properly selected grinding wheel exhibits self-sharpening action.

As cutting proceeds, the abrasive particles at cutting edge become dulled, and eventually these become cracked along the cleavage planes due to resistance offered by workpiece material which resists the cutting action. Thus new cutting points are produced which carry out further cutting action.

This process continues till the abrasive grains get worn down till the level of bond. At this point the bond allows the remainder of the worn grains to be torn from the wheel, exposing new grains which were previously below the surface of the wheel and the new grains do further cutting action.

Two problems often encountered either by wrong selection of grinding wheel or by improper cutting conditions are wheel glazing and wheel loading. Wheel glazing refers to the condition when the grains are worn down to the level of bond and held for too long for efficient cutting. This results due to use of a hard wheel (wheel with a strong bond strength and too fine grains).

The problem can be remedied by changing the wheel and sometimes by changing the cutting conditions. Wheel loading occurs when workpiece chips are embedded in the cutting face of the wheel, thereby reducing the rate of cutting because the depth of penetration is reduced. It occurs due to too small voids and can be cured by increasing the wheel speed or using different wheel even.

Thus the selection of the grinding wheel for correct, continuous and efficient cutting demands the correct selection of the type of abrasive, the size of the grains, the type of bonding agent and its strength, and the size of the voids. Further the behaviour of the grinding wheel is affected by the workpiece material, cutting speed, depth of cut and the feed rate.

Though diamond is the hardest material but because of its high cost, its applications are restricted. Al2O3, SiC and B4C have high hardness in comparison to hardened steel and thus can be used for metal removal by plastic deformation. It may be mentioned that cutting tool material has to be harder for material removal by plastic deformation and also to maintain its shape and for less wear.

Since it is not possible to make usual shape of cutting tool with these materials use is made of them in the form of grains, the form in which they are available in natural form. The grains of these materials (abrasives) are bonded with some bonding material in the shape of wheel. The abrasive grains on the surface of wheel act as cutting edges. These are randomly distributed and randomly oriented.

Fig. 20.2 (b) shows the elaborated view of scheme of chip formation during surface grinding. The cross-section of uncut chip is found to be approximately triangular having thickness t and width w. However, the uncut thickness and width vary and let their maximum values be tmax and wmax. Average value may be half of these. The average length of chip l = D/2 x (D = grinding wheel diameter and is very small)

It will be seen from here that wheel will appear to be softer, if N, D, or decrease, or f or d increase, because the value of Fav will increase and cause a more frequent dislodging of the abrasive grains. In surface grinding operation, radial force FR = 2F. (Refer Fig. 20.3)

A very high temperature is attained by the tip of the abrasive particle when cutting. However no serious heating of the wheel occurs because such high temperature is only for a very short duration and the temperature gradient at the cutting grains is very steep.

By using fluid in grinding, not only workpiece temperature decreases and wheel wear decreases, but wheel is less loaded which reduces frequency of wheel dressing. However fluid cant prevent surface damage to workpiece due to high momentary temperature.

In a grinding wheel, the cutting tools (points) are irregularly shaped and randomly distributed. The sharp edges on the periphery of the wheel take part in material removal process and gradually they become blunt i.e., worn out (dull). Due to greater forces on them during machining, they either fracture to present new sharp cutting edge, or get lodged out and new grains below it become exposed and take part in material removal.

This process imparts grinding wheels the characteristic of self-sharpening. It would be realised that the strength of bond (called its grade) decides the maximum force an abrasive grain can withstand and this is an important characteristic of grinding wheel. A wheel with a strong bond is called hard.

The small and hot chips produced in grinding operation have tendency to weld to wheel or workpiece. Further a large number of grains may have a large negative rake angle due to random grit orientation, and these instead of cutting, may rub. These factors make grinding process to be inefficient and consume high specific energy.

The temperature at the grain-chip interface during grinding reaches very high value (around 1500C). Due to high temperature, the micro structural changes may take place due to rapid heating and quenching (due to cutting fluid). The thermal and mechanical effects can affect the ground surface to a depth of about 0.2 mm.

These would result in development of high residual tensile stresses and if these attain high values, surface cracks may occur. Fig. 20.7 shows how the residual stress may occur at various depths with different speeds of wheel in a workpiece after surface grinding. Grinding temperature can be assumed to be proportional to the energy spent per unit surface area ground,

The increase in wheel speed (with constant feed rate) results in reduction of the chip size removed by a single abrasive grain, thereby reducing the wear of the wheel. Higher wheel speed is limited by the wheel design, type of bond, grinding operation, power and rigidity of the grinding machine, etc. Wheel speed normally varies between 20 to 40 m/sec depending on type of bond and different grinding operations.

Increase in work speed increases the wheel wear, but decreases the heat produced. High work speed is limited by premature wheel wear and vibrations induced by wear. Low work speed results in local overheating, which deforms/tempers the hardened workpiece and affects its mechanical properties.

In order to decrease wheel wear, the work speed should be reduced. If the heat produced is more, clogging occurs, particularly with hard wheels, the work speed should be increased. For roughing operation, work speed varies from 11 to 50 m/min and for finishing operation from 6 to 30 m/ min in case of cylindrical grinding. Work speed for internal grinding varies between 15 to 30 m/min and for surface grinding between 8 to 15 m/min.

Increase of traverse-feed or cross-feed increases the wheel wear and produces poor surface. Usually its value is adjusted to 2/3 to 3/4 of the wheel width in case grinding of steel and 3/4 to 5/6 of wheel width in the case of cast iron workpiece.

When area of contact is large (as in the case of internal grinding, surface and with larger diameters of work with small diameter wheel), unit pressure is low, and for continuous free cutting action a soft grade wheel is used. Coarser grit is used to provide adequate chip clearance between abrasive grains. Finer grit and harder grade wheels are used when area of contact is small.

A lot of heat is generated at the contact of grinding wheel and the workpiece during grinding operation, majority of which is transferred to the workpiece. Grinding fluids help in preventing excessive heating of workpiece and flush the wheel.

Grinding fluids containing sulphur or chlorine additives help in reducing the cutting force and improving the surface finish and increasing the life of the grinding wheel. Usually water based emulsions and grinding oils in ample quantity (15-20 litres/min for normal medium sized grinding machine) are used for this purpose.

The fluid is directed to the interface between wheel and workpiece so that it can create a film of low shear strength between the wheel and the work. The fluid is supplied under pressure using special nozzles, so that air film around the wheel surface due to high speed, is penetrated. In order to prevent clogging in the wheel due to fine particles, the grinding fluid is finely filtered.

The maximum wheel speed is determined by the ultimate bursting strength of the wheel and it depends on the abrasive used, grit size, bond, structure, grade, shape and size of the wheel. Its value is specified by the manufacturers which should never be exceeded.

Wheels before mounting should be checked for damage in transit, cracks and other defects. Ringing test is good enough for vitrified bond. Sound wheels, when tapped lightly at 45 from the vertical line with a plastic hammer sound like a clear metallic ring but the cracked wheel will not ring.

When grinding dry, provision for extracting grinding dust should be made. Protective covers of machine should never be removed while machine is in use. Operator should wear safety devices to protect his eyes and body from flying abrasive particles and dust.

Loading occurs when spaces between the abrasive grains become clogged with particles of the metal being ground. As such grains do not project sufficiently to promote efficient cutting. It occurs due to grinding of soft metals with open structured wheel. Glazing is easily recognised by shiny appearance on the face of the wheel.

It occurs due to abrasive grains becoming dull and not breaking away from the bond. This happens when wheels are too hard for the material being ground. Glazing can be reduced by increasing wheel or work speed.

Surface finish and specific power requirement could also be incorporated to assess the overall performance of grinding wheel. In that case, grinding ratio is equal to the ratio of the amount of material ground per amount of wheel wear and the product of specific grinding power and surface finish on test piece.

During the process of grinding a lot of heat is generated between the cutting tool and workpiece. A major portion of the heat is dissipated in the workpiece and the remaining is retained by the grinding wheel.

Oxidation of surfaces takes place at 200C producing metallic oxide. These oxides have different colours unlike the parent metal. In other words, we can say that this leads to discoloration of workpiece. The generation of heat is due to the dull grains which will lead to burning of surface.

Surface roughness in grinding depends on grinding wheel (its diameter, abrasive, hardness, dressing, wear) and grinding conditions (wheel speed, workpiece speed, longitudinal feed, workpiece diameter). Figs. 20.14 shows variation of surface roughness in grinding with change in various parameters.

This occurs due to incorrect dressing, wrong wheel selection and using slow traverse and high work speed. It can be taken care of by keeping the wheel sharp, using softer wheel or coarser grit, reducing wheel speed and fast traverse, using a greater depth of infeed and increasing depth of cut.

This can be taken care of by using softer or porous structure wheel; using sharper dresser, using a copious quantity of clean coolant. Irregular marks of different lengths and widths could occur due to dirty coolant. Deep irregular marks occur due to loose wheel flanges.

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fine grinding with impact mills - chemical engineering | page 1

fine grinding with impact mills - chemical engineering | page 1

Many branches of the chemical process industries (CPI) make use of impact comminution to process solid matter, such as minerals, foodstuffs, pharmaceutical products, and above all, products for the chemicals industry. Impact comminution is also used for coarse crushing, but the focus of this article is fine grinding with end-product particle sizes below 500 m. The technology of impact comminution is, however, not particularly popular with the users of impact grinding systems because it is energy-intensive, associated with a high noise level and frequently also gives rise to time-consuming maintenance work. In spite of this, impact comminution is still the most cost-effective solution in many processing operations.

With every method of comminution, one has to generate a level of stress in the particles that is so high that the particles fracture as a result. Beside other methods, this stress can be generated by pressure (compression) or impact (Figure 1). In the case of compression, the particle is stressed between two solid elements, whereas in the case of impact comminution, the particle is in contact with only one other element at the moment of fracture, either an impact plate or another particle.

A prerequisite for impact comminution is brittle-elastic material behavior. Materials scientists call a material brittle-elastic if deformation of the sample is initially proportional to the applied stress and the fracture occurs suddenly (Figure 2). The dark area under the plotted line is equivalent to the work that is necessary to deform the particle. With impact comminution, the kinetic energy of the particles is employed to generate the requisite degree of deformation. In the linear range, the deformation is elastic and reversible. As soon as higher stresses occur, the material strength is exceeded locally and cracks are triggered. The cracks grow extremely quickly and lead to destruction of the particle.

Equipment has been built for scientific experiments in which individual particles are subjected to one single impact under defined conditions. From these single-particle impact tests the following three things are known: that a minimum fracture energy must be applied to the particles, that the probability of fracture is dependent on the kinetic energy and that the resultant particle-size distribution is dependent on the properties of the material being processed.

According to theory, a speed multiplication of 5.6 would be necessary to double the stress in the particles. In other words, increasing the impact speed has only a limited influence on the expected fineness. On the other hand, the impact speed is the only parameter with which it is possible to effectively change the stress condition in a particle, which is why impact mills usually run at high peripheral speeds of up to 150 m/s. When two rotors are driven to rotate in opposite directions, relative speeds of up to 250 m/s can be achieved. In jet mills, compressed gas is expanded in Laval nozzles. At common gas pressures and temperatures, the exit velocity of the gas jets is around 500 m/s.

As Figure 1 shows, a single fracture event leads to a number of coarse fragments but to relatively little fine product. Because of this, the aim is multiple stressing of the particles in mills in order to obtain a fine end product. One can assume that a feed material is subjected to between 5 and 20 impact events in simple rotor impact mills. With fine grinding, air classifiers can be integrated into mills that allow only those particles with the desired end-particle size to pass through the classifying wheel, but which return coarser particles for final grinding. For jet mills, up to 100 stressing events can be necessary to grind the feed material to high fineness values if it is of poor grindability. The number of stressing events is therefore a parameter that has a greater influence on the product fineness than the stressing speed.

The particle size distribution of the ground product is a function of the mill parameters, stressing frequency and stressing intensity, as well as the feed material characteristics. Today it is not possible to accurately predict the result of a comminution trial with an impact mill based on scientific principles. This applies to particle size distributions and to the specific grinding energy.

If impact comminution is to be economically viable, the feed material must fulfill a number of general requirements. In the case of fine impact mills, there is a maximum feed size that must not be exceeded if the mill is to remain undamaged by any large lumps in view of the high peripheral speed. A particle size of 5 to 10 mm can be assumed as the maximum, whereby the faster the rotor rotates, the finer the feed material should be. Tramp material must be removed from the feed material.

Mechanical impact grinding can be used on materials with a Mohs hardness of up to 34 (see Table 1). But even small amounts of harder components in the feed material can lead to an uneconomical degree of wear. When grinding natural gypsum which is actually soft a few percent of quartz in the feed will make it necessary to exchange the wear plates in the mill frequently. The same or similar phenomenon applies to vegetable products that are contaminated with sand. In the case of especially fine feed materials, harder materials can also be processed, provided that the wear protection in the mill is well adapted to the product properties.

The feed material should not be heat-sensitive, that is, the softening or melting point has to be above 70C if the material is to be ground in a mechanical impact mill. The reason is that the energy of the motor is converted almost completely into heat, and mills and systems heat up to 5060C under full load. Heat-sensitive products can be processed only by cooling the feed material or the mill air, or both, which ultimately means additional energy costs.

Liquid components in the feed material can also have an extremely disruptive effect. The product should be dry, with the maximum moisture content of normally only a few percent. If liquid is released during comminution, this frequently leads to the formation of build-up. This also applies to feed material that contains oil or fat.

Besides the specifications related to the particle size distribution, the product properties mentioned here play a major role in the selection and design of impact mills. For this reason, trials are always carried out with a test system for new applications.

Rotor impact mills have been in use for over 100 years. As a result of the wide range of feed products, a great number of different machine types have established themselves on the market during this time. Jet mills, which operate with a gaseous medium, have also been on the market for a long time. In this article, only a few of the widely available machine types can be described.

Mechanical impact mills. Simple impact mills consist essentially of a high-speed rotor. Fine particles follow the flow of air in the mill after extremely short acceleration paths. Because of this, the clearance between rotating and stationary grinding elements should only be a few millimeters. Characteristic for fine impact mills are a high-speed rotor and stationary grinding elements located in its immediate proximity. The grinding zone can be disc-shaped, in which case the product is fed centrally and the feed material migrates in radial direction across the disc, just as with the pin mill. The grinding zone can also be cylindrical, in which case the feed material migrates along the cylindrical surface through the mill. The transport of the material can take place against the force of gravity, in the direction of the force of gravity, or even at right angles to it. In addition, impact mills can be equipped with a classifying discharge, for example sieves, screens or classifying wheels. The design most suitable for a given application must be determined during the course of trials.

Classic rotor impact mill. These machines are characterized by a flat-cylindrical, vertically upright housing and a horizontal shaft supporting the rotor (Figure 3). These machines have a big door, which can be easily opened for maintenance of the grinding equipment. The product is fed to the center of the rotor and exits in ground condition at the periphery of the mill. Air flowing through the mill assists transport of the product and cools the machine and product. The high-speed rotor with impact elements grinds the feed material and assists the transport of the air, in a similar way to a radial fan. The fineness is set as a function of the rotor speed and the product throughput. Higher throughputs lead to a coarser product, which is attributed to increasingly ineffective particle-particle impacts. The feed metering unit is controlled by the current loading of the mill motor.

Sieve inserts with various kinds and arrangement of perforations have the benefit of top-size control, but are always more prone to wear. Sieves can only be employed down to a minimum aperture size of approximately 0.5 mm. The design shown in Figure 3a is therefore suitable for coarser grinding tasks. In the fine range and with coarse feed materials, grinding tracks are used. Grinding tracks usually have an annular discharge gap for the ground product. In the case of the plate beater unit (Figure 3b), exchangeable impact plates permit the processing of mildly abrasive materials. At high speeds and low throughputs and in combination with a grinding track, fine products are achieved. When employed in combination with a grinding track or sieve ring, or both, the plate beater unit is suitable for fine grinding, defibration, chipping and deglomeration.

With pin discs (Figure 3c), comminution takes place between the rotating and stationary concentric rows of pins. The diameter of the pins and the pitch diameter for the pins are geared to each other such that particles cannot flood through the pin rows. The fineness is regulated as a function of the speed. The principle of multiple stressing is implemented in this mill in an extremely graphic manner: the particles have to pass through every row of pins before they are able to exit the mill and impact against many pins in the grinding process. The narrow gap between the rows of pins ensures high impact speeds, even for fine particles. Tramp material in the feed material is a risk to the relatively fragile pins and can cause a lot of damage.

The largest mills of this type have rotor diameters of some 1.5 m and a drive power of up to 315 kW. The maximum peripheral speeds reach 150 m/s. The maximum fineness that can be expected for simple impact mills is, for many products, around 100 m. When reference is made in this article to the product fineness but is otherwise not specified, this is understood as the cumulative undersize of the particle size distribution of 97%. Table 2 shows some applications for simple impact mills.

Pin mills with two rotating pin discs (disintegrators). The basic design of this machine corresponds to that of the classic, fine impact mill, although here, both pin discs are driven separately (Figure 4). The fineness of the end product is set as a function of the peripheral speeds of the counter-or co-rotating pin discs. The relative speed of the outside row of pins can reach up to 250 m/s. Compared with the simple, fine impact mill, the counter-rotating pin mill achieves significantly higher fineness.

The use of two rotating discs reduces the formation of deposits on the pins in comparison with pin mills equipped with one stationary disc or mills with grinding tracks. This can be accomplished by a generously dimensioned housing, the so-called wide-chamber housing. Therefore, this machine is especially suitable for the grinding of sticky feed material. Applications for this machine type are given in Table 3. The largest pin mill of this type ever to be built has a pin disc diameter of approximately 1.1 m and a drive power of 500 kW.

Long gap mills. In contrast to the classic, fine impact mill, the rotor here is vertically arranged (Figure 5). The feed material is charged from below, entrained in the transport air and is conveyed pneumatically through the grinding zone, but can also be fed to the lower area of the grinding zone. The grinding zone extends over the entire cylindrical area between the rotor beaters and the peripheral grinding track. The product must travel all the way along this gap, which is longer compared with other mills. Mills of this type are therefore called long gap mills, although the name air vortex mill is also known. This name, however, implies that comminution is the result of particle-particle impacts in an air vortex. Because an efficient fine-grinding operation necessitates unhindered impact of the particles on the grinding elements of the mill, grinding in air vortices can only be a minor effect. The fineness in this mill is also set by the rotor speed and the throughput of the feed material.

The rotor of the long gap mill consists of grinding stages located one on top of the other and separated from each other by discs. Each grinding stage is equipped with a number of impact plates. Exchanging the many impact plates is time-consuming, which is why machines are now available that are equipped with continuous impact bars that can be exchanged easily. The rotor is surrounded by the grinding track, which is composed of grooved grinding track segments. An air classifier can be installed above the grinding zone. The classifier, however, does not make a real classifier mill out of the long gap mill, because the recirculation of the coarse material upstream of the grinding zone is complicated.

The long gap mill is especially suitable for simultaneous grinding and drying. (Further applications are given in Table 4.) This is due to the fact that there are no dead zones in which the moist product could cake and deposit. Long gap mills are operated at peripheral speeds of up to 150 m/s, and can grind finer than the simple impact mill as a result of the higher number of stressing events. They can also produce steeper particle size distributions as a result of a narrow residence time distribution. The largest mills of this type have rotor diameters of over 2 m and a drive power of over 1,000 kW. Large long gap mills are by far the largest fine impact mills.

Fine impact mills with air classifiers. Because the grinding elements and an air classifier are integrated into a single machine housing, this type of mill is known as a classifier mill. With classifier mills it is the integrated classifier that controls the product fineness and not the speed of the grinding rotor. Classifier mills thus offer the advantage of the highest finenesses among the mechanical impact mills and stable product properties even if the properties of the feed material are changing. These reasons are the motivator behind the increasing use of classifier mills. However, these advantages give rise to higher costs because a more powerful fan is needed than with the simple rotor-impact mills. The fan sucks the transport air through the mill against the resistance of the classifying wheel. The pressure drop at the classifying wheel can be several thousand Pascals. The feed rate is usually controlled with the current of the mill motor.

A schematic of the most-widespread classifier mill is shown in Figure 6. The maximum peripheral speed of these mills is up to 150 m/s; the air classifiers run at peripheral speeds of up to 60 m/s. This mill type has been on the market since about 1970 and is built in over 20 machine sizes. The largest mills have a drive power of up to 500 kW.

The grinding disc is driven from below via a hollow shaft. The shaft for the conical deflector classifying wheel, which has its own frequency-controlled drive, runs through the hollow shaft. The feed material is charged pneumatically, for which a partial flow of the mill air has to be branched off. Comminuted material follows the flow of air around the guide cone to the classifying wheel. The high-speed classifying wheel allows only fines to pass through it; coarse material is rejected and returned to the grinding disc where it is reground. The cover for the machine can be hinged back so that internals are easily accessible for cleaning.

Dictated by their function, deflector wheels cannot be set to any coarse value desired, but are limited to a top value of around 200 m (assuming a feed material with a bulk density of 2,000 kg/m3). At high speeds, classifier mills compete with jet mills, and at coarser fineness values, also with pin mills. Compared with jet mills, the energy consumption of the classifier mill is comparatively low, and compared with pin mills, it has advantages in terms of operating stability, an exact top cut and a higher resistance to wear. Over the course of the years, a number of different classifier mills have been developed, each of which have their strengths for certain applications (Table 5).

Jet mills use the effect that compressed gas is accelerated to extremely high speeds when it is expanded in a nozzle. Thereby, the energy contained in the compressed gas in the form of heat is converted to kinetic energy. The gas can even be accelerated to supersonic speed in a Laval nozzle. A Laval nozzle is characterized by its hourglass shape, which widens downstream of the narrowest diameter in a similar way to Venturis.

Compressed air at 20C and between 6 and 8 bar overpressure is frequently used, in which case the exit velocity of the air is approximately 500 m/s. If the product permits, the compressed air is not cooled downstream of the compressor, and jet mills are operated at elevated temperatures. Air velocities of approximately 600 m/s can be achieved in this way. After exiting the nozzle, the speed of the jet drops rapidly as a result of air and product being sucked in from the surroundings.

If superheated steam is used as the propellant, it is possible to achieve speeds of over 1,000 m/s. A significant disadvantage of grinding with steam, however, is the tricky operation of a system where the risk of condensation in the downstream filter is high. This is the reason why more and more jet mill owners have meanwhile switched from steam operation to compressed air mode.

Increasing demands on the product quality and the development of the fluidized-bed opposed jet mill (described below) have helped jet milling gain acceptance, even though the energy consumption of jet mills is extremely high. Besides taking a look at the fluidized-bed opposed jet mill, the spiral jet mill, which continues to be popular in the pharmaceuticals industry is also considered.

Spiral jet mill. The spiral jet mill is a simple piece of equipment. At the periphery of the flat-cylindrical grinding-classifying chamber, compressed air is expanded in nozzles that are pitched at an angle of between 30 and 50 deg. to the radius (Figure 7). This causes a rotating air stream in the grinding chamber. The feed material, charged to the grinding chamber through an injector, becomes caught up in the rotating flow of air, is centrifuged and ultimately forms a rotating ring of material at the periphery. This transports the feed material into the jets of grinding air, where it is comminuted mainly as the result of impacts between the particles traveling at different speeds. The air stream in the grinding chamber effects a spiral classification: fine material is conveyed to the central discharge opening, whereas coarse material is centrifuged back out to the periphery. A high pressure builds up in the mill as a result of the air rotating at high speed. This makes it necessary to use an injector operated with compressed air to feed the material; with approximately 30%, the injector requires a considerable share of the total air flow.

The spiral jet mill has no fineness control. At a constant air flowrate, the feedrate is the main parameter used to adjust the fineness. A high throughput results in coarse product because the spiral is decelerated, and this leads to a coarser classification.

The advantages of the spiral jet mill simple design, simple cleaning [(clean-in-place (CIP) capable] and simple sterilization [sterilize-in-place (SIP) capable] have all combined to ensure that this machine has remained the standard machine in the pharmaceutical industry for fine grinding. And this is in spite of the disadvantages: high noise level in operation (injector), additional gas requirement for the injector, sensitivity to wear, and no fineness adjustment. Spiral jet mills are employed in the chemicals industry for the dispersion of pigments. During a dispersion process, the final particle size is dictated more by the primary particle size in the feed material than by the air classification. Large mills have a diameter of the grinding chamber of approximately 1 m and consume up to 3,000 m3/h of compressed air. Small mills for product development have diameters of only 30 mm.

Fluidized-bed jet mills. The fluidized-bed opposed-jet mill came onto the market around 1980. The big advantage of this jet mill, when compared with the spiral jet mill, is the integrated deflector-wheel classifier, which, together with the constant air flowrate, ensures an extremely constant product quality.

The nozzles expand the compressed grinding air horizontally in the grinding chamber (Figure 8). In the case of frequent product change that is, the desire to completely empty the vessel additional bin floor nozzles can also be used. The nozzle diameters range from 1 mm with the small mills to 30 mm with the largest ones. The rising flow of air transports ground product to the integrated classifying wheel. Fines are able to pass through the classifying wheel, whereas coarse material is rejected and falls back into the grinding zone. To ensure that a constant material level is maintained, the metering unit is controlled by the power consumption of the classifier drive or the weight of the filled mill.

Grinding takes place both in the individual jets themselves and in the focal point of the jets. The gas jets introduced into the particle bed fluidize the product and draw individual particles into the jets. Fine and light particles are accelerated and blasted away at the circumference of the jet and cannot enter into the center with the highest velocity. This problem can be reduced with special multiple nozzles, which, in some cases, leads to energy savings of 30%.

The major difference between the fluidized-bed opposed-jet mill and conventional jet mills is that comminution takes place exclusively in the fluidized bed as a result of the particles impacting against each other, and is thus largely free from wear, because the particles never impact at high speed against the machine wall. The only wear-prone component in the mill is the classifying wheel, which can be protected by selection of a suitable construction material. Monobloc classifying wheels made of aluminum oxide and silicon carbide have proven themselves in operation for even the hardest and most abrasive products.

To prevent high pressure drops and increased wear, it is necessary to operate the classifying wheels at the lowest possible peripheral speeds. For large jet mills with high air flowrates, the highest fineness values can best be achieved with several small classifying wheels. This is due to the fact that at the same peripheral speed, the cut point of classifying wheels shifts into the coarse range with increasing classifying wheel diameter.

The fluidized-bed opposed-jet mill has the following strengths: finenesses down to 3 m, depending on the product density; low degree of wear, regardless of the product hardness; low product contamination; cool grinding; easy cleaning; quiet operation; and SIP capabilities. These advantages have served to open up a wide range of applications for this mill (Table 6). The largest mills require up to 15,000 m3/h of compressed air, and the compressors needed to operate the mill are equipped with up to 1,000 kW drive power.

Figure 9 uses the example of grinding sugar in a pin mill to show that a parallel shift of the particle size distribution is achieved by changing the speed of the pin disc and by changing the feedrate. The highest fineness of 99% < 90 m is achieved at the highest speed and the lowest feedrate.

In the example shown in Figure 10, the same feed material was used for all machines, namely marble with a particle size of between 0.1 and 2 mm. In each case, the finest particle size distribution produced in the tests with the specified mill type is shown. In the coarser range, one can see that the particle size distribution merely makes a parallel shift. In the fine range, it is not possible to achieve more than 10% under 1 m; this is due to the integrated classification and the high internal circulation factors.

The energy consumption increases strongly with increasing fineness, which means that for a given system the capacity drops with increasing fineness. Figure 11 shows the energy consumption versus the median particle size for the same feed material as in Figure 10. The power consumption of the mill only is considered, without classifier, fan and other auxiliary units. With the jet mill, the jet power was used for the calculation, and not the drive power of the compressor. In the range of median finenesses between 10 and 100 m, the specific grinding energy is around 10 kWh/m.t. (m.t. = metric ton). For the highest fineness, the energy consumption goes up to around 1,000 kWh/m.t. There are only few products with a corresponding value-added factor allowing such a high effort for the size reduction. (Marble is not among these products, it is just used as an example here.)

Figure 10. The particle size distributions for marble achieved in different mill types. (1) feed material; (2) impact mill with crushing disk (Figure 3a); (3) impact mill with plate beater (Figure 3b); (4) double rotor pin mill; (5) classifier mill; (6) fluidized-bed jet mill

Certain product properties can lead to a mill being particularly suitable for a specific application or to it not being suitable at all. Table 7 gives an overview of the suitability of various machine types on the basis of different criteria.

An impact mill on its own is not functional; it needs a more-or-less elaborate system for operation. A standard system for the classic impact mill is shown in Figure 12. Feed metering channels or screws (1) ensure a uniform feedrate. A magnet in the feed chute (2) protects the grinding elements from metallic tramp material. The door interlock (3) ensures that the mill cannot be switched on if the door is open and that the door cannot be opened if the rotor is still running. A suction-side silencer (4) reduces the noise at the site of machine installation. A large part of the ground product accumulates directly in the fines collection bin (5), whereas fine dust is collected in the automatic filter (6). A suction fan (7) compensates the filter resistance in order to maintain a slight under-pressure in the system and thus prevent formation of dust. The rotary valve at the base of the fines collection bin discharges the product and serves as an air-lock.

Figure 12. A standard impact mill system is composed of: a feeder (1), magnetic separator (2), a mill plus safety switch (3), a silencer (4), a product collection bin (5), an automatic filter (6) and a fan (7)

In times with the focus on customized solutions, standard systems play an increasingly insignificant role. Today, solutions are developed for the individual market segments that are more and more specific, whereby the peripheral conditions specified by a product itself must always be taken into account.

Even though dust explosions are relatively rare, they can cause serious damage to people and machines when they do occur. Besides preventive measures, such as the avoidance of potentially explosive dust concentrations, the avoidance of critical oxygen concentrations by inerting and the avoidance of ignition sources, there are a number of design measures that can limit the damage in the event of a dust explosion. In laboratories, for example, inerting is often used likewise in the pharmaceuticals industry. In the case of large systems, an explosion-pressure, shock-proof design is too expensive, and pressure venting and a reduced explosion pressure is therefore used (Figure 13). Conformance with the explosion protection directives 94/9/EC for manufacturers and 99/92/EC for owners became mandatory in the EU member countries in recent years.

Figure 13. Flowchart of a pressure-relieved processing system with classifier mill. [(A) feed; (B) ground material; (1) metal separator; (2) feed metering screw; (3) classifier mill; (4) reverse jet filter; (5) fan; (6) explosion-barrier valve (7) explosion venting; (8) fire extinguishing system; (9) rupture disk]

In the case of brittle products that have a low grinding energy, there is a high mass flowrate of product through the grinding system. Thus, the system can be cooled by the product and does not need additional cooling by an air flow through the system. A compact system without dust collector can be designed for these applications. This is especially advantageous for potentially dust-explosive products, because the system is so compact that it can easily be built in a 10 barg design to withstand dust explosions (Figure 14). This ensures a safe operation of the system and saves investment costs. An example for the use of such compact systems is milling sugar, which is preferably ground with pin discs (see also Figure 9).

Some materials that are subject to plastic deformation at ambient temperature can be cooled to make them brittle enough to be subsequently ground by impact. Cryogenic grinding is used for spices to make sure that the flavor and aroma is preserved. At the same time, cryogenic grinding also increases the throughput. Other applications are the fine grinding of plastics and rubber. The supply of nitrogen is controlled as a function of the mill outlet temperature. The temperatures downstream of the mill often range between 0 and 20C. The nitrogen requirement is considerable and usually ranges between 1 and 3 kg of liquid N2 per kilogram of product, which naturally raises the costs significantly.

Figure 15 shows a cryogenic grinding system operated with liquid nitrogen. Large sections of the system are insulated to reduce the nitrogen requirement, and the cold air is circulated. Operating in the through-air mode is out of the question because freezing water from the air would cause the mill to ice up.

Figure 15. Cryogenic grinding system operated with liquid nitrogen [(A) feed; (B) ground material; (1) feed metering channel; (2) screw cooler supplied with liquid nitrogen (LN2); (3) dual-rotor pin mill; (4) automatic filter; (5) temperature sensor]

The demands posed by the pharmaceutical industry are very different, depending on whether active substances or additives are to be processed and in what form the medicine will be administered. In the case of highly active substances, the batches are relatively small, and thus so are the machines and systems used to process these products. Another important point is that the production personnel must be afforded effective protection. This has led to the increasing use of isolators (Figure 16). A machine is much more difficult to operate if housed in an isolator, than under normal conditions. Grinding systems in isolators are unique systems with every detail designed to users needs.

During the last decades impact grinding has gone through several developments. Dust emissions of systems have been reduced. Products have become finer and finer. Processes have become more stable by using classifiers. Machines have become more reliable in continuous operation. Nowadays customized solutions are available for many applications. Future developments will be: machine diagnosis for planned preventative maintenance, noise reduction, energy efficient grinding processes and use of wear-resistant construction materials to process harder products by impact grinding.

Bodo Furchner is general manager of the technical division of Hosokawa Alpine AG (Peter-Drfler-Str. 13-25, D-86100 Augsburg, Germany; Phone: +49-821-5906-0; Fax: +49-821-5906-234; Email: [email protected]), a position he has held since 1993. Prior to this, he was manager of Hosokawa Alpines Test Center Mechanical Processing from 19951999, and worked in the companys R&D department since 1987. Furchner earned a process-engineering degree from the Technical University of Munich, as well as a Ph.D., which he earned while working as scientist at the Institute for Process Engineering in the team of Professor Mersmann.

This publication contains text, graphics, images, and other content (collectively "Content"), which are for informational purposes only. Certain articles contain the author's personal recommendations only. RELIANCE ON ANY INFORMATION SUPPLIED IN THIS PUBLICATION IS SOLELY AT YOUR OWN RISK. 2021, Access Intelligence, LLC. All rights reserved. | Privacy Policy | Diversity Inclusion & Equity

grinding noise when braking [9 possible causes and how to fix] road sumo

grinding noise when braking [9 possible causes and how to fix] road sumo

If you hear sharp grinding noise when you step on the brakes, it could be that the brake disc and the caliper are rubbing against each other. You can fix this problem by replacing the brake pads immediately. You may also need to have the rotors or discs replaced at this point.

When you have worn-out brake pads, your cars exposed metal parts will grind against the rotor each time you step on the brakes. If you continue driving your car with this grinding noise, you can damage the brakes rotors and calipers.

But when the brake pads are already excessively worn out, exposure of some of its metal parts happens. These exposed metal parts will rub against the rotors each time you step on your brake. In this situation, there is metal-to-metal contact when you step on the brakes, producing the grinding noise.

If you continue driving with the noise in the background, you will likely damage the brake rotors and the calipers. You can fix this problem by replacing the bad brake pads immediately. While fixing this issue, you may also need to have the rotors or discs replaced as well.

You should not drive your car too long once you start hearing this grinding noise. While you may still apply the brakes, you will cause more damage to the rotors and the calipers. This may result in more expensive repairs. So, you have to tow your car to a car service center right away so that it can have the necessary brake system repair.

The car parts that can produce a grinding noise are the drum brake shoes and the disc brake pads. When they are new, they have full brake linings or brake friction materials. But as you use them over time, these linings get thinner and thinner.

If the brake pads are not replaced in due time, the brake linings will get so thin that some of the metal parts will be exposed. When that time comes, the metal brake pad will rub against the steel brake rotor.

Metal-to-metal contact will occur each time you apply the brakes. That produces the grinding noise. The noise is usually deafening. Generally, the noise comes from the front or rear brakes. It is seldom that both front and rear brakes create this noise.

If the grinding noise persists and does not go away every time you step on the brakes, something causes it. It may even get worse if you do not determine what causes this problem. Below are 9 possible causes for this grinding noise when braking:

Worn-out brake pads are the most common cause of this grinding noise. The brake pads on the backing plate get thinner as they are used over time. In due time, there will be portions of the backing plate that has no more pad. Metal to metal contact will now occur.

It can be the metal of the backing plate rubbing against the metal of the rotor or the rotor metal rubbing against the brake caliper. Either way, grinding noise is produced because metal is rubbing against metal. You need to replace the bad part as soon as possible to minimize the damage.

So, what if you hear grinding noise when braking but pads are fine? If there is a grinding noise, but the brake pads are fine, it could be solid objects between the caliper and rotor, damaged shims, lack of lubrication, bad wheel bearings, or worn-out rotor discs.

If you drive your car frequently, you cant avoid dirt from getting into the car parts, especially those that are under the chassis. There are times when solid objects such as small stones from the pavement can lodge between the brake rotor and the caliper.

When such things happen, youll hear grinding sounds as you step on the brakes of your car. The hard objects will damage the rotor and the caliper if they are not removed right away. They will scrape the friction material and cause uneven wear of the brake pads.

In the normal driving scenario, the typical life of a brake pad ranges from 30,000 to 70,000 miles. If you notice grinding noises sooner, it could be that you are not driving your car too often. Rotors dont get their needed exercise when you dont drive your car enough.

Rust can form on these rotors. They may also get corroded when they are just in the garage, especially during the whole winter. Other parts of the braking system are prone to developing rusts, like the calipers. They can get stuck.

With rusts on their metal surfaces, the rotors wont have smooth surfaces anymore. So, once you start driving and have to step on the brakes, you will hear a grinding noise. The best way to avoid it is not to let your car sit idly in the garage for far too long. Drive it once in a while to avoid this grinding noise problem.

If you use low-quality brake pads, they will actually cost you more in the long run. Cheap brake pads usually contain tiny metal chunks. These tiny pieces of metal will rub against the surface of the rotor and scrape it. They may cause heavy damage to your brake system. Only use quality brake pads when replacing worn pads.

If the shims are damaged, they will also produce grinding sounds in your car. Metal is usually exposed when a shim is worn out. Once this metal rubs against a metal part of the rotor, it will create a grinding sound.

If you are doing brake repairs, you should also have the shims replaced. Some mechanics want to finish the job quickly and forget all about the shims. Make sure that they replace the shims every time you have the brakes fixed.

Sometimes the grinding noise can be caused by the insufficient lubrication of the brake pads. Whenever new brake pads are installed, their backsides should be lubricated slightly with a brake caliper lube.

Additionally, you should lubricate the caliper slider pins or bolts as well before they are re-installed. These are the pins or bolts that connect the two sides of the brake caliper. If they are not lubricated, their slides will produce grinding sounds. Reputable car service centers will lubricate these pins after a brake repair job. Some even provide new bolts to their clients.

Rotor discs that are already too old can also create grinding noises. Worn-out rotor discs are no longer flat. They will create scraping sounds aside from causing vibrations from the cars brake system.

Old rotors become warped, cracked, or gouged. Some mechanics try to resurface them if they are only slightly warped. However, if they are already past their usable service lives, you should replace them.

A bad wheel bearing is the least likely reason for the grinding noise in your car. If you suspect that it is in the wheels that this annoying noise is coming from, faulty wheel bearings are probably the reason. Aside from the noise, you may also feel the steering wheel vibrating while you are driving.

You should consider strange noises while braking as a warning that one of the most critical parts of your car is having some problems. Dont ignore the noise, especially if it comes right after you stepped on the brakes.

Brake grinding is an issue that you need to address promptly. Automotive brakes perform a tough job. You expose them to tremendous forces, and they generate too much heat every time you activate your cars braking system.

The excessive amount of friction developed by stopping a speeding vehicle is enough to cause the brakes to become red hot. So, you will understand why over time, they wear out, malfunction, and finally expire.

That is why, at the first sign of a brake problem, such as grinding noise, have your braking system checked by a qualified auto mechanic. Doing so will help you avoid costly repairs and may even save your life.

Auto mechanics say that grinding noises are small voices whispering in your ears, saying, you are killing me. They created an acronym for this type of car problem: CPR, which stands for calipers, pads, and rotors.

Once you hear this grinding noise, stop your car on the roadside. Then call for a tow truck. Dont worry about the cost of the tow. You need to think about the further damage your car can sustain if your car makes this noise when braking.

So, dont think that you can still drive your car safely once this grinding noise hits. The longest distance that you can drive once you hear a grinding noise in your cars braking system is the distance from the road to the shoulder of the road.

In general, the cost of a brake repair job that involves brake pad replacement, new caliper, and new rotor, including labor, ranges from $300 to $800. The actual cost will depend on the make and model of your car and the required fix.

If all these parts are to be replaced, the cost will increase to $1000 plus. The average cost of this kind of auto brake system repair is $500. Repair costs also vary depending on the quality of the braking system parts.

If you are lucky, a mechanic will only change the brake pads, and the grinding noise will go away. You will be able to use the rotors still. But if you insist on driving your car with this noise in the background, the time will come that you may also need to replace the rotors. They are more expensive than the pads.

If you step on the brakes and instantly hear a grinding noise, the brake disc is likely rubbing against the caliper. You can fix this problem by replacing the brake pads right away. But as you perform this repair, you may also need to replace the rotors or discs.

Brake pads that are excessively worn out will have exposed metal parts. These exposed metal parts of the brake pads will rub against the brake rotors every time you step on the brakes. You will likely damage the brake rotors and calipers if you continue driving your car with this grinding noise in the background.

What if you hear a grinding noise when braking, but the pads are fine? If you hear a grinding noise but the brake pads are fine, it could be solid objects between the caliper and rotor, damaged shims, bad wheel bearings, lack of lubrication, or worn-out rotor discs.

metallographic grinding and polishing insight

metallographic grinding and polishing insight

Mechanical preparation is the most common method of preparing materialographic specimens for microscopic examination. The specific requirement of the prepared surface is determined by the particular type of analysis or examination. Specimens can be prepared to the perfect finish, the true structure, or the preparation can be stopped when the surface is acceptable for a specific examination.

Mechanical preparation is the most common method of preparing materialographic specimens for microscopic examination. The specific requirement of the prepared surface is determined by the particular type of analysis or examination. Specimens can be prepared to the perfect finish, the true structure, or the preparation can be stopped when the surface is acceptable for a specific examination.

The basic process of mechanical specimen preparation is material removal, using abrasive particles in successively finer steps to remove material from the surface until the required result is achieved. There are three mechanisms for removing material: grinding, polishing, and lapping. They differ in the tendency to introduce deformation in the specimen's surface.

Proper grinding removes damaged or deformed surface material, while limiting the amount of additional surface deformation. The goal is a plane surface with minimal damage that can easily be removed during polishing in the shortest possible time. Grinding removes material using fixed abrasive particles that produce chips of the specimen material (see below). The process of making chips with a sharp abrasive grain produces the lowest amount of deformation in the specimen, while providing the highest removal rate.

The grain is entering the specimen surface. The grain is totally fixed in the X-direction; movement (resilience) in the Y-direction can take place. The chip is started when the grain enters into the specimen material.

This is normally the first step in the grinding process. Plane grinding ensures that the surfaces of all specimens are similar, despite their initial condition and their previous treatment. In addition, when processing several specimens in a holder, care must be taken to make sure they are all at the same level, or "plane," before progressing to the next step, fine grinding. To obtain a high, consistent material removal rate, short grinding times and maximum flatness, totally fixed grains with a relatively large grain size are preferred for plane grinding. Suitable PG surfaces will provide perfectly plane specimens, thus reducing the preparation time on the following fine grinding step. In addition, some surfaces can provide good edge retention. During wear, new abrasive grains are revealed, thus ensuring a consistent material removal.

Fine grinding produces a surface with little deformation that can easily be removed during polishing. Because of the drawbacks with grinding papers, alternative fine grinding composite surfaces are available, in order to improve and facilitate fine grinding, A high material removal rate is obtained by using grain sizes of 15, 9.0 and 6.0 m. This is done on hard composite disks (rigid disks) with a surface of a special composite material. Thus, the diamond grains, which are continuously supplied, are allowed to embed the surface and provide a fine grinding action. With these disks, a very plane specimen surface is obtained. The use of a diamond abrasive on the fine grinding disks guarantees a uniform removal of material from hard, as well as soft, phases. There is no smearing of soft phases or chipping of brittle phases, and the specimens will maintain a perfect planeness. Subsequent polishing steps can be carried out in a very short time.

Diamonds are used as an abrasive to accomplish the fastest material removal and the best possible planeness. No other available abrasive can produce similar results. Because of its hardness, diamonds cut extremely well through all materials and phases. During polishing, a smaller chip size is desirable to ultimately achieve a specimen surface without scratches and deformation. More resilient cloths are used, along with smaller grain sizes, such as 3.0 or 1.0 m, to obtain a chip size approaching zero. A lower force on the specimens will also reduce the chip size during polishing.

Certain materials, especially those that are soft and ductile, require a final polish, using oxide polishing to obtain the best quality. Colloidal silica, with a grain size of approximately 0.04 m and a pH of about 9.8, has shown remarkable results. The combination of chemical activity and fine, gentle abrasion produces scratch-free and deformation-free specimens.

In lapping, the abrasive is applied in a suspension onto a hard surface. The particles cannot be pressed into the surface and secured there. They roll and move freely in all directions, hammering small particles out of the specimen surface and introducing deep deformations. The reason is that the free moving abrasive particle is not able to produce a real "chip" of the specimen surface.

The X-axis represents the hardness in Vickers (HV). The values are not shown in a linear progression, because the variety of preparation methods for softer materials is greater than for hard ones. The shape of the Metalogram results from soft materials generally being more ductile and hard materials usually being more brittle.

The Metalogram is based on ten preparation methods. Seven methods, A - G, cover the complete range of materials. They are designed to produce specimens with the best possible results. In addition, three short methods, X, Y, and Z, are displayed. These methods are for very quick, acceptable results.

Some materials such as composites, coatings, or other materials consisting of various phases or components cannot be easily placed in the Metalogram. In these cases, the following rules can be applied when deciding on the preparation method:

Surfaces are carefully selected according to relevant equipment in use, sample material, and requirements for preparation. Within each group of surfaces: grinding stones, grinding or polishing paper, disks or cloth, the difference in characteristics include type of abrasive bond, abrasive type, hardness, resilience, surface pattern, and projections of fibers.

The preparation is always started with the smallest possible grain size to avoid excessive damage to the specimens. During the subsequent preparation steps, the largest possible intervals from one grain size to the next are chosen in order to minimize preparation time.

The removal rate in grinding and polishing is closely related to the abrasives used. Diamonds are one of the hardest known materials, as they have a hardness of approximately 8,000 HV. That means it can easily cut through all materials and phases. Different types of diamonds are available. Tests have shown that the high material removal, together with a shallow scratch depth, is obtained because of the many small cutting edges of polycrystalline diamonds. Silicon carbide, SIC, with a hardness of about 2,500 HV, is a widely used abrasive for grinding papers for mainly non-ferrous metals. Aluminium oxide, with a hardness of about 2,000 HV, is primarily used as an abrasive in grinding stones. It is mainly used for the preparation of ferrous metals. It was also extensively used as a polishing medium, but since the introduction of diamond products for this purpose, it has largely lost its usefulness in this application. Colloidal silica is used to produce a scratch-free finish in oxide polishing steps In general, the abrasive must have a hardness of 2.5 to 3.0 times the hardness of the material to be prepared. Never change to softer abrasives - this might lead to preparation artifacts. The amount of abrasive applied depends on the grinding/polishing surface and the hardness of the specimen. The combination of cloths with low resilience and hard specimens requires a larger amount of abrasive than cloths with high resilience and softer specimens, because the abrasive particles wear faster.

Depending on the type of material and the grinding/polishing disk used for preparation, the amounts of lubrication and cooling have to be balanced. Generally, it can be said that soft materials require high amounts of lubricant to avoid damage, but only small amounts of abrasive as there is very little wear on the abrasive. Hard materials require less lubricant but higher amounts of abrasive, due to faster wear. The amount of lubricant has to be adjusted correctly to get the best result.

The polishing cloth should be moist, not wet. Excess lubricant will flush the abrasive from the disk and remain as a thick layer between the specimen and disk, thus reducing material removal to a minimum.

For PG, a high disk speed is used to get a fast material removal. For FG, DP, and OP, speeds of 150 rpm are used for both grinding/polishing disks and specimen holders. They are also both turning in the same direction. When working with loose abrasives, high speeds would throw the suspension from the disk, thus requiring higher amounts of both abrasive and lubricant.

The force is expressed in Newton. The figures stated in the preparation methods are typically standardized for six specimens of 30 mm diameter, clamped in a specimen holder. The specimens are mounted, and the specimen area should be approximately 50% of the mount. If the specimens are smaller, or there are fewer specimens in a holder, the force has to be reduced to avoid damage, such as deformations. For larger specimens, the force only needs to be slightly increased. Instead, the preparation time shall be extended. Higher forces increase the temperature because of higher friction, so thermal damage may occur.

Preparation time is the time during which the specimen holder is rotating and pressed against the grinding/polishing disk. The preparation time is stated in minutes. It should be kept as short as possible to avoid artifacts such as relief or edge rounding. Depending on the specimen size, the time may have to be adjusted. For larger specimens, the time shall be extended. With specimens smaller than the standard, the time is kept constant and the force reduced.

The plastic deformation of larger sample areas is called smearing. Instead of being cut away or removed, material is pushed across the surface. Smearing occurs because of an incorrect application of abrasive, lubricant, polishing cloth, or a combination of these, which makes the abrasive act as if it was blunt. There are three ways to avoid smearing:

If your polisher is not equipped with automatic water flushing after the oxide polishing step during the last ten seconds of OP polishing, flush the polishing cloth with water to clean both the specimens and the cloth.

There are two types of deformation:elasticandplastic. Elastic deformation disappears when the applied load is removed. Plastic deformation, which may also be referred to as cold work, can result in subsurface defects after grinding, lapping, or polishing. Remaining plastic deformation can first be seen after etching.

Only deformation introduced during the preparation is covered here. All other types from previous operations like bending, drawing, and stretching are not considered, because they cannot be changed or improved by changing the preparation method.

Using a polishing surface with high resilience will result in material removal from both the sample surface and the sides. The effect of this is edge rounding and can be seen with mounted specimens if the resin wears at a higher rate than the sample material.Please check your samples after each step to see when the fault occurs so you can determine what changes you will need to make in the preparation.

Relief is usually not noted until polishing begins, so it is important to begin the preparation with grinding media that will keep the samples as flat as possible. However, for the best possible starting conditions, MD-Largo should be used for fine grinding of materials with a hardness below 150 HV, and MD-Allegro should be used for fine grinding of materials with a hardness of 150 HV and higher.

Gaps are voids between the mounting resin and sample material. When examining samples with a microscope, it is possible to see if there is a gap between the resin and the sample. Gaps can result in a variety of preparation faults: edge rounding, contamination of polishing cloth, problems when etching, and staining.

Note:Vacuum impregnation will only fill cracks and cavities connected with the surface. Be careful not to use mounting materials with high shrinkage. They might pull layers away from the base material.

Some materials have natural porosity, for example, cast metals, spray coatings, or ceramics. It is important to get the correct values, and not to provide incorrect readings because of preparation faults.

Contrary to the ductile material, where the initial porosity seems to be low and pores have to be opened, brittle materials seem to have a high porosity. The apparent fracturing of the surface has to be removed.

Contrary to the ductile material, where the initial porosity seems to be low and pores have to be opened, brittle materials seem to have a high porosity. The apparent fracturing of the surface has to be removed.

Comet tails occur adjacent to inclusions or pores, when the motion between sample and polishing disk is unidirectional. Their characteristic shape earns the name "comet tails." A key factor in avoiding comet tails is the polishing dynamics.

3. Polishing for extended time on a soft cloth is a contributing factor. Ensure that as little deformation as possible must be removed by the next polishing step, especially when a cloth with high resilience is needed.

An embedded abrasive is a loose abrasive particle pressed into the surface of a specimen. With soft materials, abrasive particles can become embedded. Embedded abrasives can occur because of a small abrasive particle size, the grinding or polishing cloth used has a low resilience, or a lubricant with a low viscosity is used. Often, a combination of these reasons takes place.

Lapping tracks are indentations on the sample surface made by abrasive particles moving freely on a hard surface. These are not scratches, like from a cutting action, but are the distinct tracks of particles tumbling over the surface without removing material.

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