crusher product gradation charts
Aggregates required for a given job are generally specified by a full set of gradation limits and other relevant properties of the material.When rock is crushed, the product includes material of the size of the crusher setting, some slightly larger and the rest of the material smaller than the crusher setting. Crusher manufacturers publish grid charts, particle size cumulative distribution curves, and/or product size distribution tables to help predict the gradation of the crusher product. These charts, curves, and tables give the percentages passing or retained on standard size screens for each given setting of the crusher.
The distribution of product sizes given in the table above is based on crushed limestone weighing 100 lb/cu ft with a specific gravity of 2.6. This same sort of information may be presented by the manufacturer in a set of curves for the various settings of the crusher. The curves, one for each closed side setting, will give an estimate of the cumulative percentage ofmaterial passing a given screen size on the horizontal scale with the screen opening in inches on the vertical scale.
(a) How much of the output will pass a 1-in. screen (i.e., minus 1-in. material), and (b) how much of the materialpercentage and tonnagewill pass the 1-in. screen and be retained on the -in. screen?
(b) In the column for a 2 in. setting, it is found that 20% of the output is between 1 in. and 1 in. size (i.e., -1 +1 in.) and 13% is between 1 in. and in. ( 1 +). Therefore, the quantity of output passing the 1 in. screen and retained on the in. screen is 33%. The rate of production in the 1 in. to in. size range is 0.33 x 60 = 20 tph.
how does an impact crusher work? | rubble master
Impact crushers reduce mineral materials such as concrete, asphalt and natural rock in size to produce a valuable commodity product. A fast spinning rotor throws the material against a solid stationary impact wall. The striking and impacting causes the material to shatter into smaller pieces. The result is a very homogenous and cubical product leaving the crusher box.
The horizontal shaft impactors are the most common impactor type that can be used in recycling, primary and secondary crushing applications. This type impactor will take reasonable size pieces and produce small output material.
The crusher box includes a rotor with hammers (also called blow bars). Depending on the rotor style you will have either 3 bars or 4 bars. Hammers are cast iron replaceable wear parts that are actually in contact with the material. They are designed to withstand the many impacts of the material. The impact wall (also called apron) has several crushing stages and is armoured by thick wear plates.
Once the hammer hits the big material entering the crusher box it is thrown against the wall and starts ricocheting between hammers, wall and other material particles. As soon as the material is small enough the fit in between the rotor and the lowest crushing stage of the impact wall it will leave the crusher box at the bottom.
The beauty of impact crushers is their versatility in terms of input material and output size. There are many different designs out there but generally speaking impact crushers can produce material from 3" down. The smaller the input material the harder it gets to crush. The output gradation can be adjusted through various settings.
On most crushers this works hydraulically. The aprons need to be adjusted when you want to produce a different output material or when you need to readjust your crusher settings to accomodate the wear progress.
RUBBLE MASTER impact crushers use a simple design to change the crusher setup easily, quickly and safely within minutes. The unique proprietary crushing chamber design allows operators with limited impact crushing experience to operate our machine efficiently from day one.
crushing products size and shape -what to expect
I have madea number of general remarks regarding the character of product delivered by crushers of various types, and under different conditions of operation. Generalities are of value only if we have some standard to which comparisons may be referred; therefore, we should like to present more specific information on the kind of product to be expected from crushing equipment under average operating conditions. Much of the data on which sizing/designcurves and tables are based comes from operations involving those two very important types: gyratory and jaw crushers; therefore these curves and tables are more nearly representative of the work of these types than of rolls or hammermills. They may be used for these latter types however if due allowance is made for peculiarities of each type, as pointed out in the descriptions of the different machines.
The preparation of a set of product gradation curves involves a considerable amount of work in the collection of the necessary test data, and a certain degree of discrimination in sorting such data and weeding out erroneous results. There are several reasons why no set of product gradation curves can be regarded as more than reasonably close approximations. First among these is the variation in physical structure of the many materials for which crushers are used; rocks exhibit a high degree of rugged individualism in their reaction to crushing. This variation is frequently quite pronounced between different ledges in the same quarry.
Gradation of the crusher feed also has its effect upon the product analysis. This is true even of screened feed, although deviations from the average are not likely to be so wide as they are for unscreened material, such as quarry-run or mine-run rock. We have commented on other variable factors, such as choke versus regulated feed, straight versus curved concaves, and so forth.
Fortunately, most materials do follow a certain definite gradation pattern and, by averaging a large number of test results, it is possible to plot a group of curves which can be classed as fairly close approximations. Even though approximate, these curves are of great value in crushing-plant design, or in the solution of problems concerning additions or alterations in the plant flowsheet. They simplify the problem of selecting secondary and tertiary crushers, as well as elevating and conveying equipment, and they are invaluable in the calculation of screen sizes. In short, they eliminate much of the old-time guess work in the preparation of the plant flowsheet.
Gyratory and jaw crushers are always rated at certain open-side or close-side discharge settings. In order that we may select the particular curve, of a group of curves, which will most nearly represent the product of a crusher having any given discharge setting, it is important to know approximately what percentage of the total output will pass a screen opening of equal dimension. It was universal practice in past years to designate such screen openings as ring-size for the very logical reason that the leading screen of that day, the revolving type, was, almost without exception, fitted with sections having round holes. Now that the vibrating screen, with its wire cloth or square-punched steel plate sections, has pre-empted the field there is no longer any excuse for adhering to the ring-size product designation.Above is alist of the approximate percentages of product passing a square opening test sieve whose holes are equal to the discharge setting of the crusher. Several different conditions are tabulated, and each condition is accompanied by estimates for four different classes of material.
In gravel pit operations it will usually be found that some one of these listed base rocks will predominate, and no great error will be introduced if this predominant rock is used as the basis for product calculations. Most base rocks will be close enough in physical structure to one of the listed varieties so that the percentages can be used for them without serious error. The same statement applies to the product gradation curves to be discussed. It must be remembered that the entire process of securing and compiling data of this nature is, at best, one which is susceptible of only approximate results.
It was formerly the custom to consider one set of product gradation, or screen analysis, curves as being suitable to represent the products of both primary (unscreened) and secondary (screened) feeds, making no allowance for the undersize material which is always present, to some extent, in quarry-run and mine-run materials. The average quarry does not produce as much of this undersize rock as the average mine, but the usual practice in mining operations is to scalp off most of the undersize ahead of the primary crusher, whereas this practice is the exception rather than the rule in quarry operations. As a matter of fact, where the secondary crushers are fitted with straight concaves, or jaw plates, as used to be standard practice, the dif-ference between product curves on screened and unscreened feed was not significant, and no great discrepancy was introduced by considering them under the one heading.
With the introduction of non-choking concaves in the standard gyratory crushers and reduction crushers, and the development of high speed fine-reduction crushers with high choke points, it soon became apparent that there was a substantial difference in the screen analyses of the two kinds of product, that is, crusher products on unscreened and screened feeds. The difference is especially significant in the lower part of the curve, where undersize in the feed would naturally show up, and where the cleaner breaking of the non-choke crushing chamber would likewise be reflected.
Here above isshown a family of curves for primary crushing of unscreened feed, such as the average quarry-run material in which the undersize (minus crusher setting) rock is present in proportions normally resulting from blasting operations. The same curves may be used for mining operations with stationary bar grizzlies ahead of the primary crusher.
In such operations the amount of undersize going into the crusher will usually be about the same as for the quarry operation without pre-scalping.
It should be noted that the test data on which these curves are based were taken from gyratory and jaw crusher operations, but, as we have stated before, they may be used for other types of crushers if allowance is made for the characteristics peculiar to each type. As a matter of fact, so far as crushers of the Fairmount single-roll type are concerned, there is a natural compensation which brings the curves fairly well into line. The Fairmount crusher is inherently a somewhat cleaner breaking machine than either the standard gyratory or standard jaw types, but the class of rock for which the former crusher is largely used is usually subject to greater than average degradation during the blasting and loading operations in the quarry, which tends to level out the difference in crushing performance.Using Crusher and Screen Charts
The method of using the curves is so simple as to require little comment. The vertical axes represent material sizes, which may be taken as either square or round openings; provided of course that the same shape of opening is used throughout any particular analysis. The horizontal axes represent cmmdative percentages passing corresponding screen openings. If we wish to check the product to be expected from a crusher set at some predetermined discharge opening, we first refer to the table showing the approximate percentage of product which will pass an opening equivalent to the crusher setting. This gives us a point in the group of curves which may, or may not, be exactly on one of them. In the latter case we interpolate by following an imaginary curve between the two curves on either side of our point. We can thus tabulate cumulative percentages passing all of the product sizes in which we may be interested. Non-cumulative percentages; which are important because they are used to determine expected amounts of specific products are simply the difference between the upper and lower cumulative percentages for the particular product limits under consideration.
For those not familiar with the use of product gradation curves an example may be helpful. Suppose that a tentative selection of a 3.5 open- side discharge setting has been made for a standard gyratory primary crusher to be used for crushing quarry-run limestone. Referring to the table which lists percentages of product passing an equivalent square opening, we find that 85 to 90% of the crusher product should pass a 3.5 square opening. Choosing the lower percentage, to be on the conservative side,, we follow the horizontal line, denoting the 3.5 product size in the curve chart, over to the vertical line marking the 85% value. We find that the point we have established does not fall directly upon any of the group of curves, but lies so close to one of them that it may be used without appreciable error into our calculations.
Let us suppose that we wish to know how much of the product of our primary crusher will be retained on a 1.5 square opening screen, so that we may estimate the size and number of secondary crushers required to recrush the plus 1.5 contingent. Following the curve down to the 1.5 line, we find that 43% of the primary crusher output may be expected to pass this screen opening; 57% will be retained, which means that we must provide secondary crushing capacity to take care of 57 tons for each 100 tons fed to the primary crusher.
Occasionally it happens that we wish to scalp off a salable product from the output of the primary crusher; for example, a plus 1.5 minus 3.5 material for highway base- rock. The difference between the cumulative percentages at the 3.5 and 1.5 points on the curve gives us the amount, of such product to be expected from the output of the primary crusher This is 85 minus 43, or 42% of the primary crusher product.
If our problem had covered a crushing condition calling for 80 instead of 85%passing the opening equivalent to the crusher setting, we would have found that our point fell exactly on a curve, regardless of what crusher setting we had selected. This is because all of the family of curves are based on the 80% line. Obviously a group of curves might be based on any percentage line, but it is usual practice to choose the 80 or 85% values.
It will be noted that the curves bend upward in very marked fashion above the 75-85% region. This simply reflects the tendency of practically all materials to slab, or spall, to some extent in the crusher. As a matter of fact, product gradation in this upper range (above the open- side setting of the crusher) is of a distinctly uncertain and variable nature, and about all that a group of curves can do is to reflect the general tendency. Fortunately the exact screen analysis in this fraction of the primary crusher output is recrushed in succeeding stages, and all that is required is to know approximately how much of it there will be to recrush.
Although the group of curves we have been considering are intended for calulations involving primary crushing operations, they may also be used for secondary crusher products in those cases where no screening is performed between primary and secondary stages. Such an arrangement is seldom encountered in modern plant design, except where large jaw crushers, set very wide, are followed by a secondary, usually of the standard gyratory type, to reduce further the very coarse output of the jaw crusher to a size which can be handled by the recrushing, screening, and elevating equipment in the balance of the plant. In such cases it is simplest to consider the two-stage set-up as a single machine with discharge opening equal to that of the secondary crusher.
The group of curves on the rightischarted from screen analyses of the products of crushers receiving screened feed. They are useful in predicting the character of output from secondary and tertiary crushers, and are of great value in the preparation of plant flowsheets, and in calculating vibrating screen capacities. Their use in the latter connection will be discussed in the screening section of this series.
There is no need for extended comment on this group of curves; the method of taking off cumulative percentages, and non-cumulative fractions, is exactly the same as for the chart we previously discussed. The difference in the shape of these curves is attributable to the absence of fines in the crusher feed, and to the cleaner breaking action of the modem reduction crusher.
The product gradation curves for screened feed, described under the preceding sub-heading, can be used as a basis for calculating approximate screen analysis of products from closed-circuit crushing stages, but the values cannot be taken directly from the curves.
For example, consider a crusher set to turn out a product 70% of which will pass a 5/8 square opening, and in closed circuit with a screen which is equipped to remove the minus 3/4 product. Thecurve shows that approximately 85% of the crusher product will pass the 3/4 square openings.
Suppose that we wish to know how much minus 0.25 fines we may expect from the circuit.We do not go to the curve which touches the 100 percent ordinate at the 3/4 value; we calculate the percentage from the same curve which was used to predict the proportion of minus 0.75 in the crusher discharge. This curve shows approximately 29 percent of minus 3/4 in the material as it comes from the crusher, or 29 tons of fines in each 100 tons of crusher output. But, for the circulating load, we are only interested in that fraction of the crusher output which will pass the 3/4 screen, which is 85 tons.That part of the product gradation curve which lies below the 85 percent valuerepresents the gradation of the finished product, and 29 tons out of each 85 would be minus 0.25.
Let x equal percentage of minus 0.25 in the finished product, then x:100=29:85 or x = 34.1 percent of minus 0.25 rock from the closed circuit operation. Any other size of product may be estimated in a similar manner. Note that if we had used a curve touching the 100 percent ordinate at the 0.75 value, we would have arrived at a value approximately 50 percent for the minus 0.25 fraction; a value which is obviously erroneous for rock of average characteristics. We will comment on closed circuit crushing, and upon certain assumptions which have to be made in closed circuit calculations, in a later discussion of reduction-crushing.
Although the long established practice of designating crusher products by ring-size is not compatible with present-day screening practice, there are occasions when it is desirable to convert our calculations from one shape of opening to the other. So far as the curves themselves are concerned, once we have established the shape of screen openinground or squarewe can use them for either so long as we stick to one shape throughout the process of taking off percentages-passing. If, as occasionally happens, we have to deal with both shapes of screen opening in the same set of calculations, one or the other of them must be converted to equivalent sizes of the opposing shape. For example, if most of the screen openings are to be square, but one or two of them must be round, the round-hole sizes should be expressed in terms of equivalent square openings.
Inasmuch as the table of crusher settings versus equivalent product percentages is based on square openings, it is necessary to convert to equivalent round openings before this table can be used for such openings.
Below is the information needed to make conversions from round to square holes, or vice versa. The two columns at the left showing equivalent sizes for flat testing screens, are the columns to use in connection with crusher product calculations.Admittedly, listings of equivalent round and square holes, such as we show in this table, can be only approximately correct for the many different materials with which we must deal in crushing and screening computations. The infinite variety of shapes encountered renders absolute accuracy an impossible attainment. Practical experience, however, indicates that the comparisons shown in our table are in most cases close enough for all practical purposes.
Product SizeCorresponding Size Holes
Through a flat testing screen Allis-Chalmers vibrating screenRevolving Screen
Round holes Square holesRound holes Square holesRound holes
17/81 1/1612/101 1/4
1 3/811 2/181 1/181 3/8
1 1/41 1/161 3/81 1/71 2/14
1 3/81 1/81 1/161 1/41 3/4
1 1/21 1/41 3/181 3/81 7/8
1 5/81 3/81 3/41 3/102
1 3/41 1/21 7/81 3/162 1/4
1 7/81 5/821 3/42 3/8
21 3/42 1/81 7/82 1/2
2 1/81 7/82 1/422 5/8
2 1/41 15/182 3/82 1/162 3/4
2 3/822 1/22 1/82 11/16
2 1/22 1/82 6/82 1/43 1/8
2 5/82 1/42 3/42 3/83 5/12
2 3/42 3/82 7/82 1/23 1/2
2 7/82 1/232 5/83 5/8
32 5/83 1/42 3/43 3/4
3 1/42 3/43 1/234
3 1/233 3/43 1/44 3/8
3 3/43 1/443 1/24 3/4
43 1/24 1/43 3/45
4 1/23 7/84 3/44 1/85 1/2
54 1/45 1/44 1/26 1/4
5 1/24 3/45 3/456 7/8
65 1/46 1/25 1/27 1/2
6 1/25 1/275 3/48
767 1/26 1/28 3/4
7 1/26 1/2879 3/8
878 3/47 1/210
8 1/27 1/49 1/47 3/410 1/2
97 3/49 1/28 1/411 1/4
9 1/28108 1/211 3/4
108 1/210 1/2912 1/2
impact crusher stone crushers & grinding mills for mines and quarry
Impact crusher made in Liming Heavy Industry adopts quality steels and wear-resistant parts, which makes it superior and reliable. This machine is possess of rotor with large inertia, and its capacity is improved largely. Impact crusher is usually used as secondary crusher in the production line.
how to control the discharge size in crushing stone and sand? | fote machinery
Sand and stone crushing equipment can crush large size stones into stones or sand with different particle sizes to meet the different requirements of sand and stone materials for construction, railway, highway, and other projects.
Crusher is the common equipment of sand and stone industry that is often used to break large stones, and it has a lot of different types and specifications with different discharge sizes. Understanding the specifications of finished materials can provide necessary reference for users to select equipment.
The main objectives of particle size control are: firstly, to make the configuration and operation of the crushing machinery layer reasonable, secondly, to reduce the proportion of needle-like and flake aggregate in finished products, thirdly, to adjust the proportion of each particle size of the finished aggregate.
In the case of smooth operation of the crusher, the particle size of the sand and stone should be controlled and the acicular and flaky particles should be reduced. The acicular particles are those whose length of the stone particles is larger than 2.4 times the average particle size of the grade to which the particles belong.
And flaky particles are those whose thickness is less than 0.4 times of the average particle size (mean particle size refers to the average particle size of the upper and lower limit of the particle size). Well, how can we control the discharge sizes to produce the high-quality stones with different particle sizes of 5-10 mm gravel, 10-20 mm (1/4 to 1/2 inch) gravel, and 15-25 mm (1/2 to 3/4 inch) gravel that we need? This article explains it in detail.
According to the crusher discharging particle size for preliminary control, there are many different types of crushers, each type of working principle is different, and the discharging control mode is also different.
The finished product of sand and stone production line includes not only the stone with smaller particle size, but also the stone with larger one. Sand and stone production is divided into crushing, screening, sand-making and other chains.
Sandstone aggregate quality control is mainly based on sandstone aggregate particle size and gradation requirements, and adopts the advanced and mature crushing equipment and vibrating screen, to ensure that the production of sand and stone aggregate is in line with the standards and regulations of grading quality.
In the sand and stone aggregate market, stones or sand the customers need to have a certain standard particle size, for example: gravel is divided into 5-10 mm, 10-20 mm, 16-31.5 mm, sand is divided into coarse sand (average particle size of 0.5 mm or more), medium sand (average particle size of 0.35-0.5 mm), fine sand (average particle size of 0.25-0.35 mm).
However, the materials are mixed with particles in various sizes, which cannot meet the demand. Therefore, most of the crushing process is equipped with a vibrating screen, which is used to classify the discharge materials and screen out the stones or sand of various specifications that they need. If the requirements are not met, they can return to the crusher to continue crushing.
Those materials whose size are less than the 3/4 size of the sieve hole of the particles can easily cross the sieve hole, known as easy-to-sieve particles. Particles larger than 3/4 of the sieve hole are difficult to pass through the sieve hole, known as difficult-to-sieve particles. Particles whose particle size is 1-1.5 times of the size of the sieve hole are called stoppers.
Therefore, the screening containing a large number of fine grade materials can increase the method of auxiliary screening of larger size in sieve hole to discharge the coarse size products in advance.
In general, single layer vibrating screen can screen out two kinds of materials, double-layers vibrating screen can screen out three kinds of materials, three-layers vibrating screen can screen out four kinds of materials, and five-layers vibrating screen can screen out six kinds. Users can make reasonable choices according to their needs for finished stones and sand and suggestions from equipment manufacturers.
Usually the circular vibrating screen is used to assist the crusher in the crushing production line. In the whole process, customers can adjust each device according to their own needs to adjust the material size. Through our analysis, do you have a general understanding of how to control the particle size in your sand and stone production?
We hope to help you to buy a suitable crusher and to operate your machines smoothly. Now many equipment manufacturers are designing production lines for customers. If you are new to this industry, you can listen to the suggestions of equipment manufacturers because they have professional knowledge and rich experience to help you solve problems.
As a leading mining machinery manufacturer and exporter in China, we are always here to provide you with high quality products and better services. Welcome to contact us through one of the following ways or visit our company and factories.
Based on the high quality and complete after-sales service, our products have been exported to more than 120 countries and regions. Fote Machinery has been the choice of more than 200,000 customers.
vsi vertical shaft impact crusher stone crushers & grinding mills for mines and quarry
Adopting quality raw materials and advanced technologies, VSI Vertical Shaft Impact Crusher ensures high-quality and good abrasion performance. This machine switches the working principle crushing between materials to crushing between materials and liners, which can be used to make sand and shape stones.
1. Center Feeding:Raw material falls down into feed hopper, then enters impellor through central entrance hole. It is accelerated in high-speed impellor, then is thrown out at speed of 60-75m/s. When hitting impact plate, it is crushed. Final products come downwards through outlet.2. Ring Feeding:Raw material falls down into feed hopper, then through ring, it is divided into two parts by material-dividing plate. One enters into impellor through the center of material-dividing plate. The other falls down from outside of material-dividing plate. Material, which is thrown out by impellor at speed of 60-75m/s, hits material coming down from outside of material-dividing plate. In this way, material is crushed.
what is a vertical shaft impactor (vsi) primer? | stedman machine company
All roads, you might say, lead to the Vertical Shaft Impactor (VSI) because these crushers make it possible to create roadways and just about everything else. Francis E. Agnew of California patented one of the first Vertical Shaft Impactors in 1927. His configuration stacked three VSIs atop each other to produce sand, thus starting the VSI evolution.
Today, VSI crushers and the folks who rely on them have produced many configurations to include everything from the addition of cascading material into the crushing chamber, to air swept separation of lighter product. One version suspends the shaft from above like a sugar centrifuge. Its also one of the most feature-patented crushers, so some of the things mentioned here might be unique to a single manufacturer. VSIs apply a large amount of energy to crush material and thats why its one of the most versatile crusher configurations today.
When it comes to producing materials such as aggregate for road making, VSI crushers use a high-speed rotor and anvils for impact crushing rather than compression force for the energy needed for size reduction. In a VSI, material is accelerated by centrifugal force by a rotor against the outer anvil ring, it then fractures and breaks along natural faults throughout the rock or minerals. The product is generally of a consistent cubical shape, making it excellent for modern Superpave highway asphalt applications. The rotor speed (feet per minute) controls final particle size.
The VSIs high cubical fracture percentage maximizes first-pass product yield and produces tighter particle size distribution. It has a high-throughput capacity ideal for beneficiation (elimination of soft material). Properly configured the VSI accepts highly abrasive materials. It has simple operation and maintenance. You can quickly change product size by changing rotor speed or cascade ratio. Some models have reversible wear parts to reduce downtime. The VSI typically has low operating costs even in high-moisture applications because of reduced energy costs and low wear cost per ton.
There are some feed size limitations with a VSI because of the small feed area available in the center of the rotor. Tramp material in the feed such as gloves, tools, etc. can cause problems with imbalance. The high RPM and HP require careful balance maintenance such as replacing shoes on both sides of the rotor at the same time. High wear part cost may be a problem for some hard abrasive materials, but the VSI may still be the best option.
Major limestone applications are for Superpave asphalt aggregates, road base, gravel, sand and cement. Industrial uses include: corundum, corundite, ferro silicon, glass, refractories, silicon carbide, tungsten carbide and zeolite. Mining applications include: bauxite, burnt magnesite, iron ore, non-ferrous metal ore, perlite and trona sulfate. VSIs are excellent for everything from abrasive materials to waste and recycling applications.
Feed size and characteristics will affect the application of a VSI. The feed size is limited by the opening in the center of the rotor. Normally less than 5-inch material is desired, but very large VSIs can handle up to 12-inch feed. Another feature that will affect application is moisture, which can make the feed sticky. Required production capacity is the final limiting criteria. Large primary horizontal shaft impactors can output up to 1600 TPH and more. 1000 TPH is about the maximum for a VSI because of the limiting motor size and the rising G-force of a high-speed rotor, which is calculated by multiplying the radius times the square of the RPM.
Shoe configurations are many: rock on rock, groups of rollers, special tip wear parts and many others. The metallurgy of the shoes is also highly varied. Rotors can have three to six shoes. The number of shoes is typically governed by the diameter of the rotor. The larger the diameter rotor, the more openings are possible. Computational Fluid Dynamics (CFD) mathematical models are utilized to simulate the flow and collision forces to reveal solutions for lower wear cost, consistent final product, and higher energy efficiency.
The material to be crushed is fed into the center of an open or closed rotor. The rotor rotates at high rpm, accelerating the feed and throwing it with high energy into the crushing chamber. When the material hits the anvil ring assembly, it shatters, and then the cubical shaped product falls through the opening between the rotor and the anvil and down to the conveyor below.
The typical VSI is fed, from above, into the center of its rotor. The material is then flung across an open void to the crushing chamber. It then impacts the outer anvil ring. This crushing action imparts very high energy to the material and is very effective on most types of material. It gives a very uniform and consistent grade of product.
In cascade feeding, material bypasses the rotor and enters the crushing chamber from above. Its called cascade feeding because as material fills up a large feed bowl, with an outer diameter larger than the outer diameter of the rotor, it spills over the side and falls into the crushing chamber from above, bypassing the rotor. The effect of increasing feed through cascade is similar to slowing the rotor. Cascade feeding in amounts up to 10 percent may have no effect on particle size distribution or quality. The product gradation curve and product shape will change, if an increased amount of cascade feeding is used.
The VSI features multiple rotor/anvil configurations for various applications. From open or enclosed rotors to the tubular rotor, each machine is configured for their unique application. In many cases the rotor table, rotor assemblies, anvil ring or rock shelf are interchangeable, allowing maximum application flexibility.
The open top metal rotor is good for large feed or medium to very hard material, but it will work best for softer materials. It can handle medium abrasive, dry or wet, but not sticky materials. High reduction ratios are common, which are excellent for sand and gravel production in closed loop systems. Shoe shape can change the production size range. A straight shoe face design produces finer product, and a curved shoe face design produces coarser material.
The tubular rotor creates higher tip-speeds, which increases first pass yield with tighter particle size distribution and also reduces the recirculation loads. One unique feature is that the rotor rotation is reversible, allowing wear on both sides of the tube. Rotating the tube itself one-quarter turn also doubles the wear.
Any time the material or rock is used as an impact wear surface the term autogenous is used. Putting a top on the rotor table and shoes allows autogenous use. During operation of the VSI, a bed of material can be designed to build up inside the rotor against each of the shoe wall segments. The bed, which is made up of material that has been fed to the rotor, extends to a wear tip. The bed protects the shoe wall segment from wear.
Concerning the rock shelf anvil, it forms a near vertical wall of material upon which the accelerated material impacts. Rock-on-rock crushing reduces maintenance but can require up to 30 percent of material recirculation before meeting size requirements. Also, the rock shelf anvil absorbs energy that could otherwise be used for breaking, which may reduce efficiency. More RPM may be needed to achieve the same result as a solid metal anvil.
Good for medium abrasive materials, rock-on-rock configurations of either or both rotor and anvil may produce consistent material with low-wear cost and can handle wet but not sticky conditions. Reduction ratios from 2:1 to 5:1 can be expected. Its widely used for quarried materials, such as sand and gravel.
The VSI is one of the most versatile crushers available on the market today. Even with some limitations, like feed size and output capacity, VSI features have been and continue to be developed to maximize first-pass yields and lower operating costs. If you test your process on full-scale equipment before choosing your VSI, you wont be disappointed.
Stedman Machine Company works closely with its customers to determine the best, most cost-effective, efficient size reduction method and equipment for specific applications. Stedmans line of equipment includes: Cage Mills, Grand Slam and Mega Slam Horizontal Shaft Impactors, V-Slam Vertical Shaft Impactors, Hammer Mills, Aurora Lump Breakers, Micro-Max and Vertical Roller Mill Air Swept Fine Grinders. Stedman operates a complete testing and toll processing facility staffed by experienced technicians with full-scale equipment, allowing customers to witness accurate crushing test results, predicted output capacities and processing data. Support services include system design and 24-hour parts and service.
impact crusher - eastman rock crusher
Impact crusher is a machine that uses high speed impact energy rather than pressure to reduce material size.Applicationswidely utilized in aggregate, mining, energy, brick and so on industrial applications, depending to the type of an impact crusher, they can be used as a primary, secondary, or tertiary crushers to meet final-product-size needs.Materialsvarious soft and medium hardness ores, such as limestone, feldspar, calcite, talc, barite, fluorite, rare earth, kaolin, coke, coal gangue, gypsum, etc
Horizontal Shaft Impact Crushers can be used in different stages from primary crushing to the last step of the crushing process.Discharge material particle is controlled by rotor speed and discharge gap, the faster the speed the finer the output, the smaller the discharge gap the finer the output.
Impact crusher are named after the method that reducing rock material size, just as its name implies, impact crusher crushes materials by the impact energy. An impact crusher speeds up the feed material to high speed, then throws fast-moving rocks against the crushing chamber walls and each other. This collision and impact causes the rock to break down into smaller sizes.
Eastman provides you with complete original impact crusher spart parts, form and function are a perfect fit.Those wear parts are made of high manganese steel, chromium, manganese and other wear resistant materials cast or forged, prolong service life.
Impact Crusher ApplicationsAggregates Industry: Common materials crushed by impact crushers include cement, concrete, limestone, asphalt, crushed stone, sand and gravel,Mining & Energy Industry: Size reduction for a variety of minerals like coal, iron, pyrites, gypsum, bauxite, gangueGeneral industry: crush waste product, construction waste, brick, clay, ceramics, glass, plastic and more.
Types of impact crusherImpact crushers, or called impactors, are generally divided into two types, the one is Horizontal Shaft Impact Crusher or HSI crusher, and the another type is configuration with a vertical shaft, and for that reason it is known as Vertical Shaft Impact Crusher (VSI), also called as Sand Making Machine.Besides, we supply different configuration of impact crushers to meet various tough applications, includes stationary impact crushers, mobile impact crushers, and portable impact crushers.
impact crusher - an overview | sciencedirect topics
The impact crusher (typically PE series) is widely used and of high production efficiency and good safety performance. The finished product is of cube shape and the tension force and crack is avoided. Compared with hammer crusher, the impact crusher is able to fully utilize the high-speed impact energy of entire rotor. However, due to the crushing board that is easy to wear, it is also limited in the hard material crushing. The impact crusher is commonly used for the crushing of limestone, coal, calcium carbide, quartz, dolomite, iron pyrites, gypsum, and chemical raw materials of medium hardness. Effect of process conditions on the production capacity of crushed materials is listed in Table8.10.
Depending on the size of the debris, it may either be ready to enter the recycling process or need to be broken down to obtain a product with workable particle sizes, in which case hydraulic breakers mounted on tracked or wheeled excavators are used. In either case, manual sorting of large pieces of steel, wood, plastics and paper may be required, to minimise the degree of contamination of the final product.
The three types of crushers most commonly used for crushing CDW materials are the jaw crusher, the impact crusher and the gyratory crusher (Figure 4.4). A jaw crusher consists of two plates, with one oscillating back and forth against the other at a fixed angle (Figure 4.4(a)) and it is the most widely used in primary crushing stages (Behera etal., 2014). The jaw crusher can withstand large and hard-to-break pieces of reinforced concrete, which would probably cause the other crushing machines to break down. Therefore, the material is initially reduced in jaw crushers before going through any other crushing operation. The particle size reduction depends on the maximum and minimum size of the gap at the plates (Hansen, 2004).
An impact crusher breaks the CDW materials by striking them with a high-speed rotating impact, which imparts a shearing force on the debris (Figure 4.4(b)). Upon reaching the rotor, the debris is caught by steel teeth or hard blades attached to the rotor. These hurl the materials against the breaker plate, smashing them into smaller particle sizes. Impact crushers provide better grain-size distribution of RA for road construction purposes, and they are less sensitive to material that cannot be crushed, such as steel reinforcement.
Generally, jaw and impact crushers exhibit a large reduction factor, defined as the ratio of the particle size of the input to that of the output material. A jaw crusher crushes only a small proportion of the original aggregate particles but an impact crusher crushes mortar and aggregate particles alike and thus generates a higher amount of fine material (OMahony, 1990).
Gyratory crushers work on the same principle as cone crushers (Figure 4.4(c)). These have a gyratory motion driven by an eccentric wheel. These machines will not accept materials with a large particle size and therefore only jaw or impact crushers should be considered as primary crushers. Gyratory and cone crushers are likely to become jammed by fragments that are too large or too heavy. It is recommended that wood and steel be removed as much as possible before dumping CDW into these crushers. Gyratory and cone crushers have advantages such as relatively low energy consumption, a reasonable amount of control over the particle size of the material and production of low amounts of fine particles (Hansen, 2004).
For better control of the aggregate particle size distribution, it is recommended that the CDW should be processed in at least two crushing stages. First, the demolition methodologies used on-site should be able to reduce individual pieces of debris to a size that the primary crusher in the recycling plant can take. This size depends on the opening feed of the primary crusher, which is normally bigger for large stationary plants than for mobile plants. Therefore, the recycling of CDW materials requires careful planning and communication between all parties involved.
A large proportion of the product from the primary crusher can result in small granules with a particle size distribution that may not satisfy the requirements laid down by the customer after having gone through the other crushing stages. Therefore, it should be possible to adjust the opening feed size of the primary crusher, implying that the secondary crusher should have a relatively large capacity. This will allow maximisation of coarse RA production (e.g., the feed size of the primary crusher should be set to reduce material to the largest size that will fit the secondary crusher).
The choice of using multiple crushing stages mainly depends on the desired quality of the final product and the ratio of the amounts of coarse and fine fractions (Yanagi etal., 1998; Nagataki and Iida, 2001; Nagataki etal., 2004; Dosho etal., 1998; Gokce etal., 2011). When recycling concrete, a greater number of crushing processes produces a more spherical material with lower adhered mortar content (Pedro etal., 2015), thus providing a superior quality of material to work with (Lotfi etal., 2017). However, the use of several crushing stages has some negative consequences as well; in addition to costing more, the final product may contain a greater proportion of finer fractions, which may not always be a suitable material.
Reduction of the broken rock material, or oversized gravel material, to an aggregate-sized product is achieved by various types of mechanical crusher. These operations may involve primary, secondary and even sometimes tertiary phases of crushing. There are many different types of crusher, such as jaw, gyratory, cone (or disc) and impact crushers (Fig. 15.9), each of which has various advantages and disadvantages according to the properties of the material being crushed and the required shape of the aggregate particles produced.
Fig. 15.9. Diagrams to illustrate the basic actions of some types of crusher: solid shading highlights the hardened wear-resistant elements. (A) Single-toggle jaw crusher, (B) disc or gyrosphere crusher, (C) gyratory crusher and (D) impact crusher.
It is common, but not invariable, for jaw or gyratory crushers to be utilised for primary crushing of large raw feed, and for cone crushers or impact breakers to be used for secondary reduction to the final aggregate sizes. The impact crushing machines can be particularly useful for producing acceptable particle shapes (Section 15.5.3) from difficult materials, which might otherwise produce unduly flaky or elongated particles, but they may be vulnerable to abrasive wear and have traditionally been used mostly for crushing limestone.
Reduction of the broken rock material, or oversized gravel material, to an aggregate-sized product is achieved by various types of mechanical crusher. These operations may involve primary, secondary and even sometimes tertiary phases of crushing. There are many different types of crusher, such as jaw, gyratory, cone (or disc) and impact crushers (Figure 16.8), each of which has various advantages and disadvantages according to the properties of the material being crushed and the required shape of the aggregate particles produced.
Fig. 16.8. Diagrams to illustrate the basic actions of some types of crusher: solid shading highlights the hardened wear-resistant elements (redrawn, adapted and modified from Ref. 39). (a) Single-toggle jaw crusher, (b) disc or gyrosphere crusher, (c) gyratory crusher, and (d) impact crusher.
It is common, but not invariable, for jaw or gyratory crushers to be utilised for primary crushing of large raw feed, and for cone crushers or impact breakers to be used for secondary reduction to the final aggregate sizes. The impact crushing machines can be particularly useful for producing acceptable particle shapes (section 16.5.3) from difficult materials, which might otherwise produce unduly flaky or elongated particles, but they may be vulnerable to abrasive wear and have traditionally been used mostly for crushing limestone.
The main sources of RA are either from construction and ready mixed concrete sites, demolition sites or from roads. The demolition sites produce a heterogeneous material, whereas ready mixed concrete or prefabricated concrete plants produce a more homogeneous material. RAs are mainly produced in fixed crushing plant around big cities where CDWs are available. However, for roads and to reduce transportation cost, mobile crushing installations are used.
The materiel for RA manufacturing does not differ from that of producing NA in quarries. However, it should be more robust to resist wear, and it handles large blocks of up to 1m. The main difference is that RAs need the elimination of contaminants such as wood, joint sealants, plastics, and steel which should be removed with blast of air for light materials and electro-magnets for steel. The materials are first separated from other undesired materials then treated by washing and air to take out contamination. The quality and grading of aggregates depend on the choice of the crusher type.
Jaw crusher: The material is crushed between a fixed jaw and a mobile jaw. The feed is subjected to repeated pressure as it passes downwards and is progressively reduced in size until it is small enough to pass out of the crushing chamber. This crusher produces less fines but the aggregates have a more elongated form.
Hammer (impact) crusher: The feed is fragmented by kinetic energy introduced by a rotating mass (the rotor) which projects the material against a fixed surface causing it to shatter causing further particle size reduction. This crusher produces more rounded shape.
The type of crusher and number of processing stages have considerable influence on the shape and size of RA. In general, for the same size, RAs tend to be coarser, more porous and rougher than NAs, due to the adhered mortar content (Dhir etal., 1999). After the primary crushing, which is normally performed using jaw crushers (Fong etal., 2004), it is preferable to adopt a secondary crushing stage (with cone crushers or impact crushers) (CCANZ, 2011) to further reduce the size of the CDW, producing more regularly shaped particles (Barbudo etal., 2012; Ferreira etal., 2011; Fonseca etal., 2011; Pedro etal., 2014, 2015; Gonzlez-Fonteboa and Martnez-Abella, 2008; Maultzsch and Mellmann, 1998; Dhir and Paine, 2007; Chidiroglou etal., 2008).
CDW that is subjected to a jaw crushing stage tends to result only in flatter RA (Ferreira etal., 2011; Fonseca etal., 2011; Hendriks, 1998; Tsoumani etal., 2015). It is possible to produce good-quality coarse RA within the specified size range by adjusting the crusher aperture (Hansen, 1992). In addition, the number of processing stages needs to be well thought out to ensure that the yield of coarse RA is not affected and that the quantity of fine RA is kept to the minimum (Angulo etal., 2004). This is because the finer fraction typically exhibits lower quality, as it accumulates a higher amount of pulverised old mortar (Etxeberria etal., 2007b; Meller and Winkler, 1998). Fine RA resulting from impact crushers tends to exhibit greater angularity and higher fineness modulus compared with standard natural sands (Lamond etal., 2002; Hansen, 1992; Buyle-Bodin and Hadjieva-Zaharieva, 2002).
One of the commonly known issues related to the use of RCA is its ability to generate a considerable amount of fines when the material is used (Thomas etal., 2016). As the RCA particles are moved around, they impact against one another, leading to the breakage of the friable adhered mortar, which may give rise to some technical problems such as an increase in the water demand of concrete mixes when used as an NA replacement (Thomas etal., 2013a,b; Poon etal., 2007).
The coarse fraction of RMA tends to show a higher shape index owing to the shape of the original construction material (e.g., perforated ceramic bricks) (De Brito etal., 2005). This can pose a problem in future applications as RMA may not compact as efficiently as RCA or NA (Khalaf and DeVenny, 2005). Its shape index may be reduced if the material is successively broken down to a lower particle size (De Brito etal., 2005).
Impact crushers (e.g., hammer mills and impact mills) employ sharp blows applied at high speed to free-falling rocks where comminution is by impact rather than compression. The moving parts are beaters, which transfer some of their kinetic energy to the ore particles upon contact. Internal stresses created in the particles are often large enough to cause them to shatter. These forces are increased by causing the particles to impact upon an anvil or breaker plate.
There is an important difference between the states of materials crushed by pressure and by impact. There are internal stresses in material broken by pressure that can later cause cracking. Impact causes immediate fracture with no residual stresses. This stress-free condition is particularly valuable in stone used for brick-making, building, and roadmaking, in which binding agents (e.g., tar) are subsequently added. Impact crushers, therefore, have a wider use in the quarrying industry than in the metal-mining industry. They may give trouble-free crushing on ores that tend to be plastic and pack when the crushing forces are applied slowly, as is the case in jaw and gyratory crushers. These types of ore tend to be brittle when the crushing force is applied instantaneously by impact crushers (Lewis et al., 1976).
Impact crushers are also favored in the quarry industry because of the improved product shape. Cone crushers tend to produce more elongated particles because of their ability to pass through the chamber unbroken. In an impact crusher, all particles are subjected to impact and the elongated particles, having a lower strength due to their thinner cross section, would be broken (Ramos et al., 1994; Kojovic and Bearman, 1997).
Figure 6.23(a) shows the cross section of a typical hammer mill. The hammers (Figure 6.23(b)) are made from manganese steel or nodular cast iron containing chromium carbide, which is extremely abrasion resistant. The breaker plates are made of the same material.
The hammers are pivoted so as to move out of the path of oversize material (or tramp metal) entering the crushing chamber. Pivoted (swing) hammers exert less force than they would if rigidly attached, so they tend to be used on smaller impact crushers or for crushing soft material. The exit from the mill is perforated, so that material that is not broken to the required size is retained and swept up again by the rotor for further impacting. There may also be an exit chute for oversize material which is swept past the screen bars. Certain design configurations include a central discharge chute (an opening in the screen) and others exclude the screen, depending on the application.
The hammer mill is designed to give the particles velocities of the order of that of the hammers. Fracture is either due to impact with the hammers or to the subsequent impact with the casing or grid. Since the particles are given high velocities, much of the size reduction is by attrition (i.e., particle on particle breakage), and this leads to little control on product size and a much higher proportion of fines than with compressive crushers.
The hammers can weigh over 100kg and can work on feed up to 20cm. The speed of the rotor varies between 500 and 3,000rpm. Due to the high rate of wear on these machines (wear can be taken up by moving the hammers on the pins) they are limited in use to relatively non-abrasive materials. They have extensive use in limestone quarrying and in the crushing of coal. A great advantage in quarrying is the fact that they produce a relatively cubic product.
A model of the swing hammer mill has been developed for coal applications (Shi et al., 2003). The model is able to predict the product size distribution and power draw for given hammer mill configurations (breaker gap, under-screen orientation, screen aperture) and operating conditions (feed rate, feed size distribution, and breakage characteristics).
For coarser crushing, the fixed hammer impact mill is often used (Figure 6.24). In these machines the material falls tangentially onto a rotor, running at 250500rpm, receiving a glancing impulse, which sends it spinning toward the impact plates. The velocity imparted is deliberately restricted to a fraction of the velocity of the rotor to avoid high stress and probable failure of the rotor bearings.
The fractured pieces that can pass between the clearances of the rotor and breaker plate enter a second chamber created by another breaker plate, where the clearance is smaller, and then into a third smaller chamber. The grinding path is designed to reduce flakiness and to produce cubic particles. The impact plates are reversible to even out wear, and can easily be removed and replaced.
The impact mill gives better control of product size than does the hammer mill, since there is less attrition. The product shape is more easily controlled and energy is saved by the removal of particles once they have reached the size required.
Large impact crushers will reduce 1.5m top size ROM ore to 20cm, at capacities of around 1500th1, although units with capacities of 3000th1 have been manufactured. Since they depend on high velocities for crushing, wear is greater than for jaw or gyratory crushers. Hence impact crushers are not recommended for use on ores containing over 15% silica (Lewis et al., 1976). However, they are a good choice for primary crushing when high reduction ratios are required (the ratio can be as high as 40:1) and the ore is relatively non-abrasive.
Developed in New Zealand in the late 1960s, over the years it has been marketed by several companies (Tidco, Svedala, Allis Engineering, and now Metso) under various names (e.g., duopactor). The crusher is finding application in the concrete industry (Rodriguez, 1990). The mill combines impact crushing, high-intensity grinding, and multi-particle pulverizing, and as such, is best suited in the tertiary crushing or primary grinding stage, producing products in the 0.0612mm size range. It can handle feeds of up to 650th1 at a top size of over 50mm. Figure 6.22 shows a Barmac in a circuit; Figure 6.25 is a cross-section and illustration of the crushing action.
The basic comminution principle employed involves acceleration of particles within a special ore-lined rotor revolving at high speed. A portion of the feed enters the rotor, while the remainder cascades to the crushing chamber. Breakage commences when rock enters the rotor, and is thrown centrifugally, achieving exit velocities up to 90ms1. The rotor continuously discharges into a highly turbulent particle cloud contained within the crushing chamber, where reduction occurs primarily by rock-on-rock impact, attrition, and abrasion.
This crusher developed by Jaques (now Terex Mineral Processing Solutions) has several internal chamber configurations available depending on the abrasiveness of the ore. Examples include the Rock on Rock, Rock on Anvil and Shoe and Anvil configurations (Figure 6.26). These units typically operate with 5 to 6 steel impellers or hammers, with a ring of thin anvils. Rock is hit or accelerated to impact on the anvils, after which the broken fragments freefall into the discharge chute and onto a product conveyor belt. This impact size reduction process was modeled by Kojovic (1996) and Djordjevic et al. (2003) using rotor dimensions and speed, and rock breakage characteristics measured in the laboratory. The model was also extended to the Barmac crushers (Napier-Munn et al., 1996).
Figure 9.1 shows common aluminum oxide-based grains. Also called corundum, alumina ore was mined as early as 2000 BC in the Greek island of Naxos. Its structure is based on -Al2O3 and various admixtures. Traces of chromium give alumina a red hue, iron makes it black, and titanium makes it blue. Its triagonal system reduces susceptibility to cleavage. Precious grades of Al2O3 are used as gemstones, and include sapphire, ruby, topaz, amethyst, and emerald.
Charles Jacobs (1900), a principal developer, fused bauxite at 2200C (4000F) before the turn of the 20th century. The resulting dense mass was crushed into abrasive particles. Presently, alumina is obtained by smelting aluminum alloys containing Al2O3 in electric furnaces at around 1260C (2300F), a temperature at which impurities separate from the solution and aluminum oxide crystallizes out. Depending upon the particular process and chemical composition there are a variety of forms of aluminum oxide. The poor thermal conductivity of alumina (33.5W/mK) is a significant factor that affects grinding performance. Alumina is available in a large range of grades because it allows substitution of other oxides in solid solution, and defect content can be readily controlled.
For grinding, lapping, and polishing bearing balls, roller races, and optical glasses, the main abrasive employed is alumina. Its abrasive characteristics are established during the furnacing and crushing operations, so very little of what is accomplished later significantly affects the features of the grains.
Aluminum oxide is tougher than SiC. There are four types of gradations for toughness. The toughest grain is not always the longest wearing. A grain that is simply too tough for an application will become dull and will rub the workpiece, increasing the friction, creating heat and vibrations. On the other hand, a grain that is too friable will wear away rapidly, shortening the life of the abrasive tool. Friability is a term used to describe the tendency for grain fractures to occur under load. There is a range of grain toughness suitable for each application. The white friable aluminum oxide is almost always bonded by vitrification. It is the main abrasive used in tool rooms because of its versatility for a wide range of materials. In general, the larger the crystals, the more friable the grain. The slower the cooling process, the larger are the crystals. To obtain very fine crystals, the charge is cooled as quickly as possible, and the abrasive grain is fused in small pigs of up to 2ton. Coarse crystalline abrasive grains are obtained from 5 to 6ton pigs allowed to cool in the furnace shell.
The raw material, bauxite, containing 8590% alumina, 25% TiO2, up to 10% iron oxide (Fe2O3), silica, and basic oxides, is fused in an electric-arc furnace at 2600C (4700F). The bed of crushed and calcined bauxite, mixed with coke and iron to remove impurities, is poured into the bottom of the furnace where a carbon starter rod is laid down. A couple of large vertical carbon rods are then brought down to touch and a heavy current applied. The starter rod is rapidly consumed, by which time the heat melts the bauxite, which then becomes an electrolyte. Bauxite is added over several hours to build up the volume of melt. Current is controlled by adjusting the height of the electrodes, which are eventually consumed in the process.
After cooling, the alumina is broken up and passed through a series of hammer, beater, crush, roller, and/or ball mills to reduce it to the required grain size and shape, producing either blocky or thin splintered grains. After milling, the product is sieved to the appropriate sizes down to about 40 m (#400). The result is brown alumina containing typically 3% TiO2. Increased TiO2 content increases toughness while reducing hardness. Brown alumina has a Knoop hardness of 2090 and a medium friability.
Electrofused alumina is also made using low-soda Bayer process alumina that is more than 99% pure. The resulting alumina grain is one of the hardest, but also the most friable, of the alumina family providing a cool cutting action. This abrasive in a vitrified bond is, therefore, suitable for precision grinding.
White aluminum oxide is one of the most popular grades for micron-size abrasive. To produce micron sizes, alumina is ball-milled or vibro-milled after crushing and then traditionally separated into different sizes using an elutriation process. This consists of passing abrasive slurry and water through a series of vertical columns. The width of the columns is adjusted to produce a progressively slower vertical flow velocity from column to column. Heavier abrasive settles out in the faster flowing columns while lighter particles are carried over to the next. The process is effective down to about 5 m and is also used for micron sizing of SiC. Air classification has also been employed.
White 99% pure aluminum oxide, called mono-corundum, is obtained by sulfidation of bauxite, which outputs different sizes of isometric corundum grains without the need for crushing. The crystals are hard, sharp, and have better cleavage than other forms of aluminum oxides, which qualifies it for grinding hardened steels and other tough and ductile materials. Fine-grained aluminum oxide with a good self-sharpening effect is used for finishing hardened and high-speed steels, and for internal grinding.
Not surprisingly, since electrofusion technology has been available for the last one hundred years, many variations in the process exist both in terms of starting compositions and processing routes. For example:
Red-brown or gray regular alumina. Contains 9193% Al2O3 and has poor cleavage. This abrasive is used in resinoid and vitrified bonds and coated abrasives for rough grinding when the risk of rapid wheel wear is low.
Chrome addition. Semi-fine aloxite, pink with 0.5% chromium oxide (Cr2O3), and red with 15% Cr2O3, lies between common aloxite, having less than 95% Al2O3 and more than 2% TiO2, and fine aloxite, which has more than 95% Al2O3 and less than 2% TiO2. The pink grain is slightly harder than white alumina, while the addition of a small amount of TiO2 increases its toughness. The resultant product is a medium-sized grain available in elongated, or blocky but sharp, shapes. Ruby alumina has a higher chrome oxide content of 3% and is more friable than pink alumina. The grains are blocky, sharp edged, and cool cutting, making them popular for tool room and dry grinding of steels, e.g., ice skate sharpening. Vanadium oxide has also been used as an additive giving a distinctive green hue.
Zirconia addition. Aluminazirconia is obtained during the production process by adding 1040% ZrO2 to the alumina. There are at least three different aluminazirconia compositions used in grinding wheels: 75% Al2O3 and 25% ZrO2, 60% Al2O3 and 40% ZrO2, and finally, 65% Al2O3, 30% ZrO2, and 5% TiO2. The manufacture usually includes rapid solidification to produce a fine grain and tough structure. The resulting abrasives are fine grain, tough, highly ductile, and give excellent life in medium to heavy stock removal applications and grinding with high pressures, such as billet grinding in foundries.
Titania addition. Titaniaaloxite, containing 95% Al2O3 and approximately 3% Ti2O3, has better cutting ability and improved ductility than high-grade bauxite common alumina. It is recommended when large and variable mechanical loads are involved.
Single crystal white alumina. The grain growth is carefully controlled in a sulfide matrix and is separated by acid leaching without crushing. The grain shape is nodular which aids bond retention, avoiding the need for crushing and reducing mechanical defects from processing.
Post-fusion processing methods. This type of particle reduction method can greatly affect grain shape. Impact crushers such as hammer mills create a blocky shape while roll crushers cause splintering. It is possible, using electrostatic forces to separate sharp shapes from blocky grains, to provide grades of the same composition but with very different cutting actions.
The performance of the abrasive can also be altered by heat treatment, particularly for brown alumina. The grit is heated to 11001300 C (20152375 F), depending on the grit size, in order to anneal cracks and flaws created by the crushing process. This can enhance toughness by 2540%.
Finally, several coating processes exist to improve bonding of the grains in the grinding wheel. Red Fe2O3 is applied at high temperatures to increase the surface area for better bonding in resin cut-off wheels. Silane is applied for some resin bond wheel applications to repel coolant infiltration between the bond and abrasive grit, and thus protect the resin bond.
A limitation of electrofusion is that the resulting abrasive crystal structure is very large; an abrasive grain may consist of only one to three crystals. Consequently, when grain fracture occurs, the resulting particle loss may be a large proportion of the whole grain. This results in inefficient grit use. One way to avoid this is to dramatically reduce the crystal size.
The earliest grades of microcrystalline grits were produced as early as 1963 (Ueltz, 1963) by compacting a fine-grain bauxite slurry, granulating to the desired grit size, and sintering at 1500C (2735F). The grain shape and aspect ratio could be controlled by extruding the slurry.
One of the most significant developments since the invention of the Higgins furnace was the release in 1986, by the Norton Company, of seeded gel (SG) abrasive (Leitheiser and Sowman, 1982; Cottringer et al., 1986). This abrasive was a natural outcome of the wave of technology sweeping the ceramics industry at that time to develop high strength engineering ceramics using chemical precipitation methods. This class of abrasives is often termed ceramic. SG is produced by a chemical process. In a precursor of boehmite, MgO is first precipitated to create 50-m-sized aluminamagnesia spinel seed crystals. The resulting gel is dried, granulated to size, and sintered at 1200C (2200F). The resulting grains are composed of a single-phase -alumina structure with a crystalline size of about 0.2m. Defects from crushing are avoided; the resulting abrasive is unusually tough but self-sharpening because fracture now occurs at the micron level.
With all the latest technologies, it took significant time and application knowledge to understand how to apply SG. The abrasive was so tough that it had to be blended with regular fused abrasives at levels as low as 5% to avoid excessive grinding forces. Typical blends are now five SGs (50%), three SGs (30%), and one SG (10%). These blended abrasive grades can increase wheel life by up to a factor of 10 over regular fused abrasives, although manufacturing costs are higher.
In 1981, prior to the introduction of SG, the 3M Co. introduced a solgel abrasive material called Cubitron for use in coated abrasive fiber discs (Bange and Orf, 1998). This was a submicron chemically precipitated and sintered material but, unlike SG, had a multiphase composite structure that did not use seed grains to control crystalline size. The value of the material for grinding wheel applications was not recognized until after the introduction of SG. In the manufacture of Cubitron, alumina is co-precipitated with various modifiers such as magnesia, yttria, lanthana, and neodymia to control microstructural strength and surface morphology upon subsequent sintering. For example, one of the most popular materials, Cubitron 321, has a microstructure containing submicron platelet inclusions which act as reinforcements somewhat similar to a whisker-reinforced ceramic (Bange and Orf, 1998).
Direct comparison of the performance of SG and Cubitron is difficult because the grain is merely one component of the grinding wheel. SG is harder (21GPa) than Cubitron (19GPa). Experimental evidence suggests that wheels made from SG have longer life, but Cubitron is freer cutting. Cubitron is the preferred grain in some applications from a cost/performance viewpoint. Advanced grain types are prone to challenge from a well-engineered, i.e., shape selected, fused grain that is the product of a lower cost, mature technology. However, it is important to realize that the wheel cost is often insignificant compared to other grinding process costs in the total cost per part.
The SG grain shape can be controlled by extrusion. Norton has taken this concept to an extreme and in 1999 introduced TG2 (extruded SG) grain in a product called ALTOS. The TG2 grains have the appearance of rods with very long aspect ratios. The resulting packing characteristics of these shapes in a grinding wheel create a high strength, lightweight structure with porosity levels as high as 70% or even greater. The grains touch each other at only a few points, where a bond also concentrates in the same way as a spot weld. The product offers potential for higher stock removal rates and higher wheelspeeds due to the strength and density of the resulting wheel body (Klocke and Muckli, 2000).
Recycling of concrete involves several steps to generate usable RCA. Screening and sorting of demolished concrete from C&D debris is the first step of recycling process. Demolished concrete goes through different crushing processes to acquire desirable grading of recycled aggregate. Impact crusher, jaw crusher, cone crusher or sometimes manual crushing by hammer are preferred during primary and secondary crushing stage of parent concrete to produce RA. Based on the available literature step by step flowchart for recycling of aggregate is represented in Fig. 1. Some researchers have also developed methods like autogenous cleaning process , pre-soaking treatment in water , chemical treatment, thermal treatment , microwave heating method  and mechanical grinding method for removing adhered mortar to obtain high quality of RA. Depending upon the amount of attached mortar, recycled aggregate has been classified into different categories as shown in Fig. 2.
Upon arrival at the recycling plant, CDW may either enter directly into the processing operation or need to be broken down to obtain materials with workable particle sizes, in which case hydraulic breakers mounted on tracked or wheeled excavators are used. In either case, manual sorting of large pieces of steel, wood, plastics and paper may be required, to minimize the degree of contamination.
The three types of crushers most used for crushing CDW are jaw, impact, and gyratory crushers (Fig.8). A jaw crusher consists of two plates fixed at an angle (Fig.8a); one plate remains stationary while the other oscillates back and forth relative to it, crushing the material passing between them. This crusher can withstand large pieces of reinforced concrete, which would probably cause other types of crushers to break down. Therefore, the material is initially reduced in jaw crushers before going through other types. The particle size reduction depends on the maximum and minimum size of the gap at the plates. Jaw crushers were found to produce RA with the most suitable grain-size distribution for concrete production (Molin etal., 2004).
An impact crusher breaks CDW by striking them with a high speed rotating impact, which imparts a shearing force on the debris (Fig.8b). Materials fall onto the rotor and are caught by teeth or hard steel blades fastened to the rotor, which hurl them against the breaker plate, smashing them to smaller-sized particles. Impact crushers provide better grain-size distribution of RA for road construction purposes and are less sensitive to material that cannot be crushed (i.e. steel reinforcement).
Gyratory crushers, which work on the same principle as cone crushers (Fig.8c), exhibit a gyratory motion driven by an eccentric wheel and will not accept materials with large particle sizes as they are likely to become jammed. However, gyratory and cone crushers have advantages such as relatively low energy consumption, reasonable amount of control over particle size and production of low amount of fine particles.
Generally, jaw and impact crushers have a large reduction factor, defined as the relationship between the input's particle size and that of the output. A jaw crusher crushes only a small proportion of the original aggregate particles but an impact crusher crushes mortar and aggregate particles alike, and thus may generate twice the amount of fines for the same maximum size of particle (O'Mahony, 1990).
In order to produce RA with predictable grading curve, it is better to process debris in two crushing stages, at least. It may be possible to consider a tertiary crushing stage and further, which would undoubtedly produce better quality coarse RA (i.e. less adhered mortar and with a rounder shape). However, concrete produced with RA subjected to a tertiary crushing stage may show only slightly better performance than that made with RA from a secondary crushing stage (Gokce etal., 2011; Nagataki etal., 2004). Furthermore, more crushing stages would yield products with decreasing particle sizes, which contradicts the mainstream use of RA (i.e. coarser RA fractions are preferred, regardless of the application). These factors should be taken into account when producing RA as, from an economical and environmental point of view, it means that relatively good quality materials can be produced with lower energy consumption and with a higher proportion of coarse aggregates, if the number of crushing stages is prudently reduced.