bond rod mill work index equipment & apparatus review
The Bond Third Theory of comminution was originally divided into three size classes reflecting the varieties of comminution equipment common during the time period when Bond (and his collaborators) were gathering the information to calibrate comminution models. The middle size class, represented by rod milling, is fitted to a tumbling test, referred to as the Bond rod mill work index (WiRM, or RWi). The apparatus used to determine this work index was described in 1943 by Bond & Maxton. The author has noted there are some laboratories that have deviated from the apparatus specified by Bond & Maxton and there are modern comminution models that are calibrated to this non-standard mill geometry.
The specification for the apparatus to determining a Bond rod mill work index is first described in Bond & Maxton (1943). It states that the apparatus is a tumbling rod mill to be operated in a locked cycle test at a fixed circulating load. The geometry of the grinding chamber is described as:
The test procedure also describes a rocking of the mill every 10 revolutions to avoid coarse particles collecting in the empty space between the end of the grinding rods and the end of the grinding chamber.
The author is aware of three issues with this specification and the actual implementation of the test in commercial laboratories world-wide. Specifically, the meaning of mill inside diameter in the context of a wave liner, the use of a smooth liner in some laboratories, and the consistent implementation of the rocking behaviour. Of these three issues, the Author believes use of a smooth liner is the biggest issue with respect to standardization of the test.
The length of the grinding chamber is longer than the rods, resulting a void space at the ends of the mill where little or no grinding happens. To avoid the collection of coarse material in this space, the test procedure includes rocking the mill every 10 revolutions through a 10 rotation forward for one revolution and then backward for one revolution, after which the mill is returned to a level position for the next ten revolutions before being rocked again.
The laboratory rod mills common in North and South America are all configured to be rocked, and this is believed to be a standard procedure in all the laboratories that the Author is familiar with (one laboratory presently lacks the rocking mechanism but is working towards implementing it).
A Bond rod mill work index is to be determined in an apparatus with a wave liner. The author is aware of four laboratories that offer a rod mill work index test where the lining of the mill is either smooth, or smooth with a small number of primitive lifters that do not constitute a wave liner (one of the four laboratories is known to be investigating replacing the liner with a wave). Work index values determined by this alternative geometry should not be marketed as Bond work index values because they deviate from the specification and calibration of a proper Bond rod mill work index.
The first problem comes from the equation derived by Bond to calibrate a rod mill work index to the parameters of the rod mill tumbling test. The term in the calibrated formula that is affected by the liner is the grams (therefore, the energy) evolved per revolution of the laboratory mill. Since the equation expects a certain amount of energy (Joules) per mill revolution, the equation for a laboratory mill with smooth liner must re-calibrate Bonds empirical equation (below, converted to Wi metric units) to the Joules per revolution generated in a machine with a smooth liner.
The second problem is related to how a rock breaks inside the apparatus. There are generally three mechanisms of breakage recognized as significant in milling: crushing, attrition and abrasion. A particular ore in a particular mill will have a characteristic combination of these three mechanisms that describes both the breakage energy consumed and the size distribution of the mill product. The action of a wave liner in a rod mill is to lift the mill charge and spread the charge as the mill rotates. This causes both crushing and attrition action by trapping particles between the rods as they are alternatively lifted and dropped. This lifting action is greatly diminished in a mill with a smooth liner, meaning that the relative amount of crushing and attrition will be less in the smooth liner design; most of the breakage will instead consist of abrasion.
Attempts to convert work index determinations from one mill geometry to the other must account for this difference in breakage mechanism. It is not enough to say deduct 2 kWh/t from the smooth liner result and expect an equivalent work index for a wave liner design. An empirical conversion determined for a particular type of ore (eg. Paleozoic meta-granitoids) is only valid for rock types that have similar ratios in the resistance to abrasion, attrition and crushing. A completely different rock type (eg. Tertiary andesite) will have a completely set of ratios, and therefore will likely require a different empirical calibration between the two styles of mill liner.
Bailey et al. (2009) described a rod mill work index round-robin program between different international laboratories with a normalized standard deviation of 12%. It is believed that the round-robin is a mixture of smooth and wave liner designs. The Author is aware of three Australian laboratories have have smooth designs, and these are expected to give higher work index determinations than the wave designs. The paper reveals that the two maximum values are Australian laboratories (therefore, smooth liner designs). If one excludes them and re-calculates the statistics, then the normalized standard deviation drops to 6.3%.
The author is aware that most laboratories with wave liners have settled on designs involving eight waves with inch wave height. Minor variations in height mostly affects the mill inside diameter calculation (discussed in the next section) and the Author expects the wave height will not otherwise affect the validity of the rod mill work index calculation (for reasonable heights where the rod trajectories are normal). If the lifting action of the rods is reasonably similar to what Bond calibrated his equations to, then the geometry is valid.
The Nordberg rod mill power draw model (Outokumpu, 2002) is an easy way to check the effect of diameter by comparing the Factor A in the power model against three potential mill diameters. In all cases, assume a inch lifter height. The middle measurement case will be a 12 inch effective diameter; the trough-to-trough will be 11 inches; and the crest-to-crest design will be 12 inches.
Calculating the Nordberg Factor A for all three liner cases and assuming that all other parameters are the same (Factor B, filling; Factor C, speed; ore density), then the difference in the Factor A should equal the difference in the power draw of the laboratory mill (this is over-simplified because the Factors B and C will change slightly). Assuming the middle measurement is a base case, the predicted variation in a work index determination due to measurement position is indicated in Table 1.
The ambiguous definition of Bond & Maxtons specification of the inside diameter of a wave liner can reasonably result in up to 20% variation in the results of a Bond rod mill work index. Which of the definitions is correct depends upon which definition was used in the Allis Chalmers laboratory where Bond and his collaborators calibrated the original work index equations. The Author is not aware of any publication that describes these details of the apparatus used at Allis Chalmers.
The Author is aware that other comminution consultants will have different opinions. Comminution is not climate science consensus among practitioners is not mandatory. There are comminution models calibrated to use the smooth liner test results, and it is completely appropriate to use a smooth liner apparatus when using such a model. Calibration is more important than dogma.
More generally, the Industry needs a more exact definition of the specification of a Bond rod mill for work index determination. There is presently (2015-2016) a drive underway to better standardize the use of Bond work indices and testing procedures under the auspices of the Global Mining Standards Group (GMSG), and this may be a reasonable venue to better standardize the specification of the rod mill apparatus and the test procedures.
The Steel Head Rod Mill(sometimes call a bar mill)gives the ore dressing engineer a very wide choice in grinding design. He can easily secure a standard Steel Head Rod Mill suited to his particular problem. The successful operation of any grinding unit is largely dependent on the method of removing the ground pulp. The Steel Head Rod Mill is available with five types of discharge trunnions and each type trunnion is available in small, medium, or large diameter. The types of Rod Mill discharge trunnions are:
The superiority of the Steel Head Rod Mill is due to the all-steel construction. The trunnions are an integral part of the cast steel heads and are machined with the axis of the mill. The mill heads are insured against breakage due to the high tensile strength of cast steel as compared to that of the cast iron head found on the ordinary rod mill. Trunnion Bearings are made of high-grade nickel babbitt, dovetailed into the casting. Ball and socket bearings can be furnished if desired.
Head and shell liners for Steel Head Rod Mills are available in Decolloy (a chrome-nickel alloy), hard iron, electric steel, molychrome steel, and manganese steel. The heads have a conical shaped head liner construction, both on the feed and discharge ends, so that there is ample room for the feed from the trunnion helical conveyor discharge to enter the mill betweenthe rods and head liners on the feed end of the mill. Drive gears are furnished either in cast tooth spur gear and pinion or cut tooth spur gear and pinion. The gears are furnished as standard on the discharge end of the mill, out of the way of the classifier return feed, but can be furnished at the mill feed end by request. Drives may be obtained according to the customers specifications.
The following table clearly illustrates why Steel Head Rod Mills have greater capacity than other mills. This is due to the fact that the diameters are measured inside the liners, while other mills measure their diameter inside the shell.
Rod Mills may be considered either fine crushers or coarse grinding equipment. They are capable of taking as large as 2 feed and making a product as fine as 35-48 mesh. Of particular advantage is their adaptability to handling wet sticky ores, which normally would cause difficulty in crushing operations. Under wet grinding conditions of course the problem of dust is eliminated.
The grinding action of a rod mill is line contact. As material travels from the feed end to the discharge end it is subjected to crushing forces inflicted by the grinding rods. The rods both tumble in essentially a parallel alignment and also spin, thus simulating the crushing and grinding action obtained from a series of roll crushers. The large feed tends to spread the rods at the feed end which imparts still an additional action which may be termed scissoring. As a result of this spreading the rods tend to work on the larger particles and thereby produce a minimum amount of extremely fine material.
The Rod Mill encourages the use of a thick pulp coating both the liners and the rods, thus minimizing steel consumption. Continuous movement of the pulp through the rod mass eliminates the possibility of short circuiting any material. The discharge end of the Rod Mill is virtually open and larger in diameter than the feed end, providing a steep gradient of material flow through the mill. This is described in more detail on pages 20 and 21.
Normally Rod Mills are furnished of the two trunnion design. For special applications they may be furnished of the tire trunnion or two- tire construction. These mills can be equipped with any type of feeder and type of drive, discussed separately in this catalog.
The above tables list some of the most common Open End Rod Mill sizes. Capacities are based on medium hard ore with mill operating in closed circuit under wet grinding conditions at speeds indicated. For dry grinding, speeds and power are reduced and capacities drop 30 to 50%.
The End Peripheral Discharge Rod Mill is designed to produce a minimum amount of fines when grinding either wet or dry. Material to be ground enters through a standard trunnion and is discharged through port openings equally spaced around the mill periphery. These ports are in a separate ring placed between the shell and the discharge head.
The construction of the end peripheral discharge mill emphasizes the principle of grinding. Due to the steep gradient between the point of entry and the point of discharge the pulp flows rapidly through the mill providing a fast change of mill content with a relatively small amount of pulp within the grinding chamber.
The sloping or conical shaped feed head proves ample space for a feed pocket to accommodate large quantities of material and assure their entrance into the grinding rods. Any type of feeder listed on pages 22 and 23 can be furnished for these mills; however, since the mills are not usually operated in closed circuit grinding, the drum or spout feeder is normally preferred.
No other type of mill is so well adapted to dry grinding materials to -4 or -8 mesh in single pass with the production of a minimum amount of fines. A major factor in dry grinding is the rapid removal of finished material to prevent cushioning of the rods. This is accomplished in the End Peripheral Discharge Rod Mill.
The free discharge feature permits the grinding of material having a higher moisture content than with other types of rod or ball mills. Our Peripheral Discharge Mills have found wide application in grinding coke and friable non-metallics, material for glass, pyroborates, as well as gravel to produce sand. Another application is for grinding and mixing sand lime brick materials. The rod action gives a thorough mixture while grinding of the hydrated lime and sand.
For specifications of End Peripheral Discharge Rod Mills use table of standard open end rod mills given on pages 24 and 25. The capacity of the end peripheral discharge rod mill is slightly higher than shown for the Open End Rod Mills.
The CPD (Center Peripheral Discharge) Rod Mill has been developed to produce sand to meet U. S. Government or State specifications. It has also found application in grinding friable non-metallics, and industrial materials and ores which tend to slime excessively. Another application is in the field of abrasion milling on ores such as found on the Mesabi Iron Range. In this latter application true grinding is not desired, but more of a surface scrubbing of the individual particles.
Again with this construction grinding may be done either wet or dry. In this design, however, feed enters both ends by means of feeders and is discharged at the center through rectangular discharge ports equally spaced around the mill periphery. The center discharge openings are generally contained in a separate ring placed between shell halves. The ground material is discharged and directed to either side or directly under the mill by the use of a discharge ring housing.
In standard rod-milling it will be found that rods spread apart at the feed end in the amount of the maximum size of feed entering the mill. In the center peripheral discharge mill the rods are spread at both ends and parallel throughout the length of the mill. This feature results in more space between the rods and thereby lessens the amount of fines produced. Furthermore, fines are also diminished because the material moves rapidly through the mill due to the steep gradient of travel and the distance of travel is reduced by half. Similarly time of contact with the grinding media is reduced by half.
Another center peripheral discharge advantage is that a cubical shaped particle is produced. Maintenance is negligible and grinding media is relatively inexpensive. Other types of sand manufacturing equipment lose efficiency with wear and require excessive maintenance. This loss of efficiency increases rapidly as hardness of feed increases. The Center Peripheral Discharge Rod Mill can be easily maintained at peak operating efficiency by the periodical addition of rods. CPD Rod Mills give a wide range of flexibility to sand plant operation. By changing the rate of feed, pulp dilution (wet grinding), and discharge port area it is possible to produce and blend sand of virtually any fineness modulus and maintain it within Government specifications.
Unlike many crushers or grinders the CPD Mill can easily handle wet or sticky material. When grinding wet, the dust nuisance is completely eliminated. For dry grinding applications the mill is furnished with a dust proof discharge housing.
Various items must be considered in computing the cost of producing manufactured sand. These include wear on the constituent parts, power consumption, lubrication, labor and general maintenance. Maintenance of the center peripheral discharge mill is definitely much lower than that of any other sand manufacturing machine. The greater portion of the wear which takes place is on the inexpensive high carbon steel rods. Field installations show an average of less than 1 # per ton of sand ground as rod consumption, and from 0.08# to 0.10# per ton of sand ground as the steel liner wear. The overall cost of mill operation, exclusive of amortization, is generally less than 30c per ton (year 1958).
Every possible operating convenience has been incorporated in the center peripheral discharge mill design. On most sizes the trunnions are carried in large lead bronze bushed bearings. The interior of the mill is readily accessible through these large trunnion openings. The peripheral ring housing is furnished with a door for inspection and another lower door to facilitate sampling of the mill discharge. Covers for the discharge ports are furnished allowing any variation in discharge area which might be desired.
Given below are approximate capacities for several sizes of the center peripheral discharge mills. Such capacities are expressed in dry tons per hour, based on - x 4 mesh screened feed of medium hard gravel. Mill discharge is generally less than 5% + 4 mesh in wet open circuit operations, for dry grinding work reduce the capacities indicated by approximately 30% to 50%.
A Rod Mill has for Working Principle its inside filledgrinding media, in this case STEEL RODS. These rods run the length of the machine, which is most commonly between eight and sixteen feet in length. The diameter of these rods will range from, when new, between two and four inches. The rods arefree inside the mill. When the mill is turned, the rods tumble against one another grinding all the ore that is between them to aid in the grinding, water is added with the ore as it enters the mill.So from that you can see why it is called a wet tumbling mill. The ore is ground wet and the mill revolves. This causes the grinding media inside of it to tumble grinding the ore.
Historically there has been three basic ways of grinding ore, hammer mills, rolls, or wet tumbling mills. Hammer mills and rolls are not used that often and then usually only for special applications as in lab work or chemical preparation.
The type of mill that is used for grinding ore in a modern concentrator is the wet tumbling mill. These mills may be divided into three types ROD MILLS, BALL MILLS andAUTOGENOUS MILLS. In the first type, the ROD MILL, the ore is introduced into the mill.
From the trunnion liner out wards first we will come to the FACE PLATE. It is slightly concave to create the POOLING AREA for the rock to collect in before entry to the ROD-LOAD. On the outside attached to the face plate is the BULL GEAR. This gear completely circles the mill and provides the interface between the motor and the mill. The bull gear and drive line may be at the other end of the mill instead. There are advantages and disadvantages to either end this will be explained later when we are discussing the motor and drive line. But for now back to the face plate, attached to the other side of the face plate is the SHELL. The shell is the body of the mill. On the inside of the mill there are two layers of material, the first layer is the BACKING for the liners. This is customarily constructed from rubber but wood may be used as well. The purpose of this backing is two-fold, one to absorb the shock that is transmitted through the liners from normal running. And to provide the shell with a protective covering to eliminate the abrasion that is produced by the finely ground rock and water. Without this rubber or wood backing, the life of the mill is drastically reduced due to metal fatigue and simply being worn away.For those of you arent familiar with METAL FATIGUE I will explain. When metal is continually pounded or vibrated, the molecular structure of the metal begins to change, it is said to CRYSTALLIZE, and the metal becomes hard and finally loses all ability to give with the vibration. Thousands of microscopic cracks will begin to appear, as the fatigue of the metal continues, these cracks will grow to become major problems.
Later for interest sake we will explain the difference in some of them, but for now lets stay with identifying the parts of the mill. We have already mentioned the trunnion liner so let start from there.
The trunnion liner may also be referred to as the THROAT LINER. You will find that many of these parts will be called two or even sometimes three names, All I can say is try not to let it confuse you, The name isnt as important as the job that it does. As long as everybody that you work with agree on which name to use, it doesnt matter that much.
Next to this liner is the END LINERS, or to some, the PACE PLATE LINERS.The FILLER RING which is next is not standard in all mills, some mills have them, and some dont. Their job is to fill the corner of the mill up so the shell will not wear at that point. They dont provide any lift to the media, in fact quite often the media will not come into contact with them at all, but what they do is make changing liners that much easier. With different liner designs the replacement of a single liner may be quite difficult and to change one could become a lengthy project.
The liner that butts into the filler liner is known as a BELLY LINER or SHELL LINER, and in some designs LIFTER BARS. These liners and/or lifters give the media its CASCADING action and also receive the most wear. They cover the complete body of the mill and have the largest selection of types to choose from.
As the two ends of the mill are the same there isnt any reason to go over the other face plate. The discharge trunnion assembly is very much like the feed trunnion except that, it wont have a worm as part of the liner. Instead of a feed seal bolted to it, it may have a screen.
This is called a TRUMMEL SCREEN and its purpose is to screen out any rock that didnt get ground as well as any TRAMP METAL or REJECT STEEL that may be coming out of the mill. Reject steel is the old grinding media that has been worn so small that it comes out of the mill. If this tramp metal and steel is allowed to get into pumps and classifiers damage and plug- ups may be caused.
With regards to Rod Mills, let us start by identifying the different portions of the rod load as it goes through one revolution, as you will see, each of these areas will hold interest for the Grinding operator.
As the rod mill turns, the rods are carried by the lifting portion of the liners. The height that they are lifted is referred to as the lift of the liners. As they roll off of the liners, the rods enter the cascade zone. The rods roll through the cascade zone until they come to the toe of the load. At this point the rods come to rest in relation to the shell of the mill. The liners lift the rods back to begin the cascade again. You will notice, that as you go deeper into the rod load, the rod movement becomes less and less until the movement is very slight at the deepest part. This area is called the core of the load. As a description of the normal grinding action, the rods and the ore react together like this. The ore enters-the mill and is deposited in the pooling area directly under the feed trunnion.
This pooling area allows the large rock to fall towards the outside portion of the load, the TOE area. This is the zone with the greatest movement in it, which means the area that will have the highest impact on the ore.
The rock will be carried up by the rods as they go through the CASCADE ZONE reducing the size of the rock. As each particle of ore becomes smaller it will work towards the CORE ZONE while travelling the length of the mill. That makes for a rather neat arrangement doesnt it. The larger rock is deposited in the area where the maximum impact from the rod load occurs and then as each particle gets smaller it slowly travels inwards towards the centre of the load.
This is where the maximum surface contact takes place, producing the finer grind. When the ore has travelled from one end of the mill to the other end it will have completed its grinding cycle in this mill. As it exits the rod load it will be deposited in another POOLING AREA prior to leaving the mill by way of the DISCHARGE TRUNNION.
Prom that you can see how a mill will become over loaded. If for some reason the rock begins to separate the rods over their entire length, the larger rock will prevent the intermediate rock from being ground. Which in turn will begin to invade the area that the fine material is being ground in. As the rods become separated through the entire load, the grind will get progressively worse until the unground rock is in the discharge pooling area. At this point, the operator will notice, that large rock is being discharged from the discharge trunnion.
During normal operations there is usually a certain amount of this larger rock that wont get ground. These are known as REJECTS and they serve as one of the tattle tales as to how the mill is grinding. If there is an increase of these rejects then the mill isnt grinding that well and the operator will have to do something about it. If he doesnt the mill load will continue to climb, until the rods in the lifting zone are completely separated. When this happens those rods will have quit grinding.
There is a visual warning of this happening that the operator can take advantage of. The lift on the rods will get higher and higher until they are being carried to the very top of the mill before cascading. I think falling would be a better word for it though.
As this is happening, the core of the load will be slowly moving away from the shell towards the center of the mill. This is because the volume of the mill is being filled with unground rock. This will continue until the load hits a critical volume and a critical density. The rock still coming in to the mill will have to have some where to go so it tries pushing the rods out of the mill. Unfortunately they wont make it, the first hunch of rods that get far enough into the discharge trunnion will be- hit by the rest of the load bending and twisting them until they look like SPAGHETTI. This usually shuts the mill down for a couple of days while the millwrights cut the bent rods out of the mill.
On the other end of the scale, if the density is to light, the rod load will become too active, not having the solids in the mill to cushion the impact of rod on rod and rod on liner. As the rods enter the cascade zone, the pattern of the movement of the rods will be different. Instead of having a tightly tumbling mass of rods, the rods will be separated. The lift will be higher and the cascade will form more of an arc. The impact of the rods on the rock will be less because there will be more give in the rod load, with high amount of steel on steel causing the rods to bounce.
Letslook at how these Rod mills work, as I mentioned earlier there are steel rods inside the mill, it is their job to do the actual grinding. If you look at the mill in a cross section of an end view. You will get a very good illustration of the grinding action, of the mill.
The LINERS provide the tumbling action of the rods. When the mill rotates the rods are lifted until they roll off of the liners, this is known as CASCADING. The ore enters the mill at the feed end, as the rods cascade and tumble, the rock is caught between the rods and is ground. The size that the rock will be ground to is dependent on the amount of time the ore is in the mill, how many rods there are in the mill V and the size of the incoming ore.
mill test report (mtr) aka material test reports
We understand the importance of quality assurance. Online Metals is dedicated to providing our customers with quality materials. Unlike other suppliers, we offer Mill Test Reports (MTR) free of charge with available material purchases. Simply check the Mill Test Report box at checkout on qualifying materials and we will include a free Mill Test Report with your order.
And, if you ever need a second copy or misplace any of your Mill Test Reports, just log-in to your Online Metals account to download a free copy. Digital versions of all your Mill Test Reports are accessible for download through the My Account portal after purchase and remain accessible forever, for free.
Online Metals My Account portal makes material purchases easier for professionals, businesses, and hobbyist. Easily track your purchases and access MTRs anytime, anywhere for free. Small businesses and professionals can set job numbers for tracking project costs, billing clients, and printing invoices to help improve efficiency and save you time and money. Create your Online Metals account now!
Mill Test Report (MTR) also referred to as a Certified Mill Test Report, Certified Material Test Report, Metallurgical Test Report, Mill Test Certificate (MTC), Inspection Certificate or Certificate of Test certifies a materials chemical and physical properties and states a product made of metal is in compliance with an international standards organizations specific standards.
Some metals don't come with MTR's. Copper C110, for example. In that case, Metal Service Centers create their own "Certificate of Conformance" documents to stand behind the product, and confirm it is what they say it is. Online Metals also provides our own Certificate of Conformance as well. If you have any questions just give us a call at (800) 704-2157
what is a mill test certificate (en 10204 2.1, 3.1, 3.2)? - projectmaterials
A Mill Test Certificate (MTC), or Mill Test Report (MTR), is issued by a manufacturer to certify the chemical and mechanical features of a product and its compliance to the applicable norms and technical specifications. Typically, Mill Test Certificates conform to the EN 10204 standard and are related to steel products.
Actually i dont know they can or not but i require 3.1 certificates of the electrodes and they send me. For any metallic materials 3.1 certificates needs to show heat number, required test results, applicable standards etc. In this case for electrodes, they can send you raw material test results for each batch (heat), but if you need after welding condition they need to make sample weld and test it. it is relative what you need it for. If you will use this certificates for a project you demand a sample certificate (3.1 or 2.1 according to your customer specs) and get approval from your customer beforehand. but i know electrode company can give any type of certificate you need.
Hello members,, I am working in a erw steel tube making company as a QC manager, Now when I make a mill test certificate at the enclosure I use to mention that the certificate is as per EN-10204/3.1B standard , as the said standard is referring our process, so mentioning the said standard directly in mtc is ok or shall i have to ask an organisation to have this certificate first,then only i can put EN-10204/3.1 B standard in my certificate, Secondly I want to know,we are receiving our raw material, supplier certificate is inspection certificate/sometime mill test certificate,after receiving this raw material we are manufacturing steel tubes,sheets etc,so while making MTc I am writing the certificate is mill test certificate,is it okay or it should be material test certificate?
I think the statement, Typically, Mill Test Certificates conform to the EN 10204 standard and are related to steel products is misleading. Arent we really takling about all metallic materials i.e. ferrous and non-ferrous e.g. Aluminium or Cast Iron?
Thanks dear for the information. Who can issue MTC? I received 3.1 MTC from a machining company(raw material is from other manufacturer) I know its not acceptable but I dont have any reference(since machining company is saying I am certifying that this material meets the requirements of PO)
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bond work index tests - grinding solutions ltd
The Bond Low-Energy Impact test can be used to determine the Crusher Work index (CWi), also known as the Impact Work Index. The test determines the impact energy at which a specimen fails and allows approximation of net power requirements for sizing crushers. The open and closed sized settings for given product sizes can also be determined.
The Bond Ball Mill Work Index (BBWi) test is carried out in a standardised ball mill with a pre-defined media and ore charge. The Work Index calculated from the testing can be used in the design and analysis of ball mill circuits
rod mill - an overview | sciencedirect topics
Rod mills have an industrial yield that is less than that of a ball mill, which explains the fact that balls have a much larger grinding surface than rods. The power needed to operate a rod mill could exceed 30% of the power used in a ball mill.
Rod mills have the highest rolling speeds, with interpass times in the finishing stand of 15150 ms. This is too short for either static recrystallization or strain-induced precipitation, and dynamic recrystallization is the main grain refining mechanism. Microalloying could limit grain growth during rolling by particle pinning and solute drag. However, austenite grain sizes of 10m can be achieved in CMn steels with optimally designed rod rolling schedules, so the main purpose of microalloying is precipitation strengthening. As-rolled rod is typically controlled-cooled at 15C s1 in loose coils (Stelmor process) to achieve a desired final microstructure and precipitate distribution. The principle application for HSLA rod steels is as cold-formed fasteners. An example of such a steel is given in Table 2.
Rod mill charges usually occupy about 45% of the internal volume of the mill. A closely packed charge of single sized rods will have a porosity of 9.3%. With a mixed charge of small and large diameter rods, the porosity of a static load could be reduced even further. However, close packing of the charge rarely occurs and an operating bed porosity of 40% is common. Overcharging results in poor grinding and losses due to abrasion of rods and liners. Undercharging also promotes more abrasion of the rods. The height (or depth) of charge is measured in the same manner as for ball mill. The size of feed particles to a rod mill is coarser than for a ball mill. The usual feed size ranges from 6 to 25mm.
For the efficient use of rods it is necessary that they operate parallel to the central axis and the body of the mill. This is not always possible as in practice, parallel alignment is usually hampered by the accumulation of ore at the feed end where the charge tends to swell. Abrasion of rods occurs more in this area resulting in rods becoming pointed at one end. With this continuous change in shape of the grinding charge, the grinding characteristics are impaired.
The bulk density of a new rod charge is about 6.25t/m3. With time due to wear the bulk density drops. The larger the mill diameter the greater is the lowering of the bulk density. For example, the bulk density of worn rods after a specific time of grinding would be 5.8t/m3 for a 0.91m diameter mill. Under the same conditions of operation, the bulk density would be 5.4t/m3 for a 4.6m diameter mill.
In the rod mill, high carbon steel rods about 50 mm diameter and extending the whole length of the mill are used in place of balls. This mill gives a very uniform fine product and power consumption is low, although it is not suitable for very tough materials and the feed should not exceed about 25 mm in size. It is particularly useful with sticky materials which would hold the balls together in aggregates, because the greater weight of the rods causes them to pull apart again. Worn rods must be removed from time to time and replaced by new ones, which are rather cheaper than balls.
As mentioned by earlier wire rod mills housed within smelter plant premises rejects large volume of waste emulsions which because of its toxic oil contents can not be discharged in open drains. Further since above toxic oil contain in the waste emulsion being only around 7% it is imperative that the residual water after breaking the emulsion needs to be recirculated to the plant itself. Present authors developed a process  for breaking the emulsion and release of the residual the water conforming to statutory norms for disposal of treated water in the open drain. In this process the waste emulsion was treated with calcium hydroxide in order to coagulate the toxic oil and separate it out from the residual water. Small contaminants in the residual water were finally removed by activated charcoal, pH adjusted to 7 and the water released. Typically for 7% oil content in waste emulsion, application rate of 3wt% calcium hydroxide and 2.5wt% charcoal brought down C.O.D. of treated water within permissible range. Table3.5 gives an example of such treatment process.
Powder milling process, using ball or rod mills, aim to produce a high-quality end-product that can be composites and nanocomposites, and nanocrystalline powder particles of intermetallic compounds, amorphous, hydrides, nitrides, silicates, etc. Powder milling process has been continuously improving by introducing numerous innovative types of ball mills in order to improve the quality and homogeneity of the end-products and to increase the productivity. This chapter discusses the factors affecting the mechanical alloying, mechanical disordering, and mechanical milling processes and their effects on the quality of the desired end-products. Moreover, we will present some typical examples that show the effect of these factors on the physical and chemical properties of the milled powders.
To equalize the charge segregation at the ends of the mill, the mill is rotated in the level position for eight revolutions then tilted up 5 for one revolution, tilted down 5 for one revolution then returned to the level position for eight revolutions and the cycle repeated throughout the test.
A study of the movement of materials in a rod mill indicates that at the feed end the larger particles are first caught between the rods and reduced in size gradually towards the discharge end. Lynch  contended that the next lower size would break after the sizes above it had completely broken. He described this as stage breakage, the stages being in steps of 2. The size difference between the particles at the two ends of the mill would depend on
The presence of this size difference indicates that a screening effect was generated within a rod mill and that the movement of material in the mill was a combination of breakage and screening effects. The breaking process was obviously repetitive and involved breakage function, classification function and selection functions. Therefore for rod mills, an extension of the general model for breakage within each stage applies, where the feed to stage (i + 1) is the product from stage i. That is, within a single stage i, the general model defined by Equation (11.18) applies
The number of stages, v, is the number of elements taken in the feed vector. A stage of breakage is defined as the interval taken to eliminate the largest sieve fraction from the mill feed or the feed to each stage of breakage. The very fine undersize is not included as a stage.
The breakage function described by Equation (11.2) could be used. For the classification matrix, which gives the proportion of each size that enters the next stage of breakage, the value of the element in the first stage C11 equals 1. That is, all of size fraction 1 is completely reduced to a lower size and all the particles of the classification underflow are the feed to the second stage of breakage and so on. Hence, the classification matrix is a descending series. If we take the 2 series, then the classification matrix C can be written as
The selection matrix S is machine dependent. It is affected by machine characteristics, such as length (including length of rods) and the speed of operation. Both B and C have to be constant to determine the selection function S within a stage.
Thus for each stage a similar matrix can be developed resulting in a step matrix which provides a solution of the rod mill model. Calculations are similar to that shown previously for grinding mill models.
The industrial comminution process under consideration has the following four units: Rod mill, Ball mill, hydro-cyclones, and water sumps. Fresh feed from the bin is fed to the rod mill along with water. The slurry generated from the rod mill is mixed with the slurry from the ball mill in a primary sump. The primary sump outlet stream is sent to the primary cyclone. The overflow from the primary cyclone goes to the secondary sump and the underflow is taken as a feed to the ball mill. The slurry generated in the secondary sump is taken to another hydro-cyclone which is called as secondary cyclone. The underflow of the secondary cyclone is recycled back to the ball mill for grinding and the final product is the overflow which goes to a flotation circuit as feed. Water is added to both sumps to facilitate the flow of the slurry smoothly within the circuit. Complete circuit configuration can be found in Figure 1.
Modeling of individual unit operations of the grinding circuit is performed separately using an amalgamated approach of population balance and empirical correlations. A simulation of an entire circuit is done by using a connectivity matrix which connects all the unit operations in terms of binary numbers. Here 0 denotes no connection and 1 denotes existence of a connection. Multiple simultaneous differential algebraic equations were formed using the entire set of equations which can be solved using well tested public domain software, called DASSL (Petzold, 1983). Details on these model equations can be found elsewhere (Mitra and Gopinath,2004) and not attached here for the sake of brevity.
The product size from HPGR can be much finer than the corresponding ball or rod mill products. As an example, the results by Mrsky, Klemetti and Knuutinen  are given in Figure6.8 where, for the same net input energy (4kWh/t), the product sizes obtained from HPGR, ball and rod mills are plotted.
laboratory rod mill
The 21 Liter (5 gallon) 911METALLURGY 911MPE21BM dual function Laboratory RodMill / BallMill is designed to meet the industrial requirements to grind coal, cement and a wide variety of ores. The dual dutyLaboratory Grinding Mill consists of a gear motor mounted on a high precision solid steel underframe complete with outlet funnel and a set of separation screens plus sample collector.
The mill incorporates a yoke and locking mechanism to facilitate easy access to the contents of the mill. An appropriate ball or rod charge is provided with the mill. The motor incorporates a solid-state controller to accurately control the drum speed of up to 70 RPM. This controller has an internal overload protection. A revolution counter is included to allow accurate control of milling which will automatically stop the mill when the desired milling duration is reached. The lid incorporates a quick release locking mechanism.
Easy convertible from Ball Mill to Rod Mill. Drums, balls and rods available in different grades of steel: SS304, SS316, SS303, ST37, ST52 and other steel materials or liners on request. Easy tilt to empty the drum
As stated above, the purpose of this research was primarily to establish a quantitative relationship between a laboratory ball mill capacity and fineness of finished product. As is nearly always the case in research, the major problem cannot be attacked until a number of smaller ones have been disposed of: apparatus must be decided upon and designed to meet the needs of the research; experimental technic must be developed to accord with good scientific procedure, which will give data of practical use; and the data must be interpreted. This investigation, however, instead of being one of merely determining mill capacity (for a given mill) as related to fineness of finished product, also became a study of batch grinding in a laboratory ball mill as related to time of grind.
The selection of apparatus was necessarily more or less arbitrary. A cylinder 16 inches in diameter by 7 inches in length was chosen to contain the grinding mediaa 43 per cent full load of 1-inch steel balls. Mechanism was provided to rotate the cylinder, at a constant speed of 55 r.p.m. This speed was decided upon on the basis of observation made at one end of the mill, which was closed with a coarse-mesh screen. The mill speed chosen was not necessarily exactly the speed which would give maximum mill output, but it probably was close to what may be termed the best speed. That there is a best speed for each size of ball, ball load, feed size, etc., is shown in the researches of Fahrenwald and Lee and this is just one example of the complexity of the grinding problem. The selected speed must therefore be considered a more or, less arbitrary one, but it fully served the purpose of this investigation.
In the experiments of this study, grinding was done wet. Thirty per cent of water by weight was added to each charge. This ore-water ratio was arrived at from a series of experiments in which the percentage of water was the variable. Thirty per cent of water by weight gave approximately the maximum mill outputgrinding through 100 mesh.
The weight of feed charge introduced into the mill also was determined from a series of experiments in which weight of feed charge was the variable. The weight of feed charge giving the greatest number of grams of finished minus- 100 mesh sand was approximately 1,750 grams. As data later presented will show, this is not exactly the weight of charge which will give maximum mill output in a unit of time; it is, however, approximately that weight of charge which gives maximum output under the conditions of (1) the size (sieve analysis) of feed used, and (2) a short-period grind. This weight of charge served the purpose of the batch-grind experiments of this study.
Having established the apparatus to be used and, in part, the conditions of the experiments, other factors and variables having even greater bearing upon mill output came up. The most important among these was the time of grind. For a given weight of feed charge to be ground in a batch laboratory ball mill, there was no information available to show how the rate of production of finished product in the mill varied with the time, of operation of the mill; that is, for a 10-minute grind it was not known if the output was greatest for the first minute, the second minute, or the sixth or tenth minute of operation. This question seemed of such importance that a decision was made to investigate it rather thoroughly.
In this study, rate of grinding or mill efficiency is stated in terms of grams per minute, abbreviated GPM. A more scientific basis on which to calculate mill efficiency probably would have been that of total new surface produced per unit of time. This basis, however, was not thought to offer any advantage over the one stated.
The size analysis of the feed for experimentation was also more or less arbitrarily selected; and, as these experiments, show, it is not the proper sieve analysis to give maximum mill output. Here again the proper feed size could not be known in advance, and the arbitrary feed size selected serves for the work in hand. Quartz of the white massive variety was selected for this study because of its homogeneity and its known surface constants.