All Grinding Mill & Ball Mill Manufacturers understand the object of the grinding process is a mechanical reduction in size of crushable material. Grinding can be undertaken in many ways. The most common way for high capacity industrial purposes is to use a tumbling charge of grinding media in a rotating cylinder or drum. The fragmentation of the material in that charge occurs through pressure, impact, and abrasion.
The choice of mill design depends on the particle size distribution in the feed and in the product wanted. Often the grinding is more economic when executed in a primary step, followed by a secondary step, giving a fine size product.
C=central trunnion discharge P=peripheral discharge R=spherical roller trunnion bearing, feed end H=hydrostatic shoe bearing, feed end R=spherical roller trunnion bearing, discharge end K=ring gear and pinion drive
Type CHRK is designed for primary autogenous grinding, where the large feed opening requires a hydrostatic trunnion shoe bearing. Small and batch grinding mills, with a diameter of 700 mm and more, are available. These mills are of a special design and described on special request by allBall Mill Manufacturers.
The different types of grinding mills are based on the different types of tumbling media that can be used: steel rods (rod mills), steel balls (ball mills), and rock material (autogenous mills, pebble mills).
The grinding charge in a rod mill consists of straight steel rods with an initial diameter of 50-100 mm. The length of the rods is equal to the shell length inside the head linings minus about 150 mm. The rods are fed through the discharge trunnion opening. On bigger mills, which need heavy rods, the rod charging is made with a pneumatic or manual operated rod charging device. The mill must be stopped every day or every second day for a few minutes in order to add new rods and at the same time pick out broken rod pieces.
As the heavy rod charge transmits a considerable force to each rod, a rod mill can not be built too big. A shell length above 6100 mm can not be recommended. As the length to diameter ratio of the mill should be in the range of 1,2-1,5, the biggest rod mill will convert maximum 1500 kW.
Rod mills are used for primary grinding of materials with a top size of 20-30 mm (somewhat higher for soft materials). The production of fines is low and consequently a rod mill is the right machine when a steep particle size distribution curve is desired. A product with 80% minus 500 microns can be obtained in an economical manner.
The grinding charge in a ball mill consist of cast or forged steel balls. These balls are fed together with the feed and consequently ball mills can be in operation for months without stopping. The ball size is often in the diameter range of 20-75 mm.
The biggest size is chosen when the mill is used as a primary grinding mill. For fine grinding of e.g. sands, balls can be replaced by cylpebs, which are heat treated steel cylinders with a diameter of 12-40 mm and with the same length as the diameter.
Ball mills are often used as secondary grinding mills and for regrinding of middlings in concentrators. Ball mills can be of the overflow or of the grate discharge type. Overflow discharge mills are used when a product with high specific surface is wanted, without any respect to the particle size distribution curve. Overflow discharge mills give a final product in an open circuit. Grate discharge mills are used when the grinding energy shall be concentrated to the coarse particles without production of slimes. In order to get a steep particle size distribution curve, the mill is used in closed circuit with some kind of classifier and the coarse particles known as classifier underflow are recycled. Furthermore, it should be observed that a grate discharge ball mill converts about 20% more energy than an overflow discharge mill with the same shell dimensions.
Ball mill shells are often furnished with two manholes. Ball mills with small balls or cylpebs can produce the finest product of all tumbling mills. 80% minus 74 microns is a normal requirement from the concentrators.The CRRK series of wet grinding ball mills are tabulatedbelow.
No steel grinding media is used in a fully autogenous mill. When choosing primary autogenous grinding, run of mine ore up to 200-300 mm in size is fed to the mill. When using a crushing step before the grinding, the crusher setting should be 150-200 mm. The feed trunnion opening must be large enough to avoid plugging. The biggest pieces in the mill are important for the size reduction of middle size pieces, which in their turn are important for the finer grinding. Thus the tendency of the material to be reduced in size by pressure, impact, and abrasion is a very important question when primary autogenous grinding is proposed.
When autogenous grinding is used in the second grinding step, the grinding media is size-controlled and often in the range of 30-70 mm. This size is called pebbles and screened out in the crushing station and fed to the mill in controlled proportion to the mill power. The pebble weight is 5-25% of the total feed to the plant, depending on the strength of the pebbles. Sometimes waste rock of high strength is used as pebbles.
Pebble mills should always be of the grate discharge type. The energy that can be converted in a mill depends on the total weight of the grinding charge. Consequently, pebble mills convert less power per mill volume unit than rod and ball mills.
High quality steel rods and balls are a considerable part of the operating costs. Autogenous grinding should, therefore, be considered and tested when a new plant shall be designed. As a grinding mill is built to last for decades, it is more important to watch the operation costs than the price of the mill installation. The CRRK series of wet grinding pebble mills are tabulated below.
Wet grinding is definitely the most usual method of grinding minerals as it incorporates many advantages compared to dry grinding. A requirement is, however, that water is available and that waste water, that can not be recirculated, can be removed from the plant without any environmental problems. Generally, the choice depends on whether the following processing is wet or dry.
When grinding to a certain specific surface area, wet grinding has a lower power demand than dry grinding. On the other hand, the wear of mill lining and grinding media is lower in dry grinding. Thus dry grinding can be less costly.
The feed to a dry grinding system must be dried if the moisture content is high. A ball mill is more sensitive to clogging than a rod mill. An air stream through the mill can reduce the moisture content and thus make a dry grinding possible in certain applications.
Due to the hindering effect that the ball charge gives to the material flow in dry grinding, the ball charge is not more than 28-35% of the mill volume. This should be compared with 40-45% in wet grinding. The expression used for this phenomenon is that the charge in a dry grinding mill is swollen.
Big dry grinding ball mills are often two-compartment mills, with big balls in the first compartment and small balls or cylpebs in the second one. An extra grate wall is used to separate the two charges.
The efficiency of wet grinding is affected by the percentage of solids. If the pulp is too thick, the grinding media becomes covered by too thick a layer of material, which hinders grinding. The opposite effect may be obtained if the dilution is too high, and this may also reduce the grinding efficiency. A high degree of dilution may sometimes be desirable in order to suppress excessive slime formation.
The specific power required for a certain grinding operation, usually expressed in kWh/ton, is a function of both the increase in the specific surface of the material (expressed in cm/cm or cm/g) and of the grinding resistance of the material. This can be expressed by the formula
where c is a material constant representing the grinding resistance, and So and S are the specific surfaces of the material before and after the grinding operation respectively. The formula is an expression of Rittingers Law which is shown by tests to be reasonably accurate up to a specific surface of 10,000 cm/cm.
When the grinding resistance c has been determined by trial grinding to laboratory scale, the net power E required for each grinding stage desired may be determined by the formula, at least as long as Rittingers Law is valid. If grinding is to be carried out not to a certain specific surface S but to a certain particle size k, the correlation between S and k must be determined. The particle size is often expressed in terms of particle size at e.g. 95, 90 or 80% quantity passing and is denoted k95, k90 or k80.
where E =the specific power consumption expressed in kWh/short ton. Eo = a proportionality and work factor called work index k80p = particle size of the product at 80% passage (micron) k80f =the corresponding value for the raw material (micron)
The value of Eo is a function of the physical properties of the raw material, the screen analyses of the product and raw material respectively, and the size of the mill. The value for easily-ground materials is around 7, while for materials that have a high grinding resistance the value is around 17.
Eo is correlated to a certain reduction ratio, mill diameter etc. Corrections must be made for each case. The simplest method of calculating the specific power consumption is test grinding in a laboratory mill, and comparison of the results with a known reference material. The sample is ground in batches for 3, 6,12 minutes, a screen analysis is carried out after each period, after which the specific surface is determined. A good estimate of the grinding characteristics of the sample can be obtained by comparison of the specific surfaces with corresponding values for the reference material.
When the net power required has been determined, an allowance is made for mechanical losses. The gross power requirement thus arrived at, should with a satisfactory margin be utilised by the mill selected.
The critical speed of a rotating mill is the RPM at which a grinding medium will begin to centrifuge, namely will start rotating with the mill and therefore cease to carry out useful work. This will occur at an RPM of ncr, which may be determined by the formula
where D is the inside diameter in meters of the mill. Mills are driven in practice at a speed corresponding to 60-80% of the critical speed, the choice of speed being influenced by economical considerations. Within that range the power is nearly proportional to the speed.
The charge volume in the case of rod and ball mills is a measure of the proportion of the mill body that is filled by rods or balls. When the mill is stationary, raw material and liquid should fill the voids between the grinding media, in order that these should be fully utilized.
Maximum mill efficiency is reached at a charge volume of approximately 55%, but for a number of reasons 45-50% is seldom exceeded. The efficiency curve is in any case quite flat about the maximum. In overflow mills the charge volume is usually 40%, while there is a greater choice in the case of grate discharge mills.
For coarse grinding in rod mills, the rods used have a diameter of 50-100 mm and their lengths are approx. 150 mm below the effective inside shell length. Rods will break when they have been worn down to about 20 mm and broken rods must from time to time be taken out of the mill since otherwise they will reduce the mill capacity and may cause blockage through piling up. The first rod charge should also contain a number of rods of smaller diameter.
It may be necessary to charge the mill with rods of smaller diameter when fine grinding is to be carried out in a rod mill. Experience shows that the size of the grinding media should bear a definite relationship to the size of both the raw material and the finished product in order that optimum grinding may be achieved. The largest grinding media must be able to crush and grind the largest pieces of rock, while on the other hand the grinding media should be as small as possible since the total active surface increases in inverse proportion to the diameter.
A crushed mineral whose largest particles pass a screen with 25 x 25 mm apertures shall be ground to approx. 95% passing 0.1 mm in a 2.9 x 3.2 m ball mill of 35 ton charge weight. In accordance with Olewskis formula
Grinding media wear away because of the attrition they are subjected to in the course of the grinding operation, and in addition a continuous reduction in weight takes place owing to corrosion. The rate of wear will in the first place depend on the abrasive properties of the mineral being ground and naturally also on the hardness of the grinding media themselves.
The wear of rods and balls is usually quoted in grammes per ton of material processed (dry weight) and normal values may lie between 100 and 1500 g/ton. Considerably higher wear figures may however be experienced in fine wet grinding of e.g. very hard siliceous sand.
A somewhat more accurate way of expressing wear is to state the amount of gross kWh of grinding power required to consume 1 kg of grinding media. A normal value in wet grinding is 15 kWh/kg.The wear figures in dry grinding are only 10-30 % of the above.
where c is a constant which, inter alia, takes into consideration the mean slope a of the charge, W is the weight in kp of the charge n is the RPM Rg is the distance in metres of the centre of gravity from the mill centre
W for rod and ball mills shall be taken as the weight of the rod or ball charge, i.e. the weight of the pulp is to be ignored. For pebble mills therefore W is to be calculated on the basis of the bulk weight of the pebbles.
It should be pointed out that factor c in the formula is a function of both the shape of the inner lining (lifter height etc.) and the RPM. The formula is however valid with sufficient accuracy for normal speeds and types of lining.
The diagram gives the values of the quantity Rg/d as a function of the charge volume, the assumption being that the charge has a plane surface and is homogeneous, d is the inside diameter of the mill in metres. The variation of the quantity a/d, where a is the distance between the surface of the charge and the mill centre, is also shown in the same figure.
In order to keep manufacturing costs at a minimum level, Morgardshammar has a series of standard mill diameters up to and including 6.5 m. Shell length, however, can be varied and tailor made for each application. The sizes selected are shown on the tables on page 12-13 and cover the power range of 200-5000 kW.
Shells with a diameter of up to about 4 m are made in one piece. Above this dimension, the shell is divided into a number of identical pieces, bolted together at site, in order to facilitate the transport. The shell is rolled and welded from steel plate and is fitted with welded flanges of the same material. The flanges are machined in order to provide them with locating surfaces fitting into the respective heads. The shells of ball and pebble mills are provided with 2 manholes with closely fitting covers. The shells have drilled holes for different types of linings.
Heads with a diameter of up to about 4 m are integral cast with the trunnion in one piece. Above this diameter the trunnion is made as a separate part bolted to the head. The head can then be divided in 2 or 4 pieces for easy transport and the pieces are bolted together at site. The material is cast steel or nodular iron. The heads and the trunnions have drilled holes for the lining.
Spherical roller (antifriction) bearings are normally used. They offer the most modern and reliable technology and have been used for many years. They are delivered with housings in a new design with ample labyrinth seals.
For very large trunnions or heavy mills, i.e. for primary autogenous grinding mills. Morgardshammar uses hydrostatic shoe bearings. They have many of the same advantages as roller bearings. They work with circulating oil under pressure.
The spherical roller bearing and the hydrostatic shoe bearing take a very limited axial space compared to a conventional sleeve bearing. This means that the lever of the bearing load is short. Furthermore, the bending moment on the head is small and as a result of this, the stress and deformation of the head are reduced. Ask Morgardshammar for special literature on trunnion bearings.
Ring gears are often supplied with spur gears. They are always split in 2 or 4 pieces in order to facilitate the assembly. Furthermore, they are symmetrical and can be turned round in order to make use of both tooth flanks. The material is cast steel or nodular iron. They are designed in accordance with AGMA.The ring gear may be mounted on either the feed or the discharge head. It is fitted with a welded plate guard.
The pinion and the counter shaft are integral forged and heat treated of high quality steel. For mill power exceeding about 2500 kW two pinions are used, one on each side of the mill (double-drive). The pinion is supported on two spherical roller bearings.
The trunnion bearings are lubricated by means of a small motor- driven grease lubricator. The gear ring is lubricated through a spray lubricating system, connected to the electric and pneumatic lines. The spray nozzles are mounted on a panel on the gear ring guard.
In order to protect the parts of the mill that come into contact with the material being ground, a replaceable lining of wear-resistant material is fitted. This may take the form of unalloyed or alloyed rolled or cast steel, heat treated if required, or rubber of the appropriate wear resistant quality. White cast iron, unalloyed or alloyed with nickel (Ni-hard), may also be used.
The shape of the mill lining is often of Lorain-type, consisting of plates held in place between lifter bars (or key bars) of suitable height bolted on to the shell. This system is used i.e. of all well-known manufacturers of rubber linings. Ball mills and autogenous mills with metal lining also can be provided with single or double waved plates without lifter bars.
In grate discharge mills the grate and the discharge lifters are a part of the lining. The grate plates with tapered slots or holes are of metal or rubber design. The discharge lifters are fabricated steel with thick rubber coating. Rubber layer for metal linings and heavy corner pieces of rubber are included in a Morgardshammar delivery as well as attaching bolts, washers, seal rings, and self-locking nuts. A Morgardshammar overflow mill can be converted into a grate discharge mill only by changing some liner parts and without any change of the mill. Trunnion liners are rubber coated fabricated steel or cast steel. In grate discharge mills the center cone and the trunnion liner form one piece.
Scoop feeders in combination with drum feeders are used when retaining oversize from a spiral or rake classifier. As hydrocyclones are used in most closed grinding circuits the spout feeders are used most frequently.
Vibrating feeders or screw feeders are used when charging feed to dry grinding mills. Trommel screens are used to protect slurry pumps and other transport equipment from tramp iron. Screens can have perforated rubber sheets or wire mesh. The trommel screens are bolted to the discharge trunnion lining.
Inching units for slow rotation of the mills are also furnished. Rods to the rod mills are charged by means of manual or automatic rod charges. Erection cradles on hydraulic jacks are used when erecting medium or big size mills at site.
A symbol of dependable quality ore milling machinery manufacturing, industrial and mining equipment, ball mills and rod mills as well as supplies created for your specific needs. During this period thousands of operators have experienced continuous economical and unequalled service through their use.As anindustrial ball mill manufacturer and supplier, we havecontinuously accumulated knowledge on grinding applications. It has contributed greatly to the grinding process through the development and improvement of such equipment.
Just what is grinding? It is the reduction of lump solid materials to smaller particles by the application of shearing forces, pressure, attrition, impact and abrasion. The primary consideration, then, has been to develop some mechanical means for applying these forces. The modern grinding mill applies power to rotate the mill shell and thus transmits energy to some form of media which, in turn, fractures individual particles.
Through constant and extensive research, in the field of grinding as well as in the field of manufacturing. Constantly changing conditions provide a challenge for the future. Meeting this challenge keeps our company young and progressive. This progressive spirit, with the knowledge gained through the years, assures top quality equipment for the users of our mills.
You are urged to study the following pages which present a detailed picture of our facilities and discuss the technical aspects of grinding. You will find this data helpful when considering the selection of the grinding equipment.
It is quite understandable that wetakes pride in the quality of our mills.Complementing the human craftsmanship built into these mills, our plants are equipped with modern machines of advanced design which permit accurate manufacturing of each constituent part. Competent supervision encourages close inspection of each mill both as to quality and proper fabrication. Each mill produced is assured of meeting the high required standards. New and higher speed machines have replaced former pieces of equipment to provide up-to-date procedures. The use of high speed cutting and drilling tools has stepped up production, thereby reducing costs and permitting us to add other refinements and pass these savings on to you, the consumer.
Each foundry heat is checked metallurgically prior to pouring. All first castings of any new design are carefully examined by the use of an X-ray machine to be certain of uniformity of structure. The X -ray is also used to check welding work, mill heads, and other castings.
Each Mills, regardless of size, is designed to meet the specific grinding conditions under which it will be used. The speed of the mill type of liner, discharge arrangement, size of feeder, size of bearings, mill diameter and length, and other factors are all considered to take care of the size of feed, tonnage, circulating sand load, selection of balls or rods, and the final size of grind.
All Mills are built with jigs and templates so that any part may be duplicated. A full set of detailed drawings is made for each mill and its parts. This record is kept up to date during the life of the mill. This assures accurate duplication for the replacement of wearing parts during the future years.
As a part of our service our staff includes experienced engineers, trained in the field of metallurgy with special emphasis on grinding work. This knowledge, as well as a background gained from intimate contact with various operating companies throughout the world, provides a sound basis for consultation on your grinding problems. We take pride in manufacturing rod mills and ball millsfor the metallurgical, rock products, cement, process, and chemical industries.
As an additional service we offer our testing laboratories to check your material for grindability. Since all grinding problems are different some basis must be established for recommending the size and type of grinding equipment required. Experience plays a great part in this phase however, to establish more direct relationships it is often essential to conduct individual grindability tests on the specific material involved. To do this we have established certain definite procedures of laboratory grinding work to correlate data obtained on any new specific material for comparison against certain standards. Such standards have been established from conducting similar work on material which is actually being ground in Mills throughout the world. The correlation between the results we obtain in our laboratory against these standards, coupled with the broad experience and our companys background, insures the proper selection and recommendation of the required grinding equipment.
When selecting a grinding mill there are many factors to be taken into consideration. First let us consider just what constitutes a grinding mill. Essentially it is a revolving, cylindrical shaded machine, the internal volume of which is approximately one-half filled with some form of grinding media such as steel balls, rods or non-ferrous pebbles.
Feed may be classified as hard, average or soft. It may be tough, brittle, spongy, or ductile. It may have a high specific gravity or a low specific gravity. The desired product from a mill may range in size from a 4 mesh down to 200 mesh, or into the fine micron sizes. For each of these properties a different mill would be indicated.
The Mill has been designed to carry out specific grinding work requirements with emphasis on economic factors. Consideration has been given to minimizing shut-down time and to provide long, dependable trouble-free operation. Wherever wear takes place renewable parts have been designed to provide maximum life. A Mill, given proper care, will last indefinitely.
Mills have been manufactured in a wide variety of sizes ranging from laboratory units to mills 12 in diameter, with any suitable length. Each of these mills, based on the principles of grinding, provides the most economical grinding apparatus.
For a number of years ball mill grinding was the only step in size reduction between crushing and subsequent treatment. Subsequently smaller rod mills have altered this situation, providing in some instances a more economical means of size reduction in the coarser fractions. The principal field of rod mill usage is the preparation of products in the 4-mesh to 35-mesh range. Under some conditions it may be recommended for grinding to about 48 mesh. Within these limits a rod mill is often superior to and more efficient than a ball mill. It is frequently used for such size reduction followed by ball milling to produce a finished fine grind. It makes a product uniform in size with only a minimum amount of tramp oversize.
The basic principle by which grinding is done is reduction by line contact between rods extending the full length of the mill. Such line contact results in selective grinding carried out on the largest particle sizes. As a result of this selective grinding work the inherent tendency is to make size reduction with the minimum production of extreme fines or slimes.
The small rod mill has been found advantageous for use as a fine crusher on damp or sticky materials. Under wet grinding conditions this feed characteristic has no drawback for rod milling whereas under crushing conditions those characteristics do cause difficulty. This asset is of particular importance in the manufacture of sand, brick, or lime where such material is ground and mixed with just sufficient water to dampen, but not to produce a pulp. The rod mill has been extensively used for the reduction of coke breeze in the 8-mesh to 20-mesh size range containing about 10% moisture to be used for sintering ores.
Grinding by use of nearly spherical shaped grinding media is termed ball milling. Strictly speaking, such media are made of steel or iron. When iron contamination is detrimental, porcelain or natural non-metallic materials are used and are referred to as pebbles. When ore particles are used as grinding media this is known as autogenous grinding.
Other shapes of media such as short cylinders, cubes, cones, or irregular shapes have been used for grinding work but today the nearly true spherical shape is predominant and has been found to provide the most economic form.
In contrast to rod milling the grinding action results from point contact rather than line contact. Such point contacts take place between the balls and the shell liners, and between the individual balls themselves. The material at those points of contact is ground to extremely fine sizes. The present day practice in ball milling is generally to reduce material to 35 mesh or finer. Grinding in a ball mill is not selective as it is in a rod mill and as a result more extreme fines and tramp oversize are produced.
Small Ball mills are generally recommended not only for single stage fine grinding but also have wide application in regrind work. The Small Ball millwith its low pulp level is especially adapted to single stage grinding as evidenced by hundreds of installations throughout the world. There are many applications in specialized industrial work for either continuous or batch grinding.
Wet grinding may be considered as the grinding of material in the presence of water or other liquids in sufficient quantity to produce a fluid pulp (generally 60% to 80% solids). Dry grinding on the other hand is carried out where moisture is restricted to a very limited amount (generally less than 5%). Most materials may be ground by use of either method in either ball mills or rod mills. Selection is determined by the condition of feed to the mill and the requirements of the ground product for subsequent treatment. When grinding dry some provision must be made to permit material to flow through the mill. Mills provide this necessary gradient from the point of feeding to point of discharge and thereby expedites flow.
The fineness to which material must be ground is determined by the individual material and the subsequent treatment of that ground material Where actual physical separation of constituent particles is to be realized grinding must be carried to the fineness where the individual components are separated. Some materials are liberated in coarse sizes whereas others are not liberated until extremely fine sizes are reached.
Occasionally a sufficient amount of valuable particles are liberated in coarser sizes to justify separate treatment at that grind. This treatment is usually followed by regrinding for further liberation. Where chemical treatment is involved, the reaction between a solid and a liquid, or a solid and a gas, will generally proceed more rapidly as the particle sizes are reduced. The point of most rapid and economical change would determine the fineness of grind required.
Laboratory examinations and grinding tests on specific materials should be conducted to determine not only the fineness of grind required, but also to indicate the size of commercial equipment to handle any specific problem.
This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.
I have been grinding materials or particle size reduction for over 30 years. I was introduced to making powder out of lead pigs in a ball mill at my fist job, and have been working in the field of particle size reduction in one form or another for most of my life. The purpose of this article is not to show a complete listing of all types of particle size reduction machinery, but to list the ones that I have used and found to be effective in their capabilities in grinding very hard or abrasive materials. This grinding takes a little more thought and consideration for wear and the potential contamination that may become imparted on the material which is being attempted to be ground. Primary Reduction Jaw Crusher In quarry operations, very large jaw crushers can be found. These are primarily used to reduce shot blast size materials such as limestone and road bed materials to a wide variety of sizes. In specialty particle size reduction, one discovers very hard to grind or specialty materials. In the area of very abrasive or just extremely hard materials (i.e. mohs of up to 7 or 8), jaw crushers of 36 x 24 in. have been found to be able to reduce large chunks of material from about 24 in. top size to -6 in. For very abrasive products that are ground, it is one of the most economical ways of reducing the particle size. The need to replace jaws for processing hard, abrasive materials is routine, but it sure beats trying to hydraulically jackhammer the materials. Jaw crushers can easily work in tandem with other jaw crushers. The smaller the jaw opening, the smaller the top size of the finished material can be delivered. Often the need is to initially take up to 24-in. material and reduce it to a nice beginning size for secondary grinding machines (a maximum size of 3-4 in.). To accomplish this, the primary jaw (36x20 in.) has been successfully used as a pre-crusher to feed a 16x10-in. jaw crusher. Average top size has been around 3 in. with minimal fines and minimal wear using this equipment configuration, although very large and some smaller jaw crushers are also available. The use of manganese steel wear parts is preferred, but other materials of construction can be engineered to each specific need. Further Reduction Some industries need particle sizes in the screened or grit size ranges. To further reduce these particles different machines can be used, depending on the final product required and the abrasiveness of the materials. All of the following pieces of machinery are used in circuit with a multi-deck screener. The fraction required is recovered as final product and the oversized materials are returned to the grinding machine for additional particle reduction. Impact Mill Abrasive grinding operations can utilize an impact mill, which is basically a set of rotating hammers with breaker plates that can be set to a specific gap between the hammer and the breaker plate to affect the particle size required. However, this type of milling can have high wear on the hammers. There are a variety of wear materials of construction that can be used in the hammers and breaker blocks which can be tailored to the type of material being ground. Although the wear can be very high, the cost of the wear parts is relatively low, but replacement must be performed often. Some materials require hammer changes every eight hours. Impact milling gives a long distribution of fines in the particle size distribution. For materials that need to have a fines component, the impact mill performs this task well. Cone There are also cone crushers that can reduce the amount of fines collected. A cone crusher is generally used as a secondary crusher in a crushing circuit. Pre-crushed product is fed through the top of the crusher and flows over the mantle. The vertical cone crusher drive shaft rotates the mantle eccentrically below the concave, or bowl liner, squeezing the product and crushing it between the mantle and concave. Cone crushers are used extensively throughout the aggregate and mineral processing industry. The wear parts can also be made out of a variety of materials specific to individual processing needs. The benefit is that the wear parts last longer but the tradeoff is that they are more expensive and it takes longer to change out the wear components. This type of crushing produces a final distribution with fewer fines in it. This can be advantageous to some companies specific needs. Roll A roll crusher is a set of opposed rolls, spinning in opposite directions which at the top of the mill, material is pulled in and crushed between the rolls and drops it out the bottom of the rolls. Setting the gap between the rolls allows an operator to obtain the desired particle size. The operating speeds and wear on this unit is low, and if set up properly, this method of grinding creates very few fines in the particle size distribution. The roll crusher limitations are in the reduction percentage, in that it takes the material and reduces the particle by up to 10 fold. For larger reduction percentages, the roll can be set up in a series from wider gapped rolls to progressively smaller roll sets. This gives a very nice reduction in size, without contamination and minimal fines creation. The drawback to roll crushing is the cost of the parts and the time needed to change out the roll shells. Fine Grinding Fine grinding abrasive materials is typically needed to create particle sizes in the minus 50 mesh range (297 microns) down to about 95% minus 325 mesh (45 microns). Some of these sizes are typically referred to as talc, flour, pulverized, or ball-mill fine grades. Following are three different types of machines that can be used to obtain the grinds. Ring-Roll Air Swept Pulverizer This grinding unit uses a set of grinding rolls suspended on a pendulum assembly. When rotated, the rolls spin outward against a grinding ring where the material is delivered for crushing. The force between the roll and the ring crushes the material, and the fines are swept upward by the air flow through the mill. Integral to and at the top of the mill is a classifier of some sort which rejects any oversized materials and returns them internally to the mill for further grinding. Again, the material type of roll and ring can be designed specifically for the type of material being ground. The mill does impart some metal to the products, but in some cases it is below the threshold of perceived contamination for that particular product. There is a nice efficiency to the pulverize style of grinding, and the changing of particle sizes is easy. Depending on the mill size, starting particle sizes can be from 2 to in. The mill is versatile and it is relatively easy to clean out the system. Ball Mill The ball mill has been around for eons. There are many shapes and sizes and types. There is a single enclosed drum-type where material is placed in the drum along with a charge of grinding media. These can be in various shapes, and typically they are balls. There is a whole science in the size of the starting material versus the ball size, shape material of construction and charge percentage of grinding media. All of these variables affect particle size, shape, and grinding efficiency. This type of grinding is very good for abrasive materials to prevent contamination. The grinding media as well as the interior surfaces of the mill can be lined with abrasion resistant materials suited to the material being ground. In some cases, it can even be the material being ground. However, the batch type system is not a very efficient means of grinding. There is a variety of ball mill that is a continuous process versus a batch process. It has an external classifier which returns the oversized material to the ball mill for further milling. This system is much more efficient in the grinding ability, but it is much more difficult to line the entire system with wear parts to grind an abrasive material. Vibrating Mills A vibrating mill is almost a version of a rotating ball mill, but the unit is set to vibrate. Media of balls, cones, rods, etc., are loaded into the mill, and with batch or continuous processing the material is introduced into the grinding zone and reduced in particle size. This equipment can be effectively lined with wear parts and the material of construction of the grinding media can be designed for the particular material being ground to have minimal impact on contamination. These systems can be used in concert with a mechanical separator, but have also been used with screeners to minimize contamination. The particle sizes are typically not as fine as the rotating ball mill or the fine grinding mills listed below. These systems however can be very compact and effective for small to handle high value materials. Micron and Nano-Sizing A number of materials need to be reduced to sizes smaller than 95% minus 325 mesh (45 microns). Typically, top sizes of 44 microns to 10 or 15 microns with average particle sizes in the 3 micron to 30 micron range for abrasive materials can be processed using a jet mill. There a few different types of jet mills for grinding abrasive products to the particle sizes listed above. Spiral Jet Mill Spiral jet mills use compressed gas (typically air) at over 100 psig (6.9 bar(g)) to form a spiral air stream in the mill at rates of about 500 m/sec. The material to be ground is injected into this air stream to where the particles collide with each other as well as the sidewalls to reduce the particles. An internal cyclonic effect classifies the materials and they exit through the central portion of the spiral. The benefit to this type of mill for grinding abrasive materials is limited to very small quantities to be processed. These mills have been made with wear liners appropriate for the material being ground. However, the wear on the liners is great and can prove costly in terms of parts as well as downtime. Fluid Bed Jet Mill The fluid bed jet mill is ideal for, but not limited to, abrasive materials. The difference in grinding action between the spiral mill and the fluidized bed is that the jet mill reduces the high speed incidental wall collisions to near zero. In a fluid bed, the air nozzles convert the pressure to velocity in a bed of material at the bottom of the mill, entraining and accelerating the particles within the bed. This grinding action utilizes the extreme edges of the bed as a wear liner, preventing contact at high velocities to parts of the machine. It prevents pick up of contamination to the material being ground to less than parts per million, and depending on the material, even to less than parts per billion. The mill has an internal mechanical classifier to perform the particle sizing, and it is easy to change the particle cut required. The oversized material is rejected from the classifier wheel within the mill and returned to the grinding section of the mill for further size reduction. This particular machine can also be run with hot gasses. This can make the mill more efficient by using heat to raise the escape velocity of the gas without requiring the 100 psig (6.9 bar) pressure, making the cost of compressing the gasses less. It still maintains the same 500 m/sec velocity. It can also perform some drying of the material. Steam Fluidized Bed Jet Mill A version of the fluidized bed jet mill that can grind even finer than noted above utilizes superheated high-pressure steam (up to 1450 psig/100 barl) to perform dry grinding of material. It can reach grinding velocities of 1500 m/sec and grind about 2.6 times finer than possible when utilizing ambient temperate gasses. So in the example above, if the best particle size achieved is a dv50% of 3 microns, the steam operated mill can produce a 1 micron dv50% material. Some dense materials have been successfully ground using this dry processing method to 100% less than 1 micron. Traditionally, wet processing systems were the only method to process materials to less than 1 micron. Again, the bed action of the mill prevents the material from hitting the sidewalls of the mill at high velocities, giving a very pure grind to the end material. This system does not wet the product, and it can even initialize chemical reactions on some products or it can even dry other materials from some levels of moisture. Wet Processing High Flow Bead Mills There are a number of types and designs of wet processing mills. Some refer to these mills as sand or bead or media mills. They all typically have a set of media that is stirred and, in some fashion or another, a slurry of material to be ground is pumped through this rotated volume of grinding media. A screen or separator is typically used to keep the media in the mill while passing the finished product through the screen. This type of milling process can also have lined walls and coated stirring parts, and the media can be of the type needed for a particular material to be ground, to have the least impact on contamination. Particles in this type of process can be reduced to 100% less than 1 micron with dv50% ranges in the 20-30 nanometer range. This milling is also effective for economically grinding materials in the 2 to 30 micron dv50% range. This milling can be performed in an aqueous or solvent based slurry. Depending on the type of material that needs to be ground, solids levels up to 75% can be achieved. If the material must remain in a slurry, this type of processing is very effective as it grinds and mixes the solids in one step. Additional surfactants or other reaction materials can also be included in the slurry. There is some wear on this type of system, but it is minimal. Wet Autogenous Mills For those materials that cannot withstand much of any contamination, autogenous grinding is preferred. Autogenous means arising from within or from a thing itself. In this case, the grinding media is made from the same material that is being ground. This type of grinding has been successful in grinding materials as hard as diamond without contamination. The milling system is specially designed to handle the autogenous grinding media with specialty separators to keep the grinding media in the mill while allowing the fines to pass. Like its wet milling counterpart listed above, the autogenous grinding mill can make particles up to a fineness of less than 1 micron in aqueous or solvent slurries. This is an excellent way to manufacture ultra-fine materials without contamination. Gregory J. Gregg Shemanski is president and founder of Custom Processing Services Inc., Reading, PA, and Custom Processing Services LLC, East Greenville, PA. Shemanski and Jeff Klinger formed the company in 1998, and it has grown to be one of the leading contract manufacturing firms in the field of particle size reduction. For more information, visit www.customprocessingservices.com. For related articles, news, and equipment reviews, visit our Size Reduction Equipment Zone
Grinding is usually performed wet, although in certain applications dry grinding is used. When the mill is rotated, the mixture of medium, ore, and water, known as the mill charge, is intimately mixed; the medium comminuting the particles depends on the speed of rotation of the mill and the shell liner structure. Generally, grinding in mineral processing is a continuous process, material being fed at a controlled rate from storage bins into one end of the mill and overflowing at the other end after a suitable dwell time. Control of product size is exercised by the type of medium used, the speed of rotation of the mill, the nature of the ore feed, and the type of circuit used.
Due to the rotation and friction of the mill shell, the grinding medium is lifted along the rising side of the mill until a position of dynamic equilibrium is reached, when the bodies cascade and cataract down the free surface of the other bodies, about a dead zone where little movement occurs, down to the toe of the mill charge. Grinding Mill liners form.
A lining element (10) for mounting onto an inner surface of a drum mantle (56) in a grinding mill, comprising an elongated lifter member (12) of a wear resistant material adapted to be axially oriented with respect to the drum mantle and to project radially into the drum, and an elongated single-piece support member (26) of an elastomeric material adapted to resiliently support the elongated lifter member over a full length thereof above the inner surface of the drum mantle. The support member is extended peripherally in a rearward direction with respect to an operational forward direction of rotation of the drum into contact with a subsequent lining element (10) to be mounted onto the inner surface, and to cover entirely therebetween the inner surface of the drum mantle.
The present invention relates to lining elements for mounting onto an inner surface of a drum mantle in a grinding mill. More specifically, the invention relates to lining elements having an axially oriented elongated wear resistant lifter member projecting radially into the drum, and a resilient support member for the lifter member.
In a lining element of this type, disclosed for example in U.S. Pat. No. 4,848,681, Eriksson et al, the lifter member made of a hard metal alloy or a ceramic material is effective as a wear resistant component of the mill lining whereas the support member made of a resilient elastomeric material is effective as an impact absorbing component protecting the wear resistant lifter member from breaking. By combining the wear-resistant and impact absorbing materials in this known way, the lifter element will be more resistant to failure and have a longer service life, as compared, for example, with mill linings entirely made of steel.
The invention provides a lining element for mounting onto an inner surface of a drum mantle in a grinding mill, comprising an elongated lifter member of a wear resistant material adapted to be axially oriented with respect to the drum mantle and to project radially into the drum, and an elongated single-piece support member of an elastomeric material adapted to resiliently support the elongated lifter member over a full length thereof above the inner surface of the drum mantle, said support member being extended peripherally in a rearward direction with respect to an operational forward direction of rotation of the drum to contact a subsequent lining element to be mounted onto said inner surface, and to cover therebetween the inner surface of the drum mantle.
The invention also provides a mill lining comprising a plurality of lining elements for mounting onto an inner surface of a drum mantle in a grinding mill to cover said inner surface, each lining element comprising an elongated lifter member of a wear resistant material adapted to be axially oriented with respect to the drum mantle and to project radially into the drum, and an elongated single-piece support member of an elastomeric material adapted to resiliently support the elongated lifter member over a full length thereof above the inner surface of the drum mantle, said support member being extended peripherally to contact a subsequent of said lining elements in a rearward direction with regard to an operational direction of rotation of the drum mantle, and to cover entirely therebetween the inner surface of the drum mantle.
In a mill lining according to the invention, the support member also serves as a wear plate entirely covering the drum mantle rearwardly of the lifter member to the following lining element in the drum. Thereby also the full volume of the single-piece elastomeric element will effectively participate in resiliently supporting the lifter member against the impact forces from grinding charge striking the leading face of the lifter member during operation of the mill. The peripherally wide support member also presents a large base for safely securing the lining element to the drum mantle to better withstand bending moments imposed on the support member. Due to fewer components, this single-piece lifter-wear plate element is also mounted or replaced in shorter time as compared to known composite material mill linings.
In both embodiments of the invention, the respective lining elements 10 and 11 are elongated lining elements adapted to completely cover the inner mantle surface of a drum 56 in a grinding mill (not shown) for grinding materials such as metal ore, by tiling the elements peripherally and lengthwise onto the mantle surface.
Each lining element is comprised of a bottom support member 26/27 made of polymeric material, such as rubber, and a top lifter member 12/13 made of a hard wear resistant metal alloy, such as hi-chrome white iron or steel, but ceramic materials, such as alumina oxide, are also possible. The support member 26 extends peripherally in a rearward direction as a wear plate having a flat top surface 34 into contact with a support member 26 of the subsequent lining element 10 in the drum mantle 56. In the forward direction, the flat surface 34 is continued in an upward sloping surface 36 adding the back-up volume of the support member. The sloping surface 36 is in turn continued by still another upward sloping curved surface 38 adjoining the lifter portion of the lining element. In the FIG. 1 embodiment, the lifter portion is exclusively comprised of the hard wear resistant member 12 having bottom, leading, top, and trailing faces 22, 14, 16, and 18, respectively. In this embodiment, the drum 56 can optionally also be rotated in the opposite rearward direction during operation, for example, in order to extend the service life of transmission components and the lining itself. In the FIG. 2 embodiment, the hard wear resistant member having respective bottom, leading, top, and rear faces 23, 15, 17, and 19, is rearwardly supported by a lifter back portion of the support member 27, which accordingly has a top face 41, as well as a lifter trailing face 39.
The lifter member 12/13 and support member 26/27 are integrally joined by molding and vulcanizing the polymer material to intimately adhere to the respective surfaces of the lifter member in a manner well-known in the rubber industry.
In addition to the vulcanized bond, the lifter member 12/13 is also secured for safety by a mechanical bond to the support member by securing elements embedded in the polymer material. In the embodiment of FIG. 1, the securing elements are a plurality (only one is visible) of arc-shaped protrusions 24 integral with the lifter member 12 and extending downwards into the polymer material from the concavely profiled bottom surface of the lifter member 12, to form closed loops in the elastomeric material molded thereon. In the embodiment of FIG. 2, the securing elements are a plurality (only one is visible) of brackets 21 likewise integral with the lifter member 15 and extending rearwardly into the polymer material from the flat rear surface 19 of the lifter member 13. To complete the mechanical bond in this embodiment, a metal pin 24' extending substantially over the full length of the lining element is inserted through corresponding holes 25 in the brackets 21 prior to forming the elastomeric material by molding the support member 27 onto the wear resistant lifter member 15.
As will be seen from the drawing, the wear resistant lifter member of each embodiment is effectively backed-up by the massive resilient support member against impact forces resulting from grinding media striking the lifter member from the various most likely directions as approximately indicated by the arrows in FIGS. 1 and 2 during operation of the mill when the drum mantle 56 rotates in a clock-wise direction. Compared to known mill linings where the lifter elements, although made of composite wear resistant and resilient materials, are each separately mounted between separate bottom lining elements in the form of wear plates, the integral mill lining elements according to the invention will better withstand the impact forces from the mill charge.
Each lining element is mounted to the drum mantle 56 by a plurality of bolt arrangements 50 located near the center between the sloping front and rear surfaces 30, 32 of the support member and distributed evenly along the length of the lining element.
The bolt arrangements 50 each include a threaded bolt 52 received in a through-bore 40 opening in the curved top surface 38 and in the bottom surface 28 of the support member. Adjacent and parallel to the bottom surface 28 of the support member, a plate 42 of rolled steel having elastic properties is embedded in the polymer material in order to distribute the clamping force from the bolt arrangements 50 evenly over the bottom portion of the support member when the lining element is mounted to the drum mantle 56 as shown in the FIG. 2 embodiment. The conical inner portion of each bolt 52 is engaged into a bolt head locking device 46 embedded in the polymer material around the through-bore 40 above the steel plate 42, and a U-shaped steel beam 44 located between steel plate 42 and locking device 46 distributes the clamping forces from the bolt arrangements 50 evenly along the length of the lifter element in the mounted state thereof. Each bolt arrangement 50 is completed at the outer surface of the drum mantle 56 by the engagement of the treaded radially outer portion of bolt 52 with a nut 54, sealer 58 and a washer 48.
As is apparent from FIG. 1, the steel plate 42 and the bottom surface 28 of the support member are planar in the unclamped state of the lining element. When the bolt arrangements 50 are tightened to a clamped mounted state as shown in FIG. 2, the steel plate 42 will be deflected and stressed to distribute the clamping force effectively also over the full peripheral width of the support member, thereby minimizing the likelihood of the peripheral end portions of the support member lifting from the surface of drum mantle 56. In the unbiased state prior to mounting, the steel plate may advantageously also have a curved cross section (not shown)-concave or convex and with varied curvature depending on desired clamping characteristics.
As during mill operation, the trailing end of an isolated support member may be less inclined to lift from drum mantle 56 than the leading end, the backward-upward sloping wedge interface (FIG. 3) between adjoining rear and front peripheral end surfaces 32, 30 is also effective to distribute the clamping force through interfaces to prevent the more inclined front end of each support member to lift from drum mantle due to impact forces from mill charge striking the leading face of lifter member by firmly wedging the front end onto the surface of the drum mantle 56.
In operation, the impact forces resulting from the mill charge striking the wear resistant lifter members of the lining elements inside the drum mantle 56 will be effectively endured by the backing support members 26, 27 which serve not only on efficiently resiliently dampen the shocks imposed to the lifter members and thereby protect them from breaking but also to lengthen the life of the lining elements by distributing the impact evenly over a large backing volume of rubber polymer material of unbroken integrity. Compared with known composite linings, full steel linings or full rubber linings, the single piece lifter-wear plate element according to the invention also has an improved lifespan and, resulting from fewer and larger components, drastically shortens the time and cost for the relining of a mill.
1. A single-piece lining element for mounting onto an inner surface of a drum mantle in a grinding mill, comprising an elongated lifter member of a wear resistant material adapted to be axially oriented with respect to the drum mantle and to project radially into the drum, and an elongated single-piece support member of an elastomeric material adapted to resiliently support the elongated lifter member over a full length thereof above the inner surface of the drum mantle, the lifter and support members being integrally bonded together to form said single-piece lining element, said support member being extended peripherally in a rearward direction with respect to an operational forward direction of rotation of the drum to contact a subsequent lining element to be mounted onto said inner surface, and to cover entirely therebetween the inner surface of the drum mantle, said wear resistant material being different from said elastomeric material.
2. A lining element as defined in claim 1, including clamping means comprising bolts arranged substantially centrally in a peripheral direction of the support member in the drum mantle and spaced over the length of the support member.
3. A lining element as defined in claim 2, wherein said clamping means comprises a steel plate in the elastomeric material of the support member, and wherein said plurality of bolts extend through the steel plate and the support member for clamping the steel plate and the support member to said inner surface.
4. A lining element as defined in claim 3, wherein said steel plate is adapted to be elastically deflected for distributing clamping force peripherally over said inner surface when being clamped together with the support member to said inner surface.
5. A lining element as defined in claim 3, further including a U-shaped beam member embedded in the elastomeric material of the support member above said steel plate and extending over a full length of the support member, and a plurality of bolt head locking devices located above and spaced along the U-shaped beam for engagement with a respective of said bolts for clamping the steel plate and the support member to said inner surface.
6. A lining element as defined in claim 1, wherein peripherally opposite ends of the support member are made sloping so as to wedge a front end of a subsequent support member onto said inner surface by engagement of the rear end of a preceding support member.
9. A single-piece lining element for mounting onto an inner surface of a drum mantle in a grinding mill, comprising an elongated lifter member of a wear resistant material adapted to be axially oriented with respect to the drum mantle and to project radially into the drum, and an elongated single-piece support member of an elastomeric material adapted to resiliently support the elongated lifter member over a full length thereof above the inner surface of the drum mantle, the lifter and support members being integrally bonded together to form said single-piece lining element, said support member being extended peripherally in a rearward direction with respect to an operational forward direction of rotation of the drum to contact a subsequent lining element to be mounted onto said inner surface, and to cover entirely therebetween the inner surface of the drum mantle and further including securing means mechanically securing the lifter member to the support member, said securing means comprising a plurality of arc-shaped brackets projecting from a bottom face of the lifter member, each bracket forming a closed loop in the elastomeric material of the support member.
10. A single-piece lining element for mounting onto an inner surface of a drum mantle in a grinding mill, comprising an elongated lifter member of a wear resistant material adapted to be axially oriented with respect to the drum mantle and to project radially into the drum, and an elongated single-piece support member of an elastomeric material adapted to resiliently support the elongated lifter member over a full length thereof above the inner surface of the drum mantle, the lifter and support members being integrally bonded together to form said single-piece lining element, said support member being extended peripherally in a rearward direction with respect to an operational forward direction of rotation of the drum to contact a subsequent lining element to be mounted onto said inner surface, and to cover entirely therebetween the inner surface of the drum mantle and further including securing means mechanically securing the lifter member to the support member, said securing means comprising a plurality of brackets projecting from a rear face of the lifter member, said brackets being joined by a pin forming closed loops between adjacent pairs of brackets in the elastomeric material of the support member.
11. A mill lining comprising a plurality of single-piece lining elements for mounting onto an inner surface of a drum mantle in a grinding mill to cover said inner surface, each lining element comprising an elongated lifter member of a wear resistant material adapted to be axially oriented with respect to the drum mantle and to project radially into the drum, and an elongated single-piece support member of an elastomeric material adapted to resiliently support the elongated lifter member over a full length thereof above the inner surface of the drum mantle, the lifter and support members being integrally bonded together to form said single-piece lining elements, said support member being extended peripherally to contact a subsequent of said lining elements in a rearward direction with regard to an operational direction of rotation of the drum mantle, and to cover entirely therebetween the inner surface of the drum mantle, said wear resistant material being different from said elastomeric material.
Ball Mill, Jaw Crusher, Mine Hoist manufacturer / supplier in China, offering Mining Parts Forging or Casting Transmission Shaft /Pinion Gear Shaft/Hoist Casting Shaft, Rotary Kiln Spare Parts Rotary Kiln Tyre/Ring, Factory Sell Vertical Shaft Impact Crusher for Sand Stone Making/Limestone Crusher and so on.
CITICTIC Luoyang Heavy Machinery Co., Ltd. The former was CITICHL Heavy Industries Co., Ltd. It was used be subsidiary of CITIC heavy machinery Co., Ltd. The company was founded in 1981 and finished joint stock reform in 2005, which is located in Luoyang city, capital city of nine dynasties in ancient times. With a garden-like industrial park and modern standard plant covering 80000 square meters, CITICTIC possesses advanced equipments, technologies and detecting methods. After more than 30 years ...