In all ore dressing and milling Operations, including flotation, cyanidation, gravity concentration, and amalgamation, the Working Principle is to crush and grind, often with rob mill & ball mills, the ore in order to liberate the minerals. In the chemical and process industries, grinding is an important step in preparing raw materials for subsequent treatment.In present day practice, ore is reduced to a size many times finer than can be obtained with crushers. Over a period of many years various fine grinding machines have been developed and used, but the ball mill has become standard due to its simplicity and low operating cost.
A ball millefficiently operated performs a wide variety of services. In small milling plants, where simplicity is most essential, it is not economical to use more than single stage crushing, because the Steel-Head Ball or Rod Mill will take up to 2 feed and grind it to the desired fineness. In larger plants where several stages of coarse and fine crushing are used, it is customary to crush from 1/2 to as fine as 8 mesh.
Many grinding circuits necessitate regrinding of concentrates or middling products to extremely fine sizes to liberate the closely associated minerals from each other. In these cases, the feed to the ball mill may be from 10 to 100 mesh or even finer.
Where the finished product does not have to be uniform, a ball mill may be operated in open circuit, but where the finished product must be uniform it is essential that the grinding mill be used in closed circuit with a screen, if a coarse product is desired, and with a classifier if a fine product is required. In most cases it is desirable to operate the grinding mill in closed circuit with a screen or classifier as higher efficiency and capacity are obtained. Often a mill using steel rods as the grinding medium is recommended, where the product must have the minimum amount of fines (rods give a more nearly uniform product).
Often a problem requires some study to determine the economic fineness to which a product can or should be ground. In this case the 911Equipment Company offers its complete testing service so that accurate grinding mill size may be determined.
Until recently many operators have believed that one particular type of grinding mill had greater efficiency and resulting capacity than some other type. However, it is now commonly agreed and accepted that the work done by any ballmill depends directly upon the power input; the maximum power input into any ball or rod mill depends upon weight of grinding charge, mill speed, and liner design.
The apparent difference in capacities between grinding mills (listed as being the same size) is due to the fact that there is no uniform method of designating the size of a mill, for example: a 5 x 5 Ball Mill has a working diameter of 5 inside the liners and has 20 per cent more capacity than all other ball mills designated as 5 x 5 where the shell is 5 inside diameter and the working diameter is only 48 with the liners in place.
Ball-Rod Mills, based on 4 liners and capacity varying as 2.6 power of mill diameter, on the 5 size give 20 per cent increased capacity; on the 4 size, 25 per cent; and on the 3 size, 28 per cent. This fact should be carefully kept in mind when determining the capacity of a Steel- Head Ball-Rod Mill, as this unit can carry a greater ball or rod charge and has potentially higher capacity in a given size when the full ball or rod charge is carried.
A mill shorter in length may be used if the grinding problem indicates a definite power input. This allows the alternative of greater capacity at a later date or a considerable saving in first cost with a shorter mill, if reserve capacity is not desired. The capacities of Ball-Rod Mills are considerably higher than many other types because the diameters are measured inside the liners.
The correct grinding mill depends so much upon the particular ore being treated and the product desired, that a mill must have maximum flexibility in length, type of grinding medium, type of discharge, and speed.With the Ball-Rod Mill it is possible to build this unit in exact accordance with your requirements, as illustrated.
To best serve your needs, the Trunnion can be furnished with small (standard), medium, or large diameter opening for each type of discharge. The sketch shows diagrammatic arrangements of the four different types of discharge for each size of trunnion opening, and peripheral discharge is described later.
Ball-Rod Mills of the grate discharge type are made by adding the improved type of grates to a standard Ball-Rod Mill. These grates are bolted to the discharge head in much the same manner as the standard headliners.
The grates are of alloy steel and are cast integral with the lifter bars which are essential to the efficient operation of this type of ball or rod mill. These lifter bars have a similar action to a pump:i. e., in lifting the product so as to discharge quickly through the mill trunnion.
These Discharge Grates also incorporate as an integral part, a liner between the lifters and steel head of the ball mill to prevent wear of the mill head. By combining these parts into a single casting, repairs and maintenance are greatly simplified. The center of the grate discharge end of this mill is open to permit adding of balls or for adding water to the mill through the discharge end.
Instead of being constructed of bars cast into a frame, Grates are cast entire and have cored holes which widen toward the outside of the mill similar to the taper in grizzly bars. The grate type discharge is illustrated.
The peripheral discharge type of Ball-Rod Mill is a modification of the grate type, and is recommended where a free gravity discharge is desired. It is particularly applicable when production of too many fine particles is detrimental and a quick pass through the mill is desired, and for dry grinding.
The drawings show the arrangement of the peripheral discharge. The discharge consists of openings in the shell into which bushings with holes of the desired size are inserted. On the outside of the mill, flanges are used to attach a stationary discharge hopper to prevent pulp splash or too much dust.
The mill may be operated either as a peripheral discharge or a combination or peripheral and trunnion discharge unit, depending on the desired operating conditions. If at any time the peripheral discharge is undesirable, plugs inserted into the bushings will convert the mill to a trunnion discharge type mill.
Unless otherwise specified, a hard iron liner is furnished. This liner is made of the best grade white iron and is most serviceable for the smaller size mills where large balls are not used. Hard iron liners have a much lower first cost.
Electric steel, although more expensive than hard iron, has advantage of minimum breakage and allows final wear to thinner section. Steel liners are recommended when the mills are for export or where the source of liner replacement is at a considerable distance.
Molychrome steel has longer wearing qualities and greater strength than hard iron. Breakage is not so apt to occur during shipment, and any size ball can be charged into a mill equipped with molychrome liners.
Manganese liners for Ball-Rod Mills are the world famous AMSCO Brand, and are the best obtainable. The first cost is the highest, but in most cases the cost per ton of ore ground is the lowest. These liners contain 12 to 14% manganese.
The feed and discharge trunnions are provided with cast iron or white iron throat liners. As these parts are not subjected to impact and must only withstand abrasion, alloys are not commonly used but can be supplied.
Gears for Ball-Rod Mills drives are furnished as standard on the discharge end of the mill where they are out of the way of the classifier return, scoop feeder, or original feed. Due to convertible type construction the mills can be furnished with gears on the feed end. Gear drives are available in two alternative combinations, which are:
All pinions are properly bored, key-seated, and pressed onto the steel countershaft, which is oversize and properly keyseated for the pinion and drive pulleys or sheaves. The countershaft operates on high grade, heavy duty, nickel babbitt bearings.
Any type of drive can be furnished for Ball-Rod Mills in accordance with your requirements. Belt drives are available with pulleys either plain or equipped with friction clutch. Various V- Rope combinations can also be supplied.
The most economical drive to use up to 50 H. P., is a high starting torque motor connected to the pinion shaft by means of a flat or V-Rope drive. For larger size motors the wound rotor (slip ring) is recommended due to its low current requirement in starting up the ball mill.
Should you be operating your own power plant or have D. C. current, please specify so that there will be no confusion as to motor characteristics. If switches are to be supplied, exact voltage to be used should be given.
Even though many ores require fine grinding for maximum recovery, most ores liberate a large percentage of the minerals during the first pass through the grinding unit. Thus, if the free minerals can be immediately removed from the ball mill classifier circuit, there is little chance for overgrinding.
This is actually what has happened wherever Mineral Jigs or Unit Flotation Cells have been installed in the ball mill classifier circuit. With the installation of one or both of these machines between the ball mill and classifier, as high as 70 per cent of the free gold and sulphide minerals can be immediately removed, thus reducing grinding costs and improving over-all recovery. The advantage of this method lies in the fact that heavy and usually valuable minerals, which otherwise would be ground finer because of their faster settling in the classifier and consequent return to the grinding mill, are removed from the circuit as soon as freed. This applies particularly to gold and lead ores.
Ball-Rod Mills have heavy rolled steel plate shells which are arc welded inside and outside to the steel heads or to rolled steel flanges, depending upon the type of mill. The double welding not only gives increased structural strength, but eliminates any possibility of leakage.
Where a single or double flanged shell is used, the faces are accurately machined and drilled to template to insure perfect fit and alignment with the holes in the head. These flanges are machined with male and female joints which take the shearing stresses off the bolts.
The Ball-Rod Mill Heads are oversize in section, heavily ribbed and are cast from electric furnace steel which has a strength of approximately four times that of cast iron. The head and trunnion bearings are designed to support a mill with length double its diameter. This extra strength, besides eliminating the possibility of head breakage or other structural failure (either while in transit or while in service), imparts to Ball-Rod Mills a flexibility heretofore lacking in grinding mills. Also, for instance, if you have a 5 x 5 mill, you can add another 5 shell length and thus get double the original capacity; or any length required up to a maximum of 12 total length.
On Type A mills the steel heads are double welded to the rolled steel shell. On type B and other flanged type mills the heads are machined with male and female joints to match the shell flanges, thus taking the shearing stresses from the heavy machine bolts which connect the shell flanges to the heads.
The manhole cover is protected from wear by heavy liners. An extended lip is provided for loosening the door with a crow-bar, and lifting handles are also provided. The manhole door is furnished with suitable gaskets to prevent leakage.
The mill trunnions are carried on heavy babbitt bearings which provide ample surface to insure low bearing pressure. If at any time the normal length is doubled to obtain increased capacity, these large trunnion bearings will easily support the additional load. Trunnion bearings are of the rigid type, as the perfect alignment of the trunnion surface on Ball-Rod Mills eliminates any need for the more expensive self-aligning type of bearing.
The cap on the upper half of the trunnion bearing is provided with a shroud which extends over the drip flange of the trunnion and effectively prevents the entrance of dirt or grit. The bearing has a large space for wool waste and lubricant and this is easily accessible through a large opening which is covered to prevent dirt from getting into the bearing.Ball and socket bearings can be furnished.
Scoop Feeders for Ball-Rod Mills are made in various radius sizes. Standard scoops are made of cast iron and for the 3 size a 13 or 19 feeder is supplied, for the 4 size a 30 or 36, for the 5 a 36 or 42, and for the 6 a 42 or 48 feeder. Welded steel scoop feeders can, however, be supplied in any radius.
The correct size of feeder depends upon the size of the classifier, and the smallest feeder should be used which will permit gravity flow for closed circuit grinding between classifier and the ball or rod mill. All feeders are built with a removable wearing lip which can be easily replaced and are designed to give minimum scoop wear.
A combination drum and scoop feeder can be supplied if necessary. This feeder is made of heavy steel plate and strongly welded. These drum-scoop feeders are available in the same sizes as the cast iron feeders but can be built in any radius. Scoop liners can be furnished.
The trunnions on Ball-Rod Mills are flanged and carefully machined so that scoops are held in place by large machine bolts and not cap screws or stud bolts. The feed trunnion flange is machined with a shoulder for insuring a proper fit for the feed scoop, and the weight of the scoop is carried on this shoulder so that all strain is removed from the bolts which hold the scoop.
High carbon steel rods are recommended, hot rolled, hot sawed or sheared, to a length of 2 less than actual length of mill taken inside the liners. The initial rod charge is generally a mixture ranging from 1.5 to 3 in diameter. During operation, rod make-up is generally the maximum size. The weights per lineal foot of rods of various diameters are approximately: 1.5 to 6 lbs.; 2-10.7 lbs.; 2.5-16.7 lbs.; and 3-24 lbs.
Forged from the best high carbon manganese steel, they are of the finest quality which can be produced and give long, satisfactory service. Data on ball charges for Ball-Rod Mills are listed in Table 5. Further information regarding grinding balls is included in Table 6.
Rod Mills has a very define and narrow discharge product size range. Feeding a Rod Mill finer rocks will greatly impact its tonnage while not significantly affect its discharge product sizes. The 3.5 diameter rod of a mill, can only grind so fine.
Crushers are well understood by most. Rod and Ball Mills not so much however as their size reduction actions are hidden in the tube (mill). As for Rod Mills, the image above best expresses what is going on inside. As rocks is feed into the mill, they are crushed (pinched) by the weight of its 3.5 x 16 rods at one end while the smaller particles migrate towards the discharge end and get slightly abraded (as in a Ball Mill) on the way there.
We haveSmall Ball Mills for sale coming in at very good prices. These ball mills are relatively small, bearing mounted on a steel frame. All ball mills are sold with motor, gears, steel liners and optional grinding media charge/load.
Ball Mills or Rod Mills in a complete range of sizes up to 10 diameter x20 long, offer features of operation and convertibility to meet your exactneeds. They may be used for pulverizing and either wet or dry grindingsystems. Mills are available in both light-duty and heavy-duty constructionto meet your specific requirements.
All Mills feature electric cast steel heads and heavy rolled steelplate shells. Self-aligning main trunnion bearings on large mills are sealedand internally flood-lubricated. Replaceable mill trunnions. Pinion shaftbearings are self-aligning, roller bearing type, enclosed in dust-tightcarrier. Adjustable, single-unit soleplate under trunnion and drive pinionsfor perfect, permanent gear alignment.
Ball Mills can be supplied with either ceramic or rubber linings for wet or dry grinding, for continuous or batch type operation, in sizes from 15 x 21 to 8 x 12. High density ceramic linings of uniform hardness male possible thinner linings and greater and more effective grinding volume. Mills are shipped with liners installed.
Complete laboratory testing service, mill and air classifier engineering and proven equipment make possible a single source for your complete dry-grinding mill installation. Units available with air swept design and centrifugal classifiers or with elevators and mechanical type air classifiers. All sizes and capacities of units. Laboratory-size air classifier also available.
A special purpose batch mill designed especially for grinding and mixing involving acids and corrosive materials. No corners mean easy cleaning and choice of rubber or ceramic linings make it corrosion resistant. Shape of mill and ball segregation gives preferential grinding action for grinding and mixing of pigments and catalysts. Made in 2, 3 and 4 diameter grinding drums.
Nowadays grinding mills are almost extensively used for comminution of materials ranging from 5 mm to 40 mm (3/161 5/8) down to varying product sizes. They have vast applications within different branches of industry such as for example the ore dressing, cement, lime, porcelain and chemical industries and can be designed for continuous as well as batch grinding.
Ball mills can be used for coarse grinding as described for the rod mill. They will, however, in that application produce more fines and tramp oversize and will in any case necessitate installation of effective classification.If finer grinding is wanted two or three stage grinding is advisable as for instant primary rod mill with 75100 mm (34) rods, secondary ball mill with 2540 mm(11) balls and possibly tertiary ball mill with 20 mm () balls or cylpebs.To obtain a close size distribution in the fine range the specific surface of the grinding media should be as high as possible. Thus as small balls as possible should be used in each stage.
The principal field of rod mill usage is the preparation of products in the 5 mm0.4 mm (4 mesh to 35 mesh) range. It may sometimes be recommended also for finer grinding. Within these limits a rod mill is usually superior to and more efficient than a ball mill. The basic principle for rod grinding is reduction by line contact between rods extending the full length of the mill, resulting in selective grinding carried out on the largest particle sizes. This results in a minimum production of extreme fines or slimes and more effective grinding work as compared with a ball mill. One stage rod mill grinding is therefore suitable for preparation of feed to gravimetric ore dressing methods, certain flotation processes with slime problems and magnetic cobbing. Rod mills are frequently used as primary mills to produce suitable feed to the second grinding stage. Rod mills have usually a length/diameter ratio of at least 1.4.
Tube mills are in principle to be considered as ball mills, the basic difference being that the length/diameter ratio is greater (35). They are commonly used for surface cleaning or scrubbing action and fine grinding in open circuit.
In some cases it is suitable to use screened fractions of the material as grinding media. Such mills are usually called pebble mills, but the working principle is the same as for ball mills. As the power input is approximately directly proportional to the volume weight of the grinding media, the power input for pebble mills is correspondingly smaller than for a ball mill.
A dry process requires usually dry grinding. If the feed is wet and sticky, it is often necessary to lower the moisture content below 1 %. Grinding in front of wet processes can be done wet or dry. In dry grinding the energy consumption is higher, but the wear of linings and charge is less than for wet grinding, especially when treating highly abrasive and corrosive material. When comparing the economy of wet and dry grinding, the different costs for the entire process must be considered.
An increase in the mill speed will give a directly proportional increase in mill power but there seems to be a square proportional increase in the wear. Rod mills generally operate within the range of 6075 % of critical speed in order to avoid excessive wear and tangled rods. Ball and pebble mills are usually operated at 7085 % of critical speed. For dry grinding the speed is usually somewhat lower.
The mill lining can be made of rubber or different types of steel (manganese or Ni-hard) with liner types according to the customers requirements. For special applications we can also supply porcelain, basalt and other linings.
The mill power is approximately directly proportional to the charge volume within the normal range. When calculating a mill 40 % charge volume is generally used. In pebble and ball mills quite often charge volumes close to 50 % are used. In a pebble mill the pebble consumption ranges from 315 % and the charge has to be controlled automatically to maintain uniform power consumption.
In all cases the net energy consumption per ton (kWh/ton) must be known either from previous experience or laboratory tests before mill size can be determined. The required mill net power P kW ( = ton/hX kWh/ton) is obtained from
Trunnions of S.G. iron or steel castings with machined flange and bearing seat incl. device for dismantling the bearings. For smaller mills the heads and trunnions are sometimes made in grey cast iron.
The mills can be used either for dry or wet, rod or ball grinding. By using a separate attachment the discharge end can be changed so that the mills can be used for peripheral instead of overflow discharge.
Ball mills are among the most variable and effective tools when it comes to size reduction of hard, brittle or fibrous materials. The variety of grinding modes, usable volumes and available grinding tool materials make ball mills the perfect match for a vast range of applications.
RETSCH is the world leading manufacturer of laboratory ball mills and offers the perfect product for each application. The High Energy Ball Mill Emax and MM 500 were developed for grinding with the highest energy input. The innovative design of both, the mills and the grinding jars, allows for continuous grinding down to the nano range in the shortest amount of time - with only minor warming effects. These ball mills are also suitable for mechano chemistry. Mixer Mills grind and homogenize small sample volumes quickly and efficiently by impact and friction. These ball mills are suitable for dry, wet and cryogenic grinding as well as for cell disruption for DNA/RNA recovery. Planetary Ball Mills meet and exceed all requirements for fast and reproducible grinding to analytical fineness. They are used for the most demanding tasks in the laboratory, from routine sample processing to colloidal grinding and advanced materials development. The drum mill is a type of ball mill suitable for the fine grinding of large feed sizes and large sample volumes.
A ball mill is a type of grinder used to grind and blend bulk material into QDs/nanosize using different sized balls. The working principle is simple; impact and attrition size reduction take place as the ball drops from near the top of a rotating hollow cylindrical shell. The nanostructure size can be varied by varying the number and size of balls, the material used for the balls, the material used for the surface of the cylinder, the rotation speed, and the choice of material to be milled. Ball mills are commonly used for crushing and grinding the materials into an extremely fine form. The ball mill contains a hollow cylindrical shell that rotates about its axis. This cylinder is filled with balls that are made of stainless steel or rubber to the material contained in it. Ball mills are classified as attritor, horizontal, planetary, high energy, or shaker.
Grinding elements in ball mills travel at different velocities. Therefore, collision force, direction and kinetic energy between two or more elements vary greatly within the ball charge. Frictional wear or rubbing forces act on the particles, as well as collision energy. These forces are derived from the rotational motion of the balls and movement of particles within the mill and contact zones of colliding balls.
By rotation of the mill body, due to friction between mill wall and balls, the latter rise in the direction of rotation till a helix angle does not exceed the angle of repose, whereupon, the balls roll down. Increasing of rotation rate leads to growth of the centrifugal force and the helix angle increases, correspondingly, till the component of weight strength of balls become larger than the centrifugal force. From this moment the balls are beginning to fall down, describing during falling certain parabolic curves (Figure 2.7). With the further increase of rotation rate, the centrifugal force may become so large that balls will turn together with the mill body without falling down. The critical speed n (rpm) when the balls are attached to the wall due to centrifugation:
where Dm is the mill diameter in meters. The optimum rotational speed is usually set at 6580% of the critical speed. These data are approximate and may not be valid for metal particles that tend to agglomerate by welding.
The degree of filling the mill with balls also influences productivity of the mill and milling efficiency. With excessive filling, the rising balls collide with falling ones. Generally, filling the mill by balls must not exceed 3035% of its volume.
The mill productivity also depends on many other factors: physical-chemical properties of feed material, filling of the mill by balls and their sizes, armor surface shape, speed of rotation, milling fineness and timely moving off of ground product.
where b.ap is the apparent density of the balls; l is the degree of filling of the mill by balls; n is revolutions per minute; 1, and 2 are coefficients of efficiency of electric engine and drive, respectively.
A feature of ball mills is their high specific energy consumption; a mill filled with balls, working idle, consumes approximately as much energy as at full-scale capacity, i.e. during grinding of material. Therefore, it is most disadvantageous to use a ball mill at less than full capacity.
Grinding elements in ball mills travel at different velocities. Therefore, collision force, direction, and kinetic energy between two or more elements vary greatly within the ball charge. Frictional wear or rubbing forces act on the particles as well as collision energy. These forces are derived from the rotational motion of the balls and the movement of particles within the mill and contact zones of colliding balls.
By the rotation of the mill body, due to friction between the mill wall and balls, the latter rise in the direction of rotation until a helix angle does not exceed the angle of repose, whereupon the balls roll down. Increasing the rotation rate leads to the growth of the centrifugal force and the helix angle increases, correspondingly, until the component of the weight strength of balls becomes larger than the centrifugal force. From this moment, the balls are beginning to fall down, describing certain parabolic curves during the fall (Fig. 2.10).
With the further increase of rotation rate, the centrifugal force may become so large that balls will turn together with the mill body without falling down. The critical speed n (rpm) when the balls remain attached to the wall with the aid of centrifugal force is:
where Dm is the mill diameter in meters. The optimum rotational speed is usually set at 65%80% of the critical speed. These data are approximate and may not be valid for metal particles that tend to agglomerate by welding.
where db.max is the maximum size of the feed (mm), is the compression strength (MPa), E is the modulus of elasticity (MPa), b is the density of material of balls (kg/m3), and D is the inner diameter of the mill body (m).
The degree of filling the mill with balls also influences the productivity of the mill and milling efficiency. With excessive filling, the rising balls collide with falling ones. Generally, filling the mill by balls must not exceed 30%35% of its volume.
The productivity of ball mills depends on the drum diameter and the relation of drum diameter and length. The optimum ratio between length L and diameter D, L:D, is usually accepted in the range 1.561.64. The mill productivity also depends on many other factors, including the physical-chemical properties of the feed material, the filling of the mill by balls and their sizes, the armor surface shape, the speed of rotation, the milling fineness, and the timely moving off of the ground product.
where D is the drum diameter, L is the drum length, b.ap is the apparent density of the balls, is the degree of filling of the mill by balls, n is the revolutions per minute, and 1, and 2 are coefficients of efficiency of electric engine and drive, respectively.
A feature of ball mills is their high specific energy consumption. A mill filled with balls, working idle, consumes approximately as much energy as at full-scale capacity, that is, during the grinding of material. Therefore, it is most disadvantageous to use a ball mill at less than full capacity.
Milling time in tumbler mills is longer to accomplish the same level of blending achieved in the attrition or vibratory mill, but the overall productivity is substantially greater. Tumbler mills usually are used to pulverize or flake metals, using a grinding aid or lubricant to prevent cold welding agglomeration and to minimize oxidation .
Cylindrical Ball Mills differ usually in steel drum design (Fig. 2.11), which is lined inside by armor slabs that have dissimilar sizes and form a rough inside surface. Due to such juts, the impact force of falling balls is strengthened. The initial material is fed into the mill by a screw feeder located in a hollow trunnion; the ground product is discharged through the opposite hollow trunnion.
Cylindrical screen ball mills have a drum with spiral curved plates with longitudinal slits between them. The ground product passes into these slits and then through a cylindrical sieve and is discharged via the unloading funnel of the mill body.
Conical Ball Mills differ in mill body construction, which is composed of two cones and a short cylindrical part located between them (Fig. 2.12). Such a ball mill body is expedient because efficiency is appreciably increased. Peripheral velocity along the conical drum scales down in the direction from the cylindrical part to the discharge outlet; the helix angle of balls is decreased and, consequently, so is their kinetic energy. The size of the disintegrated particles also decreases as the discharge outlet is approached and the energy used decreases. In a conical mill, most big balls take up a position in the deeper, cylindrical part of the body; thus, the size of the balls scales down in the direction of the discharge outlet.
For emptying, the conical mill is installed with a slope from bearing to one. In wet grinding, emptying is realized by the decantation principle, that is, by means of unloading through one of two trunnions.
With dry grinding, these mills often work in a closed cycle. A scheme of the conical ball mill supplied with an air separator is shown in Fig. 2.13. Air is fed to the mill by means of a fan. Carried off by air currents, the product arrives at the air separator, from which the coarse particles are returned by gravity via a tube into the mill. The finished product is trapped in a cyclone while the air is returned in the fan.
The ball mill is a tumbling mill that uses steel balls as the grinding media. The length of the cylindrical shell is usually 11.5 times the shell diameter (Figure 8.11). The feed can be dry, with less than 3% moisture to minimize ball coating, or slurry containing 2040% water by weight. Ball mills are employed in either primary or secondary grinding applications. In primary applications, they receive their feed from crushers, and in secondary applications, they receive their feed from rod mills, AG mills, or SAG mills.
Ball mills are filled up to 40% with steel balls (with 3080mm diameter), which effectively grind the ore. The material that is to be ground fills the voids between the balls. The tumbling balls capture the particles in ball/ball or ball/liner events and load them to the point of fracture.
When hard pebbles rather than steel balls are used for the grinding media, the mills are known as pebble mills. As mentioned earlier, pebble mills are widely used in the North American taconite iron ore operations. Since the weight of pebbles per unit volume is 3555% of that of steel balls, and as the power input is directly proportional to the volume weight of the grinding medium, the power input and capacity of pebble mills are correspondingly lower. Thus, in a given grinding circuit, for a certain feed rate, a pebble mill would be much larger than a ball mill, with correspondingly a higher capital cost. However, the increase in capital cost is justified economically by a reduction in operating cost attributed to the elimination of steel grinding media.
In general, ball mills can be operated either wet or dry and are capable of producing products in the order of 100m. This represents reduction ratios of as great as 100. Very large tonnages can be ground with these ball mills because they are very effective material handling devices. Ball mills are rated by power rather than capacity. Today, the largest ball mill in operation is 8.53m diameter and 13.41m long with a corresponding motor power of 22MW (Toromocho, private communications).
Modern ball mills consist of two chambers separated by a diaphragm. In the first chamber the steel-alloy balls (also described as charge balls or media) are about 90mm diameter. The mill liners are designed to lift the media as the mill rotates, so the comminution process in the first chamber is dominated by crushing. In the second chamber the ball diameters are of smaller diameter, between 60 and 15mm. In this chamber the lining is typically a classifying lining which sorts the media so that ball size reduces towards the discharge end of the mill. Here, comminution takes place in the rolling point-contact zone between each charge ball. An example of a two chamber ball mill is illustrated in Fig. 2.22.15
Much of the energy consumed by a ball mill generates heat. Water is injected into the second chamber of the mill to provide evaporative cooling. Air flow through the mill is one medium for cement transport but also removes water vapour and makes some contribution to cooling.
Grinding is an energy intensive process and grinding more finely than necessary wastes energy. Cement consists of clinker, gypsum and other components mostly more easily ground than clinker. To minimise over-grinding modern ball mills are fitted with dynamic separators (otherwise described as classifiers or more simply as separators). The working principle is that cement is removed from the mill before over-grinding has taken place. The cement is then separated into a fine fraction, which meets finished product requirements, and a coarse fraction which is returned to mill inlet. Recirculation factor, that is, the ratio of mill throughput to fresh feed is up to three. Beyond this, efficiency gains are minimal.
For more than 50years vertical mills have been the mill of choice for grinding raw materials into raw meal. More recently they have become widely used for cement production. They have lower specific energy consumption than ball mills and the separator, as in raw mills, is integral with the mill body.
In the Loesche mill, Fig. 2.23,16 two pairs of rollers are used. In each pair the first, smaller diameter, roller stabilises the bed prior to grinding which takes place under the larger roller. Manufacturers use different technologies for bed stabilisation.
Comminution in ball mills and vertical mills differs fundamentally. In a ball mill, size reduction takes place by impact and attrition. In a vertical mill the bed of material is subject to such a high pressure that individual particles within the bed are fractured, even though the particles are very much smaller than the bed thickness.
Early issues with vertical mills, such as narrower PSD and modified cement hydration characteristics compared with ball mills, have been resolved. One modification has been to install a hot gas generator so the gas temperature is high enough to partially dehydrate the gypsum.
For many decades the two-compartment ball mill in closed circuit with a high-efficiency separator has been the mill of choice. In the last decade vertical mills have taken an increasing share of the cement milling market, not least because the specific power consumption of vertical mills is about 30% less than that of ball mills and for finely ground cement less still. The vertical mill has a proven track record in grinding blastfurnace slag, where it has the additional advantage of being a much more effective drier of wet feedstock than a ball mill.
The vertical mill is more complex but its installation is more compact. The relative installed capital costs tend to be site specific. Historically the installed cost has tended to be slightly higher for the vertical mill.
Special graph paper is used with lglg(1/R(x)) on the abscissa and lg(x) on the ordinate axes. The higher the value of n, the narrower the particle size distribution. The position parameter is the particle size with the highest mass density distribution, the peak of the mass density distribution curve.
Vertical mills tend to produce cement with a higher value of n. Values of n normally lie between 0.8 and 1.2, dependent particularly on cement fineness. The position parameter is, of course, lower for more finely ground cements.
Separator efficiency is defined as specific power consumption reduction of the mill open-to-closed-circuit with the actual separator, compared with specific power consumption reduction of the mill open-to-closed-circuit with an ideal separator.
As shown in Fig. 2.24, circulating factor is defined as mill mass flow, that is, fresh feed plus separator returns. The maximum power reduction arising from use of an ideal separator increases non-linearly with circulation factor and is dependent on Rf, normally based on residues in the interval 3245m. The value of the comminution index, W, is also a function of Rf. The finer the cement, the lower Rf and the greater the maximum power reduction. At C = 2 most of maximum power reduction is achieved, but beyond C = 3 there is very little further reduction.
Separator particle separation performance is assessed using the Tromp curve, a graph of percentage separator feed to rejects against particle size range. An example is shown in Fig. 2.25. Data required is the PSD of separator feed material and of rejects and finished product streams. The bypass and slope provide a measure of separator performance.
The particle size is plotted on a logarithmic scale on the ordinate axis. The percentage is plotted on the abscissa either on a linear (as shown here) or on a Gaussian scale. The advantage of using the Gaussian scale is that the two parts of the graph can be approximated by two straight lines.
The measurement of PSD of a sample of cement is carried out using laser-based methodologies. It requires a skilled operator to achieve consistent results. Agglomeration will vary dependent on whether grinding aid is used. Different laser analysis methods may not give the same results, so for comparative purposes the same method must be used.
The ball mill is a cylindrical drum (or cylindrical conical) turning around its horizontal axis. It is partially filled with grinding bodies: cast iron or steel balls, or even flint (silica) or porcelain bearings. Spaces between balls or bearings are occupied by the load to be milled.
Following drum rotation, balls or bearings rise by rolling along the cylindrical wall and descending again in a cascade or cataract from a certain height. The output is then milled between two grinding bodies.
Ball mills could operate dry or even process a water suspension (almost always for ores). Dry, it is fed through a chute or a screw through the units opening. In a wet path, a system of scoops that turn with the mill is used and it plunges into a stationary tank.
Mechanochemical synthesis involves high-energy milling techniques and is generally carried out under controlled atmospheres. Nanocomposite powders of oxide, nonoxide, and mixed oxide/nonoxide materials can be prepared using this method. The major drawbacks of this synthesis method are: (1) discrete nanoparticles in the finest size range cannot be prepared; and (2) contamination of the product by the milling media.
More or less any ceramic composite powder can be synthesized by mechanical mixing of the constituent phases. The main factors that determine the properties of the resultant nanocomposite products are the type of raw materials, purity, the particle size, size distribution, and degree of agglomeration. Maintaining purity of the powders is essential for avoiding the formation of a secondary phase during sintering. Wet ball or attrition milling techniques can be used for the synthesis of homogeneous powder mixture. Al2O3/SiC composites are widely prepared by this conventional powder mixing route by using ball milling . However, the disadvantage in the milling step is that it may induce certain pollution derived from the milling media.
In this mechanical method of production of nanomaterials, which works on the principle of impact, the size reduction is achieved through the impact caused when the balls drop from the top of the chamber containing the source material.
A ball mill consists of a hollow cylindrical chamber (Fig. 6.2) which rotates about a horizontal axis, and the chamber is partially filled with small balls made of steel, tungsten carbide, zirconia, agate, alumina, or silicon nitride having diameter generally 10mm. The inner surface area of the chamber is lined with an abrasion-resistant material like manganese, steel, or rubber. The magnet, placed outside the chamber, provides the pulling force to the grinding material, and by changing the magnetic force, the milling energy can be varied as desired. The ball milling process is carried out for approximately 100150h to obtain uniform-sized fine powder. In high-energy ball milling, vacuum or a specific gaseous atmosphere is maintained inside the chamber. High-energy mills are classified into attrition ball mills, planetary ball mills, vibrating ball mills, and low-energy tumbling mills. In high-energy ball milling, formation of ceramic nano-reinforcement by in situ reaction is possible.
It is an inexpensive and easy process which enables industrial scale productivity. As grinding is done in a closed chamber, dust, or contamination from the surroundings is avoided. This technique can be used to prepare dry as well as wet nanopowders. Composition of the grinding material can be varied as desired. Even though this method has several advantages, there are some disadvantages. The major disadvantage is that the shape of the produced nanoparticles is not regular. Moreover, energy consumption is relatively high, which reduces the production efficiency. This technique is suitable for the fabrication of several nanocomposites, which include Co- and Cu-based nanomaterials, Ni-NiO nanocomposites, and nanocomposites of Ti,C .
Planetary ball mill was used to synthesize iron nanoparticles. The synthesized nanoparticles were subjected to the characterization studies by X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques using a SIEMENS-D5000 diffractometer and Hitachi S-4800. For the synthesis of iron nanoparticles, commercial iron powder having particles size of 10m was used. The iron powder was subjected to planetary ball milling for various period of time. The optimum time period for the synthesis of nanoparticles was observed to be 10h because after that time period, chances of contamination inclined and the particles size became almost constant so the powder was ball milled for 10h to synthesize nanoparticles . Fig. 12 shows the SEM image of the iron nanoparticles.
The vibratory ball mill is another kind of high-energy ball mill that is used mainly for preparing amorphous alloys. The vials capacities in the vibratory mills are smaller (about 10 ml in volume) compared to the previous types of mills. In this mill, the charge of the powder and milling tools are agitated in three perpendicular directions (Fig. 1.6) at very high speed, as high as 1200 rpm.
Another type of the vibratory ball mill, which is used at the van der Waals-Zeeman Laboratory, consists of a stainless steel vial with a hardened steel bottom, and a single hardened steel ball of 6 cm in diameter (Fig. 1.7).
The mill is evacuated during milling to a pressure of 106 Torr, in order to avoid reactions with a gas atmosphere. Subsequently, this mill is suitable for mechanical alloying of some special systems that are highly reactive with the surrounding atmosphere, such as rare earth elements.
In spite of the traditional approaches used for gas-solid reaction at relatively high temperature, Calka etal. and El-Eskandarany etal. proposed a solid-state approach, the so-called reactive ball milling (RBM), used for preparations different families of meal nitrides and hydrides at ambient temperature. This mechanically induced gas-solid reaction can be successfully achieved, using either high- or low-energy ball-milling methods, as shown in Fig.9.5. However, high-energy ball mill is an efficient process for synthesizing nanocrystalline MgH2 powders using RBM technique, it may be difficult to scale up for matching the mass production required by industrial sector. Therefore, from a practical point of view, high-capacity low-energy milling, which can be easily scaled-up to produce large amount of MgH2 fine powders, may be more suitable for industrial mass production.
In both approaches but with different scale of time and milling efficiency, the starting Mg metal powders milled under hydrogen gas atmosphere are practicing to dramatic lattice imperfections such as twinning and dislocations. These defects are caused by plastics deformation coupled with shear and impact forces generated by the ball-milling media. The powders are, therefore, disintegrated into smaller particles with large surface area, where very clean or fresh oxygen-free active surfaces of the powders are created. Moreover, these defects, which are intensively located at the grain boundaries, lead to separate micro-scaled Mg grains into finer grains capable to getter hydrogen by the first atomically clean surfaces to form MgH2 nanopowders.
Fig.9.5 illustrates common lab scale procedure for preparing MgH2 powders, starting from pure Mg powders, using RBM via (1) high-energy and (2) low-energy ball milling. The starting material can be Mg-rods, in which they are processed via sever plastic deformation, using for example cold-rolling approach, as illustrated in Fig.9.5. The heavily deformed Mg-rods obtained after certain cold rolling passes can be snipped into small chips and then ball-milled under hydrogen gas to produce MgH2 powders.
Planetary ball mills are the most popular mills used in scientific research for synthesizing MgH2 nanopowders. In this type of mill, the ball-milling media have considerably high energy, because milling stock and balls come off the inner wall of the vial and the effective centrifugal force reaches up to 20 times gravitational acceleration. The centrifugal forces caused by the rotation of the supporting disc and autonomous turning of the vial act on the milling charge (balls and powders). Since the turning directions of the supporting disc and the vial are opposite, the centrifugal forces alternately are synchronized and opposite. Therefore, the milling media and the charged powders alternatively roll on the inner wall of the vial, and are lifted and thrown off across the bowl at high speed.
In the typical experimental procedure, a certain amount of the Mg (usually in the range between 3 and 10g based on the vials volume) is balanced inside an inert gas atmosphere (argon or helium) in a glove box and sealed together with certain number of balls (e.g., 2050 hardened steel balls) into a hardened steel vial (Fig.9.5A and B), using, for example, a gas-temperature-monitoring system (GST). With the GST system, it becomes possible to monitor the progress of the gas-solid reaction taking place during the RBM process, as shown in Fig.9.5C and D. The temperature and pressure changes in the system during milling can be also used to realize the completion of the reaction and the expected end product during the different stages of milling (Fig.9.5D). The ball-to-powder weight ratio is usually selected to be in the range between 10:1 and 50:1. The vial is then evacuated to the level of 103bar before introducing H2 gas to fill the vial with a pressure of 550bar (Fig.9.5B). The milling process is started by mounting the vial on a high-energy ball mill operated at ambient temperature (Fig.9.5C).
Tumbling mill is cylindrical shell (Fig.9.6AC) that rotates about a horizontal axis (Fig.9.6D). Hydrogen gas is pressurized into the vial (Fig.9.6C) together with Mg powders and ball-milling media, using ball-to-powder weight ratio in the range between 30:1 and 100:1. Mg powder particles meet the abrasive and impacting force (Fig.9.6E), which reduce the particle size and create fresh-powder surfaces (Fig.9.6F) ready to react with hydrogen milling atmosphere.
Figure 9.6. Photographs taken from KISR-EBRC/NAM Lab, Kuwait, show (A) the vial and milling media (balls) and (B) the setup performed to charge the vial with 50bar of hydrogen gas. The photograph in (C) presents the complete setup of GST (supplied by Evico-magnetic, Germany) system prior to start the RBM experiment for preparing of MgH2 powders, using Planetary Ball Mill P400 (provided by Retsch, Germany). GST system allows us to monitor the progress of RBM process, as indexed by temperature and pressure versus milling time (D).
The useful kinetic energy in tumbling mill can be applied to the Mg powder particles (Fig.9.7E) by the following means: (1) collision between the balls and the powders; (2) pressure loading of powders pinned between milling media or between the milling media and the liner; (3) impact of the falling milling media; (4) shear and abrasion caused by dragging of particles between moving milling media; and (5) shock-wave transmitted through crop load by falling milling media. One advantage of this type of mill is that large amount of the powders (100500g or more based on the mill capacity) can be fabricated for each milling run. Thus, it is suitable for pilot and/or industrial scale of MgH2 production. In addition, low-energy ball mill produces homogeneous and uniform powders when compared with the high-energy ball mill. Furthermore, such tumbling mills are cheaper than high-energy mills and operated simply with low-maintenance requirements. However, this kind of low-energy mill requires long-term milling time (more than 300h) to complete the gas-solid reaction and to obtain nanocrystalline MgH2 powders.
Figure 9.7. Photos taken from KISR-EBRC/NAM Lab, Kuwait, display setup of a lab-scale roller mill (1000m in volume) showing (A) the milling tools including the balls (milling media and vial), (B) charging Mg powders in the vial inside inert gas atmosphere glove box, (C) evacuation setup and pressurizing hydrogen gas in the vial, and (D) ball milling processed, using a roller mill. Schematic presentations show the ball positions and movement inside the vial of a tumbler mall mill at a dynamic mode is shown in (E), where a typical ball-powder-ball collusion for a low energy tumbling ball mill is presented in (F).
Our small-scale miners Ball Mills use horizontal rotating cylinders that contain the grinding media and the particles to be broken. The mass moves up the wall of the cylinder as it rotates and falls back into the toe of the mill when the force of gravity exceeds friction and centrifugal forces. Particles are broken in the toe of the mill when caught in the collisions between the grinding media themselves and the grinding media and the mill wall. In ball mills, the grinding media and particles acquire potential energy that becomes kinetic energy as the mass falls from the rotating shell. Ball mills are customarily divided into categories that are mainly defined by the size of the feed particles and the type of grinding media.
Intermediate and fine size reduction by grinding is frequently achieved in a ball mill in which the length of the cylindrical shell is usually 1 to 1.5 times the shell diameter. Ball mills of greater length are termed tube mills, and when hard pebbles rather than steel balls are used for the grinding media, the mills are known as pebble mills. In general, ball mills can be operated either wet or dry and are capable of producing products on the order of 100 um. This duty represents reduction ratios as great as 100.
The ball mill, an intermediate and fine-grinding device, is a tumbling drum with a 40% to 50% filling of balls. The material that is to be ground fills the voids between the balls. The tumbling balls capture the particles in ball/ball or ball/liner events and load them to the point of fracture. Very large tonnages can be ground with these devices because they are very effective material handling devices. The feed can be dry, with less than 3% moisture to minimize ball coating, or a slurry can be used containing 20% to 40% water by weight. Ball mills are employed in either primary or secondary grinding applications. In primary applications, they receive their feed from crushers, and in secondary applications, they receive their feed from rod mills, autogenous mills, or semi-autogenous mills. Regrind mills in mineral processing operations are usually ball mills, because the feed for these applications is typically quite fine. Ball mills are sometimes used in single-stage grinding, receiving crusher product. The circuits of these mills are often closed with classifiers at high-circulating loads.
All ball mills operate on the same principles. One of these principles is that the total weight of the charge in the mill-the sum of the weight of the grinding media, the weight of the material to be ground, and any water in the millis a function of the percentage of the volume of the mill it occupies.
The power the mill draws is a function of the weight of the charge in the mill, the %of volumetric loading of the mill, the %of critical speed, which is the speed in RPM at which the outer layer of the charge in the mill will centrifuge.
For closed grinding circuits producing typical ball mill products, indirect and direct on-line measurements of the product size are available. The indirect means are those which assume that the product size is relatively constant when the feed condition to the classifying unit and the operating conditions in the classifying unit are constant. One example is maintaining a constant mass flow, pulp density and pressure in the feed to the cyclone classifier.
By using math modeling, it is possible to calculate the product size from measured cyclone classifier feed conditions and circuit operating data, thus establishing the effect on the particle size distribution in the product for changes in the variables.
Direct on-line means to measure either particle size or surface area are available for typical ball mill circuit products. These require the means to obtain representative or at least consistent samples from the grinding circuit product stream. These direct means and the calculated product particle size distributions can be used to:
Small variations in the feed size to ball mill circuits generally is not critical to the calculation of operating work index because they make a very small change in the 10F factor. Thus, a computer program can be developed to calculate operating work indices from on-line data with the feed size a constant and with the program designed to permit manually changing this value, as required to take into account changes in feed size resulting from such things as drawing down feed bins, crusher maintenance, work screen surfaces in the crushing plant, etc. which are generally known in advance, or can be established quickly. Developments underway for on-line measurement of particle size in coarser material which when completed will permit measuring the feed size used to calculate operating work indices.
recorded by a data logger, gives continuous means to report comminution circuit performance and evaluate in-plant testing. Changes in Wio indicated on data loggers alert operating and supervisory personnel that a change has occurred in either the ore or in circuit performance. If sufficient instrumentation is available, the cause for a problem can often be located from other recorded or logged data covering circuit and equipment operation, however, generally the problem calls for operator attention to be corrected.
Wio can be used to determine the efficiency of power utilization for the entire comminution section of a mill, and for the individual circuits making up the comminution section. The efficiency of a comminution circuit is determined by the following equation.
Wi is obtained by running the appropriate laboratory tests on a composite sample of circuit feed. Wio is calculated from plant operating data covering the period when the feed sample was taken. Since Wi from laboratory tests refers to specific conditions for accurate efficiency determinations, it is necessary to apply correction factors as discussed in The Tools of Power Power to Wio to put the laboratory and operating data on the same basis.
To-date, there is no known way to obtain standard work index data from on-line tests. Continuous measurement of comminution circuit efficiency is not possible and thus efficiency is not available for circuit control. Using laboratory data and operating data, efficiency can be determined for overall section and individual circuit for evaluation and reporting. Just monitoring Wio and correcting operating problems as they occur will improve the utilization of the power delivered to the comminution circuits.
Samples taken from the chips around blast hole drillings and from broken ore in the pit or mine for laboratory work index and other ore characteristic determinations before the ore is delivered to the mill, can be used to predict in advance comminution circuit performance. Test results can also be used for ore blending to obtain a more uniform feed, particularly to primary autogenous and semi-autogenous circuits.
We sell Small Ball Mills from 2 to 6 (600 mm X 1800 mm) in diameter and as long as 10 (3000 mm) in length. The mills are manufactured using a flanged mild steel shell, cast heads, overflow discharge, removable man door, spur type ring gear, pinion gear assembly with spherical roller bearings, replaceable roller bronze trunnion bearings, oil lubrication, replaceable trunnion liners with internal spirals, rubber liners and lifters, feed spout with wash port, discharge trommel with internal spiral, motor and gear reducer drive, direct coupled to pinion gear, gear guard and modular steel support frame. All ball mills always come withOSHA-type gear guard.
A PULP level sufficiently high to interpose a bed of pulp, partly to cushion the impact of the balls, permits a maximum crushing effect with a minimum wear of steel. The pulp level of theseSmall Ball Millscan be varied from discharging at the periphery to discharging at a point about halfway between the trunnion and the periphery.The mill shell is of welded plate steel with integral end flanges turned for perfect alignment, and the heads are semi-steel, with hand holes in the discharge end through which the diaphragm regulation is arranged with plugs.The trunnion bearings are babbitted, spherical, cast iron, and of ample size to insure low bearing pressure; while the shell and saddle are machined to gauge so that the shells are interchangeable.
Data based on:Wet grinding, single stage, closed circuit operation: feed:( one way dimension); Class III ore. All mills:free discharge, grated type, rapid pulp flow. N. B.for overflow type mills: capacity 80%power 83%. Dimensions :diameters inside shell without linerslengths working length shell between end liners.
The CIW is a Small Ball Mill thats belt driven, rigid bearing, wet grinding, trunnion or grate discharge type mill with friction clutch pulley and welded steel shell. The 7 and 8 foot diameter mills are of flange ring construction with cut gears while all other sizes have cast tooth gears. All these mills are standard with white iron bar wave type shell liners except the 8 foot diameter mill which is equipped with manganese steel liners. The horsepowers shown in the table are under running conditions so that high torque or wound rotor (slip ring) motors must be used. Manganese or alloy steel shell or head liners and grates can be supplied with all sizes of mills if required. Alloy steel shell liners are recommended where 4 or larger balls are used and particularly for the larger sized mills.
Small (Muleback Type) Ball Mill is built for muleback transportation in 30 and 3 diameters (inside liners). A 4 (Muleback Type) Ball Mill is of special design and will be carefully considered upon request. Mankinds search for valuable minerals often leads him far away from modern transportation facilities. The potential sources of gold, silver and strategic minerals are often found by the prospector, not close by our modern highways, but far back in the mountains and deserts all over the world. The Equipment Company has realized this fact, and therefore has designed a Ball Mill that can be transported to these faraway and relatively inaccessible properties, either by the age old muleback transportation system, or by the modern airplane. As a result these properties may now obtain a well-designed ball mill with the heaviest individual piece weighing only 350 pounds.
The prime factor considered in this design was to furnish equipment having a maximum strength with a minimum weight. For this reason, these mills are made of steel, giving a high tensile strength and light weight to the mills. The muleback design consists of the sturdy cast iron head construction on the 30 size and cast steel head construction on the larger sizes. The flanges on the heads are arranged to bolt to the rolled steel shell provided with flanged rings. When required, the total length of the shell may consist of several shell lengths flanged together to provide the desired mill length. Liners, bearings, gears and drives are similar to those standard on all Ball Mills.
This (Convertible) and Small Ball Mill is unique in design and is particularly adapted to small milling plants. The shell is cast in one piece with a flange for bolting to the head. In converting the mill from a 30x 18 to a 30x 36 unit with double the capacity, it is only necessary to secure a second cast shell (a duplicate of the first) and bolt it to the original section.
30 Convertible Ball Mills are furnished with scoop feeders with replaceable lips. Standard mills are furnished with liners to avoid replacement of the shell; however, themill can be obtained less liners. This ball mill is oftendriven by belts placed around the center, although gear drive units with cast gears can be furnished. A Spiral Screen can be attached to the discharge.
This mill may be used for batch or intermittent grinding, or mixing of dry or wet materials in the ore dressing industry, metallurgical, chemical, ceramic, or paint industries. The material is ground and mixed in one operation by rotating it together with balls, or pebbles in a hermetically sealed cylinder.
The cast iron shell which is bolted to the heads is made with an extra thick wall to give long wearing life. Two grate cleanout doors are provided on opposite sides of the shell by means of which the mill can be either gradually discharged and washed, while running, or easily and rapidly emptied and flushedout while shut down. Wash-water is introduced into the interior of the mill through a tapped opening in the trunnion. The mill may be lined with rubber, silex (buhrstone) or wood if desired.
The Hardinge Conical Ball Mill has been widely used with outstanding success in grinding many materials in a wide variety of fields. The conical mill operates on the principle of an ordinary ball mill with a certain amount of classification within the mill itself, due to its shape.
Sizes of conical mills are given in diameter of the cylindrical section in feet and the length of the cylindrical section in inches. Liners can be had of hard iron, manganese steel or Belgian Silex. Forged steel balls or Danish Flint Pebbles are used for the grinding media, depending upon the material being milled.
The Steel Head Ball-Rod Mill gives the ore dressing engineer a wide choice in grinding design so that he can easily secure a Ball-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 Ball-Rod Mill is available with five types of discharge trunnions, each type obtainable in small, medium or large diameters. The types of discharge trunnions are:
The superiority of the Steel Head Ball-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 assured against breakage due to the high tensile strength of cast steel as compared to that of the cast iron head found on the ordinary ball mill. Trunnion Bearings are made of high- grade nickel babbitt.
Steel Head Ball-Rod Mills can be converted intolarger capacity mills by bolting an additional shell lengthonto the flange of the original shell. This is possible because all Steel Head Ball or Rod Mills have bearings suitable for mills with length twice the diameter.
Head and shell liners for Steel Head Ball-Rod Mills are available in Decolloy (a chrome-nickel alloy), hard iron, electric steel, molychrome steel, and manganese steel. 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.
Thats one characteristic of Traylor Ball Millsliked by ownersthey are built not only to do a first class job at low cost but to keep on doing it, year after year. Of course, that means we do not build as many mills as if they wore out quicklyor would we? but much as welike order, we value more the fine reputationTraylor Ball Mills have had for nearly threedecades.
Thats one characteristic of Traylor Ball Mills We dont aim to write specifications into thisliked by ownersthey are built not only to do advertisementlet it suffice to say that theresa first class job at low cost but to keep on do- a Traylor Ball Mills that will exactly fit anyanything it, year after year. Of course, that means requirement that anyone may have.
If this is true, there is significance in the factthat international Nicked and Climax Molybdenum, theworlds largest producers of two important steel alloys, areboth users of MARCY Mills exclusively. With international interest centered on increasingproduction of gold, it is even more significant that MARCYMills are the predominant choice of operators in everyimportants gold mining camp in the world.
Ball Mill. Intermediate and fine size reduction by grinding is frequently achieved in a ball mill in which the length of the cylindrical shell is usually 1 to 1.5 times the shell diameter. Ball mills of greater length are termed tube mills, and when hard pebbles rather than steel balls are used for the grinding media, the mills are known as pebble mills. In general, ball mills can be operated either wet or dry and are capable of producing products on the order of 100 pm. This duty represents reduction ratios as great as 100.
The ball mill, an intermediate and fine-grinding device, is a tumbling drum with a 40% to 50% filling of balls (usually steel or steel alloys). The material that is to be ground fills the voids between the balls. The tumbling balls capture the particles in ball/ball or ball/liner events and load them to the point of fracture. Very large tonnages can be ground with these devices because they are very effective material handling devices. The feed can be dry, with less than 3% moisture to minimize ball coating, or a slurry can be used containing 20% to 40% water by weight. Ball mills are employed in either primary or secondary grinding applications. In primary applications, they receive their feed from crushers, and in secondary applications, they receive their feed from rod mills, autogenous mills, or semiautogenous mills. Regrind mills in mineral processing operations are usually ball mills, because the feed for these applications is typically quite fine. Ball mills are sometimes used in single-stage grinding, receiving crusher product. The circuits of these mills are often closed with classifiers at high-circulating loads.
These loads maximize throughput at a desired product size. The characteristics of ball mills are summarized in the Table, which lists typical feed and product sizes. The size of the mill required to achieve a given task-that is, the diameter (D) inside the liners-can be calculated from the design relationships given. The design parameters must be specified.
The liner- and ball-wear equations are typically written in terms of an abrasion index (Bond 1963). The calculated liner and ball wear is expressed in kilograms per kilowatt-hour (kg/kWh), and when multiplied by the specific power (kWh/t), the wear rates are given in kilograms per ton of feed. The wear in dry ball mills is approximately one-tenth of that in wet ball mills because of the inhibition of corrosion. The efficiency of ball mills as measured relative to single-particle slow-compression loading is about 5%. Abrasion indices for five materials are also listed in the Table.
The L/D ratios of ball mills range from slightly less than 1:1 to something greater than 2:1. The tube and compartment ball mills commonly used in the cement industry have L/D ratios 2.75:1 or more. The fraction of critical speed that the mill turns depends on the application, and most mills operate at around 75% of critical speed. Increased speed generally means increased power, but as the simulations presented in Figure 3.26 show, it can also produce more wasted ball impacts on the liners above the toe. causing more wear and less breakage.
There are three principal forms of discharge mechanism. In the overflow ball mill, the ground product overflows through the discharge end trunnion. A diaphragm ball mill has a grate at thedischarge end. The product flows through the slots in the grate. Pulp lifters may be used to discharge the product through the trunnion, or peripheral ports may be used to discharge the product.
The majority of grinding balls are forged carbon or alloy steels. Generally, they are spherical, but other shapes have been used. The choice of the top (or recharge) ball size can be made using empirical equations developed by Bond or Azzaroni or by using special batch-grinding tests interpreted in the content of population balance models. The effect of changes in ball size on specific selection functions has been found to be different for different materials. A ball size-correction method can be used along with the specific selection function scale-up method to determine the best ball size. To do this, a set of ball size tests are performed in a batch mill from which the specific selection function dependence on ball size can be determined. Then, the mill capacities used to produce desired product size can be predicted by simulation using the kinetic parameter corresponding to the different ball sizes.
The mill liners used are constructed from cast alloy steels, wear-resistant cast irons, or polymer (rubber) and polymer metal combinations. The mill liner shapes often recommended in new mills are double-wave liners when balls less than 2.5 in. are used and single-wave liners when larger balls are used. Replaceable metal lifter bars are sometimes used. End liners are usually ribbed or employ replaceable lifters.
The typical mill-motor coupling is a pinion and gear. On larger mills two motors may be used, and in that arrangement two pinions drive one gear on the mill. Synchronous motors are well suited to the ball mill, because the power draw is almost constant. Induction, squirrel cage, and slip ring motors are also used. A high-speed motor running 600 to 1,000 rpm requires a speed reducer between the motor and pinion shaft. The gearless drive has been installed at a number of locations around the world.
Gang Huang, Chuncheng Lv, Junxi He, Xia Zhang, Chao Zhou, Pan Yang, Yan Tan, Hao Huang, "Study on Preparation and Characterization of Graphene Based on Ball Milling Method", Journal of Nanomaterials, vol. 2020, Article ID 2042316, 11 pages, 2020. https://doi.org/10.1155/2020/2042316
Taking advantage of the state-of-the-art graphene preparation technologies in China and abroad, this work studied the preparation processes of graphene for road applications based on the preliminary high-speed vibration ball milling method. This work combined numerical modeling and microscopic experiments. The preparation parameters were optimized through a multifactor and multilevel test scheme. The materials, influencing factors, and parameters in the preparation process were systematically studied. A graphene preparation method was proposed that considered vibration frequency, static filling rate, material-to-ball volume ratio, and the void percentages of media. Flake graphite, aluminum powder, and 304 stainless-steel grit were used as the preparation materials. The preparation parameters and process model were established based on the uniform design method. The preparation parameters were proposed, calculated, and optimized. Microscopic analysis showed that the proposed preparation method can improve the quality of graphene. This study provides a new source of raw materials for the application of graphene in road engineering.
Graphene has attracted widespread attention from researchers in China and abroad since the discovery of fullerene, a quasi-zero-dimensional material, in the 1980s. In 2004, two British scientists (Andre K. Geim and Kanstantin Novoselov) successfully isolated graphene, a two-dimensional carbon nanomaterial composed of single-layer carbon atoms, by peeling pyrolytic graphite sheet with adhesive tape . Graphene is a two-dimensional honeycomb-like nanomaterial made of sp2-hybridized carbon atoms. The strong intermolecular force (- interaction) between graphene molecules makes the graphene structure very stable . Graphene has high transmittance (97.7%) , high Youngs modulus (1 TPa) [6, 7], high specific surface area (2630m2/g) , high thermal conductivity (5000W/mK), and high carrier mobility () . It has received widespread attention in the fields of biology, medicine, environmental science, electronics, energy, and materials science because of its unique physical structure and excellent electrical, optical, thermal, and mechanical properties .
It is particularly difficult to peel off graphene nanosheets from graphite because of the van der Waals force between the graphite layers. In the past decade, graphene preparation technology has developed rapidly in China and abroad with the widespread attention given to carbon nanomaterials. At present, common graphene preparation methods include mechanical exfoliation, oxidation-reduction, liquid-phase exfoliation, electrochemical exfoliation, supercritical fluid exfoliation, chemical vapor deposition (CVD), and epitaxial growth . Graphenes that are prepared by different methods have different qualities and application prospects. For example, CVD-prepared graphene sheets have a large area, good uniformity, high quality, and controllable number of layers. They are suitable for high-end fields such as optics, electronics, sensors, energy, and biology. However, they are rarely used as road materials because of the strict preparation process and high cost. Currently, graphene oxide and (nonfunctional group) graphene are used in the road field. Relevant research at home and abroad mainly focuses on the performance of graphene composite road materials, For example, Habib et al.s  research suggests that graphene oxide asphalt helps improve the resistance to deformation of the road surface and reduce rutting in the road surface. According to Lis  research, the high-temperature performance and plasticity of the graphene-modified asphalt have been significantly improved, Hes  research shows that the addition of graphene improves the low temperature stability of asphalt to a certain extent. However, there is no research on the preparation process of road graphene. The mechanical exfoliation method is relatively simple. Graphene materials prepared by this method have low size requirements and low cost. High-performance graphene composite road materials can be developed by combining the mechanically exfoliated graphene with road engineering materials to employ the advantages of the graphene. This study was funded by the National Natural Science Foundation of China. According to a patented graphene preparation technology, this study aimed to develop graphene with good quality and low cost based on mechanical exfoliation and ball milling. A numerical method was employed to optimize the graphene preparation parameters. This work provides a new source of raw materials for the application of graphene in road engineering and provides a reference for the development of graphene composite road materials .
In this study, a QM-3B high-speed vibrating ball mill (specification: 80ml, vibration frequency: 1200r/min, motor specification: 220V, 180W) produced by Nanjing University Instrument Factory was used. X-ray diffraction (XRD) was performed with a D8-ADVANCE (Bruker, Germany) X-ray diffractometer (Cu-K radiation source, voltage 40kV, current 40mA, scan speed 0.1sec/step, wavelength 1.5418). The specific surface area was measured on a Quadrasorb SI analyzer (Quantachrome Instruments). High-resolution transmission electron microscopy (HRTEM) was performed with a Tecnai G2 F20 field emission transmission electron microscope (FEI, USA).
The materials used in this study included aluminum (Tenghui Metal Material Co., Ltd., Qinghe, China; particle size: 1.2mm, 40 mesh, 80 mesh, 100 mesh, 200 mesh, and 300 mesh; ), 304 stainless-steel grit (Lianzhiyan Surface Treatment Material Co., Ltd., Dongguan, China; particle size: 0.2mm, 0.4mm, and 0.8mm), and flake graphite (Qingdao Chenyang Graphite Co., Ltd., Qingdao, China; particle size: 50 mesh).
In this study, graphene was prepared using a QM-3B high-speed vibrating ball mill (specification: 80ml; vibration frequency: 1200r/min; motor specification: 220V, 180W) . 304 stainless-steel balls were used as grinding balls. The working principle is as follows: the high-speed rotation of the motor drives the cylinder to rotate at a high speed on the springs. This process is accompanied by simple harmonic vibration. During the rotation process, the frictional resistance between the cylinder and the steel ball causes accelerated motion of the steel ball. The kinetic energy gained by the steel ball is then transferred to the material as the ball collides with the material and other steel balls. As a result, the material is ground by the balls. At the same time, the generated vibration prevents the steel balls from centrifugal movement due to the high-speed rotation and provides more impact energy to ensure the balls have enough kinetic energy. Therefore, the kinetic energy of the high-speed vibrating ball mill is generally greater than that of the planetary ball mill. However, the cylinder volume of the high-speed vibrating ball mill is only 80ml. Its grinding capacity is small, so this type of ball mill is mostly used for laboratory grinding studies. There are few studies on the working parameters of high-speed vibrating ball mills. The parameters are generally designed based on the theoretical calculation of tumbling ball mills and are optimized based on experience [29, 30]. Gonzlez-Domnguez  prepared graphene by planetary ball milling. The raw material ratio is only 25mg, and the ball mill speed is only 100r/min. In Buzaglos  study, the content of graphite was only 36mg. In summary, these two ball milling methods have low production efficiency and high cost, so they are not suitable for road materials.
During the ball milling process, the rotation and vibration of the cylinder drive the steel balls and materials to rise. Then, the steel balls and materials drop into the cylinder. The steel balls and the materials crush and collide with each other to generate impact energy, shear energy, and friction energy, thereby achieving the purpose of grinding. The grinding process of the ball mill is essentially the movement process of discrete particles. At present, most of the domestic and foreign studies on the grinding process of ball mills determine the relevant parameters by discrete element methods and molecular dynamics . The ball mill grinding is a complex process with many influencing factors, and these influencing factors restrict and affect each other. The grinding efficiency of the ball mill is determined by the rotation speed of the ball mill, the grinding media (material, size, static filling rate, etc.), the material-to-ball volume ratio (MBVR), the grading of the grinding media, and the grinding time. (1)The rotation speed is defined as the ratio of the actual rotation speed to the critical rotation speed , which is denoted as : (2)The static filling rate refers to the ratio of the loose volume of the material to the effective volume of the ball mill in the static state, which is denoted , where is the radius of the cylinder and is the distance from the center of the cylinder bottom to the top surface of the material (3)The MBVR is the ratio of the volume of the material to the void volume between the steel balls in the static state, which is denoted (4)The void percentage of the media is defined as the ratio of the void volume to the bulk volume of the grinding media, which is denoted . is the total volume of the media including voids, is the volume of a single grinding medium particle, and is the number of medium particles
In studying the grinding process, there are many differences in the boundary conditions between the theoretical calculation and the actual process. For example, the lubricating effect of the graphite will reduce the frictional resistance between the cylinder and the steel balls; relative sliding movement exists between the steel balls and the cylinder, which lowers the proportion of useful work and the mechanical efficiency; the grading of the steel balls will change the way energy is transferred. It is difficult to apply the theoretical calculation results directly to the actual process. Therefore, the process parameters need to be determined by a combination of theoretical calculation and empirical analysis. Peng Huang, Guojun Shi, and others have performed discrete element simulation analysis on ball mills of different specifications and found that the optimal rotation speed was 80-85%. According to production practices, the grinding effect is good when the filling rate is in the range of 20-50%, and the percentage of voids between the steel balls is 0.35 .
The raw material used to prepare graphene was flake graphite . In the study of Prato and Regev [31, 32], melamine and fully conjugated aromatic diluents were used as grinding aids, respectively. However, the surface energy and cohesive energy of molecular crystals are much smaller than that of aluminum; the aluminum powder is used as the grinding aid in this experiment. Graphite is a crystalline mineral of pure carbon. The crystal lattice of graphite has a hexagonal layered structure, and the layered structures can slide against each other in parallel direction. Aluminum has strong plasticity and ductility. The surface of unoxidized aluminum has a strong adsorption capacity. During the ball milling process, the kinetic energy and shear energy generated by the high-speed impact of the grinding balls can break the aluminum to form fresh aluminum surfaces. The surface of the graphite is continuously adsorbed by the freshly generated aluminum surface. The impact from the balls causes the fresh aluminum to peel off the graphite layer by layer, yielding a layered structure of graphite with graphene in the product.
According to the theoretical calculation, the filling rate was kept between 40% and 50%. In Pratos study, ten stainless steel balls (1cm in diameter) were used for grinding, but one size of steel balls would make the energy transfer efficiency lower, so three grades of steel balls were used (8mm particle size, 10g, 5 pieces; 5mm particle size, 70g, 137 pieces; 3mm particle size, 98g, 889 pieces). As the rotation speed of the high-speed vibrating ball mill was not adjustable, the factory default setting of 1200r/min was used. It is generally believed that the ball mill has good grinding efficiency when the interstitial filling fraction of the material is 0.6-1.2 [49, 50]. The parameter setting of the ball mill is shown in Table 1.
The densities of aluminum and graphite are similar. To ensure full contact between aluminum and graphite, the content of aluminum should not be less than that of graphite. On this basis, processes G-1 through G-4 with different combinations of aluminum particle size, aluminum content, and grinding time were obtained. It was found that graphene was obtained in G-1 and G-2 but was not obtained in G-3 or G-4. This may be because the energy of the steel balls could not be effectively transferred to the material when the particle size of aluminum powder was too small. 304 stainless-steel grit with a particle size of 0.4mm was added to effectively disperse energy and increase the number of contact points for load transfer. Thus, process combinations G-5 through G-8 were obtained. The volume of steel grinding grit was determined based on the volumes of graphite and aluminum powder. The volume of the steel grit was chosen to be equal to that of the material to ensure effective contact and was then converted to the corresponding mass.
The ground products showed two types of macroscopic appearance. As shown in Figure 1, one was silver-gray powder with metallic luster, and the other was pure black powder. According to the optical properties of graphene, the black powder can be used as an indicator to preliminary determine whether graphene is successfully prepared.
When light is shone on graphene, the electrons in the valence band (the energy band occupied by valence electrons) are excited to the conduction band (the energy space formed by free electrons) by absorbing the energy of the photons. The photoconductivity of single-layer graphene depends on the fine structure constant .
The light absorbance of single-layer graphene is 2.3%. In the visible light region, the reflectance of single-layer graphene is less than 0.1%, and the reflectance of 10-layer graphene is only 2%, which suggests that graphene has extremely strong light absorption. The transmittance of single-layer graphene is as high as 97.7%, and only 0.1% of the visible light will be reflected. Therefore, single-layer graphene is transparent under light. Within several layers of graphene, each additional layer increases the absorbance by 2.3%. The few- and multiple-layer graphenes appear black due to their absorbance and reflectance . Graphites with different structures have different physical properties, and the 50-mesh flake graphite itself has a silver-gray metallic luster.
The products of processes G-1 and G-2 were black powders (Figure 1(b)), which preliminarily indicated that the products contained a large amount of graphene. The grinding time of G-1 was too long, and the efficiency of G-1 was low compared to that of G-2. The G-2 product was selected for the microscopic characterization and was compared with DY-1 (graphene produced by Deyang Carbonene Technology Co., Ltd.). X-ray diffraction (XRD), specific surface area measurement, and HRTEM were performed for the microscopic characterization.
The principle of X-ray crystal structure analysis is to measure the angle using the diffraction of X-rays with a known wavelength and then calculate the crystal plane spacing . X-rays are electromagnetic waves with short wavelengths (approximately 20 to 0.06). They can generate diffraction peaks when passing through the gaps between the graphite layers. The interlayer spacing of graphite is 3.35, and the corresponding peak of the 3.35 crystal plane spacing is approximately 26. The lower the peak intensity, the lower the crystal content and the higher the graphene content. XRD was performed with a D8 Advance diffractometer (Bruker, Germany). The result of the flake graphite analysis is shown in Figure 2.
Figure 2 shows that the peak of the graphite crystal appeared at approximately 26. The peak value of the flake graphite crystal reached 374,826, and the relative strength of the crystal was high, which indicated a good crystallinity of the sample. XRD was also performed on DY-1 and G-2 and is shown in Figure 3.
Figures 2 and 3 show that the peak value of DY-1 was 4090, which was higher than that of G-2 (1767). This result indicated that G-2 had lower graphite crystal content, higher graphene content, and therefore higher product quality than DY-1.
The BET method for specific surface area measurement is widely used in the study of particle surface adsorption. It has become the most widely used and most accurate method in contemporary research . The specific surface area measurement in this study was performed with a Quadrasorb SI instrument (Quantachrome Instruments). The result is shown in Table 3.
A HRTEM is a high-resolution transmission electron microscope that consists of an electro-optical part, a vacuum part, and an electronic part. An accelerated and focused electron beam is projected onto a target sample, and the electrons collide with the atoms in the sample and scatter. The scattering angle of the electron beam is related to information such as the density, thickness, and spacing of the sample. Thus, the electrons after the collision carry the relevant information of the sample, and such information can be converted back to images . In this study, HRTEM was performed on a Tecnai G2 F20 field-emission TEM (FEI, USA). The characterization results of the two samples are shown in Figures 4 and 5.
Figures 4 and 5 show obvious layered structures in the two samples. G-2 and DY-1 show shadows in the 50nm scanning range. Scanning the shadow in the 5nm range, a large number of layers are observed. This is because the graphene obtained is not completely flat, and some of it has wrinkles due to curling. It can be seen that G-2 and DY-1 are not all single-layer graphene. It contains a small amount of single-layer graphene, but multilayer graphene  is the majority, so the sample of G-2 is not uniform. G-2 contained more dark spots in the 50nm scanning range, which indicated that the impurity content in G-2 was higher than that in DY-1. Further cleaning and purification should be performed on G-2. In the application of engineering materials, graphene-modified asphalt has a very small amount of graphene. The effect of trace impurities in G-2 on engineering materials has yet to be verified.
Microscopic analysis and comparison of the two samples showed that the folds of sample DY-1 are more dense, which indicates that the G-2 prepared by the vibrating ball mill was significantly better than the DY-1 purchased on the market. However, the quality of the G-2 graphene was still not high. Therefore, further optimization of the process was needed.
According to Table 2 and the preliminary test results, it was considered that the G-1, G-2, G-7, and G-8 processes were best out of the eight preparation processes. Therefore, XRD was performed on samples prepared by these four processes, and the results are shown in Figure 6.
It can be seen from Figure 6 that the peak intensity of G-1 was lower than that of G-2, but the efficiency of G-1 was low because the grinding time was too long. Therefore, the grinding time was fixed at 30min to ensure grinding efficiency. G-8 graphite had the lowest peak value, so the optimization was performed based on the G-8 process.
Through previous experience and exploration, we found that many factors affected the quality of the graphene, such as the particle size of the material, MBVR, grinding time, and the grading and content of the steel grit. Since there are many influencing factors and these factors interact with each other, some variables were determined first to reduce the number of experiments. The particle size of the aluminum powder was selected first by the control variates method based on the G-8 process. However, a large amount of chromium impurity was found in the G-8 sample in the subsequent product purity test. It was determined that the chromium originated from the 40-mesh aluminum. Therefore, aluminum powders with four particle sizes (40 mesh, 100 mesh, 200 mesh, and 300 mesh) were reselected for testing. The process parameters are shown in Table 4.
Table 4 shows that the XRD peak intensity of G-9 multilayer graphene was higher than that of G-8 multilayer graphene, which indicates that chromium was helpful for the grinding of graphene. Although the G-8 multilayer graphene had higher quality, the chromium in the product could not be removed in the posttreatment, so the produced graphene could not be purified. In addition, the chromium content could not be quantitatively analyzed, and the calibration was difficult. Therefore, process G-8 was discarded. The experimental results of processes G-9 to G-12 were compared. The relationship between the peak value and the aluminum particle size is shown in Figure 7.
It can be seen from Figure 7 that under the same process conditions, the XRD peak intensity of the produced multilayer graphene was the lowest when the aluminum particle size was 200 mesh. Therefore, the aluminum particle size was first set at 200 mesh, and the design of process parameters was carried out based on this condition.
Uniform experimental design was adopted for the process parameter design. The uniform experimental design was proposed by Chinese mathematicians Kaitai Fang and Yuan Wang in 1978. It is one of the main methods of fractional factorial design. Compared with the common orthogonal experimental design, the uniform experimental design gives the researchers more choices, and the desired results can be obtained with fewer experiments [56, 57]. The percentage of voids between the grinding balls was measured to be 0.35. Ball mills have a good grinding efficiency when the interstitial filling fraction of the material is 0.6-1.2 . This study selected 1.2 as the limit value, and the amount of the material was controlled in this range. The limit amount of flake graphite (50 mesh) and aluminum (200 mesh) were both set to 5g based on the size of the sample cylinder. Nine levels were fractioned in the range of 1g to 5g. Three particle sizes (0.2mm, 0.4mm, and 0.8mm) of steel grit were selected. To construct a uniform design table with equal-level factors, the steel grit was set to have a single particle size or a mixture of multiple particle sizes. The three particle sizes were configured in accordance with the configuration principle of grinding balls. To facilitate the energy dispersion and increase the contact points, the following principles were employed: equal proportions, fewer 0.4mm balls but more 0.2mm and 0.8mm balls, and fewer balls with larger sizes. The total mass of steel grit was kept unchanged at 6g to ensure that the bulk volumes of steel grits were basically the same. In this paper, three factors were selected: graphite content, aluminum content, and steel grit grading, each having 9 levels. The factor-level table is shown in Table 5.
The design was assisted by the Data Processing System (DPS) analysis software. DPS is a data processing system that integrates functions such as numerical calculation, statistical analysis, model simulation, and chart and table creation. It has many experimental design functions, including uniform design and mixture uniform design [58, 59]. The obtained uniform design scheme and the corresponding XRD results are shown in Table 6.
A mathematical model was established based on Table 6 with , , and as independent variables and as a response variable. The independent variables and and the dependent variable could be directly input into the model. However, the independent variable is a single-particle-size steel grit or a triple-particle-size steel grit (both types of grit had the same mass) and could not be directly inputted into the model. Therefore, the steel grit grading was first converted into a specific surface area and then inputted into the modeling calculation. The specific surface area of steel grit was calculated as follows:
The specific surface areas of the steel grits with particle sizes of 0.8mm, 0.4mm, and 0.2mm calculated by equation (6) were 3/3172m2/g, 3/1586m2/g, and 3/793m2/g, respectively. Then, the specific surface area corresponding to different can be obtained. At the same time, the G-13, G-14, and G-21 test groups with large and obviously poor process capabilities were excluded from the test scheme. The results after data processing are shown in Table 7.
A mathematical model was established using graphite concentration (), aluminum concentration (), and the specific surface area of steel grit () as independent variables and the XRD peak intensity () as the response value. The model was optimized to obtain the preparation parameters. Graphene was prepared based on the simulated preparation parameters and was analyzed to verify the reliability and significance of the model.
Partial least squares regression analysis is a method to study the quantitative relationship between multiple explanatory variables and multiple response variables. Therefore, the partial least squares quadratic polynomial regression, partial least squares (considering interaction terms) regression, and partial least squares (considering quadratic terms) regression were first selected in the DPS software to establish the model. The model calculation parameters are shown in Table 8.
Table 8 shows that when the model was established using the partial least squares (considering quadratic terms) regression, the sum of the squared errors was the smallest, the coefficient of determination was the highest (approaching 1), and the PRESS statistic was the smallest. Therefore, we chose to use the partial least squares (considering quadratic terms) regression for modeling.
First optimization (1stOpt) is a set of integrated software tools for mathematical analysis and optimization. It was independently developed by 7D-Soft High Technology Inc. (China)  and has strong computing ability in the fields of nonlinear regression, curve fitting, and parameter estimation for nonlinear complex engineering models. Therefore, the 1stOpt software was used for modeling, and the model was compared with that established by the DPS software. The partial least squares (considering quadratic terms) model was fitted by 1stOpt [61, 62]. The model parameters are shown in Table 9.
The closer the correlation coefficient is to 1, the better the model is; the smaller the sum of squared residuals is, the better the model is. Therefore, the 1stOpt model was better than the DPS model.
The approach to obtain the optimal solution of the model is to find the values of , , and so that is equal to 0. indicates that the crystal structure of graphite has completely disappeared, the graphene content in the product is high, the sample quality is high, and the purpose of optimization is achieved. Equation (7) was solved by 1stOpt taking into consideration the XRD results of the nine tests in the uniform design. When was greater than , the XRD peak intensities of the obtained sample were all very high. To achieve a better exfoliation effect, the contents of graphite and aluminum should satisfy , and the total mass of and must be kept within a reasonable range. If the volume is too large and the optimal range of the interstitial filling fraction (0.6-1.2) is exceeded, the grinding efficiency will decrease. Therefore, the constraint conditions were set as follows: and ( was set as the boundary condition). Since there are multiple solutions to the equation, the optimized solution summary is shown in Table 10.
The obtained in Table 10 was the specific surface area, which had to be converted into a preparation parameter. The values of in Table 10 were compared with the values of in Table 7, but no corresponding values were found. Therefore, the particle size combination closest to each solution was first determined based on Table 7. Two specific surface areas closest to each solution were chosen from Table 7 and were then converted to a combination of the steel grit particle sizes. The optimized experimental scheme is shown in Table 11.
Samples were prepared according to the six schemes in Table 10 and were characterized by XRD. The test results of samples prepared by the above six processes were compared with that of the best sample in Table 7 (G-19). The results are in Figure 8.
G-19 was the best process in the uniform design. G-22 to G-27 were processes obtained by model optimization. The XRD peak intensities of the G-22 to G-27 samples were lower than that of the G-19 sample, which indicated that the crystal contents of graphite in G-22 to G-27 were further reduced, and the qualities of multi-layer graphene in G-22 to G-27 products were improved. The effectiveness of process parameter optimization was confirmed. The peak value of the G-22 product was 134, so G-22 was the best process in the current optimization scheme.
Table 12 shows that the specific surface area of the G-22 product was the largest. At the same time, the peak intensity of the G-22 product was the lowest by XRD. Therefore, the sample prepared by the G-22 process had the highest graphene content, and G-22 was the best process.
(1)Multilayer graphene with good quality can be effectively prepared by mechanical exfoliation of graphite by ball milling(2)The process parameters of multilayer graphene production by a vibrating ball mill were designed and optimized using the uniform design method and mathematical modeling. The preparation materials were flake graphite, 200-mesh aluminum powder, and 304 stainless-steel grit. The vibration frequency was 1200r/min, and the grinding time was 30min(3)Many factors affect the multilayer graphene production by ball mills. In this study, the vibration frequency was 1200r/min, the static filling rate was 40%, the MBVR was 51%, and the void percentage of the media was 0.38. More influencing factors can be selected in the future for further optimization of the preparation process(4)Our findings show that for the preparation of multilayer graphene by a vibrating ball mill, the process parameters can be designed and optimized with the assistance of mathematic modeling. However, the yield of multilayer graphene produced in the laboratory was low(5)This study provides a parameter design reference for the preparation of multilayer graphene by planetary ball mills
The authors would like to gratefully acknowledge the financial supports from the National Natural Science Foundation of China and Municipal Foundation Project of CQEC and Natural Science Foundation Project of CQ CSTC. This research was funded by the National Natural Science Foundation of China (No.51778096) and the Natural Science Foundation Project of CQ CSTC (No. cstc2016jcyjA0119).
Copyright 2020 Gang Huang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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The generation of electrical energy from renewable energy sources is rapidly increasing across the world due to its many advantages. Renewable energy source is also known as clean energy source. The energy storage devices are playing an important role in both renewable generation and distribution of power. The energy storing devices also helps to improve stability of electrical power grid. The electrode, electrolyte and separators are the main components of ultracapacitors. The performance of ultracapacitors mainly depends on the properties of electrode material, the type of separator used, properties of electrolyte used and its concentration level. Nylon as a separator material for ultracapacitors is investigated. Various parameters of nylon-based ultracapacitors are compared with conventional polyethylene-based ultracapacitors. Very less research work has been done on the processing of electrode material. Ball milling is the most commonly used material processing method in energy storage devices such as ultracapacitors, battery and fuel cells. The effect of ball milling parameters on the performance of ultracapacitors needs to be investigated. Most significant factors of ball milling parameters of electrode material for ultracapacitor are identified. Modeling of ball milling process on electrode material is done by using the statistical method- design of the experiment. The novel ball mill machine with some unique features is also presented. Pulse current density is taken as new output parameters which is more important than an internal resistance and specific capacitance. Most significant ball mill machine parameters are taken as input parameters and specific capacitance, internal resistance along with pulse current density are taken as output parameters for the modeling of nylon-based ultracapacitors.
A.K. Namik, AyhanDemirbas, Promising sources of energy in the near future. J Energy sources Part- A Recover Utilization Environ Eff 38(12), 17301738 (2017). https://doi.org/10.1080/15567036.2014.966179
Andrew Burke, Zhengmao Liu, Hengbing Zhao, 2014, Present and future applications of supercapacitors in electric and hybrid vehicles , IEEE international Electric Vehicle Conference,7(5): 353368. https://doi.org/10.1109/IEVC.2014.7056094
M.Jayalakshmi, K Balasubramanian, Review-Simple capacitor to supercapacitor-An overview International Journal of Electrochemical Science,3(2008), pp.11961217. http://www.electrochemsci.org/papers/vol3/3111196.pdf
A.M. Obeidat, M.A. Gharaibeh, M. Obaidat, Solidstate supercapacitors with ionic liquid liquid gel polymer electrolyte and polypyrrole electrodes for electrical energy storage. J Energy Storage 13, 123128 (2017). https://doi.org/10.1016/j.est.2017.07.010
A.R. Mainar, E. Iruin, L.C. Colmenares, A. Kvasha, An overview of progress in electrolytes for secondary zinc-air batteries and other storage systems based on zinc. J Energy Storage 15, 304328 (2018). https://doi.org/10.1016/j.est.2017.12.004
E.E. Miller, F. Ye Hua, H. Tezel, Materials for energy storage: review of electrode materials and methods of increasing capacitance for supercapacitors. J Energy Storage 20, 3040 (2018). https://doi.org/10.1016/j.est.2018.08.009
L.S Godse, P.B Karandikar, M.Y Khaladkar, 2014, Study of carbon materials activated and effect of its ball milling on capacitance of super capacitor, ELSEVIER, Energy Procedia, 54, pp.302-309. https://doi.org/https://doi.org/10.1016/j.egypro.2014.07.273
R Rain, P Gangola, P.B Karandikar, S Sharma, 2018. Effect of Inclined ball milling on Capacitance of Supercapacitor, 2nd International Conference on Inventive Systems and Control (ICISC2018) Coimbatore, pp.946951. https://doi.org/https://doi.org/10.1109/icisc.2018.8398976
I.S. MansoorSarfraz, Recent advances in layered double hydroxides as electrode materials for high- performance electrochemical energy storage devices. J Energy Storage 13, 103122 (2017). https://doi.org/10.1016/j.est.2017.06.011
M. Robotti, S. Dosta, M. Gardon, G. Cano, R. Wills, Enhancing the performance of common electrode material by means of atmospheric plasma spray coating. J Energy Storage 5, 127133 (2016). https://doi.org/10.1016/j.est.2015.12.001
H.U. Shah, F. Wang, M.A. Ahmad, Muhammad, SufyanJaved, Y. Li, In-situ growth of MnO2 nano rods forest on carbon textile as efficient electrode material for supercapacitors. J Energy Storage 17, 318326 (2018). https://doi.org/10.1016/j.est.2018.03.015
B.B. Sapkota, S.R. Mishra, A simple ball milling method for preparation of p-Cuo/n- Zno Nanocomposite photo catalyst with high photo catalytic activity. J Nano sci nanotechnol 13(10), 65886596 (2013). https://doi.org/10.1166/jnn.2013.7544
T.P. Yadav, R.M. Yadav, D.P. Singh, Mechanical milling: a top down approach for the synthesis of nanomaterials and nanocomposites. Nanosci Nanotechnol 2(2), 2248 (2012). https://doi.org/10.5923/j.nn.20120203.01
Myoungsoo Shin, Woo-Jinsong and Hye Bin Son, Highly strechable separator membrane for deformable energy storage devices, Advanced energy materials, Vol No- 8, Issue No.23, pp. 1-10. https://doi.org/https://doi.org/10.1002/aenm.201801025
Kyung Min Lee, Minjae Kim, Kunsoo Lee, Nylon 6, 6/polyaniline based sheath nanofibres for high performance supercapacitors. J Eletrochimica Acta 213, 124131 2016. https://doi.org/10.1016/j.electacta.2016.07.104
P.B. Karandikar, D.B. Talange, U. Mhaskar, R. Bansal, Validation of capacitance and equivalent series resistance model of manganese oxide-based aqueous super-capacitor. Electric Power Compon Syst 40(10), 11051118 (2012). https://doi.org/10.1080/15325008.2012.682247
I.S. Ike, IakovosSigalas, S.E. Iyuke, Modeling and optimization of electrodes sutilization in symmetric electrochemical capacitors for high energy and power. J Energy Storage 12, 261275 (2017). https://doi.org/10.1016/j.est.2017.05.006
L.W. Juang, P.J. Kollmeyer, A.E. Anders, T.M. Jahns, D. Gao, Investigation of the influence of superimposed AC current on lithium-ion battery aging statistical design of experiments. J Energy Storage 11, 93103 (2017). https://doi.org/10.1016/j.est.2017.02.005
P.B. Karandikar, D.B. Talange, R.C. Uday Mhaskar, Bansal, Development, characterization and modeling of aquesous metal oxide based supercapacitor. Energy 40(1), 131138 (2012). https://doi.org/10.1016/j.energy.2012.02.020
P.B. Karandikar, D.B. Talange, U. Mhaskar, R. Bansal, Investigations for parameter improvement of manganese oxidebased aqueous supercapacitor. Mater Manuf Processes Taylor and Francis 27(11), 11641170 (2012). https://doi.org/10.1080/10426914.2012.663139
H Upreti, A Dixit, A Paul, S Kumari, P.B Karandikar, 2014, Optimization of electrode parameters of stack structured ultracapacitors, ELSEVIER, Energy Procedia- 54, pp. 367375. https://cyberleninka.org/article/n/515860/viewer
P.B.Karandikar, D.B Talange, Material based characterization of aqueous metal oxide based supercapacitors Power and Energy Conference (PECon), 2010 IEEE International, Vol No1, Issue No 1, pp.485-488.DOI:https://doi.org/10.1109/PECON.2010.5697631
The authors gratefully acknowledge and thank to Green vision Technologies Pvt. Ltd., Bangalore, India and TATA Motors, Pune, India for useful inputs. The authors would also gratefully acknowledge Army Institute of Technology, Pune, India for their support.
Godse, L.S., Karkaria, V.N., Bhalerao, M.J. et al. Process-Based Statistical Modeling for Ball Mill Machine to Improve Performance of Nylon Ultracapacitor. J. Inst. Eng. India Ser. B (2021). https://doi.org/10.1007/s40031-021-00570-0
A simulation of the three-dimensional motion of grinding media in the stirred media mill for the research of grinding mechanism has been carried out by 3-dimensional discrete element method (DEM). The movement of ball assemblies was graphically displayed with some snapshots from start of the milling to 0.20 s. From these simulation results, the grinding zone in the mill was confirmed to be distributed into two regions, which is near the stirrer and the side wall of mill around the stirrer. The power changing the rotation speed of stirrer was examined based on the micro interactive forces at all the contact points between ball-to-ball and between ball-to-stirrer. DEM is a very powerful tool for the microanalysis of movement of balls, which could not have been solved by a conventional experimental method.
Dept. of Precision & Mechanical Engineering and Eco-Friendly Heat & Cooling Energy Mechanical Research Team, BK21, Gyeongsang National University, 445 Inpyeong-dong, Tongyoung, Gyeongnam, 650-160, Korea
Kim, S., Choi, W.S. Analysis of ball movement for research of grinding mechanism of a stirred ball mill with 3D discrete element method. Korean J. Chem. Eng. 25, 585592 (2008). https://doi.org/10.1007/s11814-008-0099-x
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