characteristics of ball mills for cement

ball mills - an overview | sciencedirect topics

ball mills - an overview | sciencedirect topics

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 [23].

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 [70]. 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 [71].

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 [11]. 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.[44] 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.[58] and El-Eskandarany etal.[59] 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.[60] 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,[61] using for example cold-rolling approach,[62] 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.[8]

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).

how many types of ball mill? - jxsc machine

how many types of ball mill? - jxsc machine

Ball mill is important grinding equipment in the beneficiation plant, used for grinding ores to powders before they are magnetically or chemically processed. How Many Types of Ball Mill? There are many manufacturers producing ball mills on the market, how to choose the right one suits for your production? Here are a quick introduction and classification of ball mills for your reference.

1. Short-cylinder ball mill: The length (L) of the cylinder is less than twice the diameter (D) of the cylinder, that is, the ball mill with L 2D is a short-cylinder ball mill. Single-bin structure ball mill, which is mainly used for coarse grinding or primary grinding, has high efficiency.

2. Rod mills usually equipped with steel rod which diameter mostly between 50-100mm, need a longer grinding time. The number of bins in a rod mill is generally two to four, and there are some differences in the grinding media loaded in each bin. To ensure the final effect of grinding, the staff will place the cylindrical steel rod in the first bin, and the steel ball or steel segment in several other bins.

3. The grinding media in the gravel mill mainly include pebbles, gravel, sandstone, ceramic balls, etc. Gravel mills mostly use porcelain or granite as lining boards, and are widely used in the production fields of cement, ceramics and so on.

1. Overflow type: discharge ore through the hollow shaft. When the ore discharge surface is higher than the slurry surface, the finished product is discharged and the ore is automatically discharged by gravity, thus the overflow ball mill saves energy.

2. Grate discharge ball mill: the ore is discharged through the grate plate. The grating part can strictly control the minerals discharge size that meets the demand, it has a good effect on fine particle grinding.

2. The intermittent ball mill can not continuous operation, at the same specification, its output is lower. The feeding and discharging time is set according to the characteristics of the grinding material. The intermittent ball mill is suitable for the mixing and grinding of materials, lower power consumption. Many ball mill has been transformed into continuous, so users do not have to worry about the production output problem.

1. Central transmission ball mill: The driving power of this type of mill is in the center of the fuselage, and the motor realizes the operation of the ball mill through a reducer. During operation, the hollow shaft in the center of the ball mill drives the grinding body to rotate under the drive of the power system.

1. Wet ball mill: Water is added at the same time as the material is fed, and the material is discharged into a certain concentration of slurry and discharged. In a closed-circuit system, it is composed of a closed-circuit operation with a hydraulic classification device.

2. Dry ball mill: Some discharges are drawn by air current, and the mill and wind classification device form a closed circuit. For example, the cement mill adopts self-flow discharge. The capacity of the dry ball mill is larger, and the energy-saving effect of wet ball mill is better.

1. According to the working conditions and material characteristic Minerals that cannot be touched with water, minerals that are sticky after adding water, and the mining plant in areas where water resources are scarce, are suitable for grinding with a dry ball mill. Under other conditions, it is better to use a wet ball mill which has a better grinding effect, and energy-saving performance. 2. Energy consumption Choose an energy-saving ball mill or ordinary ball mill according to the capacity of electric power supply and energy consumption limitation. 3. Capacity If you require high capacity, choose a continuous ball mill. The vibrating feeder can automatically feed, so the continuous ball mill can keep running for 24 hours. JXSC provides you free selection service, engineers online!

cement grinding in ball mills and vortex layer devices - globecore. oil purification systems

cement grinding in ball mills and vortex layer devices - globecore. oil purification systems

Cement and concrete are the second most used substances in the world, after water. On average, the per capita consumption of cement is one ton. This material is widely used as a binder in the production of concrete, reinforced concrete and various construction mixes. The demand for cement in construction of new buildings, repairs and reconstruction is always high.

The process of cement production includes several stages and concludes by grinding clinker with the addition of gypsum. Grinding precision is an important characteristic of cement, since it defines the amount of material capable of hydration. The rate of hydration and strength increase also depends on this parameter. Grinding processes are quite energy intensive, with up to 20% of the worlds energy production consumed by grinding equipment. Clinker grinding accounts for approximately 70% of energy costs in cement production. The objectives of the cement production industry at the modern stage are therefore as follows:

The principle of the ball mill operation is simple: it consists of a rotating drum and grinding media (cylinders, balls etc). The material is placed into the drum which starts rotating. The grinding media and the substance both come in circular motion and at a certain point drop from the walls the bottom of the drum. The grinding is achieved by attrition (particles of the ground substance and the grinding media move relative to each other) and impacts. Ball mills are most commonly used in cement factories to grind the raw material and finely grind the cement.

The use of ball mills in cement grinding is due to several factors, among which are relatively simple design and high processing rate. However, these machines have certain limitations as well. It is known that only 2 to 20% of the energy is consumed by the grinding proper, while the rest is expanded on overcoming friction, on vibrations and is dissipated as heat. Ball mills also are material-intensive due to high wear of the components. These mills are also very noisy.

The vortex layer device is, in a sense, similar to the ball mill, but the effect on the processed material is different in principle. The first similarity is the chamber, where the material is ground. However, the chamber of the vortex layer device is stationary, smaller than a drum and is always made of a non-magnetic material. The second similarity is the presence of grinding media (which, in the case of the vortex layer device, are cylindrical and made of ferromagnetic material). While the grinding media in the ball mill is put into motion by the motion of the drum, in the case of the vortex layer device, the grinding media moves along complex trajectories under the influence of a rotating electromagnetic field. This field is generated inside the chamber by electromagnetic induction coils. In fact, the design of the machine is similar to a short-circuited cage motor without the rotor (the rotor being replaced with a tube, i.e. the processing chamber).

Mean power of these effects is such that not only cement is ground and activated, but the process is sharply intensified as well. Every ferromagtnetic particle is both a grinding and mixing medium. Moving along complex trajectories, these particles cover the entire volume of the chamber another important distinction of the vortex layer device from a ball mill. If the process takes tens of minutes and hours in other mills, the required retention time in vortex layer devices is measured in seconds or minutes.

Vortex layer devices are superior to ball mills in several respects. Specifically, vortex layer devices are multifunctional. Unlike the ball mills, they can grind cement extremely fine without loss of efficiency, while at the same time activating the material with the electromagnetic field. All the processes occur a lot faster. E.g., increasing the mean surface area from 2800 to 6800 cm2/g is achieved as soon as within 120 seconds of processing. The noise output of the device is negligible, as compared to the ball mill. Cement can be activated even without ferromagnetic particles, simply passing it through process chamber. In this case, the processing capacity increases severalfold.

Brief processing of cement in the vortex layer device ensures a reduction of concrete hardening time under natural conditions, a reduction of cement consumption or improved concrete grade, as well as achievement of high mix plasticity. The use of activated cement in all cement compounds ensures high physical and mechanical characteristics of the products.

The vortex layer device can also magnetize water for concrete mixes. Using magnetic water for mixing significantly improves the product strength. Regular water involves a lengthy period of cement crystallization, whereas in the case of magnetic water, the plastic strength starts growing almost immediately after mixing.

The conclusion is that the vortex layer device used for cement grinding addresses three main issues of the cement production industry: it increases grinding fineness and reduces the energy costs of the process, while at the same time remaining simple and reliable in operation.

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cement grinding in ball mills and vortex layer devices

cement grinding in ball mills and vortex layer devices

Cement and concrete are the second most used substances in the world, after water. On average, the per capita consumption of cement is one ton. This material is widely used as a binder in the production of concrete, reinforced concrete and various construction mixes. The demand for cement in construction of new buildings, repairs and reconstruction is always high.

The process of cement production includes several stages and concludes by grinding clinker with the addition of gypsum. Grinding precision is an important characteristic of cement, since it defines the amount of material capable of hydration. The rate of hydration and strength increase also depends on this parameter. Grinding processes are quite energy intensive, with up to 20% of the worlds energy production consumed by grinding equipment. Clinker grinding accounts for approximately 70% of energy costs in cement production. The objectives of the cement production industry at the modern stage are therefore as follows:

The principle of the ball mill operation is simple: it consists of a rotating drum and grinding media (cylinders, balls etc). The material is placed into the drum which starts rotating. The grinding media and the substance both come in circular motion and at a certain point drop from the walls the bottom of the drum. The grinding is achieved by attrition (particles of the ground substance and the grinding media move relative to each other) and impacts. Ball mills are most commonly used in cement factories to grind the raw material and finely grind the cement.

The use of ball mills in cement grinding is due to several factors, among which are relatively simple design and high processing rate. However, these machines have certain limitations as well. It is known that only 2 to 20% of the energy is consumed by the grinding proper, while the rest is expanded on overcoming friction, on vibrations and is dissipated as heat. Ball mills also are material-intensive due to high wear of the components. These mills are also very noisy.

The vortex layer device is, in a sense, similar to the ball mill, but the effect on the processed material is different in principle. The first similarity is the chamber, where the material is ground. However, the chamber of the vortex layer device is stationary, smaller than a drum and is always made of a non-magnetic material. The second similarity is the presence of grinding media (which, in the case of the vortex layer device, are cylindrical and made of ferromagnetic material). While the grinding media in the ball mill is put into motion by the motion of the drum, in the case of the vortex layer device, the grinding media moves along complex trajectories under the influence of a rotating electromagnetic field. This field is generated inside the chamber by electromagnetic induction coils. In fact, the design of the machine is similar to a short-circuited cage motor without the rotor (the rotor being replaced with a tube, i.e. the processing chamber).

Mean power of these effects is such that not only cement is ground and activated, but the process is sharply intensified as well. Every ferromagtnetic particle is both a grinding and mixing medium. Moving along complex trajectories, these particles cover the entire volume of the chamber another important distinction of the vortex layer device from a ball mill. If the process takes tens of minutes and hours in other mills, the required retention time in vortex layer devices is measured in seconds or minutes.

Vortex layer devices are superior to ball mills in several respects. Specifically, vortex layer devices are multifunctional. Unlike the ball mills, they can grind cement extremely fine without loss of efficiency, while at the same time activating the material with the electromagnetic field. All the processes occur a lot faster. E.g., increasing the mean surface area from 2800 to 6800 cm2/g is achieved as soon as within 120 seconds of processing. The noise output of the device is negligible, as compared to the ball mill. Cement can be activated even without ferromagnetic particles, simply passing it through process chamber. In this case, the processing capacity increases severalfold.

Brief processing of cement in the vortex layer device ensures a reduction of concrete hardening time under natural conditions, a reduction of cement consumption or improved concrete grade, as well as achievement of high mix plasticity. The use of activated cement in all cement compounds ensures high physical and mechanical characteristics of the products.

The vortex layer device can also magnetize water for concrete mixes. Using magnetic water for mixing significantly improves the product strength. Regular water involves a lengthy period of cement crystallization, whereas in the case of magnetic water, the plastic strength starts growing almost immediately after mixing.

The conclusion is that the vortex layer device used for cement grinding addresses three main issues of the cement production industry: it increases grinding fineness and reduces the energy costs of the process, while at the same time remaining simple and reliable in operation.

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what is ball mill | how many types of ball mills | m&c

what is ball mill | how many types of ball mills | m&c

Ball mill is a very important mineral grading equipment, which is indispensable for mineral processing, building materials, metallurgy and chemical industry. With the need of market, a variety of different types of ball mills have emerged. According to different standards, there are many types of ball mills.

1. Short Cylinder Ball Mill: The ball mill with the cylinder length (L) less than 2 times of the cylinder diameter, i.e. the ball mill with L 2D is short cylinder ball mill, which is usually of single bin structure, mainly used for rough grinding or primary grinding operation, and can realize the wide use of 2-3 ball mills in series.

3. Gravel Mill: The grinding medium mainly includes pebble, gravel, sand, porcelain ball, etc. Most of the gravel mills use porcelain or granite as lining plates, which are widely used in the production of color cement, white cement, ceramics and other fields.

1. Tail Discharge Mill: The head and tail of tail discharge mill are used as the inlet and outlet of materials. When the mill is working, the material is fed from the inlet end and discharged from the other end.

2. Middle Discharge Mill: The inlet of the middle discharge mill is at both ends, and the outlet is in the middle of the mill. Generally, materials are fed from both ends and then discharged from the middle of the cylinder.

1. Center Drive Ball Mill: The drive power device is in the center of the fuselage, and the motor realizes the operation of the ball mill through the reducer. In operation, the hollow shaft in the center of the ball mill drives the grinding body to rotate under the drive of the power system.

1. Wet Type Ball Mill: Water is added at the same time of feeding, and the material is discharged into a certain concentration of slurry. In the closed-circuit system, it forms a closed-circuit operation with the hydraulic grading equipment.

1. Vertical Ball Mill: The vertical ball mill is a new type of ball mill which places the cylinder upright. Through a large number of experiments, it is found that the vertical ball mill has the advantages of high grinding efficiency, low energy consumption and low noise.

2. Horizontal Ball Mill: The horizontal ball mill is used for grinding and dispersing under the closed condition to prevent solvent volatilization. It is especially suitable for fine grinding and mixing of high-purity materials.

energy efficient cement ball mill from flsmidth

energy efficient cement ball mill from flsmidth

You decide whether to operate the mill in open or closed circuit, with or without a pre-grinder and with side or central drive, according to your plant layout and end product specifications. Even the lining types are tailored to your operating parameters.

In addition, the large through-flow areas enable the mill to operate with large volumes of venting air and a low pressure drop across the mill. This reduces the energy consumption of the mill ventilation fan and keeps your energy costs down.

The mill is based on standard modules and can be adapted to your plant layout, end product specifications and drive type. The horizontal slide shoe bearing design enables much simpler foundations and reduced installation height, making installation quicker and less expensive.

Our shell linings are designed to suit the task at hand. In our two-compartment cement mills, the first compartment (for coarse grinding) has a step lining suitable for large grinding media. It protects the shell while ensuring optimum lifting of the mill charge. In the second compartment (and also in our one-compartment cement mills) we use a corrugated lining designed to obtain the maximum power absorption and grinding efficiency. For special applications, we can supply a classifying shell lining for fine grinding in the mill.

In fact, the entire mill is protected with bolted on lining plates designed for the specific wear faced by each part of the mill. This attention to detail ensures both minimal wear and easy maintenance. When a wear part has reached the end of its life, it is easily replaced.

The grinding media are supplied in various sizes to ensure optimum grinding efficiency. The STANEX diaphragm is designed to maximise the effective grinding area, enabling a higher throughput. It is fitted with adjustable lifters to ensure the material levels in each compartment are right. Best of all, the STANEX diaphragm works for all applications, even when material flow rates are high and the mill feed is moist.

The mills are typically driven by our FLSmidth MAAG LGDX side drive - gearing rated to the latest proven AGMA standards. The mill drive is provided with an auxiliary drive for slow turning of the mill. The LGDX includes two independent lubrication systems, one which services the girth gear guard and intakes more dust, and a second which supplies oil for the fast-rotating gearing and bearings and stays clean. If requested, however, the mills can be provided with a central drive: the FLSmidth MAAG CPU planetary gearbox. The mill design differs slightly, depending on whether the side or central drive is chosen.

Each grinding compartment has two man-hole covers to give easy access for maintenance. As there are minimal moving parts, the maintenance requirement is low and simple changes like replacing wear linings and topping up grinding media can be completed quickly and easily. Horizontal slide shoe bearings prevent oil spillages from the casing and offers easy replacement of slide shoes.

Buying a new mill is a huge investment. With over a century of ball mill experience and more than 4000 installations worldwide, rest assured we have the expertise to deliver the right solution for your project. Our ball mill is based on standard modules and the highly flexible design can be adapted to your requirements. The mill comprises the following parts.

The mill body consists of an all-welded mill shell and a T-sectional welded-up slide ring at either end, the cylindrical part of which is welded onto the ends of the shell. The mill shell has four manholes, two for each grinding compartment.

Each slide ring runs in a bearing with two self-aligning and hydrodynamically lubricated slide shoes. One of the slide shoes at the drive end holds the mill in axial direction. In the others, the slide rings can move freely in axial direction to allow for longitudinal thermal expansion and contraction of the mill body.

The slide shoes are water-cooled, and each bearing is provided with a panel-enclosed lubrication unit including oil tank, motorised low- and high-pressure oil pumps, as well as an oil conditioning circuit with motorised pump for heating/cooling and filtration of the oil.

The stationary steel plate inlet duct leads the venting air into the mill. It is equipped with a manually operated throttle valve and a pressure monitor to adjust the pressure at the inlet end, thus preventing dust emission from the inlet. The feed chute is lined with bolted-on wear plates and slopes down through the air duct to the mill inlet opening.

The more control you have over the mill, the better your grinding efficiency is likely to be. Our ball mills include monitoring systems to continuously measure the material and air temperatures as well as the pressure at the mill exit. The venting of the mill is adjusted by a damper in the inlet to the mill fan. And the material fill level is continuously monitored by means of sensors. For ball mills operating in closed circuit, the circulation load is monitored by weighing the flow of reject material from the separator. These measures ensure you achieve optimum mill performance, giving you the quality, efficiency, safetyand reliability that you need.

FLSmidth provides sustainable productivity to the global mining and cement industries. We deliver market-leading engineering, equipment and service solutions that enable our customers to improve performance, drive down costs and reduce environmental impact. Our operations span the globe and we are close to 10,200 employees, present in more than 60 countries. In 2020, FLSmidth generated revenue of DKK 16.4 billion. MissionZero is our sustainability ambition towards zero emissions in mining and cement by 2030.

basic cement plant layout process cement forum the cement institute forum

basic cement plant layout process cement forum the cement institute forum

00 Limestone Quarry and Crushing PlantThe major raw material for cement production is limestone. The limestone most suitable for cement production must have some ingredients in specified quantities i.e., calcium carbonates, silica, alumina, iron, etc. Typically, cement plant locations are based upon the availability of good quality limestone in the vicinity. The quarrying operations are done by the cement producer using the open cast mining process. Quarrying is done through drilling and subsequently, using heavy earth moving equipment such as bulldozers, payloaders, and dumpers. The quarried raw material is then transported to the cement plant, using mechanical conveying equipment such as ropeways or belt conveyors, or by vehicles like wagons and trucks. The quarried limestone is normally in the form of big boulders, ranging from a few inches to meters in size. These varying sizes of limestone need to be crushed to a size of about 10 mm in order to be prepared for finish-grinding. There are mainly two types of crushers available for this purpose- compression type or impact type crushers. There are many types of compression type crushers such as jaw crusher, gyratory crusher, cone crusher, roll crusher. The impact of technology is used in a hammer crusher/impact crusher. Crushing is done either in two stages or in a single stage. In the two-stage crushing system, a compression type crusher is used in the first stage for raw crushing, followed by impact/hammer crusher in the second stage. In single-stage crushing, an impact-type crusher is used. The selection of the crusher depends mainly on the characteristics of the raw materials. This selection is further guided by the particle-size distribution requirements of the downstream equipment such as raw mills and lastly by financial considerations.

The raw material is stored at either the quarry or at the plant. Typically, circular or longitudinal stockpiles are used to store the material. A number of layers are stacked in circular or longitudinal piles and are reclaimed in transverse, cross-sectional slices. The stockpiles consist of separate layers/piles of different kinds of raw material. This is used in segregating the raw material quality-wise. The required quantity of the various raw materials is thus easily extracted for use. The extraction of different qualities of raw material is monitored and controlled in order to maintain the desired composition of raw meal, suitable for feeding into the kiln.

In order to get the required composition of raw material, certain additives such as iron ore, bauxite, laterite, quartzite, and fluorspar are added in the required quantities. These additives are stored at the plant in separate hoppers and are extracted using belt conveyors in conjunction with belt-weighing equipment. This ensures that only the required quantities are extracted and added to the raw material.

The raw material is finish-ground before being fed into the kiln for clinkering. This grinding is done using either ball mills or vertical roller mills (VRM). The raw material is simultaneously dried. Ball mills use impact with attrition principles for grinding the raw material. Inside the ball mills, various sizes of balls are used and classifying liners are used to maintain the position of different sizes of balls. The larger sized balls are utilized for impact grinding and the smaller balls for attrition. VRM uses the compression principle to grind the raw material. The choice between a ball mill and VRM is governed by many factors such as the moisture content of the raw material, the size of the plant, the abrasiveness of the material, the energy consumption levels, reliability, and finally financial considerations. Ball mills are suitable for low and medium moisture content in the range of five to six percent and are preferred for abrasive material. The main advantage of VRM is higher grinding efficiency and the ability to accept material with higher moisture content. Normally the energy consumption level in VRM is 10 to 20 percent lower than in ball mills.

Normally there are various sources of limestone, each with different qualities, which are added with various additives to get the required composition of raw mix. As there are various sources of raw materials, it becomes necessary to blend and homogenize these different materials efficiently to counteract fluctuation in the chemical composition of the raw meal. The variations in the composition of kiln feed have very adverse impacts on the efficiency of the kiln. It results in undesired coating and ring formation inside the kiln. In order to blend and homogenize the raw materials properly, continuous blending silos are used.

The most important activity in cement manufacturing is clinkering (or burning) of raw material. Clinkering takes place in the kiln and the preheater system. Preheater systems offer heat transfer from the hot kiln gases.

The conditioning tower is used to reduce the temperature and to increase the moisture level of the dusty exhaust gas from the kiln, before it is passed through the baghouse and ESPs. It is called a conditioning tower because it conditions the hot gas, thus making it more suitable for the ESP and baghouse to extract dust from it. Electrostatic Precipitators are used in cement plants particularly for removal of dust from the exit gases of cement kilns and from the exhaust air discharged by dryers, combined grinding and drying plants, finishing mills, and raw mills through water injection. Through ESPs, the dust-laden gas is made to flow through a chamber usually horizontally, during which it passes through one or more high voltage electric fields formed by alternate discharge electrodes and plate type collecting electrodes. By the action of an electric field, the dust particles, which have become electrically charged by negative gas ions that are formed at the discharge electrodes and attach themselves to the particles, fly to the collecting electrodes and are deposited there. The dust is dislodged from these electrodes by rapping and thus falls into the receiving hopper at the base of the precipitator casing.

A kiln is the heart of any cement plant. It is basically a long cylindrical-shaped pipe and rotates in a horizontal position. Its internal surface is lined by refractory bricks. Limestone and additives are calcined in this. The output of the kiln is called clinker.

The output of the kiln is stored before it is fed to the cement mill for conversion to cement. This storage is called clinker storage, if it is used for clinker storage purpose. If the storage space is used for gypsum storage, it is called gypsum storage. The storage may be of silo type or covered stacker reclaimer type or simply a gantry type. Silo type clinker storage has the advantage that there is no dust pollution and spillage of clinker. The same advantage can be achieved through the stacker reclaimer type as well. However, there is a little bit of dust generated. Gantry type is not used in modern cement plants because of its environmental unfriendly nature.

The output of the kiln is stored before it is fed to the cement mill for conversion to into cement. This storage is called clinker storage, if it is used for clinker storage purpose. If the storage space is used for gypsum storage, it is called gypsum storage. The storage may be of silo type or covered stacker reclaimer type or simply a gantry type. Silo type clinker storage has the advantage that there is no dust pollution and spillage of clinker. The same advantage can be achieved through stacker reclaimer type as well However, there is a little bit of dust generated. Gantry type is not used in modern cement plants because of its environmental unfriendly nature. Limestone coming out of the quarry is crushed in multiplestages in a sizing plant before it is put in limestone stockpile. Crusher are mainly of two types viz. Jaw crusher and Hammer crusher. Jaw crusher is basically a simple mechanism having two plates one fixed and another moving. This is also called primary crusher. Hammer crusher has got metallic hammer mounted on the axes and the sizing achieved by the impact of the hammer.

The coal mill building houses the mill for grinding lumpy coals. This fine ground coal is used for burning in the kiln. The mills used for coal grinding and drying are either trumbling mills (tube mills) or roller mills.

Clinker, along with additives, is ground in a cement mill. The output of a cement mill is the final product viz. Cement. In a cement mill, there is a cylindrical shell lying horizontal which contains metallic balls and as it rotates, the crushing action of the balls helps in grinding the clinker to a fine powder. The term baghouse is applied to large filters containing a number of tubular bags mounted in a usually rectangular casing. The dust-laden air is drawn through them by suction. The baghouse is used to remove dusty particles from discharge of different equipment such as cement mill, coal mill, and kiln. In a baghouse system discharge gas containing dusty particles is passed through a series of bags made of strong fabrics.

CHAENG have advanced technology production equipment and a professional technical team. CHAENG holds deep domain knowledge of the industry and hence, is equipped to offer customized service that are directed to meet the needs of clients from cement plants.

Cement production line includes crushing and pre-homogenization, raw material preparation & homogenization, preheating & decomposition, cement clinker sintering, cement grinding and packaging etc. CHAENG have the ability to built 300t / d ~ 3000 t /d cement production line independently, And has extensive experience in the design and construction, built many large cement production line

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