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copper wet ball mill improvement

wet ball mill/wet type ball mill/wet ball milling machine--zhengzhou bobang heavy industry machinery co.,ltd

wet ball mill/wet type ball mill/wet ball milling machine--zhengzhou bobang heavy industry machinery co.,ltd

Wet type ball mill are mostly used in the industry production. It is to increase the high grinding efficiency under the ball mill grinding and striking, from which the granularity is even and no flying dust with little noise, being the most universal powder machine in the benefication as powder grinding the ferrous metal like gold, silver, plumbum, zinc,copper,molybdenum,manganese,tungsten etc, as the nonmetal powder grinding like graphite,feldspar, potash feldspar, phosphorus ore, fluorite, clay, and swell soil etc. The wet type ball mill need to add the liquid into the grinding ball media auxiliary (water or ethanol). The material output gate is trumpet shape, with screw device inside, easy to discharging the material.

Copyright Zhengzhou Bobang Heavy Industry Machinery Co.,Ltd. E-mail : [email protected] Tel0086- 86656957 Address No.11 West Construction Road, Zhongyuan District,Zhengzhou City,Henan Province, China

henan seasun heavy industry machinery co., ltd

henan seasun heavy industry machinery co., ltd

Wet ball mill's application: Wet ball mill (wet grinding ball mill)is a kind of energy-saving ball mill, in industrial production, especially in mineral processing industry, has the most common application of grinding machine. Grind non-ferrous metal, such as: gold, silver, lead, zinc, copper, molybdenum, manganese, tungsten,etc;grind nonmetal,such as graphite, feldspar, potassium feldspar, rock phosphate, fluorite, clay, bentonite, etc.The wet ball mill produced by Henan shisheng has the reasonable price,welcome customers to plant for choosing. Wet ball mill's working principle: Wet ball mill ( wet grinding ball mill)is a horizontal rotating device transmitted by the outer gear.The material goes to the first hopper after the spiraling by the quill shaft from the feeding equipment. The hopper has ladder sheathing or corrugated sheathing with steel balls inside, which will fall under the effect of centrifugal force by barrel turning to ram hard and grind material. After the kibbling in the first hopper, by monolayer partition panel, the material will enter the second hopper, which has plane scale board with steel ball inside to grind material. The powder material will be discharged from the grid plate to finish the grinding operation. Wet ball mill's structure: 1, feed screw to feed materials. 2, barrel part,barrel body has a manhole for maintenance and replacement of the lining board in the barrel. 3, discharge part to discharge the qualified products for ball mill. 4, main bearing parts. 5, drive part. Wet ball mill's technical parameters: Model Cylinder Speed (r/min) Ball Charge (t) Feed Particle Size (mm) Discharge Size (mm) Output (t/h) Motor Power (kw) Weight (t) 900*1800 38 1.5 <=20 0.075-0.89 0.65 - 2 18.5 3.6 900*2100 38 1.3-1.4 <=15 0.075-0.83 0.7 - 3.5 18.5 3.9 900*3000 38 2.7 <=20 0.075-0.89 1.1 - 3.5 22 4.5 1200*2400 32 3.8 <=25 0.075 -0.6 1.5 - 4.8 30 11.5 1200*2800 32 3.3-3.5 <=25 0.075-0.6 2 - 6 30 13 1200*4500 32 7 <=25 0.074-0.4 1.6 - 5.8 45 13.8 1500*3000 27 8 <=25 0.074-0.4 2 - 5 75 17 1500*3500 27 6.75-6.4 <=25 0.075-0.4 3 - 7 75 17.5 1500*4500 27 14 <=25 0.074-0.4 3.5 - 12 110 21 1500*5700 27 15 <=25 0.074-0.4 3.5 - 8 115 24.7 1830*3000 24 18 <=25 0.074-0.4 4 - 10 130 28 1830*3600 24 10.6-11.35 <=25 0.075-0.4 5 - 22 130 33.5 1830*7000 24 25 <=25 0.074-0.4 7.5 - 17 210 36 2100*3600 22 14-15.2 <=25 0.075-0.4 15 - 36 370 46.8 2200*5500 21 30 <=25 0.074-0.4 10 - 22 210 48.5 2200*6500 21 31 <=25 0.074-0.4 14 - 26 380 52.8 2200*7500 21 33 <=25 0.074-0.4 16 - 29 380 56 2400*3000 20.6 15.5-16.6 <=25 0.075-0.4 22 - 24 245 59 2400*4500 21 30 <=25 0.074-0.4 8.5 - 60 380 65 2700*3600 20.6 39 <=25 0.074-0.4 12 - 70 400 91.3 2700*4000 20.7 40 <=25 0.074-0.4 12 - 80 400 94 2700*4500 20.7 48 <=25 0.074-0.4 12 - 90 430 102 3200*4500 18 65 <=25 0.075-0.4 set according to the process conditions 800 137

Wet ball mill's application: Wet ball mill (wet grinding ball mill)is a kind of energy-saving ball mill, in industrial production, especially in mineral processing industry, has the most common application of grinding machine. Grind non-ferrous metal, such as: gold, silver, lead, zinc, copper, molybdenum, manganese, tungsten,etc;grind nonmetal,such as graphite, feldspar, potassium feldspar, rock phosphate, fluorite, clay, bentonite, etc.The wet ball mill produced by Henan shisheng has the reasonable price,welcome customers to plant for choosing.

Wet ball mill's working principle: Wet ball mill ( wet grinding ball mill)is a horizontal rotating device transmitted by the outer gear.The material goes to the first hopper after the spiraling by the quill shaft from the feeding equipment. The hopper has ladder sheathing or corrugated sheathing with steel balls inside, which will fall under the effect of centrifugal force by barrel turning to ram hard and grind material. After the kibbling in the first hopper, by monolayer partition panel, the material will enter the second hopper, which has plane scale board with steel ball inside to grind material. The powder material will be discharged from the grid plate to finish the grinding operation.

Wet ball mill's structure: 1, feed screw to feed materials. 2, barrel part,barrel body has a manhole for maintenance and replacement of the lining board in the barrel. 3, discharge part to discharge the qualified products for ball mill. 4, main bearing parts. 5, drive part.

Model Cylinder Speed (r/min) Ball Charge (t) Feed Particle Size (mm) Discharge Size (mm) Output (t/h) Motor Power (kw) Weight (t) 900*1800 38 1.5 <=20 0.075-0.89 0.65 - 2 18.5 3.6 900*2100 38 1.3-1.4 <=15 0.075-0.83 0.7 - 3.5 18.5 3.9 900*3000 38 2.7 <=20 0.075-0.89 1.1 - 3.5 22 4.5 1200*2400 32 3.8 <=25 0.075 -0.6 1.5 - 4.8 30 11.5 1200*2800 32 3.3-3.5 <=25 0.075-0.6 2 - 6 30 13 1200*4500 32 7 <=25 0.074-0.4 1.6 - 5.8 45 13.8 1500*3000 27 8 <=25 0.074-0.4 2 - 5 75 17 1500*3500 27 6.75-6.4 <=25 0.075-0.4 3 - 7 75 17.5 1500*4500 27 14 <=25 0.074-0.4 3.5 - 12 110 21 1500*5700 27 15 <=25 0.074-0.4 3.5 - 8 115 24.7 1830*3000 24 18 <=25 0.074-0.4 4 - 10 130 28 1830*3600 24 10.6-11.35 <=25 0.075-0.4 5 - 22 130 33.5 1830*7000 24 25 <=25 0.074-0.4 7.5 - 17 210 36 2100*3600 22 14-15.2 <=25 0.075-0.4 15 - 36 370 46.8 2200*5500 21 30 <=25 0.074-0.4 10 - 22 210 48.5 2200*6500 21 31 <=25 0.074-0.4 14 - 26 380 52.8 2200*7500 21 33 <=25 0.074-0.4 16 - 29 380 56 2400*3000 20.6 15.5-16.6 <=25 0.075-0.4 22 - 24 245 59 2400*4500 21 30 <=25 0.074-0.4 8.5 - 60 380 65 2700*3600 20.6 39 <=25 0.074-0.4 12 - 70 400 91.3 2700*4000 20.7 40 <=25 0.074-0.4 12 - 80 400 94 2700*4500 20.7 48 <=25 0.074-0.4 12 - 90 430 102 3200*4500 18 65 <=25 0.075-0.4 set according to the process conditions 800 137

how to improve ball mill performance

how to improve ball mill performance

Application of value engineering techniques to grinding process modelling led to the identification of two basic functions of the ball mill-classifier circuit. In terms of a specified circuit product size which is used to differentiate between coarse or oversize material and fines or undersize material, these basic functions are (a) breakage of the coarse material and (b) removal of the fines. It was proposed that it may be useful to relate circuit design and operating variables to these basic circuit functions, which although related, are conceptually quite distinguishable. If each could be quantified by a suitable parameter, then either or the two together may be correlated to overall circuit efficiency, and hence used to link individual design and operating variables to overall circuit performance.

Major design and operating variables in closed circuit ball milling of a specified feed to a desired product size are summarized in Table 1. The purpose of process modelling is to establish cause and effect relationships between physical design and operating variables and the performance objectives of the circuit. Subsequently, output and efficiency can be maximized. The fundamental issue addressed by ball mill circuit modelling is thus depicted in Figure 1 (McIvor, 1989).

In the simplest form of plant experimentation, a key performance parameter (such as the fineness of the final product) is measured with and without a specific change to the circuit. Within the constraints imposed by the accuracy of measurements and assumptions about the constancy of other inputs (including the ore characteristics), the relative values of this parameter are used to evaluate the effect of the change on circuit performance.

Bond work index analysis takes this method of experimentation several steps further. During comparative testwork, variations in the ore grindability, grinding energy input, and feed and product sizing are measured and accounted for through the grinding circuit model embodied in the work index formulation. For each set of data, both the circuit operating work index and the laboratory test work index of the circuit feed are determined. Relative work index efficiencies with and without the change to the circuit can then be calculated and compared.

Consider a ball mill circuit processing material of a given feed size and at a given throughput rate to a target product size, the latter which once again distinguishes the fines from the coarse material. The production rate of fines or new product size material can be calculated from the circuit feed and product size distributions and the throughput rate of the circuit. Based on the energy expended in the ball mill, the production rate of new product size material (tonnes/h) equals the amount produced per unit of energy applied (tonnes/kwh) times the rate at which energy is applied (kwh/h). The rate at which energy is applied is the power draw of the ball mill. If we then define the production per unit, of energy applied as the energy specific production rate of the circuit, then we can write the following equation:

All the production of new product size material takes place in the mill as coarse is ground into fines. However, the proportion of the total mill power applied to size reduction of coarse particles is equal to the fraction of coarse solids inventory, or the so defined circuit classification system efficiency.

The mill specific grinding rate reflects both the efficiency of the mill environment in breaking the coarse particles, as well as the grindability characteristic of the ore over the particular size reduction range.

To arrive at a term which reflects only the efficiency of the mill environment, we must factor out the grindability of the ore, such as the net grams per revolution measured in a Bond work index test. This will yield the specific grinding rate in the plant ball mill relative to the measured specific grinding rate in a standard test mill, and may be termed the grinding rate ratio.

The grinding rate ratio may be considered dimensionless because each revolution of the test mill requires a fixed amount of power. It is based on breakage of only the coarse material in both the plant ball mill and the standard laboratory test mill. It is therefore proposed that the grinding rate ratio is a direct measure of the relative overall breakage efficiency of the environment of the plant ball mill.

The above described parameters for system breakage and classification system efficiency factor the overall task of the ball mill circuit into its two distinct basic functions, namely, fines generation and fines removal. The effect of design and operating variables on each can be studied separately, and when the product of the two is maximized, maximum overall circuit efficiency will be achieved. Equation 2 may be re-written as:

This has been termed the ball mill circuit functional performance equation (McIvor, 1989). It states that the output of new product size material of a ball mill circuit with a given feed size is determined by:

a. the total mill power draw; b. the classification system efficiency, which defines the fraction of the total mill power effectively applied to the grinding of coarse material; c. the grindability characteristic of the ore over the size reduction range of the circuit; and, d. the breakage efficiency of the ball mill environment on the coarse material.

While all four factors clearly influence the circuit output, overall circuit efficiency will be determined by classification and breakage efficiency. Specific design and operating variables can now be considered in terms of their individual effects on classification and breakage efficiency, and subsequently on the overall efficiency of the circuit. This provides an intermediate level of ball mill circuit performance characterization, as shown in Figure 5.

wet grinding mill

wet grinding mill

Wet Grinding Mills is mainly used for separation of gold, silver, lead, zinc, molybdenum,iron, copper, antimony, tungsten, tin and other minerals selected. With less investment, fast results, small footprint saving power, sturdiness and durability, ease of maintenance and high return on investment. It is the preferred production for alternative ball mill, is ideal for smalland medium enterprises dressing.

1.Firstlythemotorwilltransmitthemotivepowertoreductiongears,underthedriveofreductiongearsthatpassingthroughlargeverticalspindle,thenthepowercabienttransferstoabovewhippletree.

3.Afteraddingintoore,thematerialsareundertheextrusionofgrindingrollerweighttorevolutingandrotatingwithrunnerwheels,whentwistingthatcomingintobeinghugefrictionforcewithgrindingbase,aftersufferingrepeatedextrusion,rub,grindingthatbecrushedthoroughly.

4.Undertheeffectionofgrindingrolleroperating,thecrushedmaterialsandthewater mixed intensively to float on it uniformly,then passing through the overflow discharge gate that setting up on the mill basin to discharge,after thatenter intonext operation procedure to process.

ball mills

ball mills

Ball Mills What Are These Machines and How Do They Work? Short flash video at bottom of page showing batch ball mill grinding in lab. May have to click on browser "Allow Active X blocked content" to play A Ball Mill grinds material by rotating a cylinder with steel grinding balls, causing the balls to fall back into the cylinder and onto the material to be ground. The rotation is usually between 4 to 20 revolutions per minute, depending upon the diameter of the mill. The larger the diameter, the slower the rotation. If the peripheral speed of the mill is too great, it begins to act like a centrifuge and the balls do not fall back, but stay on the perimeter of the mill. The point where the mill becomes a centrifuge is called the "Critical Speed", and ball mills usually operate at 65% to 75% of the critical speed. Ball Mills are generally used to grind material 1/4 inch and finer, down to the particle size of 20 to 75 microns. To achieve a reasonable efficiency with ball mills, they must be operated in a closed system, with oversize material continuously being recirculated back into the mill to be reduced. Various classifiers, such as screens, spiral classifiers, cyclones and air classifiers are used for classifying the discharge from ball mills. This formula calculates the critical speed of any ball mill. Most ball mills operate most efficiently between 65% and 75% of their critical speed. Photo of a 10 Ft diameter by 32 Ft long ball mill in a Cement Plant. Photo of a series of ball mills in a Copper Plant, grinding the ore for flotation. Image of cut away ball mill, showing material flow through typical ball mill. Flash viedo of Jar Drive and Batch Ball Mill grinding ore for testing Return To Crushing Info Page Contact Us Copyright 1994-2012 Mine-Engineer.Com All Rights Reserved

dry ball milling and wet ball milling for fabricating copperyttria composites | springerlink

dry ball milling and wet ball milling for fabricating copperyttria composites | springerlink

Yttria-reinforced copper matrix composites were prepared by dry ball milling (DBM) and wet ball milling (WBM), respectively, followed by spark plasma sintering (SPS). It is to determine which milling process is better for fabricating CuY2O3 composites. It is found that CuY2O3 composites synthesized by DBM exhibit better densification, mechanical and electrical properties than those by WBM. Less agglomeration of reinforcements in the bulk composites by DBM is responsible for the better performances. To further understand the reason of less agglomeration of Y2O3 in the bulks by DBM, morphologies of prepared powders were investigated and analyzed. Higher balls impact energy and the formation of copper oxide on the matrix surface during DBM process contribute to small matrix particles, which is beneficial for less agglomeration.

Avettand-Fnol MN, Simar A, Shabadi R, Taillard R, de Meester B. Characterization of oxide dispersion strengthened copper based materials developed by friction stir processing. Mater Design. 2014;60:343.

Akbarpour MR, Salahi E, Alikhani FH, Simchi A, Kim HS. Fabrication, characterization and mechanical properties of hybrid composites of copper using the nanoparticulates of SiC and carbon nanotubes. Materi Sci Eng A. 2013;572:83.

Chandrasekhar SB, Wasekar NP, Ramakrishna M, Babu PS, Rao TN, Kashyap BP. Dynamic strain ageing in fine grained Cu1wt%Al2O3 composite processed by two step ball milling and spark plasma sintering. J Alloys Compd. 2016;656:423.

Su W, Sun Y, Feng J, Liu J, Ruan J. Influences of the preparation methods of WCCo powders on the sintering and microstructure of coarse grained WC8Co hardmetals. Int J Refract Met Hard Mater. 2015;48:369.

Zhang Y, Wang L, Jiang W, Chen L, Bai G. Microstructure and properties of Al2O3TiC nanocomposites fabricated by spark plasma sintering from high-energy ball milled reactants. J Eur Ceram Soc. 2006;26(15):3393.

Boytsov O, Ustinov AI, Gaffet E, Bernard F. Correlation between milling parameters and microstructure characteristics of nanocrystalline copper powder prepared via a high energy planetary ball mill. J Alloys Compd. 2007;432(12):103.

This study was financially supported by the National Key Research and Development Program of China (No. 2016YFB0301400), the Organization Department of Jiangxi Province (No. 2012215), the Education Department of Jiangxi Province (No. KJLD13041) and the Outstanding Doctoral Dissertation Project Fund of JXUST (No. YB2017011). One of the authors Fei Huang would like to thank Prof. Hao Chen and Dr. Xue-Hui Zhang for their advice.

Huang, F., Wang, H., Chen, JS. et al. Dry ball milling and wet ball milling for fabricating copperyttria composites. Rare Met. 37, 859867 (2018). https://doi.org/10.1007/s12598-018-1086-y

ball mill - an overview | sciencedirect topics

ball mill - an overview | sciencedirect topics

The ball mill accepts the SAG or AG mill product. Ball mills give a controlled final grind and produce flotation feed of a uniform size. Ball mills tumble iron or steel balls with the ore. The balls are initially 510 cm diameter but gradually wear away as grinding of the ore proceeds. The feed to ball mills (dry basis) is typically 75 vol.-% ore and 25% steel.

The ball mill is operated in closed circuit with a particle-size measurement device and size-control cyclones. The cyclones send correct-size material on to flotation and direct oversize material back to the ball mill for further grinding.

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.

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).

Planetary ball mills. A planetary ball mill consists of at least one grinding jar, which is arranged eccentrically on a so-called sun wheel. The direction of movement of the sun wheel is opposite to that of the grinding jars according to a fixed ratio. The grinding balls in the grinding jars are subjected to superimposed rotational movements. The jars are moved around their own axis and, in the opposite direction, around the axis of the sun wheel at uniform speed and uniform rotation ratios. The result is that the superimposition of the centrifugal forces changes constantly (Coriolis motion). The grinding balls describe a semicircular movement, separate from the inside wall, and collide with the opposite surface at high impact energy. The difference in speeds produces an interaction between frictional and impact forces, which releases high dynamic energies. The interplay between these forces produces the high and very effective degree of size reduction of the planetary ball mill. Planetary ball mills are smaller than common ball mills, and are mainly used in laboratories for grinding sample material down to very small sizes.

Vibration mill. Twin- and three-tube vibrating mills are driven by an unbalanced drive. The entire filling of the grinding cylinders, which comprises the grinding media and the feed material, constantly receives impulses from the circular vibrations in the body of the mill. The grinding action itself is produced by the rotation of the grinding media in the opposite direction to the driving rotation and by continuous head-on collisions of the grinding media. The residence time of the material contained in the grinding cylinders is determined by the quantity of the flowing material. The residence time can also be influenced by using damming devices. The sample passes through the grinding cylinders in a helical curve and slides down from the inflow to the outflow. The high degree of fineness achieved is the result of this long grinding procedure. Continuous feeding is carried out by vibrating feeders, rotary valves, or conveyor screws. The product is subsequently conveyed either pneumatically or mechanically. They are basically used to homogenize food and feed.

CryoGrinder. As small samples (100 mg or <20 ml) are difficult to recover from a standard mortar and pestle, the CryoGrinder serves as an alternative. The CryoGrinder is a miniature mortar shaped as a small well and a tightly fitting pestle. The CryoGrinder is prechilled, then samples are added to the well and ground by a handheld cordless screwdriver. The homogenization and collection of the sample is highly efficient. In environmental analysis, this system is used when very small samples are available, such as small organisms or organs (brains, hepatopancreas, etc.).

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.

A ball mill is a relatively simple apparatus in which the motion of the reactor, or of a part of it, induces a series of collisions of balls with each other and with the reactor walls (Suryanarayana, 2001). At each collision, a fraction of the powder inside the reactor is trapped between the colliding surfaces of the milling tools and submitted to a mechanical load at relatively high strain rates (Suryanarayana, 2001). This load generates a local nonhydrostatic mechanical stress at every point of contact between any pair of powder particles. The specific features of the deformation processes induced by these stresses depend on the intensity of the mechanical stresses themselves, on the details of the powder particle arrangement, that is on the topology of the contact network, and on the physical and chemical properties of powders (Martin et al., 2003; Delogu, 2008a). At the end of any given collision event, the powder that has been trapped is remixed with the powder that has not undergone this process. Correspondingly, at any instant in the mechanical processing, the whole powder charge includes fractions of powder that have undergone a different number of collisions.

The individual reactive processes at the perturbed interface between metallic elements are expected to occur on timescales that are, at most, comparable with the collision duration (Hammerberg et al., 1998; Urakaev and Boldyrev, 2000; Lund and Schuh, 2003; Delogu and Cocco, 2005a,b). Therefore, unless the ball mill is characterized by unusually high rates of powder mixing and frequency of collisions, reactive events initiated by local deformation processes at a given collision are not affected by a successive collision. Indeed, the time interval between successive collisions is significantly longer than the time period required by local structural perturbations for full relaxation (Hammerberg et al., 1998; Urakaev and Boldyrev, 2000; Lund and Schuh, 2003; Delogu and Cocco, 2005a,b).

These few considerations suffice to point out the two fundamental features of powder processing by ball milling, which in turn govern the MA processes in ball mills. First, mechanical processing by ball milling is a discrete processing method. Second, it has statistical character. All of this has important consequences for the study of the kinetics of MA processes. The fact that local deformation events are connected to individual collisions suggests that absolute time is not an appropriate reference quantity to describe mechanically induced phase transformations. Such a description should rather be made as a function of the number of collisions (Delogu et al., 2004). A satisfactory description of the MA kinetics must also account for the intrinsic statistical character of powder processing by ball milling. The amount of powder trapped in any given collision, at the end of collision is indeed substantially remixed with the other powder in the reactor. It follows that the same amount, or a fraction of it, could at least in principle be trapped again in the successive collision.

This is undoubtedly a difficult aspect to take into account in a mathematical description of MA kinetics. There are at least two extreme cases to consider. On the one hand, it could be assumed that the powder trapped in a given collision cannot be trapped in the successive one. On the other, it could be assumed that powder mixing is ideal and that the amount of powder trapped at a given collision has the same probability of being processed in the successive collision. Both these cases allow the development of a mathematical model able to describe the relationship between apparent kinetics and individual collision events. However, the latter assumption seems to be more reliable than the former one, at least for commercial mills characterized by relatively complex displacement in the reactor (Manai et al., 2001, 2004).

A further obvious condition for the successful development of a mathematical description of MA processes is the one related to the uniformity of collision regimes. More specifically, it is highly desirable that the powders trapped at impact always experience the same conditions. This requires the control of the ball dynamics inside the reactor, which can be approximately obtained by using a single milling ball and an amount of powder large enough to assure inelastic impact conditions (Manai et al., 2001, 2004; Delogu et al., 2004). In fact, the use of a single milling ball avoids impacts between balls, which have a remarkable disordering effect on the ball dynamics, whereas inelastic impact conditions permit the establishment of regular and periodic ball dynamics (Manai et al., 2001, 2004; Delogu et al., 2004).

All of the above assumptions and observations represent the basis and guidelines for the development of the mathematical model briefly outlined in the following. It has been successfully applied to the case of a Spex Mixer/ Mill mod. 8000, but the same approach can, in principle, be used for other ball mills.

The Planetary ball mills are the most popular mills used in MM, MA, and MD scientific researches for synthesizing almost all of the materials presented in Figure 1.1. In this type of mill, the milling media have considerably high energy, because milling stock and balls come off the inner wall of the vial (milling bowl or 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, as schematically presented in Figure 2.17.

However, there are some companies in the world who manufacture and sell number of planetary-type ball mills; Fritsch GmbH (www.fritsch-milling.com) and Retsch (http://www.retsch.com) are considered to be the oldest and principal companies in this area.

Fritsch produces different types of planetary ball mills with different capacities and rotation speeds. Perhaps, Fritsch Pulverisette P5 (Figure 2.18(a)) and Fritsch Pulverisette P6 (Figure 2.18(b)) are the most popular models of Fritsch planetary ball mills. A variety of vials and balls made of different materials with different capacities, starting from 80ml up to 500ml, are available for the Fritsch Pulverisette planetary ball mills; these include tempered steel, stainless steel, tungsten carbide, agate, sintered corundum, silicon nitride, and zirconium oxide. Figure 2.19 presents 80ml-tempered steel vial (a) and 500ml-agate vials (b) together with their milling media that are made of the same materials.

Figure 2.18. Photographs of Fritsch planetary-type high-energy ball mill of (a) Pulverisette P5 and (b) Pulverisette P6. The equipment is housed in the Nanotechnology Laboratory, Energy and Building Research Center (EBRC), Kuwait Institute for Scientific Research (KISR).

Figure 2.19. Photographs of the vials used for Fritsch planetary ball mills with capacity of (a) 80ml and (b) 500ml. The vials and the balls shown in (a) and (b) are made of tempered steel agate materials, respectively (Nanotechnology Laboratory, Energy and Building Research Center (EBRC), Kuwait Institute for Scientific Research (KISR)).

More recently and in year 2011, Fritsch GmbH (http://www.fritsch-milling.com) introduced a new high-speed and versatile planetary ball mill called Planetary Micro Mill PULVERISETTE 7 (Figure 2.20). The company claims this new ball mill will be helpful to enable extreme high-energy ball milling at rotational speed reaching to 1,100rpm. This allows the new mill to achieve sensational centrifugal accelerations up to 95 times Earth gravity. They also mentioned that the energy application resulted from this new machine is about 150% greater than the classic planetary mills. Accordingly, it is expected that this new milling machine will enable the researchers to get their milled powders in short ball-milling time with fine powder particle sizes that can reach to be less than 1m in diameter. The vials available for this new type of mill have sizes of 20, 45, and 80ml. Both the vials and balls can be made of the same materials, which are used in the manufacture of large vials used for the classic Fritsch planetary ball mills, as shown in the previous text.

Retsch has also produced a number of capable high-energy planetary ball mills with different capacities (http://www.retsch.com/products/milling/planetary-ball-mills/); namely Planetary Ball Mill PM 100 (Figure 2.21(a)), Planetary Ball Mill PM 100 CM, Planetary Ball Mill PM 200, and Planetary Ball Mill PM 400 (Figure 2.21(b)). Like Fritsch, Retsch offers high-quality ball-milling vials with different capacities (12, 25, 50, 50, 125, 250, and 500ml) and balls of different diameters (540mm), as exemplified in Figure 2.22. These milling tools can be made of hardened steel as well as other different materials such as carbides, nitrides, and oxides.

Figure 2.21. Photographs of Retsch planetary-type high-energy ball mill of (a) PM 100 and (b) PM 400. The equipment is housed in the Nanotechnology Laboratory, Energy and Building Research Center (EBRC), Kuwait Institute for Scientific Research (KISR).

Figure 2.22. Photographs of the vials used for Retsch planetary ball mills with capacity of (a) 80ml, (b) 250ml, and (c) 500ml. The vials and the balls shown are made of tempered steel (Nanotechnology Laboratory, Energy and Building Research Center (EBRC), Kuwait Institute for Scientific Research (KISR)).

Both Fritsch and Retsch companies have offered special types of vials that allow monitoring and measure the gas pressure and temperature inside the vial during the high-energy planetary ball-milling process. Moreover, these vials allow milling the powders under inert (e.g., argon or helium) or reactive gas (e.g., hydrogen or nitrogen) with a maximum gas pressure of 500kPa (5bar). It is worth mentioning here that such a development made on the vials design allows the users and researchers to monitor the progress tackled during the MA and MD processes by following up the phase transformations and heat realizing upon RBM, where the interaction of the gas used with the freshly created surfaces of the powders during milling (adsorption, absorption, desorption, and decomposition) can be monitored. Furthermore, the data of the temperature and pressure driven upon using this system is very helpful when the ball mills are used for the formation of stable (e.g., intermetallic compounds) and metastable (e.g., amorphous and nanocrystalline materials) phases. In addition, measuring the vial temperature during blank (without samples) high-energy ball mill can be used as an indication to realize the effects of friction, impact, and conversion processes.

More recently, Evico-magnetics (www.evico-magnetics.de) has manufactured an extraordinary high-pressure milling vial with gas-temperature-monitoring (GTM) system. Likewise both system produced by Fritsch and Retsch, the developed system produced by Evico-magnetics, allowing RBM but at very high gas pressure that can reach to 15,000kPa (150bar). In addition, it allows in situ monitoring of temperature and of pressure by incorporating GTM. The vials, which can be used with any planetary mills, are made of hardened steel with capacity up to 220ml. The manufacturer offers also two-channel system for simultaneous use of two milling vials.

Using different ball mills as examples, it has been shown that, on the basis of the theory of glancing collision of rigid bodies, the theoretical calculation of tPT conditions and the kinetics of mechanochemical processes are possible for the reactors that are intended to perform different physicochemical processes during mechanical treatment of solids. According to the calculations, the physicochemical effect of mechanochemical reactors is due to short-time impulses of pressure (P = ~ 10101011 dyn cm2) with shift, and temperature T(x, t). The highest temperature impulse T ~ 103 K are caused by the dry friction phenomenon.

Typical spatial and time parameters of the impactfriction interaction of the particles with a size R ~ 104 cm are as follows: localization region, x ~ 106 cm; time, t ~ 108 s. On the basis of the obtained theoretical results, the effect of short-time contact fusion of particles treated in various comminuting devices can play a key role in the mechanism of activation and chemical reactions for wide range of mechanochemical processes. This role involves several aspects, that is, the very fact of contact fusion transforms the solid phase process onto another qualitative level, judging from the mass transfer coefficients. The spatial and time characteristics of the fused zone are such that quenching of non-equilibrium defects and intermediate products of chemical reactions occurs; solidification of the fused zone near the contact point results in the formation of a nanocrystal or nanoamor- phous state. The calculation models considered above and the kinetic equations obtained using them allow quantitative ab initio estimates of rate constants to be performed for any specific processes of mechanical activation and chemical transformation of the substances in ball mills.

There are two classes of ball mills: planetary and mixer (also called swing) mill. The terms high-speed vibration milling (HSVM), high-speed ball milling (HSBM), and planetary ball mill (PBM) are often used. The commercial apparatus are PBMs Fritsch P-5 and Fritsch Pulverisettes 6 and 7 classic line, the Retsch shaker (or mixer) mills ZM1, MM200, MM400, AS200, the Spex 8000, 6750 freezer/mill SPEX CertiPrep, and the SWH-0.4 vibrational ball mill. In some instances temperature controlled apparatus were used (58MI1); freezer/mills were used in some rare cases (13MOP1824).

The balls are made of stainless steel, agate (SiO2), zirconium oxide (ZrO2), or silicon nitride (Si3N). The use of stainless steel will contaminate the samples with steel particles and this is a problem both for solid-state NMR and for drug purity.

However, there are many types of ball mills (see Chapter 2 for more details), such as drum ball mills, jet ball mills, bead-mills, roller ball mills, vibration ball mills, and planetary ball mills, they can be grouped or classified into two types according to their rotation speed, as follows: (i) high-energy ball mills and (ii) low-energy ball mills. Table 3.1 presents characteristics and comparison between three types of ball mills (attritors, vibratory mills, planetary ball mills and roller mills) that are intensively used on MA, MD, and MM techniques.

In fact, choosing the right ball mill depends on the objectives of the process and the sort of materials (hard, brittle, ductile, etc.) that will be subjecting to the ball-milling process. For example, the characteristics and properties of those ball mills used for reduction in the particle size of the starting materials via top-down approach, or so-called mechanical milling (MM process), or for mechanically induced solid-state mixing for fabrications of composite and nanocomposite powders may differ widely from those mills used for achieving mechanically induced solid-state reaction (MISSR) between the starting reactant materials of elemental powders (MA process), or for tackling dramatic phase transformation changes on the structure of the starting materials (MD). Most of the ball mills in the market can be employed for different purposes and for preparing of wide range of new materials.

Martinez-Sanchez et al. [4] have pointed out that employing of high-energy ball mills not only contaminates the milled amorphous powders with significant volume fractions of impurities that come from milling media that move at high velocity, but it also affects the stability and crystallization properties of the formed amorphous phase. They have proved that the properties of the formed amorphous phase (Mo53Ni47) powder depends on the type of the ball-mill equipment (SPEX 8000D Mixer/Mill and Zoz Simoloter mill) used in their important investigations. This was indicated by the high contamination content of oxygen on the amorphous powders prepared by SPEX 8000D Mixer/Mill, when compared with the corresponding amorphous powders prepared by Zoz Simoloter mill. Accordingly, they have attributed the poor stabilities, indexed by the crystallization temperature of the amorphous phase formed by SPEX 8000D Mixer/Mill to the presence of foreign matter (impurities).

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