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laboratory ball mill

A Laboratory Ball Millis used for grinding in laboratory flotation test work, wet grinding is necessary in several stages in order to approximate the actual grinding conditions of a ball mill and classifier in plant operation. With this small ball millit is possible to grind successfully in several stages without dilution, because the large feed opening and discharge hole (which retains the balls while the mill is being discharged) permits quick and thorough draining with the use of a minimum of wash water. Used in conjunction with a (Closed) Ball Mill, and a laboratory batch classifier saves time.

The (Open) Batch Mill makes possible simulation of grinding in a ball mill-classifier circuit by grinding a fixed time, then hand classifying with a sieve and a bucket and returning the sand to the mill for further grinding. Pulp volume can be kept at a minimum by control of wash water since the ball load does not dump out. Thus fine or coarse grinding is accomplished with ease of manipulation. The mill is used considerably as a regrind unit for further size reduction of flotation concentrates, table concentrates, middlings, and other mill products. Air may be introduced to the pulp, if desired, through theopen end of the cast steel drum.The (Open) Laboratory Ball Mill can beused for the amalgamation of table and flotation concentrates, by using one 4 ball during the grinding action.A few slight changes provide for mounting an Abbe Jar onthe driving shaft opposite the drum. This affords anexcellent combination laboratory grinding unit.

Laboratory Ball-Rod Mill is for grinding large quantities of ore in batch or continuous work. A grate discharge allows quick emptying for batch work; and a trunnion discharge, for continuous work. This flexible unit can also be used as an amalgamator.

The welded steel base can be provided in lengths suitable for supporting one, two, or three drums. One drum constitutes a ball mill; two, a rod mill; and three, a tube mill. The constructionpermits easy and rapid addition or removal of drums forconversion from one type to another, the trunnion being moved along the channels to accommodate the various lengths.The grinding drums are made with thick walls, thus eliminating the necessity of liners and the possibility of salting samples.This grinding mill has many commercial applications, since special acid resisting drums and heads can be furnished. Hard iron or alloy steel replaceable liners are easily inserted where wear is an item as in continuous use.

For continuous pilot test plants utilizing No. 7 or No. 8 Sub-A Flotation Machines, ball mills with larger grinding capacities are required. The 30 Convertible Ball Mill is ideal for this application. Capacity of this mill with single section is 3 to 5 tons per 24 hours while the double section mill, illustrated above, has a capacity of 6 to 9 tons per 24 hours.

The Buckboard and Muller ball mills are an extremely useful addition to most ore dressing or industrial laboratories. It accomplishes the quick reduction of small quantities of ore or other crushable materials to a fine powder. The unit consists of a chilled iron buckboard grinding surface, two sides of which are rimmed, and the desired type and weight of muller. Thebuckboard grinding surface is planed smooth and standard mullers have rounded crushing faces. Mullers may be purchased separately from either standard types shown or special from the three sizes of each type listed in the table and classified by rounded or flattened crushing faces. Rounded face mullers as listed have hickory axe type handles and flattened face mullers are equipped with hickory pick type handles.

MILL, Ball, Braun-WelschA laboratory ball mill particularly suitable for the metallurgical laboratory for flotation, cyanidation or amalgamation tests, but useful for any type of fine grinding. Will grind either wet or dry.

The ball mill body, or shell, is of gray cast iron, 12 inches inside diameter, 7 inches between the two machined driving ribs. Openings in the centers of heads allow free access of air during the grind, duplicating commercial scale plant conditions. The driving power is peripheral, applied frictionally through the supporting rollers. For loading, discharging and cleaning, the mill body is raised from the rollers by a rack and pinion device. This allows it to be turned, bringing its axis into the vertical position shown above. Removing the upper head by loosening five lug screws makes the inside completely visible and accessible. Pulp can be discharged through the lower opening, the balls being retained by a spider. Discharging and cleaning are rapid and thorough. All possibility of salting is eliminated, provided advantage is taken of the facilities for thorough cleaning.

The capacity is from 10 grams up to 12 pounds. Preliminary crushing to minus 10 mesh is recommended. The time for reducing an average sample to minus 65 mesh is about 15 minutes. Iron balls are used. The usual ball charge is 22 pounds, assorted sizes, 1, 1 and 2 inch being used. Steel rods 1 inch diameter may be used with good results. The mill operates at 50 R. P. M. and is driven by a 1/6 H. P. 110 volt, belt-connected motor. Mounted on steel table; floor space required, 30 x 30 inches. Height over all, 51 inches. Net weight, including balls, 270 pounds. Gross shipping weight, approximately 350 pounds.

A Ball Mill of Laboratory size, for grinding wet or dry material. Specially recommended for experimental flotation work where the oil or reagent is mixed with the samples, and gives results in harmony with those obtained in regular practice. Can be used for any type of fine grinding.

The maximum capacity is 25 pounds of ore. An assortment of iron balls inches, 1 inch and 1 inch sizes are included. The sample should be ground 20 mesh or finer (preferably with a Braun type U A Pulverizer) before being placed in the ball mill.

Designed for laboratory needs with ready access for charging and discharging the sample. The oval opening measures approximately 10 x 4 inches, and is large enough for all practical purposes. The receiving pan is in two parts, the upper portion being fitted with a screen to catch the iron balls while the ground materials fall through into the lower pan.

Ball Mill Dimensions: Cylinder, 12 x 12 inches ; floor space 27 x 13 x 22 inches ; pulley, 12 x 2 inches. Speed recommended, 40-50 RPM. Shipping weight, 300 pounds.Iron Balls, ExtraFor use with above.Receiving Pan, Extra.Source

The Abbe Pebble Mill is particularly adapted to pulverizing or mixing either dry or wet materials. This unit is of the batch or intermittent type. The cylinder is approximately half filled with flint pebbles, porcelain balls, or metal balls; the material is put into the cylinder; a tight cover is fastened securely, to seal the mill hermetically; and the cylinder is then revolved until the fineness required is obtained. After that the tight cover is replaced by a grate discharge cover and the cylinder is revolved until the material is discharged, the grate retaining the pebbles or balls. For dry grinding it is customary to enclose the cylinder to prevent the spread of undesirable dustand also to preserve all of sample to insure accuracy of testingprocedures.

In wet grinding, the same directions are followed except there is no casing required; and instead of replacing the tight cover with a grate cover, a special wet discharge cover, or the Abbe patented discharge valve, is used for emptying the mill.

The Abbe Laboratory Jar Mill pulverizes materials by friction and the fall of pebbles or balls contained within a rotating jar. In operation the jar is filled almost to the center plane with pebbles, and enough crushed material is added to fill the interstices between the pebbles and bring the charge to about 3/5 of the capacity of the jar. Usually a coarse screen is used to separate the pebbles from the material after grinding.

This unit is particularly adapted to pulverizing and mixing dry or wet materials and is manufactured in many sizes and styles for various capacities and conditions. Number of jars handled varies with mill size.

Jars are manufactured in many sizes and are of the best material. The three kinds available are: (1) Porcelain Jars carefully molded and fired to obtain the proper degree of vitrification so as to give acid and wear resisting qualities for grinding and agitation. (2) Metal Jarsmade of the metal most resistant to the action of a grinding charge, such as Monel, stainless steel, cast steel, and bronze. (3) Pyrex Jarsare transparent and enable observation during grinding or agitating action.

The Jar type Laboratory Ball Mill is ideal for use in pulverizing, mixing of dry and wet materials, and agitation of all types of pulps. Two large bottles or as many as six smallbottles can be used at the same time, thus providing a very flexible type of jar mill. When used for agitation, large ammonia bottles filled with pulp can be agitated continuously for any length of time.

The Laboratory Pebble Mill is a simple, efficient laboratory batch grinding unit. This machine is also an effective laboratory bottle type agitator for use on all types of pulps especially cyanide pulp. Two large bottles or jars or as many as six small jars may be used at the same time. This provides a wide range of capacity for batch laboratory grinding, and, at thesame time, affords a very flexible unit for batch agitation.The speed reducer and chain drive mechanism is positiveand the entire unit is mounted on a steel base. Idler rolleris adjustable to various bottle sizes. Data on jar sizes and types given under Laboratory Agitator, (Bottle Type).

Pulverizing is effected in these ball mills by the friction and fall of balls or pebbles contained within a rotating porcelain or glass jar. In general practice, the jar is filled to a little below the centre plane with pebbles; well crushed material then being added to fill the interstices and bring the charge to about three-fifths of the total space in the jar. After the operation, the pebbles and ground material are usually separated by means of a coarse grid.

Either hard or soft material may be ground, but it should not be moist to the extent that it will pack in the cylinder. If sufficient liquid is present, this method is superior to others for fine pulverization. Equipment is supplied complete with porcelain jar and flint pebbles.

A complete laboratory service that includes preliminary examination, batch or pilot-grinding test, open or closed circuit grinding, both wet and/or dryprovides important data for determining accurate mill size, for determining circulating loads, sizing accessories, grindability indexes and power requirements. Preliminary tests are made at no cost to you. Send 100 lb. sample of material prepaid.

Under the foregoing conditions experiments were designed to obtain data on (1) the relation of time of grind to mill output in g.p.m., and (2) the relation of mill output in g.p.m. to size of finished product. The relation of time of grind to mill output was studied by two procedures: (1) By a batch continuous grind technic and (2) by a batch cycle grind technic. The batch cycle grind technic is described in Part II of this Paper, Batch Closed-Circuit Grinding.

A short period of grind was selected, which far purposes of discussion can be assigned a value of x minutes. A number of individual 1,750-gram charges were weighed out. One of them was ground for x minutes, one for 2x minutes, one for 3x minutes, and so on up to 8x minutes.

The g.p.m. output of the mill for any x-minute time increment is readily calculated by simple arithmetic. If Wx is the weight of finished product resulting in the first x-minute grind, the g.p.m. output is Wx % x. If W2x is the weight of finished product produced in 2x minutes time, the mill output for the second x-minute increment is W2x Wx/x g.p.m., and so on.

It is obvious that the maximum percentage (by weight) of unfinished product (feed) is present in the mill when x is zero, and that although the mill load remains constant, the weight of unfinished feed starts diminishing at the initial turn of the mill. For this reason it was thought that in batch grinding, which may be assumed to compare in a limited way to open-circuit grinding, the efficiency of the mill possibly should be a maximum at the very initial revolution of the mill. This proved not necessarily to be the case, as may be seen by reference to the experimental data given.

The many missing links in the science of ball-mill grinding as revealed in mailing the study here presented and as brought out in the subsequent analysis of the experimental data, led to the studies by the author and H. E. Lee which are presented elsewhere under the title of Ball Mill Studies, Parts I, II, III, etc., and to Part II of this paper.

The condensed experimental data of this research and calculations based on these data are given in Table 1. The time of grind is given in vertical column 1. The sieve analysis of the product of each grind test is given, showing total grams, weight per cent, weight per cent cumulative, grams per minute, grams per minute cumulative, total surface, and total surface cumulative of each sieve size. There is also a horizontal column for each time, increment of grind, giving grams per minute cumulative for each three-minute grind increment throughout the entire 24-minute time, rangethat is, the g.p.m. output for the 0 to 3 minute period, for the 3 to 6 minute period, for the 6 to 9 minute period, and so on for each period.

Figure 1 shows the finished product-per cent of total mill charge plotted vertically against time of grind horizontally for each of the finished sizes considerednamely, 65, 100, 150, 200, and 250 mesh. These lines may be termed cumulative rate curves.

A set of tests similar to those previously described for quartz was made with Morning mine ore. The data are presented in Table 2. This ore is an aggregate largely of quartzite, siderite, sphalerite, and galena. These, data are shown graphically in Figure 4, in which finished product, g.p.m. is plotted vertically against time of grind increment horizontally. These curves indicate that at all sizes the highest rate of production of finished product is for the initial two-minute grind increment, except in the cases of the finished minus-48 mesh and minus-65 mesh products. In the absence of surface data, such as were calculated for quartz, it can not be known if the maximum finished product points for the minus-48 and minus-65 mesh sizeswhich occur at the second two-minute grind incrementsare due to increases in unfinished sand surface in the mill or to some other element.

The significant fact to note from this set of experiments is that finished product is made most rapidly at the very beginning of the grind. This suggests that in the practical closed-circuit plant the circulating load should be large in order to keep a high percentage of unfinished sand in the mill.

For quartz grinding to, say, finished minus-100 mesh sand, a 100 per cent circulating load should give approximate maximum efficiency. For Morning ore the circulating load should be high for maximum efficiency. The charge should not remain in the mill longer than two minutes, or possibly one minute. For this (two min.) length of grind for, say, finished minus-100 mesh product, 20.6 per cent of the charge is reduced to finished size. Therefore, for high efficiency, a circulating load of not less than 500 per cent is required. This corresponds closely to practice now in vogue in the Morning Mill, Mullan, Idaho, where this material is being milled. In designing a plant to treat a new ore, a test of this kind should be of much value in selecting the type of ball mill and classifier to be used. These experiments led to the batch closed-circuit experiments, which are to be described in Part II of this paper.

If the capacity of the mill used in these experiments be rated at one unit of finished minus-65 mesh product in a unit of time, its capacity to make finished product at any finer mesh may be calculated from Table I for quartz and from Table 2 for Morning ore. See Table 3.

These data show that the mill has four times as much capacity when grinding to finished minus-65 mesh as when grinding to finished minus-250 mesh. It has approximately three times as much capacity to produce finished minus-150 mesh Morning ore as finished minus-150 mesh quartz. These figures all are based on the output of the mill for the initial grind periodthree minutes for quartz and two minutes for Morning ore.

To learn if a greater mill output could be obtained than in any of the previous tests, an experiment was designed in which the period of grind was one minute. Quartz was used, and all other experimental conditions were the same as in previous experiments. At the end of each one-minute grind the charge was removed from the mill and the weight, in grams, of finished minus-100 mesh sand was determined. A quantity of new ore equal to the determined weight of finished product with the original charge was returned to the mill. The grind was conducted for another one-minute period. This process was repeated seven times, and each time enough new water was added to keep the water-ore ratio at 30:70 by weight. At seven new ore additions the mill became choked, and further additions could not be made.

The object in the plan of this experiment was to keep in the mill a nearly constant weight of unfinished feed, without removing the finished product. This procedure should, of course, result in high unfinished sand surface in the mill. The experimental data of this run are compiled in Table 4.

The output of finished minus-100 mesh sand produced the first minute is 175 grams; the output per minute for the first two minutes is 154 grams; for the first three minutes, 127 grams; for the first four minutes, 143 grams; for the first five minutes, 108 grams; for the first six minutes, 119 grams; and for the full seven minutes, 106 grams. On the basis of these figures the output is a maximum for the initial one-minute grind during, which only original feed is in the mill. Considered on the basis of output for each of the time increments, calculation shows that the output of the mill is greatest during the fourth minute grind increment, when 195 grams were produced. This result may be due to experimental error, and it is believed to be, for during the next minute (the fifth) increment the output is negative and for the sixth-minute increment the output is 166 grams. That the mill output was less for the third and fifth minute increments than for the fourth-minute increment is almost proof of experimental error, and the conclusion may safely be drawn that nothing is to be gained by overfeeding a ball mill, and that choking of the mill with finished product cuts down the mill efficiency.

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ball mills | industry grinder for mineral processing - jxsc machine

Max Feeding size <25mm Discharge size0.075-0.4mm Typesoverflow ball mills, grate discharge ball mills Service 24hrs quotation, custom made parts, processing flow design & optimization, one year warranty, on-site installation.

Ball mill, also known as ball grinding machine, a well-known ore grinding machine, widely used in the mining, construction, aggregate application. JXSC start the ball mill business since 1985, supply globally service includes design, manufacturing, installation, and free operation training. Type according to the discharge type, overflow ball mill, grate discharge ball mill; according to the grinding conditions, wet milling, dry grinding; according to the ball mill media. Wet grinding gold, chrome, tin, coltan, tantalite, silica sand, lead, pebble, and the like mining application. Dry grinding cement, building stone, power, etc. Grinding media ball steel ball, manganese, chrome, ceramic ball, etc. Common steel ball sizes 40mm, 60mm, 80mm, 100mm, 120mm. Ball mill liner Natural rubber plate, manganese steel plate, 50-130mm custom thickness. Features 1. Effective grinding technology for diverse applications 2. Long life and minimum maintenance 3. Automatization 4. Working Continuously 5. Quality guarantee, safe operation, energy-saving. The ball grinding mill machine usually coordinates with other rock crusher machines, like jaw crusher, cone crusher, to reduce the ore particle into fine and superfine size. Ball mills grinding tasks can be done under dry or wet conditions. Get to know more details of rock crushers, ore grinders, contact us!

Ball mill parts feed, discharge, barrel, gear, motor, reducer, bearing, bearing seat, frame, liner plate, steel ball, etc. Contact our overseas office for buying ball mill components, wear parts, and your mine site visits. Ball mill working principle High energy ball milling is a type of powder grinding mill used to grind ores and other materials to 25 mesh or extremely fine powders, mainly used in the mineral processing industry, both in open or closed circuits. Ball milling is a grinding method that reduces the product into a controlled final grind and a uniform size, usually, the manganese, iron, steel balls or ceramic are used in the collision container. The ball milling process prepared by rod mill, sag mill (autogenous / semi autogenous grinding mill), jaw crusher, cone crusher, and other single or multistage crushing and screening. Ball mill manufacturer With more than 35 years of experience in grinding balls mill technology, JXSC design and produce heavy-duty scientific ball mill with long life minimum maintenance among industrial use, laboratory use. Besides, portable ball mills are designed for the mobile mineral processing plant. How much the ball mill, and how much invest a crushing plant? contact us today! Find more ball mill diagram at ball mill PDF ServiceBall mill design, Testing of the material, grinding circuit design, on site installation. The ball grinding mill machine usually coordinates with other rock crusher machines, like jaw crusher, cone crusher, get to know more details of rock crushers, ore grinders, contact us! sag mill vs ball mill, rod mill vs ball mill

How many types of ball mill 1. Based on the axial orientation a. Horizontal ball mill. It is the most common type supplied from ball mill manufacturers in China. Although the capacity, specification, and structure may vary from every supplier, they are basically shaped like a cylinder with a drum inside its chamber. As the name implies, it comes in a longer and thinner shape form that vertical ball mills. Most horizontal ball mills have timers that shut down automatically when the material is fully processed. b. Vertical ball mills are not very commonly used in industries owing to its capacity limitation and specific structure. Vertical roller mill comes in the form of an erect cylinder rather than a horizontal type like a detachable drum, that is the vertical grinding mill only produced base on custom requirements by vertical ball mill manufacturers. 2. Base on the loading capacity Ball mill manufacturers in China design different ball mill sizes to meet the customers from various sectors of the public administration, such as colleges and universities, metallurgical institutes, and mines. a. Industrial ball mills. They are applied in the manufacturing factories, where they need them to grind a huge amount of material into specific particles, and alway interlink with other equipment like feeder, vibrating screen. Such as ball mill for mining, ceramic industry, cement grinding. b. Planetary Ball Mills, small ball mill. They are intended for usage in the testing laboratory, usually come in the form of vertical structure, has a small chamber and small loading capacity. Ball mill for sale In all the ore mining beneficiation and concentrating processes, including gravity separation, chemical, froth flotation, the working principle is to prepare fine size ores by crushing and grinding often with rock crushers, rod mill, and ball mils for the subsequent treatment. Over a period of many years development, the fine grinding fineness have been reduced many times, and the ball mill machine has become the widest used grinding machine in various applications due to solid structure, and low operation cost. The ball miller machine is a tumbling mill that uses steel milling balls as the grinding media, applied in either primary grinding or secondary grinding applications. The feed can be dry or wet, as for dry materials process, the shell dustproof to minimize the dust pollution. Gear drive mill barrel tumbles iron or steel balls with the ore at a speed. Usually, the balls filling rate about 40%, the mill balls size are initially 3080 cm diameter but gradually wore away as the ore was ground. In general, ball mill grinder can be fed either wet or dry, the ball mill machine is classed by electric power rather than diameter and capacity. JXSC ball mill manufacturer has industrial ball mill and small ball mill for sale, power range 18.5-800KW. During the production process, the ball grinding machine may be called cement mill, limestone ball mill, sand mill, coal mill, pebble mill, rotary ball mill, wet grinding mill, etc. JXSC ball mills are designed for high capacity long service, good quality match Metso ball mill. Grinding media Grinding balls for mining usually adopt wet grinding ball mills, mostly manganese, steel, lead balls. Ceramic balls for ball mill often seen in the laboratory. Types of ball mill: wet grinding ball mill, dry grinding ball mill, horizontal ball mill, vibration mill, large ball mill, coal mill, stone mill grinder, tumbling ball mill, etc. The ball mill barrel is filled with powder and milling media, the powder can reduce the balls falling impact, but if the power too much that may cause balls to stick to the container side. Along with the rotational force, the crushing action mill the power, so, it is essential to ensure that there is enough space for media to tumble effectively. How does ball mill work The material fed into the drum through the hopper, motor drive cylinder rotates, causing grinding balls rises and falls follow the drum rotation direction, the grinding media be lifted to a certain height and then fall back into the cylinder and onto the material to be ground. The rotation speed is a key point related to the ball mill efficiency, rotation speed too great or too small, neither bring good grinding result. Based on experience, the rotat

ion is usually set between 4-20/minute, if the speed too great, may create centrifuge force thus the grinding balls stay with the mill perimeter and dont fall. In summary, it depends on the mill diameter, the larger the diameter, the slower the rotation (the suitable rotation speed adjusted before delivery). What is critical speed of ball mill? The critical speed of the ball mill is the speed at which the centrifugal force is equal to the gravity on the inner surface of the mill so that no ball falls from its position onto the mill shell. Ball mill machines usually operates at 65-75% of critical speed. What is the ball mill price? There are many factors affects the ball mill cost, for quicker quotations, kindly let me know the following basic information. (1) Application, what is the grinding material? (2) required capacity, feeding and discharge size (3) dry or wet grinding (4) single machine or complete processing plant, etc.

laboratory rod mill

The 21 Liter (5 gallon) 911METALLURGY 911MPE21BM dual function Laboratory RodMill / BallMill is designed to meet the industrial requirements to grind coal, cement and a wide variety of ores. The dual dutyLaboratory Grinding Mill consists of a gear motor mounted on a high precision solid steel underframe complete with outlet funnel and a set of separation screens plus sample collector.

The mill incorporates a yoke and locking mechanism to facilitate easy access to the contents of the mill. An appropriate ball or rod charge is provided with the mill. The motor incorporates a solid-state controller to accurately control the drum speed of up to 70 RPM. This controller has an internal overload protection. A revolution counter is included to allow accurate control of milling which will automatically stop the mill when the desired milling duration is reached. The lid incorporates a quick release locking mechanism.

Easy convertible from Ball Mill to Rod Mill. Drums, balls and rods available in different grades of steel: SS304, SS316, SS303, ST37, ST52 and other steel materials or liners on request. Easy tilt to empty the drum

As stated above, the purpose of this research was primarily to establish a quantitative relationship between a laboratory ball mill capacity and fineness of finished product. As is nearly always the case in research, the major problem cannot be attacked until a number of smaller ones have been disposed of: apparatus must be decided upon and designed to meet the needs of the research; experimental technic must be developed to accord with good scientific procedure, which will give data of practical use; and the data must be interpreted. This investigation, however, instead of being one of merely determining mill capacity (for a given mill) as related to fineness of finished product, also became a study of batch grinding in a laboratory ball mill as related to time of grind.

The selection of apparatus was necessarily more or less arbitrary. A cylinder 16 inches in diameter by 7 inches in length was chosen to contain the grinding mediaa 43 per cent full load of 1-inch steel balls. Mechanism was provided to rotate the cylinder, at a constant speed of 55 r.p.m. This speed was decided upon on the basis of observation made at one end of the mill, which was closed with a coarse-mesh screen. The mill speed chosen was not necessarily exactly the speed which would give maximum mill output, but it probably was close to what may be termed the best speed. That there is a best speed for each size of ball, ball load, feed size, etc., is shown in the researches of Fahrenwald and Lee and this is just one example of the complexity of the grinding problem. The selected speed must therefore be considered a more or, less arbitrary one, but it fully served the purpose of this investigation.

In the experiments of this study, grinding was done wet. Thirty per cent of water by weight was added to each charge. This ore-water ratio was arrived at from a series of experiments in which the percentage of water was the variable. Thirty per cent of water by weight gave approximately the maximum mill outputgrinding through 100 mesh.

The weight of feed charge introduced into the mill also was determined from a series of experiments in which weight of feed charge was the variable. The weight of feed charge giving the greatest number of grams of finished minus- 100 mesh sand was approximately 1,750 grams. As data later presented will show, this is not exactly the weight of charge which will give maximum mill output in a unit of time; it is, however, approximately that weight of charge which gives maximum output under the conditions of (1) the size (sieve analysis) of feed used, and (2) a short-period grind. This weight of charge served the purpose of the batch-grind experiments of this study.

Having established the apparatus to be used and, in part, the conditions of the experiments, other factors and variables having even greater bearing upon mill output came up. The most important among these was the time of grind. For a given weight of feed charge to be ground in a batch laboratory ball mill, there was no information available to show how the rate of production of finished product in the mill varied with the time, of operation of the mill; that is, for a 10-minute grind it was not known if the output was greatest for the first minute, the second minute, or the sixth or tenth minute of operation. This question seemed of such importance that a decision was made to investigate it rather thoroughly.

In this study, rate of grinding or mill efficiency is stated in terms of grams per minute, abbreviated GPM. A more scientific basis on which to calculate mill efficiency probably would have been that of total new surface produced per unit of time. This basis, however, was not thought to offer any advantage over the one stated.

The size analysis of the feed for experimentation was also more or less arbitrarily selected; and, as these experiments, show, it is not the proper sieve analysis to give maximum mill output. Here again the proper feed size could not be known in advance, and the arbitrary feed size selected serves for the work in hand. Quartz of the white massive variety was selected for this study because of its homogeneity and its known surface constants.