UNTIL THE THIRD THEORY OF COMMINUTION of Work Index method of determining crushing and grinding mill size was introduced, there was no way of accurately figuring the most applicable, most economical size of crushing and grinding mill.
Naturally, with little or no factual operating data correlated in useful form, it was easy enough, even for the most experienced, to arrive at an incorrect size of crusher or grinding mill, especially when a slightly smaller unit carried an advantage in initial investment.
The Work Index method, frequently referred to as the Bond* method, is based on extensive field operating data and equally extensive laboratory data covering wide varieties of materials, ranges of reduction sizes and types of equipment.The correlation of all this factual material enabled the establishment of a consistent common factor, known as the Work Index, for accurately determining crushing and grinding mill sizes.
Knowing the Work Index, one has but to apply the proper given equation to determine the power input required. The calculated power input in turn enables you to select the proper crusher or grinding mill unit. Selection of various sizes of machines is made from the power requirements listed in equipment manufacturers published bulletins. The following example will help clarify the above procedure.
Assume a capacity of 2000 short tons of average material per day. A Work Index of 13 over the entire size range. A feed 80% passing 3 and a final desired product of 80% passing 100 mesh. These, then, work out as follows:
By referring to equipment manufacturers bulletin on crushers, Fig. 1, a crusher producing 80% passing 3/4 requires a close side setting of approximately 5/8. Since the selected crusher capacity must be in excess of 143 tons per hour, the next higher figure (159) is chosen. The 159 indicates a 548 crusher size with 1 eccentric throw. With 1-in. eccentric throw, the motor hp allowed on the crusher is a maximum of 125. However, since only 90.3 hp is required for this average material, a 100-hp motor is sufficient.
Fig. 2, taken from manufacturers bulletin, lists horsepower requirements and Rod Mill sizes. The calculatedpower input or horsepower in the above example is 316. Therefore, a 350-hp motor is required and this in turn indicates that an 812 (8 x 12) Rod Mill is required.
For your convenience, this manual lists over 1200 work indexes. Table I lists the Work Indexes alphabetically by company and deposit. Table II lists the Work Indexes alphabetically by materials. Table III lists the average Work Indexes alphabetically by different types of materials. In the event these 1200 listings of Work Indexes do not include the particular one that applies to your particular material, you can readily determine it, since the WorkIndex expresses the resistance or a material to crushing and grinding and the relative efficiency of any machine.
Let W represent the work input in Kwhr/T, F the feed size or diameter in microns of the square hole which 80% of the feed passes, P the product size or microns which 80% of the product passes, and Rr the reduction ratio F/P. To find the Work Index (IF/) use Equation 1.
The 80% passing size in microns is a convenient term for expressing the fineness of a crushed or ground product. It is also a convenient base for calculating the reduction ratio and the work required for reduction. It is readily found by plotting the percent passing on log-log paper, as in Fig. 5, to determine the size distribution curve.
When the size distribution curves of the feed and product are parallel, the reduction ratio remains constant for all particle sizes, and the Work Index calculated from the 80% passing size is equivalent to that calculated on the basis of any other selected percent passing size.
Small differences between the slopes of the plotted feed and product lines have only a slight effect on the Work Index, proportional to the square root of the effect upon the surface areas. However, when the feed has had the fines removed the feed size is changed and the Work Index may be considerably in error. In cases where a crusher feed is scalped by passing over a grizzly screen, with openings equal to or smaller than the crusher openings, the tonnage and size distribution of the fines removed are rarely known. It is preferable, therefore, to consider the feed to the grizzly as being equivalent to the feed to the crusher and calculate the Work Index on this basis.
Several methods (2) have been used to correct the calculated Work Index for large differences between the product and feed slopes, when plotted as in Fig. 5. A newer method is the use of the average reduction ratio Rra. This can be obtained by averaging the reduction ratios at 90, 70, 50, 30 and 10% passing. The reduction ratio, at any percent passing, can be obtained quickly. Place a piece of the log- log paper (the same as used in plotting) along the percent passing line as indicated by the dotted lines A and B, Fig. 5. With point A coinciding with 100 on the micron scale and B coinciding with 773 on the same scale, 7.73 is the reduction ratio at that percent passing.
The Work Index values listed in Table I and II apply directly to a wet grinding overflow type rod mill 7.5 feet in diameter in open circuit; and to a wet grinding overflow type ball mill 7.5 feet in diameter in closed circuit with a rake classifier at 250% circulating load, and with 80% or more of the feed passing 4 mesh. Correction factors should be applied for over-size feed and other operating conditions which change the grinding efficiency. When Work Index values at several different product sizes are available (see Tables I and II), the value nearest the actual product size should be used. The Work Index represents the total work input necessary in installations of average efficiency.How to Find Work Index From Impact Crushing Tests
The Work Index is found from the first stage of the wet open circuit grinding tests (1) by multiplying the grinding index Iw by 0.0082, and from the first stage of the dry open circuit grinding tests by multiplying the dry grinding index Id by 0.00546.
The Work Index is found from the second stage of the wet open circuit grinding tests(1) by multiplying the grinding index IIw by 0.0022, and from the second stage of the dry open circuit grinding tests by multiplying the dry grinding index IId by 0.00147. The second stage dry open circuit grinding tests may show an increased Work Index because of ball coating, and are not reliable if ball coating exists.
The Work Index can be calculated by Equation 1 from commercial crushing or grinding data or from pilot mill tests, and compared with the listed Work Indexes in Tables I and II to obtain the relative mechanical efficiency.
In cases where the capacity is found to vary more than this amount, some condition causing inefficient operation should be suspected. These may include packing in a crusher, oversize feed or improper ball and rod sizes in a tumbling mill, and coating dry in grinding.
Impact crushing tests, as well as rod mill and ball mill grindability tests, can be made at cost by thewww.911metallurgist.com Laboratories. To run a proper test, a representative sample of 50 pounds minimum is required. The sample for an impact crushing test should be no finer than 2. The sample for a rod mill grindability test should be no finer than 80% passing 0.5, and the sample for a ball mill grindability test should be no finer than 80% passing 6 mesh.
FRED C. BOND Special Engineer with Allis-Chalmers Mfg. Co. Standard Grindability Tests Tabulated, Trans. AIME (1949) vol. 183, page 313, TP 2180, Mining Technology, July 1947. FRED C. BONDThe Third Theory of Comminution, Trans. AIME, TP 3308B, Mining Engineering, May 1952.
Every ore is distinctive and presents its own individual problems in profitable mineral recovery. 911Metallurgys experience in treating the many different ores submitted to our laboratories assures the development of the best treatment with most economical and profitable recovery. This will prevent any weak links and makes your mill make money.
911Metallurgystrives to develop the simplest flowsheets even in complex problems to give you optimum return for your investment. There are undoubtedly many ore dressing methods for a particular ore, but the practical solution produces milling economy and profits. 911Metallurgyflowsheets also provide FLEXIBILITY for changing conditions.
Getting into production quickly means greater profit. By centralizing your purchases with one manufacturer, you save money and simplify labor problems at the mill site. Unit and Portable Mills are especially valuable in enabling you to get into production quickly with a minimum of design problems or construction difficulties.
During the past 15 or 20 years, the trend in exploiting ore bodies has been toward larger and larger plants to handle increasingly lower grade, but larger, ore bodies. Smaller, but higher grade, ore bodies have been neglected because they did not contain sufficient ore reserves to warrant installation of a permanent mill and they could not be mined at a grade high enough to ship directly to the smelter at a profit.
Today, however, more effort is given to producing ores which usually do not occur in large deposits, such as columbite-tantalite, beryl and others which are becoming more important. The increasing use of portable and semi-portable millswhich offer mobility with a minimum of cost, time and loss of initial investmenthas played a very important part in recovering these ores.
These portable units are being successfully used for exploiting small ore bodies and for pilot plant installations on large ore bodies. The chief advantages in using Portable Mills for pilot plant work in developing a large ore body are:
First, the three persons most closely involved in developing the project successfullythe geologist, the mining engineer and the metallurgist are able to work closely together in solving the problems of exploiting the ore body to greatest advantage;
The mills shown in this bulletin are standard designs with flowsheets flexible enough to readily adapt to most problems. If you have a special problem, 911Metallurgy can design and build a mill to meet this special need.
The drawings on these pages clearly show the wisdom of planning your mill to permit expansion in production without sacrificing equipment or going through a costly downtime while a new mill is being installed.
The facing page shows the same basic mill, but with equipment added, as indicated in color, for 200 tons a day production. The new units can be installed without interfering with production for a long period. Operation with the machines in the basic mill will have familiarized all personnel with them so there will be no trial and error period.
21.Steel-Head Ball Mill.4 x 5 22.Super-Agitator5x 5 23.Duplex Wet Reagent Feeders (2) 24.10-cell Sub-A Flotation Machine.No. 18 Sp. 25.Vertical Sand Pump2 26.Disc Filter..44 Disc 27.Automatic Sampler 28.Electric Generator.D364 29.Concentrate Bin No. 2.12x 12
Each Portable Mill is completely erected at our shops and each part is match-marked before dismantling and packing for shipment. The mill shown is a standard 25-35 ton per 24 hours unit. Note the location of the Disc Filter above the concentrate storage bins.
All models are extremely flexible in flowsheet design, combining both gravity and flotation concentration so that either section may be used alone or in conjunction with the other to produce the most efficient and profitable results.
These Portable Mills are of bolted construction, with all elements match-marked so they can be readily assembled or dismantled by the operators. Complete drawings and instructions are supplied, as well as operating instructions for the machines.
The plan and elevation views of the mill shown on page 9 indicate the plant arrangement for the Portable Mill of 25-35 ton capacity, arranged for gravity and flotation concentration. The arrangement is flexible enough, however, to adapt to new operating requirements as they arise.
(Top Left) A Portable Mill in the yard at the shops undergoing examination and match-marking before crating for shipment. Note the efficient layout of equipment to utilize maximum flexibility of the flowsheet. Bins shown are for concentrate storage.
(Top Right) Grinding section on lower floor of portable mill shows a Type E Steel-Head Ball Mill with Spiral Screen on discharge end, Cross-Flow Classifier, Sub-A Unit Flotation Cell and two Vertical Centrifugal Sand Pumps. The Sub-A Flotation Machines are on the floor above. All machines in this mill are standard, full-scale units.
(Bottom Right) A Selective Mineral Jig is installed in the grinding circuit to recover mineral as soon as freed from unclassified ball mill discharge, after which pulp is fed to the Unit Cell. Pump elevates unit cell concentrate to filter on top deck.
Wilfley Concentrating Table is operated off the mill platform, in this case to handle tailings from the Sub-A Flotation Machine. It may also be used to table jig tailings in straight gravity concentration.
A Portable Truck Mill ready for transporting. The water tank and top of bucket elevator have been removed and side platforms lifted. These simple steps are all that need be done to prepare the mill for shipment.
Central control panel is equipped with master control switch and individual machine circuit breakers. Starting switches are located near each machine. Complete wiring is included with each Portable Mill.
Flowsheet No. 3 is flexible enough to handle most types of ore dressing problems. It permits gravity concentration, flotation, or a combination of gravity and flotation methods. This is particularly useful for pilot plant work or for exploiting deposits in a number of places.
Flowsheet No. 4 is used for selective flotation concentration of two minerals. It makes full use of the flexibility of the Sub-A Flotation Machine by permitting the operator to use any cell as a rougher, cleaner or recleaner and allowing return of middlings to any cell in the circuit. The Unit Cell provides recovery of coarse mineral as soon as it is free, thus reducing losses due to sliming. For concentrating more than two minerals additional flotation cells may be added.
The 7-10 ton per 24-hour Portable Truck Mill iscompactly arranged for maximum efficiency andease of operation. Machines in crushing, grinding,classifying and flotation sections shown here are allstandard, full-size units.
This mill is constructed so that there is extreme flexibility of operation. Additional machines can be added as desired, such as a second 18 diameter shell to the Ball Mill, another 2-cell flotation machine, a second classifier if required, etc.
15x 6 Type H Jaw Crusher 1Belt Ore Feeder 130x 18 Ball Mill 1Spiral Screen 14x 6 Selective Mineral Jig 16x 6 Drag Classifier 22-cell No. 8 Sub-A Flotation Machines 14-compartment Midget Wet Reagent Feeder 16 Cone-Type Dry Reagent Feeder 1No. 12-S Wllfley Concentrating Table 1 Ore Bin, 1 Welded Steel Water Tank, Steel Structure, Transmission Equipment, Launders and Piping and 1 Model D-311 Caterpillar Diesel Engine.
This complete plant economically handles material as coarse as to produce a matte type high grade product with low moisture. There are no installation problems and operation is simple and trouble-free. High capacity units available, in addition to 2, 5, 10 or 20 ton/hour units.
25 OR 50 CU. YDS. PER HOUR The Portable Placer Unit comes in two models, one handling 25 cubic yards an hour and the other 50 cubic yards an hour. It is a more flexible machine than the dredge type unit, as it does not require a large pond for operation.
Feed Hopper with Chute Nugget Trap Revolving Scrubbing Trommel 16x 24 Duplex Selective Mineral Jig (Rougher) Dewatering Screw Conveyor 8x 12 Duplex Selective Mineral Jig (Cleaner) 2 Vertical Centrifugal Sand Pumps 24x 36 Amalgamation Unit Caterpillar Diesel Electric Set 24x 30L Portable Stacking Conveyor
Modern cyanide plant design, anticipating increaseto double original capacity by adding a secondgrinding circuit and filters in the same buildingspace. The primary crushing plant (not shown)utilizes single-stage crushing. For the doubled capacity, a secondary crusher and screen are added.
Photo shows the grinding, classification and amalgamation section of a two part portable mill designed for use and still operating in Mexico after more than ten years. This unit was supplied with a belt drive because of the remote location of the property, where the only power available was from the Diesel power unit.
This unit is similar to the Trommel-Jig Placer unit in that mineral values are washed and separated in the trommel screen. The freed sands are then fed to a Mechanical Gold Pan, where both the coarse and fine gold values are concentrated with an action duplicating hand panning.
This compact gravity unit combines a trommel screenfor separating the fine mineral values from clays and coarse gravelswith a Selective Mineral Jig, which separates valuable heavy minerals from lighter gangue. A centrifugal water pump provides water for the trommel screen and the jig.
The entire unit is mounted on a steel skid base with angle iron framework. Steel sides (not shown) are provided to protect the unit. Three different sizes are available with a capacity range from 1 to 6 cubic yards per hour.
Two No. 6 Trommel Jig units were effectively used during the development of a lead mine in Mexico. The trommel jig units were operated 8 to 10 hours a day. Each unit handled from 6-8 metric tons of ore, producing 1.3 to 1.7 metric tons of concentrates. As shown on the flowsheet below, the combined concentrates from the Jigs and hand jigs, plus the lead from hand picking, averaged in excess of 70% lead with about 90% recovery.
Aadvanced Machinerys warehouse is home to the largest inventory of used Powder Compacting Presses. These presses are sometimes known as Powdered Metal Presses, PM Presses, Preform Presses, Powder Molding Presses, Powder Presses or Tablet Presses. Whatever you call em, weve got em, as well as related equipment including isostatic presses, piston extruders, mixers, blenders, spray dryers, screeners, crushers, pulverizers, granulators, attritors, ball mills and a wide array of process equipment to meet your needs!
Our online catalog providesdetails and actual photographs of all of our In-Stock Inventory. All the machinery and equipment shown is what we have in-house and ready for immediate purchase. If you would like additional details or a price quote on a machine, or if you are looking for a machine we dont have listed, please contact us.
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