In conventional milling, the ore is crushed to, plus or minus, 3/8 of an inch, before it is put into a mill for grinding. In a autogenous mill the ore is fed directly into the mill from either the primary crusher or the mine itself. The size of the rock will be between four and eight inches. It will be this type of mill that will use a stock pile instead of a bin as fine ore storage. The feed is large enough that moisture and freezing wont bother it. The mill design itself is a little different. In conventional mills the diameter of the mill is smaller than its length. In autogenous mills the diameter is greater than the length. They can be as much as 40+ feet in diameter.
This large diameter of mill is required to achieve the impact necessary to grind the ore. The main source of reduction comes from the impact of the rock falling on rock. The mill has only twenty five to thirty percent of its volume taken up with ore. With that diameter of mill the cascade point is very high from the toe of the load. Which is the impact zone for the media. This means that the ore is being broken up by falling against the liners and being hit by the larger rock. Some of the rock will only be broken in this manner just so far. The rock that reaches this critical size will build up in the mill until it either has to be taken out or large steel balls will have to be introduced to the mill to continue crushing it.
Autogenous grinding tests were run in a 10-ft x 4-ft Rockcyl mill. The principle of prepared feed and media was utilized to determine how coarse a feed could be commercially fed to a rock mill. Secondary rock milling was expanded toward the particle sizes of primary milling while still utilizing the practices of secondary milling.
The closed circuit test mill was installed in an operating plant in parallel with existing conventional rod mill-ball mill circuits. Three stages of open circuit crushing were used to prepare rod mill feed. Grinding media was selected from various areas of the mine and tested separately. Impact tests on the three basic types of ore give Work Indices varying from 14.8 to 9.1 with two types appearing to be suitable as media and the third type questionable. The test mill was fed plant run ore with an average Work Index of 16.
Critical size buildup occurred in the first series of tests run, with a feed 80% passing 1 in. The size of media required for this size feed could not be obtained from the discharge of a primary crusher in commercial practice.
Using mill feed averaging 80% passing 5/8 in. critical size buildup occurred only when there was an excess of tramp oversize due to bin segregation and when using soft ore for grinding media. Screening mill feed at 1 in. square mesh solved the problem. It was established that rock milling could be applied to the product of a closed circuit tertiary crusher.
Media all plus 5 in. square and averaging 6 in., weighing 1015 lb. was found to be ample to perform the desired grind. Depending upon the type of ore used as media the average rate of media addition was 8 to 12% of the total feed rate, (new feed plus media). Mill power was used as a guide for media additions.
The test mill drew maximum power with about a 40% load and was run with from a 35 to 40% load. With no critical size buildup and with controlled rate of media addition there w:as no need for crushing in the mill so the load could be carried at near maximum power level. The media wore through the critical size range at least as fast as critical size material was generated. Critical size material not being in the feed must be generated in the mill and is probably only a small percentage of the total mill charge.
The Bond Work Index Formula was used to determine the operating Work Indices for the test rock mill and the parallel rod millball mill circuits. This formula, taking into account feed size, product size and power, proved an accurate tool for comparison. The operating Work Indices compared favorably and checked laboratory Work Index data.
Mill length was the primary variable investigated in an autogenous pilot mill circuit. The 5- diameter mill had both pebble ports and wide slotted grates. The plus mill product was crushed in a cone crusher and returned to the mill feed along with the minus plus 4 or 6 mesh fraction. Tests were run with a short mill, inside length of 26-3/8, or diameter-to-length ratio of 2.50 to 1. The same mill was then lengthened to 48-3/8, diameter-to-length ratio of 1.36 to 1.
Autogenous Pilot Mill Drive 30 HP, 440 V motor, speed reducer and chain drive Inside diameter 66 inches measured inside of shell liners Short = 26-3/8 inches; long = 48-3/8 inches measured inside end liners. Diameter to length ratio: short = 2.50 to 1; long = 1.36 to 1 Speed = 25- RPM, 77.3% of critical speed; lifters, 12 x 4 high evenly spaced. Discharge low-grate trunnion Grate inch wide slotted
In spite of small variations in mill charge level, and, in one case, an apparent variation of feed size structure, in all three series the same general relationships were found between short and long mill grinding characteristics. Those trends are:
The fall-off in circuit capacity or feed rate per unit of length with the longer mill is clearly shown. The long mill is 1.83 times the length (or volume) of the short mill, but the increase in capacity of the long mill is only 1.34 or 1.56, depending upon whether the grate open area is increased in the same proportion as the length. The circuit capacities per foot of mill length also show that the mill capacity favors the shorter mill configuration.
Power per ton of circuit product favors the shorter mill by a substantial margin in Series 1 and 2, and by a small margin in Series 3. The average of all three tests gives a short mill power of 9.5 KWH per ton compared with 11.35 KWH per ton for the longer mill circuit. Again, however, the effects of the finer grind become apparent when power per ton of minus 200 mesh produced is compared for the short and long mill runs.
It is not known whether the relationships found in these tests on the 5--foot diameter mill are valid for commercial size mills. However, if it is assumed that they are, the relative grinding characteristics of a 20-foot diameter mill of different lengths would be as follows:
General information on hardfacing materials and steels for rock-breaking tools is presented. Some problems of the cost-effectiveness and resistance of sintered cermet hard alloys are discussed. It is shown that expensive wear-resistant alloys can be replaced by cost-effectively alloyed white iron with enhanced mechanical properties, hardness, wear-resistance, and shock-resistance achieved by treating the melt with nitrogen and increasing the carbon content. Possible ways to improve cermet sintered alloys by heat and chemical-heat treatment are briefly discussed.
A. S. Anokhin, S. S. Strelnikova, E. V. Kukueva, et al., Properties of large-size superhard composite blanks based on cubic boron nitride, Steklo Keram., No. 8, 26 29 (2015); A. S. Anokhin, S. S. Strelnikova, E. V. Kukueva, et al., Properties of large-size superhard composite blanks based on cubic boron nitride, Glass Ceram., 72(7 8), 290 293 (2015).
A. Yu. Vakhrushin, N. S. Gryaznov, B. V. Safronov, et al., Method of obtaining hard alloys based on cast eutectic tungsten carbide and hard alloy obtained by this method, Russian Federation Patent 2470083, IPC C22C1/05, C22C29/08, Byull. Izobr. Polezn. Modeli, No. 35 (2012), declared June 27, 2011; published December 20, 2012.
TU 48-19-33480: Composite Alloy based on Relit; KGS: Metals and Metal Parts, Non-Ferrous Metals and Their Alloys, Rolling form Non-Ferrous Metals, Hard Alloys, Cermet Parts and Metallic Powders, Moscow (1981), introduced January 1, 1981.
S. N. Grigorev and V. V. Kuzin, Prospects for tools with ceramic cutting plates in modern metal working, Steklo Keram., No. 8, 17 22 (2011); S. N. Grigorev and V. V. Kuzin, Prospects for tools with ceramic cutting plates in modern metal working, Glass Ceram., 68(7 8), 253 257 (2011).
T. N. Oskolkova and A. B. Shcheglov, Method of quenching of hard alloys based on tungsten carbide, Russian Federation Patent 23355513, ICP B22F3/24, C22C29/08, Byull. Izobr. Polezn. Modeli, No. 14 (2009), declared September 11, 1997; published May 20.
S. I. Bogodukhov, A. D. Prockurin, E. S. Kozik, E. V. Solosina, and B. M. Sheinin, Method of heat-treatment of cutting tools with hard-alloy plate welded on, Russian Federation Patent 2517093, IPC C21D9/22, B23B27/18, Byull. Izobr. Polezn. Modeli, No. 15 (2014), declared April 9, 2012; published May 27.
Nikitenko, S.M., Kolba, A.V., Anokhin, A.S. et al. Prospects for Using Superhard Materials and Wear-Resistant Alloys for Rock-Breaking Tools. Glass Ceram 72, 458464 (2016). https://doi.org/10.1007/s10717-016-9811-1
Prediction of the tool wear and life, as well as secondary wear on machine components, in soft ground tunneling using shielded machines with a pressurized face has been a difficult task due to the lack of a universally accepted measurement system for soil abrasion. While some existing abrasion tests have been adopted in recent years to measure soil abrasion, these systems have inherent mismatches with the actual working conditions at the tunnel face. This paper reviews some of the background studies in this area and introduces the initial steps towards the development of a new soil abrasion testing system. The design and operational parameters for a proposed device that is under development for measuring a soil abrasion index are discussed and the preliminary results of testing on various soil samples are presented.
Soil abrasion has a major impact on soft ground mechanized tunneling but not well quantified in contract documents and source of delays and claims. Previous soil abrasion tests are reviewed and initial steps for developing a new soil abrasion index are discussed. The preliminary results of testing on various soils have been presented and showed a promise for future application in soft ground tunneling.
A ball mill also known as pebble mill or tumbling mill is a milling machine that consists of a hallow cylinder containing balls; mounted on a metallic frame such that it can be rotated along its longitudinal axis. The balls which could be of different diameter occupy 30 50 % of the mill volume and its size depends on the feed and mill size. The large balls tend to break down the coarse feed materials and the smaller balls help to form fine product by reducing void spaces between the balls. Ball mills grind material by impact and attrition.
Several types of ball mills exist. They differ to an extent in their operating principle. They also differ in their maximum capacity of the milling vessel, ranging from 0.010 liters for planetary ball mills, mixer mills, or vibration ball mills to several 100 liters for horizontal rolling ball mills.
Im grateful for the information about using a ball mill for pharmaceutical products as it produces very fine powder. My friend is working for a pharmaceutical company and this is a good article to share with her. Its good to know that ball mills are suitable for milling toxic materials since they can be used in a completely enclosed for. Thanks for the tips!
Friction and wear impact on energy, costs and emission was calculated for mining.40% of energy (= 4.6EJ) used in mining goes to overcome friction.2EJ energy is annually used to remanufacture worn out parts in mining.New tribology can save 31,100M, 280TWh energy, 145Mt CO2 emission annually.
Calculations on the global energy consumption due to friction and wear in the mineral mining industry are presented. For the first time, the impact of wear is also included in more detailed calculations in order to show its enormous tribological and economic impacts on this industry. A large variety of mining equipment used for the extraction, haulage and beneficiation of underground mining, surface mining and mineral processing were analysed. Coefficients of friction and wear rates of moving mechanical assemblies were estimated based on available information in literature in four general cases: (1) a global average mine in use today, (2) a mine with today's best commercial technology, (3) a mine with today's most advanced technology based upon the adaptation of the latest R&D achievements, and (4) a mine with best futuristic technology forecasted in the next 10 years. The following conclusions were reached:
Total energy consumption of global mining activities, including both mineral and rock mining, is estimated to be 6.2% of the total global energy consumption. About 40% of the consumed energy in mineral mining (equalling to 4.6EJ annually on global scale) is used for overcoming friction. In addition, 2EJ is used to remanufacture and replace worn out parts and reserve and stock up spare parts and equipment needed due to wear failures. The largest energy consuming mining actions are grinding (32%), haulage (24%), ventilation (9%) and digging (8%).
The total estimated economic losses resulting from friction and wear in mineral mining are in total 210,000 million Euros annually distributed as 40% for overcoming friction, 27% for production of replacement parts and spare equipment, 26% for maintenance work, and 7% for lost production.
By taking advantage of new technology for friction reduction and wear protection in mineral mining equipment, friction and wear losses could potentially be reduced by 15% in the short term (10 years) and by 30% in the long term (20 years). In the short term this would annually equal worldwide savings of 31,100 million euros, 280TWh energy consumption and a CO2 emission reduction of 145 million tonnes. In the long term, the annual benefit would be 62,200 million euros, 550TWh less energy consumption, and a CO2 emission reduction of 290 million tonnes.
Potential new remedies to reduce friction and wear in mining include the development and uses of new materials, especially materials with improved strength and hardness properties, more effective surface treatments, high-performance surface coatings, new lubricants and lubricant additives, and new designs of moving parts and surfaces of e.g. liners, blades, plates, shields, shovels, jaws, chambers, tires, seals, bearings, gearboxes, engines, conveyor belts, pumps, fans, hoppers and feeders.
Raw materials are so diverse. Even within a single mine or quarry you could be dealing with an extreme range: hard to soft, dry to sticky. Your crushing and sizing solutions need to be able to cope with whatever you throw at them reliably, and in good time.
We have been working in mines and rock quarries for more than 100 years, supplying machines for every stage of the manufacturing process. Our crushers, sizers, hammer mills and breakers have been precision engineered to handle all kinds of materials, whether abrasive, fragile, soft or sticky. The applications are different, but our solutions are always robust and reliable. Designed to last. And when youve got crushers still in operation more than 100 years after they were first commissioned, you know youre on the right track.
No two sites are the same. Thats why we work with you to determine the best solution for your application. Were continually expanding our knowledge of rock and ore and developing ever more powerful technology to reduce mountains to smithereens.
FLSmidth provides sustainable productivity to the global mining and cement industries. We deliver market-leading engineering, equipment and service solutions that enable our customers to improve performance, drive down costs and reduce environmental impact. Our operations span the globe and we are close to 10,200 employees, present in more than 60 countries. In 2020, FLSmidth generated revenue of DKK 16.4 billion. MissionZero is our sustainability ambition towards zero emissions in mining and cement by 2030.