System of rubber lining of ball-tube mill

Disintegration of minerals in drum mills is, and for a long time will remain, the most common and energy-intensive method of grinding. Huge volumes of processed materials, traditional processing technology lead to fact that energy costs ultimately determine possibility of production development. Reducing energy intensity of grinding process, increasing productivity of drum-type ball mills is a constant requirement of production. Construction of tumbling mill reach some limit of perfection. A large number of mills used makes it impossible for rapid fundamental changes in grinding technology. Therefore, improving designs and materials of lining of drum mills has been and continue to be relevant task.[1] 

 Since the second half of last century, rubber was used to make lining instead of metal. Rubber has ability to large reversible deformations, high resistance to hydroabrasive and fatigue wear, to corrosion. Rubber lining for ball milling drills is now widely used in the mining and processing industry. Their advantages are an increase in yield of a given size, a decrease in consumption of grinding media and energy consumption for grinding process, an increase in overhaul cycle of lining set, and a reduction in noise. However, until now area of use of rubber lining for tumbling mill is limited to the 2-3rd stage of grinding with balls of 60-40 mm and a stage of grinding with cipples. In mills with balls of 100mm rubber lining is not used. 

To further improve the process of grinding mineral raw materials in drum mills, «SIC VALSA GTV» LLC (Belaya Tserkov) has developed an energy-saving ES-technology of grinding (ES-Technology - EnergySavingTechnology). Purpose of this work is to increase efficiency of a single mill, rather than an individual mill, and entire technological line consisting of existing ball-type ball mills. Main difference of proposed technology is a change in mechanism of interaction between grinding mass and lining of ball mill drum, change in trajectories of movement of grinding bodies in loading volume by using a suitable construction for each stage of grinding of rubber lining [2]. Structure of the lining elements of mill shell: the loading and unloading lids, separation grid and elevators, composition and properties of the rubber used for their manufacture are selected for each grinding stage, taking into account the size and strength of incoming material, its abrasiveness. When choosing shape of working surface of lining elements, their dimensions take into account diameter of grinding balls used, the size of mill and way it is unloaded, nature and intensity of wear of lining along length of drum. Such a solution allows to increase mill productivity, to reduce energy consumption and consumption of milling bodies, to predict warranty period of operation of lining set. Proposed designs of lining sets do not require mill to be replaced to replace individual lining elements during entire warranty period of operation. 

The unique development of the company «SIC VALSA GTV» LLC is drum liner with rubber plates H-wave miller mill with balls ≤ 100mm. Working surface of plates is formed by two planes, one of which is horizontal, and second is inclined to it at an angle in range 100 - 1750 (Fig. 1) [3]. Rubber of slab has a high strength and resistance to puncture, cutting large pieces of ore. Slab of lining has a variable height along length of mill's drum, taking into account the intensity of their wear (Fig. 2) [4]. The choice of the proposed design is confirmed by the results of its industrial tests of various mining and processing combined works with balls of 100 mm and size of loaded pieces of iron ore of 25-0mm.

Production tests of rubber lining have shown that for rubber lining of mills with balls of 100 mm, it is necessary to ensure reliability of operation not only of lining of drum, but also of rubber partition net, and in particular of liner lining of mill. Lining of mill head incur most intense wear. 

Discharge grate of mill is made of rubber and has a metal frame. Metal frame of discharge grate is only partially recessed into rubber array, which facilitates movement of pieces of ore through holes in lattice (Fig. 3) [5]. In area of maximum wear of rubber grate, closer to surface of drum, there are elevations on grate that smooth out wear of rubber grate surface along diameter of mill [6]. Lining of mill head is made of special materials, which have exceptional resistance to cuts and mechanical damage to large pieces of feed material. 

For drum mills with balls Ø 40 - 60 mm, lining "wave" is proposed (specify name). Slab lining made of rubber with high resistance to abrasive and water abrasion. Working surface of plates has form of triangular trapezium. Geometry of working surface of plates is made taking into account diameter of grinding balls used and ensures sliding of layer of balls adjacent to lining along its surface. (Fig. 4) [7]. This ensures participation in grinding process of material by abrasion of entire surface of lining contacting load body and all balls adjacent to lining. When sliding, vertical movements in layers of balls closest to surface of lining are additionally activated. Result of sliding of balls on surface of lining, activation of their vertical displacements, is an increase in mill's productivity in yielding product of a given size. During operation of liner, along diameter of mill, annular streams are formed on surface of slabs, corresponding to diameter of balls used (Fig. 5). They increase total surface area of product's grinding by abrasion. At the same time, smaller particles are concentrated in pulp located at surface of lining. As a result of their abrasion between surface of lining and balls in finished product, fraction of fine fraction increases.

Sliding of loading along surface of lining reduces point of separation of outer layer of balls from surface of lining. The mass flow of falling balls becomes more retentive which increases intensity of material's grinding between balls in the area of where the main volume of grinding passes [8].

These design features of proposed rubber lining and materials for their manufacture increase productivity of mills, reduce specific energy consumption at each grinding stage. Lowering separation point from drum of outer layer of balls reduces probability of falling balls on surface of lining, probability of its mechanical damage. Change in the shape of grinding mass flow, use of rubbers with a high resistance to abrasive and hydroabrasive wear can increase life of rubber lining, reduce consumption of balls.

Utilization efficiency rubber lining constructions made using energy-saving ES-technology of grinding is confirmed by results of operational tests for several years of sets of rubber lining at Poltava, Northern, Southern, Inguletsk mining and processing combined works (Ukraine), SSGPO (Kazakhstan), “SGOK” Stary Oskol, “RUSAL” Achinsk (Russia), Asarel-Medet AD (Bulgaria). In total more than ______ sets of linings have been manufactured and tested in operation.

Operational experience has shown that proposed lining designs can be used both in processing of iron ores and in enrichment of non-ferrous metals, aluminum and other industries.

It is possible to fully exploit advantages of proposed energy-saving ES-technology of grinding only if for each mill in production line optimal design and lining material is chosen.

Bibliography:
1. Chizhik Ye.F., Dyrda V.I. Conceptual foundations for creation of modern ore-grinding mills with rubber lining. // Geotechnical Mechanics.-2002. Issue.31.c. 20-31.
2. Dyrda V.I., Kalashnikov V.A., Evenko S.L., Markelov A.E., Khmel I.V., Stoyko V.A., Energy-saving ES-Technology of grinding mineral raw materials in ball mills with rubber lining. IX Congress of Enrichers of CIS countries. Collection of materials, Moscow, 2013. p.231 - 234.
3. Lining of tumbling mill. Patent RU 2535395.
4. Lining of tumbling mill. Patent RU 2535396.
5. Discharge grating of tumbling mill. Patent UA 75885.
6. Discharge grating of tumbling mill. Patent UA 67370.
7. Lining of tumbling mill. Patent UA 95268.
8. Powell M. S., Nurick G.N. A study of charge motion in rotary mills. Part 3. Minerals Engineering, Vol.9, No.4, 1996, pp.399-418.