Crushing is the process in which the bulk material becomes smaller under the action of mechanical force. Crushing is an important part of the mineral processing process. The pulverization can be divided into four stages: crushing, grinding, superfine pulverization, and ultrafine pulverization. The pulverization process is a high-energy operation, and the basic principle of the pulverization process is “more and less grindingâ€. 1.1 crushing process (1) A process of crushing. A section of the crushing process is generally used to provide a suitable feed for the self-grinding machine , often with a self-grinding machine. The process is simple, the equipment is small, and the plant has a small footprint. (2) Two-stage crushing process. This process is mostly used by small factories. (3) Three-stage crushing process. The basic form of the process is three-stage open circuit and three-stage one closed circuit. (4) The crushing process with washing operations. When the amount of feed mud (-3mm) exceeds 5%~10% and the water content is more than 5%~8%, the washing operation should be increased in the crushing process. 1.2 Grinding and grading process (1) Ball grinding and rod grinding process For beneficiation , one or two stages of grinding can be used to economically grind the ore to any particle size required for beneficiation. Two or more stages of grinding are usually determined by the requirements for stage selection. Compared with the two-stage process, the main advantages of a grinding process are: less equipment, low investment, simple operation, no work due to one grinding section shutdown to another grinding section, and less downtime. However, the mill has a wide range of grain size, reasonable ball loading, and it is difficult to obtain a fine final product, and the grinding efficiency is low. When the final product is required to have a maximum particle size of 0.2 to 0.15 mm (i.e., 60% to 79% to 200 mesh), a grinding process is generally employed. For small plants, to simplify the process and equipment configuration, a grinding process can be used when the grinding fineness requires 80%-200 mesh. The outstanding advantage of the two-stage grinding is that it can obtain a finer product, which can be coarsely ground and finely ground in different grinding sections, especially suitable for stage treatment. In large and medium-sized factories, when the grinding fineness is less than 0.15mm (ie 80%-200 mesh), it is economical to use two-stage grinding, and the product has uniform particle size composition and less over-grinding. According to the different connection modes of the first section of the mill and the classifier, the two sections of the grinding process can be divided into three types: the first section is open; the second section is fully closed; the first section is partially closed, and the second section is always closed. Grinding process. (2) Self-grinding process The self-grinding process has two types: dry grinding and wet grinding. Wet grinding is often used in the concentrator. In order to solve the problem of difficult-to-grind particles in self-grinding and improve the grinding efficiency, a small amount of steel balls are added to the self-grinding machine, which is called semi-self-grinding. Self-grinding often works in combination with crushing equipment such as fine crushing, ball milling, gravel grinding, etc., and can form a variety of processes according to the coupling method. 1.3 crushing and screening equipment There are many types of crushing equipment used in the industry, and there are many classification methods. The crushing equipment can be divided into: jaw crusher , cone crusher , roller crusher , impact crusher and grinder according to working principle and structural characteristics. (1) Jaw Crusher The jaw crusher is crushed by pressing the jaws periodically to the fixed jaws, crushing the material sandwiched between the jaws. According to the trajectory of the moving movement, it can be divided into a simple pendulum jaw crusher and a complex swing jaw crusher. The jaw crusher, commonly known as the "Tiger Port", is one of the longest-established crushers and is still the most effective equipment for crushing hard materials. (2) cone crusher The cone crusher is a conical surface that is moved by means of a swirling motion, and is periodically close to the fixed cone surface, so that the material of the two tapered surfaces is crushed and bent. It can be divided into a gyratory crusher for coarse crushing and a cone crusher for medium and fine crushing. (3) Roller Crusher The working part of the roller crusher is two relatively rotating rollers. The surface of the roller can be toothed, called a toothed roller crusher. It is mainly composed of splitting and crushing and crushing. According to the number of tooth rolls, it can be divided into single tooth roll, double tooth roll and multi tooth roll crusher. (4) Impact crusher Both the hammer crusher and the impact crusher are impact crushers. The crusher has a high-speed rotating rotor with an impact hammer. When the material enters the crusher, it is crushed by a high-speed rotating hammer or energy is obtained from a high-speed rotating rotor, which is thrown at a high speed to the crusher wall or specially designed. The hard board was crushed. (5) Grinder The grinder is a hollow cylinder with hollow journals at both ends, the material entering from one end of the cylinder and the product exiting from the other end. Grinding medium (steel ball, steel rod or gravel) is installed in the cylinder. The grinding machine is divided into a ball mill , a rod mill or a gravel mill depending on the grinding medium. When the cylinder rotates, the medium is brought to a certain height and falls, which causes impact and abrasion on the material to crush the material. The process of dividing a mixture of different particle sizes into a plurality of different particle size levels by a single layer or a multi-layer sieve is called sieving. The screening equipment has a fixed sieve, an inertial vibrating screen, a self-centering vibrating screen, a heavy-duty vibrating screen, a resonance screen, and a linear vibrating screen. (1) fixed screen The fixed sieve is composed of steel bars or steel bars arranged in parallel. The steel bars and steel bars are called grid bars, and the bars are connected by the cross bars. The size of the gap between the bars is the size of the mesh holes. The fixed sieve is divided into two types: a sieve and a sieve. (2) inertial vibrating screen Vibrating screen is a kind of sieve commonly used in the industry. It has a wide range of applications and is suitable for medium and fine crushing pre- and inspection screening. According to the characteristics of the movement of the screen frame, it can be divided into two types: circular motion vibration sieve and linear vibration motion sieve. The former includes a single-axis inertial vibrating screen, a self-centering vibrating screen and a heavy-duty vibrating screen; the latter includes a two-axis inertial vibrating screen and a resonant screen, which can be classified into a single-layer sieve and a double-layer sieve according to the number of sieve layers. (3) Self-centering vibrating screen The self-centering vibrating screen is suitable for screening medium and fine grain materials in large and medium-sized plants. The model of the domestic self-centering sieve is SZZ, which is divided into SZZ1 (single layer) and SZZ2 (double layer) according to the number of sieve layers. It is usually a hanging screen, but it also has a seat screen. (4) Heavy-duty vibrating screen The principle of the heavy-duty vibrating screen is similar to that of the self-centering vibrating screen, but the main shaft of the vibrator is not eccentric at all, and the shaft hole of the pulley is eccentric to achieve the purpose of self-centering during operation. The heavy-duty vibrating screen is relatively strong and can withstand large impact loads. It is suitable for screening large-sized and relatively dense materials. The maximum feeding capacity is up to 350mm. It is mainly used for pre-screening of medium-cropped pre-separation. In addition, for materials with high water content and high mud content, it can be pre-screened and washed before being crushed, and the sieved material is put into the crusher, and the sieved material enters the washing and removing. Mud system. (5) Resonance screen Resonant screen is also called elastic link type vibrating screen. It has large amplitude, high screening efficiency, large processing capacity, low power consumption and compact structure. However, the manufacturing process is complicated, the machine quality is large, the amplitude is difficult to stabilize, the adjustment is complicated, and the rubber spring is prone to aging. (6) Linear vibrating screen The linear vibrating screen has large vibration force, large amplitude, strong vibration, high screening efficiency and high productivity, and can screen coarse materials. Due to the horizontal installation, the installation height is small, and the straight-line movement is beneficial to dewatering, de-sludge and heavy medium beneficiation. However, the structure is relatively complicated, and the rotation speed of the two shafts is high, so the manufacturing and lubrication requirements are high, and the vibration is not easily adjusted. 1.4 grinding classification equipment Grinding equipment widely used in concentrators is a ball mill and a rod mill. In ball mills, only lattice type and overflow type are currently used. Cone ball mills are not manufactured because of their low productivity, but some old concentrators still use them. The specifications of the ball mill and the rod mill are expressed by the simplified inner diameter D and the barrel length L. (1) lattice type ball mill The structure of various specifications sub-type ball mills is basically the same. The cylinder of the ball mill is rolled and welded with a steel plate with a thickness of about 18 to 36 mm. The two ends of the ball mill are welded with a flange made of cast steel, and the cylinder body is provided with a lining plate. with manganese steel, made of chrome steel, cast iron or the like wear-resistant rubber material, wherein the wide application of high manganese steel, rubber is still in the trial stage. The lining is about 50-130 mm thick and has a gap of 10-14 mm from the shell. It is paved with plywood, asbestos mat, or plastic pole or rubber to slow the impact of the steel ball on the simplified body. (2) Overflow ball mill The overflow ball mill overflows by the mine itself by the lower edge of the hollow shaft because it does not need to install a heavy grid plate. Further, in order to prevent the small balls and the coarse ore nuggets in the ball mill from being discharged together with the slurry, the inner surface of the hollow journal bush is provided with a reverse spiral blade. (3) Rod mill At present, the rod mill used in the concentrator has only two types of overflow type and open type. The former is more commonly used, and the latter has been stopped. The structure of the rod mill is approximately the same as that of the overflow type ball mill. The grinding medium used is a long round bar. (4) Centrifugal mill Centrifugal mill is a new type of high-efficiency and ultra-fine equipment. It is divided into vertical and horizontal. According to the number of tubes, the former can be divided into single-tube and three-tube (planetary) centrifugal mills. (5) Vibration grinding machine The vibration mill works at high frequencies, and the high-frequency vibration easily causes cracks in the material, and can generate a relatively high stress concentration in the crack, so it can effectively perform ultra-fine grinding. However, such mechanical springs are prone to fatigue and damage, the lining plate consumption is also large, the amplitude used is small, the ore is not too thick, and it is required to be evenly added, so it is generally suitable for grinding materials of 1 to 2 mm to 85~. 5 microns (dry mill) or 5 to 0.1 microns (wet mill). . (6) Jet mill Jet mill is a new type of dry grinding equipment that combines fine grinding of materials with grading and drying. Mainly used in the chemical and building materials industries, but recently there is a trend for grinding. The operation of the jet mill is: using high temperature compressed air, or superheated steam, or other preheated gas as the medium. Compared with the ball mill and the gravel mill, the concentrate grade of the jet mill product containing iron-bearing quartzite is about 2 to 3% higher than that of the ball mill and the gravel mill, and the iron recovery rate is about 2 to 15% higher. (7) Spiral classifier The spiral classifier is a device matched with a wet ball mill and a ball mill to complete the grinding and grading. The specifications are expressed by diameter, and can be classified into a single spiral classifier and a double spiral classifier according to the number of spirals. According to the level of the liquid separation surface, it can be divided into high-grade, immersed and low-lying. (8) Hydrocyclone The upper part of the hydrocyclone has a cylindrical shape, and the lower part has a conical shape. The center of the cylinder is inserted into an overflow pipe, and the outer side of the upper part has a feed pipe which is tangential to the outside. The hydrocyclone has been applied for many years in China's concentrator, mainly for fine fractionation, slurry concentration, dewatering and dewatering. 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Mineral processing technology and mineral processing equipment (1)
Crushing process and equipment