Discussion on the effect of crushing ore grinding

2 Improvement of the grinding process

The crushing operation of ore generally involves two parts: crushing and grinding of ore. Grinding operation is the final operation of allowing the mineral to dissociate from the monomer and making the particle size meet the selection requirements. Grinding is a high energy efficiency and low efficiency. The operation of the crushing operation only accounts for 8% to 12% of the grinding operation. Therefore, improving the grinding process is an effective way to achieve high efficiency, low consumption and increase economic benefits.

2. 1 more broken and less grinding process

The crushing of materials is mainly achieved by the extrusion and impact of the equipment on the minerals, and the grinding is mainly achieved by the impact, grinding and grinding of the equipment. The energy utilization efficiency of the crushing operation is much higher than that of the grinding operation. The crushing ore and grinding can be considered as a whole to determine the reasonable particle size of the crushed product, to exert the advantages of low energy consumption, and to implement multiple economical benefits. In order to effectively achieve more and more grinding, in general:

1) High-efficiency fine crusher can be used. For example, A. C company's bottom single-cylinder hydraulic cone crusher , Nordberg's HP series cone crusher, small-scale plant adopts domestic JC56, JC4060 jaw crusher , SX series double-action jaw crusher, these fine crusher In the case of closed-circuit crushing, a crushed product of 10 mm or less can be obtained.

2) Improve the crushing process. According to the scale of the plant, the nature of the ore, the size of the ore, the size of the product, etc., select the appropriate crushing process. For example, the silkworm village of Shandong Province has been transformed into a two-stage and semi-crushing process based on the two-stage and one-stage crushing process, which solved the problem of reasonable matching between the production capacity and the crushing ratio of the second-stage crushing equipment, and achieved remarkable results in production. Economic benefits.

2. 2 stage grinding stage selection process

The principle of mineral processing is “can receive early harvest and can be thrown early”. The stage grinding phase can be used to remove the gangue minerals in time, which not only can reduce the burden of grinding operations, but also can reduce the cost of sorting operations. In production practice.

In 1997, the Beijing Municipal Institute of Mining and Metallurgy carried out a technical transformation of the Wulai Gold Mine Flotation Plant, and changed the two sections directly after grinding and flotation to the stage grinding stage flotation process. After production practice, the flotation recovery rate index was improved. A percentage point, the gold concentrate grade increased by 7.68 g / t, the concentrate yield decreased by 1. 72 percentage points, and received good results. Qi Dashan Concentrator has changed from the original continuous grinding, weak magnetic-strong magnetic process to phase grinding and heavy-magnetic-floating process. After years of practice, it has reached 63.50% of gold concentrate. The production level of 72% has reached the advanced level of gold ore beneficiation technology .

2. 3 Promote conventional fine crushing to replace conventional grinding

Since the smelting operation of the concentrator is very inefficient, and about 85% of the pulverizing operation is consumed in the grinding operation, the cone crusher can be used to produce the fine product instead of the conventional mill, although the wet crushing is carried out by the cone crusher. There are still many blank areas in the process knowledge of rock, but in the case of hard rock crushing, the water-punching cone crusher can gradually replace the conventional barrel mill.

2. 4 Renovation of the original process of the old factory

Some original plants have a large design scale, but for a variety of reasons, the production scale is only about half of the original design. With the gradual reduction of mineral resources, there is no economic benefit for large-scale equipment renovation of these old factories. The method is to improve the energy-saving and efficiency improvement, improve the crushing process, and ensure the crushing granularity while achieving energy saving and energy efficiency. After the completion of the factory construction of Tangdan Company, due to various reasons, it is basically in a semi-discontinued state. The company loses more than 10 million yuan per year. After the technical transformation of its crushing process, it will form a three-stage closed-circuit double-circuit crushing process. The capacity is increased by 30%, and the annual electricity saving is 1,403,500 yuan, and the comprehensive economic benefit is 4,889,900 yuan. Hunan Xinlong Mining Co., Ltd. has reconstructed and expanded its crushing system, increasing the processing capacity from 150 t /d to 800 t /d, saving more than 50 million yuan for the company and creating good economic benefits.

3 Proposal and application of new grinding theory

3. 1 microwave assisted grinding

In the current mining production, the crushing method of mineral materials is mainly mechanical crushing, but mechanical crushing has the disadvantages of high energy consumption, high material consumption, and poor product particle size. In order to reduce the steel consumption of crushing operations and improve energy utilization. Efficiency, mining workers have developed a new method of crushing, in which microwave pretreatment is a promising method of crushing.

The microwave is an electromagnetic wave having a frequency of approximately 300 MHz to 300 GHz and a wavelength of 2500 px to 1 mm. Microwave is a high-frequency electromagnetic wave that can penetrate into the interior of a mineral to cause orientation polarization and deformation polarization of the material molecules. As the electrode changes, the polarization direction also changes constantly, resulting in the self-heating effect of the mineral body. Elevated, but due to the different mineral properties in the ore, the absorbing properties are also different, resulting in a temperature difference between the minerals in the ore, and the thermal expansion coefficient of each mineral is also different, resulting in thermal cracking and the like. The microcracks are generated in the mineral system and the original microcracks are expanded, thereby facilitating subsequent pulverization operations. Although microwave heating treatment has the incomparable advantages of traditional heating methods, the current theoretical research on microwave grinding is not deep enough, and there are some problems that need to be solved urgently. I believe that with the research and development of microwave equipment by many researchers, In the near future, microwaves will play a huge role in reducing energy consumption and steel consumption in crushing operations.

3. 2 selective grinding

The so-called selective grinding is the use of selective dissociation of minerals and selective grinding of the grinding, the purpose is to cause some selectivity in grinding operations. The main purpose of the grinding operation is not to reduce the ore particle size, but to dissociate the useful minerals from the gangue minerals. Therefore, the ultimate development goal of the grinding operation is to obtain the highest monomer dissociation degree with the minimum energy input. . Selective grinding in the production of metal ore mining, non-metallic ore and coal mines, etc. are widely used, especially in the production of bauxite in practice, play an important role.

China's bauxite resources are abundant, but the ratio of aluminum to silicon is very low. With the depletion of rich ore resources, China's alumina producers will be forced to use low-aluminum-silicon ratio raw materials. The current production process uses sintering and mixing processes. Technology, but its high energy consumption, long process and high production cost make the alumina production industry face serious challenges in its survival and development. In order to resolve the contradictions, many researchers have developed new processes such as Bayer process to produce alumina, Bayer method. In the production of alumina, the beneficiation concentrate requires not only an aluminum to silicon ratio of more than 10, but also requires a + 0. 075 mm particle size of not less than 25%, -0.30 mm of greater than 90%, - 0. 700 mm of a grain size of 100%, In order to reduce the cost of grinding operations, selective grinding is the best choice. The selective grinding of bauxite is the use of the abrasive between the aluminum-containing minerals and the silicon-containing minerals in the bauxite-type bauxite mines in China. The difference is to study the grinding method and grinding conditions suitable for the selective grinding of bauxite, in order to achieve the selective dissociation of diaspore and silicon-containing minerals under rough grinding conditions. Zhengzhou Alumina No. 1 Plant uses a vertical ball mill to selectively grind alumina raw materials with an aluminum to silicon ratio of about 5.6, and has achieved good economic benefits. The amount of ore processed, the enrichment of selective grinding products, Energy consumption is superior to horizontal ball mills, and vertical ball mills are also expected to become new equipment for selective grinding.

3. 3 micro-stage grinding

Because the ore materials of different particle sizes have different requirements on the grinding form of grinding: coarse-grained materials are suitable for the grinding method based on impact crushing, while the fine materials should be ground by grinding because their surface area is much larger than coarse materials. Grinding the main form of grinding, in order to obtain higher grinding efficiency. The so-called micro-stage grinding is to install barrel linings with different surface shapes along the axial direction of the barrel of the ball mill. The surface of the ball mill is installed with a non-smooth lining to form a high steel ball drop height and impact. Grinding; installing a smoother cylinder liner on the discharge end of the ball mill to form a lower steel ball drop height, resulting in grinding and pulverizing; from the feeding end to the discharge end, the pulverized form gradually moves from impact pulverizing to grinding The stripping and pulverizing transition causes the ground form to change along the axis of the ball mill to achieve stage grinding in a billiard mill. This can better meet the different needs of the ore material in different stages of the grinding process, different particle size composition, and meet the ore crushing law, thus improving the grinding efficiency.

The implementation of micro-stage grinding technology requires only the modification of the surface of part of the cylinder liner, which is simple and easy. Tongling Nonferrous Metals Company Jinkouling copper comminution process was transformed, the use of micro-stage grinding, grinding station for some time to improve the processing capacity of more than 16%, saving 796,000 kWh, saving electricity costs 410 000 Yu Yuan.

3. 4 superfine grinding

When the ore is dissociated by conventional grinding technology, the energy consumption of grinding is quite high. Even if the grinding particle size can make the useful minerals dissociate, the over-grinding phenomenon will occur, and many useful minerals will be lost. In the slime, after the unremitting efforts of the mining industry, ultra-fine grinding technology came into being, and it is widely used in chemical, metallurgy, mining, building materials, daily chemicals, food, medicine, agriculture, environmental protection, aerospace and other fields, micron-scale Or sub-micron powder processing technology is maturing. After several years of continuous development, the ultra-fine grinding technology of the mill has become one of the important deep processing technologies of industrial minerals and raw materials, which is of great significance to the development of modern high-tech industries.

Application of Ultrafine Grinding Technology in refractory gold ore pretreatment also a growing concern, gold is wrapped pyrite, microscopic gold or gold present in solid solution submicroscopic gold ore, leaching is highly insoluble A type of gold ore that is gold. The key to gold extraction is to destroy the pyrite package and expose the gold to dissociation. The pyrite is very stable and difficult to decompose. With the development of ultra-fine grinding technology, the ultra-fine grinding can be used to open the package of sulfide to dissociate the gold.

The mixing mill technology has also been applied to the production practice of metal mines. The first application in the production is the tower mill, which uses a spiral agitator to agitate the grinding medium. It is a vertical low-speed agitating mill. The machine is widely used in grinding to a P80 (80% particle size through particle size) 15 to 30 μm regrind circuit. The HCM series ultra-fine grinding machine independently researched and developed by Guilin Hongcheng Mining Equipment Manufacturing Co., Ltd. combines the advantages of high-speed impact grinding and airflow grinding, is highly efficient and energy-saving, and reduces the operating cost of ultra-fine grinding.

The roller mill also plays an important role in the ultra-fine pulverizing equipment. The mining workers have analyzed the grinding mechanism, structural form and pressing method of the roller mill, and developed the grinding machine in addition to the YMP1000C superfine mill. The machine has strong processing ability for low-hardness ultra-fine powder such as heavy calcium, kaolin and talc, and has an ideal effect on crushing high-hardness materials such as bauxite, zircon sand, silicon carbide and gangue.

3. 5 pressure grinding

There are many types of internal stress in ball mills, such as impact, extrusion, shearing, grinding, etc. Some stress electric energy consumption is large and the pulverizing efficiency is not high. Research shows that when the compressive stress with high pulverization efficiency is selected as the main stress, it is crushed by pressure. The process conforms to the smashing law of the material layer. When the pressure is small, the free loose material is first sufficiently dense. When the pressure is increased, the squeezed particles transfer stress to each other. When the strength value of the particles is exceeded, the mineral particles are broken and Produce a large number of micro-cracks, adjust and strengthen the energy input for different material properties, and also constrain the action area of ​​the stress, so that the material passes through the stress zone regularly, and the mechanical energy is effectively converted into pulverizing energy, making the particle become a kind of pore. The billet product with low rate can obtain the product with the qualified particle size through the subsequent process, thereby achieving the goal of high production and energy saving.

The high-pressure roller mill developed based on this theory has been applied to large-scale industrial production, and has achieved good economic benefits, which can significantly improve the processing capacity of the equipment system, reduce the power consumption per unit, and also save the infrastructure investment of the equipment and simplify the process. , to reduce the number of broken sections, the applicability is very extensive, the general ore materials can be used, the feed water content can reach 15%. With the in-depth study of grinding technology, pressure grinding technology will be widely used and developed, contributing to improving the economic efficiency and technical level of crushing operations.

4 Application and improvement of grinding equipment

Since the 1980s, China's grinding equipment has developed rapidly. In addition to self-development, it has also introduced many new product design and manufacturing technologies from developed countries such as the United States and Europe. Through digestion and absorption, it has basically formed mass production capacity, which has broken China. The technical level of grinding equipment has reached a new level.

4. 1 Application and development of crusher

In the past 10 years, the new grinding equipment has been continuously introduced, with the aim of obtaining a larger crushing ratio and obtaining more fine-grained crushing products to reduce the particle size of the grinding material, save energy and reduce consumption, and at the same time carry out structural innovation, adopting new technology, New materials improve traditional equipment to improve reliability, durability, performance and efficiency [17].

4. 1. 1 Rotary Crusher

The development of the gyratory crusher has a history of 100 years. Due to its large processing capacity, large grain size and can handle hard ore, it is still an important equipment for crushing various hard materials in large mines and other industrial sectors. The crushing process of the gyratory crusher is continuously carried out along the ring-shaped crushing cavity. Therefore, its production capacity is large, the unit power consumption is low, and the work is stable. It is suitable for processing sheet materials, and the crushed product has uniform particle size and can be widely used. In the coarse crushing, medium crushing ore of various hardness. However, compared with the jaw crusher, the structure is complicated, the price is high, the maintenance is difficult, the repair cost is high, and the capital construction cost is high.

4. 1. 2 jaw crusher

With the adoption of large-scale carrying equipment, the crushing mill's ore feeding size has reached 1.2 to 2 m, which has promoted the development of the jaw crusher to large-scale, and the complex pendulum crusher has the advantages of high efficiency and low price. With the large market share of jaw crushers, several new jaw crushers have been successfully developed with the promotion of energy saving, energy saving and efficient production methods.

The Beijing Research Institute of Mining and Metallurgy has introduced a new type of low-low-size crushing machine that is a new generation of high-efficiency, energy-saving and low-wear crushing equipment. The machine uses the connecting rod of the traditional compound pendulum breaker as the crusher side. The board, which is separated from the connecting rod, has changed the traditional design of the traditional compound pendulum jaw crusher with the connecting rod in the four-bar linkage mechanism for many years. It is only necessary to change the structural parameters to adjust the moving jaw. The trajectory of the movement is better, and the crushing ratio is 2 to 3.5 times that of the conventional jaw crusher. The processing capacity can be increased by 20%, the energy consumption is reduced by 20% to 30%, and the economic benefit is good. .

High-efficiency vibratory jaw crusher is also a new type of high-efficiency energy-saving crushing equipment. It can crush hard and brittle materials such as alloy, silicon carbide, metallurgical slag, etc. It can also process special structural materials such as reinforced concrete, providing a new treatment for difficult materials. Way. In theory, vibration crushing is also an efficient crushing method. This crushing method can achieve the purpose of multiple crushing, less grinding, high efficiency and energy saving. It has many advantages, the crushing ratio can be increased by 2 to 3 times, and it can be started in the case of full mine. And parking, by adjusting the working parameters of the equipment, you can get different sizes of products, especially for hard and difficult to break brittle materials, with a good development prospects.

4. 1. 3 cone crusher

The introduction of the spring cone crusher has been invented for centuries. It was invented by the American Symons brothers using the principle of a gyratory crusher. So far, its structure has not changed much, and because of its stable performance, it has a certain market share. In order to meet the current high throughput production, achieve high energy, achieve higher crushing ratio and finer product granularity, the new cone crusher has also been continuously developed and applied to production practice, such as hydraulic cone crusher with hydraulic instead of spring. And the inertia cone crusher, which can replace the rough grinding operation, has achieved good economic benefits in production and operation. In recent years, more than 100 HPs have been used in metal mines such as Baotou Steel Company's concentrator and Anshan Iron and Steel Group Anshan Mining Company Qidashan Plant. The series of multi-cylinder hydraulic cone crusher replaces the traditional crusher to achieve more crushing and less grinding, greatly improving the grinding efficiency and the production capacity of the plant, and the economic benefits are remarkable. A non-ferrous metal mine selection plant in Chenzhou, Hunan, is transforming its crushing mill. In the operating system, the inertia cone crusher is used. The open-circuit product has a particle size of -5 mm, accounting for 90%. The improved grinding system has a 20% lower energy consumption than the original system, and the output has increased by about 28%. The economic benefit is very significant.

In the future, the cone crusher should be developed in the direction of hydraulic cone and automatic control, and strive to achieve large-scale, high-efficiency and energy-saving, obtain a larger crushing ratio, reduce the grinding grain size of the mill, and reduce the production cost and infrastructure investment of the crushing operation of mining enterprises. Improve the competitiveness of China's metal mining enterprises in the international arena.

4. 1. 4 high pressure roller mill

The high-pressure roller mill, also known as the roller crusher, works on the principle of material layer pulverization. It is a new type of high-efficiency energy-saving grinding equipment, which is gradually being applied and popularized at home and abroad. The high-pressure roller mill was originally designed and applied. It is mainly used for the crushing of limestone and brittle metal ore with less hardness, and is used for the middle and fine broken sections of the crushing operation. After years of promotion and development, it has been used in fine crushing of medium hardness and above. Especially in the case of iron ore crushing, its technology has become increasingly mature. It has a large crushing ratio, fine product size, high efficiency, low energy consumption, etc. The utility model can also be applied to replace a rough grinding operation, and the ore can be crushed by a high-pressure roller mill to obtain a product of 3 to 10 mm in size, and the magnetite can be greatly improved after pre-magnetic separation. The grade of the mine has the characteristics of water saving, electricity saving and production increase. At present, the high-pressure roller mill is developing in the direction of large-scale, the diameter of the roller and the surface of the roller are further increased, and the particle size range of the grinding is larger, and the processing amount is also increased. The production practice shows that the single-machine production capacity of the high-pressure roller mill can reach 1,500 to 2 000 t / h, and the energy consumption of the crushed metal ore is 1.2 to 2. 8 kWh / t. Under the same conditions, the unit energy consumption is broken than the conventional one. The machine is 20% ~ 50% lower, the roll surface wear resistance is good, the service life of the embedded hard alloy grain nail roll surface can reach 8 500 h, and the automation level is high. With the improvement of the performance of the high pressure roll mill, it is necessary in the metal mine. There will be broad application prospects.

4. 2 Mill application and development

In the late 1980s, due to the application of mill scale-up simulation technology and the improvement of mill manufacturing technology, and the use of gearless ring motor, the mill was further developed to large-scale, and the diameter of the mill was changed for the grinding process. There are significant changes. Large mills usually have a higher specific crushing rate and can handle coarser-grained materials. However, when the diameter of the mill is too large, the dead zone of the ball will increase and the mill will increase the processing capacity. It will also reduce the residence time of mineral materials, hinder the transfer of energy from the ball medium to the ore particles, resulting in a decrease in the output per unit volume and an increase in the energy consumption per unit of grinding products. Therefore, the development direction of the mill has shifted from large-scale to high-efficiency energy-saving. development of.

4. 2. 1 self-grinding, semi- autogenous grinding machine

Since the use of self-grinding and semi-self-grinding technology in the 1950s, it has evolved from a controversial technology to a mature, reliable and continuously applied technology. In the self-grinding process, the ore larger than 100 mm in the mill acts as a grinding medium. The ore material with less than 80 mm and more than 20 mm has poor grinding ability, and it is not easily broken by large ore materials, sometimes When this material is crushed, steel balls occupying about 4% to 8% of the mill volume are often added to the mill, which improves the grinding efficiency of the mill, and thus semi-self-grinding occurs. The semi-autogenous mill belongs to a cylindrical mill with heavy load, low speed and large starting torque. Nowadays, both the new expansion and the transformation of the old factory, almost all use self-grinding and semi-self-grinding technology. The self-grinding and semi-self-grinding technology simplifies the process by eliminating the two-stage crusher and screening equipment . The improved operating conditions not only reduce the capital cost of the construction of the plant, but also reduce the production and operation costs, and also facilitate the automation of the plant. The Dongguashan Copper Mine of Anhui Tongdu Copper Industry Co., Ltd. introduced the semi-autogenous grinding machine with the specification of 8.53 m × 4. 42 m produced by Svedala Group of Sweden for the first time. The driving method is advanced and the control system is perfect and reliable, replacing the traditional one. The crushing process greatly reduces the difficulty and floor space of the infrastructure, reduces the maintenance intensity and maintenance in production, and plays a vital role in the reduction of the comprehensive cost of mineral processing. The Kunming Iron and Steel Company Dahongshan, which was put into production in 2007. The iron ore beneficiation plant uses a 8.53 m × 4. 42 m semi-autogenous mill produced by the Finnish Metro Group, with a loading power of 5,500 kw, and has achieved good economic benefits.

4. 2. 2 ball mill

The ball mill is a traditional material crushing device. It has a history of more than 100 years. It is still an important equipment for fine material refining of solid materials. It is widely used in metallurgy, chemical industry, cement, ceramics, construction, electricity and In the industrial sectors such as national defense, dry and wet grinding of various ores and materials is possible. In recent years, the development of ball mills has focused on energy saving and consumption reduction, continuously improving and perfecting the grinding machine transmission mode, researching and developing new lining plates and grinding media, striving to achieve automatic control of the grinding process, and improving on the premise of ensuring grinding grain size. The processing capacity and grinding efficiency of the mill. After many unremitting efforts by researchers, it has achieved remarkable results.

As we all know, the liner of the ball mill is a key part of the mill that can achieve high efficiency, energy saving and consumption reduction. After research and development, it has made good progress. The angle spiral lining is also called energy-saving lining. After using this lining, the unit output power consumption is reduced by 10% to 25%, the mill output is increased by 15% to 20%, and the unit yield ball consumption is reduced by 10% to 20%. has a smooth, pulverized products too small, low noises, particularly suitable for comminution of the cement production operation; rubber lining is resistant to corrosion, wear-resistant non-metallic material lining, as compared to manganese steel liner plate having Light weight, low energy consumption, high output, low noise, etc.; on the basis of rubber lining, a composite magnetic lining has been developed. This lining is magnetically adsorbing a layer of magnetic particles and media fragments on the surface of the lining. The protective layer is formed to extend the service life of the lining plate. The lining plate is almost half lighter than the ordinary manganese steel lining plate, and can be directly adsorbed on the inner surface of the grinding machine barrel without bolt fixing, thereby greatly reducing the work of installation and maintenance. The quantity not only reduces the energy consumption, but also improves the processing capacity of the mill. The Benxishan Iron Ore Concentrator of Benxi Iron and Steel Co., Ltd. uses the Puma-type metal magnetic lining plate originally created by China Metallurgical Mining and Metallurgy Corporation, and the product fineness is improved by 1.69. %, mill processing The force increased by 5.6%, the power saving was 7.4%, the steel ball consumption was reduced by 10.37%, which created huge economic benefits; Pangang Group Mining Company's Midi Concentrator transformed the mill liner into a wavy lining The plate has been used well, which has improved the processing capacity of the ball mill by about 3 t, and the unit consumption of the liner has been reduced by 0.005 kg / t. The service life of the liner is also greatly extended.

In addition to achieving significant energy-saving effects in improving the shape and material of the lining, the ball mill can also reduce the energy consumption of the grinding by changing the transmission mode of the running part of the ball mill. It is one of the effective measures to start the static pressure bearing or the dynamic and static hybrid bearing. The static pressure bearing is lubricated by high-pressure hydraulic system at the start, and the ball mill cylinder is jacked up with high-pressure oil. After the start-up operation, the low-pressure hydraulic system is used for lubrication, which ensures that the hollow shaft diameter of the ball mill is always in a good lubrication state and the friction resistance is small. low starting current, thereby reducing power consumption of grinding, at 2. 8 × 3. 6 QSG ball mill Qinghai xitiesan lead zinc plant using, as compared with the conventional grinding ore processing capacity increased by 7% to 10%, The unit steel consumption has dropped by 5%, and the economic benefits are considerable.

In addition, reducing the grinding medium ball diameter, rational ball loading, improving operation, strengthening management, and actively developing and promoting grinding aids can also reduce grinding power consumption to varying degrees.

4. 2. 3 rod mill

The rod mill is developed on the basis of the ball mill. It has the advantages of reliable processing technology, low investment, less auxiliary equipment and simple process flow. There is no special technical requirement in use, and it can form a different grinding process with the ball mill. The rod mill mainly grinds the ore by the pressure and the grinding force of the grinding rod. When the rod hits the ore, it first strikes the coarser grade ore, and then pulverizes the smaller-sized material, between the rod and the rod. When the rod is in contact with the rod wall, the coarser-grained ore particles are mixed with it, which acts as a rod sieve. The finer-grained material can pass through the gap between the rod and the rod, which is beneficial to the clip. The coarser-grained material also allows the coarser-grained ore particles to be concentrated in the place where the grinding media strikes. Therefore, the rod mill has the function of selective grinding, and the product has uniform particle size and less pulverization.

4. 2. 4 vertical spiral mixing mill

The vertical spiral mixing crusher is a new type of high-efficiency energy-saving grinding equipment successfully developed by Changsha Research Institute of Mining and Metallurgy. Its grinding effect is mainly grinding and peeling, as well as a small amount of impact and shearing, so that the original material can be kept. Lattice shape, make full use of energy to effectively grind materials, because in fine grinding and ultra-fine grinding, friction grinding grinding is the most effective grinding method, and it has been applied to regrind or fine grinding of metal mines. After the iron ore concentrate of the Zhuyuan non-ferrous metal tailings is re-grinded by the vertical mixing mill to replace the ordinary horizontal ball mill, the grinding grain size - 38 μm reaches 95.10%, and the iron concentrate grade reaches 65.20%. The iron concentrate grade has significant economic benefits.

4. 2. 5 high speed impact pulverizer

High-speed impact pulverizer refers to a kind of impact pulverizing equipment that strongly impacts the material around the horizontal or vertical high-speed rotating body (rotor, hammer, blade). It is produced by Japan Hosokawa-Mitlan company introduced by domestic mining companies. CM superfine high-speed impact pulverizer, has been widely used non-metallic ultra-fine grinding, 8 mm or less material may be pulverized to a - 10 μm more than 70%, such as coupled with grading equipment, - 10 μm can be up to 95% . At present, the Xianyang Non-Metal Research Institute and the Wafangdian Chemical Machinery Plant both produce such equipment, which can be applied to ultra-fine pulverization of non-metal such as talc, clay , barite , calcium carbonate, mica and graphite .

5 Ways to improve grinding efficiency

There are many factors affecting the grinding efficiency, including the nature of grinding feed, the size of the ore, the filling rate of the steel ball, the size and proportion of the steel ball, the ball filling system, the grinding system, the grinding process, the mill operation, and the classification. Factors such as efficiency and amount of sand return, but these factors are not independent of each other and have a certain impact on each other.

5. 1 Grinding feed properties

The mechanical properties of the ore, such as hardness, toughness, dissociation and structural defects, determine the grindability of the ore, which determines the difficulty of grinding. The small grindability indicates that the ore is easy to grind, the ore is on the mill, The smaller the wear of the lining and grinding media, the smaller the power consumption. On the contrary, if the wearability is large, the wear and power consumption of the mill is large, so the nature of the ore will directly affect the productivity. The impact on grinding operations is of the utmost importance. In the modern grinding operation, a grinding aid process has been added, which is to add some specific chemicals in the grinding process to reduce the grindability of the ore and increase the productivity of the mill.

5. 2 mill feeding size

The grain size of the mill has a great influence on the grinding efficiency of the mill. Generally speaking, the smaller the grain size, the smaller the work done by the mill on the ore; on the contrary, the larger the grain size, the mill The more work done on the ore. The steel ball crushing ore is a random crushing, and the crushing efficiency is very low. Some researches have pointed out that the crushing efficiency of the ball mill is only 6% to 9%. It can be seen that the grinding grain size has a great influence on the mill. In order to achieve the final grinding fineness, it will inevitably increase the workload of the ball mill, and the energy consumption and power consumption of the ball mill will also increase.

5. 3 mill operating parameters

The structural parameters of the mill mainly include the rotation rate and filling rate of the mill, the size of the steel ball, the ball ratio, and the lining.

5. 3. 1 Mill rotation rate and filling rate

There is a close relationship between the rotation rate and the filling rate of the mill. The two are related to each other. Generally speaking, once the mill is installed, its rotation rate is fixed, it will not change easily, and the operation of changing the rotation rate is compared. It is cumbersome, so in actual production, the transfer rate is generally not analyzed as a factor affecting the grinding efficiency. It is only necessary to analyze the suitable ball filling rate at a certain speed, and the transfer rate is constant. When the filling rate is large, the steel ball has many hits on the material, the grinding area is large, the grinding effect is strong, but the power consumption is also increased, and the filling rate is too high, which also affects the movement state of the steel ball, and reduces the large The impact of the material; conversely, if the filling rate is small, the grinding area is small, the grinding effect is relatively weak, but the power consumption and energy consumption are also small. Therefore, at the production site, whether the filling rate is appropriate has a great influence on the grinding efficiency of the plant.

5. 3. 2 steel ball size and ball ratio

In the mill, the steel ball and the mill are in point contact. When the ball diameter is too large, the crushing force is also large, so that the ore is broken along the penetrating force direction, instead of being broken along the crystal surface of different minerals with weak bonding force, resulting in no fracture. Selective, and in the case of the same filling rate of the steel ball, the ball diameter is too large, resulting in too few steel balls, low breaking probability, severe crushing, and uneven product size; on the contrary, if the steel ball is too small, its ore is broken. The effect is also small, and the grinding efficiency is low, so the precise steel ball size and the ball ratio have a great influence on the grinding efficiency.

5. 3. 3 liner

The main function of the ball mill liner is to protect the mill. When the mill is running, the steel balls and materials inside the mill are brought to a certain height by the liner to be thrown or smashed, and the material is ground and pulverized. It will also be affected by the impact, sliding and rolling of steel balls and materials, and will also be affected by temperature. Therefore, the main form of wear of the lining plate is abrasive wear under a small number of times of energy, so which material lining is selected, Reducing its wear and tear is always an important issue for ball mills. Currently widely used lining materials mainly have three categories; high manganese steel; low and medium alloy wear-resistant steel; high chromium cast iron, high manganese steel with good wear resistance, good economic applicability, but low yield strength, suitable for Use under high impact load and wear conditions. The comprehensive performance of medium and low alloy wear-resistant steel is higher than that of high manganese steel, which is suitable for medium impact wear conditions. High-chromium cast iron has higher wear resistance than the former two and is more widely used. Therefore, when selecting the lining material, the use of the ball mill and the economical factors should be taken into consideration to extend the service life of the mill lining and achieve the most ideal effect.

5. 4 Supplementary ball system

Accurate calculation of the diameter of the steel ball can only solve the exact calculation of the required ball diameter of the single-grade ore. In the production, the grinding of the steel ball and the ore will cause the ratio of the steel ball to change, affecting the grinding process and causing the grinding product. The fineness changes, so in order to maintain the accuracy of the ball load in the mill, it is necessary to solve the problem by adding the ball. Only a reasonable ball-filling system can guarantee the normal production needs.

5. 5 grinding concentration

Grinding concentration is also an important factor affecting the grinding efficiency. Its size will affect the specific gravity of the slurry, the adhesion of the ore around the steel ball and the fluidity of the slurry. When the grinding concentration is low, the fluidity of the slurry Fast, the adhesion of the material around the steel ball is low, so that the impact and grinding effect of the steel ball on the material is weakened, and the grinding efficiency is low; when the grinding concentration is high, the adhesion of the material around the steel ball is good, the steel ball is The impact and grinding effect of the material are better, but the slurry flow is poor, the over-crushing is more serious, and it is not conducive to increase the processing capacity of the mill. Therefore, determining the optimal grinding concentration will have an important impact on the grinding efficiency.

5. 6 Grinding classification process and classification efficiency

For a long time, people tend to pay attention to the realization of grinding purposes, while ignoring the means and methods of grinding, patronizing the grinding grain size of the pursuit of requirements, and neglecting the monomer solution of various useful materials of ore containing various metals. The difference in degree of separation will cause some minerals to be pulverized and some minerals to be insufficiently pulverized. In this case, if the conventional rough grinding process is still used, the grinding and sorting effects will not be good.

分级机与磨矿机闭路工作，可以控制磨矿产品粒度和提高磨机生产率，因此分级效率的高低对磨矿效率有一定的影响，分级效率高时，合格粒级的产品可以及时的排除，避免了过粉碎降低了能耗;分级效率低时，到达合格粒级的产品不能及时有效的排出而返回磨机再磨，很容易造成过粉碎，也会影响到后期的选别效果。

5. 7 返砂比

所谓反砂比就是球磨机的返砂量与原矿给矿量之比，分级反砂的作用不仅是返回不合格的粗粒，还有另一个重要作用，使球磨机的给矿变粗，让钢球在磨机整个轴向长度上能高效率破碎，从而提高磨机的生产率，一般情况下，返砂量一段不宜超过500%，二段不宜超过690%。

5. 8 磨矿回路自动控制

磨矿分级机工作中可变的因素很多，而且一个因素的变动可以引起众多因素的相继变动，对于这种变化采用人工操作是跟不上的，满足不了生产过程的要求，采用自动控制才能使磨矿分级保持在稳定及适合要求的状态，从而提高生产率降低能耗。据报道，磨矿分级回路的自动控制可以使生产能力提高2. 5% ～ 10%，处理1 t 矿石可节省电耗0. 4 kWh。

6 Conclusion

我国破磨设备经过技术引进、技术合作、消化吸收、自行开发，有了长足发展。目前我国破磨设备种类繁多、品种齐全，制造质量不断提高，产量也逐年增加，已成为当今世界上生产破磨设备最多的几个国家之一，但与国外产品相比，在规格品种、整机性能、耐磨材料的研发与应用以及自动化方面还有不小的差距，因此今后破磨设备的发展应以科技为先导，以节能减耗、提高效益为目标，以满足国家重点工程需要的重大技术装备为主要任务，以关键技术、关键配套件和耐磨材料为突破口，大力开展技术攻关和科学研究，努力缩小与国外先进水平的差距.

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