Application Research of Rubber-metal Composite Liners in Large Semi-automatic Mills

Abstract: The operating conditions of the lining plate of large semi-self-grinding machine in mining industry were analvzed. The advantages and disadvantages of traditional metal liner and rubber metal composite liner were compared. The rationality and application prospect of using rubber metal composite liner in large semi-self-grinding machine were presented. The successful experience, shortage and problems needing attention of the existing application are summarized.
Key words: rubber; composite liner; semi-self-grinding machine; grinding efficiency

1 Development Trends of Large Semi-Self-Grinding Machine Applications in the Mining Industry at Home and Abroad

In most beneficiation plants, the traditional beneficiation process uses multi-stage crushing and ball milling. Its equipment investment accounts for more than 50% of the total equipment investment of the ore dressing plant, and energy consumption accounts for 60% -70% of the total energy consumption of the ore dressing plant. In recent years, a large number of researches and improvements have been made on the crushing process at home and abroad.The semi-self-grinding production process uses a larger diameter mill on the basis of full self-grinding, and a small amount (6% -14%) is added to the mill ) Steel balls to make up for the lack of ore alone as a medium in the self-mill. After the ore mined by the mine is crushed to less than 250-300 mm by a multi-stage crusher, it is directly fed into the semi-automatic mill-ball mill grinding circuit. Grind. This process is simple and easy to operate, with low investment and operating expenses, which provides greater space for investment and operating expenses reduction of large-scale beneficiation plants.

China began to apply self-grinding and semi-self-grinding technology to industry in the early 1970s. Since the 1990s, self-grinding and semi-self-grinding technologies have become more mature, and more and more new ore dressing plants have adopted self-grinding and semi-self-grinding mills. It can be expected that with the further technological transformation and continuous development of the black and non-ferrous beneficiation industry, the demand and application of this new type of beneficiation production process and large-diameter semi-automatic mill will increase even more.

2 Analysis of working conditions of large-scale semi-self-grinding liners in mining industry and comparison of advantages and disadvantages and development trends of metal and rubber-metal composite liners

2.1 Operating conditions of linings for large-scale semi-self-grinding machines in mining industry

After the large-diameter semi-self-grinding machine is used, new requirements are placed on the performance of typical wear-resistant parts such as grinding balls and liners originally used in small and medium-sized ball mills. In the ordinary small-diameter ball mill grinding process, the lining plate is mainly used to lift the grinding ball to a certain height, and then hit the material when it is dropped in a parabolic state.At the same time, the material and the grinding ball and the lining plate are mutually ground to achieve Crushing and grinding effect. Therefore, the impact energy of its liner is relatively small. In most cases, the liner of ordinary ball mills is mostly invalidated and scrapped due to abrasion. During the use of the semi-automatic mill currently in use, due to the use of large-diameter mills and grinding balls, its impact energy has greatly increased, and the size of the material entering the mill is relatively allowed to increase, and the discharge gap of the partition plate It is also increased, so the impact wear of the liner is greater, and the abrasive effect of the liner and the grinding balls and materials is relatively small. Therefore, in the large-diameter semi-self-grinding machine, the selected grinding balls and liners are required to have higher impact fatigue resistance. Moreover, once the grinding ball and the lining board are broken in the semi-automatic mill, the loss of production downtime and the manpower and material resources for subsequent processing and replacement will be more serious than in ordinary ball mills. At present, the early casting and low service life (2-6 months) of the metal casting liner used in the semi-white mill due to the greater impact energy has also become the primary bottle And puzzles out. The traditional metal liner materials used in ordinary ball mills are high manganese steel, medium and low alloy steel, and ADI ductile iron. In actual use, their hardness should be controlled above HRC> 50. The service life of such liners is mostly around one year or more. High-manganese steel linings are basically not used because they are easy to deform and difficult to replace. Due to the large number of broken pieces in the production process of semi-self-milling alloy steel linings, manufacturers have to take various measures to Improve the performance of liners. Among them, the more effective measures are:

(1) Improve the structure of the liner, increase the thickness of the impacted part, and improve the angle of the liner at the grinding ball. The disadvantage is that it increases the weight of the liner and the power consumption of the mill.

(2) Reduce the hardness of the metal lining (HRC = 38-42), improve toughness and impact fatigue resistance (ax needs to be controlled to 245 J / cm²)

(3) Strictly control casting quality and prevent micro defects (using ultrasonic testing, etc.). To some extent, these technical measures have achieved certain results. In Jiangxi Yinshan Copper Mine’s semi-automatic mill of φ7.0 mx3.5m, the service life of the liner can be increased from the original 3 months to 6-8 months, but this service life for some users Not satisfied enough.

2.2 Structural characteristics of the new rubber composite liner

In 1980, Skega introduced its rubber liner technology to China and established a joint venture in China’s Hainan Province. Since the 1980s, rubber linings have been used in small ball mills and medium-sized two-stage ball mills, but due to increased volume and poor wear resistance, the effective volume of the mill has been reduced, affecting production and service life, and reducing the cost per ton. Too obvious, domestic users do not recognize rubber linings. In the metal mining industry, the domestic use of rubber liners for ball mills does not exceed 3% of the total demand. Foreign countries have systematically studied the materials and structures of liners based on the characteristics of semi-automatic mills and have been widely used in North America and other places. This design concept must first carry out a detailed analysis of the production process of different ore dressing plants and specific semi-automatic mills, and then determine the best materials and structures that should be used according to the stress state and action mechanism of the lining board of the semi-automatic mill. . At the same time, it is important to solve the problem of rubber formula and improve the performance of rubber liners. The basic principle of this new type of semi-self-grinding rubber composite liner is to avoid the disadvantages of traditional cast metal liners that are not resistant to severe impact. The composite structure using high-performance rubber materials and wear-resistant steel plates (see Figure 1) is supported by rubber linings. The impact of the grinding ball and the use of the metal backing to increase the strength and stiffness and drive and promote the fall of the grinding ball, to achieve the purpose of not only improving the service life of the lining plate, but not reducing the grinding production efficiency, but also greatly save electricity and improve environmental protection conditions . In North America, the ball mill is almost 100% rubber-lined. Self-grinding machines and semi-self-grinding machines use rubber linings for more than 70%, and show a rising trend.

3 the use of new rubber metal composite liner

3.1 The role of the new rubber-like metal composite liner

In March 2016, China’s first set of rubber composite liners was introduced from Canada and running tests were performed on a φ7.0 mx3.5 m semi-automatic mill at the Jiangxi Yinshan Copper Mine Concentrator. The design capacity of the mill is 5000t / day, and the actual capacity is 7000t / day. The total weight of the composite lining board was finally 30t. It was installed on March 15, 2016, and was deactivated and removed on March 2, 2017. The entire service life was 11 months and 17 days, and the total processing capacity of 2.32 million tons was completed. Through the exploration and measurement of the parameters of the mill, it is proved that the use of this composite rubber liner not only shows no signs of rupture, but also has obvious effects in terms of grinding efficiency, energy saving and environmental protection, etc. 11 months and 17 days. (Figure 1) Compared with traditional steel lining, rubber (composite) village board has the following advantages: (1) The weight is 15% -40% of traditional steel lining, which greatly reduces the weight of the equipment. Reduce equipment transmission loss, there are cases in foreign countries that can save 5% -30%

(2) Extending the life of the liner, reducing downtime and avoiding emergency shutdown, thereby increasing the efficiency of the mill.

(3) Reduce noise. Using rubber lining can reduce noise by about 15 decibels, which greatly improves the working environment.

(4) Increase the output of the mill. Especially for semi-automatic mills, because the rubber grid plate is not easy to block cold and can be maintenance-free, the efficiency of the mill can be improved.

(5) Easy installation and replacement, greatly reducing labor intensity and saving installation time; convenient installation and replacement, greatly reducing labor intensity and saving installation time

Large Semi-automatic Mills

3.2 Comparative analysis of the actual measured usage data on the φ07.0 mx3.5 m semi-automatic mill of the Yinshan Copper Mine Concentrator in Jiangxi Province

(1) The comparison and analysis of the operating efficiency of the composite liner and the metal liner are affected by the speed of the semi-self-grinding process. The advantages of applying the composite liner in the first few months are not obvious. After adjusting the mill speed, it will start in late June. There is a significant increase in Taiwan’s efficiency every month. Compared with the data of the same period last year, the average increase in throughput per hour is 4.395 t (Table 1)

(2) Comparison and analysis of electricity consumption and grinding ball wear of composite liner and manganese steel liner

The physical density of rubber is 1/7 of steel. Under the same conditions, compared with metal linings, using rubber linings can greatly reduce the weight of the mill, thereby reducing the starting load of the motor and saving electrical energy. However, the energy saving in the first three months was not obvious. In April, the power consumption of semi-automatic grinding was 0.7 degrees / t higher than that of metal linings. Through the semi-self-grinding speed increase in late June, the unit power consumption has decreased, and the average unit power consumption has dropped by 0.23 kWh during the same period, which can save about 1.28 million kWh of electricity in a year (Table 2). One year can save more than 154t steel balls.

manganese-steel-liner lining

4 Application effect analysis and issues needing attention

4.1 Application effect analysis

At the beginning of the use of rubber composite liners, according to the original production process using metal liners, the semi-self-grinding steel ball filling rate was maintained at about 10%, and the pre-semi-self-grinding speed was controlled at 75% -82% of the original design speed. Highlight the advantages of composite liners. According to the theory, the grinding efficiency should be improved. In the first few months of actual operation, the grinding efficiency decreased, and the amount of steel balls and power consumption also increased. After a summary analysis of the previous operation experience and theory, it was found that the original mill speed was too low, and most of the high-energy collisions in the mill’s internal system were wasted on the lining wear without acting on the particle crushing. After adjustment, after increasing the speed of the semi-mill from 82% to 92%, the efficiency of the semi-self-grinding increased, and the energy saving was obvious. Compared with the same period of data, the economic benefits brought by the application of the composite liner were obvious. In addition, the application of rubber composite liners not only greatly reduces the workload from maintenance time and maintenance during use, but also improves the details of the on-site operating environment and greatly reduces noise pollution. The actual parking time using rubber composite liners can be changed in one working day, while replacing metal liners takes 3-4 days. In addition, the diameter of the fastening bolts of the mill can be reduced after the rubber composite liner is used, which not only reduces the weight of the mill, but also facilitates operation. After one year of exploration, there is still a lot of room for improvement in the use efficiency of rubber composite liners; for example, the design and installation of barrel wall and barrel rubber liners also have many improvements. At present, the Jiangxi Yinshan Copper Mine has begun to use rubber composite liners produced by Ningguo Tianyi Technology Co., Ltd. and continuously summarize its experience and improvements. At the same time, it is also promoted and applied in other domestic mining industries such as Minmetals Anhui Development Mining, Gansu Jinhui Mining, Yunnan Hualian Zinc Indium Company and Yunxi Datun Company.

4.2 Matters needing attention when using rubber-metal composite liners in large-scale semi-self-grinding machines in mining industry

(1) The range of the process balance point of the rubber composite liner is relatively narrow, requiring strict and refined improvement of the original operation process.For example: the requirements for the control of the particle size and size of the feed are relatively strict. For a long time, the processing capacity will decrease to some extent compared to the metal lining.

(2) The production process and structural dimensions of using a composite rubber liner to replace the original steel liner cannot be based entirely on the original mill design.For example, some parts of the liner may wear abnormally, resulting in failure to perform maintenance according to the normal maintenance time. The semi-self-grinding operation rate cannot be well guaranteed, and computer simulation technology should be used as far as possible to predict, evaluate and improve, and systematically solve the various problems of replacing the metal lining by rubber composite linings. (3) Operation without materials Rubber liners are deadly damage. Therefore, during the stop and start-up process, the running time without material can not exceed 15 minutes. If the material breaks during the mill operation, it should also be stopped within 15 minutes.

(4) The appearance of large metal parts and sharp metal parts in the mill will damage the rubber lining and shorten the service life of the rubber lining.

(5) If the original metal lining is still used at the feed end and the discharge end, it should be avoided that the flame directly ablates the composite rubber lining when the metal lining is replaced during the maintenance or when the metal lining is cut. board.

(6) Since the shape of the rubber composite liner can increase the lifting height, it is recommended that users use 100 mm steel balls. A small amount of 120 mm steel balls can be added when encountering difficult-to-grind ore. Oversized steel balls cannot improve the grinding effect, but will damage the liner and reduce the life of the liner. Using pure rubber liners, the diameter of the steel ball should not be greater than 80mm.

(7) Rubber liners are not suitable for flotation agents that need to be added directly into the mill. These agents may reduce rubber performance.

(8) It is not suitable for the temperature exceeding 80 ° C. When the temperature exceeds 85 ° C, the rubber will gradually lose its elasticity, resulting in increased wear. Compared with the case at 50 ℃, the wear of rubber lining at 100 ℃ increased by 5-6 times.

(9) The rubber lining is usually thicker than the steel lining, which reduces the effective grinding space or grinding capacity of the mill. This effect may be more significant for small mills.

5 Conclusion

In short, the gradual promotion and use of rubber-metal composite liners for large-diameter semi-self-grinding machines in the mining industry is conducive to increasing the service life of the liners, reducing the power consumption of the mills and various performance properties, and has been successfully applied in large numbers. China is gradually realizing localization and exploring and improving the use performance, structure and various application conditions of rubber. This aspect also requires close cooperation and communication between manufacturers and mining users to gradually solve various problems in production and use. I believe that soon In the future, the large-scale use of this new type of rubber-metal composite liner in semi-automatic mills will have broad prospects and make greater contributions to the country.