Influence of the loading system of grinding media on the grinding process

Grinding medium loading system mainly refers to the influence of medium filling rate, medium shape and size, medium proper ratio and reasonable addition on the productivity of grinding machine.

1. The shape and material of the media     For a long time, the shape of the grinding medium that people used to use is that the sphere is a long round rod. The former grinding method is point-to-point contact, which is suitable for fine grinding. The latter grinding method is line-to-line contact, which is suitable for rough grinding, but the grinding efficiency is higher than the former. In recent years, people have designed a kind of medium shape that is higher in grinding efficiency than the ball, but second to the rod, and has a wider application range than the ball and the rod—baseball. Its grinding method is a bit, line and surface contact, and can be used for coarse, medium and fine grinding.

The choice of media material should consider the specific gravity, hardness, wear resistance, price and ease of processing. Our long-term use steel balls and cast iron ball. The steel ball has a large specific gravity, and its impact and abrasion are much better than the iron balls of the same size. At the same time, because the ratio is large, the size of the ball can be reduced correspondingly and the number is increased, thus increasing the unit time. The number of strikes of ore. In addition, the filling rate of the large specific gravity medium is low, thereby increasing the effective volume of the loaded material, increasing the feeding amount and increasing the productivity of the grinding machine. However, the processing of steel balls is troublesome and the price is 40 to 50% higher than that of cast iron balls. The outstanding feature of cast iron balls is their low price and easy to manufacture on site. At present, in order to overcome the shortcomings of low strength and poor wear resistance of iron balls, rare earth, magnesium and other elements are added to the cast iron to produce rare earth magnesium manganese cast iron balls, which are used well.

2. Dimensions of the media (diameter)     The size of the grinding media depends primarily on the physical and mechanical properties of the ore and the particle size composition. When dealing with ore with a high hardness and a coarse particle size, a large impact force is required, so a ball of a larger size should be loaded. When the ore is soft and the ore size is not very large. When the particle size of the grinding product is required to be fine, the grinding force is mainly required, and the ball of smaller size can be loaded (the surface area of ​​the small ball is large and the grinding effect is strong).

There are many calculation formulas for the relationship between the size of the medium and the size of the nugget, but there are limitations or large deviations in the calculation results. According to long-term production practices, we have accumulated experience that is more in line with objective reality. The table below lists the relationship between the appropriate ball diameter and the feed size.

Relationship between ball diameter and grain size

3. Suitable ratio of medium     In production, ball mills are loaded with a variety of ball diameter balls to process materials consisting of different sizes of ore particles. In theory, good grinding results can only be achieved if the weight ratio of the various balls is matched to the particle size composition of the material being ground. Since the particle size composition of the material to be milled and the size of the medium are constantly changing during the grinding process, it is impossible to absolutely match the ball ratio with the particle size composition of the material to be ground. Beneficiation plant through the initial ball mill and continue to make reasonable efforts to cause the ball to the media as much as possible in an appropriate ratio, in order to improve the grinding effect.

The ball-to-load ratio of the initial ball of the grinding machine can be determined according to the principle that the ball diameter is adapted to the grain size of the ore and the ball volume is adapted to the grain size of the ore. To this end, we must first determine the particle size characteristic curve of the total ore feeding of the grinding machine based on the results of the original ore and back-sand screening, and then determine the appropriate ball diameter and the ratio of the various balls according to the above table, and then according to the total ball loading. Calculate the loading weight of each ball. The following table lists examples of calculations for the loading ratio of a selected plant.

Matching situation of a selected factory

The grinding machine runs continuously, and the medium is continuously worn. In order to keep the loading amount and the ratio of the medium stable, a certain number of new balls must be added regularly. In production, only one or two large balls are often added, because the small balls can be worn by the large balls. The amount of supplementation is generally determined by the consumption quota of the medium.

4. The loading amount of the medium and the ball filling rate     When the grinding machine has a higher transfer rate, the ball loading should be less. Conversely, when the grinding machine has a low transfer rate, the ball loading should be more. Under the premise of a certain rate of rotation, it should find out the appropriate amount of ball loading, and strive to maintain stability in production to improve grinding efficiency.

The meaning of the media fill rate is the percentage of the volume occupied by the medium in the mill (including the voids) and the effective volume of the mill. The test proves that when the ball mill rotation rate is 80 ~ 85% , the medium filling rate is 40 ~ 50% ; when the ultra-speed grinding (speed rate is 100 ~ 120% ), the medium filling rate should be reduced to 35 ~ 40 % or so. The filling rate of the rod mill is lower than that of the ball mill, generally 35 to 45% .

Complied with ASME standards,the heater is designed to heat natural gas using water vapor. Then the natural gas can enter sequential combustor directly.