Ball mill

In the production cost of cement, the power consumption of grinding accounts for 35%~40% of the cement cost. Cement grinding is the last and most important key link to control cement quality. To a certain extent, the quality of cement clinker grinding can make up for the lack of clinker quality (that is, grinding can improve cement quality), and maximize the qualified rate of cement leaving the factory while saving raw materials.

Cement ball mill has two transmission modes, center transmission and edge transmission. The material is fed into the first bin of the mill evenly through the feeding device and the hollow shaft spiral. There is a stepped lining or corrugated lining in the bin, which contains steel balls of different specifications. The centrifugal force generated by the rotation of the cylinder brings the steel balls to a certain height and then falls, which produces a heavy impact and grinding effect on the material. After the material is coarsely ground in the first bin, it enters the second bin through a single-layer partition plate. The bin is inlaid with a flat lining plate and contains steel balls to further grind the material. The powder is discharged through the discharging grate plate to complete the grinding operation.

1. High chromium alloy lining is one of the most common lining materials in cement mills. The main component of high chromium alloy is chromium. After the addition of chromium reaches more than 12%, its hardness can reach HRC58-65. It has excellent wear resistance and is a common material for cement ball mill linings. High chromium alloy linings are usually produced using investment casting technology. The advantage is low cost, but the disadvantage is that the thermal expansion coefficient is large and it is prone to cracking, so there are certain requirements for installation workers.

2. Aluminum silicate ceramic lining has a small thermal expansion coefficient, high hardness, outstanding wear resistance, and can resist high temperature and acid and alkali corrosion. The advantages of aluminum silicate ceramic lining are corrosion resistance, wear resistance, and long service life, but the price is relatively high. Some customers cannot contain iron in their materials, so this ceramic lining will be used.

3. Rubber lining is rarely used in cement mills, mainly for earthquake resistance and vibration reduction, but rubber lining also has certain wear resistance and is also used in some occasions. The advantages of rubber lining are good wear resistance and can reduce noise and vibration. It is more commonly used in mining ball mills.

For a small cement plant with an annual output of 25 million tons, a ball mill with a capacity of 3.2x14m is generally selected to meet production needs. For large cement plants with an annual output of more than 50 million tons, it is recommended to choose a ball mill with a larger capacity, such as 5.5.0x15m or even larger models, to ensure the continuity and efficiency of production. The hardness and humidity of different cement raw materials will affect the selection of ball mills. Generally, we recommend that customers send us the raw material report, and our technicians will select the model according to the moisture content of the material.

1. Uniform grinding effect: The cement ball mill adopts the working principle of rolling grinding. Through the contact and friction between the ball and the material, the material is uniformly squeezed and sheared during the grinding process. Compared with other grinding equipment, ball mills can better control the distribution of cement particles, so that the ground cement has a more uniform fineness. The uniformity of fineness is an important indicator to ensure the quality of cement, which directly affects the hydration reaction speed and strength growth performance of cement.

2. Excellent morphology of cement particles: The cement particles ground by the ball mill are spherical or polyhedral in shape. This morphology is conducive to the full contact of cement with water during use and promotes the hydration reaction. In contrast, the cement particles ground by the vertical mill often have a certain flat shape, and the hydration reaction rate is relatively slow. Studies have shown that cement produced by ball mills has good performance in strength, fluidity and durability.

3. Improve cement strength: In the process of cement grinding, there is a direct relationship between grinding fineness and cement strength. Cement ball mills can effectively control the fineness of cement powder, usually grinding to a standard range of 300-400㎡/kg of specific surface area, which can ensure that the cement forms a dense structure during the hardening process and enhances early and late strength. In addition, by optimizing the liner design and ball ratio, the ball mill can further improve the grinding efficiency, increase the fineness of the powder, and further improve the compressive strength of cement.

4. Improve cement fluidity: The cement powder produced by the ball mill has good fluidity and is easy to operate in the subsequent mixing, conveying and pouring process. Good fluidity not only improves construction efficiency, but also reduces the void ratio in concrete, thereby improving the density and durability of concrete. In contrast, the cement ground by the ball mill is more plastic during use and is suitable for different construction environments and technical requirements.

5. Compensate for insufficient clinker quality: In actual production, the quality of clinker may be affected by various factors, such as fluctuations in mineral composition or unstable burning quality. The ball mill can make up for the shortcomings in clinker quality through its powerful grinding capacity. Through appropriate fineness control and grinding technology, the ball mill can improve the early strength and hydration heat release of cement, effectively compensate for the impact of clinker quality, and ensure the qualified rate and stability of cement leaving the factory.

The output of cement grinding system is affected by the grindability of clinker, and the power consumption of grinding varies greatly. The grindability of clinker is related to the content of each mineral component in clinker and the cooling rate of clinker. When the content of C3S in the clinker mineral composition is high, the content of C4AF is low, the cooling rate of clinker is fast, the clinker mineral forms fine crystal glass, and the texture is brittle, the grindability is good; if the content of C2S and C4AF in the clinker mineral composition is high, the clinker is tough, and the grindability coefficient is small, the clinker is difficult to grind and the power consumption is relatively high. In addition, the grindability of clinker is also related to the calcination atmosphere, calcination temperature, heating rate, etc. For example, the grindability of overburned material or yellow core material is relatively poor.