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Suitable moisture content of pipe mill grinding materials an

Date:2019-06-28 13:44     writer:cement editor     Views:

At present, the tube mill grinding system is basically dry grinding, and the moisture content of the material in the mill has a great influence on the grinding condition and the grinding efficiency. How to properly handle the moisture problem of the grinding materials is a problem often encountered by various powder manufacturing companies. Some of the experience we have accumulated in our actual work may be helpful in solving this problem.

1.Relationship between moisture content and paste

Zimbabwe Pacsatr Cement Company has a medium-sized 2.2×7.0m open-flow cement mill. The first warehouse is often full-grinding. When the grinding door is opened, we find that the material is agglomerated in the pores of the compartment plate, the pupil is blocked, the steel ball, The surface of the liner is heavily wrapped. Further investigation found that the average moisture content of the milled material is as high as 5% to 6%, which is the main reason for the grinding of the mill. In order to explore the relationship between the moisture content of the material and the paste, we used the Ф500×5OOmm ball mill to test with the company.

The test materials and their ratios are the same as the actual production. The clinker is the wet kiln clinker of Zimbabwe Huajin Cement Plant. The slag is taken from Zimbabwe Steel Company. The material ratio is: clinker: slag: gypsum=61.7:36.2:2.1. The results after grinding for 3Omin are shown in Table 2.
It can be seen from Table 2 that as the moisture content of the material increases, the pasting phenomenon becomes more and more serious, and at the same time, the steel segment has better anti-widiness than the ball and the liner.

In actual production, Pacsatr found that if the moisture content of the material exceeds 2.8%, the clogging of the paste ball, the paste liner and the partition plate will occur. However, when the water content was 2.5%, the grinding machine did not have these scouring phenomena. This is different from the results of the above small grinding test, because the grinding machine has good ventilation during actual production, and the residence time of the material in the grinding is short, making the grinding difficult to occur.

2.The effect of low moisture content

Pacsatr also found that when the grinding water content is less than 1.5%, the specific surface area of ​​the product is reduced from 350m2/kg to 31Om2/kg, and the compressive strength and flexural strength of the 7-day and 28-day-old ages also decrease. Some of our domestic powder companies often encounter similar situations. For example, Tianjin Huanjin Building Materials Co., Ltd. has a Zhongyu 3.O×13m open-flow tube mill, grinding 100% slag powder, and the moisture content of the grinding slag is generally controlled at 1.5%-1.8%, and the Taiwanese production reaches 21t/h. The surface area is 420m2/kg, but when the moisture content of the milled material drops below 1.0%, the specific surface area will drop below 380m2/kg. There is also a mineral powder company in Jiangsu. Sometimes, because the slag is too dry, the specific surface area of ​​the product is difficult to reach the requirement of 400m2/kg or more. However, as long as the proper amount of water is sprayed on the grinding material, the problem will be solved.

In short, water can improve the efficiency of tube mill grinding. What is the reason? In general, SiO2 or other silicate materials, the surface-broken Si-O-Si bond and the unbroken Si-O-Si bond can be chemically adsorbed with water vapor to form a surface adsorption layer with OH-group. The water molecules are then adsorbed by hydrogen bonds on the OH-layer. The formation of the adsorption film reduces the free enthalpy of the surface of the powder, making it more difficult to agglomerate into a ball, and it is difficult to adhere to the lining plate and the abrasive body. Secondly, the adsorption film also significantly reduces the mechanical strength of the material. According to Griffith's glass fracture theory, the relationship between the actual fracture strength R of the material and the surface free a:.

Since the adsorption film lowers the surface energy of the inner wall of the microcrack on the solid surface, the breaking strength thereof is drastically lowered. For example, ordinary soda lime silicate glass has a strength of 25,000 psi in vacuum and only 12,000 psi in saturated steam. Therefore, water can improve the grinding efficiency.

3.Factors affecting optimal moisture content

Whether the moisture content of the grinding material is too high or too low will have an adverse effect on the production of the tube mill, that is, there is an optimum moisture content. Its scope is closely related to the specific mill, materials, grinding process, etc. In the long-term work, we have summarized the following rules:

(l) The better the fluidity of the material, the less likely it is to be ground. For example, if 5% of fly ash is blended in the slag, the fluidity of the material is greatly improved, and the suitable moisture content of the milled material can be relatively increased;

(2) Materials that are stored for too long are particularly easy to smear. We encountered a kind of slag in Zimbabwe and stored for 10 years. Even if the material is strongly dried and the water content is below 0.8%, it is easy to be smeared;

(3) The smaller the pupil of the compartment plate, the more likely it is to block, which leads to a paste. Enlarging the pupil can increase the proper moisture content of the grinding material;

(4) The larger the air volume in the mill, the higher the wind speed, and the higher the moisture content of the milled material;

(5) The higher the temperature inside the mill, the higher the moisture content of the milled material;

(6) Steel segments are harder to grind than steel balls and fine grinding bins compared to coarse grinding bins.

In short, the suitable moisture content of the milled material is not constant and can be improved by optimizing the above items, thereby improving the efficiency of the drying equipment and the grinding equipment.

4.in conclusion

If the moisture content is too high, it will cause the mill to grind and the moisture content is too low, which will not only reduce the output of the dryer, increase the coal consumption, but also reduce the production and quality of the tube mill. There is an optimum range of moisture content, which is closely related to the internal structure and process conditions of the tube mill and the external environment during actual production. Each factory should find the best value according to the specific conditions, and fully consider the influence of material flow, ventilation, grinding body and other water requirements in the design of the mill process.

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