Ceramic abrasives are non-metallic abrasives. Compared with traditional metal abrasives, they have low density, high hardness, high temperature resistance and wear resistance.
Take the cement industry as an example: in 2014, ceramic balls began to be popularized and applied in the cement grinding industry, which is obvious for the reduction of power consumption in cement grinding, especially for the power-saving efficiency in the combined grinding with large roller press.
So, in the field of cement grinding, what specific conditions are needed to apply ceramic Abrasives?
1. Grinding material conditions
When the grinding material (＞ 1mm) changes from large to small, it needs impact crushing; when the material (＜ 1mm) changes from coarse to fine, it needs grinding.
Maximum particle size of grinding material: open circuit grinding ≤ 1mm; closed circuit grinding ≤ 2mm;
The average particle size of grinding materials: open grinding ≤ r0.08 @ 35%; closed grinding ≤ r0.08 @ 45%;
The average particle size of materials entering the ceramic ball Bin: open grinding ≤ r0.08 @ 15%; closed grinding ≤ r0.08 @ 25%;
The average moisture content of the grinding material is ≤ 1.5%.
2. Grinding system equipment conditions
The combination grinding system of roller press and ball mill is preferred, especially suitable for large roller press system. The control of the length of the chamber in the mill must be matched according to the particle size of the material provided to the mill by the roller press system and the stability of the system; the spiral feeding mode is preferred for the ball mill, and the control flow grate plate is used for the compartment plate; the impact of the broken material of the grinding head on the grinding body in the mill is avoided, because the flow rate of the material in the mill is about ten minutes, so the grinding must be stopped about ten minutes after the broken material.
3. Quality requirements for ceramic abrasives
The grinding body of microcrystalline alumina ceramics formed by isostatic pressing is preferred, with density ≥ 23.6g/cm3, bulk density ≥ 22.2t/m3, hardness (Mohs) ≥ 8, grinding P · o 42.55 cement, industrial operation for more than 2000 hours, single silo ball crushing rate ≤ 0.8%, and single silo ball consumption ≤ 20g per ton of cement.
4. Requirements for grading
In principle, ceramic balls instead of steel balls should follow the original matching, but considering the weight effect, we should increase one level and increase the filling rate; at the same time, we should compare the best value of the ball material ratio and control the flow rate of materials in the mill.
Ceramic balls are generally four graded balls, and the loading capacity at all levels should take into account the principle of close packing, so as to minimize the void ratio, improve the contact opportunity and grinding efficiency between ceramic balls and materials, which is conducive to the spheroidization of cement particles and improve the performance of cement. After many industrial tests, we found that the loading capacity of ceramic balls at all levels should adopt the distribution scheme of "2:3:3:2" The effect is better, but it should be determined according to the grinding materials, boring grain size and bin length.
The particle size distribution of ceramic balls and steel balls produced with the same clinker of the same variety shows that there is almost no difference between the cement produced by ceramic balls and steel balls.
5. Requirements for grinding equipment
It can adapt to the activation ring with high filling, the coordination between the reduction of central flange and ventilation, and the possible change of lining plate, etc.
6. Requirements for filling rate
Because the bulk density of ceramic abrasives is only about 40% of that of high chromium metal abrasives, in order to make up for the lack of abrasives, the filling rate is increased. Generally speaking, it is 6% - 10% higher than that of high chromium abrasives, that is to say, the filling rate is about 36% - 40%. Otherwise, the power and ventilation of the mill will be affected. According to this conclusion, it is necessary to have certain requirements for the internal structure of the mill.
7. Requirements for the internal structure of the mill
In order to adapt to the high filling rate of ceramic abrasives, it is generally necessary to adjust the mill content structure properly.
Take 4.2m × 13m mill as an example:
In addition to the structural transformation of the separator plate and the discharge grate plate of the mill to adapt to the ceramic grinding outside, the length of the grinding body in the first bin of the mill shall be reasonably adjusted according to the particle size of the materials supplied to the mill by the roller press system, especially the particle size of the materials supplied to the mill by the large roller press is basically less than 1mm, and the specific area is more than 220cm2 / g.
The second warehouse pays attention to the arrangement form of the activation ring and the adjustment of the height of the activation ring. The arrangement of the activation ring adopts dislocation or spiral arrangement, which can also be combined with the special-shaped lining plate or the activation lining plate alone. The activation ring of the 4.2m mill is adjusted from 1m to 1.4m to adapt to the high filling rate to break the dead zone and increase the activation energy. At the same time, the activation exchange and the edge of the lining plate must adopt arc transition to reduce the impact on the ceramic abrasive body Strike and destroy.
In addition, the lining plate and the activation ring in the grinding process should be treated with special corner arc to avoid impact on the ceramic products, and the manufacturing of ceramic grinding body should also avoid sharp edges and corners. From this point of view, the rolling ball and the pressing ball have special adaptability, while the relative damage and wear rate of the ceramic grinding body of the grinding and breaking ball combination will be higher in the early stage.
In recent two years, through the mutual running in and mutual understanding between ceramic ball industry and cement industry, the problems of "good ball" and "using good ball" have been gradually solved. Therefore, in the next few years, with the external and internal demand of capacity reduction and energy saving, it is imperative for ceramic balls to replace high chromium balls as the main market force of abrasives.
By extension, ceramic products such as ceramic lining or ceramic composite lining, ceramic roller and ceramic blade of powder concentrator will become a trend, which will bring new opportunities and possibilities for energy conservation and consumption reduction of building materials and other industries.
reference material:
[1] Wu Hongming, Zhou Guihong. Use of ceramic balls in cement industry [C]. Proceedings of the 10th domestic and foreign cement grinding new technology exchange conference and exhibition, 2018:111-116
[2] Yu Sheng. Application of ceramic abrasives in cement grinding system [J]. Ceramics, 2017 (11): 46-49
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