Effect of classifier on cement qualityDate: 2019-06-21 Views:
The ball mill is equipped with a classifier and is called a closed loop system. The function of the powder sorting machine is to grind the mill to a fine powder of a certain particle size to separate the qualified product, and the coarse powder is returned to the mill for re-grinding; and the fine powder can be prevented from causing a buffering effect in the grinding inner body with the grinding body. Improve the grinding efficiency of the mill, adjust the particle composition, and prevent the unevenness of the fine powder, so the powder selection machine can guarantee the quality of the grinding. The comprehensive performance of the classifier depends not only on the efficiency of the powder selection, but also on the percentage of particles in the 3~30μm part of the finished product. Because the particles in this section are the best part of the cement strength. The efficiency of powder selection not only affects the production of mills, but also has a great relationship to the quality of the products.
Too low powder selection efficiency will not only increase the output of the mill, but also directly affect the quality of the product. The φ2.4x7m cement mill of a cement plant in Guangxi is equipped with a 4.0m centrifugal type ordinary classifier. The output is only 17~18 tons, and its specific surface area is high, but the cement strength is low. The reason is as follows: First, the φ2.4x7m mill is equipped with a 4.0m classifier which is relatively small; the second is that the centrifugal classifier has a low powder selection efficiency of only 30%. This situation not only curtails the output of the mill, but also the grinding machine has a serious phenomenon of grinding. According to the test, the particles below 3 mm account for about 50%, because the particles in this interval have little effect on the formation and growth of cement strength. . Therefore, the specific surface area is high and the cement strength is low. Particles below 3 μm are generally required to be less than 10%.
Too high powder selection efficiency will greatly increase the mill output, but it will have a greater impact on the quality of the cement. The 1# cement mill of a cement plant in Sichuan Province uses a cyclone rotor type separator. The fineness of the cement is controlled between 1.5% and 1.8%, the specific surface area is only 240~250m2/kg, and the strength of the cement is 3d and 28d. In any case, the control requirements are not met. The main reason for the formation of such a low specific surface area and low strength is that since the powder selection efficiency of the classifier is too high, the proportion of the separated 3 to 30 μm particles is too small, and the particles of 30 to 80 μm are The proportion of finished products is large. Two 2.2×6.5m cement mills in a cement plant in Hebei Province, equipped with a 3.5m centrifugal classifier and a 500 cyclone rotor classifier. In order to meet the requirements of the new national cement standard, they put the 3.5m centrifugal type. The fineness control index of the powder separator is set at 4%~5%, and the fineness control index of the 500 cyclone rotor type separator is set at 2%. The production time of the two mills is basically the same as the specific surface area of the produced cement. It also shows that the powder selection efficiency of the classifier is too high, and the specific surface area is rather reduced.
When the powder selection efficiency is reached, the specific surface area and strength requirements of cement are most favorable. After many experiments and comparisons, we believe that the powder selection efficiency of the closed-circuit grinding system of cement production should be controlled at 60%. A 65% or so is more appropriate, and the highest is not more than 70%. In the finished product, the proportion of particles of 3~3μm can be larger, which can exceed 65%. It will not form the grinding phenomenon due to the low efficiency of the powder selection, and will not reduce the cement due to the high efficiency of the powder selection. strength.
The product fineness index and specific surface area index are the control means. Through these means, the purpose of achieving the 3d and 28d strength indicators is finally achieved, and finally meets the requirements of the new national cement standard.
Through the above analysis and demonstration, we have to meet the requirements of the new national cement standard. Too high powder selection efficiency forces you to lower the fineness control index of the product. Of course, the output of the mill will also decrease at the same time. Too low the efficiency of the powder selection, the mill's production time will not be very high, and it will form a grinding phenomenon, and it is likely that a higher specific surface area will occur. At this time, it is not possible to look at the specific surface area alone. If the proportion of particles below 3 um is large, the cement strength will decrease.