Comparison of detection methods of cement fineness in cement production process Henan Hongxing

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Comparative introduction of detection methods of cement fineness in cement production process

The fineness of cement is an important index to measure the finished cement. In order to produce high cement, each large cement plant needs to carry out reasonable inspection on the cement fineness. Through the reasonable inspection, we can analyze whether the cement fineness is reasonable, so as to determine the final finished cement. Therefore, this paper comprehensively introduces the detection method of cement fineness.

 Cement production site

summary

The fineness of cement is the index of fineness or dispersion of cement. It is related to the cement products and the economic rationality of production. In the preparation of raw meal, raw materials such as limestone, clay and iron powder should be ground down. The fineness of raw meal is closely related to the sintering of clinker. A suitable raw meal can ensure a certain chemical reaction rate between raw meal particles, so as to obtain high cement clinker.

In the process of grinding cement, the fineness of clinker directly affects the properties of cement. The smaller the clinker particles, the larger the surface of water reaction, the faster the hydration reaction, which is conducive to the formation of hydration products. Therefore, scholars at home and abroad have studied the reasonable gradation of cement particles, and generally believe that 3 μ M-30 μ m particles play an important role in cement strength. Reasonable control of fineness is of great significance not only to improve the quality of cement products, but also to save energy.

Cement fineness detection method

Fineness is one of the main indexes of cement production control. The fineness of cement can be detected by the following three methods.

Sieve analysis

The fineness is expressed by the percentage of the residue remaining on the standard sieve with a certain aperture. According to the different measurement methods, it can be divided into dry sieve analysis, wet sieve analysis and negative pressure sieve analysis. China's cement standard stipulates that the fineness of ordinary portland cement, slag Portland cement, pozzolanic Portland cement and fly ash Portland cement is 80 μ m, and the residue of square hole sieve shall not exceed 10%.

Dry and wet methods can be selected according to specific materials and requirements. But generally speaking, wet method is used if the material with fine particles is mixed with water, because the wet method can avoid very fine particles sticking on the screen hole and blocking the screen hole. And the influence of wet material temperature and atmospheric humidity. For this reason, wet and dry methods are listed as national standards and used as test methods for determining cement fineness.

According to the performance of the water screen method, the operation equipment is simple, the cost is low, it is easy to master, and the accuracy is high. As long as the test screen strictly implements the system of periodic correction, it is not difficult to keep the error within ± 0.2%. Therefore, this method is widely used.

Determination of specific surface area

The specific surface area determination method can be divided into air permeability method, low pressure ventilation method and dynamic adsorption method.

1. The permeability method is to measure the specific surface area of cement according to the resistance of air passing through a certain thickness of cement layer under normal pressure.

2. The low-pressure air permeability method is to measure the specific surface area of cement according to the different resistance of gas passing through a certain thickness of cement layer under negative positive pressure.

3. The dynamic adsorption method takes advantage of the asymmetry of the force on the solid surface molecules, so that the molecules and atoms on the solid surface are unsaturated and adsorb gas or liquid. The specific surface area is calculated according to the adsorption capacity of single molecular layer according to B and t adsorption formula.

Determination of particle size distribution

It can be divided into settlement analysis method and air separation method.

1. The settlement analysis method is based on Stokes settlement law. That is, the cement particles settle freely in the liquid medium, and the settling velocity of the particles is proportional to the square of the particle size to determine the particle gradation.

2. The air separation method is to determine the particle size distribution of cement by using different sizes of cement particles taken away by different speed of air to achieve particle separation.

Comparison between sieve analysis method and surface area method

Although the sieve analysis method is relatively simple, the separation of coarse particles is more appropriate, but also very good. However, if we want to determine the fine particle powder, the sieve analysis method can not reflect the size of the fineness correctly. Compared with the surface area method, the sieve analysis method has the following disadvantages:

1. There is a certain limit to the size of the sieve pore, especially for the particles less than 40 μ m, it is difficult to determine the size of the sieve pore.

2. Due to the irregular shape of cement particles and the great change of particle size distribution, the true fineness of cement can not be seen from the sieve analysis. 80 μ m square hole sieve. The cement particle gradation with the same sieve residue is not necessarily the same, and the specific surface area can be greatly different, so it is difficult to obtain a certain relationship with the strength.

3. It takes longer time to determine the specific surface area by dry screening method than by air permeability method, and the labor intensity of dry sieve is also greater than that of air permeability method. In the manufacture of screen mesh, the size of mesh is not easy to be uniform.

From the above points, it is much better to detect the fineness of cement by measuring specific surface area method than by sieve analysis method. Therefore, it is of great significance to control cement production by using specific surface area method instead of sieve analysis method to ensure and improve production.

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