Superfine Powder Classification Technology and Its Typical Equipment

Ultrafine powder is not only the basis for preparing structural materials, but also a material with special functions.

With the application of ultra-fine powder in modern industry more and more widely, the position of powder classification technology in powder processing becomes more and more important.

1. The meaning of classification

In the pulverization process, only a part of the powder usually meets the particle size requirements. If the products that have reached the requirements are not separated in time, and then pulverized together with the products that do not meet the particle size requirements, it will cause energy waste and over-crushing of some products. In addition, after the particles are refined to a certain extent, the phenomenon of crushing and agglomeration will appear, and even the crushing process will deteriorate due to the larger particle agglomeration.

For this reason, in the process of ultrafine powder preparation, it is necessary to classify the product. On the one hand, the particle size of the product is controlled to be within the required distribution range; Then crush to improve the crushing efficiency and reduce energy consumption.

With the improvement of the required powder fineness and the increase of output, the difficulty of classification technology is getting higher and higher. The problem of powder classification has become the key to restrict the development of powder technology, and it is one of the most important basic technologies in powder technology. one. Therefore, the research on ultrafine powder classification technology and equipment is very necessary.

2. The principle of classification

Classification in a broad sense is to divide the particles into several different parts by using the different characteristics of particle size, density, color, shape, chemical composition, magnetism, and radioactivity.

Classification in a narrow sense is based on the fact that particles of different particle sizes are subjected to centrifugal force, gravity, inertial force, etc. in the medium (usually air and water), resulting in different motion trajectories, so as to realize the classification of particles of different particle sizes.

3. Classification of classifiers

According to the medium used, it can be divided into dry classification (the medium is air) and wet classification (the medium is water or other liquids). The characteristic of dry classification is that air is used as fluid, which is low in cost and convenient.

According to whether it has moving parts, it can be divided into two categories:

(1) Static classifier: There are no moving parts in the classifier, such as gravity classifier, inertia classifier, cyclone separator, spiral airflow classifier and jet classifier, etc. This type of classifier has a simple structure, does not require power, and has low operating costs. The operation and maintenance are more convenient, but the classification accuracy is not high, so it is not suitable for precision classification.

(2) Dynamic classifier: There are moving parts in the classifier, mainly referring to various turbine classifiers. This type of classifier is complex in structure, requires power, and consumes a lot of energy, but it has high classification accuracy and is easy to adjust the particle size of the classifier. As long as the rotation speed of the impeller is adjusted, the cutting particle size of the classifier can be changed, which is suitable for precision classification.

Typical Grading Equipment

(1) wet classifier

The wet classification of ultrafine powder is mainly divided into gravity type and centrifugal type according to the current market situation.

(2) Dry classifier

Most of the dry classifiers use centrifugal force field and inertial force field to classify powder, and they are important fine classification equipment with rapid development at present. The following are several representative devices.

Conical centrifugal air classifier. The conical centrifugal air classifier realizes the separation of coarse powder and fine powder under the action of centrifugal force. The finest particle size of the finished product of this equipment can reach about 0.95μm, and the classification accuracy d75/d25 can reach 1.16.

The equipment does not have any moving parts, and the angle of the deflector can be adjusted between 7° and 15°. The equipment has compact structure, high classification efficiency, and safe and reliable operation.