Overview of ultrafine powder classification

Ultrafine powder is not only the basis of preparing structural materials, but also a kind of material with special functions. It is necessary for many fields such as fine ceramics, electronic components, biological engineering processing, new photocopying materials, high-quality refractory materials and materials related to fine chemicals. With the wide application of ultrafine powder in modern industry, the classification technology of ultrafine powder is becoming more and more important in powder processing.

I. purpose and significance of classification

At present, the use of mechanical production of ultra-fine powder, it is difficult to make the material a mechanical crushing can achieve the required particle size requirements, the product is often in a large particle size distribution range. But in the use of modern industrial fields, often requires the ultrafine powder products in a certain size distribution range. In addition, in the process of crushing, powder, often only part of the product meet the requirements of the particle size, and the other part of the product failed to meet the size requirements, if you don't put these has reached the requirements of the product separation in time, and put them together with products that do not meet the requirements to crush, can cause energy waste and some products had shattered. For this reason, the products should be graded in the process of ultrafine powder production. On the one hand, the product particle size is controlled in the required distribution range; on the other hand, the products with the required particle size in the mixed powder are separated in time.

Principle of ultrafine classification

At present, the common classification method is based on gravity field and centrifugal force field.

The classification principle of gravity field is the oldest and most classical theory, which is based on stokes' law in laminar flow. In the classification process, it is assumed that the flow field is carried out according to the laminar flow state, and the ultra-fine solid particles are assumed to be spherical and free sedimentation in the medium. These are quite different from the actual situation. In the centrifugal force field, the particle can obtain the centrifugal acceleration which is much larger than the gravity force acceleration. Therefore, the sedimentation velocity of the same particle in the centrifugal field is much larger than that in the gravitational field. In other words, even the smaller particles can obtain the larger sedimentation velocity.

In addition, ultrafine powder classification can be divided into dry classification and wet classification according to the medium used. Dry classification is characterized by the use of air as a fluid, low cost, convenient, but it has two shortcomings, one is easy to cause air pollution, two is not high precision classification. There are many problems of post-treatment in the wet classification of liquid as the grading medium, that is, the graded powder needs to be dehydrated, dried and dispersed wastewater treatment, etc., but it has the characteristics of high classification accuracy and no explosive dust.

Three, ultra-fine classification equipment

So far, ultrafine grading equipment is in full bloom. According to the different fluid media can be divided into dry classification and wet classification, in dry classification, according to the different classification principles can be divided into gravity type, centrifugal type, inertia type and other types.

1. Gravity type ultrafine classifier

The gravity type ultrafine classifier classifies the particles with different size with different settling speed in the gravity field. Gravity classifier has two types: horizontal flow type and vertical flow type.

2. Inertia classifier

When particles move, they have a certain amount of kinetic energy. When they move at the same speed and with a large mass, their kinetic energy is also large, that is, their motion inertia is large. When they are affected by changing their motion direction, different trajectories will be formed due to different inertia, so as to achieve the classification of particles. At present, the size of the classifier has reached 1 m. If the particle agglomeration and the existence of indoor eddy current can be avoided effectively, the size of the classifier can reach sub-micron level, and the classification accuracy and efficiency can also be significantly improved.

3. Centrifugal classifier

Because centrifugal classifier is easy to produce centrifugal force field which is much stronger than gravity field, it is a kind of super fine classifier developed so far. According to the different flow patterns in centrifugal force field, they can be divided into free vortex type and forced vortex type. The common free vortex type (or quasi-free vortex type) includes DS classifier, SLT classifier, etc. Forced vortex classifiers include MC classifier, MS classifier, MSS classifier, ATP classifier, MP classifier, turbine classifier, etc.

4. Jet classifier

The jet classifier is a classifier which integrates the principles of inertia classification, rapid classification and Coanda effect of fine particles. Simply speaking, Coanda effect is the characteristic of fine particles moving along the curved wall surface with airflow. Compared with other classifiers, the jet classifier has the following characteristics:

(1) classification of non-moving parts, small maintenance workload, reliable work.

(2) the jet stream can make the powder get good pre-dispersion.

(3) once the particles are dispersed, they are immediately put into the classifier for rapid classification, thus avoiding the secondary agglomeration of particles to the greatest extent.

(4) multi-level products can be obtained, and the granularity of products at each level can be adjusted flexibly through the graded blade Angle and outlet pressure.

(5) high grading efficiency and granularity.

Four, the ultra fine classification should pay attention to the question

1. Grading operation and material nature

The physical properties of powders to be graded are one of the important factors affecting the grading process. If to the powdery body with strong abradability, should use wear-resisting material or add wear-resisting lining; For powders with strict requirements on iron pollution, an iron insulating lining should be used to prevent the powder from being coated with iron.

2. Pre-dispersion of powder

Powder dispersion is not good, agglomerated fine particles tend to behave as coarse particles. In order to achieve a good grading effect, the seed

Full particle dispersion is an important embodiment of grading technology. The selection of the right dispersants can not only improve the efficiency of superfine grading but also not affect the properties of powders.

3. Smooth grading area

The smooth grading area is the key to the success of the grading process. No matter what the grading field is, the common requirements are strong grading ability, clear grading surface and quick grading. In addition, it is also required to minimize or avoid the existence of eddy current, that is, it is required to streamline the form of a single.

summary

The powder industry as a multi-disciplinary, multi-professional horizontal cross-industry, in recent years by the attention of various industries, ultra-fine powder grading technology has also been rapid development, but with the rapid development of modern high-tech and new materials industry, ultra-fine powder grading technology problems and challenges are also increasingly prominent. Therefore, it is necessary to strengthen the research on the ultrafine classification technology and equipment.

Sichuan zhongjin powder equipment co., LTD. Is an enterprise specializing in the design, development and manufacture of crushers. The company specializes in the production of air mill, impact mill, classifier; Airflow pulverizer classifier, ultrafine pulverizer impactor, inert gas pulverizer classifier, dust remover, horizontal disc pulverizer, jet pulverizer classifier, steam kinetic energy pulverizer and other ultrafine powder equipment. Welcome to visit our company.

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