6 common ultrafine grinding process flows, which one is suitable for your powder?

Impact ultrafine grinding process generally refers to the grinding and grading process for preparing powders with a particle size distribution of d97≤10μm, which is divided into dry method and wet method. At present, the ultrafine grinding unit operation (i.e. one-stage ultrafine grinding) used in industry has the following process flows:

1. Open circuit process

Generally, flat or disc-type, circulating tube-type and other air flow mills often use this open circuit process flow because they have the function of self-grading. In addition, intermittent ultrafine grinding also often uses this process flow.

The advantage of this process flow is that the process is simple, but for ultrafine grinders that do not have the function of self-grading, since there is no classifier in this process flow, qualified ultrafine powder products cannot be separated in time. Therefore, the particle size distribution range of general products is relatively wide.

2. Closed circuit process

Its characteristic is that the classifier and ultrafine grinder form an ultrafine grinding-fine grading closed circuit system. This process flow is often used for continuous grinding operations of general ball mills, stirred mills, high-speed mechanical impact mills, vibration mills, etc.

Its advantage is that it can timely separate qualified ultrafine powder products, thus reducing the agglomeration of fine particles and improving the efficiency of ultrafine grinding.

3. Open-circuit process with pre-grading

Its characteristic is that the material is first graded before entering the ultrafine grinder, and the fine-grained material is directly used as the ultrafine powder product. The coarse-grained material enters the ultrafine grinder for grinding. When the feed contains a large number of qualified ultrafine powders, this process can reduce the load of the grinder, reduce the energy consumption of the unit ultrafine powder product, and improve the operation efficiency.

4. Closed-circuit process with pre-grading

This combination of operations not only helps to improve the grinding efficiency and reduce the energy consumption per unit product, but also controls the particle size distribution of the product.

This process can also be simplified to only set up one classifier, that is, the same classifier is used for pre-grading and inspection and grading.

5. Open-circuit process with final classification

The characteristic of this grinding process is that one or more classifiers can be set after the grinder to obtain more than two products with different fineness and particle size distribution.

6. Open-circuit process with pre-classification and final classification

This process can not only pre-separate some qualified fine-grained products to reduce the load of the crusher, but also the final classification equipment can obtain more than two products with different fineness and particle size distribution.

How to set the number of ultra-fine grinding stages?

In terms of grinding methods, ultra-fine grinding processes can be divided into three types: dry (one or more stages) grinding, wet (one or more stages) grinding, and dry-wet combined multi-stage grinding.

The number of grinding stages mainly depends on the particle size of the raw materials and the required product fineness.

For raw materials with relatively coarse particle size, a process flow of first fine grinding or fine grinding and then ultra-fine grinding can be adopted. Generally, the raw materials can be crushed to 74μm or 43μm and then a stage of ultra-fine grinding process can be adopted;

For materials with very fine product particle size requirements and easy to agglomerate, a multi-stage ultra-fine grinding process flow can be adopted in series to improve operating efficiency.

However, generally speaking, the more grinding stages there are, the more complex the process flow and the greater the engineering investment.