7 basic process flows of ultrafine grinding
The mechanical ultrafine grinding process generally refers to the grinding and classification process for preparing particle size distribution d97≤10μm, which is divided into dry method and wet method. The ultra-fine grinding unit operation (i.e. one-stage ultra-fine grinding) currently used in industry has the following process flows:
Opening process
Generally, airflow mills such as flat or disc type, circulating tube type, etc. often use this open circuit process because they have self-grading function. In addition, this process is often used for intermittent ultrafine grinding.
The advantage of this process flow is that the process is simple. However, for ultra-fine grinders that do not have the function of self-classification, since there is no classifier in this process, qualified ultra-fine powder products cannot be separated in time. Therefore, the particle size distribution range of general products is wide.
Closed circuit process
This process consists of a classifier and an ultra-fine grinder forming an ultra-fine crushing-fine classification closed-circuit system. This process is often used in continuous crushing operations of ball mills, stirrer mills, high-speed mechanical impact mills, vibration mills, etc.
Its advantage is that it can separate qualified ultrafine powder products in a timely manner, thereby reducing the agglomeration of fine particles and improving the efficiency of ultrafine crushing operations.
Opening process with pre-grading
In this process, the materials are classified before entering the ultra-fine grinder, and the fine-grained materials are directly used as ultra-fine powder products. The coarse-grained materials then enter the ultra-fine grinder for crushing.
When the feed contains a large amount of qualified ultrafine powder, using this process can reduce the load on the crusher, reduce energy consumption per unit of ultrafine powder product, and improve operating efficiency.
Closed circuit process with pre-grading
This combined operation not only helps improve crushing efficiency and reduce energy consumption per unit product, but also controls the particle size distribution of the product.
This process flow can also be simplified to only one grader, that is, the same grader is used for pre-grading and inspection and grading.
Opening process with final grading
The characteristic of this crushing process is that one or more classifiers can be installed after the crusher to obtain two or more products with different fineness and particle size distribution.
Opening process with pre-grading and final grading
The essence of this process flow 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 two or more products with different fineness and particle size distribution.
The number of crushing stages mainly depends on the particle size of the raw materials and the required product fineness. For raw materials with relatively coarse particle sizes, a process of fine crushing or fine grinding and then ultra-fine crushing can be used. Generally, the raw materials can be crushed to 74 μm or 43 μm and then an ultra-fine crushing process can be used.
For materials that require very fine particle size and are easy to agglomerate, a multi-stage ultra-fine crushing process in series can be used to improve operating efficiency. However, generally speaking, the more crushing stages, the more complex the process will be.