Grinding and grading operations are within the scope of ore preparation operations and are the follow-up process after crushing and screening. The position and function of the classification operation in the process are divided into 5 types.
1. Pre-grading
Pre-classification is generally not used before the first stage of grinding. It is only considered when the feed size is less than 6-8mm and the qualified product content in the feed is greater than 15%. The main function of pre-classification in the process is to pre-separate qualified products for minerals, so as to increase the processing capacity of the ore mill, or to separate secondary sludge for further processing.
2. Fully closed circuit grinding inspection and classification
The function of closed-circuit grinding inspection and classification is to control the particle size of grinding products. The classification returns to the grinding machine to increase the ore throughput per unit time of the grinding machine and increase the production capacity of the grinding machine. However, the circulating load of the returned sand will affect the production capacity of the grinding machine.
The inspection and classification in the first stage of grinding and the second stage of grinding can make the grinding machine work effectively, avoid over-grinding and meet the requirements of grinding fineness in the next stage of sorting operations. Therefore, it is always necessary to check the classification work.
3. Overflow control classification
In the first stage of grinding, a very fine final product must be obtained, or when stage separation is required in the first stage of grinding, or a hydrocyclone is required for classification, the coarser must be removed in a mechanical classifier. In the case of particles, the overflow control is used to control the classification operation.
4. Return sand control grading
The purpose of the returned sand control classification is to reduce the content of qualified products in the returned sand. Although the effect is not significant, and a classifier needs to be added to increase the complexity of the configuration, it is still used in practice.
5. Local closed-circuit grinding inspection and classification
The local closed-circuit grinding inspection classification is not only the inspection classification of the first stage grinding, but also the pre-grading of the second stage grinding. The main feature of this classification process is that the load of the second-stage grinder is not changed by overflow, but by sedimentation, so the load between the two-stage grinder is easy to distribute and adjust. However, the classification process also has drawbacks. One stage of classification removes a large amount of sludge, which greatly reduces the amount of sludge in the second stage of classification, reduces the slurry viscosity, and makes the classifier work unstable.