How Can You Improve Screw Classifier Efficiency in Mineral Processing?

In the mineral processing industry, many concentrators encounter the issue of significantly reduced classification efficiency in their screw classifiers. The primary cause of this problem is the disordered settling of fine and heavy ore particles alongside coarse and light particles during the classification process. This leads to the phenomenon of “equal fall,” where fine particles overflow while coarse particles settle, reducing the overall efficiency of the screw classifier.

Double roller screw classifier manufacturers 1 - How Can You Improve Screw Classifier Efficiency in Mineral Processing?

Measures to Improve Classification Efficiency
1.Optimizing Screw Speed
The rotational speed of the screw is crucial for effectively conveying settled coarse particles. If the screw shaft rotates too quickly, it increases the stirring effect of the slurry, causing more coarse grains to be entrained in the overflow product. To achieve a larger overflow and process denser materials that settle faster, the spiral speed can be increased appropriately. However, it is essential not to exceed the optimal speed to avoid disrupting the classification effect. Generally, the speed should be controlled within the range of 1.5-10 revolutions per minute (r/min).
In classifiers used for second-stage grinding or grinding cycles, the screw speed should be reduced as much as possible. For large screw classifiers, lower speeds are generally used. For example, to obtain a coarse overflow, the speed of a 2-meter diameter spiral should not exceed 6 r/min, and for spirals with a diameter of 1 meter or more, the speed should be controlled between 2-8 r/min.
2.Controlling Slurry Concentration
The viscosity of the pulp decreases as the pulp concentration decreases, which accelerates the settling velocity of ore particles and results in finer overflow products. Conversely, higher concentrations lead to coarser overflow products.
However, if the pulp concentration is reduced too much, the overflow product may become coarser. This is because a significant decrease in concentration increases the pulp volume and flow rate (both upward and horizontal), causing coarser particles to be washed into the overflow. Therefore, the pulp concentration must be controlled according to specific regulations.

When the feed contains more mud or fine grains, increasing the water content to reduce the pulp concentration can help achieve the desired overflow fineness. Conversely, when the feed has less mud or has undergone desliming treatment, the slurry concentration should be increased to minimize the entrainment of fine-grained materials in the back sand.

Best Practices for Spiral Classification
For effective spiral classification beneficiation, it is recommended to purchase equipment from professional manufacturers and adhere to the technical parameters they provide. Additionally, operators should enhance their skills, pay attention to every detail in the selection process, and promptly address any emergencies to ensure smooth classification operations.

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