In the formal operation process of ore dressing plants, the role of classification operation is to work in conjunction with grinding operations, promptly separating products with qualified particle sizes, reducing over-grinding, and improving the production capacity and efficiency of the grinding machine.
1.Definition of Classification Operation: Classification operation refers to the operation of dividing mineral particles with different sizes, shapes, and densities into several narrow levels based on their settling velocities in water. This process is known as wet classification.
2.Purpose of Classification Operation: The primary purpose is to promptly separate qualified products, avoid over-grinding, and simultaneously allow unqualified (coarse) materials to be returned for regrinding.
3.Significance of Classification Operation:
Classification and grinding together form a grinding cycle operation.
It separates qualified grinding products to prevent over-crushing and mud formation.
It avoids unnecessary grinding processes and expedites the material's transfer to the sorting operation.
Coarse sand particles with inadequate granularity are returned to the grinder for regrinding.
Classification Process: Classification is a production process coordinated with grinding operations. In a closed-circuit grinding cycle, the discharge from the grinding machine enters the classifier. The classifier then separates it into qualified products (overflow) and coarse sand (returned sand). The coarse sand is sent back to the grinder for regrinding, while the overflow proceeds to the next operation.
4.Nature of Classification:
Preliminary Classification: Separating qualified products from the original ore entering the grinder in advance, improving grinding efficiency.
Check Classification: Separating unqualified products from the grinding discharge, returning them to the grinder for regrinding. It controls the maximum particle size in qualified products, reduces over-crushing, and enhances grinding efficiency.
Preliminary and Check Classification: In closed-circuit grinding, preliminary and check classification are often combined, referred to as preliminary and check classification.
Control Classification: Operating on the overflow after check classification to further separate any unqualified products, making it conform to the granularity requirements of the next operation.
5.Difference Between Classification and Screening:
Classification and screening share similar properties; screening strictly separates materials based on geometric dimensions.
Classification separates materials based on differences in settling velocities, possessing a wider range of particle sizes.
6.Classification Equipment:
Classification equipment includes spiral classifiers, hydraulic cyclones, rake classifiers, flotation classifiers, etc.
(I) Spiral Classifier:
Basic Structure: Consists of a U-shaped trough, spiral device, transmission device, lifting mechanism, supporting bearings, etc.
Types of Spiral Classifiers:
High Weir Spiral Classifier: The position of the overflow weir is higher than the bearing center of the lower end of the spiral shaft. Suitable for separating coarse particles in the range of 0.15-0.20mm, often used in the first-stage grinding.
Submerged Spiral Classifier: 4-5 turns of the spiral are immersed in the pulp. It is suitable for fine particle classification and can achieve an overflow fineness with a particle content greater than 65% for particles smaller than -0.074mm. Mainly used in the second-stage grinding.
Low Weir Spiral Classifier: The overflow end is lower than the lower end bearing center, with a small classification area. Rarely used, mainly for tin ore or dewatering.
(II) Hydraulic Cyclone (Hydraulic Classifier):
Structure: Mainly composed of a feeding pipe, cylindrical shell, conical container, sand discharge nozzle, and overflow pipe. The upper part is cylindrical, and the lower part is conical, with a central overflow pipe and a sand discharge port at the bottom.
Classification Principle: Utilizes centrifugal force to classify materials.
Features: Simple structure, no moving parts, small size, small footprint, large processing capacity per unit area, easy operation and maintenance, and low cost.
Application: Used for preliminary classification, often forming a closed-circuit grinding with a second overflow-type ball mill. It has a large ore supply pressure and a thick cylinder diameter, making it suitable for classifying particles in the range of -800um to -74um.
This provides you with an overview of the definition, significance, and working process of classification operations. While classification equipment may seem unimportant in ore dressing, selecting the right equipment is crucial for improving the grinding efficiency and processing capacity of ball mills. Therefore, scientifically choosing suitable classification equipment becomes particularly important.
