Dry classifiers are designed to separate particles based on their size, shape, and density using the principle of differential settling velocities in air. The different types of dry classifiers include the air classifier, zigzag classifier, and centrifugal classifier.
Air classifiers are perhaps the most widely used dry classifiers in the mineral processing industry. They are capable of separating particles in the size range of 1-100 microns based on their shape, density, and terminal velocity in air. An air classifier operates by injecting a stream of air into the housing containing the feed material, which is then dispersed and separated based on the principle of differential settling velocities in air. The fine particles are carried upwards by the air stream and collected in a cyclone separator, while the coarse particles are ejected from the bottom of the classifier.
The zigzag classifier is another type of dry classifier that is designed to separate particles based on their density and size. It is particularly useful for separating lightweight particles from heavier particles. The zigzag classifier operates on the principle of particle inertia, where the heavier particles are deflected to a greater extent than the lighter particles as they pass through a series of angled plates. The lighter particles move to the outer edge of the zigzag plates and are collected in a hopper, while the heavier particles travel to the center of the plates and are ejected from the bottom of the classifier.
The centrifugal classifier is another type of dry classifier that is designed to separate particles based on their size and density. It operates on the principle of centrifugal force, where the feed material is injected into a rotating drum at high speed, creating a vortex in the housing. The heavier particles are forced to the outer edge of the vortex due to centrifugal force and collect in a hopper at the bottom of the classifier, while the lighter particles are carried upwards by the air stream and collected in a cyclone separator.
In conclusion, dry classification is a crucial process in mineral processing, and the use of air as the fluid medium provides an efficient method for separation of fine particles. The different types of dry classifiers, including air classifiers, zigzag classifiers, and centrifugal classifiers, offer flexibility and versatility in the separation process, making them a key component in the mineral processing industry. Properly understanding the principles and applications of dry classifiers can help improve the efficiency and effectiveness of mineral processing operations.