Classification monitors the crushing process. It also tracks the size of the final product. Dry classification is achieved with gas (usually air) as the medium. It is used in water shortage and arid areas, and when the process does not allow for the presence of water. Dry grading is the only option. In severe cold areas, the application of dry grading is also not affected. Dry classification saves a lot of water. This also stops the problem of dehydration in wet classification. It is an effective method for energy-saving classification. Common dry classification equipment includes double impeller air classifier, O-Sepa vortex classifier, cyclone separator, turbine classifier, gravity sedimentation classifier, inertial classifier and jet classifier.
Double impeller air classifier
The classifier has two impellers. It uses gravity and centrifugal sedimentation to classify. The product’s particle size can be as fine as -40 μm.
O-Sepa type eddy current classifier
It is an O-Sepa type eddy current classifier. The main parts of the machine are a spreading plate, impeller, and several air ducts. It has a primary, secondary, and tertiary air ducts. It also has guide blades and a shell.
Cyclone separator
The cyclone separator is a typical dry centrifugal sedimentation and classification equipment. Its main body consists of an upper cylinder and a lower truncated cone. A core tube is inserted from top to bottom along the center. It’s put in at the top of the cylinder. At the bottom of the cone, there is a coarse product outlet. The feed enters from the top of the cylinder near the outer edge. It moves with the air flow and is shaped by the chamber. This shaping makes it swirl. The material particles produce radial centrifugal sedimentation motion in the air flow. Large particles settle faster. They move closer to the cylinder wall. Then, they slide along it and are discharged from the bottom. The fine particles have a slow centrifugal sedimentation speed. They are held close to the axis. Then, they enter the core tube with the air flow and are discharged upward. Many products have improved. They are for practical use. They adapt to different grading requirements and get higher grades. The particle size classification of the cyclone separator is related to its size (cylinder diameter). The smaller the specification, the finer the classification particle size.
Turbine classifier
The turbine classifier is widely used for dry ultra-fine classification. It utilizes the principle of centrifugal sedimentation classification. Its main part is the turbine, also called the grading wheel. It has many blades to make a radial gap.
Dry gravity sedimentation classification equipment
The main dry gravity sedimentation classifiers include three types. They are horizontal flow, vertical flow, and meandering flow. They are used in the ultra-fine stage.
Dry inertia classification equipment
The main dry inertial classification equipment includes linear and curved inertial classifiers. It also includes louver and K-type classifiers. They have cut-point sizes from 0.5 to 50 μm.
Air classifier
An air classifier is a dry, ultra-fine classification tool. It uses jet technology, the inertia principle, and the Coanda effect. Jet technology is used for feeding materials. It lets the feed particles get the needed inlet speed and the air flow to make a Coanda effect. The Coanda effect happens when fluid (liquid or gas) and the surface of the object have friction. This friction causes the fluid to slow down. The surface can’t be too curved. In fluid mechanics, Bernoulli’s principle says slow flow will make fluid to stick to the surface.
