Screening involves separating granular ore material into different grades by particle size. Industrial screening is extensively used for size variations from 300 mm to around 40µm, although the efficiency decreases rapidly with fineness. Dry screening is generally limited to the material above 5 mm in size, while wet screening down to around 250µm is standard.
There are numerous types of industrial screen products available in the market today. The dominant screen type in industrial applications is the vibrating screen, of which there are many sub-types in use for coarse and fine-screening applications.
- Vibrating screens
Vibrating screens are the most essential and multifaceted screening machines for mineral processing applications. The success rate of the vibrating screen has made much older screen types in the mineral market industry, including shaking and reciprocating screens.
Vibrating screens have a rectangular screening surface with feed and oversize discharge at opposite ends. They perform size separations from 300mm to 45µm and are used in various sizing, grading, scalping, dewatering, wet screening, and washing applications.
- Inclined screens
Inclined or circular motion screens are widely used as sizing screens. A vertical circular or elliptical vibration is induced mechanically by rotating unbalanced weights or flywheels attached to a single drive shaft. The amplitude of the throw can be adjusted by adding or removing weight elements bolted to the flywheels.
The rotation direction can be contra-flow or in-flow. Contraflow slows the material more and permits more efficient separation, whereas in-flow allows greater throughput. Single-shaft screens must be installed on a slope, usually between 15 °and 28 °, to help material flow along the screen.
- Grizzly screens
Very coarse material is usually screened on the base of an inclined screen, now described as a grizzly screen. Grizzlies are distinguished by straight steel bars or rails set at a fixed distance from the steel and installed in line with ore flow. The gap between the grizzly bar is usually greater than 50 mm and can be as large as 300 rams, with feed top size as large as 1 m. Vibrating grizzlies are generally inclined at around 20 ° and have a circular throw mechanism.
- Horizontal screen
Horizontal screens use elliptical force to generate high performance and efficiency. Their proven design helps ensure operational safety and simple maintenance to drastically improve their service life and profitability.
- Resonance screen
RT, known as resonance screens, are similar to horizontal screens that function on the moto of resonance, with two oscillating frames connected by springs. It consists of a screen frame attached by rubber buffers to a dynamically balanced frame having a natural resonance frequency that is the same as that of the vibrating screen body.
The vibration energy imparted to the screen frame is stored in the balancing structure and re-imparted to the screen frame on the return stroke. The energy losses are reduced to a minimum, and the sharp return motion produced by the resonant action imparts a lively movement to the deck and promotes good screening.
Industrial screen products fit into two standard categories: dry screening and wet screening. Understanding the different types of these products makes your industry grow and increases your knowledge in the screening market.
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