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Difference between revisions of "Screeners"
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A screening machine consist of a drive that induces vibration, a screen cloth that causes particle separation, and a deck which holds the screen cloth and the drive and is the mode of transport for the vibration. | A screening machine consist of a drive that induces vibration, a screen cloth that causes particle separation, and a deck which holds the screen cloth and the drive and is the mode of transport for the vibration. | ||
There are physical factors that makes screening practical. For example, vibration, | There are physical factors that makes screening practical. For example, vibration, g force, bed density, and material shape all facilitate the rate or cut. Electrostatic forces can also hinder screening efficiency in way of water attraction causing sticking or plugging, or very dry material generate a charge that causes it to attract to the screen itself. | ||
As with any industrial process there is a group of terms that identify and define what screening is. Terms like blinding, contamination, frequency, amplitude, and others describe the basic characteristics of screening, and those characteristics in turn shape the overall method of dry or wet screening. | As with any industrial process there is a group of terms that identify and define what screening is. Terms like blinding, contamination, frequency, amplitude, and others describe the basic characteristics of screening, and those characteristics in turn shape the overall method of dry or wet screening. | ||
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==Physical principles== | ==Physical principles== | ||
*Vibration - either | *Vibration - either sinusoidal vibration or gyratory vibration. | ||
**Sinusoidal Vibration occurs at an angled plane relative to the horizontal. The vibration is in a wave pattern determined by frequency and amplitude. | **Sinusoidal Vibration occurs at an angled plane relative to the horizontal. The vibration is in a wave pattern determined by frequency and amplitude. | ||
**Gyratory Vibration occurs at near level plane at low angles in a reciprocating side to side motion. | **Gyratory Vibration occurs at near level plane at low angles in a reciprocating side to side motion. | ||
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There are generally three types of mechanical screening equipment that cause segregation. These types are based on the motion of the machine through its motor drive. | There are generally three types of mechanical screening equipment that cause segregation. These types are based on the motion of the machine through its motor drive. | ||
*Circle-throw vibrating equipment - This type of equipment has an eccentric shaft that causes the frame of the shaker to lurch at a given angle. This lurching action literally throws the material forward and up. As the machine returns to its base state the material falls by gravity to physically lower level. This type of screening is used also in mining operations for large material with sizes that range from six inches to +20 mesh. | *Circle-throw vibrating equipment - This type of equipment has an eccentric shaft that causes the frame of the shaker to lurch at a given angle. This lurching action literally throws the material forward and up. As the machine returns to its base state the material falls by gravity to physically lower level. This type of screening is used also in mining operations for large material with sizes that range from six inches to +20 mesh. | ||
*High frequency vibrating equipment - This type of equipment drives the screen cloth only. Unlike above the frame of the equipment is fixed and only the screen vibrates. However, this equipment is similar to the above such that it still throws material off of it and allows the particles to cascade down the screen cloth. These screens are for sizes smaller than 1/8 of an inch to +150 mesh. | *High frequency vibrating equipment - This type of equipment drives the screen cloth only. Unlike above the frame of the equipment is fixed and only the screen vibrates. However, this equipment is similar to the above such that it still throws material off of it and allows the particles to cascade down the screen cloth. These screens are for sizes smaller than 1/8 of an inch to +150 mesh. | ||
*Gyratory equipment - This type of equipment differs from the above two such that the machine gyrates in a circular motion at a near level plane at low angles. The drive is an eccentric gear box or eccentric weights. | *Gyratory equipment - This type of equipment differs from the above two such that the machine gyrates in a circular motion at a near level plane at low angles. The drive is an eccentric gear box or eccentric weights. | ||