Mechanical Screening - Screening Terminology

Screening Terminology

Like any mechanical and physical entity there are scientific, industrial, and layman terminology. The following is a partial list of terms that are associated with mechanical screening.

• Amplitude - This is a measurement of the screen cloth as it vertically peaks to its tallest height and troughs to its lowest point. Measured in multiples of the acceleration constant g (g-force).
• Acceleration - Applied Acceleration to the screen mesh in order to overcome the van der waal forces
• Blinding - When material plugs into the open slots of the screen cloth and inhibits overflowing material from falling through.
• Brushing - This procedure is performed by an operator who uses a brush to brush over the screen cloth to dislodged blinded opening.
• Cloth, screening cloth - it is the material defined by mesh size, which can be made of any type of material such steel, stainless steel, rubber compounds, brass, etc.
• Contamination - This is unwanted material in a given grade. This occurs when there is oversize or fine size material relative to the cut or grade. Another type of contamination is foreign body contamination.
  • Oversize contamination occurs when there is a hole in the screen such that the hole is larger than the mesh size of the screen. Other instances where oversize occurs is material overflow falling into the grade from overhead, or there is the wrong mesh size screen in place.
  • Fines contamination is when large sections of the screen cloth is blinded over, and material flowing over the screen does not fall through. The fines are then retained in the grade.
  • Foreign body contamination is unwanted material that differs from the virgin material going over and through the screen. It can be anything ranging from tree twigs, grass, metal slag to other mineral types and composition. This contamination occurs when there is a hole in the scalping screen or a foreign material's mineralogy or chemical composition differs from the virgin material.
• Deck - a deck is frame or apparatus that holds the screen cloth in place. It also contains the screening drive. It can contain multiple sections as the material travels from the feed end to the discharge end. Multiple decks are screen decks placed in a configuration where there are a series of decks attached vertically and lean at the same angle as it preceding and exceeding decks. Multiple decks are often referred to as single deck, double deck, triple deck, etc.
• Frequency - Measured in hertz (Hz) or revolutions per minute (RPM). Frequency is the number of times the screen cloth sinusoidally peaks and troughs within a second. As for a gyratory screening motion it is the number of revolutions the screens or screen deck takes in a time interval, such as revolution per minute (RPM).
• Gradation, grading - Also called "cut" or "cutting." Given a feed material in an initial state, the material can be defined to a have a particle size distribution. Grading is removing the maximum size material and minimum size material by way of mesh selection.
• Shaker - A generic term that refers to the whole assembly of any type mechanical screening machine.
• Stratification - This phenomenon occurs as vibration is passed through a bed of material. This causes coarse (larger) material to rise and finer (smaller) material to descend within the bed. The material in contact with screen cloth either falls through a slot or blinds the slot or contacts the cloth material and is thrown from the cloth to fall to the next lower level.
• Mesh - Mesh refers to the number of open slots per linear inch. Mesh is arranged in multiple configuration. Mesh can be a square pattern, long-slotted rectangular pattern, circular pattern, or diamond pattern.
• Scalp, scalping - this is the very first cut of the incoming material with the sum of all its grades. Scalping refers to removing the largest size particles. This includes enormously large particles relative to the other particle's sizes. Scalping also cleans the incoming material from foreign body contamination such as twigs, trash, glass, or other unwanted oversize material.