Vibrating screens are the most important and versatile screening machines for mineral processing applications. Vibrating screens have a rectangular screening surface with feed and oversize discharge at opposite ends. They perform size separations from 300mm in size down to 45μm and they are used in a variety of sizing, grading, scalping, dewatering, wet screening, and washing applications.

Vibrating screens of most types can be manufactured with more than one screening deck. On multiple-deck systems, the feed is introduced to the top coarse screen; the undersize falling through to the lower screen decks, thus producing a range of sized fractions from a single screen. 

Inclined or circular motion screens (refer attached picture four-deck vibrating screen) are widely used as sizing screens.

A vertical circular or elliptical vibration is induced mechanically by the rotation of unbalanced weights or flywheels attached usually to a single drive shaft.

The amplitude of 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 permits a greater throughput.

Single-shaft screens must be installed on a slope, usually between 15 degree and 22 degree to permit flow of material along the screen.

Different types of vibrating screen working principles

Circular motion (Single-shaft) screens.

When the shaft of an inclined screen is located precisely at the screen's centre of gravity, the entire screen body vibrates with a circular vibration pattern (Figure 1). Occasionally, the shaft is installed above or below the centre of gravity as in the system shown in figure 2. This placement results in an elliptical motion, slanting forward at the feed end; a circular motion at the centre; and an elliptical motion, slanting backwards at the discharge end. Forward motion at the feed end serves to move oversize material rapidly out of the feed zone to keep the bed as thin as possible. This action facilitates passage of fines which should be completely removed in the first one-third of the screen length. As the oversize bed thins down, near the centre of the screen, the motion gradually changes to the circular pattern to slow down the rate of travel of the solids. At the discharge end, the oversize and remaining near-size materials are subjected to the increasingly retarding effect of the backward elliptical motion. This allows the near-size material more time to find openings in the screen cloth.

Linear vibration screen working principle

Linear-vibration (Double-shaft) screens. A linear vibration is induced by using mechanical exciters containing matched unbalanced weights rotating in opposite directions on two shafts as shown in Figure 3. Linear stroke screens can be installed on a slope, horizontally or even on a small up-hill incline. The angle of stroke is typically between 30 and 60 degree to the screen deck. Linear-vibration exciters are used on horizontal screens and banana screens. 

Oval motion (Triple-shaft) screens.

A three-shaft exciter design can be used to generate an elliptical vibratory motion as shown in Figure 4, which can also be used on horizontal and banana screens. The three shafts are connected by gears and one of the shafts is driven. The elliptical motion is claimed to offer the efficiency benefit of a linear vibrating screen with the tumbling action of a circular motion screen. Higher capacities and increased efficiencies are claimed over either linear or circular motion machines.

Figure 1, Figure 2, Figure 3, Figure 4 shows different vibration patterns that generated by various exciter designs. The star represents the location of the screen's centre of gravity.