Mechanical screening
This practice occurs in a variety of industries such as mining and mineral processing, agriculture, pharmaceutical, food, plastics, and recycling.
Before crushing large boulder are scalped on a shaker with 0.25 in (6.4 mm) thick shielding screening.
For example, vibration, g force, bed density, and material shape all facilitate the rate or cut.
At the same time, other high energy sieves like the Elcan Industries' advanced screening technology allow for much finer separations down to as fine as 10um and 5um, respectively.
This type of equipment has an eccentric drive or weights that causes the shaker to travel in an orbital path.
Rubber balls and trays provide an additional mechanical means to cause the material to fall through.
When the clamp rail bolts are tightened, the cloth is tensioned or even stretched in the case of some types of self-cleaning screen media.
Commonly, vibratory-type screening equipment employs rigid, circular sieve frames to which woven wire mesh is attached.
Conventional methods of producing tensioned meshed screens has given way in recent years to bonding, whereby the mesh is no longer tensioned and trapped between a sieve frame body and clamping ring; instead, developments in modern adhesive technologies has allowed the industry to adopt high strength structural adhesives to bond tensioned mesh directly to frames.
This larger surface design compensates for the fact that rubber and polyurethane modular screen media offers less open area than wire cloth.
Over the years, numerous ways have been developed to attach modular panels to the screen deck stringers (girders).
Woven wire cloth, typically produced from stainless steel, is commonly employed as a filtration medium for sieving in a wide range of industries.
A twill weave allows a mesh to be woven when the wire diameter is too thick in proportion to the aperture.
Today wire cloth is woven to strict international standards, e.g. ISO1944:1999,[16] which dictates acceptable tolerance regarding nominal mesh count and blemishes.
The nominal mesh count, to which mesh is generally defined is a measure of the number of openings per lineal inch, determined by counting the number of openings from the centre of one wire to the centre of another wire one lineal inch away.
Other calculations regarding woven wire cloth/mesh can be made including weight and open area determination.
[19][20][21] Today, woven cloth is still widely used primarily because they are less expensive than other types of screen media.
Over the years, different weaving techniques have been developed; either to increase the open area percentage or add wear-life.
Unfortunately flat-top woven wire cloth is not widely used because of the lack of crimps that causes a pronounced reduction of passing fines resulting in premature wear of con crushers.
[25] Most likely installed on a tensioned deck, punch plates offer excellent wear life for high-impact and high material flow applications.
Large producers such as mines or huge quarries use them to reduce the frequency of having to stop the plant for screen deck maintenance.
Due to the 7-degree demoulding angle, polyurethane screen media users can experience granulometry changes of product during the wear life of the panel.
This would allow the wires to be free to vibrate between the support bars, preventing blinding, clogging and pegging of the cloth.
This higher throughput would be a direct result of the higher vibration frequency of each independent wire of the screen cloth (calculated in hertz) compared to the shaker vibration (calculated in RPM), accelerating the stratification of the material bed.
