Winnowing

Air separation means a mechanical separation process in which particles are separated according to their ratio of inertia or gravity, and resistance to flow in a gas stream. It is a classification method and uses the principle of centrifugal force, gravity or separation from. Fine particles follow the flow, gross mass of power.

Winnow

Air classification is a technical advancement of the Worfelns. The principle has remained unchanged. When the winnowing threshed ears are thrown with shallow basket shells into the air. The ratio of air resistance to gravity is considerably smaller than for the husks and chaff for the grains. Side wind blowing therefore carries them chaff and husks, and only the grain falls back to the basket. The method is as old as the cereal crops. In the Neolithic practice Worfelschaufeln and sieves were used.

In the book of Sirach 5.9 says: " Worfle not in any wind ...", since too little wind and finds no separation takes in too much wind, the grains are blown.

With the motive of Worfelns rarely shown (see picture right) also a moralizing statement about the value of work is connected, the backlog and fruitful as the corn, and will not blow away like chaff.

Species

Air Classifiers are generally manufactured in two designs: This mixture is separated by either a vertical or a horizontal air flow ( counter-current or cross- current classifier) ​​.

Zigzag classifier

The zigzag classifier is an evolution of Steigrohrsichters with improved selectivity. The rectangular passage in which the rising air current is divided by walls arranged in zig-zag in a number of smaller tubes. The flow of air with the contained particles is deflected to the zigzag walls, which again heavier parts are discarded.

Horizontal flow air classifier

In contrast to the various forms of Steigrohrsichters the air flow runs horizontally here. The solid particles falling from above in this air flow. Depending on the weight and air resistance, they are differentially deflected. Heavy and compact pieces fall straight down, others are being entrained in the air stream. By various collection devices at the bottom of the classifying duct, the feed can be separated into several fractions.

Riser classifier

The riser classifier is the simplest form of an air classifier. By an upright shaft, an air flow is generated from bottom to top. The mixture to be separated is placed in the upper third of the shaft. The heavier material falls against the air flow downwards, while the lighter is blown up in a cyclone and where it is separated from the supporting air.

Floating sifter

When floating sifter is a special form of Steigrohrsichters. Here, the air -flow space is formed as a cylinder which tapers conically upwards and in which the mixture to be separated is supplied from above.

Special Form: dry stoner

Depending on use, these are also known as Fließbettseparatoren, air ovens, separation tables or stove scrubber. In the dry stoners the mixture to be separated is placed on a arranged as an inclined plane screen. The screen is there so moved that heavy material to be transported to the heavy parts, such as stones, " uphill ". A stream of air from below through the screen causes lighter components, such as grains, do not migrate with the heavier uphill, but stand out from the screen and downhill are transported to the light material through the downhill slope. Without this airflow would feed the whole, with the exception of the small components that fall through the sieve ( Siebaustrag ) unsorted move upwards.

Applications

  • Separation of chaff, grain and stones in threshing or cleaning machines in the grain intake of mills
  • Separation of ground grain into semolina, bran, flour and again to be milled fractions
  • Remove from glass and other hard substances from compost
  • Production of paper and plastics from the waste
  • Dispersitätsanalyse of solid particles
  • Metal industry
  • Refractory Industry
  • Cement industry to separate oversize material and finished product
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