Sifter

Graphic representation of a classifier

The sifter is a device for classifying solids according to defined criteria such as particle size , density , inertia , floating or stratification behavior. The process is used in flour mills , for example .

The sifting uses the different inertia forces and flow resistances of the different sized solid particles in a medium , for example in an air stream. In this way it is technologically different from sieving .

function

Sieving scheme of a plansifter in a flour mill

In an air classifier , the separation takes place in an air stream, with the less dense and floating particles being carried along. The threshing process of grain , which has been known for a long time, is based on this principle. The flail separates the grain from the chaff , with some of the chaff being blown away by the wind. The grain and husk mixture is then thrown up with a shovel - the wind separates the components and transports the lighter chaff away, while the heavier grain falls back to the ground. Wind sweeps were later used for this purpose .

Plan sifters can be used to separate solid particles that have the same density but different sizes. The material to be separated is moved over vibrating sieves , whereby the smaller particles sink down and fall through the sieve fabric. A forerunner of these machines, which came from mill construction , is the hexagonal and Askanier classifier.

In particle measurement technology , measuring cyclones , (cascade) impactors or beam deflection classifiers are used to classify gas-borne particles according to their size. This makes use of the fact that the particle path within the separating apparatus depends on the inertia of the particles.

application

Askania sifter from Heinrich Hecht's mill construction institute in Radegast , Anhalt

• Separation of grain and straw, the winnowing
• Separation of ground grain into semolina , low-mineral and mineral-rich flours .
• Separation of particles above a certain size from a gas flow (e.g. PM ₁₀ measurement)
• Cleaning of plastic granulate from dust / foreign matter and angel hair
• Determination of the fineness of the coal dust inside a coal mill

Executions

Askania sifter Bag passage Centrifugal separator

Impactor Plansifter Gravity separator

Sight cylinder Beam deflector Air separator

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  Plansifter

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  Old hexagon classifier

See also

• Separator
• Beutler

literature

• Claus Bernhardt: Granulometry. Classification and sedimentation methods. German publishing house for basic industry, Leipzig 1990, ISBN 3-342-00415-0 .
• Matthias Stieß: Mechanical Process Engineering - Particle Technology. Volume 1. 3., completely revised edition. Springer, Berlin 2009, ISBN 978-3-540-32551-2 .

Individual evidence

1. ↑ Helmut Düntzsch, Rudolf Tschiersch, Eberhard Wächtler , Otfried Wagenbreth : mills. History of the flour mills. Technical monuments in Central and Eastern Germany . 1st edition, German publishing house for basic industry, Leipzig / Stuttgart 1994, ISBN 3-342-00672-2 , 1 The mechanical development of the grain mills. 1.1 Grinding units, sieving machines and other working machines of the grain mills. Sieving (sifting) the grist, p. 21–24, here p. 21.
2. ↑ Werner Schnelle (author), Rüdiger Hagen (editing): Mühlenbau. Preserve and preserve water wheels and windmills . Ed .: German Institute for Standardization . 2nd, revised edition, Beuth Verlag, Berlin / Vienna / Zurich 2012, ISBN 978-3-410-21342-0 , 4 Construction of traditional processing machines for windmills and water mills. 4.3 Classifying machines. On the development of the classifier, p. 130.