Sifter
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
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
- 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
See also
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
- ↑ 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.
- ↑ 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.