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Home  Filtration technology  History of filtration

History of filtration

Efforts to increase quality of casts and effectiveness of their manufacture have accompanied foundry business since its origin. For centuries founders have tried to produce casts of higher purity, quality surface and better properties, i.e. to reduce the metal contamination. As late as in 1930s flow principles and empirical experience began to govern a systematic approach to construction and dimensioning of the metal feed systems. Effectiveness of inclusion separation was one of the crucial aspects of the feed pipeline construction. Inclusions were separated by special devices installed in particular sections of the feed pipelines – slag separation sections – on the basis of the difference between metal and inclusion density. 


Massive pouring basin

Rotational slag trapper

Various slag trappers

(massive, jags)

This principle can mainly be used for ferrous alloys where the density of inclusions is much lower than the density of the metal. On the other hand, with other metal alloys, such as aluminium alloys, where the inclusion density is virtually the same as the metal density, this mechanism cannot be used and other principles of inclusion separation must be applied. There is for example the fact that inclusions stick to the mould walls. Flat channels of the feed pipeline therefore separate inclusions, especially oxide films, quite well. Effectiveness of these separation methods is limited, though.


Flat gatings on bottom of slag trapper (aluminium)

Since about mid sixties foundries have used ceramic strainers, placed mainly to the feed bowl in the transitory section to post. Their purpose was mainly to separate coarse slag particles. Since late 1970s sieves and filters for inclusion separation across the feed pipeline have been used. Originally their use was linked to aluminium casting, mainly for aircraft industry. Ferrous alloy filtration is complicated by the considerably higher temperatures of the metal and therefore higher demand for the filter behaviour at high temperatures. Mass deployment of filters came with development of alloys with ball graphite in the course of the eighties, and mainly in 1990s. Steel filtration is complicated by high requirements for resistance of the ceramic material to high temperatures, up to 1700 °C, and the related higher prices of the filters. For that reason filtration has been used in steel alloy manufacture just for special and high-demand casts. Enormous growth of filtering of (not only) steel has been registered only at the beginning of the 21st century, conditioned in particular by dramatic increase of metal prices and by mass extension of the technology of direct metal casting through the riser (feeder), using exothermic sleeves and special carbon-based filters.

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