Supercooling of metal in fine filters
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A commercially available technique for assessing the quality of liquid aluminium alloys is the Prefil-Footprinter test in which a quantity of liquid metal is forced to pass through a fine filter. Normally the filtration rate is measured and compared with recorded information. A clean melt retains the open pore structure of the filter keeping its resistance to a minimum and achieving a high rate of filtration. In contrast, a low flow rate would indicate the build up of inclusions leading to partial choking of the filter . The curve of filtrate weight versus time provides a measure of the relative cleanliness of an aluminium melt by comparison with a wide variety of benchmark results . The filter and its deposit can be subsequently sectioned and the inclusions identified by metallographic techniques.
Some of the most important and common types of inclusions detectable by the test are those entrained from the surface as films, such as oxides. The entrainment mechanism is a folding...
KeywordsRapid Freezing Good Metal Fine Filter Gravity Casting Liquid Aluminium Alloy
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