In metallurgy a veining (or ''finning'') is the occurrence of a sheet like casting defect, produced by molten metal penetration into a

sand casting Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced i ...

mould.

Description

Veining occurs as 'vein' like projections from a casting, usually at right angles to the casting's surface; the phenonoma can occur in any alloy, and is commonly seen in ferrous or copper based castings. Veining has been attributed to temperature differences at distance from the molten metal resulting in differential thermal expansion in the sand leading to strain in, and failure of the sand mould. Research has shown that a main cause of veining is thermal expansion of the silica sand in combination with reduction in sand volume above 573C (after the alpha to beta silica phase transformation) due to softening/sintering and/or melting of sand grains, which results in cracking/voids. Veining can be reduced or avoided by the use of more refractory non-silica sands (

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of the r ...

chromite Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can s ...

etc); by flux additives which lower the temperature of silica transition to tridymite or

cristobalite Cristobalite is a mineral polymorph of silica that is formed at very high temperatures. It has the same chemical formula as quartz, SiO2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the ...

, or which sinter the sand increasing resistance to failure; or by organic additives which are decomposed to carbon at high temperature, which then bonds to silica increasing strength, imparting veining resistance.

Description

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Further reading