![]() Interdendritic shrinkage: very small shrinkage cavities associated with dendrite solidification. ![]() Shrinkage defects are not normally associated with gas, but a high gas content will magnify their extent. Other shrinkage defects may occur in steel castings where there is a localized variation in section thickness. The top of an ingot casting is removed to get rid of the primary pipe. A primary pipe is surface breaking secondary pipes are those which exist sub-surface. This is a cavity in the centre of the ingot/casting caused by shrinkage during solidification. Non-metallic inclusions are impurities such as slag, oxides, and sulphides, which exist in the molten metal and finally the solidified metal. They are caused by gas evolution from the decomposition of grease, moisture etc., but not from the mould itself.įor example, during the sand casting operation, moisture from the mould produces steam, this is normally forced through the mould due to the absorbent nature of the sand but sometimes the steam cannot get through to the outside and is forced back into the casting, blowing holes in the casting surface. These are small holes in or on the surface of the casting. The gas is trapped within the metal when if solidifies and remains in the form of spherical or tubular cavities.Ī cavity formed by air which has been trapped in the mould by the metal during pouring. This is formed by gas which is insoluble in the molten metal. All casting defects are therefore inherent. The following defects are present in the material before any further processing operations such as forging, or rolling have begun. The following is a non-exhaustive list of some of the defect types which can be found during the non destructive testing process.
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