What Does Hot Tear Mean?
A hot tear is a discontinuity that occurs during the solidification stage of a casting operation, when the material being cast is part solid and part liquid. A hot tear can occur because as a material solidifies, it will generally want to contract. If some force or restraint impedes this contraction then a hot tear will occur; this can make the casting more vulnerable to corrosion and failure.
Corrosionpedia Explains Hot Tear
A hot tear can render a casting completely defective and unsuited for its intended purpose. Even if the hot tear is small, it can continue to propagate during its service life and fail during use.
There are various specifications that are used to determine if a hot tear is acceptable or not. Organizations that create these standards such as the ASTM and AMS define inspection and acceptance criteria for hot tears and other casting defects and discontinuities.
A hot tear can be created as a result of impeding the contraction forces that occur during material solidification. Removing these impediments will reduce the risk of a hot tear forming. This can be achieved by improving the casting mold design. If the mold is made from a weaker material that allows some flexibility during the shrinkage phase of the casting operation, then the risk of a hot tear is reduced. Also decreasing the likelihood of a hot tear is to not overheat the casting material. Increasing the temperature of the mold may also reduce the chance of a hot tear forming.