Hot tear is a kind of common defect appears in grain boundary when solidification temperature
range near solidus, the appearance is curve with oxidation color. The position of hot
tear is usually occurring in the radius of the castings, the thickness has major changes
point of fraction surface, etc. The influence factors mainly are: casting alloy material
character, mould character, pouring condition, casting structure. Specifically,
1, the hot tear usually occur in the thermal center where shrinking suffocate,
solidification temperature, feeding capacity and thermal center pitch diameter all will
affect the hot tear.
2, the non-uniform line shrink during solidification and cooling process is the direct
factor to stress, shape change and hot tearing.
3, the deformability during casting thermal expansion decides the stress intensity.
4, the castings shrinkage and suffocate level also decide the stress intensity.
5, the bigger pitch diameter of castings in suffocate position, the resist area to hot tear
is bigger with the same shrinkage level.
6, the pouring condition is also one of the major reasons lead to crack. The pouring
temperature will influence the whole temperature field distribution, that's why it is also
one of the major reasons. The lower pouring temperature will reduce or remove the hot
tear; and higher temperature can lead to much serious crack, also easy left sand, which
create more suffocate and make castings crack easily.
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