The process involved in creating investment castings is so complex that the chances for things to go wrong can result in certain casting defects. Here’s a list of the usual categories of defects in investment castings:
Inclusions
Non-metallic foreign particles, including slag, that are contained within a casting can result in negative defects called inclusions. These inclusions are cavities in various sizes and small, angular or irregular craters that can be formed by missing areas of metal in the investment castings. Inclusions are usually caused by cracks in the wax mold that cause ceramic and refractory material to get into the mold cavity.
Hot Tear
Hot tears look like jagged cracks that have an irregular pat. This occurs during the cooling and solidification process when the contraction of the molten metal is restricted by the ceramic shell mold. To keep this from happening, manufacturers often modify casting designs.
Misrun
A misrun is a negative type of defect that occurs when the mold cavity isn’t completely filled by the metal. This usually happens when the metal is too cold, the fill rate is too slow, or the shell is too cold.
Coldshut
This occurs when two metal streams fail to properly fuse in the mold cavity. Coldshuts are weak spots inside the investment casting which look like cracks. This defect is caused by slow pouring speeds, low pouring temperatures or a shell that’s too cold.
Porosity
This looks like a walled cavity that’s round and smooth or it could appear as a formation of bubbles trapped inside the metal. This defect is formed as the metal turns into solid and expels gas.
Runout
When molten metal leaks out of the mold as it is being poured, smooth or irregular voids are left as the parts are being formed. These runouts are caused by improper handling, thin ceramic shells, or dewax cracking of shells.
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