In last text, we make an introduction of investment casting parts defects and causes. Now, let's go on.
6. Thermal cracking: The crack growth along the grain boundary, whose surface has oxidation of color
a Mold temperature is low while cooling is too fast.
b Mole concession is poor, obstructing contraction.
c The structure of investment casting parts is irrational, such as large difference of the thickness.
d Unreasonable casting feeding system design, resulting in local overheating or contraction blocked casting.
7. Cold crack: Crack mostly through the grains and the surface of investment casting parts is bright.
a Cast structure is irrational.
b Pouring system unreasonable.
c Casting sand in the process of handling and by the impact.
d When the investment casting parts in the correction of improper operation or annealing.
8. Metal thorns: Surface of investment casting parts have dense or scattered small thorn
a Viscosity liquid of powder coating surface is low.
b Coatings and surface of wax is poor wet.
c Debris on the surface of wax mold is not clean.
d Sanding material is too thick.
9. Sticky sand: There are sticky sand on the surface of investment casting parts, which by blowing sand revealed a protruding burrs or pits
a High impurity content of the refractory material powder and sand are on the surface coating of powder.
b Shell-refractory or binder used improperly.
c Pouring temperature is too high.
d Unreasonable gating system design, resulting in local overheating shell.
10. Pits on the surface: Dot-intensive pits appear on some places after cleaning the investment casting parts.
a When casting, molten metal and mold temperature is high and the cooling of investment casting parts is slower.
b Cooling of investment casting parts slowly.
c The remain sodium are too much in the water glass shell.