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Correctly Proportion Inner Walls

Inner sections of castings (resulting from complex cores) cool much slower than outer sections and cause variations in strength properties. A good rule is to reduce inner sections to 0.9 of the thickness of the outer wall.

Avoid rapid section changes because they will result in porosity problems similar to what is seen with sharp angles. Whenever complex cores must be used, design for uniformity of section to avoid local heavy masses of metal.

The inside diameter of cylinders and bushings should exceed the wall thickness of castings. When the inside diameter of a cylinder is less than the wall thickness, it is better to cast the section solid, as holes can be produced by cheaper (and safer) methods than with extremely thin cores.

Fig. 6: To remedy the shrinkage defects in the original design of a hydraulic coupling, excessive metal was removed, resulting in a lighter weight casting with less strain in the light radial veins.

A cored hole through the center of the junction will help to speed solidification and avoid hot spots - illustration

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This article was adopted from a section of Casting World Magazine. Reprinted with permission.