Sand Casting: Design
 Sand Casting: Design
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Design considerations
 • Location of the parting line/plane. By properly locating the parting plane. • The number of cores can be reduced. • The gating can be made less elaborate. • The material wasted can be reduced. • The dimensional accuracy can be increased. • Use of uniform thicknesses in a casting, where possible. Uniform thicknesses lead to uniform cooling and solidification. This leads to stress free and distortion free castings. Heavier sections cool more slowly, and may have shrinkage cavities, porosities and large grain structures. Voids, porosities and cracks can be sites of subsequent failures and should gestation be prevented by minimizing variations in cross sections. • When uniform cross-sections cannot be maintained, then changes in cross-sections must be gradual. A recommended way to achieve this is to use a transition radius of 1/3 of the thicker section and blend in the radius with a 15-degree slope line. • When two or more uniform sections intersect, they create a region of heavy cross-section, resulting in the problems mentioned earlier. One way to minimize this is to core the intersection by a hole, similar to a hub hole in a wheel with spokes. • When sections intersect to form continuous ribs, contraction occurs in opposite directions as the material cools down. This leads to a high stress area at the intersections, causing cracking immediately, or in service. The way to avoid this is to stagger the ribs and thereby maintain uniform cross-sections. • Large unsupported areas tend to warp, so they should be avoided. • In addition, a minimum wall thickness must be maintained to avoid voids and non-fill areas. See casting allowance table for minimum wall thickness for some common metals.
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