Castings are mainly used as blanks for machine parts, and some precision castings can also be used directly as machine parts. Casting occupies a large proportion of mechanical products. For example, in tractors, the weight of castings accounts for about 50-70% of the weight of the whole machine, 40-70% in agricultural machinery, and 70-90% in machine tools and internal combustion engines. Among all kinds of castings, mechanical castings have the most varieties, the most complex shapes, and the largest amount, accounting for about 60% of the total casting output. Followed by ingot molds for metallurgy and pipelines for engineering.
The non-machined surface and appearance quality of castings have a considerable influence on the commercial properties of castings. They include:
(1)Surface unevenness (box expansion, shrinkage and sand inclusion);
(2) Surface or inner cavity cleanliness (sticky sand, sticky "paint layer");
(3) Flatness deviation (unworked surface undulations);
(4) Surface roughness;
(5) Contour definition (contour definition of structural units such as bosses and umbilicus, evaluated with the naked eye).
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