Casting during solidification, which are generally required to reduce the size of each part, casting size reduction percentage, called the casting line shrinkage or casting shrinkage. The manufacture of molds (including core box), casting shrinkage determined according to the number of mold amplification to ensure cooling of the casting size to meet the requirements. When casting cooling contraction amount of each size by the following formula:

　　Casting shrinkage = Size × casting shrinkage

　　Casting shrinkage factors are more, and they are:

　　1. The casting material casting material is different, casting shrinkage is also different. For example, steel shrinkage larger than gray cast iron; gray iron sulfur for a long time, the shrinkage rate increases, reduced shrinkage silicon for a long time.

　　2. Structure of the casting structure of complex casting shrinkage difficult, reduce shrinkage castings. For example, the same composition cast steel castings, due to the structure of different shapes, shown in Figure 30. Wherein the shrinkage of the largest free-contraction.

　　3. The casting mold concession concession of good casting shrinkage increases. For example, shrinkage and water glass sand with wet than dry-type casting casting casting casting large. Similarly, with the increase in the size of the casting, mold concession deteriorated, shrinkage of the casting will be reduced.

　　So casting shrinkage conjunction with the actual situation to choose. Size requires accurate casting, casting shrinkage to be amended in accordance with the test pouring castings.

　　With a cast, because of structural radial or axial length, width, high shrinkage in three directions may be inconsistent. Size requirements for more accurate casting, in all directions should be given differential shrinkage. In actual production, general casting, especially the size of small castings in all directions with the same shrinkage, although this will result in some errors, but because of the error is small, and this greatly facilitates manufacturing mold.

　　Cast iron sleeve shown in Example 1, all not working, find mold outer diameter D, length L and the inner diameter of the core box d (answer rounded to integer)

　　Solutions according to the structure, the axial shrinkage casting 0.9% 0.7% radial taken.

　　Size = part size ten mold shrinkage

　　D = 700 + 700 × 0.7% = 705 (mm)

　　L = 1000 ten 1000 × 0.9% = 1009 (mm)

　　d = 600 + 600 × 0 .7% = 604 (mm)