Views:127 Author:Site Editor Publish Time: 2020-06-18 Origin:Site
Generally speaking, during the solidification process of caster castings, the size of each part of it is generally reduced. The percentage of the size reduction of the casting is called the casting line shrinkage or casting shrinkage. When manufacturing the casting mold (including core box), the casting mold should be enlarged according to the determined casting shrinkage rate to ensure that the size of the casting after cooling meets the requirements. The amount of shrinkage of each size when the casting is cooled can be obtained by the following formula:
Shrinkage = casting size × casting shrinkage
There are many factors affecting the shrinkage of castings, the main ones are:
1. The material of the casting is different, the casting shrinkage is different. For example, the shrinkage rate of cast steel is greater than that of gray cast iron; when there is more sulfur in gray cast iron, the shrinkage rate increases, and when silicon increases, the shrinkage rate decreases.
2. The structure of the casting. The structure of the casting is complex and difficult to shrink, and the shrinkage of the casting is reduced. For example, steel castings cast with the same composition have different shrinkage rates due to different structural shapes.
3. Concession of the casting mold The concession of the casting mold is good, and the shrinkage rate of the casting increases. For example, castings cast with wet and water glass sand molds have a greater shrinkage than those cast with dry molds. For the same reason, as the size of the casting increases, the yield of the mold becomes worse, and the shrinkage of the casting decreases.
Therefore, the casting shrinkage should be selected in accordance with the actual situation. The size requires accurate castings, and the casting shrinkage rate should be corrected according to the cast castings.
For the same casting, due to structural reasons, the shrinkage rates in the axial and radial directions or in the three directions of length, width, and height may be inconsistent. For castings with more precise dimensions, different shrinkage rates should be given in all directions. In actual production, general castings, especially those with small size, use the same shrinkage rate in all directions. Although this will cause some errors, the errors are generally not large, which greatly facilitates the manufacture of casting molds.