Sand inclusion is also called as sand hole, which is a kind of metal casting defect. It looks like small or middle holes with sand grain in the internal or on the surface of castings.
There are 3 main reasons caused the sand inclusion defect.
1. sand crush, sand drop
The partial sand blocks drop because of the mechanical force on the sand molds or sand cores. It will cause the embossing metal blocks, at the same time, the positions where the sand blocks drop to will have sunk holes after sand blasting.
If the sand molds or cores have been overbaked, then their surfaces will become more fragile because the adhesive will lose its stickiness, which will cause some sand inclusion defects.
3. Sand cut, erosion, sand wash
The sand molds or cores can not stand the flush of hot metal liquid during pouring process, so on the surfaces of fragile positions, there will be some coarse, irregular metal tumors, which normally happened at the pouring gate positions. The sand blocks and grains will cause the sand inclusions at the other positions.
Repairing sand inclusion, sand holes
1. Putty, paint filler
Putty is suitable for the unimportant surface positions. After filled by putty, the painting will be needed.
2. Metal fill glue, fill agent
Metal-filled glue contain quartz and metal components, so casting surface after filled by this glue will have a certain hardness, and it can stand further machining process and a temperature of 125 to 200 Celsius degree. Repairing with metal filled glue is very common method in iron and steel foundries in China.
3. Electrical welding
Welding is used for repairing middle or large sand inclusion. After welding, the positions with sand holes will still keep good strength and can stand the high temperature as metal.
Sand inclusion is the most common defect for sand castings, and any piece of sand casting will have this defect. However, good metal foundries can control the sand holes as small as possible. Normally, it will be acceptable for few sand holes with diameter under 2.0 mm, and with depth under 1.0 mm.