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Sand inclusion, Sand hole
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.
2. Overbaking
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.
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