The cause and solution of "white defect" on skf bearing surface

There are some different casting methods for the influence of different models and properties of skf bearings. Among them, lost foam casting is a common casting method, but compared with ordinary sand casting, some technologies are immature and white defects are easy to occur.

1. Cause: During the pouring process, the EPC is flushed into the cavity by the fast flowing molten iron, which is mixed with the molten iron, causing the casting to be sanded. After machining, the castings were found to have sand on the processing surface, which was scattered or densely distributed like snowflakes. It is customarily called "white defects". This defect will cause the casting to be scrapped, which is very harmful in actual production. Therefore, it should be strictly avoided in production.

2, white defects often produce position
1) Gate cup - The gate cup is made of quartz sand with water glass as a binder to blow CO2. If the CO2 is not properly controlled, the strength of the gate cup is not good. When pouring, the sand in the cup easily falls into the cavity.
2) The connection between the gate cup and the sprue is mainly due to the direct flushing of the gate by the molten metal, which destroys the coating and causes the sand to collapse.
3) The lower part of the joint between the sprue and the sprue - due to the high sprue height, the metal liquid drop is large when pouring, and the coating of the runner is destroyed, causing the sand to break into the cavity.

3, the solution
1) Prevention of coating damage - Due to the high degree of vacuum here, the permeability of the coating at this location cannot be considered, and the thickness and strength of the coating are increased to enhance the flow of the barrier sand.
2) Combination principle outside the box - the model and the gating system are combined before packing
3) Principle of paint drying - It is necessary to connect the casting system when packing. The contact should be closed with paint, but the paint must be blown dry to prevent the wet paint from falling off.
4) Pouring - avoiding the molten iron facing the sprue during pouring, the molten iron should flow through the pouring cup and then flow into the sprue.