Sometimes the surface of precision casting will appear depression: the hot segment of the stainless steel casting is filled (there is a cavity inside). When shrinking, although the surface has a certain strength, it is still affected by the internal shrinkage and the depression appears when it does not break. This is called shrinkage.
The common defects in precision casting are bubbles. The bubbles in precision casting refer to the occurrence of trachoma defects in individual parts of the precision casting. Foam is usually found after machining.
Reasons for composition:
1. In most cases, the main reason for the appearance of bubbles is that the outer shell is not fully roasted after refining. When the molten steel is poured, a large amount of gas is instantaneously generated in the outer shell and cannot be smoothly discharged, thus entering the molten metal to form bubbles;
2. Due to the shell making process or the shell shape data, the air permeability of the shell is too poor, and the gas in the cavity is difficult to discharge, thus entering the molten metal to form bubbles;
The air involved in pouring molten steel cannot expel the bubbles formed by the casting.
Solution:
If the precision casting conditions permit, set up vent holes on the top of the casting with complex structure;
2. When designing the pouring system, fully consider the exhaust requirements of the shell; 3. The roasting temperature and time of the shell should be reasonable, and the heat preservation time should be appropriate;
4. The wax material should be completely removed when removing wax;
5. Appropriately reduce the interval from the pouring cup to the pouring cup, and the average pouring speed to ensure that the steel fills the cavity stably, and is involved in the molten steel as little as possible, so that the gas in the cavity and the molten steel is discharged smoothly .