Causes and Preventive Measures of Shrinkage in Precision Casting
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Author:hkw84f5c9
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Published time: 2018-08-20
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Cause of formation: The basic reason for the formation of shrinkage cavities is that when the alloy shrinks and solidifies in the liquid state, a certain part of the casting (usually the hot junction where it is finally solidified) cannot obtain the liquid metal in time, and shrinkage holes are formed there.For eutectic alloys or alloys with a narrow range of solidification temperatures, castings tend to produce concentrated shrinkage cavities.
Cause of formation: The basic reason for the formation of shrinkage cavities is that when the alloy shrinks and solidifies in the liquid state, a certain part of the casting (usually the hot junction where it is finally solidified) cannot obtain the liquid metal in time, and shrinkage holes are formed there.
For eutectic alloys or alloys with a narrow range of solidification temperatures, castings tend to produce concentrated shrinkage cavities. When the alloy composition has been timed, the formation of shrinkage cavities is mainly because the wall thickness of the casting is not uniform, the hot joint is too much, too large, and the design of the riser system is improper, which is not conducive to sequential solidification, so that the molten metal cannot be replenished at each hot section of the casting. Or the pouring temperature is too high.
Preventive measures:
1: Improve the structure of the casting, strive to make the wall thickness uniform, reduce the hot knot, or make the wall thickness change is conducive to the sequential solidification.
2: A reasonable setting of the riser system causes the sequence to solidify. For the complicated riser system with multiple hot sections, it should be considered more thoughtfully.
3: Reasonably assemble the module so that there is a certain distance between the castings to prevent local heat dissipation.
4: The casting temperature of the shell and metal liquid should be suitable, and the pouring temperature should not be too high.
5: When pouring, ensure that the sprue and riser are filled with molten metal, or add a heating agent to the pouring cup and the riser.
6: Improve the smelting process, reduce the gases and oxides in the molten metal, improve its fluidity and shrinkage.
