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Aluminum alloy Die castings involved in the problem of impaired porosity


Defect characteristics:
During the casting, injection and filling of the alloy, the gas is trapped or contained in the aluminum alloy liquid. As the filling process continues, the alloy may also have eddy currents, splashes, etc., the gas may be strengthened; or the ventilation slots may not open properly. Insufficient exhaust gas, gas cannot be discharged, or the vacuum flow path is unreasonable, or the vacuum effect caused by vacuum plugging is not reached; when the alloy solidifies, the gas in the alloy liquid remains in the casting to form pores. The inner wall of the stomata is smooth and flat, but it is not clean (clean), has obvious signs of contamination or corrosion, sometimes it is too big to cut off the odor, or even more, sometimes it can be seen that there is actually a roller In the hole. Enter oil, water and other contaminants, and the pores are dispersed in the casting.
Discovery method:
Visual inspection after processing or x-ray inspection.
Cause Analysis:
(1) The gating system is incorrect:
The gate (the soup mouth) is too thin.
2 tube is too large, the filling rate is too low.
3 When the alloy liquid is filled, the impact is too severe.
The door (Tangkou) is in the wrong direction.
5 eddy current enhancement.
6 The exhaust system is not properly opened.
7 exhaust is not smooth.
8 The overflow tank and exhaust vent are not set properly (position or quantity and size).
9 The vacuum flow path is not smooth.
10 vacuum valve used improperly (too small).
(2) Excessive black lead oil is used to cause combustion after the alloy is poured, resulting in a large amount of smoke.
(3) The filling speed is too fast, causing a large amount of gas to be entrained, or the alloy liquid flows to block the exhaust passage or the vacuum flow passage prematurely.
(4) Leakage of the vacuum system reduces the effect of vacuuming. Due to high-speed filling, it is impossible to eliminate the gas in the cavity.
(5) The machining allowance is too large.
(6) The mold has a deep cavity, and the gas at the deep cavity is closed and cannot be discharged.
Prevention:
(1) Change the direction in which the alloy liquid flows into the mold cavity, and preferentially fill the deep cavity portion.
(2) Properly reduce the injection speed (when the molding state is good).
(3) Under the condition of ensuring good filling, the larger the part of the soup, the better the effect.
(4) The venting groove is set so that its position should not be blocked by the flow of the first flowing alloy, or a slag bag (overflow) should be added as appropriate.
(5) The overflow tank (overflow) should be set to store the head metal and balance the mold temperature.
(6) For non-vacuum molds, the deep cavity portion can be inserted into the form to facilitate gas discharge.
(7) Appropriately reduce the amount of black lead oil and reduce the presence of gases in the material piping.
(8) Improve the filling rate.
(9) Use the vacuum device correctly.

(10) Reduce the machining allowance.



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