The internal looseness of copper casting sleeve is generally due to the slow cooling rate of copper casting, which makes the crystal of copper casting coarse, leading to the gradual internal loosening, in order to speed up the cooling rate of copper casting, which is conducive to grain refinement and can reduce the internal looseness of copper casting.
Therefore, the specific reasons for the formation of internal looseness in copper castings are as follows:
1. The slow cooling rate of copper castings makes the grain size of copper castings coarser.
2. Casting speed is too fast and easy to be involved in bubbles and inclusions.
3. High pouring temperature results in longer cooling time and coarser grain size of copper castings.
4. When pouring, the oxide scales are poured together, resulting in inconsistent internal crystallization.
5. The gate speed is too fast, the turbulence motion is too violent, and the metal flow is involved in excessive gas.
(4) Remedial measures
Welding repair. The metal in defect area is digged out, and the defect area is welded with the same or compatible electrode as the base metal, and the post-weld heat treatment is carried out after the welding is leveled.
(2) For copper castings subjected to liquid or gas pressure, partial or integral infiltration treatment can be carried out to improve the sealing performance of copper castings.
(3) Important parts can be treated by hot isostatic pressing to eliminate the looseness in copper castings.
(4) When the looseness is beyond the acceptance condition and can not be remedied, or when the copper casting cracks during solidification, cooling or heat treatment, it should be scrapped.