Common defects and prevention of metal mold casting

(1) Casting pinhole

Measures to prevent pinholes:

a. It is strictly prohibited to use polluted cast aluminum alloy materials, materials stained with organic compounds and materials severely oxidized and corroded.

b. Control smelting process and strengthen degassing refining.

c. Control the thickness of metal mold coating, too thick to produce pinholes.

d. The mold temperature should not be too high. The thick wall part of the casting should be cooled by means of quenching, such as copper inlay or watering.

e. When using sand mold, strictly control water content and try to use dry core.

(2) Casting porosity

Measures to prevent air holes:

a. Modify the unreasonable gating and riser system to make the liquid flow stable and avoid gas entrapment.

b. The mould and core should be preheated in advance, then coated, and dried thoroughly before use.

c. Enough exhaust measures should be considered in the design of mould and core.

(3) Casting oxidation slag inclusion

Measures to prevent oxidation slag inclusion:

a. Strictly control smelting process, rapid smelting, reduce oxidation and complete slag removal.

b. The furnace and tools shall be clean and free of oxide, and shall be preheated. The coating shall be dried after application.

c. The designed pouring system must have the ability of steady flow, buffer and skimming.

d. The inclined pouring system is adopted to make the liquid flow stable without secondary oxidation.

e. The selected coating has strong adhesion, so it will not peel off during pouring and enter the casting to form slag inclusion.

(4) Casting hot crack

Measures to prevent hot cracking:

a. The actual pouring system should avoid local overheating and reduce the internal stress.

b. The inclination of mold and core must be more than 2 °. Once the pouring riser is solidified, the core can be pulled out and the mold can be opened. If necessary, the sand core can be used to replace the metal core.

c. Control the coating thickness to make the cooling speed of each part of the casting consistent.

d. Select the appropriate mold temperature according to the thickness of the casting.

e、 Refine the structure of the alloy and improve the hot cracking ability.

f. Improve casting structure, eliminate sharp corner and wall thickness mutation, reduce hot crack tendency.

(5) Loose casting

Measures to prevent looseness:

a. Reasonable riser setting to ensure its solidification and feeding capacity.

b. Properly adjust the working temperature of metal mold.

c. Control the thickness of coating and reduce the thickness of thick wall.

d. Adjust the cooling speed of each part of the metal mold, so that the thick wall of the casting has greater chilling capacity.

e. Reduce the pouring temperature of metal properly.

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