Relationship between casting quality and porosity

1) Reasonable selection of casting alloy and casting structure.

2) Make reasonable technical requirements for castings (defects are allowed and regulations are provided).

3) Model quality inspection (model qualified – casting qualified)

4) Casting quality inspection (macroscopic, instrument)

5) Heat treatment of castings: eliminate stress, reduce hardness, improve machinability, ensure mechanical properties, annealing, normalizing, etc.

1 failure of metal continuity

2 less effective bearing area

  1. Stress concentration and mechanical properties are easy to be caused near the air hole

4 dispersion hole, air tightness

The gas accumulated on the surface of sand mold material intrudes into metal liquid to form gas source, water content, binder, various additives, etc

Characteristics of stomata: most of them are near the surface, with large size, and the inner surface of oval or pear shaped pores is oxidized.

Pore formation process:

Pouring – water vapor (one part is discharged from the parting surface and the vent hole, the other part is gathered on the surface as a high-pressure center point) – air pressure rises, dissolves into the metal – one part escapes from the molten metal – gate, and the rest is in the casting, forming a pore.

Prevent the occurrence of porosity: reduce the amount of molding sand (core sand) and increase the ability of mold exhaust.

Precipitated porosity: during the condensation process of gas dissolved in liquid metal, the gas will be precipitated due to the decrease of gas solubility, which will cause the formation of porosity in the casting. The reason: metal melting and gas contact during pouring (H 2O 2No Co, etc.) feature: wide distribution, very small pore size, affecting air tightness.

Reaction pore: the pore formed by gas generated by chemical reaction between molten metal and casting material, core support, cold iron or slag. For example: there is rust in cold iron, and pores are formed near Fe3O4 + C – Fe + CO cold iron to prevent: the surface of cold iron core support shall be free of rust, oil stain and dry.

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