Relationship between the hottest air hole and cast

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Relationship between porosity and casting quality

1 destroy metal continuity

2 less effective bearing area

3 stress concentration is easy to be caused near porosity, mechanical properties ↓ α k σ- 1 ↓

4 dispersion holes, air tightness ↓

two categories (by gas source)

1 invasion pore: the gas accumulated on the surface of sand mold material invades the metal liquid and forms

gas source: moisture, binder and various additives in molding materials

features: the manufacturing of test samples with large size, oval or pear shaped holes, which are mostly located near the surface, and even as important as the test accuracy of the universal material testing machine itself, the internal surface is oxidized

forming process:

pouring --- water vapor (one part is discharged from the parting surface and vent hole, and the other part is gathered on the surface of the notch and cut after aging to form a high-pressure central point) - the air pressure rises Melt into the metal - part of it escapes from the molten metal - gate, and the rest is inside the casting, forming pores

prevention: reduce the amount of molding sand (core sand) and increase the mold exhaust capacity

2 precipitated air hole: the gas dissolved in the molten metal is precipitated due to the decrease of gas solubility during the condensation process, resulting in the formation of air hole in the casting Cause: gas contact during metal melting and pouring (H2O2, no, Co, etc.) characteristics: wide distribution, small pore size, affecting air tightness

3 reaction pore: gas pore formed by chemical reaction between metal liquid and mold material, core support, cold iron or molten slag For example, the cold iron is rusty Fe3O4 + C – Fe + CO ↑ air holes are formed near the cold iron to prevent: the surface of the cold iron core support shall be dry and free of rust and oil stains

§ 5 casting quality control

1 reasonable selection of casting alloy and casting structure

2 reasonable formulation of technical requirements for castings (allowable defects, with provisions)

3 model quality inspection random signal inspection, harmonic distortion and other precision indicators are verification items formulated to ensure the uniqueness of environmental experimental conditions (model qualified - casting qualified)

4 casting quality inspection (macro, instrument)

5 casting heat treatment: eliminate stress, reduce hardness, improve machinability, ensure mechanical properties, annealing, normalizing, etc. (end)

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