Quality and control of casting parts

Common casting defects and characteristics:

1. Stomata

Mainly pear shaped, round, oval holes, the surface is smooth, generally not exposed on the surface of the casting, large holes exist independently, small holes appear in groups.

2. Sticky sand

Part or the whole surface of the casting is adhered to a mechanical mixture of metal and sand, which occurs mostly in the thick wall and hot joint of the casting.

3. Sand

There are raised metal pieces on the surface of the casting, the surface is rough, the edges are sharp, and a small part is connected with the casting body.

4. White mouth

Gray cast iron section all or the surface of the bright white organization, often in the casting thin section, edges and edges.

5. Shrink the hole and loosen

Shrinkage hole: irregularly shaped closed or open cavity with rough walls and dendritic elements, often appearing in the final solidification of the casting.

Shrinkage: Scattered and small shrinkage holes in the section of the casting.

6. Cracks

Hot crack: the section is seriously oxidized, no metallic luster, the fracture occurs and develops along the boundary, and the shape is tortuous and irregular cracks.

Cold cracking: Through the crystal without breaking along the grain boundary, the fracture has a metallic luster or a slight oxidation color.

7. Chemical composition and mechanical properties are not qualified

The chemical composition and hardness, strength, elongation, impact performance, heat resistance, corrosion resistance and wear resistance of the casting do not meet the technical requirements.

Casting defects are closely related to the casting process, modeling materials, molds, alloy melting and pouring, casting alloy selection, casting structure design, technical requirements of the design is reasonable. Therefore, the casting should be controlled from the following aspects

Part quality:

1. 1.Reasonable selection of casting alloy and casting structure.
2. 2.Reasonable development of the technical requirements of castings:defective castings are not all waste products in qualified castings, allowing the existence of those defects and the extent of their existence, should be specified in the parts drawing or relevant technical documents, as the basis for casting quality requirements.
3. 3.Casting quality inspection is an important measure to control casting quality.

Casting inspection items include: casting appearance quality, including casting surface defects, surface roughness, weight tolerances and dimensional tolerances; The internal quality of the casting, including the internal defects of the casting, chemical composition, metallographic structure and material properties; Casting performance, including casting in strong, high speed, corrosion resistance, heat resistance, low temperature resistance and other different conditions of the working ability.

The most commonly used method for casting quality inspection is macro method.

It is to find out the surface defects and subcutaneous defects of the casting by naked eye observation (or with the help of the tip hammer), such as pores, sand holes, slag inclusion,

Sticky sand, shrinkage hole, failure to pour, cold isolation, size error, etc.

For internal defects, it is necessary to use instruments for inspection, such as color penetration inspection, ultrasonic detection, X-ray detection, magnetic particle detection, fluorescent detection, pressure resistance test.

In addition, if necessary, the casting should also be subjected to anatomical inspection, phase inspection, mechanical property inspection and chemical composition analysis.