Defects in castings and forgings
Release time:
2023-05-11 16:19
Source:
The defects produced in the casting and forging process are similar to the defects produced in the ingot, but they are still process defects, including pores, inclusions, shrinkage holes, loose holes, cracks, etc.
Pores (bubbles): The metal liquid contains too much air, the model is wet, and the air permeability is poor to form pores (bubbles). The pores of castings are divided into monodisperse pores and dense pores. Inclusions: Inclusions are divided into non-metallic inclusions and metallic inclusions. Non-metallic inclusions are the chemical reaction products between metal and gas environment in the smelting production process, or the inclusions that can be formed by mixing refractory materials, molding sand and the like into molten steel in the process of pouring system. Metal inclusions are inclusions that form when different metals occasionally fall into the foundry water and cannot be dissolved. Shrinkage cavity: Shrinkage cavity is a defect that cannot be supplemented by volume shrinkage after cooling and solidification of liquid metal. Shrinkage is mostly located near the riser and large cross-section or abrupt cross-section. Looseness: due to the defects in the smelting process of students, the design of mold shape and inappropriate reasons, the research on the development of fine grain boundary cracks in the middle of the wall thickness of castings and forgings or the internal structure of loose tissues formed by learning some fine voids in grain boundaries, this part can be analyzed by analyzing the combination between grains. China's enterprise culture is quite weak (cloud-like dark shadow is formed on the radiographic film). Crack: Crack refers to the internal stress (thermal stress and tissue stress) caused by local cracking due to excessive low melting point impurities and the formation of casting defects during cooling. Under the size of casting and forging, the stress concentration is serious and easy to crack.
The process defects of casting and forging have the characteristics of complex shape, and the use defects of casting and forging are mainly fatigue cracks, including mechanical fatigue cracks and thermal fatigue cracks. The organization is uneven. After the liquid metal is injected into the mold, the liquid metal layer contacting the mold wall becomes finer particles due to the rapid temperature drop. With the increase of the distance of the die wall, the influence of the die wall gradually begins to weaken, and the crystal grows into a parallel columnar analysis crystal along the direction perpendicular to the die wall. In the central part of the casting, there is no obvious direction of heat dissipation, and it can grow freely in all directions until it contacts each other to form an equiaxed crystal region. It can be seen that the organization of the casting is not uniform, in general, the grain is relatively rough. The tissue is not dense. The liquid metal crystallizes in the form of branches, and the liquid metal between the branches finally solidifies, but the branches are difficult to be completely filled with liquid metal, resulting in a general lack of compactness of the casting. In addition, if the liquid metal injected into the mold shrinks in volume during cooling and solidification, it is not fully replenished, and pores or even shrinkage cavities may be formed. The graphite in cast iron often appears in flake, spherical or other large-sized shapes, and can also be regarded as a non-dense structure. The surface is rough. Surface quality management general enterprise development is still a relatively rough, can not be compared with the machining surface information technology level, the shape is also more complex
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