Valve Castings The Cause Of The Defect In The Production Process

1.Stomata

This is the metal solidification process can not escape the gas left in the metal inside the formation of small holes, the inner wall is smooth, containing gas, the ultrasound has a high reflectivity, but also because it is basically spherical or ellipsoid, That is, point-like defects, affecting its reflection amplitude. The stomata in the ingot are crushed into an area defect by forging or rolling and is advantageous for being found by ultrasonic testing. 

2. Shrinkage and loose

Casting or ingot cooling solidification, the volume to shrink, in the final part of the solidification because of the lack of liquid metal can form a hollow-like defects. Large and concentrated cavities are called shrinkage, and small, scattered spaces are called loosened. They are usually located in the final solidified part of the ingot or casting center. The inner wall is rough and surrounded by many impurities and fine pores. Due to the law of thermal expansion and contraction, shrinkage is inevitable, but with the processing process different methods have different shape, size and location, when it extends to the casting or ingot body becomes defective. In the case of billet forging, the ingot will become the residual shrinkage (shrinkage residual, residual shrinkage) if it is not removed from the forging. In the case of

3. slag

The slag in the smelting process or the refractory on the furnace furnace is exfoliated into the liquid metal and is entrained in the casting or ingot body during casting to form a slag defect. The slag is usually not present in a single state, often in a dense state or dispersed at different depths, which resembles volumetric defects but tend to have a certain degree. In the case of

4. mixed with

(Such as oxides, sulfides, etc.) in the smelting process - non-metallic inclusions or additives of certain components of the metal component are not completely melted and remain to form metal inclusions such as high density, high melting point components - tungsten , Molybdenum, etc.

5. segregation

The segregation in the casting or ingot mainly refers to the segregation of the components formed during the melting process or the melting of the metal due to the uneven distribution of the components. The mechanical properties of the segregated areas are different from those of the whole metal matrix. The difference is beyond the allowable standard The scope becomes a defect. In the case of

6. Casting cracks

Cracks in the casting are mainly due to the fact that the shrinkage stress of the metal cooling and solidification exceeds the ultimate strength of the material. It is related to the shape design and casting process of the casting and the cracking of the metal material. (Such as hot brittleness when the sulfur content is high, cold brittleness when the phosphorus content is high, etc.). In the ingot will also produce axial intergranular cracks in the follow-up billet forging if not forging, will remain in the forging to become the forging of the internal cracks.

7. cold separation

This is a unique delamination defect in the casting, mainly related to the casting process design of the casting, which is due to splashing, tumbling, pouring, or two strands of different directions (or multiple strands) ) Metal flow and other reasons, because the liquid metal surface formed by the semi-solid film to stay in the casting body to form a diaphragm-like area-type defects.

8.Skinning

This is when the steel from the ladle to the ingot casting ingot, because pouring interruption, pause and other reasons, the first pouring of liquid metal surface in the air quickly cooled to form an oxide film, in the continued pouring of new liquid metal Breaking through the ingot into the ingot and the formation of a layered (area type) defects, it is in the subsequent steel ingot billet forging can not be forced to eliminate. In the case of

9. Anisotropy

When the casting or ingot is cooled and solidified, the cooling rate from the surface to the center is different, resulting in different crystallographic structures, exhibiting anisotropy of mechanical properties, and leading to anisotropy of acoustic properties, The surface has a different sound velocity and sound attenuation. The presence of this anisotropy will adversely affect the size and location of the defect when evaluating the ultrasonic inspection of the casting.