Asked Questions
Analysis and solution of leakage problem of automobile engine cylinder block
The engine is the heart of the car, and the cylinder block is a heavy, complex and difficult casting of the engine.
With the reform and opening up, China's automobile industry has developed rapidly, and the production of engine cylinder block has already been localized, and the quality level of products is gradually narrowing the gap with foreign countries. However, in the casting process, there are still some problems that have not been solved, such as leakage.
Leakage can be roughly classified into inclusion, shrinkage porosity and other types according to the causes.
Inclusion defects are divided into two types, one is sand inclusion type and the other is slag inclusion type.
Let's talk about the causes of leakage caused by sand inclusion type:
1. Due to some reasons, such as loose sand core/sand mold, adhered floating sand, uncleaned coating ball and uncleaned flash of sand core, during the pouring process, due to the baking and scouring action of high-temperature molten iron, sand particles fall, move with molten iron, gather in a certain part of the casting, form sand inclusions, and penetrate through the inner and outer walls, resulting in leakage.
2. In the process of sand core assembly, sand particles fall into the cavity or the assembled sand mold is polluted twice before pouring, resulting in sand inclusion and leakage.
The causes of leakage caused by slag inclusion defects are: the molten iron is not fully skimmed, the molten iron is impure, and the slag avoidance effect of ladle, pouring cup and pouring system is not ideal, which leads to the molten slag entering the cavity with the molten iron and adhering to the surface of the cavity, forming a penetrating slag hole, which leads to leakage.
Leakage caused by shrinkage porosity: Shrinkage porosity is closely related to the shrinkage of castings. Shrinkage porosity defects generally occur at the thick hot spot of castings, and their shapes are irregularly distributed in regions. The structure of shrinkage porosity region is coarse and has the characteristics of dendritic structure. The dispersed hole structure can be clearly seen under the electron microscope, and serious holes can be seen by naked eyes. Dendritic structure exists in the shrinkage porosity area, so it can be used as a criterion for defect determination.
Other types cause leakage:
Such problems include cracks, damage, poor seal during pressure test and wall thinning caused by deviation in casting processing. Such leakage is generally an accidental accident with a relatively small proportion.
The following is a concrete analysis of the leakage problems caused by the above three types of defects.
The leakage of cylinder body is divided into the following two categories according to the leakage position:
1. There is leakage at the bolt hole of the cylinder head of the water jacket sandwich wall on the top surface of the cylinder block.
2. Leakage in the main oil pipe of the cylinder block.
Analysis of leakage at bolt hole of cylinder head with water jacket on top of cylinder block;
The thickness of the bolt hole of the cylinder water jacket is generally more than 25mm, while the thickness of the surrounding water jacket wall is about 4.5mm Therefore, the bolt hole of the water jacket is a typical hot spot area, and there is a possibility of shrinkage. By scanning electron microscopy analysis of the leakage area, it is found that there are many hole-like defects in the fracture surface of the leakage area, which have a penetrating trend with the internal and external walls, and the defects have a dendritic structure, and there are no obvious traces of sand inclusion and slag inclusion, so it can be judged as a hole-like defect formed by free solidification and contraction-shrinkage.
Analysis of leakage in main oil pipe of cylinder block;
Through sampling and scanning electron microscope analysis of the leakage part of the main oil pipe, it is found that there are sand holes and slag inclusion besides the shrinkage of the treatment.
With the reform and opening up, China's automobile industry has developed rapidly, and the production of engine cylinder block has already been localized, and the quality level of products is gradually narrowing the gap with foreign countries. However, in the casting process, there are still some problems that have not been solved, such as leakage.
Leakage can be roughly classified into inclusion, shrinkage porosity and other types according to the causes.
Inclusion defects are divided into two types, one is sand inclusion type and the other is slag inclusion type.
Let's talk about the causes of leakage caused by sand inclusion type:
1. Due to some reasons, such as loose sand core/sand mold, adhered floating sand, uncleaned coating ball and uncleaned flash of sand core, during the pouring process, due to the baking and scouring action of high-temperature molten iron, sand particles fall, move with molten iron, gather in a certain part of the casting, form sand inclusions, and penetrate through the inner and outer walls, resulting in leakage.
2. In the process of sand core assembly, sand particles fall into the cavity or the assembled sand mold is polluted twice before pouring, resulting in sand inclusion and leakage.
The causes of leakage caused by slag inclusion defects are: the molten iron is not fully skimmed, the molten iron is impure, and the slag avoidance effect of ladle, pouring cup and pouring system is not ideal, which leads to the molten slag entering the cavity with the molten iron and adhering to the surface of the cavity, forming a penetrating slag hole, which leads to leakage.
Leakage caused by shrinkage porosity: Shrinkage porosity is closely related to the shrinkage of castings. Shrinkage porosity defects generally occur at the thick hot spot of castings, and their shapes are irregularly distributed in regions. The structure of shrinkage porosity region is coarse and has the characteristics of dendritic structure. The dispersed hole structure can be clearly seen under the electron microscope, and serious holes can be seen by naked eyes. Dendritic structure exists in the shrinkage porosity area, so it can be used as a criterion for defect determination.
Other types cause leakage:
Such problems include cracks, damage, poor seal during pressure test and wall thinning caused by deviation in casting processing. Such leakage is generally an accidental accident with a relatively small proportion.
The following is a concrete analysis of the leakage problems caused by the above three types of defects.
The leakage of cylinder body is divided into the following two categories according to the leakage position:
1. There is leakage at the bolt hole of the cylinder head of the water jacket sandwich wall on the top surface of the cylinder block.
2. Leakage in the main oil pipe of the cylinder block.
Analysis of leakage at bolt hole of cylinder head with water jacket on top of cylinder block;
The thickness of the bolt hole of the cylinder water jacket is generally more than 25mm, while the thickness of the surrounding water jacket wall is about 4.5mm Therefore, the bolt hole of the water jacket is a typical hot spot area, and there is a possibility of shrinkage. By scanning electron microscopy analysis of the leakage area, it is found that there are many hole-like defects in the fracture surface of the leakage area, which have a penetrating trend with the internal and external walls, and the defects have a dendritic structure, and there are no obvious traces of sand inclusion and slag inclusion, so it can be judged as a hole-like defect formed by free solidification and contraction-shrinkage.
Analysis of leakage in main oil pipe of cylinder block;
Through sampling and scanning electron microscope analysis of the leakage part of the main oil pipe, it is found that there are sand holes and slag inclusion besides the shrinkage of the treatment.