Analysis of the causes of parts dissolution due to poor heat dissipation on the local surface of parts

Because this part is a tubular part, it is mounted vertically during the hard oxidation process, and the stirring air is at the bottom of the tank, resulting in too small cross-sectional area of the part. The compressed air at the bottom cannot be guaranteed to pass through the hole in the part. At the same time, the part is also in the tank. It is impossible to guarantee 100% verticality, and it is easy to cause the solution temperature in the center hole of the part to be too high, the film dissolution rate is greater than the growth rate, and the part dissolves locally. It can be judged from the dissolution position and characteristics of the parts that the main reason for the dissolution of the parts during the hard oxidation process is the poor heat dissipation of the parts. Research has found that similar parts often dissolve in the oxidation tank in the previous production process. The number of times and the number of parts are relatively small. The production process of this part is compared with the previous production process. The process parameters, solution composition, tooling and fixture used in hard oxidation are basically the same. The only major change is the cross-sectional area of the existing oxidation tank and the compressed air stirring at the bottom of the tank. The pipeline is different. According to the force analysis of the bubble in the solution, when the compressed air stirs the solution, the bubble does not rise vertically while moving from the bottom to the liquid surface, but rises in a curved trajectory. This makes the compressed air pipeline evenly arranged at the bottom of the tank, and the compressed air introduced is not uniform after reaching the liquid surface of the solution. There is a big difference between the center position of the bubble on the liquid surface and the position of the compressed air outlet. This difference is with the depth of the solution. Deepening and the cross-sectional area of the solution becomes larger and larger, and cannot be accurately controlled, which causes a certain degree of difficulty in production. In the actual parts operation process, after the parts are installed before and after the processing is completed, the operator usually enters the hard oxidation tank first according to the liquid surface bubble Observe the stirring of the solution and choose a well-stirred position to place the parts. However, due to the instability of the bubble movement, the bubble area of the liquid surface will also change with time, which affects the cooling effect of the parts From the point of view of the position where the part dissolves, it mainly appears in the middle and lower part of the part. This is mainly because the uppermost part of the part is about 100mm away from the liquid surface. As the bubbles continue to reach the liquid surface and continue to burst, the huge force generated by the bursting of the bubbles plays a stirring role. , So that the temperature of the shallow solution on the liquid surface is uniform, and the solution in the upper part of the part is constantly flowing, the heat is neutralized, and the continuous growth of the film is maintained. This is the reason why the upper part of the part does not dissolve. For large and deep hard anodizing baths, the only reliance on the stirring of compressed air at the bottom of the bath can only make the solution at the bottom of the bath and within about 25mm from the surface of the liquid get stable stirring, and the solution in the middle of the bath is stirred It is not good for parts with small horizontal cross-sectional area. When the horizontal cross-sectional area of the part is large (such as shell parts), the compressed air is blocked by the surface of the part during the upward movement from the bottom, and the bubbles change the direction of movement, which improves the fluidity of the solution. This is not easy for shell parts. The source of dissolution