Poor heat dissipation on the local surface of the part causes the part to dissolve

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 not possible to guarantee 100% verticality. 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 phenomenon of partial dissolution of the part appears. Poor heat dissipation of parts. Research has found that similar parts often dissolve in the oxidation tank during the previous production process, but the number of occurrences 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, and tooling fixtures 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 pipeline arranged at the bottom of the tank. Force analysis shows that when compressed air stirs the solution, the bubbles move from the bottom to the liquid surface, instead of rising vertically, but rising in a curved trajectory, which makes the compressed air pipeline evenly arranged at the bottom of the tank reach the The liquid level of the solution is not uniform. 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 that the depth of the solution increases and the cross-sectional area of the solution increases, and it cannot be accurately controlled. Production causes certain difficulties. During the actual operation of the parts, after the pre- and post-processing of the parts are completed, the operator who enters the hard oxidation tank generally observes the stirring of the solution according to the size of the liquid surface bubbles, and chooses a well-mixed position to place the parts but due to the movement of the bubbles As time changes, the bubble area of the liquid surface will also change, which affects the cooling effect of the part. From the position where the part dissolves, it mainly appears in the middle and lower part of the part. Since the top end of the part is about 100mm away from the liquid surface, as the bubbles continuously reach the liquid surface and burst continuously, the huge force generated by the bursting of the bubbles plays a role in stirring, so that the temperature of the shallow solution on the liquid surface is uniform, and the solution in the upper half of the part The continuous flow, 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 the hard anodizing bath with a large cross-sectional area and a deep depth, it is only dependent on the bottom of the tank to compress The stirring of air can only make the solution at the bottom of the tank liquid and within about 25mm from the surface of the liquid surface get a stable stirring. The solution in the middle layer of the tank liquid is poorly stirred, which is not conducive to the parts with small horizontal cross-sectional area. When the horizontal cross-sectional area of the parts is large ( Such as shell parts), when the compressed air moves upward from the bottom, it is blocked by the surface of the part, and the bubbles change the direction of movement, which improves the fluidity of the solution. This is one of the reasons why the shell parts are not easy to dissolve.