Effect of Part Dimensional Accuracy on Plating Quality

[China Aluminum Network] Because the plating layer has a certain thickness, after the parts are surface-treated, they will inevitably cause part size changes. Generally, the part dimensions and tolerances specified on the design drawings refer to the final dimensions and tolerances of the parts. If the parts do not meet the requirements for the fitting, plating or electroless plating on the final dimensions of the parts is still feasible; if the accuracy of the parts is better than High, assembly gaps after assembly can not accommodate the thickness of the plating layer and its deviation, then the plating on the relatively final size of the part, is unfavorable to the assembly and work performance of the product. In order to solve the problem of post-plating size matching of parts with matching requirements, the size of the parts before plating must be determined through consultation with the design and processing department of the parts, and the thickness of the plating and the dimensional deviation of the plating must be reserved in advance. It must be noted that it is impracticable to only reserve the thickness of the coating without revising the thickness deviation that may occur during plating.

The change in the final size of the part caused by conversion film treatment is different from that of electroplating and electroless plating. Since the conversion film layer is formed by the self-dissolution and transformation of the surface of the metal part in the chemical solution, the conversion film is usually very thin, and the part does not generally cause a significant change in the final size after being treated by the conversion film. Parts treated with conversion film cause significant changes in the final size and affect the fit of parts. Commonly used in hard anodized aluminum and aluminum alloy, thick film corrosion phosphating and other processes. Because the strength of the phosphate layer is not as good as that of the metal, it is not appropriate to use a measure that reserves the thickness of the layer on the part. In order not to affect the fit of the parts, it is advisable to use a low-membrane phosphating system solution for phosphating treatment to reduce the thickness of the film and still have good corrosion resistance.

The hard anodic oxide film on the surface of aluminum and aluminum alloy has high hardness and excellent wear resistance. It is a common means to improve the surface wear resistance of aluminum parts. In order to improve the service life of parts, the product design usually requires hard The quality of the anodized film layer has a large thickness. Therefore, after the hard anodization of the aluminum parts, the change of the final size of the parts is relatively large. Generally, following this rule, the increase in the final size of the parts is substantially It is equal to 1/2 of the film thickness, as shown in the figure. This value is widely used to estimate the dimensional change of hard anodized aluminum parts.

Parts and fasteners with common threads often encounter problems with fitting difficulties after plating. When the thread is plated, the plating thickness of the cusp and the bottom of the thread is not the same. The coating thickness at the cusp will be significantly larger than at the bottom of the valley. As the thickness of the coating increases, the difference between them will increase. The larger, therefore, the thread profile angle becomes smaller, as shown. With the difference in thread diameter and pitch, although the ratio of the thickness difference between the cusp and the bottom of the valley is different, as the thickness of the plating increases, the tendency of the angle of the angle of the cone to become smaller always remains. Thread diameter and pitch are larger and the precision is lower. After the thread is plated, there are fewer obstacles, and vice versa. Practice has proved that the main reason for the occurrence of fit obstacles after thread plating is the deformation of the tooth profile after plating, followed by the plating thickness factor.

At present, the following methods to solve the problem of thread plating and binding obstacles are roughly as follows:

1. Under the condition that the corrosion resistance is allowed, the thickness of the plating layer is properly reduced, and a plating solution having excellent dispersion ability is used for plating.

2. In case of last resort, sufficient allowance may be reserved according to the appendix of GB 197 and GB 5263 and the thickness of the selected plating layer;

The fasteners are coated with a Dacromet coating (also known as a zinc-chromium coating). The coating is composed of ultra-fine scaly zinc, aluminum powder and chromate mainly composed of trivalent chromium. The Dacromet coating liquid is applied on the surface of the part, homogenized, and then formed by sintering. Floor. The atmospheric corrosion resistance of the coating is much better than that of the electrogalvanized layer. The thickness of the coating can be arbitrarily adjusted as required, and it is relatively uniform and does not cause changes in the angle of the tooth profile. Therefore, it is an ideal protection method for fasteners.

R417A is an HFC retrofit refrigerant for R22 in direct expansion stationary air conditioning (AC) and medium temperature commercial refrigeration systems.