Analysis of mottled causes of vacuum electroplating electric heating tube

Analysis of mottled causes of vacuum electroplating electric heating tube

1. The operator who processes the part has not changed, and the human-caused mottle is excluded.

2. Other equipment in the equipment production workshop has not changed, but there are two large and small acid electroless nickel plating tanks. When the large groove is used, there is no type A variegation, only the type B variegation; when the small groove is used, both types of variegation are present. It was observed that the acid electroless nickel plating solution was stirred by circulating filtration to make the solution flow, and the stirring force was not strong. When tied with 1 mm aluminum wire, the part can shake slightly in the flowing solution. When the hanger is used to hang it, it is very firm, the parts do not shake, and the electroplating hanger has very little moving space after being placed in the small groove. Even if it is shaken by hand, the amplitude is small, which is not conducive to the movement and stirring of the parts, which may lead to electroless nickel plating. During the process, the air bubbles attached to the surface of the parts are difficult to detach, resulting in pitting and mottled defects. Therefore, the small volume of the electroless nickel plating tank may be one of the reasons for the occurrence of mottled.

3. All kinds of tank liquids are qualified, and the influence of tank liquid can be excluded. The operator reported that most of the parts showed large areas of rust spots on the surface after mixed acid corrosion (see Figure 3). It is speculated that the corrosion of the part base before plating is the cause of the mottle.

4. The operation process of the processing method is carried out according to the process requirements, and the process parameters of each process are also within the required range. According to the production, two kinds of hanging methods were used in the production process: aluminum wire with a diameter of 1 mm and stainless steel hanging. Parts tied with aluminum wires only have type B mottles after plating, while parts hung with stainless steel hangers have both types of mottles after plating.

5. Environment The failure did not occur during processing in autumn and winter, but occurred between July and August. Generally June-August is the high incidence period of rust failure of aluminum alloy parts, and rust easily leads to the subsequent coating blooming, so the rust of the substrate is also one of the possible reasons.

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