Investigation On The Vertical Tin-plating Process For The Semi-flexible Coaxial Cable

Holistic tin-plating on the outer conductor is one of the key process in the manufaction of semi-flexible coaxial cable. However, in the traditional horizontal tin-plating process, disadvantages such as the pinhole defects and low productivity effect cannot be avoided. The immersion length and the tin-plating time are the key factors that affected the tin coating quality. In order to solve the problems, such as the pinhole defects in the horizontal tin-plating process, a vertical tin-plating process was proposed in the present work. This new method can reduce the immersion length to 40mm-100mm and reduce the tin-plating time to less than 1.0s. The main missions of the research were to develop the key equipment for vertical tin-plating process, optimize the process parameter and develop a kind of special flux.The experimental results indicate that shorten immersion length and time are able to reduce the pin-holes, improve the tin coating quality and production efficiency obviously. The optimal process parameters were shown as follow: the molten tin temperature was 255℃~265℃,the immersion time was 0.5s~1s, the immersion length was 40mm-80mm, the speed of cable was 4m/min-6m/min.According to the requirement of flux, a kind of special flux with fast soldering speed and small gas generation was developed. The compositions of the flux were: A acid (1%), B acid (1%), cationic surfactant (0.3%), nonionic surfactant (0.1%) and alcohol.The minimum aperture between cable and guide hole was 0.2mm according to the calculation. A high temperature resistant rubber gasket was used to solve the problems of tin leaking and thread jamming, the aperture of the gasket was 3.5mm. In order to make the tin coating uniformity and brightness, a equipment was installed above the surface of liquid tin from 10mm~20mm to scrape redundant tin on the cable.