| ABS Plastics is light, plastic and smooth-skined. It can be made to different shapes. However, the applications of ABS plastics is limited due to its low-hardness and bad wear-resistance. Based on the ordinary electro-plating, composite plating has been developed as a new surface-treatment technology by adding high-hardness, high wear-resistant particles during plating. The hardness and the wear-resistance of ABS are evidently improved, and its serviceable life is prolonged by composite plating. Therefore, the application of ABS is expanded by composite plating..A novel process of Ni-SiC composite plating on ABS plastics grinding head was developed in this paper. Several methods including chemical coarsing, metal ion absorption, activated process, electroless plating, electroplating, composite plating, Hull cell, friction test, etc. are used. Large SiC particles were used as disperse medium, Ni as host metal, and ABS plastics as matrix. Lightweight and easy machinability of plastics were combined with high hardness and abrasion resistance of SiC particle in this process. The composite plating had good adhesion, high hardness and outstanding wear resistance.The best conditions for composite plating had been obtained by investigating in detail every working procedure. Economy and easy-to-operate were also considered.(1) First, Metallizing ABS plastics surface by chemical coarsing, metal ion absorption, metal ion reducing and chemical copper-plating. Then, the copper-coating was thickened by electroplating in order to improve adhesion between following-coating and plastics matrix, and nickel was preplating. Finally, Ni-SiC composite was plated.(2) By test various activated processes. Silver nitrate ionic activated process was choosed for its low cost and convenience.(3) Electroless copper plating was compared with electroless nickel plating about the metallizing technique of plastics surface. Influences of the component of plating solution and the chemical plating technology on stability and deposition rate of electroless plating were studied. It was found that electroless copper plating was better than electroless nickel plating.(4) A new rack was developed according to the principle of rack designing and actual shape of the plastics part. The equipment available was reformed for Ni-SiC composite plating.(5) SiC content in coating was 20.11(Vol%). Coating was fine and close. The hardness was 2.68 times pure Ni coating, and wear-resistance was 4.1 times pure Ni coating. The adhesion between the composite coating and the matrix was fine.In addition, there were several points should be mentioned in the proposed process.(1) Chemical coarsing should be moderate. The adhesion of coating would be depressed by both under-coarsing and over-coarsing. The plastics matrix might be exposed with under-coarsing. The cracks might appear on the coating with over-coarsing.(2) The thickness of copper coating should be over 5m for preventing coating wrinkle.(3) Anode envelope should be used during electroplating. Anode slime should be cleaned frequently in order to prevent Ni particle deposition on the plastics grinding head.(4) Low current density is better for Ni-SiC composite plating, the SiC particles is nonconductive. So the real surface area of the plastics grinding head is much less than the apparent area. Liberation of hydrogen gas would be increased rapidly and SiC particles on the surface might be dispersed if the current density exceed the upper limit. Furthermore, nickelous hydroxide wouldbe deposited because the pH of plating solution nearby the surface rapidly increased. All of above might result in coating deterioration.(5) The thickness of coating should be suitable with the size of SiC particles. On the one hand, the particles must be fixed on the coating. On the other hand, the grinding ability of the composite plating would be red... |
