工件内腔镀硬铬

Hard chromium electroplating of workpiece lumen

分别讨论了工件内腔镀硬铬液的组分——铬酸酐、硫酸和三价铬的含量对镀层性能的影响：铬酸酐的含量过高，镀层硬度降低。硫酸根的含量过高，镀液的分散能力和电流效率降低，并且镀液中Cr^3＋的含量上升；含量过低，会使镀件凹处的镀层薄，甚至无镀层沉积。Cr^3＋含量偏高，槽电压升高，光亮区变窄；含量偏低，分散能力降低，镀层光泽性不好，镀后工件水洗性不好。其最佳含量分别为：铬酸酐220—250g／L．硫酸与铬酸酐的质量比1：（110—120），Cr^3＋2～4g／L。分别对30℃、40℃和50℃下的铬酐的质量浓度与镀液密度的关系，电镀过程中镀液温度与阴极电流密度及其与工件形状、阳极的设计和电极间距的关系，以及工件的预热温度、冲击电流和反向蚀刻等操作规范进行了介绍。

The influences of bath components of workpiece lumen hard chromium electroplating such as chromic anhydride, sulfuric acid and trivalent chromium on deposit＇s performance were studied respectively. Deposit hardness decreases as the content of chromic anhydride is too high. The throwing power and current efficiency decrease and content of Cr^3＋ in the bath increase when the content of sulphate is too high. But less deposit or no deposit is found in recess when the content of sulphate is too low. Tank voltage increases and bright area becomes narrow when the content of Cr^3＋ is on the high side. And the throwing power decreases, deposit＇s brightness and water washability of workpiece is bad after plating when its content is on the low side. The optimized contents are as follows： 220 - 250 g/L of chromic anhydride, 1 ： （ 110 - 120） of sulfuric acid to chromic anhydride mass ratio, 2 - 4 g/L of Cr^3＋. Relationship between the mass concentration of chromic anhydride and bathg density at temperatures of 30 ℃ ,40 ℃ and 50 ℃, between bath temperature and cathode current density of cathode,and the relationship of it with workpiece shape, design of anode and distance between electrodes during plating, the operation criteria of preheating temperature of workpiece, strike current and counteretching were introduced respectively.