The method of applying a hard chromium coating to internal cylindrical surfaces

Chromium plating processes are considered in relation to the inner surfaces of cylinders of hydraulic drives with hydrostatic guides. The main factors that reduce the productivity of electrochemical chromium deposition, regardless of the type of surface, are analyzed, namely, the use of chromic acid with active anions with a low scattering ability as an electrolyte, the use of insoluble anodes and high-density currents. The features of chrome plating of the inner surfaces of the hydraulic cylinder, namely, the limited use of installations depending on the size of the parts and the unevenness of the deposition rate of chromium along the length of the part. An installation has been developed for coating internal surfaces, which includes a cathode, anode, a tank and a pipeline. Distinctive features of the installation are the way of feeding the electrolyte at an angle to the horizontal, which allows the electrolyte to be supplied in the form of a turbulent flow swirling along a helical path, and the body of the installation, which is a chrome-plated part. In the process of work, experimental studies were carried out to select the modes of applying a hard chromium coating to the inner surfaces of the hydraulic cylinder. As a result of the work, the optimal ratio of chromic anhydride and sulfuric acid in the electrolyte composition, which is 10:1, respectively, and the modes of its application were determined. Chromium coatings obtained using the developed concentrated electrolyte and chromium plating method have increased hardness by 5...20 % and reduced porosity by 10...30 times with the formation of shiny solid deposits, which corresponds to a corrosion-resistant and wear-resistant coating.