In order to improve the wear resistance of the chromium coating and prolong the life of the mold copper tube, the 0.4-0.5mm thick nickel-cobalt alloy coating is added between the inner surface of the mold copper tube and the chromium plating layer as a transition layer. So it is called nickel-cobalt alloy-hard chromium coating. Referred to as composite copper plated pipe. The metal content is: the hardness of the coating is 300-600HV.
Ni-Co alloy coating has good chemical corrosion resistance, thermal corrosion resistance and wear resistance. It not only blocks the diffusion of Zn, S, Cd and F in the molten steel to the inner surface of the copper tube of the mold. Moreover, it acts as a binder between the inner surface of the copper tube of the mold and the chrome-plated layer, which greatly improves the wear resistance of the chrome-plated layer. In addition, after the chrome plating layer is worn, the nickel-cobalt alloy plating layer can continue to work in place of the chrome plating layer, thereby prolonging the service life of the copper tube of the mold.