Role of mould copper tube - properties of mould copper tubeIn order to improve the wear resistance of chromium coating and prolong the service life of mold cop

Role of mould copper tube - properties of mould copper tube

In order to improve the wear resistance of chromium coating and prolong the service life of mold copper tube, nickel cobalt alloy coating with thickness of 0.4-0.5mm was added between the inner surface of mold copper tube and chromium plating layer as a transition layer. So it is called nickel-cobalt alloy - hard chromium coating. Composite copper tube for short. The metal content is: the hardness of the coating is 300-600HV.

Nickel-cobalt alloy coating has good chemical corrosion resistance, thermal erosion resistance and wear resistance. It not only blocks the diffusion of Zn, S, Cd and F in molten steel on the inner surface of the copper tube of mold, but also acts as a bond between the inner surface of the copper tube of mold and the chromium plating layer, so that the wear resistance of the chromium plating layer is greatly improved. In addition, after the chromium plating layer is worn, the ni-Co alloy coating can continue to work instead of the chromium plating layer, so as to prolong the service life of the mold copper tube.

Due to the contact between the inner and outer surfaces of the copper tube and high temperature molten steel, the inner and outer surfaces of the copper tube have large temperature difference, high thermal stress and extreme variability. The shape of the inner cavity of the copper tube is very important. Only when the shape of the inner cavity of the copper tube is consistent with the shape of the solidified billet shell can the air gap be small and uniform. Therefore, the material of the copper tube is required to have strong thermal deformation resistance, that is, the recrystallization temperature is high, the thermal expansion coefficient is small, the thermal conductivity is good and the thermal fatigue strength is high.

The selection of copper tube material develops along the direction of red copper → phosphorus deoxidized copper → silver copper → chromium-zirconium copper. Because the recrystallizer temperature of chromium-zirconium copper is the highest among the above materials, its thermal deformation resistance is the strongest. However, due to its high cost, there are problems such as large amount of copper tube rebound in the extrusion process, and so on. At present, domestic mold copper tube manufacturing is not much.