1) The control of zinc alloy composition starts from the purchase of zinc alloy ingots. The zinc alloy ingots must be made of high-purity zinc plus ultra-high-purity aluminum, magnesium and copper. Manufacturers with strict composition control standards shall be selected for supply. High quality raw materials are the basis of high quality products.
2) The storage area of purchased raw materials shall be kept clean and dry. Pay special attention to the impact of weather changes on the placement area. Zinc alloy ingot is not strong in corrosion resistance, and it will be corroded to produce white rust in humid environment for a long time. If the storage area is not cleaned, the zinc alloy ingot will be polluted, and the residue will increase during smelting, and the loss of zinc alloy will also increase. A clean and dry environment is essential for the purity control of zinc alloy ingots.
3) The proportion of the new material to the material returned to the furnace such as nozzle material and waste parts. In general, 70% of new materials and 30% of old materials should be recycled. In the process of die-casting, the surface of the material such as nozzle material is oxidized, and the content of zinc oxide is much higher than that of the original zinc alloy ingot. When these materials are remelted, due to the viscous state of zinc oxide at high temperature, when they are taken out of the zinc pot, they will take away the zinc and magnesium in the alloy. The proportion of zinc and magnesium in the zinc pot is reduced.
4) When remelting nozzle materials and waste parts, the remelting temperature must be strictly controlled not to exceed 430 ° C. Too high temperature has great corrosiveness to crucible and tool, which results in the loss of alloy composition.
5) The large-scale die-casting plant can adopt several kinds of melting materials and returning materials, better control the ratio of alloy ingot and returning materials, more effective use of solvent, and the melting solution can keep the composition and temperature of alloy uniform and stable. Electroplating waste and fine scraps should be melted separately from non electroplating waste, because the copper, nickel, chromium and other metals in the electroplating waste are insoluble in zinc, which will exist as hard particles in the zinc alloy, resulting in difficulties in polishing and machining.