The harmful impurities in tin bronze are aluminum, silicon and magnesium. When their content exceeds 0.005%, the resulting SiO2, MgO and Al2O3 oxide inclusions will pollute the melt and degrade some aspects of the alloy properties.
In the smelting of tin bronze, due to the relatively low boiling point of zinc and its greater affinity with oxygen, the melt should be deoxidized before melting. In this way, zinc can supplement the deoxidation, thus helping to avoid the danger of producing SnO2. The structure of zinc and phosphorus in the melt is deoxidized, and the 2ZnO·P2O5 is easily separated from the melt, which is beneficial to improve the fluidity of the melt.
The use of dry charge, or even preheating charge before melting, can reduce or even avoid melt absorption gas. The proper proportion of new metal and process waste also helps to stabilize the melt quality. The amount of process waste should not exceed 20% ~ 30%. A melt slightly contaminated with impurities may be oxidized by blowing it into air or by the addition of an oxidizing agent, such as CuO (copper oxide). Waste that is heavily contaminated with certain elements may be improved by solvent or inert gas refining, including remelting treatment.
The appropriate feeding and melting sequence, including the use of a power frequency core induction furnace with strong melt stirring function, is beneficial to reduce and avoid the occurrence of segregation. Adding an appropriate amount of nickel into the melt is beneficial to accelerate the solidification and crystallization rate of the melt, and to reduce and avoid segregation. Similar additives, zirconium and lithium can also be selected. The mixed smelting method can be adopted to melt copper and lead respectively, and then inject the lead melt into the copper melt at 1150 ~ 1180℃. In general, the smelting of tin bronze containing phosphorus mostly uses charcoal, or petroleum coke and other carbonaceous materials to cover the melt, without the use of solvent. The covering agent used in smelting tin bronze containing zinc should also include charcoal and other materials containing carbon. For continuous casting, it is appropriate to control the temperature at 100 ~ 150℃ above the liquidus of alloy.