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Adding tin to the copper metal improves its ability to withstand stresses from machining and handling. In addition to its workability, it also increases its strength and ductility to make it suitable for bearing applications. For example, high leaded tin bronzes are used in rolling mills for the support of large journal bearings. The higher the alloys tin content is, the better the machinability and pressure tightness will be.
Cheap and abundant as galena, lead has many of the ideal characteristics of a type metal; but it lacks sufficient hardness for casting characters and narrow spaces and it sags when it cools to a solid. Pewterer’s tin, obtained from cassiterite, is added to solve these problems and improve its ability to hold type against the stresses of printing.
In the method of making a lead alloy which contains aluminum, magnesium and calcium, the lead is first introduced into the molten state under a covering 0f calcium chloride; tin, as well as aluminum and magnesium, are then introduced into the lead; and finally the calcium. Then while the lead is still at a temperature which is below its melting point, rosin is added; and while it burns, lithium or potassium may be introduced into the molten body.
After this the crucible is removed from the furnace, and the alloy poured into ingots for smelting. Then the ingots are cut up and ground to the desired size. After the smelting process is complete, the alloy is rolled for use in molding.
