Soldering cast iron presents many problems, the most difficult of which is properly tinning the cast iron surface to be soldered. If plating facilities are available, it is best to copper plate the parts that are to be soldered. If not, a substitute tinning process can be developed by thoroughly cleaning the surfaces and copper plating them with a solution of copper sulphate. This solution should be made up of 30 ml(1 oz) copper sulphate and 15 ml (112 02) acid added to
240 ml (8 02) of water. The parts to be: soldered are either brushed with the solution or dipped in it. They are then rinsed and allowed to dry before soldering.
Some welders prefer to prepare cast iron for soldering by tinning it with half-and-half solder, 50% tin and 50% lead. A grinder is used to remove all of the scale from the surface so that it is clean and bright. The ground surface is then cleaned of grease by dipping it in a lye solution, then rinsed and dipped in muriatic acid. The surface is then treated with rosin and tinned with half-and-half solder. The casting may have to be dipped in acid several times before it becomes thoroughly tinned. Rubbing the surface of the iron casting with a piece of zinc while the surface is covered with acid will facilitate the tinning. The tinned surface can then be soldered with the half-and-half solder.