Wiped Joint between Lead and Cast-iron Pipes.
—In wiping a lead pipe to a cast-iron pipe perhaps the best practice is to file clean the end of the cast-iron pipe first and then coat with pure tin, sal-ammoniac being used as a flux. The pipe then is washed to remove the sal-ammoniac, and afterwards “retinned,” using resin and grease as a flux. A plumber’s joint then is wiped in the usual way. It is necessary to take great pains to make a good sound strong joint between the two metals, but even then in the course of time (it may be only a few years) the iron will come out of the solder. The first sign of decay will be a red ring of iron rust showing at the end of the joint. This rust will swell a little and cause the end of the soldering to slightly curl outwards. Eventually the rust will creep between the solder and the iron and destroy the adhesion of the one to the other. The joint would eventually become a loose ring on the iron pipe, but not on the lead pipe, as the expansion of lead and solder do not differ to any great extent. Only those metals that alloy together can be satisfactorily joined by soft soldering, and the solder should contain as great a proportion as possible of the metals to be united.
The illustrations to this chapter ([Figs. 46] to [55]) are self-explanatory.
CHAPTER VIII
Hard-soldering with Silver Solder
Hard-soldering is chiefly of two kinds, brazing and silver-soldering, the former being employed for iron and steel, the solder used being known as “spelter,” a brass alloy which can be obtained in various degrees of fineness. For copper, brass, and nickel silver, alloys containing silver are the best solders. In both forms of hard-soldering, the flux is borax.
The methods of silver-soldering vary with the size of the work. A jeweller may hold the work in his hand, on the end of a piece of binding wire or on a square of charcoal, the heat being applied by a mouth blowlamp from a horizontal gas jet, as already described. Larger work demands a flame of greater intensity, and sufficient air can be supplied only by a footblower or similar device, or, as an alternative, from the flame of a suitable blowlamp.