These results, says Mr. Hiorns, show that the hardest alloy is the one with 66% (about 2 parts) of tin and 34% (about 1 part) of lead, which also is the one having the lowest melting point of all the lead-tin alloys. The results also show that tin is slightly harder than lead.
Compositions of Soft Solders.
—As already shown, solders vary in fusibility according to their composition, and the choice should be determined by the nature of the work and the properties of the metal to be soldered. Should a solder be used of too high a melting-point, the metal will itself be fused before the solder begins to flow.
A point to be particularly observed is that the introduction of a foreign substance into the solder—for example, the addition of a little zinc to a pot of “very fine” solder—will utterly spoil it and render it unworkable. To remove zinc from solder, melt the solder in a pot, take it off the fire and stir in powdered sulphur or brimstone until the whole is of the consistency of wet sand. Replace the pot on the fire and melt, but do not stir the contents. The sulphur and zinc will rise to the surface and form into a cake. Now take the pot off the fire and carefully remove the cake without breaking by employing two pieces of hoop iron with bent ends.
It is false economy to use a rough solder for fine work on the score of cheapness, since more solder is required for a given job on account of the rough particles of solder clinging to the work; moreover, the rough appearance of the soldering may completely spoil the job.
The table on the opposite page gives the fluxes and the compositions of soft solders suited to a number of different metals.
Making Solder Strips, Wire, Tears, etc.
—Only clean, pure tin and pure lead should be employed. The lead is first melted and then the tin added. When all is melted, place a piece of resin on the molten metal to act as a flux, and after well stirring, the solder is made into strips by pouring from a ladle. Solder should not be poured into sand. It may be poured into strips on an oiled sheet of black iron, preferably corrugated to accommodate the strips. In the absence of a corrugated iron sheet, some workers use a ladle resembling a large spoon with a hole about 1⁄16 in. in diameter near the end. To form the strips, get a ladle full of solder, place it on a flat iron sheet; then, tilting the ladle to allow the solder to flow over the hole, quickly draw the ladle across the sheet. A thin strip of solder should thus be formed, and the thickness of the strip may be varied by increasing or decreasing the diameter of the hole in the ladle. A button of solder usually forms at one or both ends of the strip, and this excess should be melted off the strips by just dipping the ends into the molten solder in the pot.
Soft Solders for Various Metals
| Metal to be soldered | Flux | Soft Solder | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Tin | Lead | Other constituents | |||||||||
| Aluminium | stearin | see table on p. 59 | |||||||||
| Brass | - | [1] | zinc chloride, resin or ammonium chloride | - | 66 | 34 | |||||
| Gunmetal | 63 | 37 | |||||||||
| Copper | 60 | 40 | |||||||||
| Lead | tallow or resin | 33 | 67 | ||||||||
| Block tin | zinc chloride | 99 | 1 | ||||||||
| Tinplate | zinc chloride or resin | 64 | 36 | ||||||||
| Galvanised steel | hydrochloric acid | 58 | 42 | ||||||||
| Zinc | hydrochloric acid | 55 | 45 | ||||||||
| Pewter | gallipoli oil | 25 | 25 | bismuth, 50 | |||||||
| Iron and steel | ammonium chloride | 50 | 50 | ||||||||
| Britannia metal | tallow or resin | 25 | 25 | bismuth, 50 | |||||||
| Gold | zinc chloride | 67 | 33 | ||||||||
|
Silver
| |||||||||||
