Manual of instruction in hard soldering

The same natural laws that have been explained in relation to Hard Soldering also apply to the use of softer alloy.

The surfaces to be united must be clean and bright; the heated surfaces must be protected from the air by a suitable flux and must be heated beyond the melting point of the solder to be used.

The tools and appliances differ. While soft soldering is done over a jet of flame, as a gas burner or alcohol lamp, and the blowpipe occasionally used to direct the flame, the most common tool is the copper one, sometimes called a soldering iron. Soft solder has so much less tenacity that it is necessary to have large lapping surfaces to give it strength, or folded and locked joints, which are only to be held in position by the solder.

The ordinary solder is composed of lead 75 parts and tin 25 parts, by weight. A better flowing solder is made by adding more tin, but where much solder is used it is economy to use as little as practicable on account of its cost. When more tin is used the solder is called fat. This is used
by jewelers in repairing jewelry. For repairing plated ware, when the lean solder would cause the joint to discolor and look bad, it is preferable to use pure tin, which holds its color about as well as silver and sometimes saves re-plating the work on which it has been used.

FLUXES. Rosin is the most common flux to be used on tinned-ware where it is only necessary to protect the surface from the air. It melts and flows over the surface to be soldered but does not ignite by the heat of the copper. It is pulverized and rubbed on the seam with a small stiff pencil brush. Solder does not adhere to iron readily. For that reason a flux is prepared by dissolving strips of metallic zinc in muriatic acid until no more will be taken by the acid and diluting with from 2 to 8 times as much water. A lump of sal ammoniac added protects the soldering copper from corrosion as well as assists to clean greasy surfaces. The chemical action of this flux is that the muriatic acid unites with the iron and deposits a film of zinc to which the solder more readily adhers. Iron that is covered with a scale of oxide may have the scale removed by immersing in dilute muriatic acid and small articles are tinned by taking them from this solution, when they have turned white, and dipping in melted solder, or tin.

The copper is usually an octagonal bar drawn out to a point by hammering, and a handle attached. Its shape should be adapted to the work for which it is to be used. The point is filed bright and kept clean and well tinned. To tin the point file it bright and heat it. As soon as it is hot enough to melt rosin cover the point with it and heat until it will melt solder. Put some rosin and solder on a board together and rub the point of the copper in it turning it occasionally until the solder adhers to the copper. Now when heated and drawn across a bar of solder a drop of solder will adhere to it and can be conveyed to the point previously coated with rosin, or zinc solution, when the drop of solder will leave the copper and unite with the article to be soldered. The copper must not be overheated or the coating of solder will burn off, or alloy with the copper, and it will be necessary to dress it over and re-tin. When they become worn and blunt from use they are drawn out cold with a hammer and re-tinned. Other metals may be used to convey the heat but copper has a great capacity for heat and is easy to draw into shape and easy to coat with tin.

A wet rag is kept at hand on which to wipe the copper to keep it clean when in use. When soldering much with acid, or on a greasy surface, wet this rag in a weak solution of sal ammoniac.

The coppers are usually heated in pots made for the purpose, using for fuel charcoal, or gasoline, but may be heated in a forge or stove. For simply stopping a hole, the surface having been prepared and a lump of solder laid on may be melted with a piece of iron, or other metal, not tinned.

In repairing joints where steam pressure is to be restrained dependence should not be placed on soft solder alone. Heat and pressure cause soft solder to ooze and eventually leak unless supported by some stiffer metal. If the joint cannot be brazed, or hard soldered, make a patch of hard metal having an ample area of surface for the soft solder to flow in and solder on.

In repairing jewelry the flux used is muriate of zinc. Rosin is not used because it spreads over the work and is difficult to clean off. Soft solder should not be used when hard solder can be, but in many cases it is the only way as where the parts of the article itself are put together with soft solder or contain settings that will not stand the heat necessary for hard solder. Most parts to be repaired, such as pin joints, button backs, ear-ring loops, etc., are made for soft soldering by being provided with a large surface to attach with the solder, which not only gives strength but covers the solder. Care should be taken that the solder does not flow beyond the piece to be attached. The usual way to solder them on is to put some acid flux on the surface of the piece to be attached and holding it in or near the flame touch occasionally with a slender bar of solder until a little melts and flows over the surface. Clean the place where it is to be attached and put on the acid flux. Press the two pieces together and heat until the solder melts and unites with both pieces. Cool in water and brush with chalk to cleanse from any acid that may adhere.

Jewelry, with jet settings, may be mended with soft solder without removing the settings, if care is used in heating. It must be borne in mind, however, that the jet melts at about the same temperature as that required for ordinary soft solder, and ignites at a little higher temperature. Black glass used in imitation will stand heat but must not be mistaken for jet. Pearl settings should be re- moved, or protected from the heat. Shell and imitation cameos are held in their mountings by pieces of metal put on with soft solder and will not stand the heat necessary to hard solder. A small copper, or nickel bar, is sometimes better than the gas jet, or lamp flame, in directing the heat and solder to a certain point.

Brittannia and plated-ware may be repaired with soft solder although they sometimes melt at a lower temperature than the solder. This is done with a copper by putting on a small portion of solder at a time and removing the copper to allow the work to cool thoroughly after each application.

Cake baskets and articles of plated-ware haying wire boles and hinges of hard metal, usually brass plated over, some- times get them broken off. Clean the parts to be united and tin over the hard metal portion. Then holding the parts in position apply the flame with the blowpipe to the hard metal part, at some distance from the joint, to prevent the soft metal from melting in the joints, as soon as the solder melts promptly remove the flame. Use pure tin for such places instead of solder. The heat does not remove the plating, or injure it, if cleaned without scouring. If discolored, apply a little of the pickle solution used in hard soldering, and wash off.

Alloys are made that melt in boiling water, but they do not flow so well and lack tenacity. They are seldom used in soft soldering. Two parts bismuth, one of lead and one of tin melts at about 200 Fahrenheit and is probably as good as any of these soft alloys.