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Soldering is a relatively simple and inexpensive method for joining metal pipes, wiring, and sheets. Although a well soldered joint should last indefinitely, it can be opened without damage to its parts by heating it to the solder's melting point which is 360-460 degrees. This cannot be done with welded joints.
The tools required for soldering are:
A soldering iron, pencil or gun, a stand to keep the hot tool from burning the work surface; and cleaning tools, such as emery cloths, steel wool, a file, or a wire brush. The two secrets of soldering are to clean the joint thoroughly and to heat the work, not just the solder.
The choice of proper solder and flux is also important. Common solder is a mixture of tin and lead. A 60/40 solder (60 percent tin, 40 percent lead) is the most expensive, but it makes the strongest bond and is the easiest to work with, due to its low melting point. Less expensive 40/60 solder is more difficult to work with. A 50/50 solder is a good compromise between cost and ease of use.
Flux is used to clean the metal surfaces to be joined, to prevent oxidation of the metal when it is heated, and to lower the surface tension of the molten solder so that it spreads and penetrates more readily. Several types of flux are available in liquid or paste form. Flux-core solders are also available, and they eliminate a separate fluxing step when soldering small objects. Acid flux is highly corrosive; avoid contact with the skin and eyes, and clean any residue from the work wit alcohol or commercial cleaners.
Successful soldering requires just enough heat to melt the solder. The work should be held by wooden clamps, clothes pins, or vise jaws. A metal vise or tabletop may draw too much heat away from the work, resulting in a poor job. If you must work on a metal surface, insulate the work with scraps of lumber. Too much heat causes the solder to form a ball that will not spread.
Use a solder iron that is big and powerful enough to heat the work quickly and completely. A multi-range soldering iron or gun of 240/235 watts will handle most household soldering jobs.
The tip of the soldering iron or gun must first be tinned to assure proper heat transfer. file tip to remove all pits and black corrosion. When bright copper is exposed, clean with steel wool. It cannot be too clean.
Heat iron until new flux-core solder will just melt, then coat tip with solder. Wipe off access solder with a wad of dry rags; a smooth silver coating should remain. If the iron overheats, coating will turn black and require retinning.
Use steel wool, emery cloth, and alcohol or cleaning solvent to remove all corrosion and film from areas to be soldered. Do not touch cleaned areas with your fingers, they will leave oily deposits that will weaken the solder bond.
Make sure parts fit snugly, loose fits result in weak soldered joints. Apply the proper flux to the cleaned areas with a brush or swab, again, do not use your fingers! Skip this step if using a flux-core solder. Heat the iron to working temperature. Hold tip flat against the work for maximum heat transfer and feed solder under tip and move slowly along joint. Let work cool. Wash off flux residue with warm water.
Large joints should be sweat soldered. Clean and flux areas to be joined, then apply a thin coat of solder to each piece and let it cool. Clamp pieces together and heat until solder remelts. Protect surface or your bench with an asbestos pad.
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