When a softer alloy metal--called solder--is melted between two pieces of metal, they bond. Among solder's many uses are sheet-metal work, electrical wiring, jewelry-making and repairs.
Common solder is a tin-and-lead mix. A 60-40 solder (60% tin, 40% lead) is the most expensive, but it makes the strongest bond and is easiest to work with because of its low melting point. Less expensive 40-60 solder is more difficult to use. A 50-50 solder is a good compromise between cost and ease of use. There are also high-temperature solders that do not contain lead. Silver solder, for example, is an alloy of silver, copper and tin.
Flux, another component of solder, 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.
Solder is available in spools of hollow wire with rosin flux or acid flux in the center of the wire. For some jobs, such as copper plumbing, it is better to use solid solder and apply the flux separately.
Lead solder is toxic, so it's important to ventilate the work area, keep hands away from mouth and wash them when done. Use special lead-free solder on pipes and fittings that conduct water and on any surface that will come in contact with food.
To begin, gather materials to clean the surfaces to be joined: steel wool, emery cloth and alcohol or cleaning solvent. Next you'll need to choose the right solder and flux for the metal you're joining and choose the soldering tool.
Types of Solder
* Aluminum: special aluminum solder, special aluminum flux.
* Brass, bronze or copper: 60-40 or 50-50; rosin or acid flux. Use lead-free solder on copper pipes.
* Electrical wiring: 60-40; rosin flux.
* Galvanized metal: 60-40 or 50-50; acid flux.
* High temperature applications: silver solder; silver brazing flux.
* Silver: silver solder; rosin or silver flux.
* Steel, tin, zinc: 60-40 or 50-50; acid flux.
* Stainless steel: 60-40 or 50-50; stainless steel flux.
Acid flux is highly corrosive; avoid contact with skin and eyes. Clean any residue from the work with alcohol or commercial cleaners.
Use soldering gun, soldering iron, soldering pencil (a small soldering iron) or propane torch. Soldering guns heat up and cool quickly and are useful for soldering electrical and other fine work. Soldering irons come in a variety of sizes and work off any wall outlet. Use a torch for large jobs such as joining pipes or sheet metal.
How to Solder
Always remember when soldering to heat the metal, not the solder.
Clean the metal surfaces to be soldered so that they are free of rust, dirt, grease, tarnish and moisture. Don't touch clean areas with your fingers.
To prepare the cold gun or iron, file each face of the tip smooth and clean until bright metal is exposed.
As further preparation, heat the tool until flux-core solder just melts, then coat the tip evenly with solder. Wipe off excess with a damp sponge or clean, dry rag.
Apply paste flux to the surfaces to be joined (if you're not using flux-core solder).
Heat the work surface, preferably from below, and apply the solder from above so that it melts and runs down into the joint. The metal should be heated enough to melt the solder and boil away the flux. If too hot, the solder will form a ball that will not spread. Wash off excess flux.