A soldering iron is a tool which is designed to be used in soldering. Soldering is classically used to attach two pieces of metal to create a joint, although plastics can be soldered as well. Soldering irons provide a controlled source of heat which can be used to manipulate the materials used in the soldering process to achieve the desired goal of a smooth, clean joint. Soldering is easy enough to do that it is regularly taught in high school electronics classes.
In soldering, a highly ductile metal alloy known as solder is melted, fusing to the metal which is going to be joined. When the solder cools, a firm joint is created. In desoldering, the joint is heated to break the bonds and remove the solder, as may be done when something needs to be adjusted or reset. In both cases, a soldering iron is used to control the process.
Soldering irons classically take the form of a metal rod attached to an insulated handle. Using electricity or gas, the rod is heated, with the heat being concentrated in the tip. A small amount of solder is placed on the tip to heat up, and the iron is used to carefully apply the molten solder to the joint and to smooth out the joint. This process also requires flux, a material which prevents the solder from acquiring impurities. Of particular concern is oxidation, which can compromise the strength of the soldered joint.
Through a session of use, the tip of the soldering iron will gradually become fouled with solder, flux, and impurities. It must be cleaned off, when can be done by wiping the tip on a specialized sponge. After cleaning, a fresh layer of solder is applied to prevent oxidation of the tip. People can sometimes control the temperature of the soldering iron to achieve a desired temperature range, which allows for greater control over the process.
Working with a soldering iron does require some care, because the tip gets hot and it can become dangerous. Many people work with a stand or workstation which allows them to rest the soldering iron on a safe holder. Heat control is important, as is awareness of how long the device takes to heat and cool. Some heat up and cool down very quickly, while others may require a few minutes to warm up and cool down. It is important to avoid touching the tip while it is hot.