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A soldering iron is a device for applying heat to melt solder for soldering two metal parts together.

A soldering iron is composed of a heated metal tip and an insulated handle. Heating is often achieved electrically, by passing a current, supplied through an electrical cord or a battery, through a heating element. Another heating method includes combustion of a suitable gas, which can either be delivered through a tank mounted on the iron (flameless), or through an external torch.

Some irons stay hot as long as they are turned on, while others heat up and cool down in a few seconds.

For electrical work, wires are usually soldered to printed circuit boards, other wires, or small terminals. A low-power iron is suitable for this work. In earlier days wires were frequently soldered to large chassis made of heavy metal, but this high-power requirement is now rare. Higher power is used for non-electrical metal-work.

Small battery-operated or gas soldering irons are useful when there isn’t a convenient source of electricity.

Some soldering irons have interchangeable tips for different types of work. Pyramid tips with a triangular flat face are useful for soldering sheet metal. Fine round or chisel tips are typically used for electronics work.

When not in use, soldering irons are often placed in stands to keep them away from flammable materials. Such a stand often also come with a sponge and flux pot for cleaning the tip. Some soldering irons for continuous and professional use come as part of a soldering station, which allows the exact temperature of the tip to be adjusted, kept constant, and displayed.

A new tip needs to be coated, heated, and then covered with solder before its first use. This procedure is called "tinning". The tinning forms a liquid layer which facilitates the transfer of heat to the work piece. A dirty tip does not transfer heat well. The tip needs to be kept coated with a shiny layer of solder by occasional wiping and applying solder directly to the tip.

For best results, particularly in electrical work where good electrical contact is required, the iron should be used to heat the work piece, and solder applied to it: this helps to prevent "cold joints", where hot solder is applied by the iron to a relatively cold target, shrouding it in solder to look like a good joint, but without wetting it properly, and without forming a good connection.

While soldering is used in plumbing applications, a soldering iron is not suitable for heating the large areas of heavy metal used, and a blow-torch is the tool of choice.

A temperature-controlled soldering station is a complete unit usually used for soldering electronic components, and consisting of an electrical power supply, a soldering iron, and is different for lead-based and lead-free solders. Lead-based solder uses 250°C to 280°C or 300°C while lead-free soldering needs a higher temperature, about 350°C to 400°C.

• Often a damp sponge is sufficient
• Sand paper may be required for more heavy-duty cleaning jobs. However most soldering iron tips are plated from the factory to extend their life. This thin coating may be damaged by sand paper, wire brushes, etc, which will cause the tip to deform and wear down far faster than normal.

• Soldering gun
• Solder
• Brazing
• Welding
• ColdHeat which is a battery operated cordless iron sold via direct marketing