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Gas welding, also called oxy-fuel welding, is a system of welding that uses one of various gases and oxygen to ignite a torch. Welding is defined as the process of combining two materials, usually metal, by heating them until both ends become molten. Filler materials are generally added into this molten material, and the two ends are joined together and allowed to cool, forming one solid piece.
Common gases used in gas welding include natural gas, propane, hydrogen, MAPP gas, liquefied petroleum, propylene, and acetylene, with acetylene being the most common. In many cases, one gas is not beneficial over another, although in some situations a specific gas may be preferable. For example, one gas may heat higher or lower than another, making it more convenient to use with certain metals.
A variety of metals can be joined using gas welding techniques, although a skilled torch operator is necessary in order to ensure a smooth weld. Not all metals melt at the same temperature, so the welder must know how long to heat varying types of materials. There is also a certain level of skill required for gas welding, to ensure that the weld is flawlessly done. Less experienced welders may end up with a joint that is lumpy or uneven.
The gas welder is generally constructed using two tanks. One holds a specific type of gas, which is usually unique for each manufacturer. The other holds oxygen. These two gases combine as they enter the torch and help to maintain a consistent flame.
There are other uses for the oxy-fuel torch, many them involving materials other than metal. Gas welding torches can be used to cut metal and to flame stone for decorative purposes. There are also specialized water welders that are used for welding very small and delicate objects like jewelry. Other uses can include fire polishing glass and, formerly, to heat quicklime in order to create a bright light used in magic shows and other productions.
Another type of gas welding involves the use of a single gas without the use of oxygen. This method is generally not preferable for many types of metal, but is commonly used in soldering. Soldering is an easier form of welding that is performed by melting solder and using the molten material to join two pieces of metal. This differs from traditional welding because the two pieces are not melted, but are only conjoined by solder. The soldering method is not recommended for large items or welds that need to withstand high levels of pressure, but it works well for the inner workings of electronics and other small materials.
Back in high school, a chemistry teacher demonstrated how powerful a mix oxygen and acetylene can be. He filled a trash bag with the two gasses, took it out to a soccer field and ignited the gasses -- boom!
The lesson? Be careful when using an acetylene/oxygen welding torch. The mix of those two gasses is powerful and could hurt you if not handled carefully.