Gas welding involves using a gas-fed torch to heat the metal parts to be welded. The primary gas combination for gas welding is an oxygen-acetylene mixture, but other gases are used. The welder can change the performance of the welding torch by adjusting the ratio of the gases, which in turn changes the properties of the flame. Different types of flames are used depending on the particular welding application.
A welding torch is a tool that the welder uses to locally melt the metal material of the base part, allowing the weld to be created. The torch is connected to the gas tanks via hoses that are designed to prevent backflow of gas or shock waves to the tank. The torch has valves that allow the welder to finely adjust the flow of each of the gases.
Creating a Flame
When the welder is ready to start, he opens the valves on the gas tanks and ignites the gas exiting the torch. The welder then adjusts the ratio of oxygen and fuel gas by opening or closing valves on the torch. These valves allow the welder to change the properties of the flame depending on the task at hand.
The neutral flame is the primary flame used by gas welders. A neutral flame has two zones: a hotter, lighter inner zone and a cooler, darker outer zone. In a neutral flame, all of the fuel gas is being burned in the process, resulting in a clean flame. The welder uses the tip of the inner flame zone to heat the parts to be welded, as this is the hottest part of the flame.
If the oxygen is reduced, a carbonizing flame is created from a neutral flame. In this case, not all of the fuel gas is being burned by the flame. A carbonizing flame has three zones, and is cooler than a neutral flame because the excess carbon acts as an insulator. Carbonizing flames deposit soot on the work piece that has to be cleaned when the part is cooled, but the addition of carbon to the metal is desirable in some iron and steel welding applications.
An oxidizing flame is caused by increasing the oxygen from a neutral flame. Because of the excess oxygen, this flame is hotter than the neutral or carbonizing flames. Welders generally do not use an oxidizing flame, because it can increase the oxides in the base material. However, an oxidizing flame is used for bronze and brass work.