In order to discuss the various aspects of welding, cutting and brazing safety, first we need to cover the basics in this first module. So let us get started.
Welding is a process that joins materials together by melting a metal work piece along with a filler metal to form a strong joint. Heat metal parts to a temperature that is high enough to join the metal parts by coalescence.
Coalescence occurs when two metals seem to pull together, or grow into one body, of the base metal parts when there is the slightest contact. There are two basic requirements for coalescence: heat and intimacy of contact.
Heat: Welding processes differ depending on the source of heat, the manner in which heat is applied or generated, and the intensity of the heat. The fuel used as a heat force may be:
The intensity of heat applied or generated at the joint varies according to the metals being joined and to the welding process being used. All welding processes, except brazing, use temperatures high enough to melt the base metals.
Intimacy of contact
In the second basic requirement for coalescence, intimacy of contact, you can divide the welding processes into two groups: pressure processes and non-pressure processes.
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Brazing is a welding process using nonferrous filler alloys that do not contain iron or steel and have a melting point above 840°F but below that of the base metal. Brazing is also called ‘hard soldering’ or ‘silver soldering.’ Brazing is the only welding process in which the melting of the base metal is not necessary for coalescence. Click here for more information on brazing alloys.
Soldering is a joining process using non-ferrous filler alloys. Soft soldering uses alloys that melt between 190 to 840°F and is used in electronics, plumbing, and joining sheet metal parts. Soldering is not considered a welding process. Lead and tin are common alloys used in soldering, but there is also less common lead-free solder to decrease environmental impacts.
The term WELDABILITY, or joinability, means:
Many factors influence the weldability of metal, including:
The metals added during the welding process are known as filler materials or filler metals. In welding processes in which space is left between the parts to be joined, filler metals provide the intimacy of contact necessary for coalescence. Filler materials used in welding processes include welding rods and electrodes.
Welding Rods: The term welding rod refers to a filler metal, in wire or rod form, used in gas welding and brazing processes and in certain electric welding processes (tungsten inert gas) in which the filler metal is not a part of the electric circuit. A welding rod serves only one purpose—it supplies filler metal to the joint.
As a rule, rods are uncoated except for a thin film resulting from the manufacturing process. Welding rods for steel are often copper-coated to protect them from corrosion during storage. Most rods are furnished in 36-inch lengths and a wide variety of diameters, ranging from 1/32 to 3/8 inch. Rods for welding cast iron vary from 12 to 24 inches in length and are frequently square rather than round in cross section. The rod diameter selected for a given job is governed by the thickness of the metals being joined.
Electrodes: In electric welding, electrodes form a part of the electrical circuit. In gas tungsten arc welding, electrodes melt off and are a source of the filler metal supply.
Fluxes: Welding or brazing certain materials requires the use of flux to produce a sound joint. Fluxes are available as liquids, pastes, and powders. They have a melting point below that of the base and filler metals, and they are not incorporated into the weld. Their primary purpose is to prevent the formation of oxides on the weld joint before and during welding operations. Fluxes should never be used as a substitute for proper cleaning.
Observe the following precautions when you are working with fluxes.
Oxyacetylene equipment consists of a cylinder of acetylene, a cylinder of oxygen, two regulators, two lengths of hose with fittings, a welding torch with tips, and either a cutting attachment or a separate cutting torch.
Accessories include a friction igniter to light the torch, an apparatus wrench to fit the various connections on the regulators, the cylinders, and the torches; goggles with filter lenses for eye protection; and gloves for protection of the hands. Flame-resistant clothing is worn when necessary.
Reduce the gas pressure in a cylinder to a suitable working pressure before it can be used. This is done by a regulator or reducing valve. Regulators are either the single-stage or the double-stage type:
Acetylene regulators and oxygen regulators are of the same general type, although those designed for acetylene are not made to withstand such high pressures as are those designed for use with oxygen cylinders.
The oxyacetylene welding torch is used to mix oxygen and acetylene gas in the proper proportions and to control the volume of these gases burned at the welding tip. Torches have two needle valves, one for adjusting the flow of oxygen and the other for adjusting the flow of acetylene. They have a handle (body), two tubes (one for oxygen and one for acetylene), a mixing head, and a tip. Welding tips are made from a special copper alloy, which dissipates heat (less than 60 percent copper), and are available in different sizes to handle a wide range of plate thicknesses.
Hoses used to make the connection between a torch and a regulator are strong, nonporous, and flexible and light enough to make torch movements easy. It is made to withstand high internal pressures, and the rubber used in its manufacture is specially treated to remove sulfur to avoid the danger of spontaneous combustion.
The hoses used for acetylene and oxygen are the same in grade, but they differ in color and have different types of threads on the hose fittings. The oxygen hose is GREEN, and the acetylene hose is RED. For added protection against mixing of the hoses during connection, the oxygen hose has right-hand threads and the acetylene hose has left-hand threads. The acetylene fittings also have a notch that goes around the circumference of the fittings for an additional identification factor.
Common weld defects that you should be familiar with to ensure your safety include: