Welding is a general term for various processes used to join metal parts by producing a coalescence, called a weld, at a joint. This is usually done by applying heat and energy when bringing the pieces of metal together.
Welding has many applications. Some welded products include ships, aircraft, automobiles, electric and electronic parts, and in building and construction work. Although over 50 welding processes are used today, the most common are gas welding and arc welding.
Welding is a hazardous process that joins materials together by melting a metal workpiece and a filler metal to form a strong joint.
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.
Welding processes differ depending on the source of heat, how 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 the welding process used. All welding processes, except brazing, use temperatures high enough to melt the base metals. However, all welding, cutting, and brazing processes generate enough heat to injure workers seriously.
The second basic requirement for coalescence, the intimacy of contact, is accomplished in two ways: pressure processes and non-pressure processes. In pressure processes, there is no space between the surfaces being joined. Welders apply pressure while the contact surfaces are at a high enough temperature to allow the plastic flow of the metal. In non-pressure processes, the space between the joined surfaces is filled with molten metal.
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Oxyacetylene welding or cutting is also called torch or gas welding or cutting. Two metals are joined by melting or fusing their adjoining surfaces in the process. This is done by directing a flame from burning gas (usually acetylene) to melt metal at a joint to be welded, and is a common method for welding iron, steel, cast iron, and copper.
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 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. However, those designed for acetylene are not made to withstand such high pressures as those designed for oxygen cylinders.
The oxyacetylene welding torch is used to mix oxygen and acetylene gas in the proper proportions and control the volume of these gases burned at the welding tip.
Hoses used to connect torches and regulators are strong, nonporous, flexible, and light enough to make torch movements easy. It is made to withstand high internal pressures, and the rubber used to manufacture it 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 color codes are as follows:
For added protection against mixing of the hoses during connection:
Arc welding is the process in which fusion is produced by heating with an electric arc that is generated between an electrode and the surface of the base metal.
Arc cutting is when metals are cut or removed by melting with the heat of an arc between an electrode and base metal.
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.
Overexposure to these substances can cause injury and illness over the long-term.
For more information on arc welding, read Safe Arc Welding by Lincoln Electric.
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 melting the base metal is unnecessary for 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. 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°F to 840°F and is used in electronics, plumbing, and joining sheet metal parts. Lead and tin are common alloys used in soldering; however, there are also less common lead-free solder alloys used to decrease environmental impacts.
Defects in welds can cause unforeseen injuries and accidents. Common weld defects to be familiar with to ensure your safety include:
Protecting yourself when performing welding operations depends on your understanding of the hazards involved and the proper way to control them. Controlling welding hazards includes avoiding eye injury, respiratory protection, ventilation of the work area, protective clothing, and having safe equipment to use.
Gas welding is commonly used in general maintenance work, brazing, and soldering because it is slower and easier to control than electric arc welding.
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.
Acetylene (chemical formula C2H2) is a fuel gas made up of carbon and hydrogen. When burned with oxygen, acetylene produces a very hot flame, having a temperature between 5700°F and 6300°F. Acetylene gas is colorless, but has a distinct, easily recognized odor.
MAPP (methylacetylene-propadiene) gas is an all-purpose industrial fuel with the high flame temperature of acetylene and the handling characteristics of propane.
Oxygen is a colorless, tasteless, odorless gas that is slightly heavier than air. Oxygen will not burn by itself, but it will support combustion when combined with other gases.
Safe procedures and practices must always be used when working around or with arc welding equipment to avoid injuries.
Avoid the following hazards in arc welding:
Radiation from the arc is hazardous to the eyes. Eyes should be protected from radiation from the arc by use of an arc welding helmet or face shield with approved lenses.
When possible, shield arc-welding operations so no one may accidentally look directly at the arc or have it shine or reflect into his or her eyes.
Avoid the possibility of dangerous electric shock by using insulated electrode holders and wearing dry leathers and gloves.
Flying sparks usually accompany arc welding. These present a hazard if they strike unprotected skin, lodge on flammable clothing, or hit any other flammable material.
Hot metal and flying sparks have the potential to cause severe burns. Never handle it with bare hands until it has cooled naturally or has quenched in the quenching tank.
Be sure to use leather gloves with tight-fitting cuffs that fit over the sleeves of the jacket. Many welders wear a full set of leathers that consists of the following:
In gas welding, the high temperatures of the welding flame and the sparks will burn skin. Gas welding can also cause radiation burns due to infrared rays emitted by the red-hot material. Wear flame-resistant or flame-retardant clothing and hair protection at all times.
An employee was tasked to pin weld the inside insulation of the metal duct and wipe the surface with a propanol solution for shipment. The employee noticed that one pin weld of the duct failed. He decided to replace the defective pin. When he drove a new weld, the sparks from the weld ignited the propanol's residue on his glove. His right hand caught fire and caused second-degree burns.
Fumes produced during welding are composed of very small, easily inhaled solid particles, produced by the heat generated when welding consumables, base metals, and base metal coatings.
Shielding gases (argon, helium, carbon dioxide, etc.) may be used to protect and enhance the properties of the weld. They may present a health hazard by displacing oxygen that can result in the welding experiencing dizziness, unconsciousness, and death.
Process gases (nitric oxide, nitrogen dioxide, carbon monoxide, ozone, phosgene, hydrogen fluoride, and carbon dioxide) may also be a byproduct of the welding process itself.
Welding fumes and gases generally come from the following sources:
Click on the button to review the various health hazards of breathing welding fumes and gases.
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