Welding is a process in which metal is fused by heating the pieces to be
joined to their melting temperature then inducing the metal to flow together
before it cools. During the high-temperature process a certain amount of
metal is vaporized or otherwise lost. To replace the lost metal a filler rod is used. A filler rod is a metal piece made of the same composition as
material being welded.
The surface of the materials that are to be welded needed to be prepared.
The surface of the meal must be cleaned of all oil, grease, paint, rust, and any
other contaminants before welding. This can be done by grinding, by
sanding, with a wire brush, or by cleaning with commercial chemical removers.
According to OSHA guidelines, welders have to wear:
Although the necessity of protecting your body from being burned by sparks of
molten metal that is generated at a welding zone is obvious, the necessity of
protecting your eyes and respiratory system is not as obvious.
Differing levels of visible and ultraviolet light are generated by gas and
arc welding. Ultraviolet light can cause temporary and sometime permanent
diminution or loss of sight. It is important to wear the type of
protective lens appropriate to the type of welding in which you're engaged. Do
not weld if you are not completely certain that your using the correct eye protection for the type of welding you are doing.
Noxious or toxic gases are emitted by various metal compositions and/or
finishes, such as the silvery coating used to galvanize steel when they are
heated or burned. The use of an appropriate respirator and high volume
ventilation will reduce and eliminate this health risk. Regulations by
OSHA say that there has to be a 100-CFM (cubic feet per minute) airflow in a
welder's breathing zone or that an appropriate respirator must be worn.
Always be sure to have adequate ventilation when welding.
There are several techniques that have been developed to use with various
types of welders. These include oxyacetylene welding, arc welding,
MIG, and TIG.
The two-handed welding technique is used in oxyacetylene welding. The
welder holds the torch or welding handle in one hand and the copper-clad filler
rod in the other hand. As the flame melts the pieces that are being joined
the filler rod is fed into the welding zone. The rod melts, flows into the
joint, and replaces the metal lost by heating. The strength of the weld in
this type of welding depends on a chemically neutral flame. A proper mix
of the oxygen and acetylene gas is how this neutral flame is achieved. After the
torch flame, using acetylene gas only, is list oxygen is introduced into the
mix. A small white cone appears at the base of, and inside the flame when
the oxygen is first introduced. The cone is rather long at first and is
sometimes a double cone. The cone gets smaller as more oxygen is added.
When the white cone is short and slightly rounded the flame is neutral.
When more oxygen is added to a neutral flame produces an oxidizing flame, which
will burn the molten metal. A cutting torch is equipped with a
lever-actuated valve that introduces additional oxygen to the flame, creating an
oxidizing flame. This flame burns the metal, resulting in a cut.
Arc welding utilizes electricity in order to generate an arc that has a
temperature of about 13,000 degrees Farenheight (over 7,200 degrees Celsius).
Most common types of metal are melted instantaneously by this extremely
high heat. The ground cable is attached from the welding machine to the
work to use an arc welder. This effectively turns the work into an
electrode. When a flux-coated welding rod, which is connected to the power
side of the welding machine, comes into close proximity of the work an arc is
formed across the gap. The heat that results melts the metal, making the
weld. The electrode acts as a filler rod and is consumed in the welding
process. The process is called single-hand welding because the welding
handle is held with only one hand.
Metal inert gas (MIG) welders are another type of single hand arc welders.
This kind differs from the arc welder in that the welder handle focuses a flow
of inert gas on the welding zone as the weld is being made. Also, it has a
wire electrode. Oxidation is reduced by the inert gas. This can
weaken the weld substantially. The thin wire electrode of the MIG welder is flux coating for the wire electrode
isn't used because of the oxidation-reducing properties of the shielding gas.
The MIG welder does a great job of welding steel when it is equipped with a
steel wire electrode and carbon dioxide or argon gas. It can be used for
welding aluminum if aluminum wire and argon gas are used. The MIG welder
is easier to use even though the single-hand welding technique is used with the
arc and MIG welder is the same. The electrode is automatically fed into
the welding zone and the shielding gas yields a substantially better weld than
does either and arc or an oxyacetylene welder. This makes this type of welder
the easiest to learn how to weld with.
The tungsten inert gas (TIG) welder welder uses a nonconsumable tungsten rod as
the electrode and requires a two-handed welding technique. A filler rod of
the same composition as the materials being welded is held in the other hand and
Source: Gillette, J. Michael. Theatrical Design and Production. 4th ed. Mountain View: Mayfield, 1999.