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Arc welding)
Shielded metal arc welding (SMAW) is also known as stick welding or manual metal arc welding (MMA) and is one of the most common forms of welding. SMAW along with flux-cored arc welding are the dominant types of welding in building construction.
An electric current (either alternating current or direct current from a welding power supply) is used to form an arc between an electrode coated in flux and the metals to be joined.
The flux gives off gases to prevent oxygen reacting with the weld metal. The flux then solidifies to form slag on top of the weld. Once cool the slag can easily be chipped off.
The polarity of the electric current affects the heat transfer to the joined pieces. Normally the positive (+) pole is connected to the electrode. When welding very thin material or single-sided welding, the negative (−) pole of an DC source is connected to the electrode.
MMA welding takes a lot of manual dexterity in order to be able to make good welds. Flat welds are easiest, but skilled welders can do vertical or overhead welding. The most skilled welders undertake joints in high pressure pipes which require a continuous transition between the various welding techniques.
Relatively small, low-cost versions of arc welding equipment are available for the amateur hobbyist or non-expert; for instance, farmers often own this type of welder. Other forms of welding are usually out of the financial reach of the amateur.
The coated electrode used in manual metal arc welding was invented by Oscar Kjellberg.
When arc welding, good eye protection is needed to prevent the intense light and heat from the arc from burning holes in the retinas of the eyes, where the eye's lens has focussed it; this causes vision damage which is sometimes called arc-eye . A purpose-made arc-welding face shield with a very dark sight window must be worn. Special arc-welding visors can be bought to fasten onto safety helmets. Blowtorching goggles and sunglasses are not adequate.
Additionally, auto-darkening face shields are available, which can greatly speed and ease the process of welding. These shields use a plate of glass with liquid crystal, which can be either transparent or very darkly shaded, according to a control voltage. Coupled with a solar cell and sometimes a battery, these face shields sense when the super-bright electric arc has begun and turn the liquid crystal glass dark a few nanoseconds later. (This exposure is brief enough to be considered safe.)
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