Re: Shielded Metal Arc Welding

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Posted by Jan Jensen on January 06, 1998 at 08:51:06:

In Reply to: Shielded Metal Arc Welding posted by Valerie Weihman on September 04, 1997 at 23:03:49:

: Here is a brief overview of the SMAW process:

: Shielded Metal Arc Welding

: The arc welding process (also called SMAW or Shielded Metal Arc Welding) consists of an electrical power supply, an electrical ground connection and an electrode holder. The ground connection is attached to the metal to be welded (the base metal). A specially-coated rod of metal (the electrode) is placed in the electrode holder. When the welding power supply is turned on and the electrode tip lightly touched to the grounded metal surface, an electrical arc is generated.

: When the tip of the electrode is held at the correct distance from the base metal, the arc will produce enough heat (electrical resistance) to both melt the base metal and melt the electrode. At the optimum distance and optimum heat (amperage setting), a weld is created. Done properly, the strength of the weld will equal or exceed the strength of the original material.

: Arc welding is able to produce strong welds quickly. It takes much less time to perform an arc weld than it does to perform an oxyfuel weld. However, most welders have found it easier to learn how to make a good arc weld if they have first mastered oxyfuel welding. For metals 1/4" and up, arc welding would definitely be preferred over oxyfuel welding because of the time it takes to preheat the base metal for oxyfuel welding.

: The coating on the electrode has eleven (11) different functions, the main two being:

: 1) create a gaseous envelope which protects the molten metal from the atmospheric gases (oxygen and nitrogen) which could inhibit weld strength.

: 2)create a glass-like slag which scavenges impurities from the molten weld metal and protects the surface of the weld as it solidifies.

: Functions of Electrode Coatings

: 1) Produces gases to protect the weld form oxygen and nitrogen

: 2) Produces slag for post-protection

: 3) Controls the freezing rate (solidification rate)

: 4) Controls the burn-off rate

: 5) Stabilizes the arc

: 6) Maintains the arc

: 7) Controls the penetration (depth of fusion)

: 8) Is an alloy carrier

: 9) Is a heat insulator and an electrical insulator (from arcing through the coating)

: 10) Degasses and deoxidizes

: 11) Contains flux for cleaning action