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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

All of these functions must work together, not cancel the effects of another
function.

: Here is some basic step-by-step set-up information for the arc welding
process. Later on, I will elaborate on some of these points. If this
sparks a particular question for you, please post a followup.

: Choose the electrode size, type and amperage range needed in relation to
the metal to be welded.

: Choose the polarity (DCSP, DCRP, or AC) and connect the electrode and
ground cables accordingly.

: Connect the ground cable securely to the work or to the metal table that
the work is placed upon.

: Turn on the ventilation. Check that you will not be positioned between
"suction" type ventilation and the work.

: Obtain the proper shield lens and check it for cracks or pits. A
"gold-bond" lens should be checked for scratches in the gold layer.

: Check that the electrode holder is not in contact with the grounded metal.
Do not lay it on the metal table.

: Turn on the electrical power supply. At this point, an electric arc will
be started whenever an electrode in the holder comes in contact with
grounded metal surfaces. Be aware of where you point the electrode. (Make
sure that gas cylinders will never come in contact with the
electrical arc!) Assume the machine is always ON.

: Insert the bare end of the electrode into one of the pairs of grooves in
the electrode holder.

: Position the electrode tip slightly above the metal to be welded. You will
not be able to see where the electrode is until the arc is started once
the helmet is down. Try to get a "feel" for where the electrode is in
relation to the metal. Some people find it helpful to practice this with the
machine off.

: Lower your helmet and swing the electrode down with a twist of the wrist.
Scratch the surface of the metal. It is similar to striking a match.
Then slightly raise the electrode from the metal, creating the desired arc
length. (You will develop other techniques with practice.)

: If the electrode sticks to the metal, wiggle it back and forth to break it
loose. If the electrode doesn't break off from the metal, squeeze the
handle on the electrode holder to open the jaws and release the electrode.
It is important to do this relatively quickly or you may overheat the
electrical relays within the machine.

: After scratching the metal with one smooth motion, you should have an arc
and should be able to clearly see where the electrode is pointing.

: Adjust the angle of the electrode to 12-20 degrees off of the vertical.
Back away from the weld. Move in a relatively slow motion.

: Most welders use a slight side-to-side motion weave. The ripples in the
finished weld, however, are not created by this motion, but by the
back side of the molten puddle cooling as you move along.

: You will find that you need to continually watch that you keep the
electrode height and electrode angle consistent.

: Move your body rather than twist your wrist to move along the metal.
Otherwise, the angle of the electrode will continually be changing.

: To stop the arc, just pull the electrode away from the metal. (You may
also need to fill the crater.) Don't melt the electrode down shorter than
two inches from the end.

: The electrode stubs will be hot. One practice is to drop the electrode
from the holder onto the floor and nudge it under the table with your
boot. Then clean them all up at the end of the day.

 

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Updated Thursday, March 07 2002 @ 10:27pm