Introduction to (SMAW) Shielded Metal Arc Welding

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Transcript Introduction to (SMAW) Shielded Metal Arc Welding

Unit Objective: SWBAT Identify
and explain SMAW equipment.
Shielded metal arc welding (SMAW) is
often referred to as stick welding.
This welding process can use either
alternating current (AC) or direct
current (DC).
The electrodes (rods) that are used
have a coating called flux. During
the welding process the flux forms a
gas shield that protects the weld
puddle from atmospheric
contamination.
SMAW is currently used in a wide
variety of industry applications.
What does SMAW stand for?
A.) Shielded Metal Arc Welding
B.) Strong Metal Attaching Weld
C.) Shielded Material Air Welding
D.) Safe Metal Arc Welding
Welding can be a dangerous profession,
not so much because of the welding
itself, but because of the work
environment where the work is often
performed.
SMAW has its own safety precautions
that need to be taken when it is used.
•UV Radiation
•Hot metal and slag
•Flying sparks
•Smoke and fumes
•Electrical hazards
PPE for SMAW includes but is not
limited to:
•Safety glasses
•Welding helmets shade 10-12
•Gloves
•Welding Jacket
ARC Welding machines use electrical
power. Most machines operate on
110V, 120V, 240V, or 480V power
levels. Regardless of the voltage
level, it is important to be aware of
the electrical power source used by
your machine.
Another concern wile using electricity
is moisture, especially water.
Electricity, water, and the human
body are a dangerous mix. Make
sure that your welding cables are in
good condition and that your work
piece clamp is properly installed.
Welding machines operate on
which voltages?
A.) 110V
B.) 240V
C.) 480V
D.) All of the above
When the term current is used as a noun, in means a flow or a
stream. In electrical terms current is the flow of electricity
from one point to another. One point being a ground and the
other being a source of electricity. In welding there must be
current flow between the work piece and the welding
machine.
The arc that is produced during SMAW is an
electrical current that jumps the gap from
the tip of the electrode to the surface of the
work, as long as the work piece lead from
the machine is attached to the work.
If the electrode is held against the work piece
instead of allowing for a gap the electricity
will pass directly from the electrode to the
work without creating an arc. No welding
can take place with out an arc across the
gap to create the heat necessary to melt the
electrode and the work piece.
There are two types of welding current used.
 Alternating Current (AC)
 Direct Current (DC)
The most commonly used form for SMAW is Direct
Current (DC). In which the current always flows
in one direction, from negative to positive.
With DC we have polarity. Polarity is determined
by the way the welding leads are connected to
the machine and work. By swapping the
electrode and work leads we can change the
polarity.
SMAW is most often done with Direct Current
Electrode Negative (DCEN), but can also be used
with Direct Current Electrode Positive (DCEP).
The other and more seldom used is Alternating
Current (AC). In AC the current still flows from
negative to positive, but the positive and
negative poles alternate back and forth.
A cycle is when the pole switches from positive to
negative and back to positive. The number of
cycles per second is called the frequency and is
measured in Hertz. The frequency of AC is
determined by the generator producing the
current.
In the United States the standard frequency of AC
is 60 Hertz.
What are the two types of welding
current?
A.) Amperage and Voltage
B.) Negative and Positive
C.) Direct and Alternating
D.) Polarity and Frequency
If the tip of the electrode is held
directly against the work piece,
A.) Welding will take place.
B.) No welding will take place.
C.) The arc will be twice as hot.
D.) The electrode will not get hot.
When the SMAW machine is set
to DCEN, the current flows
A.) From the work to the electrode.
B.) From the electrode to the work.
C.) Both to and from the electrode.
D.) Depends on the electrode used.
SMAW machines can come in many
different shapes and sizes.
The size of a welding machine is
determined by its duty cycle. The
duty cycle of a welding machine is
based on its ability to produce its
rated amperage over a 10 minute
period without over heating.
Example, a 200amp machine that
has a 60% duty cycle can produce
200amps for 6 minutes out of 10
without over heating.
Running a machine above its rated
amperage will reduce its duty
cycle.
Work piece clamps often called ground
clamps establish the connection
between the work and the work piece
lead that runs to the machine. Work
piece clamps are selected based on
the amount of current it can carry
without overheating.
Electrode holders grasp the electrode
and provide electrical contact between
the electrode and the welding cable.
Electrode holders are also rated and
selected based on the amount of
current it can carry without
overheating.
What does “Duty Cycle” refer to?
A.) The % of time in a 24 hr period that a machine can run
at rated output.
B.) The % of time in a 10 min period a machine can run at
rated output.
C.) Length of time a machine can work doing the work it
was designed for.
D.) Life cycle of the machine before it needs to be serviced.
SMAW cannot take place
without electrodes, often
called sticks.
SMAW electrodes have a metal
wire core coated with a flux.
The wire core conducts the
welding current from the
electrode holder to the work.
The arc at the end of the
electrode melts the wire core,
the flux coating, and the base
metal at temperatures
exceeding 6,000o F.
The flux coating on the
electrodes creates a
slag coating that must
be cleaned from the
weld.
Chipping hammers,
hand files, and wire
brushes are a few of
the hand tools that can
be used for post weld
cleaning.
SMAW is often referred to as stick
welding.
SMAW remains one of the most widely
used forms of welding in the
industry because of its simplicity
and a relatively low cost.
SMAW is the basis on which all other
welding processes have been
developed. Understanding the
SMAW process and its techniques is
crucial for achieving success with
other welding processes.