This sample chapter is for review purposes only. Copyright © The Goodheart-Willcox Co., Inc. All rights reserved.

60 Shielded Metal Arc Welding

grip (do not hold it too tightly else your hands

Unit 11 will tire quickly). Place the clamp section of the
electrode holder toward your thumb. This will
0°

give you extra leverage for striking the arc and

Preparing to Weld moving the electrode. Use two hands whenever
possible, Figure 11-3.
Before striking an arc, there are two angles
that need to be determined: work angle and
travel angle. Work angle is defined by AWS as
90°
“the angle less than 90° between a line perpen-
After completing this unit, you will be able to: When you begin to weld, a few trail beads
should be completed. Raise or lower the welding
dicular to the major workpiece surface and a
plane determined by the electrode axis and the
Workpiece Workpiece

❍ List the two methods for striking the arc. machine current setting until you get a satisfac- weld axis.” For example, an electrode held per-
Work Angle
❍ Demonstrate the electrode position when tory weld. A weld should not burn through, but pendicular to the workpiece is at a 0° work angle,
running a flat weld. it should have sufficient penetration, Figure 11-1. Figure 11-4. 15°–20°
❍ Determine the necessary adjustments to the Position the metal, securing it with clamps Travel angle leans in the direction of travel.
current, arc length, or speed by examining if needed. Attach the work (ground) clamp According to AWS, travel angle is defined as
test welds. securely. Clamp the electrode in the electrode “the angle less than 90° between the electrode
holder at about a 90° angle to the holder jaws, axis and a line perpendicular to the weld axis, in Electrode travel
Figure  11-2. Keep the electrode and holder a plane determined by the electrode axis and the
Key Terms clear of the work area and turn on the machine. weld axis.” Holding the electrode perfectly per-
Grasp the electrode holder with a comfortable 90°
arc length pendicular to the weld joint would be a 0° travel
Workpiece
arc voltage angle, Figure 11-4. The more the electrode is tilted
downward toward the weld joint, the higher its
scratch method Travel Angle
travel angle.
tap method
travel angle Figure 11-4. Electrode position and angles when
work angle running a flat weld.
Amperage Amperage Correct Goodheart-Willcox Publisher
too low too high penetration
The first step in preparing to weld is to carefully
check over the machine. Be sure all connections are With a 0° work angle, lower the electrode to
clean and tight. Since the heat generated by the arc Figure 11-1. Weld characteristics. about 1″ (25 mm) above the work. Assume a 15°
is determined by the amount of current (amperage) Goodheart-Willcox Publisher to 20° travel angle by leaning the electrode to a
used, set the machine to the range recommended 15° to 20° angle from the vertical in the direc-
for the size of the electrode being used. tion of travel. This inclination is important. If the
If the manufacturer’s recommendations angle is more than 20°, the penetration may not
are not available, a good rule of thumb when be enough to produce a solid weld.
using standard electrodes is to adjust the weld-
ing machine to a current setting that is approxi- Striking the Arc
mately equal to the diameter of the electrode
Lower your head shield and strike the arc.
in thousandths of an inch. For example, a 1/8″
There are two methods for striking the arc: the
(0.125″ or 3 mm) diameter rod will operate at ± Electrode scratch method and the tap method, Figure 11-5.
125 amperes. (This may vary slightly for elec- holder
The scratch method is recommended for begin-
trodes made by different manufacturers.)
ning welders. The tap method is sometimes used
after the welder gets some practice.
Put on your protective clothing before
To strike an arc using the scratch method,
welding. Replace any items that Electrode
scratch the tip of the electrode over the work
are not up to standards. Remove all
much like you would strike a match. As the arc
Warning: flammable materials and solvents from
Figure 11-3. Use two hands to grasp the electrode starts, hold a slightly longer than normal arc until
the welding area and put shields in Figure 11-2. Electrode position in electrode holder for holder whenever possible. Use a comfortable grip the base metal is heated enough to form a proper
place if others will be working in the running a flat weld. else your hand(s) will tire rapidly. size pool of molten metal. Keep the electrode
immediate area. Goodheart-Willcox Publisher Goodheart-Willcox Publisher moving or it will “freeze,” or stick to the work.

Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website. 59 Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website.
This sample chapter is for review purposes only. Copyright © The Goodheart-Willcox Co., Inc. All rights reserved.

Unit 11 Preparing to Weld 61 62 Shielded Metal Arc Welding

and the rod may stick. If the arc is too long, Common mistakes made when learning to
Never attempt to observe the weld
excessive spattering may occur and an irregular weld are shown in Figure  11-7. Study them care-
Start Warning: pool or arc without having your head
Establishing bead with poor penetration will result. fully so you can identify mistakes in your welding.
arc shield in place.
In general, use an arc length equal to or
slightly less than the core diameter of the elec-
Arc length: trode. Since the arc length cannot be measured,
slightly practice running beads until you can tell when
less than
diameter of you are maintaining the correct arc length and
electrode welding speed. Many welders go by the sound
of the arc to help them determine correct arc
length.
Note that arc welding is an electric circuit,
Scratch Method which includes voltage, current, and a load
(resistance). The arc length (as maintained by
Start the space between the electrode and work-
Establishing
arc piece) can impact arc voltage and current. A
longer arc length increases resistance, which can
slightly lower current. Conversely, a shorter arc
length can reduce resistance, which can slightly
increase current. Therefore, changing arc length
can impact the heat of the weld, rate of electrode
melting, and the speed at which a weld can be
made. Be aware of the interrelation of these dif-
ferent aspects of arc welding.
Tap Method Maintaining the correct welding speed is
important. Watch the pool of molten metal
directly behind the arc. Do not watch the arc. The
Figure 11-5. Methods for starting the arc. shape of the weld pool and the ridges formed
Goodheart-Willcox Publisher
when the molten metal solidifies indicate cor- A B C D E F G
rect welding speed. See Figure  11-6. The ridges
To strike an arc using the tap method, bring should be uniform and the edges straight.
Figure 11-7. Characteristics of welds made under various conditions. The conditions are accentuated to
the electrode close to the location where the weld illustrate differences. A—Current, voltage, and speed normal. B—Current too low. C—Current too high.
is to begin or continue. Lightly tap the electrode D—Arc too short. E—Arc too long. F—Speed too low. G—Speed too high.
on the work. When the arc starts, hold a slightly Straight Lincoln Electric Co.
longer-than-normal arc for about one second and edges
then establish the proper arc length. It will require
some practice to master the force required to start Electrode
the arc by the tap method. If you apply too much
force, the electrode will stick to the work. With-
out enough force, the arc will not start. The tap
method requires less area to strike the arc and
will enable you to strike the arc without damag-
ing the base metal around the joint.
If the electrode should freeze (stick) to the Weld pool
work, break it loose by twisting or bending the
electrode by sharply moving the holder. If this Evenly spaced
does not work, squeeze the clamp section of the ridges
electrode holder and release the electrode from
the holder.
Once the length of the arc is established, try Figure 11-6. The completed arc bead should have
to maintain the correct length as the electrode straight edges, evenly spaced ridges, and uniform
burns down. If the arc is too short, not enough height.
heat will be generated to melt the parent metal Goodheart-Willcox Publisher

Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website. Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website.
This sample chapter is for review purposes only. Copyright © The Goodheart-Willcox Co., Inc. All rights reserved.

Unit 11 Preparing to Weld 63 64 Shielded Metal Arc Welding

Name ______________________________________ Date _____________ Class ____________ Name ______________________________________

Check Your Progress Things to Do

1. List three safety precautions that should be observed when preparing to weld. 1. Have your instructor or an experienced welder demonstrate the proper way to do the following:
a. ___________________________________________________________________________________________________________ a. Check out the welding machine and related equipment.
b.___________________________________________________________________________________________________________ b. Inspect your welding shield and protective clothing.
c. ___________________________________________________________________________________________________________ c. Adjust the machine(s) to get the correct setting and attach the ground cable.
d. Select the proper electrode for the job.
2. List the two methods prescribed for striking an arc: e. Install the electrode in the holder.
a. ___________________________________________________________________________________________________________ f. Strike and maintain the arc.
b.___________________________________________________________________________________________________________ g. Break free an electrode that has become welded to the work.

3. How can an electrode that has become welded fast to the work be freed? 2. Have your instructor or an experienced welder run several beads under various conditions, such
_____________________________________________________________________________________________________________ as current too low, current too high, arc too short, arc too long, speed too low, speed too high, etc.

_____________________________________________________________________________________________________________ 3. Practice checking over the welding machine.

4. Prepare a sketch showing the position of the electrode for flat welding. 4. Practice checking over your shield and protective clothing.

5. Practice inserting an electrode in the holder.

6. Practice (with the machine off) striking an arc.

5. What is the general rule for establishing the correct length of the arc?
_____________________________________________________________________________________________________________
_____________________________________________________________________________________________________________

6. In general, the current setting for an electrode is approximately equal to the diameter of the
electrode in thousandths of an inch. If this is true, what are the current settings for the following
electrodes?
a. 1/8″ (3 mm) ___________________________________________________________________________________________
b. 5/32″ (4 mm) __________________________________________________________________________________________
c. 3/16″ (5 mm) __________________________________________________________________________________________
d. 1/4″ (6 mm) ___________________________________________________________________________________________
Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website. Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website.