Chapter 29 Shielded Metal Arc Welding 809
Copyright Goodheart-Willcox Co., Inc.
beveling is usually required to ensure adequate bead penetration, and multiple
passes may be required to completely bond the joint.
On open groove welds, the two plates are fused together at the bottom
with a fl at bead of weld metal. No backing plate is used. E6010 and E6011
SMAW electrodes are commonly used on mild steel due to their fast-freeze
characteristics. To achieve complete penetration, the electrode is pushed
down through and pulled along the gap. On the back side of the completed
weld, the root bead should blend smoothly to both edges and exhibit a
uniform surface free from discontinuities. See Figure 29-57.
During welding, a keyhole, or rounded
enlargement, appears in the opening just ahead of the
pool. See Figure 29-58. Before the keyhole expands
beyond control, briefl y whip the electrode slightly
upward and ahead of the weld to allow the base metal
to cool slightly. The keyhole size should remain the
same as the bead at the back of the pool solidifi es.
Then, quickly whip the electrode back above the
molten pool to allow another drop of fi ller metal to fall
from the electrode. The entire whipping motion must
occur very quickly. The rate of motion is determined by
the level of heat observed in the weld. At the beginning
of the weld, less time out of the pool is required. As
heat builds up with the progression of the weld, the
electrode should be moving in and out of the molten
pool at a very rapid pace due to the high heat now in
the base metal.
The ability to maintain the keyhole ahead of
a uniform pool depends on understanding and
controlling the heat of the weld. Success requires the
welder to risk the application of too much heat—the
common tendency is not staying in the pool long
enough to achieve penetration. Developing skill
at open groove welding requires practice and may
involve burning through a few plates to fi nd the correct
balance between too much and too little heat.
Groove Weld Practice
Using 1 1/2″ by 4″ coupons of 1/4″ plate is an economical way to
practice performing groove welds. The following procedure outlines a simple
method of practice.
1. Obtain two 1 1/2″ × 4″ × 1/4″ steel coupons from your instructor or cut
them using the cutting torch. For practice with 1/8″ E6011 electrodes,
grind the adjoining edges of the pieces straight and smooth with a bench
or disc grinder. For practice with 3/32″ E6011 electrodes, the adjoining
edges of the pieces should be cut and ground at a 60° bevel, leaving a
3/32″ root face.
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Figure 29-57. Penetration of the root bead on the
back side of a groove weld is important to the
strength of the welded bond.
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Figure 29-58. In order to ensure adequate
penetration, the welder should observe a keyhole
effect just ahead of the weld pool.