WELDING OPERATIONS I - OD1651 - LESSON 1/TASK 2
method, shown in figure 28, view D, on the previous page, uses a
mild steel strip. When this method is used, the backing rod or
strip should be chipped out before depositing beads 3 and 4.
Another procedure, as shown in figure 28, view E, uses a copper
backing bar. The copper bar is removed after beads 1 and 2 are
deposited. (The beads will not weld to the copper bar.) Beads 3
and 4 are deposited after removal of the copper bar. In certain
cases, where plates of homogeneous armor are cracked along their
entire cross section of the plate, another method of joint
preparation, as shown at figure 28, view F, can be used. In this
other method, root beads A and B are deposited opposite from each
other at the base of the bevel. These root beads act as backing
for beads 1 through 6, which are deposited afterwards.
(3) Weld crater and fusion zone cracking, especially in the
root beads, is a major factor involved in welding cracks in armor
that terminate within the plates.
To prevent this cracking, an
intermittent backstep and overlap procedure, as shown in figure
29, view A, on the following page, is recommended. It should be
noted that all of the welding steps necessary for bead number 1
must be completed before depositing bead number 2.
By back
stepping, the craters at the end of each previous pass are
located and filled.
All craters on subsequent passes, that do
not terminate on previous deposited metal, should be filled by a
hesitation and drawback technique.
The filling up of weld
craters avoids the formation of star cracks which are caused by
the solidification of shallow deposits of molten weld metal.
(4) Each pass in beads 1 through 4, shown in figure 29, views B
and C, is limited from 1 to 2 inches in length and should be
peened while the weld metal is still hot to help overcome the
cooling stresses.
No electrode weaving motion should be used
when the root beads are deposited.
The welding should be
performed preferably with a 5/32 inch electrode.
Peening also
tends to eliminate or minimize warpage in the section being
welded. Arc blow should be controlled by properly adjusting the
method of welding.
Some of the more common defects encountered
when welding root beads on homogeneous armor plate and the proper
remedial procedures are shown in figure 30, on page 74.
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