19 Pressure
exceeding that necessary to hold the granular material against the bottom of the
joint tends to produce
a concave weld bottom. Root
Backing and Weld Backing Root
backing and weld backing are the most widely used methods of obtaining weld metal
support. In a root-backed
joint, the root face is thick enough to support the incompletely penetrated first
pass of the weld.
This method is used for butt welds (either grooved or square edge), for fillet
welds (lap or tee joints), and
for plug or slot welds. Supplementary backing or chilling is sometimes used. It
is most important that the joint
edges be tightly butted at the point of maximum penetration of the weld. (See
Fig. 7.) FIG. 6
- Backing with Submerged Arc Flux Backing
with Submerged Arc Flux Although
all grades of submerged arc flux are sometimes used for backing, certain fluxes,
such as UM 350 are
better suited for use as backing flux . The backing flux is held uniformly against
the bottom of the joint by an
air or water inflated hose. The flux is laid on top of the hose (Fig. 6.).
Greater fit up irregularities can be
tolerated when using backing flux than with other types of backing
because the granular material will
conform to the back of the plate. Continued
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