BOC Smootharc MMA 170, Руководство по эксплуатации, Страница: 15 / 36

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Multi-run horizontal fillets have each run made
using the same run lengths (run length per
electrode table). Each run is made in the same
direction, and care should be taken with the
shape of each, so that it has equal leg lengths
and the contour of the completed fillet weld
is slightly convex with no hollows in the face.
Vertical fillet welds can be carried out using
the upwards or downwards technique. The
characteristics of each are: upwards – current
used is low, penetration is good, surface is
slightly convex and irregular. For multiple run
fillets large single pass weaving runs can be
used. Downwards – current used is medium,
penetration is poor, each run is small, concave
and smooth (only BOC Smootharc 13 is
suitable for this position).
The downwards method should be used for
making welds on thin material only. Electrodes
larger than 4.0 mm are not recommended for
vertical down welding. All strength joints in
vertical plates 10.0 mm thick or more should
be welded using the upward technique. This
method is used because of its good penetration
and weld metal quality. The first run of a vertical
up fillet weld should be a straight sealing run
made with 3.15 mm or 4.0 mm diameter
electrode. Subsequent runs for large fillets may
be either numerous straight runs or several
wide weaving runs.
Correct selection of electrodes is important
for vertical welding.
In overhead fillet welds, careful attention to
technique is necessary to obtain a sound weld
of good profile. Medium current is required for
best results. High current will cause undercutting
and bad shape of the weld, while low current will
cause slag inclusions. To produce a weld having
good penetration and of good profile, a short
arc length is necessary. Angle of electrode for
overhead fillets is illustrated above.
Recommended Angles for Overhead
Fillet Welds
30˚
15˚
45˚
2.8 Typical Defects Due to
Faulty Technique
Shielded metal arc welding, like other welding
processes, has welding procedure problems
that may develop which can cause defects
in the weld. Some defects are caused by
problems with the materials. Other welding
problems may not be foreseeable and may
require immediate corrective action. A poor
welding technique and improper choice of
welding parameters can cause weld defects.
Defects that can occur when using the shielded
metal arc welding process are slag inclusions,
wagon tracks, porosity, wormhole porosity,
undercutting, lack of fusion, overlapping, burn
through, arc strikes, craters, and excessive
weld spatter. Many of these welding technique
problems weaken the weld and can cause
cracking. Other problems that can occur which
can reduce the quality of the weld are arc blow,
finger nailing, and improper electrode coating
moisture contents.
Defects caused by welding technique
Slag Inclusions
SLAG INCLUSIONS