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44
BOC RAPTOR 200C & 250R MIG Operating manual
Recommended Electrode Angles for Fillet Welds
1st Run
40°
40°
40°
40°
3rd Run
20–30°
20–30°
20–30°
20–30°
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.
15.7 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.
2nd Run
55–60°
55–60°
55–60°
55–60°
Multi-run Fillet
6
6
6
6
5
5
3
3
5
3
5
3
1
1
2
2
4
4
1
1
2
4
2
4
Recommended Angles for Overhead Fillet Welds
Defects caused by welding technique
Slag Inclusions
Slag inclusions occur when slag particles are trapped inside
the weld metal which produces a weaker weld. These can be
caused by:
erratic travel speed
•
too wide a weaving motion
•
slag left on the previous weld pass
•
too large an electrode being used
•
letting slag run ahead of the arc.
•
This defect can be prevented by:
a uniform travel speed
•
a tighter weaving motion
•
complete slag removal before welding
•
using a smaller electrode
•
keeping the slag behind the arc which is done by shortening
•
the arc, increasing the travel speed, or changing the electrode
angle.
Undercutting
Undercutting is a groove melted in the base metal next to the toe
or root of a weld that is not filled by the weld metal. Undercutting
causes a weaker joint and it can cause cracking.
This defect is caused by:
excessive welding current
•
too long an arc length
•
excessive weaving speed
•
excessive travel speed.
•
On vertical and horizontal welds, it can also be caused by too large
an electrode size and incorrect electrode angles. This defect can be
prevented by:
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