Smootharc 180 Multiprocess, Operating Manual

Page: 29 / 56

Welding Progression Angle
Weld Metal
Slag
Electrode
Arc
Weld Pool
Workpiece
70–85˚
Direction of Welding
Butt Weld with Backing Material
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
When square butt welds or single ‘V’ welds cannot be welded
from both sides it is desirable to use a backing bar to ensure
complete fusion.
Single ‘U’ Butt Weld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
Used on thick plates an alternative to a single ‘V’ preparation.
It has advantages as regards speed of welding. It takes less
weld metal than a single ‘V’, there is less contraction and
therefore a lessened tendency to distortion. Preparation is
more expensive
than in the case of a ‘V’, as machining is required. The type of
joint is most suitable for material over 40 mm in thickness.
Double ‘U’ Butt Weld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
For use on thick plate that is accessible for welding from both
sides. For a given thickness it is faster, needs less weld metal
and causes less distortion than a single ‘U’ preparation.
Horizontal Butt Weld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
The lower member in this case is bevelled to approximately 15°
and the upper member 45°, making an included angle of 60°.
This preparation provides a ledge on
the lower member, which tends
to retain the molten metal.
General notes on Butt Welds
The first run in a prepared butt weld should be deposited with an
electrode not larger than 4.0 mm. The angle of the electrode for the
various runs in a butt weld is shown.
It is necessary to maintain the root gap by tacking at intervals or by
other means, as it will tend to close during welding.
All single ‘V’, single ‘U’ and square butt welds should have a backing
run deposited on the underside of the joint; otherwise 50% may be
deducted from the permissible working stress of the joint.
Before proceeding with a run on the underside of a weld it is necessary
to remove any surplus metal or under penetration that is evident on that
side of the joint.
Butt welds should be overfilled to a certain extent by building up
the weld until it is above the surface of the plate. Excessive build-up,
however, should be avoided.
In multi-run butt welds it is necessary to remove all slag, and surplus
weld metal before a start is made on additional runs; this is particularly
important with the first run, which tends to form sharp corners that
cannot be penetrated with subsequent runs. Electrodes larger than 4.0
mm are not generally used for vertical or overhead butt welds.
The diagrams following indicate the correct procedure for welding thick
plate when using multiple runs.
Electrode Angle for 1st and 2nd Layers
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
Electrode Angle for Subsequent Layers
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
29 BOC Smootharc 180 Multiprocess operating manual