BOC Smootharc MMA 170, Руководство по эксплуатации, Страница: 12 / 36

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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
Welding Progression Angle
Weld Metal
Slag
Electrode
Arc
Weld Pool
Workpiece
70–85˚
Direction of Welding
2.7 Fillet Welds
A fillet weld is approximately triangular in
section, joining two surfaces not in the same
plane and forming a lap joint, tee joint or
corner joint. Joints made with fillet welds do
not require extensive edge preparation, as is
the case with butt welded joints, since the weld
does not necessarily penetrate the full thickness
of either member. It is important that the parts
to be joined be clean, close fitting, and that all
the edges on which welding is to be carried
out are square. On sheared plate it is advisable
to entirely remove any ‘false cut’ on the edges
prior to welding. Fillet welds are used in the
following types of joints: