Specifications

8
311
AU : IPRM 2007 : SECTION 8 : CONSUMABLES
WARNING Welding can give rise to electric shock, excessive noise, eye and skin burns due to the arc rays, and a potential health hazard if you breathe in the emitted fumes and gases.
Read all the manufacturer’s instructions to achieve the correct welding conditions and ask your employer for the Materials Safety Data Sheets. Refer to www.boc.com.au or www.boc.co.nz
Fundamentals of Manual Metal Arc (MMA) Welding
Two terms relating to the preparation of butt welds require
explanation at this stage. They are:
Root Face: the proportion of the prepared edge that has not
been bevelled (Land).
Root Gap: the separation between root faces of the parts to be
joined.
Various types of butt welds are in common use and their suitability
for different thickness of steel are described as follows:
Square Butt Weld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
The edges are not prepared, but are separated
slightly to allow fusion through the full thickness
of the steel. Suitable for plate up to 6 mm in
thickness.
Single ‘V’ Butt Weld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
This is commonly used for plate up to 16 mm
in thickness and on metal of greater thickness
where access is available from only one side.
Double ‘V’ Butt Weld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
Used on plate of 12 mm and over in thickness
when welding can be applied from both sides.
It allows faster welding and greater economy
of electrodes than a single ‘V’ preparation on
the same thickness of steel and also has less
tendency to distortion as weld contraction can
be equalised.
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 as an alternative to a single
‘V’ preparation. It has advantages in speed of
welding. It takes less weld metal than a single ‘V’,
there is less contraction and there is, therefore,
a lessened tendency to distortion. Preparation
is more expensive than in the case of a ‘V’, as
machining is required. This 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 below.
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 back-gouge or grind 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
reinforcement, 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 below indicate the correct procedure for welding
thick plate when using multiple runs.
Bead Sequence for 1st and 2nd Layers
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
Bead Sequence for Subsequent Layers
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
Welding Progression Angle
3
8
1
7
4
6
2
1
Weld Metal
2
Workpiece
3
Electrode
4
Slag
5
Welding Direction
6
70–85° Angle
7
Arc
8
Weld Pool
5
Fundamentals of Manual Metal Arc (MMA) Welding