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MIG 250GS Operating manual
Butt Welding
Face Reinforcement
Root Face
Root Gap
3.6 Types of Joints
Butt Welds
A butt weld is a weld made between two plates so as to give
continuity of section. Close attention must be paid to detail in a
butt weld to ensure that the maximum strength of the weld is
developed. Failure to properly prepare the edges may lead to the
production of faulty welds, as correct manipulation of the electrode
is impeded.
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.
•
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
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
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.
Electrode Angle for 1st and 2nd Layers
Weld Face
Layers
Layers
Layers
Weld Beads
Weld Beads
Layers
Layers
Layers
Electrode Angle for Subsequent Layers
Weld Beads
Layers
Weld Beads
Double 'V' Butt Weld
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 of a tendency to distortion as weld contraction can be
equalised.
Butt Weld with Backing Material
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
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
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
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.
Layers
Weld Beads
Electrode
Weld Pool
Slag
Weld Metal
Weld Beads
Weld Beads
Layers
Weld Beads
Weld Beads
Electrode
Weld Pool
Slag
Weld Metal
Direction Of Welding
70˚ - 85˚
Electrode
Weld Pool
Arc
Slag
Weld Metal
70˚ - 85˚
Arc
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