Operating instructions

18
BOC Smootharc Advance II MIG 250C Operating manual
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
di󹟽erent thickness of steel are described as follows:
Square Butt Weld
Weld Beads
Weld Beads
Layers
Layers
70˚ - 85˚
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
Weld Beads
Layers
Layers
70˚ - 85˚
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
Weld Beads
Layers
Layers
70˚ - 85˚
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 of a tendency to
distortion as weld contraction can be equalised.
Butt Weld with Backing Material
Weld Beads
Weld Beads
Layers
Layers
70˚ - 85˚
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
Weld Beads
Layers
Layers
70˚ - 85˚
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
Weld Beads
Layers
Layers
70˚ - 85˚
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
Weld Beads
Layers
Layers
70˚ - 85˚
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.
Electrode Angle for 1st and 2nd Layers Electrode Angle for Subsequent LayersButt Welding
Weld Face
Face Reinforcement
Root Face
Root Gap
Weld Beads
Weld Beads
Layers
Layers
70˚ - 85˚
Electrode
Slag
Weld Pool
Weld Metal
Arc
Direction Of Welding
Weld Beads
Weld Beads
Layers
Layers
70˚ - 85˚
Electrode
Slag
Weld Pool
Weld Metal
Arc
Direction Of Welding