BOC Smootharc MMA 170, Руководство по эксплуатации, Страница: 11 / 36

11
2.6 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.
Butt Welding
WELD FACE
FACE REINFORCEMENT
ROOT FACE ROOT GAP
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
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
of a 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 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.