Types Of Joints - Linde BOC RAPTOR 250R MIG Operating Manual

40
BOC RAPTOR 200C & 250R MIG Operating manual
The following table shows the current ranges generally
recommended for BOC Smootharc 13.
Generally Recommended Current Range for BOC Smootharc 13
Size of Electrode (mm)
2.5
3.2
4.0
5.0
Arc Length
To start the arc, the electrode should be gently scraped on the
work until the arc is established. There is a simple rule for the
proper arc length; it should be the shortest arc that gives a good
surface to the weld. An arc too long reduces penetration, produces
spatter and gives a rough surface finish to the weld. An excessively
short arc will cause sticking of the electrode and rough deposits
that are associated with slag inclusions.
For downhand welding, it will be found that an arc length not
greater than the diameter of the core wire will be most satisfactory.
Overhead welding requires a very short arc, so that a minimum
of metal will be lost. Certain BOC electrodes have been specially
designed for 'touch' welding. These electrodes may be dragged
along the work and a perfectly sound weld is produced.
Electrode Angle
The angle which the electrode makes with the work is important to
ensure a smooth, even transfer of metal. The recommended angles
for use in the various welding positions are covered later.
Correct Travel Speed
The electrode should be moved along in the direction of the joint
being welded at a speed that will give the size of run required. At
the same time the electrode is fed downwards to keep the correct
arc length at all times. As a guide for general applications the table
below gives recommended run lengths for the downhand position.
Correct travel speed for normal welding applications varies
between approximately 125–375 mm per minute, depending on
electrode size, size of run required and the amperage used.
Excessive travel speeds lead to poor fusion, lack of penetration, etc.
Whilst too slow a rate of travel will frequently lead to arc instability,
slag inclusions and poor mechanical properties.
Run Length per Electrode – BOC Smootharc 13
Electrode Electrode
Size (mm) Length (mm)
4.0 350
3.2 350
2.5 350
Correct Work Preparation
Current Range (Amp)
60–95
110–130
140–165
170–260
Run Length (mm)
Minimum Maximum
175 300
125 225
100 225
Layers
The method of preparation of components to be welded will
depend on equipment available and relative costs. Methods may
include sawing, punching, shearing, lathe cut-offs, flame cutting
and others. In all cases edges should be prepared for the joints that
suit the application. The following section describes the various
joint types and areas of application.

15.5 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.
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
Layers Weld Beads
Weld Beads
Electrode
70˚ - 85˚
Weld Pool
Slag