EN
TIG 185 DC. Operating manual.
TIG 185 DC. Operating manual.
13
12
Welding current
Correct current selection for a particular job is an important factor in arc
welding. With the current set too low, difficulty is experienced in striking
and maintaining a stable arc. The electrode tends to stick to the work,
penetration is poor and beads with a distinct rounded profile will be
deposited.
Excessive current is accompanied by overheating of the electrode. It will
cause undercut, burning through of the material, and give excessive
spatter. Normal current for a particular job may be considered as the
maximum which can be used without burning through the work, over-
heating the electrode or producing a rough spattered surface, i.e. the
current in the middle of the range specified on the electrode package is
considered to be the optimum.
In the case of welding machines with separate terminals for different
size electrodes, ensure that the welding lead is connected to the correct
terminal for the size electrode being used. When using machines with
adjustable current, set on the current range specified.
The limits of this range should not normally be exceeded.
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 that is 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 Ryval 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.
3.4 Welding technique
Successful welding depends on the following factors:
→ selection of the correct electrode
→ selection of the correct size of the electrode for the job
→ correct welding current
→ correct arc length
→ correct angle of electrode to work
→ correct travel speed
→ correct preparation of work to be welded
3.5 Electrode selection
As a general rule the selection of an electrode is straight forward, in that
it is only a matter of selecting an electrode of similar composition to the
parent metal. It will be found, however, that for some metals there is a
choice of several electrodes, each of which has particular properties to
suit specific classes of work. Often, one electrode in the group will be
more suitable for general applications due to its all round qualities.
Electrode size
The size of the electrode is generally dependent on the thickness of the
section being welded, and the larger the section the larger the electrode
required. In the case of light sheet the electrode size used is generally
slightly larger than the work being welded. This means that if 1.5 mm
sheet is being welded, 2.0 mm diameter electrode is the recommended
size. The following table gives the recommended maximum size of
electrodes that may be used for various thicknesses of section.
Recommended electrode sizes
Average thickness of plate or
section
≤ 1.5 mm
1.5–2.0 mm
2.0–5.0 mm
5.0–8.0 mm
≥ 8.0 mm
Maximum recommended
electrode diameter
2.0 mm
2.5 mm
3.15 mm
4.0 mm
5.0 mm
For further help on choosing the right electrode for your work please
contact your local Ryval supplier.
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.
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.
Correct work preparation
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.
3.6 Types of joints
This system is capable of several types of weld, from Butt through to
Fillet welds.
