Selco Genesis 200 AC-DC/TLH Instrucciones De Uso página 28

A.C. (Alternating Current)
Alterntating current welding is amployed when it is necessary ti
weld aluminium (and its alloys) or magnesium with high currents
(> 50A).
A mains frequency of 50/60 Hz is normally used.
During the positive half-wave (D. C. R. P .) the oxide is broken,
whereas when the electrode is negative (D.C.S.P .) it cools down
and the weld material penetrates easily since the heat supply on
the workpiece increases.
The behaviour of the arc, however, varies considerably accor-
ding to polarity. By using a simple sinusoidal generator, when
the voltage dorps to zero. It caises the arc to blow out.
These continuoius blowouts make the arc unstable and difficult
to control. These setbacks can be dealt with by using stabilizing
generators with square wave gained from the tree-phase source.
The voltage and current will then instantly drop to zero, thus
ensuring arc stability. You can thus deduce the functions of wave
balancing, which allow the ratio between the cleaning current
and the penetration current to be controlled by varying the ratio
between D.C.S.P . and D.C.R.P .
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A.C.-Pulsed (Alternating Current Pulsed)
Also when welding aluminuium, a pulsed current can be used,
with similiar effects to those described in pulsed direct current
welding.
9.2.1 Steel TIG welding
The TIG procedure is very effective for welding both carbon and
alloyed steel, for first runs on pipes and for welding where good
appearance is important.
Straight polarity is required (D.C.S.P .).
Preparing the edges
An accurate cleaning and preparation of the edges are required.
Choosing and preparing the electrode
You are advised to use thorium tungsten electrodes (2% tho-
rium-red colouring) or alternatively cerium or lanthanum elec-
trodes with the following diameters:
Ø electrode (mm)
1.0
1.6
2.4
The electrode must be pointed as shown in the figure.
(°)
30
60÷90
90÷120
Filler material
The filler rods must have mechanical characteristics com-
parable to those of the base material.
Do not use straps obtained from the base material, since they
may contain working impurities that can negatively affect the
quality of the welding.
Protective gas
Practically, pure argon (99.99%) is always used.
Welding Ø Electrode
current (A) (mm)
6-70 1.0
60-140 1.6
120-240
2.4
9.2.2 Copper TIG welding
Since the TIG welding is a process characterized by high heat
concentration, it is particularly suitable for welding materials
with high thermal conductivity, like copper.
For TIG welding of copper, follow the same directions as for TIG
welding of steel or specific instructions.
current range (A)
15÷75
60÷150
130÷240
current range (A)
0÷30
30÷120
120÷250
Gas nozzle Argon flow
n° Ø (mm) (l/min)
4/5 6/8.0 5-6
4/5/6 6.5/8.0/9.5 6-7
6/7 9.5/11.0 7-8