Selco Genesis 90, Repair Manual

Page: 14 / 47

14 Description of operation of the power sources
A-90 TORCH
4.13 TECHNICAL CHARACTERISTICS
4.14 INSTALLATION
Turn off the generator.
Connect the torch attachment to the correponding coupling on
the generator by completely screwing on the locking ring.
4.15 SETTING UP FOR USE
Fig.1 Torch body assembly
Before starting work, it is necessary to carry out the following
checks and work:
1) Check that the generator is turned off.
2) Check that all the parts of the torch are working. For the various
parts that make up the torch body (Fig.1), the sequence of cor-
rect assembly is 1-2-3-4-5-6.
3) To fit the electrode (No.2), use the key, taking care to avoid
excessive tightening that could damage the thread of the com-
ponents.
The electrode must be unscrewed only after the post-cutting air
flow is finished, and therefore with the electrode itself cooled.
4) Check that the air diffuser, or "swirl-bush" (No.3) is working cor-
rectly, which must always show access holes free of obstruction;
the use of a defective air diffuser would cause overheating, with
consequent damage to the components of the torch body.
5) The diameter of the hole in the tip (No.4) is chosen according to
table 1.
Never use a tip with a hole diameter less than that recommen-
ded; this could cause overheating with consequent damage to
the torch body.
6) With the spare parts assembled, check that by screwing the
outer nozzle (No. 5) to the torch body the corresponding alarm
on the generator is cut off; finally check that by unscrewing the
nozzle the alarm is triggered; these checks should be carried out
with the generator on, taking care not to press the torch button.
7) With manual cutting, the standard spacing spring (No.6) is used,
and on request a spacer with 4 feet is available, for cutting with
template (see detail 024 of the exploded drawing of parts).
8) The compressed air used must be filtered and maintained at a
high level of purity; humid air, oil and other contaminative
agents must be removed, by making use of suitable driers and
anti- oil filters. Thus the torch is set up for the cutting operation.
In any case it is necessary to also follow what is shown in the
instruction manual for the generator, above all in the para-
graphs "General precautions", "Connecting up" and "Normal
maintenance".
Tab. 1 Choice of appropriate tip
4.16 USING THE TORCH
4.16.1 Inclination and speed of the torch during cutting
The torch is generally held perpendicular to the workpiece
during all the cutting phases; obviously, whenever it is required
to carry out chamfering or inclined cutting, the torch must be til-
ted to a suitable inclination.
The speed must be adjusted so that the outflow of the arc below
the workpiece is perpendicular (5-10 degrees of slope are
acceptable).
A slow speed start is advisable to prevent spray of material
which could damage the tip.
4.16.2 Puncturing
In some cases it is necessary to puncture a hole in the material
using plasma cutting. In this way, the wear on the parts which
are subject to deterioration will be increased, and it becomes
very important to try to work to avoid the return of spray, which
can be dangerous, especially with sheet metal over 10 mm.
thick. We suggest starting with the torch inclined sideways, so as
to point the spray outside the cutting area, avoiding damage
and overheating of the torch body.
Immediately remove any material accumulated
on the tip or on the ceramic hood.
Caution: plasma cutting is a process with a high thermal ele-
ment, which takes both the piece to be cut and the end parts
of the torch to extremely high temperatures.
4.16.3 Circular cutting
For the preparation of flanges and opening holes, it is possible
to use a pair of compasses, equipped with rotating heads and
movement on wheels. The centering is simplified by the pre-
sence of three different guides, one magnetic, one pointed, and
one passing through the central hole.
4.16.4 Practical advice
We advise igniting the pilot arc away from the workpiece, and
then moving near until the cutting arc is struck; striking a cutting
arc repeatedly and directly by contact with the workpiece crea-
tes an increase in temperature of the torch body.
Avoid turning off the generator before the end of the post-cut
cooling flow, to avoid overheating of the components of the
torch.
4.17 MAINTENANCE AND INSPECTION
Wear on the electrode is not only determined by the cutting
time and the current, but also by the number of start-ups.
It is advisable to replace the electrode before the tungsten insert
in the point is completely worn out.
The tip, that is always of a size suggested under table 1, has an
average life similar to that of an electrode, and is replaced when
an irregular hole is present which is larger than the nominal one
(this can cause slanted cuts of poor quality).
Electrode and tip are replaced simultaneously to prolong their
active life.
Working with electrode and tip which are too spoiled can cause
damage to the torch body.
It is important to pay special attention to the fitting of the elec-
trode and tip in order not to irreparably damage the torch.
Tip diameter
Tip Ø 1.1
Tip Ø 1.4
Tip Ø 1.7
Range of current usable
22÷60A
40÷90A
80÷140A
Principle of operation
Version
Protection device
Current (x = 60%)
(x = 100%)
Pilot arc current
Pressure
Air quantity
Ignition of pilot arc with high
frequency
Monogas (air or nitrogen)
“External nozzle not screwed”
signal
90A
70A
22÷29A
5÷5.5 bars
180 Iitres/min