Telwin Practica 152 Manuel D'instructions page 7

- Use welding cables that are as short as possible.
- Do not use metal structures that are not part of the workpiece to
substitute the welding current return cable; this could endanger safety
and produce an unsatisfactory weld.
6. WELDING: DESCRIPTION OF THE PROCEDURE
These welding machines consist of a drooping specification, single phase
transformer and are suitable for welding with alternating current using
coated electrodes (E 43 R type) based on the diameters given on the data
plate.
To switch on the welding machine operate the main switch (Fig. B-1).
The intensity of the supplied welding current can be adjusted
continuously, by means of a manually operated magnetic shunt (Fig.
B-2).
The value of the current setting, (I
scale (Fig. B-3) on the top or side panel of machines where it is provided.
THERMOSTATIC PROTECTION
This welder is automatically protected from thermic overheating
(thermostat automatic re-start). When the windings reach performance
temperature, the protections cut off the supply circuit, igniting the
yellow lamp on the front panel (Fig. B-4). After a few minutes' cooling the
protection will reopen the supply line and turn off the yellow lamp. The
welder is ready for further use.
WELDING
- Use electrodes suitable for working in alternating current.
- The welding current must be regulated according to the diameter of
the electrode in use and the type of the joint to be carried out: see
below the currents corresponding to various electrode diameters:
Ø Electrode (mm)
1.6
2
2.5
3.2
4
- The user must consider that, according to the electrode diameter,
higher current values must be used for flat welding, whereas for vertical
or overhead welds lower current values are necessary.
- In addition to being determined by the selected current intensity, the
mechanical characteristics of the welded join are determined by the
other welding parameters i.e. arc length, working rate and position,
electrode diameter and quality (to store the electrodes correctly keep
them dry and protected by suitable packaging or containers).
Welding procedure
- Holding the mask IN FRONT OF THE FACE, strike the electrode tip on the
workpiece as if you were striking a match. This is the correct strike-up
method.
WARNING: do not hit the electrode on the workpiece, this could
damage the electrode and make strike-up difficult.
- As soon as arc is ignited, try to maintain a distance from the workpiece
equal to the diameter of the electrode in use. Keep this distance as
much constant as possible for the duration of the weld. Remember
that the angle of the electrode as it advances should be of 20-30 grades
(Fig. D).
- At the end of the weld bead, bring the end of the electrode backward,
in order to fill the weld crater, quickly lift the electrode from the weld
pool to extinguish the arc.
CHARACTERISTICS OF THE WELD BEAD
7. MAINTENANCE
WARNING! BEFORE
OPERATIONS MAKE SURE THE WELDING MACHINE IS SWITCHED OFF
AND DISCONNECTED FROM THE MAIN POWER SUPPLY.
EXTRAORDINARY MAINTENANCE
EXTRAORDINARY MAINTENANCE MUST ONLY BE CARRIED OUT BY
TECHNICIANS WHO ARE EXPERT OR QUALIFIED IN THE ELECTRIC-
MECHANICAL FIELD, AND IN FULL RESPECT OF THE IEC/EN 60974-4
) can be read in Amps on the graduated
2
Welding current (A)
min.
25 50
40 80
60 110
80 160
120 200
Fig. E
CARRYING OUT MAINTENANCE
TECHNICAL DIRECTIVE.
WARNING! BEFORE REMOVING THE WELDING MACHINE
PANELS AND WORKING INSIDE THE MACHINE MAKE SURE THE
WELDING MACHINE IS SWITCHED OFF AND DISCONNECTED FROM
THE MAIN POWER SUPPLY OUTLET.
If checks are made inside the welding machine while it is live, this
may cause serious electric shock due to direct contact with live parts
and/or injury due to direct contact with moving parts.
- Inspect the welding machine regularly, with a frequency depending
on use and the dustiness of the environment, and remove the dust
deposited on the transformer, using a jet of dry compressed air (max.
10 bar).
- At the same time make sure the electrical connections are tight and
check the wiring for damage to the insulation.
- At the end of these operations re-assemble the panels of the welding
machine and screw the fastening screws right down.
- Never, ever carry out welding operations while the welding machine is
open.
- If necessary use a very thin layer of grease, at a high temperature, to
lubricate the moving parts of the regulators (threaded shaft, sliding
surfaces, shunts etc.).
- Replacing the power supply cable: before replacing the cable,
identify the screw-connecting terminals L1 and L2 (N) on the switches
(Fig. F).
- After having carried out maintenance or repairs, restore the connections
and wiring as they were before, making sure they do not come into
contact with moving parts or parts that can reach high temperatures.
Tie all the wires as they were before, being careful to keep the high
voltage connections of the primary transformer separate from the low
voltage ones of the secondary transformer.
max.
Use all the original washers and screws when closing the casing.
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