TECNA 7900 Manual Del Usuario página 11

ELECTRODES
 When operating, the electrodes must be kept clean and their
diameter must be kept suitable for the work to be carried out.
Excessively worn electrodes must be replaced.
 With water cooled arms, do not use sealing products to
remove water leakage on the electrode taper. To facilitate
electrode removal and to prevent from both taper seizure and
leakage, use high conductivity grease similar to the standard
one.
COOLING CIRCUIT (ON ITEM 7903 ONLY)
 Check that cooling water circulates freely and in the required
quantity and that the input temperature is within 10 and 30°C.
 Check the status of both water hoses and corresponding
connections.
 If the welder is to be stored during the winter in a cold
environment, first carefully drain the cooling circuit to prevent
damage caused by frozen water.
ELECTRICAL CIRCUIT
 Periodically check ground efficiency.
 Periodically check the mains cable.
EXTRAORDINARY MAINTENANCE
If the welder overheats, check that the duty cycle is not too high
(table 4), the electrode tip diameter is correct (table 2); on water
cooled models check that water flow is adequate.
Item 7903 is equipped with a thermostatic protection which
stops the welder in case of insufficient water. The thermostat
does not protect the transformer against work overloading.
If performances are lower than expected check:
 that, when welding, line voltage drop is lower than 15%;
REMEDIES FOR WELDS IMPERFECTIONS.
This chapter has been introduced in order to facilitate the troubleshooting of the most common imperfections caused by incorrect
adjustment. Notice that each one can be caused by different causes as there are many parameters affecting the welding process . The
following table specifically refers to low carbon steel spot welding, but, with the due consideration, it can also be useful for other
applications.
FAULT
Weak welding
Spatter of molten
material
Burned welds or welds
showing either craters
fissures.
Work pieces stuck
on the electrode
Electrodes and connections
reduced life (position 21).
Secondary connection
reduced life and oxidation.
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POSSIBLE CAUSE
Low welding current.
Low welding time.
Too high electrodes force.
Lacking electrodes maintenance or too high
electrodes diameter.
Faulty pieces contact.
Paint or dirt among pieces.
Inadequate electrodes cooling.
Faulty pieces contact or pieces and electrodes
faulty contact.
Too high welding current.
Too high welding time.
Too small electrodes diameter.
Inadequate welding force.
Electrodes faulty clamping of the pieces.
Too high welding current.
Inadequate welding force.
Oxidised pieces to weld.
or Faulty pieces contact or pieces and electrodes
faulty contact.
Faulty pieces lining up.
Electrodes tips deformations.
Too high welding current.
Inadequate electrodes diameter.
Inadequate welding force.
Under-sized electrode in comparison with the
work to be done
Heating caused by an inadequate clamping of
the flexible connection.
Too high heating caused by a too high welding
rate.
 that the supply cables section is adequate;
 that the electrodes diameter is appropriate for the work to be
carried out;
 on item 7903 that the cooling water flows in the required
quantity;
 that the set welding force is adequate for the work in process.
SPARE PARTS
Look at the exploded views and at the spare parts list at the end
of this instruction manual to identify the code of the required
parts. The first number of the code has the following meaning:
1.... standard components widely available from industrial
suppliers (e.g. screws, washers, nuts, etc.).
2.... commercial components which, providing that the
same quality parameters are adopted, can be purchased
anywhere (hoses, switches etc.).
3.... components manufactured by TECNA
4.... components manufactured by TECNA
5.... electronic circuits and assemblies manufactured by
TECNA.
7.... assemblies composed of parts belonging to any or all
of the above codes but which for the sake of simplicity are
available ready-assembled.
All spare parts, including standard or commercial ones, are
available from TECNA. When ordering please always state code
number, and quantity of the spare parts, voltage and frequency,
the serial number, and year of manufacture of the welder. The
code number followed by an asterisk warns that the part
changes depending on the mains voltage.
POSSIBLE REMEDY
Increase it.
Increase it.
Reduce pressure.
Clean and line up the electrodes, restore their
dimensions.
Increase the electrodes force.
Clean the pieces.
Check the cooling circuit.
Increase the electrodes force by increasing
pressure.
Reduce it.
Reduce it.
Adjust diameter to the value shown on the table.
Increase pressure.
Check stroke.
Reduce it.
Increase welding pressure.
Clean them by means of emery paper.
Increase electrodes force.
Correct it.
Restore them to the correct size.
Reduce it.
Restore it to the correct dimensions.
Increase the welding pressure.
Check both size and contact diameter.
Carefully tighten the clamping screws.
Reduce it.