REHM INVERTIG.PRO COMPACT 240 DC Betriebsanleitung Seite 122

Welding with and
without additional
materials
Direct current
welding
Alternating current
welding
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Additional welding materials are added in stock form when welding manually.
The correct material for the basic material must be selected. But excellent results
can also be achieved if you just allow the welding bath of two pieces to come
together, for example, on corner seams.
When direct current welding, the minus pole is usually at the electrode. The
minus pole is the colder pole, this means that the current resilience and the stand
time of the tungsten electrode is considerably greater than when plus pole
welding.
When alternating current welding, the resilience of the electrode is heavily
influenced by the balance setting. The balance setting distributes the plus and
minus proportions of the welding current between the electrode and the work
piece. During the positive half wave, the aluminium oxide skin is destroyed and a
higher temperature occurs at the electrode. During the negative half wave, the
electrode cools down and the aluminium is heated. Since tearing the aluminium
oxide skin only need a short plus impulse, REHM TIG units can use a high minus
proportion.
This has many benefits:
1. the temperature load of the electrode is reduced
2. the electrode can be loaded with a higher current
3. the current range of the electrode increases
4. a pointed electrode can be used for welding
5. the arc is slimmer
6. the penetration is deeper
7. the heat influence zone of the weld is smaller
8. the welding speed increases
9. the application of heat to the work piece reduces
Practical values of the balance setting for alternating current welding are:
•
with butt welds 60% to 70% minus proportion
•
with hollow seam welds 70% to 80% minus proportion
Operation