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ELECTRODE WELDING AND GOUGING

Basic principles

Manual Metal Arc welding

There are three different types of current used for Welding: DC-, DC+ and AC.

Transformers: Alternating Current Inverters & Rectifiers: Direct Current + or –

Transformer power sources produce alternating current (AC). This type of current changes direction 50 or 60 times per second (50-60 Hz). There are restrictions on alternating current used on board ships because this type of current goes deep into the body and can harm vital organs if the body becomes part of the electric circuit. Rectifier and inverters produces direct current (DC) which is regarded as a safe type of current to use on board. This type of current runs in one direction (from – to +) so we can manipulate by connecting the electrode to either - or + polarity. If we want deep penetration we can connect the electrode to – polarity and thereby bombard the base material with electrons that make 70% of the heat accumulating in the base material. Connecting the electrode to + polarity gives the opposite reaction with a high burn-off rate on the electrode, high weld build up and shallow penetration. Most root runs are done with DC- polarity to get the necessary penetration, while filler passes and capping runs are done with DC+ polarity.

The principal task of all power sources is to take alternating current from the mains and bring the high voltage down to a suitable working voltage. Rectifiers and inverters also convert the AC current into DC current.

Coating Core rod Shielding smoke

Base metal Molten weld Metal transfer

Travel

–

+

30 %

electrons +

4.01

70 % DC-

– DC+

70 %

50 %

electrons

electrons

30 %

Direct current moving from – to +

+– AC

50 %

Alternating current

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