Page 65 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

A Quick Guide to Welding and Weld Inspection

Figure 5.2 MMA welding process

Polarities
Welding can be done by using an alternating current (a.c.) or
direct current (d.c.). When direct current is used the welding
electrode will be connected to either the positive or negative
pole. This is referred to as direct current electrode positive
(DCEP) or direct current electrode negative (DCEN). The
type of current and polarity is determined by the electrode
characteristics. The power source has what is termed a
‘drooping’ or constant current characteristic (Fig. 5.3). This
means that a change of arc length (which controls voltage)
will have only a small effect on the welding current as
follows:
. As arc length increases, voltage increases and current

50

Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200905QG Welding chap5.3d Page 50 of 66