Another commonly used method is the air carbon arc gouging which is mainly used to make J- or Ugrooves.
J- or U-grooves can also be made by machining, which is much more costly than air carbon
arc gouging. Figure 3.22 shows how the joint is prepared.
Compressed air carbon arc, as the name implies, consists of melting the metal to be gouged or cut
with an electric arc and blowing away the molten metal with a high-velocity jet of compressed air
parallel to the electrode. Because it does not depend on oxidation, it works on metals which do not
oxidize readily. The equipment used is a torch that directs a stream of air along the electrode and
external to it. The torch is connected to an arc welding machine and an ordinary compressed-air line
delivering approximately 100 lbs per sq. inch. Since the exact pressure is not critical, normally no
regulator is necessary. The electrode used is a composition of carbon and graphite and is usually
copper clad to increase its life and provide a uniform groove, as well as to reduce radiation heat. The
shape of the electrode may be round or half round. DCRP is used for most applications, but in some
materials DCSP is preferred. An electrode for alternating current is also available and this, when used
with either AC or DCSP, gives improved results on certain applications.