Cutting with the Electric Arc

WELDING OPERATIONS I - OD1651 - LESSON 1/TASK 2

(3) Cutting with the Electric Arc.

(a) Electric arc cutting is a procedure whereby metal is cut

using the heat of an arc maintained between the electrode and the

base metal.

Three procedures described in the following

subparagraphs are used in cutting with the electric arc.

(b) Carbon-arc cutting is a process whereby the cutting of

metals is accomplished by progressive melting with the heat of an

electric arc between a metal electrode and the base metal.

The carbon arc is used under some conditions in

conjunction with a jet of compressed air for the removal of

defective austenitic (corrosion resistant) weld metal.

Cutting

with the carbon arc is used for cutting both ferrous and

nonferrous metal, but does not produce a cut of particularly good

appearance.

The electrodes are either carbon or graphite,

preferably with a pointed end to reduce arc wandering, and thus

produce less erratic cuts.

(c) Metal-arc cutting is a process whereby the cut is produced

by progressively melting the metal.

Direct current straight

polarity is preferred for this process.

Coated electrodes

ranging in diameter from 1/8 to 1/4 inch are used; larger

diameters are not satisfactory because of excessive spatter. The

thickness of the metal that can be cut by the metal-arc process

is limited only by the length of the electrode. The coating on

the electrode serves as an insulator between the core of the

electrode and the side wall of the cut, resulting in less short-

circuiting against the kerf. Cuts made by the metal-arc process

are less ragged than those produced with carbon-arc, but they

must still be prepared by grinding or chiseling before rewelding

is accomplished.

(d) Oxy-arc cutting is accomplished by directing a stream of

oxygen into the molten pool of metal. The pool is kept molten by

the arc struck between the base metal and the coated tubular

cutting rod.

The rod is consumed during the cutting operation.

The tubular rod also provides an oxidizing flux and a means of

converging oxygen onto the surface being cut. The

68