< OXY-GAS WELDING & BRAZING
GAS CUTTING
Cutting metals with an oxy-gas flame requires the operator to fit a quite different blowpipe and nozzle arrangement to that used for welding. The cutting blowpipe has a oxygen control lever mounted in addition to the familiar oxy-fuel control valves. The copper cutting nozzle consists of a number of small pre-heat outlets which are set in a radial pattern, with a larger blow hole in the centre of the array to provide a concentrated jet of oxygen. Gas pressures for cutting are adjusted differently to those used for welding, with oxygen in particular set to a much higher pressure (typically 25 psi compared to the average 5 psi or so used for welding).
The torch is lit, and adjusted to a neutral flame. The material to be cut is then pre-heated to red heat at the start point of the cut. At red heat the oxygen jet is applied by depressing a separate control lever mounted on the blowpipe. The oxygen jet instantly removes a local amount of metal to form a cut or KERF.
It is possible to achieve fast good quality cuts in mild steel materials, (using specialist equipment) up to 8ft (2m) in thickness, though few workshops will need to cut material in excess of 2 inches (50mm) thickness. One important point to note is that oxy-gas cutting is essentially a chemical action, dependent upon the combination of steel and oxygen at 875°C, at which point steel converts into iron oxide. Iron oxide can easily removed from the area of the cut with the applied oxygen blast directed from the torch nozzle. Most other metals and alloys, including iron, stainless steel, copper and aluminium cannot normally be cut by this method – or at least not without adaptive equipment which introduces a metallic powder into the flame to encourage a similar chemical reaction to that of carbon steel. Flame/powder cutting of non-ferrous metals generally creates a less than satisfactory cut, so non-ferrous alloys are normally best cut by an alternative means such as a FRICTION (mounted disc/blade), or PLASMA CUTTNG process.
For the most part, oxy-gas welding and cutting in the foundry or artist’s studio is reserved for light steel fabrications.This includes armature building, and occasional use as a heat source for soldering, brazing and manipulation (forging, bending etc). Some smaller foundry workshops, or those on tight equipment budgets, may still use gas welding in preference to electric arc welding, though suitable arc plant is nowadays available at relatively low cost. Despite the predominance of electric arc welding in joining art and design metalwork, few foundry workshops will have dispensed totally with a piece of equipment as versatile and inexpensive as the oxy-gas set.
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