Cutting with oxyacetylene on cars

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The oxyacetylene cutting process and apparatus

Cutting with the torch is the process of burning metal with oxygen to effect separation. Wrought iron, steel, and cast iron are the metals cut by this process. Aluminium, brass, bronze, nickel, monel, and the other non-ferrous metals and alloys cannot at present be cut by the torch process.

In oxyacetylene cutting of iron, steel, and cast iron, the metal is heated to the ignition temperature with preheating flames burning at the end of the tip. The preheating flames, usually four, are spaced around the cutting orifice in the centre of the tip. When the metal to be cut is heated to a bright red the high-pressure oxygen jet is turned on, and the metal in the path is cut or burned away. Progressive movement of the torch results in cutting a narrow kerf similar to that made by a metal saw. Acetylene is the preferable fuel gas for the preheating flame, and oxygen is required both to burn the acetylene in the preheating flames and to effect cutting.

Growth of the oxyacetylene industry is reflected in the demand for a combination welding and cutting outfit adaptable to the needs of small shops, garages, plumbing and heating contractors, steam pipe fitters, and others occasionally requiring a cutting outfit but whose main activity with the torch is welding.

The Airco-Davis-Bournonville combination welding and cutting outfit No. 9898 comprises the Style 9800 torch with tips, regulators, hose, wrenches, goggles, spark lighter, and style 7790 cutting attachment.

In making up the cutting attachment with the torch handle the operator should grasp the rear end with his hand over the needle valves while applying wrench pressure. It is essential that the swivel nut be firmly tightened to prevent leaks and backfires.

The oxygen welding regulator is adaptable to cutting with this attachment inasmuch as the oxygen pressure employed for cutting the comparatively thin sections within its capacity rarely exceeds 40 pounds.

The general rules for setting up, lighting the torch, and shutting down apply to the combination outfit in all respects. Avoid the use of oil or grease on the connections, and be sure that all connections are screwed up tightly before lighting.

The cutting tips fit a tapered seat in the torch head, and care should be taken that the tip is clean before putting it in place. Screw the tip nut firmly; if for any reason the torch head should become overheated, do not tighten the tip nut until the torch head has been allowed to cool, and remove the tip nut if cooled in water. Use the smallest tip consistent with the thickness to be cut. The No. 1 tip will cut all thicknesses of steel from Vs to inch. If necessary to cut sections up to 3 or 4 inches, use a No. 4 tip.

The operation of cutting with the combination outfit is one of heating the metal to bright red with the preheating flames, and then pressing the thumb lever to turn on the oxygen jet that does the cutting. The torch is held at the angle desired for the cut and moved along slowly, keeping in step with the cutting action. All oxide and scale adhering to the cut surfaces should be cleaned off before starting to weld.

The directions for setting up apparatus, lighting the torch, and adjusting the pressures are supplemented with the following specific points not fully covered in the foregoing :

Flashbacks in general are caused by a mixture of oxygen and acetylene in either hose. This mixture may be formed in any one of a number of ways, a few of which are enumerated herewith :

  1. Lighting the torch with a sub-normal pressure in one hose and a normal or excessive pressure in the other hose.
  2. With proper pressures in both hose line but with a stoppage in the tip beyond the point of mixing.
  3. Leak between the oxygen and the acetylene in the torch head seat due to foreign substance, bruised or warped contact surfaces, or insufficient pressure on the wrench when screwed up.
  4. Temporary obstructions of gas flow in either hose caused by kinking of the hose or by external pressure applied on the hose by some heavy object dropped or lying on it.
  5. High acetylene pressure due to improper adjustment of regulator followed by stoppage or obstruction beyond the point of mixing of the gases.
  6. Bleeding either oxygen or acetylene cylinders by forcing the regulator seat away from the nozzle and allowing a mixture to form in the cylinder. This, in case of a flashback, is likely to be serious.
  7. Long lengths of hose may be indirectly responsible for flashbacks because of the practical impossibility of keeping long lengths free from kinks that may reduce the flow of gas or stop it entirely in one line.

Learning to cut

Cutting or burning wrought iron, steel, and cast iron with the oxyacetylene torch, to effect separation, requires a torch designed for cutting and torch manipulation quite different from that for welding. Cutting is essentially simple but like many other simple operations success depends upon learning that which can be acquired only by practice.

A good cutting operator is one who holds a torch steadily and moves it at uniform speed over the piece, the speed being adjusted to the thickness and cutting tip. Gas pressures and tips must be used appropriate to the job.

If the cut wavers from side to side a wider kerf will be made which means more oxygen consumption and slowing down the speed. If the operator is unable to move the torch at uniform speed but goes ahead at an irregular rate, that also slows down the cutting and increases gas consumption.

The operator should dress for cutting, and wear gloves and goggles. Always pull the goggles over the eyes before starting.

Starting to cut

As a rule a cut is started at the edge of a plate or forging. The preheating flames are held above the steel at the edge until the metal becomes bright red, and then the trigger or lever controlling the oxygen cutting jet is pulled, and cutting starts. The torch should be held with the tip vertical and should be kept in a nearly vertical position when making a square cut, or at an angle of about 45 degrees when bevelling for welding.

If necessary to start a cut in the metal away from the edge, heat the metal to a bright red and hold the heat a little longer than when starting on the edge. Now raise the torch about 1/2 inch and pull the trigger. As soon as the plate is perforated lower the torch to the normal position, and proceed with the cut.