Table E4 Recommended Cutting Tip Sizes

Plate Thickness

1/4-1 in.

1 1/4-2 3/4 in.

3-4 in.

6-5 in.

Cutting Tip Sizes







# 4

# 5

# 6

# 6

The spacer sleeve, shown in Figure E-4 clamps over the cutting tips and is used to keep the cutting tips at the proper distance from the work, which should be a minimum of 3/16 inch and a maximum of 1/4 inch for the cutting tip. This sleeve should also be perforated to allow water to circulate around the cutting tip.

After the tip and spacer sleeve are seated, the flame should be lit and adjusted. It is necessary to set the recommended regulator pressures with the flame burning and the cutting oxygen valve wide open. Work should be stopped at once when any cylinder pressure drops below the recommended operating pressure. The preheat flame, produced from the mixture of MAPP gas and oxygen, supplies heat to start the cut and maintains the cutting temperature. The central oxygen jet accomplishes the actual cutting by oxidizing and blowing out a narrow band of metal to produce the kerf.

The gas controls typically incorporated in the cutting torches are shown in Figure E-4. The torch is to be connected to the hoses and the working pressure must then be set. Before seating the cutting tip, purge the torch with each gas separately.

Gas Cutting Set

Figure E-4. Standard Surface Cutting Torch with Underwater Spacer Sleeve.

Torch Igniter. A hand mechanical igniter should be used for lighting the torch. This simple tool is safer than an electrical igniter and is equally effective.

After the steel has been pierced, cutting can proceed at approximately the same speed as it does above water. If loud popping sounds are heard, other than those made by hot slag forming in the water, add a small amount of preheat oxygen to the flame. This same procedure also applies to edge starts.

It is important to recall that the ocean is a giant heat-sink and has a cooling action at least 40 times greater than that of air and therefore, a light thickness of steel will require as much preheating as a heavy thickness because of the rapid heat transfer through lighter steel.

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