The cutting torch is a valuable tool for piercing holes in steel plate. Figure 4-29 shows the steps you should use to pierce holes in steel plate. First, lay the
Figure 4-29.-Piercing a hole with an oxygas cutting torch.
plate out on firebricks or other suitable material so the flame does not damage anything when it burns through the plate. Next, hold the torch over the hole location with the tips of the inner cone of the preheating flames about 1/4 inch above the surface of the plate. Continue to hold the torch in this position until a small spot has been heated to a bright red. Then open the cutting oxygen valve gradually, and at the same time, raise the nozzle slightly away from the plate. As you start raising the torch and opening the oxygen valve, rotate the torch with a slow spiral motion. This causes the molten slag to be blown out of the hole. The hot slag may fly around, so BE SURE that your goggles are tightly fitted to your face, and avoid placing your head directly above the cut.
If you need a larger hole, outline the edge of the hole with a piece of soapstone, and follow the procedure indicated above. Begin the cut from the hole you pierced by moving the preheating flames to the normal distance from the plate and follow the line drawn on the plate. Round holes are made easily by using a cutting torch with a radius bar attachment.
The cutting torch is an excellent tool for removing rivets from structures to be disassembled. Rivet cutting procedures are shown in figure 4-30. The basic method is to heat the head of the rivet to cutting temperature by using the preheating flames of the cutting torch. When the rivet head is at the proper temperature, turn on the oxygen and wash it off. The remaining portion of the rivet can then be punched out with light hammer blows. The step-by-step procedure is as follows:
1. Use the size of tip and the oxygen pressure required for the size and type of rivet you are going to cut.
2. Heat a spot on the rivet head until it is bright red.
3. Move the tip to a position parallel with the surface of the plate and turn on the cutting oxygen slowly.
4. Cut a slot in the rivet head like the screwdriver slot in a roundhead screw. When the cut nears the plate, draw the nozzle back at least 1 1/2 inches from the rivet so you do not cut through the plate.
5. When cutting the slot through to the plate, you should swing the tip through a small arc. This slices half of the rivet head off.
6. Swing the tip in an arc in the other direction to slice the other half of the rivet head off.
Figure 4-30.-Using a cutting torch to remove a rivet head,
By the time the slot has been cut, the rest of the rivet head is at cutting temperature. Just before you get through the slot, draw the torch tip back 1 1/2 inches to allow the cutting oxygen to scatter slightly. This keeps the torch from breaking through the layer of scale that is always present between the rivet head and the plate. It allows you to cut the head of the rivet off without damaging the surface of the plate. If you do not draw the tip away, you could cut through the scale and into the plate.
A low-velocity cutting tip is best for cutting buttonhead rivets and for removing countersunk rivets. A low-velocity cutting tip has a cutting oxygen orifice with a large diameter. Above this orifice are three preheating orifices. Always place a low-velocity cutting tip in the torch so the heating orifices are above the cutting orifice when the torch is held in the rivet cutting position.