Handbook-Manual Cutting

sparks, and the cutting oxygen stream should rapidly pass all the way through the edge of the plate. Now squeeze

the cutting lever to hold the valve wide open and start to move the nozzle down the line you marked on the plate. Your position should be such that you can actually watch the cutting action as the oxygen stream passes through the plate. Try to move the torch steadily. Your tendency, during a first cut, will probably be to move it too slowly. It should take you little more than 30 seconds to make a cut 250 mm long, so don’t be afraid to speed up a bit just as long as the oxygen stream seems to be passing straight through the steel. If you move the torch too slowly, the preheat flames will melt the top edges of the plate excessively. If you move it too fast, you will lose the cut; in other words, the reaction at the top surface of the plate will cease. If that happens, release the cutting oxygen valve lever, allow the preheating flames to bring the steel back to red heat at the point where the cut ceased, and restart the cut, remembering to open the cutting oxygen valve slowly. Fig. 21-1. (Left) The line of cut has been marked, and flames are preheating the top corner of the plate. (Center) The cutting oxygen has been turned on, and the cut is just starting. (Right) The cut is moving straight down the marked line.