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5.2.4. CUTTING PROCESS INITIATION
Bring the torch to the initial cutting position and start locally heating the work-
piece to the ignition temperature, approximately bright red or yellow. Then open
the cutting oxygen valve and switch on the torch movement in the same time.
Cutting oxygen pressure should be increased stepwise, according to the pierc-
ing process recommendation.
5.2.5. CUTTING SPEED
The optimal cutting speed is given in the Charts of cutting parameters. Correct
setting can be seen from the slag production, from the almost vertical spray of
sparks and from the cutting noise.
5.3. SWITCHING OFF OF THE MACHINE CUTTING TORCH
The gas flow shall be closed in following sequence using either automated
mode with cutting machine valves or manual mode with shut off valves on the
torch:
1. Cutting oxygen
2. Fuel gas
3. Heating oxygen
6. OPERATION FAULTS AND MAINTENANCE
6.1. BACKFIRE
Reduction of the outlet flow velocity, e. g. due to contamination of the nozzles
when the torch is applied to the material (touching the plate or slag) or due to
operating faults especially reduced gas flow. The flame enters the torch and is
extinguished with a cracking sound. Switch off the torch, allow cooling by cutting
oxygen flow if necessary, readjust, ignite and operate again.
6.2. SUSTAINED BACKFIRE
With sustained backfire the flame enters the torch and continues to burn inside
at the mixing point. A whistling noise ensues. In this case immediately close
first the heating oxygen flow and then the fuel gas. Normally, sustained backfire
can be produced in the torch by incorrect operating pressures or overheated
or damaged equipment. Therefore, only use undamaged heating and cutting
nozzles and ensure proper sealing of the nozzles and torch head.
6.3.TORCH FAILURE
Do not operate the torch with leaks at the connections of the torch and nozzles
and with damage due to torch flashback, blocked nozzles etc., and replace the
torch with a properly working torch. Make sure before each cutting operation
that nozzles are properly tightened to the torch head. Stop operating immediate-
ly in case there is leakage/flame burning between nozzle and torch head. Such
effect can cause safety risk or equipment damage. If a repair is required, please
contact your GCE partner.
