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Answers to common questions about running a modular medium-duty torch on propane or natural gas instead of acetylene, and about the cutting, heating, gouging and flame cleaning nozzles that go with it.
No. Nozzles are made for a particular fuel gas. Cutting with propane or natural gas needs different attachments and cutting nozzles from cutting with acetylene, and TWI notes that nozzle type depends on the fuel gas as well as on whether the work is manual or machine-based.The flame shape, the amount of oxygen needed and the way the gas mixes all differ between fuels, so a nozzle made for one is likely to give a poor flame on another. Pick a nozzle marked by the maker for your fuel gas and for your torch type, and use the maker's chart to set pressures.
Propane burns with a lower flame temperature than acetylene, and more of its heat sits in the outer flame rather than the inner cone. TWI notes that this makes piercing much slower. If you hold the inner cone close to the plate, as you would with acetylene, you can wait a long time.Technique changes: raise the torch a little so the outer flame does the preheating, then lower it to cut. TWI also notes that propane's lower flame temperature tolerates more distance between nozzle and work, which lowers the risk of molten metal splashing back onto the nozzle. Practise on scrap, and follow the maker's tip chart.
A gouging nozzle supplies a large flow of oxygen to a steel area heated above its ignition temperature. The oxygen reacts with the hot steel and washes the molten metal out, forming a groove, rather than cutting through the plate. TWI says it is a quick and efficient way of removing metal.Typical uses include removing an unfused root from the back of a weld, removing a weld or defect, and preparing plate edges. Torch angle and travel speed mainly set the depth, and the oxygen setting must suit the nozzle: too low and the metal is simply washed out, too high and the cut runs ahead of the pool.
The HSE says fuel gases form explosive mixtures with air and oxygen, and even small leaks can cause a flash fire or explosion, especially in a poorly ventilated room or confined space. Check all connections and equipment regularly, using a proprietary leak-detecting spray or solution suitable for oxy/fuel systems, and never look for a leak with a naked flame.Propane vapour is heavier than air and can settle and collect at low level, so take extra care in pits and enclosed spaces. Close cylinder valves when finished, and replace leaking components at once. Follow the supplier's and maker's instructions and your risk assessment.
Choose the nozzle by the thickness of metal you will cut, then set oxygen and fuel gas pressures from the maker's chart for that nozzle. A cutting chart gives the right tip size and pressures for different thicknesses, and it is specific to the fuel gas and torch type, so a chart for acetylene should not be used.The HSE advises using the correct gas pressures and nozzle size for the job, as part of avoiding flashbacks. Holding the torch too close to the work or running with a partly blocked nozzle can cause backfires, so keep the nozzle clean. If you are in between sizes, the maker's guidance is the place to check.
A backfire is when the flame burns back into the torch, often with a sharp bang. The HSE says it may happen when the torch is held too close to the workpiece or the nozzle is partly blocked, and that it can indicate a fault in the equipment.Shut off the torch valves, oxygen first and then the fuel gas, then shut off both cylinder valves. Cool the torch with water if necessary and check the equipment for damage, particularly the nozzle, before using it again. Spring-loaded non-return valves on the blowpipe and the correct lighting-up procedure help reduce the risk of flashback.