How does oxy-fuel cutting work?

Oxy-fuel cutting is a thermal cutting process that uses a torch with fuel gas and pure oxygen. Widely used on steel structure sites in Quebec.

Principle:

1. The metal is preheated by the flame to its ignition temperature — that temperature depends on the steel grade and is read in the gas supplier's tables
2. A jet of pure oxygen is directed onto the heated area
3. Oxygen reacts with iron: Fe + O₂ → FeO + heat (an exothermic reaction that sustains the cut)
4. The liquid iron oxides (slag) are blown out of the cut

Gases:

• Acetylene (C₂H₂): the hottest flame, hence the fastest preheat; the price depends on the supplier and the cylinder (deposit, delivery)
• Propane: cooler flame, slower preheat, generally lower running cost — the values for both gases are on the supplier's data sheet
• MAP-Pro: Propane alternative, hotter. For small jobs

Capabilities:

• Carbon steel only — does not work on stainless steel or aluminum (oxide is too adherent)
• Thickness: the capacity depends on the torch, the tip and the oxygen flow — the equipment manufacturer states it
• Cut quality: it depends on the tip, the speed and the cleanliness of the plate; the applicable tolerances are those in the specification

Safety rules:

• Gas cylinders must be upright and chained
• Minimum distance between cylinders and the heat source: the one prescribed by the welding safety standard (CSA W117.2) and the workplace rules
• Flashback arrestor mandatory on each regulator