An oxy-acetylene torch is a workshop tool that burns acetylene gas with oxygen to produce an extremely hot, concentrated flame. It is used for heating, brazing, welding, and cutting metals, especially steel. The torch matters because it lets a worker control heat very precisely using gas flow, flame shape, and distance from the workpiece.
Understanding the flame zones and safe setup helps prevent poor cuts, weak joints, and dangerous accidents.
Inside the torch, oxygen and acetylene flow through separate passages, mix near the tip, and burn as they exit the nozzle. A neutral flame has the correct oxygen to acetylene balance and is commonly used for welding steel because it does not strongly add carbon or oxygen to the metal. For cutting steel, the preheat flame raises the metal to ignition temperature, then a high pressure oxygen jet oxidizes the hot steel and blows molten oxide out of the kerf.
Safe operation depends on correct regulator settings, leak checks, flashback arrestors, ventilation, and careful shutdown order.
Key Facts
- Oxy-acetylene flame temperature can reach about 3200 °C when oxygen and acetylene are mixed correctly.
- Neutral flame balance is approximately O2:C2H2 = 1:1 at the torch for many welding and heating tasks.
- Complete combustion equation: 2 C2H2 + 5 O2 -> 4 CO2 + 2 H2O.
- Cutting steel uses oxidation: 4 Fe + 3 O2 -> 2 Fe2O3, and the oxygen jet removes the hot oxide.
- Heat input depends on flame temperature, gas flow rate, torch angle, travel speed, and distance from the metal.
- Acetylene should not be used above about 15 psi gauge pressure because it can become unstable and decompose violently.
Vocabulary
- Acetylene
- Acetylene is a fuel gas with the formula C2H2 that burns very hot when mixed with oxygen.
- Neutral flame
- A neutral flame is a balanced oxy-acetylene flame with a sharp inner cone and little excess oxygen or acetylene.
- Flashback
- Flashback is the dangerous burning of the flame back into the torch or hose instead of only at the tip.
- Kerf
- The kerf is the narrow slot or gap made in metal by a cutting torch or other cutting tool.
- Regulator
- A regulator is a device that reduces high cylinder pressure to a controlled working pressure for the torch.
Common Mistakes to Avoid
- Using acetylene pressure above 15 psi is wrong because acetylene can become unstable and may decompose explosively.
- Lighting both gases at once is wrong because the torch should be lit with acetylene first, then oxygen adjusted to form the correct flame.
- Holding the torch too far from the metal is wrong because the hottest inner cone will not heat the work efficiently, causing slow cuts and rough edges.
- Skipping leak checks is wrong because leaking oxygen or fuel gas can cause fire, explosion, or oxygen-enriched materials that ignite easily.
Practice Questions
- 1 A torch uses acetylene at 0.25 L/min. For a neutral flame with O2:C2H2 = 1:1 at the torch, what oxygen flow rate is needed?
- 2 A student cuts a 180 mm line in 45 s. What is the travel speed in mm/s, and what is the travel speed in mm/min?
- 3 A torch flame has a long feather around the inner cone and leaves soot on the metal before oxygen is increased. Explain what type of flame this indicates and why it is not ideal for welding steel.