Gas Welding – Working Principle with Sketch
Gas welding is a fusion welding process where metal parts are heated to their melting point using a high-temperature flame produced by burning a mixture of fuel gas (usually acetylene) and oxygen. A filler metal is added to fill the joint and form a strong bond.
Working Principle:
- Fuel Gases Used:
- Mostly Oxy-Acetylene (common)
- Sometimes Oxy-Hydrogen
- Gas Mixing and Flame Generation:
- Oxygen and acetylene are stored in separate high-pressure cylinders.
- The gases are passed through regulators and rubber hoses into the blow torch (welding torch).
- In the mixing chamber of the torch, the gases are mixed in the required ratio.
- When ignited, the flame reaches a temperature of ~3200°C, enough to melt all commercial metals.
- Welding Process:
- The flame is directed on the joint of the workpieces, melting the edges.
- A filler rod is inserted into the molten pool to add material and strengthen the joint.
- Flux (like borax) is used to prevent oxidation and remove metal oxides.
- As the molten pool cools and solidifies, it forms a strong welded joint.
Types of Flames in Gas Welding
The nature of the flame depends on the oxygen-to-acetylene ratio, and each has specific applications.
| Type of Flame | Oxygen:Acetylene Ratio | Flame Structure | Temperature | Application |
|---|---|---|---|---|
| Neutral Flame | 1 : 1 | Clear inner cone + light blue outer flame | ~3200°C | Used for welding mild steel, aluminium, copper, etc. |
| Oxidizing Flame | > 1 : 1 (excess O₂) | Small, sharp inner cone + hissing sound | ~3500°C | Used for brass, bronze, cast iron (non-ferrous metals) |
| Carburizing Flame | < 1 : 1 (excess acetylene) | Long inner cone with feather-like tip | ~3100°C | Used for lead, aluminium, case hardening |
