(a) Oxy-Acetylene Welding Process:
Oxy-acetylene welding is a gas welding technique that uses controlled combustion of oxygen and acetylene gas to generate a high-temperature flame (around 3,300°C) for melting and joining metals. The key steps involved are:
- Preparation: Clean the weld area thoroughly to remove dirt, grease, and any other contaminants that could affect the weld quality.
- Setting Up: Connect the oxygen and acetylene cylinders to the torch using appropriate regulators and hoses. Adjust the gas flow rates to get the desired flame type (neutral, oxidising, or carburizing).
- Preheating: Apply the flame to the surrounding area of the weld joint to preheat the metal. This prevents cracking and allows for smoother melting.
- Melting and Joining: Direct the hottest part of the flame at the joint edge, melting the metal. Simultaneously, add filler metal (a rod or wire of similar composition) to bridge the gap and create a continuous weld pool.
- Post-heating: Maintain the flame on the weld area for a short time after joining to allow slow cooling and prevent cracking.
- Cleaning: Allow the weld to cool completely, then remove any slag (impurities) with a chipping hammer or wire brush.
(b) Importance of Correct Gas Mixture:
Getting the gas mixture right is crucial for several reasons:
- Neutral Flame: A neutral flame with equal parts oxygen and acetylene provides the ideal temperature for most welding applications. It melts the metal effectively without excessive oxidation or carbonization, leading to strong and clean welds.
- Oxidising Flame: An oxidising flame has excess oxygen, resulting in a higher temperature but greater oxidation of the metal. This can weaken the weld joint and make it brittle. It’s used for specific applications like cleaning or brazing.
- Carburizing Flame: A carburizing flame has excess acetylene, creating a lower temperature but introducing more carbon into the weld. This can weaken the joint and make it brittle. It’s rarely used and can lead to weld defects.
Therefore, maintaining the correct gas ratio ensures optimal working temperature, prevents defects, and guarantees strong and reliable welds.