Oxy-acetylene flames — identifying the oxidising flame Is the following statement correct? “An oxidising flame resembles a neutral flame, but its inner cone is shorter and less luminous (more pointed), indicating excess oxygen.”

Introduction / Context:
Oxy-acetylene welding uses three main flame types: carburising (reducing), neutral, and oxidising. Correct flame recognition by cone shape and color is essential to avoid metallurgical problems like oxidation, porosity, or carbon pickup.

Given Data / Assumptions:

• Gas pair: oxygen and acetylene.
• Neutral flame achieved at approximately equal volumes.
• Oxidising flame achieved with excess oxygen beyond neutral.

Concept / Approach:
Relative to the neutral flame, the oxidising flame produces a shorter, sharper, and less luminous inner cone with a slight hissing sound. The reducing feather present in a carburising flame disappears before neutrality and shortens further with excess oxygen, yielding the pointed oxidising inner cone. This appearance helps welders quickly set the correct chemistry for the material (e.g., oxidising is used cautiously for copper/zinc alloys, but avoided for steels).

Step-by-Step Solution:

Verification / Alternative check:
Trial beads on steel show surface oxidation and harsh arc sound with oxidising flame, confirming oxygen excess along with visual cone changes.

Why Other Options Are Wrong:

• “No” or “longer feather”: a feather is characteristic of carburising, not oxidising.
• “Depends only on nozzle size”: nozzle affects flow but not the intrinsic cone shortening due to oxygen excess.
• “Only for brass”: appearance is a general property; application choices vary by alloy.

Common Pitfalls:
Confusing neutral with slightly oxidising; using oxidising flame on steel, causing brittleness and oxidation.

Final Answer: