Understanding Oxy-Acetylene Flame Types

In oxy-acetylene welding, the ability to adjust the flame is crucial for achieving high-quality welds. By controlling the ratio of oxygen to acetylene, welders can create three distinct types of flames: neutral, carburizing (or reducing), and oxidizing. Each flame has unique characteristics and is suited for different applications and metals.

1. The Neutral Flame

A neutral flame is created when there is a roughly one-to-one ratio of oxygen and acetylene. It is the most commonly used flame for welding and cutting because it provides complete combustion. This flame is named "neutral" because it typically has no chemical effect on the metal being welded.

• Appearance: A neutral flame is characterized by two distinct zones: a bright, well-defined, bluish-white inner cone and a larger, light blue outer envelope. To achieve a neutral flame, a welder will often start with an excess acetylene flame and gradually increase the oxygen until the "acetylene feather" disappears.
• Temperature: The temperature at the tip of the inner cone is approximately 5850°F (3232°C).
• Sound: It produces a hissing sound.
• Uses: The neutral flame is preferred for most welding applications and is used on a variety of metals, including mild steel, stainless steel, cast iron, copper, and aluminum.

2. The Carburizing (or Reducing) Flame

A carburizing flame, also known as a reducing flame, has an excess of acetylene. This type of flame will add carbon to the weld metal.

• Appearance: The most identifiable feature of a carburizing flame is the presence of an "acetylene feather," which is a whitish or reddish intermediate feather extending beyond the inner cone. This flame has three distinct zones: a bright inner cone, the acetylene feather, and a blue outer envelope. The length of the feather, often expressed as a multiple of the inner cone length (e.g., a 2X flame), indicates the amount of excess acetylene.
• Temperature: The temperature of a carburizing flame is lower than a neutral flame, around 5252°F (2900°C).
• Sound: It is a smoky and quiet flame.
• Uses: A carburizing flame is advantageous for welding high-carbon steel and hard-facing nonferrous alloys like nickel and Monel. It is not used on metals that readily absorb carbon, as it can make them brittle.

3. The Oxidizing Flame

An oxidizing flame is produced when there is more oxygen than acetylene in the mixture, making it the hottest of the three flame types.

• Appearance: This flame has a short, pointed inner cone that is purplish in color. The outer envelope is also shorter. To achieve this flame, one would typically start with a neutral flame and then increase the oxygen flow until the inner cone shortens significantly.
• Temperature: The temperature of an oxidizing flame can reach approximately 6300°F (3482°C) at the tip of the inner cone.
• Sound: A distinct hissing or roaring sound is characteristic of an oxidizing flame.
• Uses: The high temperature of an oxidizing flame makes it suitable for welding copper-base and zinc-base alloys. It should not be used for welding steel, as the excess oxygen will combine with the steel and burn it, resulting in a porous and brittle weld.