The oxy-acetylene torch is a powerful industrial tool that generates one of the highest temperatures available from a portable combustion process. This intense heat enables the torch to perform demanding tasks like welding, brazing, and flame cutting across various industries. Understanding the specific temperature range and the underlying chemical process is fundamental to safely and effectively using this heat source.
The Maximum Temperature
The maximum temperature of a properly adjusted oxy-acetylene flame reaches an extreme range of approximately 5,700°F to 6,330°F. This peak heat occurs within the small, intensely bright inner cone of the flame, which is the zone of primary combustion. The temperature drops dramatically outside this inner cone, with the surrounding outer envelope of the flame operating at a cooler temperature of roughly 2,300°F. This precise temperature control allows an operator to focus the highest thermal energy exactly where it is needed on a workpiece.
The Chemistry Behind the Extreme Heat
The extraordinary temperature is produced by combining the fuel, acetylene ($\text{C}_2\text{H}_2$), with pure oxygen ($\text{O}_2$) rather than ambient air. This combustion process occurs in two distinct and highly exothermic stages. The first stage, known as the primary reaction, takes place inside the inner cone where acetylene and the cylinder oxygen are mixed in roughly equal proportions. This initial reaction rapidly decomposes the acetylene into carbon monoxide ($\text{CO}$) and hydrogen ($\text{H}_2$), releasing a massive amount of heat that constitutes the flame’s peak temperature.
The chemical equation for this primary stage is represented as $2\text{C}_2\text{H}_2 + 2\text{O}_2 \rightarrow 4\text{CO} + 2\text{H}_2$. The resultant hot $\text{CO}$ and $\text{H}_2$ gases then travel into the flame’s outer envelope where the second combustion stage occurs. Here, these gases react with oxygen drawn from the surrounding atmosphere, fully converting the combustion byproducts into carbon dioxide ($\text{CO}_2$) and water vapor ($\text{H}_2\text{O}$).
The use of pure oxygen, a process called oxy-fuel combustion, allows the temperature to climb so high. When a fuel burns in air, the nitrogen content, which makes up about 78% of the atmosphere, absorbs a large portion of the released heat. This thermal dilution significantly lowers the overall flame temperature. By supplying oxygen directly from a cylinder, the process eliminates nitrogen dilution, concentrating the energy release and allowing the flame to achieve its maximum temperature.
Comparing Oxy-Acetylene to Other Industrial Flames
The oxy-acetylene flame is hotter than most other common industrial fuel gas and oxygen combinations used in torches. The higher temperature provides a clear thermal advantage, making it the preferred choice when the speed of heating or the ability to cut through very thick sections of steel is the primary concern.
Oxy-Propane
For comparison, an oxy-propane flame typically reaches a maximum temperature in the range of 4,000°F to 5,100°F, depending on the specific mixture. While propane is a popular alternative due to its lower cost and easier storage, its maximum temperature is considerably lower than that of acetylene.
MAPP Gas and Oxy-Hydrogen
Another common fuel is MAPP gas, a stabilized mixture of methylacetylene and propadiene, which burns with oxygen at a maximum temperature of approximately 5,300°F. Oxy-hydrogen flames, which produce a very clean flame used for specific tasks, reach temperatures around 5,072°F.
Primary Applications of the High Temperature
The extreme heat generated by the oxy-acetylene flame is primarily utilized for processes that require the rapid melting or oxidation of metal:
- Welding: The high temperature quickly fuses the edges of a metal joint and the filler rod into a shared molten pool, creating a strong, permanent bond. This is useful for welding thinner sections of steel.
- Oxy-Fuel Cutting: The flame preheats the metal to its kindling temperature (about 1,600°F for steel). A separate jet of pure oxygen then initiates a rapid, exothermic oxidation reaction to burn the steel away.
- General Heating: The torch is frequently used for applications such as bending or forming metal.
- Brazing: This process uses a lower-melting-point filler metal to join parts without melting the base material itself.