In the oxygen and acetylene gas mixture, the ideal volume ratio of acetylene to oxygen is generally 1:1 to 1.2:1, a ratio which is a neutral or slightly oxidizing flame and suitable for most carbon steel welding purposes. For example, when welding a 3 mm thick low carbon steel plate, the 1.1:1 (10 L/min oxygen, 9 L/min acetylene) blend ratio can keep the flame temperature at approximately 3100°C, increase the thermal efficiency by 15%, and reduce the risk of oxidation of the weld pool. Experiment verifies that a deviation from this ratio will lead to a loss of weld strength by 20% to 30%, such as an excess of oxygen (e.g., 1.5:1) forming an oxide flame and, in the process, reducing the weld metal carbon by 0.2% to 0.3%, having a great effect on the material’s ductility.
When it comes to cutting processes, the ratio of oxygen to acetylene has to be altered to 1.5:1 to 2:1 to enhance the effectiveness of the oxidation reaction. For instance, to cut a 20 mm thickness steel plate, the rate of oxygen consumption must be adjusted to 25 L/min, with the acetylene being 12 L/min, and the cutting speed is up to 400 mm/min, which is 18% higher than the normal ratio, with the incision surface roughness (Ra) remaining below 12.5 μm. Industry practices suggest that an automotive manufacturer reduced the percentage of cutting waste from 5% to 2.3% by enhancing the ratio, achieving a yearly saving of $120,000. In addition, oxygen and acetylene gas storage pressure must be controlled at 15 MPa and 1.7 MPa, respectively, to ensure the stability of the gas supply and avoid flame tempering accidents caused by pressure changes.
In environmental safety and protection, the proper oxygen to acetylene ratio will be able to conserve 15% to 20% of gas usage. For example, with the help of an automatic proportional control valve used in a welding plant, acetylene usage was reduced from 5000 m³ to 4200 m³ per year, with carbon emission reduced by 8.2 tons. Studies show that when the oxygen concentration is more than 30%, the scope of acetylene explosion limits (2.5%~81%) will be significantly extended, therefore the operating environment should be equipped with a gas detector, real-time monitoring of the deviation of oxygen concentration does not exceed **±0.5%.**. Historically, in 1987, a British shipyard caused an explosion due to uncontrolled oxygen ratio, with a direct loss of 2.3 million pounds **, which prompted the industry to revise the ISO 5172 standard, specifically requiring a mixing ratio error of less than **±3%**.
Technologically, the new intelligent welding machine dynamically controls the oxygen and acetylene gas flow in real-time through the closed-loop control system, i.e., the PID algorithm adopted by an equipment brand, and the proportional accuracy is increased to **±0.8%, and the welding pass rate is increased from 89%** to 97%. According to data by the Journal of Welding Engineering in 2021, when the company adopted the optimal ratio, its life against fatigue in titanium alloy welding in the aerospace sector is increased by 40%, whereas its crack rate reduces to 0.3 times/kilometer weld. In the future, once the replacement technology of hydrogen energy is created, the ratio of oxygen and acetylene can be further modified, but currently 1:1 to 1.2:1 remains the golden ratio that takes efficiency, economy, and security into consideration.