MetFab - Welding Fume Handbook - Flipbook - Page 26
9 Effect of shielding gas: ozone
9.1 Mild steel welding
The choice of shielding gas can be a significant factor in
ozone emission. The reduced ozone emissions of
Air Products Maxx® shielding gases are achieved by
adopting two formulation strategies:
• Changing the wavelength or lowering its intensity reduces
ozone producing radiation.
This is typically achieved by adding carbon dioxide or
helium to argon-based shielding gases.
• Adding chemical species that reacts with ozone to the gas
mixture. For argon, two popular choices are hydrogen and
nitric oxide. Hydrogen reacts with ozone to form water
vapour and oxygen (and also changes the UV spectrum of
the arc). Nitric oxide converts ozone to nitrogen dioxide.
MAG
MAG welding of mild steel is usually performed with argonbased shielding gases containing carbon dioxide and/or
oxygen. Helium may also be added to the mixture to improve
operability and increase productivity.
Figure 16 demonstrates the beneficial effect of larger
concentrations of carbon dioxide in the shielding gas on
the ozone level in the welder's breathing zone, during
arcing, when MAG welding mild steel with dip transfer.
This reduction is believed to arise from a change in the UV
spectrum due to the composition of the shielding gases.
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