| abstract |
Plasma arc or laser cutting uses a mix of reactive (24a) and reducing gas flows (22a) to cut sheets (14) of stainless steel, aluminum and other non-ferrous metals. The reducing gas flow (22a) to the cut varies as a percentage of the total gas flow to maintain a reducing atmosphere down through the cut (12), but to leave a predominantly oxidizing atmosphere at the intersection of the cut (12) and the bottom surface (14B) of the sheet (14) being cut. In plasma arc cutting these flows can also be characterized as eithe a plasma gas flow (22a) that forms the arc, or a shield gas flow (24a) that surrounds the arc. The reactive gas is preferably a flow of air, oxygen, nitrogen, carbon dioxide or a combination of these gases. The reducing gas is preferably hydrogen, hydrogen 35, methane, or a mixture of these gases. For aluminum, the reactive gas is preferably air or nitrogen and the reducing gas is preferably methane or a mixture of methane and air. In laser cutting the reducing gases such as methane can be used by mixing them with reactive assist gases. |