PLASMA ARC CUTTING PROCESS AND APPARATUS USING AN OXYGEN-RICH GAS SHIELD

摘要

A plasma arc torch (10) has a secondary gas flow (46) that is extremely large during piercing of a workpiece (36). The secondary flow (46) exits the torch immediately adjacent the transferred plasma arc (34) and is an extremely uniform, swirling flow. A swirl ring (60) is located in the secondary gas flow path (50) at the exit point. A prechamber (58) feeds gas to the swirl ring (60), which is in turn fed through a flow restricting orifice (56). For certain applications the secondary gas (46) is a mixture of an oxidizing gas and a non-oxidizing gas in a flow ratio of oxydizing to non-oxidizing in the range of 2:3 to 9:1. A network (44) of conduits and solenoid valves (SV1-SV17) operated under the control of a central microprocessor (90) regulates the flows of plasma gas (42) and secondary gas (46) and mixes the secondary gas (46).