Plasma arc cutting system having fluid metering and power control systems

A cutting and welding system having at least one plasma arc cutting and welding torch, and a metering system for controlling at a location remote from the plasma arc torch the amount of gas and water fed to the plasma arc torch, comprising

• a plasma arc torch which includes an electrode having an arc discharge end, a nozzle assembly positioned adjacent the discharge end of the electrode and a bore extending through the nozzle assembly, means for creating an electrical arc extending from the electrode through the bore to a workpiece located adjacent the nozzle assembly, means for generating a flow of gas between the electrode and the nozzle assembly to create a plasma flow outwardly through the bore to a workpiece positioned beneath the nozzle assembly, and means for generating an annular jet of water outward from the nozzle to envelope the plasma as it is discharged from the nozzle,
• means supporting the torch in spaced relation above the workpiece, said support means including means for moving the torch along the support means for welding or cutting of the workpiece along a predetermined path of travel,
• gas flow means communicating with a source of gas and the plasma arc torch for supplying gas to the torch,
• water flow means communicating with a source of water and the plasma arc torch for supplying water to the torch,
• a plurality of metering orifices positioned in a parallel bank within respective gas and water flow means so that the gas and water may flow through each of the metering orifices, each metering orifice having a predetermined diameter opening, and a control valve mounted adjacent each of the metering orifices within the respective gas and water flow means on the upstream side toward the supplies of gas and water, wherein each control valve has opened and closed positions for allowing gas and water to flow through a metering orifice upon actuation of the control valves, and
• control means operatively connected to the control valves for actuating selected control valves to control the gas and water flow through selected metering orifices to allow a predetermined amount of gas and water to flow to the plasma arc torch, wherein the amount of gas and water flowing to the torch may be accurately controlled by actuating selected control valves to allow gas and water flow only through selected metering orifices of a desired size.

A method of controlling the current generated to a plasma arc torch cutting and welding system comprising the steps of

• generating a predetermined cutting current form a power supply to an electrode of a plasma arc torch having an arc discharge end and a nozzle assembly positioned adjacent the discharge end of the electrode, and which includes a bore extending through the nozzle assembly, while also
• generating a flow of gas between the electrode and the nozzle assembly to create a plasma arc flow through the bore to a workpiece positioned beneath the nozzle assembly,
• controlling the cutting current generated to the electrode with an analog voltage control signal in which the value of the cutting current is linearly dependent upon the value of the analog voltage control signal,
• measuring the cutting current,
• comparing the cutting current to a predetermined value, and
• generating an analog voltage control signal corresponding to the predetermined value of the desired cutting current when the cutting current varies from the predetermined value so that a constant cutting current is generated.

An apparatus of controlling the current generated to a plasma arc torch cutting and welding system comprising

• means for generating a predetermined cutting current from a power supply to an electrode of a plasma arc torch having an arc discharge end and a nozzle assembly positioned adjacent the discharge end of the electrode, and which includes a bore extending through the nozzle assembly,
• means for generating a flow of gas between the electrode and the nozzle assembly to create a plasma flow through the bore to a workpiece positioned beneath the nozzle assembly,
• means for controlling the cutting current generated to the electrode, said control means including means for generating an analog voltage control signal in which the valve of the controlled cutting current is dependent upon the valve of the analog voltage control signal,
• means for measuring the cutting current,
• means for comparing the cutting current to a predetermined valve, and
• means for generating an analog voltage control signal corresponding to the predetermined valve of the desired cutting current when the cutting current varies from the predetermined valve so that a constant cutting current is generated.

In a plasma arc cutting and welding system in which the system includes at least one plasma arc torch, gas and fluid circuits for supplying gas and fluid to the plasma arc torch, means for generating a flow of gas between the electrode and the nozzle assembly of the torch to create a plasma arc flow outwardly to a workpiece positioned beneath the torch nozzle, means for generating an annular jet of fluid outward from the nozzle to envelope the plasma as it is discharged from the nozzle, and a plurality of metering orifices and associated fluid control valves positioned within each of the flow circuits for metering the fluid and gas flow through the channels, each fluid circuit also having a flow control valve positioned upstream of the metering orifices and associated valves for allowing on-off flow of fluid to the metering orifices and associated valves, an apparatus for controlling the starting of the cutting and welding system, comprising

• means for testing a flow control valve to determine if the flow control valve is open to allow fluid flow therethrough,
• means for energizing a fluid pump used to pump fluid from the source of fluid through the flow control valve if the switch is determined to be open, and
• means for determining if fluid is present within the flow control valve, and means for maintaining system operation if fluid flow is sensed within the flow control valve.