Arc device with adjustable cathode

A plasma generating system including a plasma gun with a tubular anode member, a rod-shaped cathode member located in spaced coaxial relationship with the anode member operable to maintain a plasma generating arc therebetween, anode fluid passage means receptive of pressurized cooling fluid for directing fluid to cool the anode member and having an anode outlet passage for discharging the cooling fluid from the anode fluid passage means at an intermediate pressure, cathode fluid passage means having a fluid inlet receptive of the pressurized cooling fluid for directing fluid to cool the cathode member and having a cathode outlet passage for discharging the cooling fluid from the cathode fluid passage at the intermediate pressure, and cathode positioning means for continually adjusting relative axial spacing between the cathode member and the anode member so as to maintain a predetermined arc voltage, the cathode positioning means comprising:

• a closed cylinder member extending rearwardly from the plasma gun;
• a piston affixed coaxially to the cathode member and slidingly positioned in the closed cylinder member partitioning therein a first chamber located on the side of the piston distal the plasma gun and a second chamber, the first chamber being receptive of the cooling fluid from the anode outlet passage and the cathode outlet passage and having an exit orifice of sufficient resistance to maintain the cooling fluid in the first chamber at the intermediate pressure, and the fluid inlet being located proximate the piston;
• first valve means for selectively infusing pressurized control fluid into the second chamber such as to move the piston against the intermediate pressure of the cooling fluid in the first chamber and thereby move the cathode member axially away from the anode member;
• second valve means for selectively discharging the control fluid from the second chamber such that the intermediate pressure of the cooling fluid in the first chamber moves the piston against the discharging control fluid in the second chamber and thereby moves the cathode member axially toward the anode member;
• an end wall bounding the cylinder member at an end opposite the arc device and having therein a fluid passage receptive of the pressurized cooling fluid;
• telescoping tubing affixed between the piston and the end wall such as to convey the pressurized cooling fluid from the fluid passage to the fluid inlet;
• a flexible electrical cable connected between the cathode member and a source of arc current and located within the cylinder member such as to be cooled by fluid therein;
• and
• voltage determining means for measuring an arc voltage between the cathode member and the anode member, and control means communicating with the voltage determining means for selectively controlling the first valve and the second valve such as to continually adjust relative spacing between the cathode member and the anode member so as to maintain a predetermined arc voltage.