INSULATING NONCONSUMABLE ARC ELECTRODE

1277936 Non-consumable arc electrodes WESTINGHOUSE ELECTRIC CORP 24 Nov 1969 [17 Dec 1968] 57377/69 Heading H5H An arc furnace electrode comprises a non- consumable annular electrode tip 10, a supporting Column-31, 32, 33, for the tip 10, and a heat shield enclosing a major portion of the supporting column, the heat shield being in the form of a metallic structure e.g. 11, 12, 13 &c. electrically insulated from the tip 10 and column 31, 32, 33 and being spaced from the column to provide a passage 44 for coolant to flow between the shield and the column. As shown, the heat shield comprises a plurality of metal segments 11-21, mutually insulated by intervening thin mica rings 26, and urged together to compress seals 23 by means of a screw clamp member (not shown) secured to the supporting column, a BELLVILLE washer (not shown) being provided to allow for thermal expansion of the metal segments 11-21. The segments of the heat shield may be biased at a potential other than the tip potential to obviate arcing to the melt and in this instance the insulating rings 26 between the metal segments may be omitted except for the two at the top and bottom of the stack. The supporting column comprises three concentric metal tubes 31, 32, 32, a coolant (water) outlet passage 124 being formed between tubes 32, 33 and a coolant inlet passage 40 being formed between tubes 31, 32. In the inlet passage are situated insulated conduits 35, 36 for current supply to a field coil 84 which rotates the arc root around the annular arc surface 61. Coolant flows through passage 40, overflows into passage 44 passes through peripheral gaps 52 in tube 31 to a U-section annular passage 60 surrounding the arcing surface 61 and thence to outlet 124. The field coil 84 is also hollow and supplied with coolant through its conduits e.g. 35, 36. A central passageway 82 is provided for supplying material to the electrode tip 65. Instead of mica spacers 26, the segments 11-21 may be sprayed with a ceramic coating. Where thermal insulation would not impair operation of the furnace the outer surfaces of the segments may be coated with a good thermal insulator e.g. alumina.