Patent GB-817504-A (GB)
Title: Improvements in or relating to metal vapour electric arc converters
Inventor: HOLLIDAY JOHN HUBERT
IPC: H01J13/02
Filed: 1955-12-30
Abstract: 817,504. Metal-vapour converters. GENERAL ELECTRIC CO. Ltd. Dec. 31, 1956 [Dec. 30, 1955], No. 37500/55. Class 39(1). In a metal vapour electric arc converter having a supply of vaporizable metal, such as a mercury pool, for producing an arc discharge and a main anode and an auxiliary anode spaced from the cathode of the converter, the said cathode includes a cathode spot anchoring member capable of being wetted by the vaporizable metal to produce a concave meniscus edge for anchoring the cathode spot and the main anode is spaced from the said cathode by a distance not exceeding that beyond which the voltage drop between the main anode and the cathode is substantially variable with such spacing. In one form, Fig. 1, the rectifier comprises a cylindrical envelope 1, an anode assembly 2, a cathode assembly 3, and an igniter 4. The envelope 1 comprises a cylindrical steel wall 5 brazed to an alloy portion 6 which is joined to a glass portion 7 and a cathode vessel 8 of alloy. The upper end wall 9 is of steel and is conical in form and provided with a connection 15 for a vacuum line. An alloy cylinder 11 joined to the end wall 9 supports a glass cylinder 10, an alloy cylinder 12 and a steel portion 13 welded to a steel flange 14 which supports the anode assembly 2. The anode 16 comprises an upper conical member 17 of steel to which is brazed a flatbottomed member 18 of molybdenum, this metal being chosen to minimise sputtering. A steel tube 19 joined to the conical member 17 is attached to the flange 14 and surrounds a tube 20 having a flanged end 21 spaced closely to the molybdenum member 18, so that cooling water forced through the tube 20 passes between the members 21 and 18 and back through the annular space between the tubes 19 and 20 to an outlet 22. During operation of the converter any charged particles which do not strike the anode are deflected to one side or the other by the electric field between the members 9 and 17 and are prevented from reaching the anode supporting arrangement. The envolope 1 is surrounded by a water-cooling jacket 23 of laminated plastic provided with windows 24 to allow observation of the cathode. The ends of the jacket 23 are joined to recessed rings 25 or 26 containing sealing rings 27 and 28. A base plate 37 and sealing ring 38 are clamped between rings 35 and 36. A tubular member 30 of alloy joined to the ring 35 is brazed to an inverted cup-shaped member 32 of molybdenum which constitutes a cathode spot anchoring member arranged to operate in the manner described in Specification 810,387 and surrounds a hollow member 34 attached to a steel tube 33 which is welded in a central hole in the base plate 37. Cooling fluid passes through an inlet pipe 39 into the annular passage between the members 32 and 34 and returns via the tube 33 to an outlet pipe 40. A mushroom-shaped auxiliary anode 42 which also serves to shield the main anode 16 from bombardment by positive ions during reverse cycles has a lead 41 and is insulated by means of a glass ring 44 from a metal tube 43 attached to a flexible bellows 45 which is joined to a flanged member 46 having a screw-threaded end. A ring 48 carrying a sealing ring 47 is screwed on to the member 46 and welded to the tube 33. An insulator 49 also screwed onto the member 46 includes means for attaching leads to the member 46 and to the lead 41. The igniter 4 is described in Specification 817,505 and includes a solenoid 50 which is preferably controlled by the circuit described in Specification 817,501. In an alternative form, Fig. 2, the rectifier comprises a cylindrical envelope 1, an anode assembly 2 as described above, a cathode assembly 3, and an igniter 4 as described in Specification 817,505. The envelope 1 comprises a cylindrical wall 5 and conical end walls 9 and 51 of stainless steel, and is surrounded by a water-jacket 23 of stainless steel. Alternatively the envelope and jacket may be of mild steel, the surfaces exposed to water being provided with a coating of chromium-nickel brazing alloy as described in Specification 817,506 or the envelope may be of mild steel and the jacket of stainless steel. The cathode assembly 3 comprises a cathode spot anchoring member 32 of molybdenum attached to a flanged member 52 of stainless steel which is welded to a tubular member 53 surrounding an inner tubular member 54 carrying a flange 55. Connections 56 and 57 are provided for inlet and outlet pipes for cooling water. A cathode vessel 58 of molybdenum is attached to the member 32 and is perforated at 59 so that excess mercury overflows to a reservoir 60. A mushroomshaped auxiliary anode 42 of graphite is separated by a quartz sleeve 66 from a molybdenum peg 65 brazed to the member 32, and is supported by a quartz ring 67. A lead 68 is attached to a steel ring 69 secured to the auxiliary anode 42 by three bolts 70. A deionizing grid 71 may be provided, and a quartz ring 72 prevents the cathode spot wandering to the envelope. To ensure a high vacuum within the envelope a getter may be introduced before the final sealing. In a modification (not shown) the auxiliary anode comprises a stainless steel tube closed at one end by a molybdenum cap and surrounded for most of its length by a quartz sleeve. The auxiliary anode is cooled internally by circulating fluid and is mounted away from the axis of the rectifier so that it does not shield the main anode, but a very low arc drop between the main anode and cathode may be obtained. Specifications 817,502 and 817,503 also are referred to,