Patent GB-456482-A (GB)
Title: Improvements in and relating to electric discharge apparatus
IPC: H01J13/50
Filed: 1936-01-02
Abstract: 456,482. Mercury-vapour rectifiers. LEHMANN, W., 45, Trabener Strasse, Grunewald, Berlin. Jan. 2, 1936, Nos. 212, 213, 214, and 215. Convention dates, Jan. 2, 1935, May 23, 1935, May 25, 1935, and June 28, 1935. [Class 39 (i)] In vacuum discharge apparatus such as metal-clad, mercury-vapour rectifiers, which are degassed at temperatures not less than 200‹ C. and are then separated from the vacuum pump, the conductor 6 to the electrode is supported by a steatite or like ceramic tube 4, the joint between the tube and (i) the conductor and (ii) the metal envelope 2 being sealed by fusible material 10, 14, Fig. 1, such as glass or enamel or by layers of iron sulphide, the material being received in pockets formed either by recesses in the tube 4 or by the ends of metal connecting parts 8, 15. The coefficients of expansion of the tube, fusible material and surrounding metal connecting parts are made as nearly the same as possible, with the metal slightly the greatest. The recesses are annular and closed at the bottom. Flexible pieces 11, 16 are included in the connecting parts 8, 15, which are welded to the conductor 6 and a metal tube 12 welded to the envelope. An anode 3 is shown in Fig. 1, a shield 19 therefor being supported from the tube 12 ; lateral movement of the anode and its insulator tube 4 is prevented by the plates 17, 18. As applied to a copper lead-in 44, Fig. 2, for a cathode the ceramic tube 46 surrounds the upper end of the iron tube 45 encasing the rod 44 ; the seals are similar to that above described. A quartz tube 35 surrounds the lower end of the lead-in, to which a perforated block 34 and springs 27 are attached for making good contact with the mercury cathode. A spring ring 49, and metal disc 48 prevent lateral movement of the lead-in with respect to the protecting tube 21. In a modified cathode construction the cathode support 124, Fig. 3, and its lead-in 125 are supported from the ceramic tube 117 with pockets 118, 119 for the sealing material. In a modification of this arrangement the tube is replaced by a thick annulus, connection to the envelope and conductor being made on the outer and inner cylindrical surfaces of the annulus ; pockets are formed in the metal connectors for the seals. When the sealing material is received in recesses such as 51, 52, Fig. 5, the tube is made thicker at the recessed part or notches are made below the recesses to obviate bending stresses in the tube due to the difference in expansion of the tube and metal parts. The sealing material may be in powdered form which is fused ; or for constructions as shown at 52, Fig. 5, a broken glass ring may be placed in the recess and then fused. The fusing is effected in a slightly oxidizing atmosphere formed by nitrogen with a small oxygen content controlled if necessary by adding hydrogen to reduce the proportion of oxygen present. As applied to an air-cooled rectifier the lead-in arrangements for the anodes 20, Fig. 7, cathode 21 and starting electrodes 22 may all be of the kind described above. One anode 22 may alternate with two normal anodes 20. Cowls 32, 33 direct the air into the jacket 28 and pins 51 increase the cooling surface where desired. For bigger rectifiers a liquid cooling agent yielding few free hydrogen ions such as trichlorethylene may be used ; or a layer may be provided on the wall of the vessel which cannot absorb free hydrogen ions.