GB318265A - Improvements in electric rectifying devices and method of making the same - Google Patents

Abstract

318,265. Lazarus, M. Aug. 31, 1929. [A Specification was laid open to inspection under Sect. 91 of the Acts, Sept. 2, 1929]. Contacting-solid resistances. -The positive plate of a static-contact rectifier is made from an alloy of copper and silver, preferably in the proportion of 25 to 40 ounces of silver to the ton of copper, provided with a rectifying layer of copper and silver oxides. The plates are formed bv a process consisting of heating in an atmosphere containing ozone, preferably in an electric furnace. until the plates are heated to between 1000 and 1030‹ C., then holding them in the open air until they reach a cherry red colour, and finally quenching quickly in a bath containing water and alcohol, glycerine, or a phenolic or cresolic ingredient with a surface layer of oily liquid such as turpentine. By this means the oxide laver is annealed and part of the outer surface thereof is reduced to the metallic state and may be provided with a coating of tin or other metal by electroplating, which facilitates the making of good electric contact between the plates. Fig. 1 shows a rectifier comprising positive plates 1 alternating with negative plates 2. The negative plates 2 may be of tin, brass, or other metal having the desired stiffness, and are provided, as shown in Fig. 2, with embossed contact portions X, which are raised slightly from the plane of the plate and may be partly severed from the body of the plate to allow free access of oil in which the rectifier unit is immersed. The plates are provided with ears or lugs 11 having slots 12 which are slipped over insulated rods 13, Fig. 1, provided with nuts 14 by which the plates are clamped together. The bodies of the plates may be slightly separated to permit ventilation and may have central apertures 15 to permit circulation of air. An insulated tube 16 may be provided to permit circulation of water or air, or the whole assembly may be immersed in oil &c. When the plates are self-cooled, the central apertures 15 may be omitted, or may be replaced by central contact bosses similar to the portions X. The rectifier shown in Fig. 1 comprises four rectifying units PI - - P4 each comprising a positive plate 1 between two negative plates 2, which are arranged with their projections X in contact with opposite sides of the positive plate 1, these plates having an oxide film on both sides. The negative plates 2 of each unit are connected by bent metal straps C. Insulating plates IL, I2 separate the unit P1 from the adjacent units. P2, P3. Metal strip connectors J1 - - J4 permit connection to the secondary winding T1 of a transformer T so as to obtain full-wave, rectification. Metal strips S, S1 form terminals for the load circuit. Additional rectifying units may be added by assembling on the rods 13, or on other rods parallel thereto, plates 27 being provided in the latter case for clamping the whole assembly together.