| 摘要 |
<PICT:1114994/C1/1> An electrode or shield for a high-power electric discharge tube, e.g. a mercury arc rectifier, is constituted by a metal member surrounding and a shrink fit on at least a part of at least one body of graphite. A rectifier anode may have a single flanged cylinder of graphite, centrally apertured to permit the escape of air during the shrink fit process, and held within a cylindrical or frusto-conical recess in a steel member, which may itself be flanged to facilitate its support from the metal envelope of the rectifier (Fig. 1, not shown) and have cooling fins or a hollow jacket to permit the circulation either of coolant, or of a hot fluid to prevent mercury condensation on the anode surface upon switching off. Alternatively, the metal member may have an array of recesses with a separate graphite body shrunk fit in each (Fig. 2, not shown). A control electrode may be constituted by a graphite annulus through which the discharge passes, held in a steel ring, which may itself be shrunk fit within a further ring which forms part of the metal envelope, and which is of a metal having a lower thermal coefficient of expansion, whereby the radial pressure between the rings, and hence the heat transfer therebetween, increases with temperature (Fig. 3(b), not shown). In a further control grid, Fig. 4, a graphite disc held within a metal ring 28 is formed by a plurality of identical sectors, each with a separate aperture 26 therethrough, and each having an upstanding ridge 27, which ridges co-operate to provide a continuous circumferential shield. A sputter shield may be formed by a hollow graphite cylinder having one end shrunk fit within an annular channel formed in a metal plate. |
