GB510993A - Improvements in and relating to the coating of articles by means of thermally vaporised material - Google Patents

Abstract

510,993. Coating with metals or metal compounds; cleaning metals. BERGHALTS, B. Aug. 23, 1938, No. 24796. Convention date. Aug. 26, 1937. [Class 82 (ii)] [Also in Groups XI and XXXVI] In coating articles by means of thermally vaporized material the vaporization is effected in a reduced pressure of 40-0.001 mm. of mercury, preferably 5-0.01 mm., the articles being connected up permanently or temporarily as a cathode of a glow discharge and the voltage being so chosen that they are completely covered by the glow. The vaporized material may be a metal, alloy, or a metal compound, e.g. a carbonyl or oxide. When a direct current voltage is used the positive pole is connected to a separate electrode or to the vacuum vessel; with alternating current half of the articles may be connected to one pole and half to the other. The residual gas is preferably one which does not react with the material to be vaporized, e.g. argon or hydrogen, and the voltage, which may be from 400 to 20,000 volts, is chosen according to the temperature to be imparted to the articles. The vacuum vessel is preferably cooled and may be provided with heat insulation. The articles, if metallic, may be treated for a time in the discharge prior to the vaporization in order to remove all impurities such as oxides, traces of fat &c. The metallization may be carried out in the apparatus shown, comprising a vessel 1 with a cover 2 which is closed by eccentric members 4 and packing 3, a cooling air passage being provided in the cover. The vessel is exhausted at 5, any desired gas being introduced at 6. The material to be vaporized is placed in a crucible 7 which has a lining 8 and is heated by a hollow cooled high frequency coil 9, the ends of the coil being introduced through the cover 2 by lead-in conductors 10, 11, each having metallic screening sleeves 12, 13, covered by a cap 14 and provided with insulating members 15, 16, a sealing member 17, and a screw-threaded clamping ring 18. The articles 20 to be metallized are mounted on a hollow lead-in conductor 21 which is cooled by fluid, e.g. water, entering at 22 and issuing at 23. Around the conductor are metallic screens 24, 25, arranged at such a short distance apart that no glow discharge takes place in the intermediate spaces. Insulating and sealing rings 26, 27 and a clamping ring 28 are provided. A cooling space 29 is formed in the vacuum vessel, cooling medium entering at 30 and issuing at 31. To produce the glow discharge one pole of the secondary 37 of an alternating current transformer 38 may be connected through a switch 39 to the conductor 21 and the other pole through a resistance 40 and switch 41 to the sleeve 24, or the negative pole of a source of direct current 32 is connected to the conductor 21 through a switch 33, the positive pole being connected either to the sleeve 24 or to the wall of the vacuum vessel.