Patent GB-695783-A (GB)
Title: Improvements relating to apparatus for forming thin films of metal within evacuated envelopes, such as cathode ray tube envelopes
Inventor: BENNETT HAROLD WALTER
IPC: H01J9/20
Filed: 1949-08-20
Abstract: 695,783. Applying metallic coatings within cathode ray tubes &c. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Aug. 21, 1951 [Aug. 20, 1949], No. 21684/49. Class 39(ii) Apparatus for forming a metallic film, e.g. of aluminium upon a surface within an envelope such as a cathode ray tube comprises a plurality of pumping or evacuating heads mounted on a platform and each provided with means for supporting vaporizable metal and means for supporting an envelope in a vacuum tight manner with the vaporizable metal within it, means being provided for moving the platform in timed sequence so as to evacuate the envelopes, apply heating current to vaporize the metal, and then to release the vacuum within the envelopes. Preferably the heating current is applied in two stages, the first stage effecting the outgassing of a vaporizing-filament which, together with a bead of aluminium, is renewed for each tube operated upon, and the-second stage resulting in the vaporization of the aluminium. In the example each pair of heads on a rotary turret is associated with a. unit comprising a control valve system and a motor-driven evacuating pump. The turret consists of two circular horizontal platforms 3, 4, Fig. 1, spaced by vertical webs 5 and provided with a central journal to receive a vertical shaft 1 about which the turret is rotated intermittently by a Geneva mechanism comprising members 19-21 driven by a worm and pinion 24, 23. Eight units, each comprising an electric motor 44, low pressure pump 45 and high pressure diffusion pump 91 with relative electromagnetic control valves, are equi-spaced around the periphery of the platform 4, each unit being associated with a pair of working heads 9 mounted on an annular platform 10 supported by brackets 11. Each of the pumping heads 9 has a hollow well portion 48, Fig. 2, formed with a shoulder 49 to support an annulus 51 of rubber or other material upon which a sleeve 52 is positioned, so that when the neck of an inverted cathode ray tube has been inserted into the well a handle 60 can be depressed to swing a bifurcated arm 53 downwardly and cause bolts 56 at the ends of the arms to bear upon the upper edge of the sleeve 52, thereby deforming the rubber annulus 51 to form an airtight seal around the neck of the cathode ray tube. A hollow tube 46 coaxial with the well 48 forms a socket to receive a pair of current conducting members 70, 71, Fig. 4, which are insulated from one another and formed with rigid fingers 76, 77 respectively, each of these fingers having a spring-pressed finger 79 pivotally mounted on a pin 80 and normally in close contact with the upper end of its supporting member 76 or 77. A plate 81 at the bottom end of each finger 79 provides manual operating means whereby the upper end is moved outwardly to enable an end of a. filament to be inserted and gripped beneath it before a cathode ray tube is positioned in the holder. Current is led to one end of the filament through a metal rod 62 which is coaxial with the holder and connected to terminal 64 through a lateral bar 63; the other end of the filament is earthed. A series of pillars 30 below the periphery of the turret support concentric arcuate cam rails 31-34 which are engaged at predetermined intervals by cam-followers 35-38 which operate switches 39-42 controlling the energization of electromagnetic valves which control the evacuating system. A valve 87, Fig. 3 (not shown) connects a pair of heads to a low pressure pump 45, Fig. 1, a second valve 90 Fig. 3 (not shown) is energized, to connect to a high-pressure diffusion pump 91, and a third valve 92 connects the high pressure pump with the low pressure pump. A further valve 96, when energized, connects to the atmosphere. Energizing current for the motors 45 and electromagnetic valves is supplied over contact fingers 15 on the turret and slip rings 16 on the rigid central axis. Filament heating current is supplied by a finger 29 engaging a contact rail 28 supported on pillars 27. Specifications 669,735 and 686,096, [Group XL(a)], are referred to.