Patent GB-778009-A (GB)
Title: Improvements in and relating to apparatus for exhausting electronic tubes and like envelopes
IPC: H01J9/385
Filed: 1955-05-27
Abstract: 778,009. Making electronic tubes. GENERAL ELECTRIC CO. May 27, 1955 [May 28, 1954], No. 15402/55. Class 39(2). [Also in Group XXVIII]  In a turret machine carrying a plurality of exhaust heads each having means for holding the exhausting tube of the envelope of an electronic tube in air-tight connection therewith while the turret is indexed through various operating stations, one of which is a leak-detecting station, each exhaust head is provided with a normally open valve and each is connected, in turn, to an exhausting circuit at the leak-detecting station which is provided with a pressure sensitive device for detecting a change in pressure within the envelope carried by the exhaust head halted at that station, so that in the event of a leak the device operates to close the valve in the head carrying the leaky envelope, thereby isolating that. head and preventing contamination of the exhausting circuit. In the example an indexing turret 1 mounted on a vertical post 4 is provided with a plurality of exhaust heads 3 carried by arms 2 and indexed counterclockwise through a succession of work stations before arriving at the leakdetecting station 6. Each head 3 includes an exhaust chamber 7 provided at its upper end with a compression head 15 which can be made to grip and hold an exhausting tube 16 inserted within its axial bore, the bottom of the chamber being adapted to be closed off by the normally open pinch-off valve 8 of rubber or like material. The valve 8, which is connected to one end of an exhaust line 9, is operated by a clamping-lever 10 mounted on a pivot 11 on the head 3 and co-operating with a lever 12 pivoted on the head at 13. Lever 12 carries an end roller 14 which is brought to bear upon the lever 11 when the lever 12 is swung through an arc, thereby pinching off the valve 8. A lateral passage 18 in each head 3 is connected to a line 19 through which compressed air may be admitted for ejecting the end of the sealed-off exhausting-tube and any fragments of glass from the chamber 7 after heat-sealing the exhausting-tube. The exhaust lines 9 connect their respective heads 3 to an associated inlet port 20, a series of which are spaced around in the rotatable portion 21 of a valve. 22 mounted about the post 4, the portion 21 being secured to the turret I and rotatable with it, whilst the stationary portion 23 is formed with outlet ports 25 corresponding with the ports 20 in number and spacing Oil glands 26 provide a vacuumtight seal between the relatively movable contact faces of the rotary valve 22. Between indexed positions the ports 20 and 25 are out of alignment, and communication and air passage across the valve are prevented. In the example there are three outlet ports 25 immediately in advance of the outlet port 25 corresponding to the leak-detecting station 6, the three being connected by a manifold 27 to the same vacuum pump 28; two outlet ports 25 immediately succeeding the leakdetecting station are connected by a manifold 29 to a vacuum pump 30, so that depending on the position of the levers 12 associated with the pinch-off valves 8 of the heads 3 which are halted at the stations stated, and the air-tightness of the envelopes held by those heads, the associated pumps 28 or 30 will evacuate the envelopes. The vacuum pump 31 at the leak-detecting station 6 is operated continuously to ensure substantially immediate evacuation of an envelope as soon as connection is made with it through a line 32 which includes a normally open solenoid valve 33. The line 32 branches out from a line 34 which has one end connected to the exhausting port 25 at station 6 and the other end connected to a pressure sensitive switch 35, which may be of the aneroid or other type and preferably can be pre-set to determine the pressure change at which it will act. The switch 35, which is mounted on the machine frame, controls a normally de-energized solenoid valve 37 which, when operated admits compressed air to a cylinder 40 and forces a piston 42 forwardly against the lever 12 of the head 3 at the leak-detecting station, thereby actuating the clamp 10 and closing the pinch-off valve 8 of that head. The switch 35 is in a series-connected electrical circuit from the A.C. supply 39, which includes the vacuum valve 33 and a lead 44 from the latter to one side of a microswitch 45, mounted on a portion 47 of the machine frame. The micro-switch 45 is spring-biased to the open position, and closed by a cam 48 which is rotated once for each indexing movement of the turret, the switch thereby being closed during the time each head 3 is indexed into and stopped at the leak-detecting station b. Thus the pressure-sensitive switch 35 is inoperative until the cam 48 closes the micro-switch 45 on the arrival of a head at the leak-detecting station. The provision of the vacuum valve 33 in the line 32 increases the sensitivity of the leakdetector by interrupting the evacuation of the circuit of the pump 31, so that the pressure - changing effect of a leak is accentuated.