Patent GB-1080235-A (GB)
Title: Method of making sealed switches
IPC: H01H11/00
Filed: 1964-09-17
Abstract: A method of automatically making sealed switches comprises the steps of heating one end of a glass tube, then concurrently heating both ends of the glass tube for a given period, terminating the heating of the one end of the tube to permit the softened glass at the one end to cool and form a seal for one magnetic element inserted therein, while continuing the heating of the other end of the glass tube, and subsequently terminating the heating of the other end to permit the glass to cool and form a second seal for the other magnetic element inserted therein.  In one cycle of operations, a completed switch is held by its upper magnetic element in an upper chuck 32a of a head 24, a number of which are carried at spaced positions on a rotating table, a glass holding chuck 36a and a lower element holding chuck 34a on the head being open.  Cam means causes the upper chuck 32a and its finished switch to be moved vertically away from upper and lower heating coils 54, 40 about the chuck 36a.  At this point, the chuck 36a and upper heating coil 54 are are also moved vertically away from the chuck 34a, the coil 40 being maintained in position by springs 50.  Then the unit, comprising chuck 36a and coils 54, 40, is moved vertically whilst simultaneously a heavy flow of inert gas is passed through nozzles 76 (Fig. 5) in a member 42 below coil 40 and the upper coil 54 is energized. Chuck 32a is then opened to release the switch and a cam means 66, 68 lifts the coil 54 against springs 60 away from chuck 36a.  A glass tube 18 is then fed into chuck 36a which closes and the already energized coil 54 is returned to its place around the top end of the tube 18 which begins to soften.  An upper magnetic element 14 is then fed to chuck 32a and held above the glass tube 18, and a lower magnetic element 16 is fed to chuck 34a and held below the tube 18.  The chucks 32a and 36a with the member 42 are then moved downwards until the member 42 is stopped by engagement with the lower chuck 34a, when further lowering of the chuck 36a compresses the springs 50 and allows the end of the tube to be received in the heating coil 40 and to surround the lower magnetic element. At the same time, the upper magnetic element is pushed into the softened upper end of the tube. A very short burst of a high volume of the gas at a high velocity is then passed through the tube to eject any foreign particles.  The gas flow is then reduced to a third low rate whilst simultaneously the coil 40 is energized.  Both ends of the glass tube 18 are heated together for about the next 70 degrees of rotation of the head 24.  The element 16 is moved slightly to bring it into contact with element 14. The chuck 32a is open at 150 degrees of rotation of the head and the coil 54 is de-energized to <PICT:1080235/C1/1> <PICT:1080235/C1/2> allow the top seal to cool.  The head 24 now passes into the field of a permanent magnet so as to align the magnetic elements 14, 16. After 225 degrees of rotation, the head moves out of the magnetic field.  At 265 degrees, the gas is shut off and the coil 40 de-energized to allow the lower seal to cool.  Just before completing the full 360 degrees of rotation the chucks 34a and 36a open and chuck 32a closes. To prevent any "blow-outs" occurring whilst the glass tube ends are still soft, the gas may be preheated.