US2177498A - Method of fabricating sealed containers - Google Patents

Description

Oct. 24, 19390 J H PAYNE 2,177,498

METHOD OF FABRICATING SEALED CONTAINERS Filed Nov. 20, 1936 Ifivfib or" John H. Payne,

by 77 (SJ S I ZAttOT'WQy Pan -a ea. 24, 1939 PATENT OFFICE METHOD OF FABRICATING SEALED CONTAINERS John H. Payne, Ballston Spa, N. Y., assignor to General Electric Company, a corporation of New York Application November 20, 1936, Serial No. 111,828

2 Claims.

This invention relates to a method of fabricating sealed containers, and more particularly for fabricating liquid contact switches of the'genera] type described and claimed in my copending application, Serial No. 759,527, filed December 28, 1934, of which the present application is a continuation in part.

The switches disclosed in my aforementioned copending application typically comprise a closed vessel consisting of a pair of dished wall members of thin metal separated and insulated from one another by an apertured disk of non-conducting material, a quantity of mercury beingprovided within the vessel to make and break an electrical circuit between the wall members. It is an object of the present invention to make it possible for such switches to be manufactured econornically and under conditions which substantially preclude the possibility of defective fabrication.

To this end I have provided a novel apparatusand mode of procedure by which the switch enclosing members may be accurately assembled and joined with a minimum of human supervision. 1

The invention as a whole may best beunderstood by reference to the following description taken in connection with the drawing, in which Fig. 1 is a perspective enlarged View showing certain of the switch parts in disassembled relationship; Fig. 2 is a plan view of apparatus suitable for the practice of the present invention; Figs. 3 to 8 are fragmentary views showing progressive steps in the switch assembly; and Figs. 9 and 10 illustrate the filling and sealing of assembled switch containers.

The switch assembly which has been chosen to exemplify the present invention comprises a refractory ceramic disk interposed between hollow metal wall members, the nature and appearance of these elements being well illustrated in Fig. 1. The wall members Ill and it each comprise a dished receptacle, typically of about'onehalf inch inside diameter, having an outwardly projecting flange thereon, such flanges being numbered l3 and M respectively. In order to facilitate mounting of the switch each wall member is further provided with a central recess (see recess I6) adapted to act as a socket for a cooperating supporting element.

The size of the dished receptacles is such as to correspond quite closely with that-of a circular ceramic body or disk 18 which may be clamped between flanges l3 and I4. An aperture 19 formed in the disk permits a closed electrical circuit to exist during certain positions or the switch while the imperforate portions of the disk form circuit-interrupting means during other positions. Accurate alinement of the wall enclosing wall members and the ceramic body as well as proper orientation of the opening 19 after assembly are facilitated by means of coacting index notches 2| provided in each of the separable parts.

The ceramic disk and the wall members should be of such materials that they are capable of being joined and sealed by a thermoplastic material for example, a glass. For the ceramic I have successfully employed a refractory oxide mixed with vitriflable material, a suitable combination being a mixture of about to per cent of magnesia and a complementary proportion of clay. The metal parts may suitably comprise an iron-chromium alloy, a very satisfactory composition being one in which the chromium forms from 26 to 30 per cent of the alloy. As a preliminary to the assembling process it is desirable to clean the metal parts with a grease solvent and to heat the flanges 13 and M with a gas flame to degas them and to oxidize the metal slightly. I

The assembling of the switch containers is car- 'ried out in accordance with my invention by means of a multi-station fabricating apparatus such as is illustrated in Fig. 2. This apparatus comprises, for example, a rotary turntable 24 driven intermittently in such a way that each switch container stops for a-definite interval at each of the circumferentially arranged stations (1, b, c, d, e, f, g, h, i and 7'. The operations performed at each of these stations will be set out more completely in the following:

Stations a and b are loading stations at which the supervisory operator may supply and position in proper relationship the principal elements of the switch assembly. These elements may for convenience be spread out on trays 25 and 26 where they are readily accessible to the operator. It will be seen by reference to Fig. 3 that at station a the ceramic disk I8 is positioned between the metal enclosing members 10 and H, these members being juxtaposed so that the flanges l3 and I4 extend outwardly beyond the disk to form an outwardly open annular channel whose bottom is formed by the outer periphery of the disk. This preliminary assembly is supported on the upper end of a hollow mounting or supporting member which comprises a rounded cap 28 fitting into the depressed face of the switch wall and which has an opening 29 communicating with an orifice 30 in such wall. The cap 28 is supported by means of a hollow metal tube 32 which is arranged to be vertically movable with respect to a supplemental mounting member 33 concentric therewith. This vertical motion, which may be accomplished by a camming surface 36 operating on the lower extremity of the tube 32, permits the relative elevation of the switch assembly to be modified from station to station in accordance with the requirements of the various operations.

After the metal wall members and theceramic disk are initially assembled as indicated in Fig. 3 the turntable is rotated to bring this assembly of parts to station b wherexthe supporting cap 28 is lowered so that the flange i 4 rests on the upper surface of the supplemental mounting member 33. This member, which is suitably of graphite, affords a rest for supporting adjacent the juxtaposed edges of the enclosing members l0 and H a premeasured quantity of glass, or other thermoplastic material, which is adapted to join with and seal the various switch parts. A particular material which has been found to be satisfactory for this puipose comprises a commercial lead glass containing about 20 per cent PbO and having a coeiiicient of thermal expansion of about x 10- centimeters per centimeter per degree centigrade. be provided in the form of a fillet or preferably a preformed closed ring 38 of such size as to be approximately co-extensive with theopening of the channel.

After the switch elements are positioned by the operator in the manner indicated, the loose assembly of separable parts is moved onward to the various succeeding stations of the fabricating apparatus. At stations c, d, and e the parts are heated at a controllable rate, for example, by means of gas burners 39 provided at the stations. In order to bring the various elements up tohigh temperature by slow degrees so that excessive thermal stresses will be avoided, the flame temperatures of the various burners may be progressively increased as one proceeds from station to station. In addition the individual switch supports may be continuously rotated about their vertical axes to subject all parts to uniform heating, such rotation being accomplished, for example, by a gear 40 secured to the member 33 as indicated in Fig; 5.

By the time the switch assembly as a whole has reached station e the ring 33 will have become sufiiciently plastic so that it starts to flow under the further application of heat. In order to controlthe nature of its flow, it is desired to exert internal suction by the application of a partial vacuum to the space enclosed by the switch wall members. This may be accomplished, for example, by connecting the tube 32 to a vacuum chamber adapted to exert the desired degree of suction. Connections for this purpose are illustrated diagrammatically in Fig. 2, in which the conduits 42 shown in dotted outline comprise vacuum ducts running to the various vertical tubular supports 32 from a central chamber 43 which may in turn be connected to a vacuum supply line 44. A combination of stationary ports 45 and movable ports 46 which are controlled by the rotation of the turntable 24 may be provided to secure the application or release of vacuum at any of the various operating stations. The suction thus developed may be communicated to the interior of the switch through the alined orifices 29 and 30 described in connection with Fig. 3.

Such material may suitably 1 As shown in 1 1g. 6, which illustrates the conditions prevailing at station a, the progressive collapse of the ring 38 will permit the thermo-. plastic material to be drawn into the annular channel defined between the flanges l3 and I4 5 and the peripheral urface of the ceramic disk l8.

If the various materials are properly related as specified in the foregoing description the final result will be to produce a hermetic seal between the thermoplastic material and the metal 10 wall members and at least a liquid-tight seal between the thermoplastic material and the ceramic disk. Under continued heating the soft- Fig. 8 'a particular mode of removal which has proven very satisfactory in actualpractice. A- '25 cording to the arrangement shown the completely assembled switch unit is subjected to a blast of air or other gas proceeding from a nozzle 41 positioned adjacent the operating station i. It being assumed that the vacuum has been removed 30 from the tube 32 at this station, a relatively slight air pressure is enough to topple the switch unit from its mounting and to caus'" it to fall on to a suitable removal means illustrated in Fig. 2 as a slide 49, whence it may be conducted to further 3:, processing apparatus. In the case illustrated this further apparatus comprises an annealing furnace 5| through which the completed switches are carried on a continuous conveyor, such asa belt 52.

After such annealing and cleaning operations as are required the switches may be filled with a desired amount oi. mercury or other liquid contact medium. This procedure, which is illustrated in Fig. 9, may suitably be accomplished 45 by means of an injection device 54 having a portion projecting through the opening 30 formed in the wall member N. Fig. 9 also shows each of the wall members as being provided internally with a small insert 56 of contact metal. These 50 inserts may suitably comprise iron finely coated with platinum and are of course provided before the assembly is begun. Their nature and utility are fully described in an application, Serial No. 47,299 of W. R. Walker, filed October 29, 1935. 55 After the addition of a suitable amount of mercury 53, the switch container may be permanentIy sealed, for example by welding into the orifice 30 a plug of a difiicultly fusible metal such as iron. The sealing operation, which may occur coinci- 60 dentally with the injection of a protective gas into the switch container, is fully described and claimed in my copending application, Serial No. 76,796, filed April 28, 1936. The nature of the sealing element is' indicated generally in Fig. 10, in which it is shown as comprising a small plug 6| welded in place in the orifice 30.

While I have described my invention in con-.

nection with specific apparatus and a. definite 2,177,498 within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of fabricating a hermetically sealed liquid contact device comprising a pair ispositively determined by said spacer, positioning a preformed solid glass member adjacent said flanges, said glass ember being coextensive with the opening of s d channel after assembly of the said members and spacer, and thereafter heating the said glass member to fusion temperature to fuse the same and producing a partial vacuum within the enclosure formed by said members and spacer to draw said fused glass member inwardly into contact with the spacer while said spacer maintains the spacing of said members constant.

2. The method of fabricating an electrical device comprising a pair of flanged metal enclosing members desired to be maintained electrically separated during at least certain conditions oi use of the device, which method comprises positioning said members on opposite sides of an insulating spacer with said flanges extending outwardly beyond said spacer to provide an outwardly directed channel defined by the said flanges and one surface of the spacer, placing about said channel a preformed conforming member of'solid thermoplastic material, heating said material to fusion temperature to fuse the same and simultaneously producing a partial vacuum within the enclosure formed by said members and spacer until the fused thermoplastic material has been drawn into the channel to form a seal between the members.

JOHN H. PAYNE.

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