US2740570A - Method and apparatus for exhausting and sealing-off lamp envelopes - Google Patents

Description

April 3, 1956 R. L. BREADNER ETAL 2,740,570

METHOD AND APPARATUS FOR EXHAUSTING AND SEALING-OFF LAMP ENVELOPES Filed Sept. 28, 1953 2 SheetsSheet l Flgi.

Inventors: RobeW-"l: L. Bveadnev,

Charles H.5imms, b5 W A Their A t torneg.

April 3, 1956 R. L. BREADNER ET AL 2,740,570

METHOD AND APPARATUS FOR EXHAUSTING AND SEALING-OFF LAMP ENVELOPES Filed Sept. 28, 1953 2 Sheets-Sheet 2 lnvervtors: Robewl: L. Breadner; Charles H.Simms, by W0 A Theiv Atto1-ne3 METHOD AND APPARATUS FOR EXHAUSTING AND SEALING-til LAl /iP ENVELGPES Robert Leonard Breadner, Kenton, and Charles Henry Simms, Twickenharn, England, assignors to General Electric ompany, a corporation of New York This invention relates to method and apparatus for the manufacture of electrical devices of the kind having a sealed envelope the gaseous pressure within which is less than one atmosphere in normal operation, and relates more particularly, though not exclusively, to the manufacture of low pressure mercury vapor fluorescent electric discharge lamps.

In the manufacture of electrical devices of the kind referred to, the envelope is usually evacuated and sealed ed by means of a glass exhaust tube projecting from a vitreous part of the envelope, the sealing off being effected after the introduction of the filling of gas and/ or volatilizable metal into the envelope, usually through the exhaust tube, if the device is of the kind requiring such a filling. This projecting glass tube, however, constitutes a weak point in the envelope since it is easily broken. For this reason, therefore, the exhaust tube is usually protected by covering it with a base or cap attached to the envelope, the base usually serving also to carry one or more terminals for the operation of the device, the terminals being connected to lead-in wires sealed through the envelope in the region of the glass exhaust tube.

The provision of such a base or cap is, however, not always convenient and it is sometimes desirable to manufacture a device of the kind referred to without a base. For protection of the glass exhaust tube in such case, the latter has then usually been arranged to project from the bottom of a recess formed by a re-entrant part of the envelope, and has been sealed off so that its tip lies within the recess. However, this is not always easy to effect, especially when the diameter of the recess is not much greater than that of the exhaust tube.

It is an object of our invention, therefore, to provide a method and apparatus for manufacturing an electrical device of the kind referred to which avoids the need for a projecting exhaust tube.

According to the invention, in the manufacture of an electrical device of the kind referred to, the envelope of the device is provided with an exhaust aperture in the wall thereof, and the said envelope wall is brought into abutment with the wall of an exhaust chamber, connected to an exhaust pump, so that the exhaust aperture registers with an aperture in the wall of the exhaust chamber, a gas-tight gasket being provided between the abutting wall surfaces of the envelope and exhaust chamber around the apertures therein. The device is then heated for degassing while being exhausted through the said exhaust aperture, and after the introduction of the enevelope filling, if any, a sealing plug or washer is applied to the exhaust aperture in the envelope wall so as to provide a hermetic closure thereof.

The sealing plug or washer for closing the exhaust aperture may be of a material, such as a non-porous rubber, sufficiently deformable, or so coated with a wax or grease, as to seal firmly and hermetically in or over the exhaust aperture under the external pressure resulting from the differential between the external atmospheric pressure and the sub-atmospheric filling pressure within States Patent ice the envelope and exhaust tube. Alternatively, the sealing plug or washer may be positively sealed to the envelope by the use of an adhesive. Preferably, however, the sealing plug or washer consists of, or is coated with a thermoplastic material and is applied to the exhaust aperture while the envelope is still hot from the degassing operation, so that the thermoplastic material softens or fuses under the heat communicated to it from the envelope and unites the plug or washer to the envelope so as to seal the exhaust aperture. The sealing plug or washer may, for example, be carried on a movable member within the exhaust chamber which member can be operated to apply the plug or washer to the exhaust aperture when the envelope processing has been completed.

The method in accordance with the invention may be applied to the manufacture of many dilferent kinds of vacuum or gas-filled electrical devices, and the nature and configuration of the apparatus used will depend on the particular device concerned, including the shape and nature of its envelope. The invention is, however, particularly concerned with the manufacture of devices Whose envelope includes a tubular glass part closed by a base or button of molded glass in which the exhaust aperture is provided and through which glass button pass lead-in wires to the interior of the device, and the invention will be further described with reference to an example of its application to the manufacture of a particular device of this kind, namely, a low pressure mercury vapor fluorescent electric discharge lamp, which example is illustrated in Figs. 1, 2 and 3 of the accompanying schematic drawings.

Further objects and advantages of our invention will appear from the following detailed description of a species thereof and from the accompanying drawings in which:

Fig. l is a fragmentary sectional view of an apparatus for performing the method of our invention;

Fig. 2 is a section, at right angles to the Fig. 1 section, of a part of the apparatus shown in Fig. 1; and

Fig. 3 is a plan view of the part of the apparatus shown in Fig. 2.

Referring now to Fig. 1, the apparatus shown comprises an exhaust chamber 1 of generally cylindrical shape which is arranged to be connected to an exhaust pump (not shown) through a side-tube 2. The base of the exhaust chamber is arranged to fit over an aperture 3' in a baking oven 3 for a low pressure mercury vapor fluorescent electric discharge lamp 4, the chamber 1 being thermally screened as far as possible from the oven 3 by a baffle plate 5, and the lower part of the chamber being provided with Water-cooling means 6. Only the upper part of the oven 3 and lamp 4 have been shown in the drawing inasmuch as the lower parts thereof are not relevant to the invention.

The lamp t comprises a tubular glass envelope 7 coated internally with fluorescent material (not shown) and closed at each end by the sealing thereto of a pressed glass base or end closure member 8 in the shape of a button or disc. These pressed glass bases or buttons carry the lamp terminal pins and electrodes, but since the section shown in Fig. 1 is taken at right angles to the line joining the terminal pins, the details of the pin and electrode which would normally be present in the sectional view have been omitted from the base 8 shown in Fig. 1 for the sake of not obscu'rin other details. The end closure member or base 8 at one end of the lamp (i. e., at the upper end of the lamp shown in Fig. 1) is perforated at its center by an aperture 9, the outer part of which is stepped to form a seating shoulder 9' for a closure washer it) which is subsequently applied to seal oh? the aperture 9, as will be described hereinafter.

The base or bottom wall of the chamber 1 is perforated by an aperture 11 around which is fitted a rubber gasket ring 12, and the lamp 4 is supported within the oven 3 with the base or end closure member 8 thereof pressed against the gasket ring 12 and with the apertures 9 and 11 in register.

A mercury chamber 13 is formed at the top of the exhaust chamber 1 by a transverse partition 14 therein. The mercury chamber 13 is closed at its top by a cover 15 and is partly filled with mercury 16.

Through one part of the partition 14 and cover 15 passes a mercury doser in the form of a rod 17 having a recess 18 formed near its lower end. The rod 17 has a mercury-tight but slidable fit through holes formed in the partition 14 and cover 15, and the upper part of the rod extends into a glass housing or tube 19 the upper end of which tube is closed and the open lower end of which is sealed to a ring flange 20 of a suitable matching metal attached to the cover 15. At its upper end the rod 1'7 is attached to a magnetic armature 21 within the glass tube 19, and this armature 21 cooperates with a solenoid 22 fitted externally around the glass tube 19 so that on energization of the solenoid the armature 21, and with it the rod 17, is drawn down against the bias of a coil spring 23 which returns the armature to the upper position on de-energization of the solenoid. The arrangement is such that normally the recess 18 in the rod 17 lies in the mercury chamber 13, but on energization of the solenoid 22 the rod 17 moves downward so as to carry the recess 18 into the exhaust chamber 1, where the globule of mercury carried down within the recess falls out into a crank-shaped (i. e., oifset) and pivoted glass funnel 24 positioned therebelow to receive it.

The tunnel 24 is supported from the side of the exhaust chamber 1 by means of a bracket 24' to which it is pivoted for pivotal movement in a vertical plane, and it is crank-shaped, as shown, so as to extend over the center of the aperture 11 in the base wall of the chamber 1 and convey the drop of mercury into the lamp envelope through the aperture 9 in the end closure wall 8 thereof. The funnel is accurately centered by means of an adjusting screw 25 which works through a vacuum-tight bushing in the Wall of the chamber 1 so as to bear against the funnel on the upper side of the funnel pivot, and by means of a torsion spring 26 on the lower side of the funnel pivot which biases the funnel into engagement with the adjusting screw 25.

Through vertically aligned holes formed in another part of the partition 14 and cover 15 passes a movable seal-off member in the form of a rod 27 which has a mercury-tight but slidable fit within the said holes. upper part of the rod 27 extends into a glass housing or tube 28 the upper end of which is closed and the open lower end of which is sealed to a ring flange 29, of a suitable matching metal, attached to the cover 15. At its upper end the rod 27 is attached to a magnetic armature 30 within the glass tube 28, and this armature 30 cooperates with a solenoid 31 fitted externally around the tube 28 so that on energization of the solenoid the armature 30, and with it the rod 27, is drawn down against the bias of a coil spring 32 which returns the armature to the upper position on de-energization of the solenoid.

Within the exhaust chamber 1 the rod 27 is oiiset or cranked so as to provide a length of rod 33 lying directly over the center of the aperture 11 in the base wall of the chamber 1, the end of the rod 33 being arranged to hold the washer 10 by any suitable means, for example by use of an adhesive. A finger 34 attached to the side of the offset part 33 of the rod 27 is arranged to abut against the side of the funnel 24 on downward movement of the rod following energization of the solenoid so as to pivot the funnel about its pivot against the bias of the spring 26 and carry the lower offset end portion of the funnel out of the path of downward movement of the washer 10, the downward movement of the rod 27 being suthcient to press the washer into the seating 9 in the The outer side of the aperture 9 in the end closure member 8 of the lamp 4. t

The rods 17 and 27 are both provided with longitudina bores 35 and 36, respectively, which communicate with g the interiors of the glass tubes 19 and 28 and with the mering process is complete, the usual argon filling forthe' lamp is introduced thereinto through the side-tube 2. The solenoid 22 is then energized and de-energized a number of times to feed the required mercury dosage into the lamp 4, after which the solenoid 31 is energized to lower and force the washer 10 down into its seating 9' in the lamp end closure member 8.

The washer 10 is made of or coated with a suitable thermoplastic material so that on contact with the hot glass of the base 8 the thermoplastic material softens or fuses and causes the washer to adhere to the glass and The washer closure member 8 of the lamp envelope. 10 may consist, for example, of a metal disc coated with a layer of polymerized ethylene, or of glass coated with such a resin or with a glass solder. Alternatively, a greased washer 10 of non-porous rubbermay in some cases be used.

After the sealing of the washer 10 into the aperture 9 of the lamp envelope, the pressure within the chamber 1 is returned to atmospheric and solenoid 31 de-energized, the rod 27 rising and leaving the washer 10 attached to the end closure member 8 of the lamp envelope, after which the lamp 4 may be Withdrawn from the oven 3.

Figs. 2 and 3 of the drawing show how the lamp 4 is accurately positioned relative to the aperture 11 in the base wall of the exhaust chamber 1, only the relevant parts of the apparatus being shown. The section in Fig. 2 is taken along the line joining the external rigid terminal pins 37 with which the envelope end closure member 8 is fitted. The pins 37 fit tightly into recesses 37' formed on the outer side of the end closure member 8, and are held in. position by the soldering thereto of wires 38 which pass through the hollow interiors of the pins and are sealed through the end closure member 8 where they support one of the lamp electrodes 39 within the envelope, as described in our co-pending U. S. application Serial No. 344,522, filed March 25, 1953, and assigned to the assignee of the present invention.

To the opposite sides of the aperture 11 are attached arcuate projections 40 of insulating material the centers of the peripheries of which are provided with grooves 41 located diametrically opposite one another and along I which the terminal pins 37 of the lamp are arranged to be inserted. The grooves 41 are covered by leaf springs 42 which are arranged to bear resiliently against the terminal pins 37 of the lamp 4. The leaf springs 42 are connected to leads 43 which are in turn connected to terminals 44 vacuum-tightly hushed through the wall of the exhaust chamber 1, the terminals 44 not appearing in Figs. 2 and 3 but one being shown in Fig. 1. These terminals 44 are used for the supply of electric heating current to the lamp electrode 39 during the processing or the lamp. 7

It will be appreciated that the arrangement described may readily be adapted for the mass production of fluorescent lamps, exhaust chambers 1 as shown being arranged to index onto the end of each of a number of lamps 4 as they are fed into an elongated baking oven 3 through which they pass, the chambers 1 travelling along with the lamps 4, and the solenoids 22 and 31 being arranged to be operated automatically by the action of suitable cam or trip contacts at the appropriate instants. The offset lower end portion 33 of the rod 27 may be arranged as a magazine containing a plurality of sealing washers and arranged to feed a fresh washer into the operating position after each sealing operation.

It will be appreciated that with modern high-speed exhaust pumps, the exhausting of the lamp 4 through a relatively wide aperture such as the aperture 9 in the end closure member 8, rather than through a relatively narrow exhaust tube as usual heretofore, enables the exhaust process to be completed more quickly and this enables the rate of production of lamps to be increased.

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

1. The method of exhausting, dosing with readily vaporizable metal, and sealing-off a lamp envelope or similar device which comprises forming the envelope with a relatively large exhaust aperture in a wall thereof, disposing within an exhaust chamber a sealing plug corresponding in configuration to and having a tight fit with the said exhaust aperture, connecting the exhaust aperture of the envelope in vacuum-tight communication with a relatively large exhaust opening in the said chamber, exhausting the said chamber and the interconnected envelope while heating the latter to degasify it, releasing the required dosage of a readily vaporizable metal into the said chamber and directing it therefrom through the exhaust aperture of and into the envelope, and then transpositioning said sealing plug from the exhaust chamber into the said exhaust aperture in the envelope to thereby seal-01f the said aperture.

2. The method of exhausting, dosing with readily vaporizable metal, and sealing-off a lamp envelope or similar device which comprises forming the envelope with a relatively large exhaust aperture in a wall thereof, disposing within an exhaust chamber a sealing plug having a heat softenable outer surface corresponding in configuration to and having a tight fit with the said exhaust aperture, connecting the exhaust aperture of the envelope'in vacuum-tight communication with a relatively large exhaust opening in the said chamber, exhausting the said chamber and the interconnected envelope while heating the latter to degasify it, releasing the re quired dosage of a readily vaporizable metal into the said chamber and directing it therefrom through the exhaust aperture of and into the envelope, and then transpositioning said sealing plug from the exhaust chamber into the said exhaust aperture in the envelope while the latter is still in a heated condition to cause the heat softenable outer surface of the plug to soften and adhere to the wall of the exhaust aperture completely therearoundwhereby to seal-off the said aperture.

3. Apparatus for exhausting and sealing-oft a lamp envelope or similar device having an exhaust aperture in the wall thereof comprising, an exhaust chamber having an exhaust opening in its bottom wall, means including a sealing ring located on the bottom wall of the exhaust chamber and bordering the said exhaust opening therein for connecting the exhaust aperture of said envelope in vacuum-tight communication with the exhaust opening in the exhaust chamber, a mercury dispenser mounted on said exhaust chamber and operative upon actuation to discharge a droplet of mercury into said exhaust chamber at a point offset to one side of the said exhaust opening therein, guide means in said exhaust chamber for receiving the said droplet of mercury and guiding it into the said exhaust opening, said guide means normally extending to a point directly above and in vertical alignment with the said exhaust opening and being movably mounted within said chamber for displacement to a position out of vertical alignment with said exhaust opening, a carrier member vertically reciprocable within the exhaust chamber and normally held in a raised position directly over the exhaust opening therein and detachably carrying at its lower end, in vertical alignment with the said exhaust opening, a sealing plug for sealing-off the exhaust aperture in the envelope, and means cooperating with said carrier member to first move it downward through the said opening in the exhaust chamber to insert the sealing plug into the exhaust aperture in said envelope and to then return the carrier member to its normal raised position.

4. Apparatus of the character set forth in claim 3 and comprising, in addition, an oven disposed immediately beneath the said exhaust chamber and enclosing the lamp envelope associated therewith to heat the said envelope to an elevated temperature.

5. Apparatus for exhausting and sealing-0E a lamp envelope or similar device having an exhaust aperture in the wall thereof comprising, an exhaust chamber having an exhaust opening in its bottom wall, means including a sealing ring located on the bottom wall of the exhaust chamber and bordering the said exhaust opening therein for connecting the exhaust aperture of said envelope in vacuum-tight communication with the exhaust opening in the exhaust chamber, a mercury dispenser mounted on said exhaust chamber and operative upon actuation to discharge a droplet of mercury into said exhaust chamber, a funnel pivotally mounted within said exhaust chamber to pivot about a horizontal axis, said funnel having an offset lower discharge end, spring means within said chamber normally holding said funnel in operative mercury-feeding position with its upper end positioned to receive the mercury droplet as it is released by the said dispenser into the exhaust chamber and with its offset lower end positioned directly above the exhaust aperture in the associated lamp envelope to guide the mercury droplet into the said exhaust aperture, a carrier member vertically reciprocable within the exhaust chamber and normally held in a raised position directly over the exhaust opening therein and detachably carrying at its lower end, in vertical alignment with the said exhaust opening, a sealing plug for sealing-off the exhaust aperture in the envelope, said carrier mem- References Cited in the file of this patent UNITED STATES PATENTS Powell Mar. 22, 1881 Rossignol Sept. 26, 1922

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