US2447158A - Sealing-in method for lamps and similar devices - Google Patents

Description

- Aug. 17, 1948. P, o, CARTUN Y 2,447,158

SEALING-IN METHOD FOR LAMPS ANI? SIMILAR DEVICES Filed Aug. 31, 194.1!`

Patented Aug. 17, 1948 SEALING-IN METHOD FOR LAMPS AND SIlVIILAR DEVICES Paul O. Cartun, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Y appiicauon August 31, 1943, serial No. 500,675

(o1. Lie- 78) 3 Claims.

rI'his invention relates to the manufacture of devices having thermoplastic bulbs or envelopes, including electrical devices such as incandescent lamps and various kinds of discharge devices, which at present usually have vitreous envelopes. The invention aims at simplifying the manufacture of such devices, reducing their cost, and improving their structural characteristics, including the inlead seals where the current supply conductors pass through the envelope Walls. The invention is especially adaptable and advantageous for rather small lamps and devices, and particularly very small glow lamps and lamps used for telephone switchboards. The invention is concerned with an operation corresponding to what in lamp manufacture is generally known as sealing-in, and it is hereinafter explained with particular reference to its use in telephone lamps having incandescent filaments as their electric translation means.

IThe manufacture of small vitreous electrical devices such as telephone lamps presents special diiculties, since their smallness makes it impracticable to employ the usual stem are type of construction generally used for lamps of ordinary sizes, in which the current leads to the filament or other electric translation means of the device and one or more auxiliary supports (if required) are fused into a sealed-up end of a hollow glass stem-tube Whose other end is flared, and an exhaust tube (as it is' termed) opens through the inlead seal, this assembly or mount being afterward fused and sealed into the neck of a glass bulb. In very small lamps, the mount is reduced to a mere pair of inleadwires joined by an insulative bead and interconnected by the filament; and sometimes even the bead may be omitted.

In the butt-seal type of construction, as it is called, the simplified mount just described is inserted into the bulb neck with its lead wires bent apart to extend outward across the end of the bulb neck Wall, and a tube about as large as the bulb neck is butted endwise against the latter and fused thereto. This tube is used as an exhaust tube and is afterward sealed off to form an end closure for the bulb; and the radially projecting lead wires are bent to extend parallel with the bulb axis and thus facilitate basing the lamp.

In other suggested types of construction, an exhaust tube smaller than the bulb is inserted into the bulb neck between the outward extending lead wires of the mount, and the bulb neck is fused around this tube and unitedrwith it.

OneV method proposed for thus uniting the bulb neck and -tube is to pinch in the softened bulb neck to the less softened tube end by suitable clamps brought together around the neck; another proposed method is simply to fuse the bulb neck around and t0 the tube end, which may be enlarged to minimize the necessary contraction of the neck and may have the mount leads fused into the periphery of the enlargement. Various measures have been proposed to prevent the tube from contracting to the point of being closed up when the bulb neck is sealed to it, such as blowing air in through the tube at just the right moment, or inserting a pin into the tube to keep it open, or preliminarily enlarging the end of the tube suiciently to obviate such closure.

However, all of these methods present drawbacks of one kind or another, which it is unnecessary to notice in detail, except to remark that the neck-pinching, air-blowing, pin-inserting, or similar measures that have been proposed to prevent closing up the'exhaust tube all entail extra operations, which must be timed with some nicety in order to be successful.

In contrast with the methods above described, I have found that it is possible to fuse and seal an exhaust tube into a bulb neck by externally heating the bulb neck and allowing-it to contract and coalesce'spontaneously with the exhaust tube end extending into it--provided al ways that the heat is suitably applied, as explained hereinafter-without any of the special measures or complications above mentioned, Incident to this, a simple mount such as above mentioned may be sealed in with its lead wires extending parallel with the lamp axis out through the fused vitreous material forming the seal. When this last is done, the" lead wires of the mount can be preliminarily attached to the tube end by fusing and embedding them sidewise in the vitreous material of the tube; or they can be preliminarily attached to the inside of the bulb neck in a somewhatsimilar way; or they may simply extend outloos'ely between the bulb neck wall and the smaller tube end within said neck, Without any preliminary attachment to either part.

Various other features and advantages of the invention will appear from the following description of a species or mode of practice of the invention, and from the drawings.

In the drawings, Fig. 1 is an exploded tilted or perspective view of parts suitable for the fabrication of one type'of electrical device according to this invention, in relations to one another that indicate one preferred mode of assembly; Fig. 2 is a view of the parts assembled in proper relations for a sealing-in operation according to the invention, also showing somewhat diagrammatically a suitable form of apparatus for use in this operation; and Figs. 3 and l are top and bottom plan views of the beginning and end of the sealing-in operation, onlythe lamp parts and the gas burners and flames being shown.

Figs. 5 and 6 are side views of a lamp device after sealing-in according to the invention, Fig. 5 being taken parallel with the plane of the lead wires, and Fig. 6 at right angles tofthis plane; and Fig. 7 is a side View of a completed lamp after exhausting and sealing or tipping off.

Fig. 1 is a sort of a exploded View of component parts suitable for the fabrication of a small switchboard lamp in accordance with my invention: viz., a bulb or bulb blank. i5 consisting of a short length` of soft glass vtubing with a hemispherical closed end I I, and with a mouth or neck portion I2 at its other end which is h'ere shown unreduced and of the same size as the rest of said bulb blank, though this is not essential; an exhaust tube or tubulature I3 consist-- ing of a plain, straight length of soft glass tubing; and a mount M shown as consisting f nlead wires I5, I fused into opposite sides of an interconnecting insulative flattened glass bead i5, with a tungsten lament Il connected between th'e inner ends of the lead wires. As here shown, the portions of the lead wires I 5, I5 at the filament side of the bead I6 are straight and parallel, while the portions at the other side of said bead are offset and spread apart at I8, some distance from the bead, as well as at I9 close to it. In Fig. l, the parallel outer portions of the leads I5, I5 beyond th'e oifsets I3, I8 are shown so spaced apart as to admit the tube I3 between them with its end against said offsets, and the tube I3 and mount M thus assembled are shown just below and aligned with the bulb neck I2, readir for introduction intothe bulb I8. However, it will be understood that the mount M might rst be inserted into the bulb Ill by itself, and the tube I3 then inserted endwise into the bulb neck I2 between the outer `lead portions.

As illustrative of the smallnessf of the parts for a switchboard lamp, it maybe vmentioned that the bulb blank' lil in Fig. limay consist ,of a 1-inch length of-soft glass tube 1A; inch inexternal diameter, with a bcre'of aboutV 3/16 inch; the tube E3 may consist of a 4% inch length' of soft glass tube 1A; inch in external diameter, with a bore of rather more than e inch; the lead wires l5, i5 may be l'l/is inch lengths of ,dumet wire of 1) mil size, with their inner portions a little over 116- inch apart; and the beadv lvmay have aV major dimension of about 1%; inch parallel with the plane of the wires I5,v I5. Of course these dimensions and lmaterials are illustrative merely: for example, iron lead wiresv I5, I5 might be used, with a suitable special glass for the parts Ill, I3; andthe invention might be used in making lamps of much larger size than switchboard lamps. Y

Fig. 2 shows the parts I0, I3, M- assembled in proper relations ready for sealing 1in. Thev bulbblank IB `is shown as held vertical in an upper chuck device comprising some five spring ngers 2I formed by longitudinal slits in the wall of a resilient metal tube of -suitable bore, while the tube I3 is shown as held vertical'in a lower hollow upright spindle. 22 in axial alignment with th'e device 20. The mount M is shown straddled on the upper end of the tube I3, with the lower portions of its leads I5, I5 held loosely in corresponding longitudinal holes 23, 23 in the end of the spindle 2|, at opposite sides of its axial bore for the tube I3 and parallel therewith. The upper end of the tube I3 extends into the open lower neck end of the bulb I0, while the lead wires I5, I5 extend downward between these parts and along the tube I3, diametrically opposite one another. A distance about equal to its own diameter is suitable for the tube I3 to extend within the bulb neck I2.

I have found that by externally heating the bulb'neck I2 in a suitable manner, it can be softened and caused to contract or shrink spontaneously into internal contact with the tube I3, and the tube can be softened so as to coalesce spontaneously with the softened bulb neck, While closing up of the tube opening or bore can be forestalled and prevented by substantially stopping the 'application of heat promptly, before the unified parts can contract suiciently to close the'tube opening. For this it is necessary to keep down or reduce the application of heat when the softened bulb neck I2 shrinks into contact with the end of the tube I3, so that th'e latter is only softened to coalesce with the former rather gradually, instead of being softened so rapidly or to such a degree that the united parts rapidly contract and close up the tube bore before the contraction can be stopped by the quick cooling that ensues when the heating is stopped.

The regulation and variation of the heating as just indicated can be brought about automatically by directing one or more external heating flames 25 tangentially of the bulb neck as shown in Fig. 2 preferably rotating the flame and the bulb relative to one another so as to heat the neck evenly and uniformly all around. A goo-d arrangement for this purpose which is shown in Fig. 2 consists of a pair of gas burners 26, 25 aimed oppositely but out of line so that their slender rat- tail flames 25, 25 play parallel with one another' tangentially and crosswise of the neck I2 at either side thereof, initially touching the unreduced neck as shown in Fig. 3. As shown, each burner 26 has three small, parallel, horizontal flames 25 lying in a vertical row one above another, so that they heat the bulb neck I2 over a substantial vertical width. With these flames ysuitably proportioned and aimed, they initially heat up and fuse or soften the neck I2 rather quickly so that it spontaneously contracts around the tube I3 and th'e lead wires I5, I5, which are thus embedded in the fused glass of the neck. As the neck I2 contracts in this way, it also draws inward away from and out of the heating flame(s) 25 as shown in Fig. 4, thus automatically reducing the application of heat to said neck I2 while the tube I3 is softening under the heat-imparted thereto from or througth the softened neck, and the parts are coalescing into a unied fused joint 2l as shown in Figs. 5 and 6. If the ames 25, 25 are kept small and are so aimed and spaced apart that they play nearly tangentially on the neck I2 before it begins to contract, as in Fig. 3, then the mere drawing away of Vth'e neck I2 out of the flames, as shown in Fig. 4, when it contracts reduces the application of heat sufficiently; so that it is generally unnecessary to shift or reduce the flames themselves during the operation.

Whenthe parts i2, I3 coalesce-to form the joint 2l, the application of heat thereto fromthenames 25, 25 is virtually or substantially stopped, as by moving the burners 26, 26 aside out of range of the joint, or by quickly turning down the flames so that they at most afford no more than an annealing heat while the joint cools off. Even though the tube opening or bore may contract to a somewhat reduced throat in the joint 21, as shown at 28, this is of no practical consequence in view of the small internal volume of the bulb I0, The joint 21 is, of course, smaller in external size than the unreduced part of the neck I2 and of the bulb I0, though larger than the tube I3. Owing to the presence of the lead wires I5, I5, which hold the glass and prevent it from contracting uniformly all around, the joint 21 is of an elongated or oval cross-section, rather than truly circular-as suiciently appears from Figs. 4, 5, and 6.

While either the burners 26, 26 or the chuck and spindle 20, 22 might rotate to equalize the heating of the parts I2, I3 al1 around, it is generally simpler, perhaps, to rotate the chuck and spindle. For this purpose, they lare shown in Fig. 2 as interconnected to revolve together by toothed gearing 29, 29 and an upright shaft 30. The shaft 30 (and through it the parts 20, 22) may be driven at Vconstant speed by any suitable means, not shown.

After completion of the sealing in operation as shown in Figs. 5 and 6, the lamp may be exhausted through the tube I3 in the usual Way and then sealed or tipped olf close as shown at 33 in Fig. 7, thus completing it ready for basing.

Besides the extreme simplicity of the operations involved in its manufacture as described, the device as shown in Figs. 5, 6, and 7 offers the advantage that its leads I5, I5 naturally extend in the direction of the bulb axis and within the limits of its cross-sectional area'as axially projected, instead of extending out radially as in the buttseal type of construction above mentioned. This simplifies the operations involved in basing the device. It also obviates any bending of the leads I5, I5 just outside their seals in the glass, which is necessary with the butt seal construction, and often results in damaging the seals so that they develop leaks. In addition, the extent of embedding glass 21 along the leads I5, I5 is greater, giving greater assur-ance of gas-and-vacuumtight lead seals, and obviating risk of short-circuiting a lamp in basing by contact of both leads I5, I5 with a base shell (not shown),

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

1. The method of making a seal of the class described which comprises assembling the end of a glass exhaust tube within an outer tubular glass member with lead-in wires extending longitudinally therebetween, rotating the assembly about its axis, directing a heating flame substantially tangentially of the outer member and maintaining the flame in its original position to cause the said outer member to soften and contract away from the ame to a predetermined extent and become fused to the exhaust tube whereby to seal portions of the lead-in wires in the resulting joint without closing up the exhaust tube.

2. The method of uniting lamp parts which comprises assembling an end of a glass exhaust tube Within the tubular neck of a glass lbulb with lead-in wires extending longitudinally therebetween, rotating the assembly about its axis, directing a heating flame substantially tangentially of said bulb neck and maintaining the flame in its original position to cause said bulb neck to soften and contract away from the flame to a predetermined extent and become fused to the exhaust tube whereby to seal portions of the leadin wires in the resulting joint without closing up the exhaust tube.

3. The method of uniting parts for lamps and similar devices which comprises assembling an end of a glass exhaust tube within an outer tubular glass member with leading-in wires extending longitudinally therebetween, and directing a name at the said assembly while rotating the flame and said assembly relative to one another, said flame being of slender proportions and aimed in a direction substantially tangential to the original peripheral outline of said outer glass member and maintaining said flame in said direction until said outer glass member is softened and contracts away from the vflame to a predetermined extent and becomes fused t0 the exhaust tube and seals portions of the leading-in wires in the resulting joint without closing up the exhaust tube.

PAUL O. CARTUN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,547,748 Grogan July 28, 1925 1,569,185 Higgins Jan. 12, 1926 1,647,999 Laskey Nov, 8, 1927 1,701,388 Remane Feb. 5, 1929 1,984,488 Mulder Dec, 18, 1934 2,020,729 Knoeppel Nov. 12, 1935 2,028,342 McGowan Jan. 21, 1936

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