US3863314A

US3863314A - Method of manufacturing miniature incandescent lamps

Info

Publication number: US3863314A
Application number: US367819A
Authority: US
Inventors: Bernard Kopelman
Original assignee: GTE Sylvania Inc
Current assignee: GTE Sylvania Inc
Priority date: 1973-06-07
Filing date: 1973-06-07
Publication date: 1975-02-04
Anticipated expiration: 1992-02-04

Abstract

In the manufacture of a single ended subminiature incandescent lamp, a helically coiled wire filament is bent into a hairpin shape and is mounted on a temporary support while the mandrel on which the wire has been coiled is still within the filament. The filament is then inserted into acid in order to dissolve the mandrel at the apex portion of the filament. The filament is then sealed within a glass envelope.

Description

United StatesfPatent n91 Kopelman METHOD OF MANUFACTURING MINIATURE INCANDESCENT LAMPS [75] Inventor: Bernard Kopelman, Magnolia,

Mass.

[73] Assignee: GTE Sylvania Incorporated,

Danvers, Mass.

[22] Filed: June 7, 1973 [21] Appl. No.: 367,819

[52] US. Cl. 29/25.l5, 313/271 511 int. Cl. H01j 9/18 58 Field or Search 29/25.14, 25.15; 25.17,-

[56] References Cited UNITED STATES PATENTS H1937 Zabel. 29/25. 13 X [451 Feb. '4, 1975 2,359,302 Curtis 29/25.13 X 3,270,238 8/1966 Mosby 313/279 3,356,884 12/1967 Decker et al. 313/212 3,594,884 7/1971 Siege] 29/2513 X Primary Examiner-Roy Lake Assistant Examiner-James W. Davie Att0rney, Agent, or FirmJames Theodosopoulos [57] ABSTRACT In the manufacture of a single ended subminiature incandescent lamp, a helically coiled wire filament is bent into a hairpin shape and is mounted on a temporary support while the mandrel on which the wire has been coiled is still within the filament. The filament is then inserted into acid in order to dissolve the mandrel at the apex portion of the filament. The filament is then sealed within aglassenvelope.

9 1 Claim, 4 Drawing Figures 1 METHOD OF MANUFACTURING MINIATURE INCANDESCENT LAMPS BACKGROUND OF THE INVENTION tric current therethrough. It especially relates to a method of making such lamps.

Subminiature lamps generally have a filament made of such fine wire that it can only be seen and handled under magnification; thus the coil mount and assembly is done by hand with consequent high costs. The filament is generally made by helically coiling fine tungsten wire on a metal mandrel wire, several times its diameter, in a long continuous length. The coiling isheat treated to set it andis then cut into predetermined filament lengths. The mandrel is dissolved in acideither before or after the cutting step. The filament is then hand mounted on a suitable support and then sealed within a small glass envelope.

It is an object of'this invention to provide a method of manufacturing that permits employment of auto-- matic assembly machines, thereby eliminating much of the hand work involved and thereby significantly re-' ducing the cost of such lamp.

THE INVENTION helically coiled wire filament mountedon a temporary support.

FIG. 2 shows the filament immersed in acid to dissolve the mandrel I FIG. 3 shows the filament, still mounted on the temporary support, sealed into one end of a glass envelope.

FIG. 4 shows the finished lamp. T In the manufacture of a single ended subminiature incandescent lamp in accordance with this invention, fine tungsten wire 1, generally less than 1 mil diameter, is continuously helically coiled on a wire mandrel 2 of larger diameter. The mandrel 2 is made of a suitable metal, say, nickel, steel or molybdenum, that can be dissolved in an acid that does not readily attack tungsten; In a typical case, the mandrel diameter is 3m 4 mils.

The coiling-with-mandrel can than be heat treated, if

necessary, to set the coiling and is then taken up on a spool in'a long continuous length. Next, the coiling is mounted on suitable apparatus where it is unreeled and cut into predetermined lengths. The cut lengths are then bent into a hairpin or U shape and the ends thereof are attached to a suitable-temporary support 3. The fact that the mandrel 2 is still within each cut length gives it sufficient bulk to permit the bending and attaching steps to be performed on automatic equip- .ment. The distance between legs of the bent-filament at the time of attaching to a suitable support 3 is small enough to permit the filament to be inserted into a tubular glass envelope 7 at the time of lamp assembly while the filament is mounted on said support 3. In a typical case, the distance between legs-was about onesixteenth inch.

The support 3 on which the bent filament is mounted must be suitable to support the filament until the filament is sealed in a glass envelope 7. The support 3 may be a small flat piece of metal to which the ends of the bent filament are attached, as by welding. In such a case, themetalpiece remains outside the lamp envelope 7 and is removed after the filament is sealed in the blocks in which the legs of the bent filament are clamped. The blockshold the filament through all operations until after the filament is sealed in the lamp envelope.

After the bent filament has'been mounted on the support 3, the filament is dipped in a suitable acid 4 to dissolve the mandrel 2. The mandrel 2 is dissolved in at least the effective lighted length of thefilament but not at theportions thereof which are part of the glass-tometalseal in the finished lamp. Thus, the support 3 is not dipped into the acid4 and the mandrel 2 is not dissolved in those portions of the filament legs which are not immersed in the acid. The acid may be heated to reduce the time for dissolving the mandrel to a few seconds. Typically, hydrochloric acid is used to dissolve a steel mandrel, while a combination of sulphuric and nitric acids is used to dissolve a molybdenum mandrel. After the filament is rinsed and dried, it is ready for sealing in. a glass envelope 7. The filament is inserted into one end of a small diameter glass tubing 5, typically, T] or Asinch diameter, and the end of the tubing is heated to its-softening point. Thesoftened end is then squeezed on the legs of the filament to form a hermetic press seal 6. The temporary support 3 remains outside the envelope 7 and is removed after the filament has been sealed in the envelope.

In any case, however, it is important that mandrel 2 remain within that'portion of the filament which is embedded in the glass which forms the glass-to-metal seal of the lamp envelope 7. The reasonfor this is to keep the electrical resistivity of the conductors which are embedded in the glass low, so that they will not overheat during lampoperation which, ifoverheating occurred, could crack the glass seal. Also, the mandrel may aid somewhat in forming a hermetic seal during the press operation if the filament has highTPl (turns per inch) coiling.

After the filament has been inserted in one end of the glass tubing and sealed there, the tubing is exhausted through the other end and is then heated and tipped off diameter to aid in tipping off the lamp.

In an example of a 5 volt 60 milliampere Tl lamp made in accordance with this invention, the filament coiling consisted of 0.6 mil tungsten wire wound on 4 mil molybdenum wire at 650 TPI. The coiling was heat treated at l,525C and then cut into lengths of 20 mm. Each cut length wasthen folded in a hairpin and the ends thereofwere welded to a temporary support consisting of a rectangular piece of 4 mil nickel, about 6 mm by 3 mm. The legs of the hairpin were about 1% mm apart. The apex of the hairpin was then inserted into heated sulfuricnitric acid to a depth of about 1 /2 mm for about 5 to 10 seconds to dissolve the molybde to exhaust and filling apparatus. The first end of the glass tubing was heated to its softening point and then pressed onto the legs of the filament to form a hermetic press seal. If necessary, the interior of the tubing could be flushed with a suitable inert gas to prevent oxidation of the filament during press sealing. The other end of the glass tubing was then heated and tipped off while a vacuum was maintained in the tubing. The temporary subminiature incandescent lamp, the steps which sequentially comprise: helically coiling a length of fine tungsten wire on a mandrel wire having a larger diameten heat treating and cutting the coiling into predetermined lengths; bending each of the cut lengths into a hairpin shape; attaching the ends of the hairpin to a temporary support; dissolving part of the mandrel at the apex end of the hairpin; inserting'the hairpin into an open ended glass tube; heating and press sealing one end of the glass tube onto a portion of the legs of the hairpin, said portion still containing mandrel wire; sealing the other end of the glass tube and removing the temporary support to form a finished lamp.

' at 1: t 4: a:

Claims

1. In the process of manufacturing a single ended subminiature incandescent lamp, the steps which sequentially comprise: helically coiling a length of fine tungsten wire on a mandrel wire having a larger diameter; heat treating and cutting the coiling into predetermined lengths; bending each of the cut lengths into a hairpin shape; attaching the ends of the hairpin to a temporary support; dissolving part of the mandrel at the apex end of the hairpin; inserting the hairpin into an open ended glass tube; heating and press sealing one end of the glass tube onto a portion of the legs of the hairpin, said portion still containing mandrel wire; sealing the other end of the glass tube and removing the temporary support to form a finished lamp.