US3551725A

US3551725A - Method of tipping-off the exhaust tube of an electric lamp,and a baseless single-ended incandescent lamp produced by such method

Info

Publication number: US3551725A
Application number: US805231A
Authority: US
Inventors: William L Brundige
Original assignee: Westinghouse Electric Corp
Current assignee: Philips North America LLC
Priority date: 1969-03-07
Filing date: 1969-03-07
Publication date: 1970-12-29
Anticipated expiration: 1987-12-29

Description

United. States Patent [72] Inventor William L. Brundige [56] References Cited I grldwell, NJ. UNITED STATES PATENTS P 2 2 2 64 .v 9 [22] F e n 969 3.16 ,50 1 '/l9 L H erbeek 33 /144 [45] "Patented Dec-29, 1970 PrunaryExammerRaymond F. Hossfeld [73] Assignee Westinghouse Electric Corporation Attorneys-A. T. Stratton. W. D. Palmer and D. S. Buleza Pittsburgh, Pa.

l is van ABSTRACT: The exhaust tube of an electric lamp is tipped off at a point which is recessed within the stem cavity by fabricating the envelope and stem from infrared-radiation transmitting glass and by fabricating the exhaust tube from inflared-radiation absorbing glass. The exhaust tube is tipped off within the stem cavity by a focused beam of infrared-radiation [54] gfi g fg g that is generated by an external source and passes through the intervening portions of the lamp envelope and stem tube. S1NGLE-ENDED INCANDESCENT LAMP since the ti ff 0 h d t rnonucnn av sucn METHOD e 8 CI i 2D in n fires. It can be performed in a pressurized chamber. T1115, m

ams, I 8 a turn, facilitates the manufacture of incandescent lamps con- [-52] [1.8. CI. 313/318, taining a till gas at supra-atmospheric pressure.

, 220/22; 316/19: 339/ 144 The recessed tipping-off of the exhaust tube also provides a [51] Int. Cl. 1-101j 5/50 practical single-ended baseless incandescent lamp wherein the [50] Field olSearch 220/22; lead wires are electrically connected to side and end contacts that are fastened directly to the sealed neck of the envelope.

- PATENTEDUEMQIQYG 3551.725

FIG.2.

INFRARED ENERGY SOURCE WITNESSES NTOR William L. Brundige METHOD OF TlPPING-OFF THE EXHAUST TUBE OF AN ELECTRIC LAMP, AND A BASELESS SINGLE-ENDED INCANDESCENT LAMP PRODUCED BY SUCH METHOD BACKGROUND OF THE INVENTION tipoff.

2. Description of the Prior Art I Conventional gas-filled incandescent lamps are charged to a 4 I pressure below atmospheric pressure due to the face that the exhaust ti'p blows out" and ruptures while in softened condition when a high-fill-gas pressure is employed. The manufacturing complications or pressure tipping or reducing the internal gas pressure by cooling the lamp and then tipping-off the exhaust tube with gas fires make these solutions impractical. As a result, the exhaust tubes of such lamps are customarily tipped off at a point beyond the sealed neck of the envelope. The protruding tip is protectively enclosed by a hollow base member having a metal shell which is secured by cement to the envelope neck. Such metal base members are quite expens'ive and materially increase the manufacturing costof the lamp. v

'Because of the aforementioned problems it has heretofore been very difficult, if not impossible from a practical standpoint, to tipoff the exhaust tube at a point which is recessed deeply enough within the stem cavity to provide the degree of protection requisite for a baseless incandescent lamp. While baseless incandescent lamps are per se known inthe art, they either completely eliminate the exhaust'tu be or employ an end cap which protectively enclosesthe protruding fragile .tip of the exhaust tube. Baseless lamps in which the exhaust tube is omitted are disclosed in U.S. Pat. Nos. 1,946,104 issued Feb. '6, 1934 to T. Ohara et all and U.S. Pat. No. 2,327,622 issued -Aug. 24, 1943, to P. H. Craig. Baseless incandescent lamps having protectively capped exhaust-tube tips are disclosed in U.S. Pat. No. 3,162,502 issued Dec. 22, 1964 to L. H. Verbeek and Canadian Pat. No. 696,040 issued Oct. 13,1964 to the same inventor.

SUMMARY OF THE INVENTION It is accordingly the general object of the present invention toprovide a practical and inexpensive means for tipping-off the vitreous exhaust tube of an electric lamp at a point which is recessed within a reentrant cavity that is formed at the end of the lamp envelope either by the stem tube or by the end wall of the envelope itself.

Another object is the provision of a method for tipping-off the exhaust tube of an electric lamp without the use of gas fires and thereby facilitating the manufacture of lamps that ing portions of the envelope and stem tub'e from a point located outside of the lamp being processed. The infrared radiation can be generated by an incandescent coil of oxidation-resistant material but it is preferably generated by a compact quartz halogen-type incandescent lamp that is fitted with a s'uitablerefl'ector which focuses the infrared energy onto the exhaust tube.

A single-ended high-pressure baseless incandescent lamp having a recessed exhaust-tube tube tip formed by the aforementioned method and having inexpensive side and end contacts is also disclosed.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention will be obtained by referring to the accompanying drawing; wherein:

FIG. 1 is a longitudinal sectional view of a single-ended baseless incandescent lamp incorporating the novel recessed tipoff of the present inventiom' an'd I l i I FIG. 2 is an enlarged view 6f the basal end portion ofthe lamp illustrating the manner inwhich the exhaust tube is tipped off by a beam of infrared 'enr'gy whilethe exhaust tube is still attached'to the sealex" machine. I

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown a single-ended baseless electric incandescent lamp l0 havinga vitreous envelope 12 that is terminated by a constrictedfneck portion 13 having threads -14 molded on its exterior'surface. The envelope contains a filament 16 of suitable coiled refractory metal wire, such as tu ngsten, which is attached as by clamping or spot welding to the inner ends of a pair of

lead wires

17,18. The

lead wires

17, 18 are hermetically sealed through a press 20'formed on the inner end of a vitreous stem tube 21 the flared end of which is sealed to the envelope neck 13in the customary fashion.

The outer ends of the

lead wires

17, 18 extend through the cavity C defined by the stem 21 and the outer end of the leadwire 17 is connected to a disclike contactor member 22 that is cemented or sealed to the end of the envelope neck 13 and closes the stem cavity C. The contactor member 22 can comprise a metal eyelet that is soldered to the lead wire 17 so as to provide a centrally located segment 23 that protrudes outwardly from the eyelet and serves as an end contact for 'the lamp 10. The end of the other lead wire 18 is sealed through a thickened end wall portion 15 of the envelope neck 13 soas to be electrically insulated from the contactor member 22, and the end of this lead is bent around the end portion of the adjacent molded thread 14. A layer 24 of electrically conductive material, such as a suitable conductive paint, is applied .over

the exposed end of the lead wire 18 and thus serves as a-side contact for the lamp l0.

The envelope 12 is evacuated and subsequently charged with an inert gas fill through a vitreous exhaust tube 26 that is sealed to the inner end of the stem 21 and communicates with an aperture 28 provided in the wall of the stem tube just below the stem press 20. After the lamp has been evacuatedand gasfilled, the exhaust tube 26 is tippedoff at a point adjacent the inner end of the stem 21 in accordance with the present invention-to provide a recessed tip T of fused vitreous material that is located deep within the stem cavity C.

The tipping-off of the exhaust tube 26 at the aforementioned recessed location within the stem cavity C is achieved in accordance with the present invention by fabricating the envelope 12 and stem tube 21 from a glass that transmits infrared radiation and by fabricating the exhaust tube 26 from a glass which absorbs such radiation.

As a specific example, the envelope 12 and stem tube 21 are composed of the customary soda-lead glass (Corning Code No. 0120) customarily used for these components. The exhaust tube 26 is composed of a green-colored potash-sodalead glass that contains a small'but sufficient amount of iron oxide to render the glass infrared absorbing. Such infrared-absorbing glasses are well known in the art and are commercially available as Corning Code 9362 and Code 9363 sealing glasses. These sealing glasses have viscosity and expansion characteristics that are almost identical with Code 0120 glass and thus permit the-exhaust tube 26 to be sealed to'the stem tube 21 in the customary manner.

Information published by Corning shows that samples of Code 9362 andCode 9363 glasses approximately 1 millimeter thick absorb approximately percent of infrared energy: in the l to 2 micron wavelength range. Thus, an exhaust tube 26 made of such tipped off can be tipped off within the stem cavity C in a very efficient and convenient manner by focusing a beam of infrared radiation which has the proper wavelength and is generated by a source located outside of the lamp being processed. While various types of infrared-generating sources (such as incandescent radiant-heat coils etc.) may be used, a high-wattage halogen-type incandescent lamp such as an infrared quartz iodine lamp is preferred since it has an output which peaks at approximately 1 micron.

As is shown in FIG. 2, the exhaust tube 26 is tipped off while it is still attached to the compression head 27 of a "sealex" machine which has evacuated and charged the envelope 12 with a suitable inert fill gas. At this stage of manufacture, the outer end of the lead wire 18 has been sealed within the end wall [5 of the envelope neck 13 and has been bent over the adjacent portion of the molded glass thread 14. The end of the other lead wire 17 is unattached and merely extends from the stem cavity C on the opposite side of the exhaust tube 26. Tipping-off is accomplished by positioning a suitable infrared energy source30, such as a pair of 400 watt quartz-iodine lamps, adjacent the envelope neck 13 and focusing the infrared radiation, as by a suitable reflector, into a concentrated beam 31 that passes through the intervening portions of the envelope neck 13 and stem tube 21 and impinges upon a segment of the exhaust tube 26 that is located deep within the stem cavity C. The beam of infrared energy quickly heat softens the exhaust tube 26 and causes it to collapse inwardly and form a constriction 32, as shown in FIG. 2. The intensity of the infrared energy is such that the exhaust tube 26 melts and fonns a fused glass tip T (shown in FIG. 1) which hermetically closes off the exhaust tube 26 and the envelope 12 from the atmosphere.

After the tipping-off operation has been completed, the metal contactor plate or eyelet 22 is fastened to the end of the envelope neck 13. the lead wire 17 is trimmed and soldered to the eyelet to provide the protruding end contact 23, thus completing the fabrication of the lamp 10.

While the invention has been illustrated and described in connection with an incandescent lamp having a cavity C that is defined by a stem tube 21, the novel tipping-off method can be employed in the manufacture of various types of lamps and devices which are terminated by an end wall which defines a reentrant type cavity through which a vitreous exhaust tube initially extends.

The novel tipping-off method of the present invention facilitates the manufacture of incandescent lamps that are charged with a fill gas (such as argon, krypton, etc.) to a pressure higher than atmospherio pressure (1 V2 to 2 atmospheres, for example) since it does not require a combustible heat source such as a gas flame. Tipping-off of lamps having supraatmospheric fill pressure is readily accomplished by pressurizing the stem cavity C to prevent the heat-softened segment of the exhaust tube 26 from distending and rupturing during the tipping-off operation. This pressurizing can be accomplished by filling the cavity C with compressed air or other suitable inert gas to a pressure which is approximately equal to that of the fill gas contained by the envelope 12 and conjoined exhaust tube 21. Alternatively, the partly fabricated lamp can be placed within a pressurized enclosure having an infraredradiation transmitting window through which the beam of infrared energy is directed onto the recessed segment of the exhaust tube. The infrared source can also be located within the pressurized enclosure.

It will be appreciated from the foregoing that the objects of the invention have been achieved in that a very convenient and inexpensive means has been provided for tipping-off the exhaust tube of an electric lamp at a location which is recessed within the stem cavity or body of the lamp envelope.

While a preferred embodiment has been illustrated and dr scribed. it will be appreciated that the various modifications can be made without departing from the spirit and scope of the invention.

lclaim: i

1. In the manufacture of an electric lamp having a vitreous envelope that is terminated at one end by a reentrant wall that defines a cavity and includes a conjoined vitreous exhaust tube which initially extends through and beyond the cavity and provides a passageway for evacuating the envelope and subsequently charging it with a fill gas, the method of hermetically closing and tipping-off said vitreous exhaust tube at a location that is recessed within the cavity defined by said reentrant end wall, which method comprises;

fabricating said envelope from a vitreous material that transmits infrared radiation; fabricating the conjoined vitreous exhaust tube from a vitreous material that absorbs infrared radiation; and subjecting a recessed segment of said exhaust tube to an externally generated beam of infrared radiation thatpasses through the intervening portion of the lamp envelope and is of sufficient intensity that it heat-softens said tube segment and causes it to collapse into a tip of fused vitreous material that hermetically seals the envelope and terminates the exhaust tube.

2. The method of claim 1 wherein;

the reentrant end wall of said envelope comprises a hollow stem that is composed of vitreous material that transmits infrared radiation; and

the heat-softening and tipping-off of said recessed segment of the exhaust tube is effected by passing said beam of infrared radiation through the intervening portions of said envelope and said vitreous stem.

3. The method of claim 2 wherein:

said envelope is charged to a pressure above atmospheric pressure with an inert fill gas through the exhaust tube prior to the tipping-off thereof; and

the tipping-off of said exhaust tube by said beam of infrared radiation is effected after the stem cavity has been pressurized with an inert gas to a pressure that is substantially equal to the pressure of the fill gas contained by said envelope and conjoined exhaust tube so that the heat-softened recessed segment of the exhaust tube and newly formed tip will not be distended and ruptured by the supraatmospheric pressure exerted by the contained fill gas.

4. The method of claim 2 wherein:

said beam of infrared radiation is type incandescent lamp; and

the infrared radiation generated by said lamp is focused onto the recessed segment of the exhaust tube which is to be collapsed and tipped off.

5. A baseless single-ended incandescent lamp comprising:

that contains an envelope of infrared-radiation transmitting glass that is terminated by a neck portion that has a molded thread formed on its exterior surface;

a hollow stern of infrared-radiation transmitting glass sealed to said envelope neck portion and defining a stem cavity that extends into said neck portion;

a pair of lead wires sealed through a press formed on the inner end of said stem;

an incandescible filament fastened to the inner ends of said lead wires;

an exhaust tube of infrared-absorbing glass sealed to the inner end of said stem and communicating with an adjacent aperture in the wall of said stem;

said exhaust tube being terminated by a fused hermeticallysealed tip that is located proximate the inner end of the stem and is thus recessed within said stem cavity;

a layer of conductive material overlying at least a part of the thread on said envelope neck portion and constituting a side contact for said lamp;

a disclike contact member secured to the end of said envelope neck portion and having an outwardly protruding segment that constitutes an end contact for said lamp;

the outer end portion of one of said lead wires being located in the stem cavity and extending through the end of said generated by a halogen said disclike contact member closes said stem cavity.

8. The incandescent lamp of claim 5 wherein:

said envelope and stem are composed of soda-lead glass;

and i said exhaust tube is composed of potash-soda-lead glass that contains an amount of iron oxide such that approximately percent ofjinfraredradiation having a wavelength of from 1 to 2 microns is absorbed by a section of said glass that is approximately 1 millimeter thick.