US3771941A

US3771941A - Photoflash lamp

Info

Publication number: US3771941A
Application number: US00294276A
Authority: US
Inventors: E Audesse; H Hough
Original assignee: GTE Sylvania Inc
Current assignee: GTE Sylvania Inc
Priority date: 1972-10-02
Filing date: 1972-10-02
Publication date: 1973-11-13
Anticipated expiration: 1990-11-13

Abstract

A percussive-type photoflash lamp having an envelope comprised of a glass having a low coefficient of thermal expansion and a depending metal primer tube which is secured to the glass envelope by means of a graded seal having an intermediate expansion glass disposed between the envelope and the primer tube.

Description

United States Patent [1 1 Audesse et al.

[ Nov. 13, 1973 1 i n0T0rLAsii LAMP [75] Inventors: Emery G. Audesse, Salem; Harold L. Hough, Beverly, both of Mass. [73] Assignee: GTE Sylvania Incorporated,

' Danvers, Mass.

[22] Filed: Oct. 2, 1972 [21] Appl. No.: 294,276

[52} U.S. Cl. 431/93 [51] Int. Cl. F21k 5/02 [58] Field of Search ..431/93-95 [56] References Cited UNIT ED STATES PATENTS 3,535,063 10/1970 Anderson et al. ..-43l/93 2,438,993 4/1948 De Boer 431/94 FOREIGN PATENTS OR APPLICATIONS 667,689 ll/l938 Germany 431/93 Primary Examiner-Carroll B. Dority, Jr. Att0rneyNorman J. OMalley et al.

57 ABSTRACT A percussive-type photoflash lamp having an envelope comprised of a glass having a low coefficient of thermal expansion and a depending meta] primer tube which is secured to the glass envelope by means of a graded seal having an intermediate expansion glass disposed between the envelope and the primer tube.

9 Claims, 2 Drawing Figures PATENTEU NOV 1 3 I973 PRIOR ART PHOTOFLASH LAMP BACKGROUND OF THE INVENTION This invention relates to the manufacture of pohotoflash lamps and particularly those of the percussive Generally speaking a percussive-type photoflash lamp comprises an hermetically sealed, lighttransmitting envelope containinga source of actinic light and having a primer secured thereto. More particularly, as described in U.S. Pat. No. 3,535,063, the percussive flashlamp may comprise a length of glass tubing constricted to a tip at one end and having a coaxially disposed metal primer tube sealed in the other end. The glass tubing defines the lamp envelope and contains a combustible, such as shredded zirconium foil, and a combustion-supporting gas, such as oxygen. To complete the primer structure, a wire anvil coated with a layer of fulminating material is coaxially disposed within the primer tube. Typically, the envelope is comprised of G-l type soft glass having a coefficient of thermal expansion within the range of 85 to 95 X per C between C, and 300C, and the primer tube is formed of a metal having a similar coefficient of thermal expansion so as to provide a match seal.

Operation of the percussive type photoflash lamp is initiated by an impact onto the tube to cause deflagration of the fulminating material up through the tube to ignite the combustible disposed in the lamp envelope and, thus, flash the lamp. During lamp flashing, the glass envelope is subject to severe thermal and mechanical shock due to hot globules of metal oxide impinging on the walls of the lamp. As a result, cracks and crazes occur in the glass and, at higher internal pressures, containment becomes impossible. In order to reinforce the glass envelope and improve its containment capability, it has been common practice to apply a protective lacquer coating on the lamp envelope by means of a dip process. To build up the desired coating thickness, and glass is generally dipped a number of times into a lacquer solution containing a solvent and a selected resin, typically'cellulose acetate. After each dip, the lamp is dried to evaporate the solvent and leave the desired coating' of cellulose acetate, or whatever other plastic resin is employed.

In the continuing effort to improve light output, higher performance flashlamps have been developed which contain higher combustible fill weights per unit of internal envelope volume along with higher fill gas pressures. In addition, the combustible material may be one of the more volatile types, such as hafnium. Such lamps, upon flashing, appear to subject the glass envelopes to more intense thermal'shock effects, and thus require stronger containment vessels. One approach to this problem has been to employ a hard glass envelope, such as the borosilicate glass envelope described in U.S. Pat. No. 3,506,385, along with a protective dip coating. More specifically, this patent describes an electrically ignitable lamp having in-leads of a metal alloy such as Kovarsecured by an internal expansion match seal in a glass envelope having a coefficient of thermal expansion in the range of 40 to 50 X 10" per C. Type 7052 glass is mentioned as typical. The patent imposes a minimum of 40 X 10 per C on the coeffici-- ent of thermal expansion of the glass to assure the necessary match seal with the Kovar in-Ieads. Further, it is theorized that glass in this thermal expansion range provides a more beneficial mode of fracture which results in a delay in crack time after flashing. More specifically, fracture of the glass is delayed to a time when the pressure in the lamp has been reduced to a point where containment is more readily assured.

As described in copending application Ser. No. 294,308, filed Oct. 2, 1972, assigned to the present assignee, it has been discovered that by using glasses having an even lower thermal expansion than that specified in the aforementioned U.S. Pat. No. 3,506,385 the flashlamp envelope can be made even more resistant to thermal shock and thereby delay crack time even further. Alternatively, the use of lower thermal expansion glass provides a lamp capable of higher thermal loadings, as the glass surface stresses 0 are proportional to the thermal expansion a of the glass. In particular, we

have found that glasses having a coefficient of thermal expansion within the range of 30 to 40 X 10 per C between 0C and 300C are particularly suitable for improving the containment offlashlamp envelopes. Hereinafter, such glass will be referred to as low-expansion glass. Of course, fused quartz has a very low coefficient of thermal expansion, in the order of 4 X 10' per C-, but it is somewhat costly for this application.

In attempting to use a low-expansion glass envelope in the above-described percussive flashlamp structure, however, a sealing problem arises as the commercially suitable metals for the primer tube all have a substantially higher coefficient of thermal expansion than the glass and, therefore, are not suitable for providing a match seal. More specifically, referring to the envelope primer assembly of FIG. 1, in the above-referenced prior art percussive flashlamp, the metal primer tube 10 is secured to the glass envelope 12 by means of an internal expansion match seal. If envelope 12 is formed of low-expansion glass (e.g., a glass having a thermal expansion of about 32 X 10 per C) and tube 10 is formed of a low thermal expansion metal alloy such as Kovar (having a minimum thermal expansion of about 45 X 10 per C), there will be a mismatch between the mating materials and, upon cooling, the Kovar will contract faster than the glass. In this event, tube 10 will continue to adhere to envelope 12, but the faster contraction of the'metaI will place the adjacent glass area under tension, as illustrated by the arrows. This results in an unacceptably weak seal area, as the strength of glass is reduced in tension.

SUMMARY OF THE INVENTION 7 In view of the foregoing, it is an object of the present invention to provide a percussive-type photoflash lamp having an improved containment vessel.

Another object of the invention is to provide an improved glass-to-metal seal for a percussive flashlamp.

A principal object is to provide a percussive-type photoflash lamp having a low-expansion glass envelope, and a strong glass-to-metal seal between the envelope and primer tube.

These and other objects, advantages and features are attained, in accordance with the invention, by sealing a body of intermediate expansion glass between the low expansion glass'envelope of the percussive flashlamp and the higher expansion metal primer tube. In a preferred embodiment, the glass envelope of the lamp has a mean coefficient of thermal expansion of about 32 X 10" per C between 0C and 300C; the primer tube is formed of a metal alloy having a mean coefficient of thermal expansion of about 50 X 10 per C between 25C and 300C; and the body of intermediate expansion glass comprises a pressed and sintered bead of glass having a mean coefficient of thermal expansion of about 46 X 10* per C between C and 300C. This provides a graded seal between the metal tube and glass envelope which avoids the creation of high stresses at the glass-to-metal interface and cracking of the seal.

BRIEF DESCRIPTION OF THE DRAWINGS This invention will be more fully described hereinafter in conjunction with the accompanying drawings, in which:

FIG. 1 is an enlarged fragmentary cross-section illustrating the glass-to-metal seal of a prior art percussive flashlamp to which previous reference has been made; and

FIG. 2 is an enlarged sectional elevation of a percussive-type photoflash lamp having a graded seal between the envelope and primer according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to FIG. 2, a percussive lamp according to the invention comprises a length of glass tubing defining an hermetically sealed lamp envelope 14 constricted at one end to define an exhaust tip 16 and having a primer 18 secured at the other end thereof. Preferably, theglass of envelope 14 is selected to be a lowexpansion glass, such as Corning Glass Works type 7070 hard glass, which has a mean coefficient of ther mal expansion of about 32 X 10 per C, between 0C and 300C, and a composition which is approximately: 71% SiO 1% A1 0 26% B 0 Li O, 0.5% Na o, and 1% K 0.

The primer 18 comprises a thin metal tube 20 which is closed at one end, a wire anvil 22 coaxially centered within tube 20, and a charge of fulminating material 24 coated on the anvil. Tube 20 preferably is formed of a metal alloy such as that commercially known as Kovar, which has a mean coefficient of thermal expansion of about 50 X per C, between 25C and 300C, and a composition which is approximately: 54% Fe, 29% Ni, 17% Co, O.'5% Mn, 0.2% Si, and 0.06% C.

A combustible 26, such as filamentary zirconium or hafnium, and a combustion-supporting gas, such as exygen, are disposed within the lamp envelope, with the fill gas being ata pressure of greater than one atmosphere. The exterior surface of the glass envelope 14 is covered with a suitable plastic coating, such as cellulose acetate.

The wire anvil 22 is held in place by a circumferential indenture 28 which loops over the head 30, or other suitable protuberance, at the lower extremity of the wire anvil. Additional means, such as lobes 32 on the wire anvil 22,-for example, may also be used instabilizing the wire anvil supporting it substantially coaxial within the tube and insuring clearance between the fulminating material 24 and the inside wall of tube 20. A deflector-shield 34, which may be a bead of refractory material or formed of metal, is attached to the wire anvil just above the inner mouth of the tube 20.

Typically, the lamp envelope has an internal diameter of less than one-half inch, and an internal volume of less than 1 cc., although the present invention is equally suitable for application to larger lamp sizes.

Operation of the percussive-type lamp of FIG. I is initiated by an impact onto tube 20 to cause deflagration of the fulminating material 24 up through the tube 20 to ignite the combustible 26 disposed within the lamp envelope.

In accordance with the invention, metal tube 20 is sealed in the end of the lamp envelope by means of a graded seal including a bead 36 of pressed and sintered intermediate expansion glass. Preferably, bead 36 is formed of a glass having a mean coefficient of thermal expassion of about 46 X 10 per C between 0C and 300C, such as Corning Glass Works type 7050 glass, which has a composition of approximately 67% SiO 2% A1 0 24% B 0 and 7% Na O To provide a strong glass-to-metal seal, 7050 glass powder is heated and pressed into a doughnut shaped preform comprising the bead 36. This doughnut shaped bead 36 is then coaxially located about tube 20 at its open end, and the assembly is rotated over the flame of a torch to seal the glass bead 36 to the metal tube 20. Thereafter, the 7070 glass envelope 14 is sealed about the 7050 glass bead in the same manner. The choice of 7050 glass, with an expansion of 46 is reasonably critical due to its suitable match to both the Kovar tube 20, with an expansion of 50, and the 7070 glass envelope, with an expansion of 32. The resulting graded seal avoids the creation of high stresses at the glass-to-metal interface and cracking of the seal.

Accordingly, a strong glass-to-metal seal is provided between a low-expansion glass envelope and the primer tube 20 to provide a significantly improved containment vessel for a percussive flashlamp. More specifically, whereas the G1 type soft glass (expansion of 93) and 7052 hard glass (expansion of 46) used on prior art flashlamps have thermal stress resistances of about 19C and 41C, respectively, the thermal stress resistance of 7070 glass (expansion of 32) is about 66C. By definition, thermal stress resistance of C is the temperature differential between the two surfaces of a tube or constrained plate that will cause a tensile stress of 1,000 pounds per square inch on the cooler ufiace envelope of FIG. 2 provides a much higher resistance to thermal shock, thereby permitting greater loading of the lamp with a combustible material and oxygen to provide increased light output.

Although the invention has been described'with respect to a specific embodiment, it will be appreciated that modifications and changes may be made by those skilled in the art without departing from the true spirit and scope of the invention.

What we claim is: I

1. A percussive-type photoflash lamp comprising:

an hermetically sealed glass envelope having a first mean coefficient of thermal expansion;

a quantity of combustible material located within said envelope;

a combustion-supporting gas in said envelope;

a primer secured to and extending from one end of said envelope and in communication therewith, said primer including a metal tube sealed in said end of said envelope and having an exposed segment outside of said envelope, and a body of fulminating material located in the exposed segment of said tube, said metal tube having a second mean coefficient of thermal expansion which is higher than said first mean coefficient;

and means for sealing said metal tube in said end of said envelope comprising a body of glass sealed between said metal tube and said envelope and having a third mean coefficient of thermal expansion which is intermediate said first and second mean coefficients.

2. A lamp according to claim 1 wherein said first mean coefficient of thermal expansion is about 32 X per C between 0C and 300C.

3. A lamp according to claim 2 wherein said envelope is composed of a glass comprising the following constituents about in the proportions stated by weight: 71% SiO 1% Al O 26% B 0 0.5% Li O, 0.5% Na O and 1% K 0.

4. A lamp according to claim 2 wherein said second mean coefficient of thermal expansion is about 50 X 10 per "C between C and 300C.

5. A lamp according to claim 4 wherein said metal tube is composed of a metal alloy comprising iron, nickel, and cobalt.

6. A lamp according to claim 4 wherein said third mean coefficient of thermal expansion is about 46 X 10" per C between 0C and 300C.

7. A lamp according to claim 6 wherein said body of glass having said third mean coefficient of thermal expansion has a composition comprising the following constituents about in the proportions stated by weight: 67% SiO 2% Al O 24% B 0 and 7% Na O.

8. A lamp according to claim 6 wherein said body of glass having said third mean coefficient of thermal expansion comprises a preformed bead of pressed and sintered glass powder, said bead being sealed about said metal tube, and said end of said glass envelope being sealed about said bead.

9. A lamp according to claim 8 wherein said primer further includes a wire anvil disposed within and substantially coaxial with said metal tube with said fulminating material being disposed thereon intermediate the ends thereof, and a deflector-shield disposed on said anvil immediately above the inner end of said tube.

Claims

1. A percussive-type photoflash lamp comprising: an hermetically sealed glass envelope having a first mean coefficient of thermal expansion; a quantity of combustible material located within said envelope; a combustion-supporting gas in said envelope; a primer secured to and extending from one end of said envelope and in communication therewith, said primer including a metal tube sealed in said end of said envelope and having an exposed segment outside of said envelope, and a body of fulminating material located in the exposed segment of said tube, said metal tube having a second mean coefficient of thermal expansion which is higher than said first mean coefficient; and means for sealing said metal tube in said end of said envelope comprising a body of glass sealed between said metal tube and said envelope and having a third mean coefficient of thermal expansion which is intermediate said first and second mean coefficients.

2. A lamp according to claim 1 wherein said first mean coefficient of thermal expansion is about 32 X 10 7 per *C between 0*C and 300*C.

3. A lamp according to claim 2 wherein said envelope is composed of a glass comprising the following constituents about in the proportions stated by weight: 71% SiO2, 1% Al2O3, 26% B2O3, 0.5% Li2O, 0.5% Na2O and 1% K2O.

4. A lamp according to claim 2 wherein said second mean coefficient of thermal expansion is about 50 X 10 7 per *C between 25*C and 300*C.

6. A lamp according to claim 4 wherein said third mean coefficient of thermal expansion is about 46 X 10 7 per *C between 0*C and 300*C.

7. A lamp according to claim 6 wherein said body of glass having said third mean coefficient of thermal expansion has a composition comprising the following constituents about in the proportions stated by weight: 67% SiO2, 2% Al2O3, 24% B2O3, and 7% Na2O.