US3840324A - Photoflash lamp - Google Patents

Abstract

A percussive-type photoflash lamp in which the powdered metallic combustible component of the fulminating material thereof includes hydrides of titanium and/or zirconium.

Description

United States Patent [191 Shaffer et al.

[ PHOTOFLASH LAMP [75] Inventors: John W. Shaffer, Williamsport, Pa.;

Stephen V. Brown, Winchester, Ky.

[73] Assignee: GTE Sylvania Incorporated,

Danvers, Mass.

[22] Filed: Sept. 10, 1973 [21] Appl. No.: 395,772

[52] U.S. Cl. 431/93, 149/29 [51] int. Cl. F2lk 5/02 [58] Field of Search 431/93 [56] References Cited UNITED STATES PATENTS 3,724,991 4/1973 'Schupp 431/93 [451 Oct. 8, 1974 5/1973 McDonough 431/93 Primary Examiner-Carroll B. Dority, Jr. Attorney, Agent, or Firm-Edward J. Coleman [5 7] ABSTRACT A percussive-type photoflash lamp in which the powdered metallic combustible component of the fulminating material thereof includes hydrides of titanium and/or zirconium.

9 Claims, 1 Drawing Figure PHOTOFLASH LAMP This invention relates to the manufacture of photoflash lamps and more particularly those of the percussive type.

Generally speaking, a percussive-type photoflash lamp comprises an hermetically sealed, lighttransmitting envelope containing a source of actinic light and having a primer secured thereto. More particularly, the percussivetype photoflash lamp may comprise a length of glass tubing constricted to a tip at one end thereof and having a primer sealed therein at the other end thereof. The length of glass tubing which defines the lamp envelope contains a combustible, such as shredded zirconium foil, and a combustionsupporting gas, such as oxygen. The primer may comprise a metal tube and a charge of fulminating material on a wire anvil supported therein. A deflector bead is disposed on the wire anvil just above the primer tube to deflect and control the ejection of hot particles of fulminating material therefrom. 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.

The requirements that must be met by a fulminating material for percussive flashlamps are unique and differ appreciably from those for flashlamps used heretofore in which a paste of fulminating material is heated by the passage of electric current through a wire filament until ignition occurs. Energy input to the paste usually extends'over a period of one or more milliseconds. In contrast, energy input to the fulminating material of 'a percussive flashlamp is in the form ofa single nearlyinstantaneous impact, the duration of which would be measured in microseconds. Unless ignition occurs during this single momentary event, the lamp has failed. Accordingly, the fulminating material for percussive flashlamps must be much more sensitive than is the ignition paste for filament-ignited lamps.

The fulminating material for percussive flashlamps comprises four major ingredients: an oxidizer, such as sodium chlorate; a fuel, such as red phosphorus that ignites by friction or impact in the presence of the oxidizer; a binding agent, such as hydroxyethyl cellulose, to adhere the fulminating material to a specified location in the flashlamp; and a combustible metal powder, such as titanium. The metal powder is not required for, and does not participate in, the attainment of mechanically initiated deflagration. It does, however, play two important roles: it slows down or attenuates the reaction between the phosphorous and oxidizer, and it transports combustion from the fulminating material to the shredded metallic combustible in the lamp.

Throughout the history of percussive flashlamps there has been a constant evolution of fulminating material performance. This has been tied principally to the nature and quantity of the powdered metallic combustible used. The choice and relative amount of powdercd metallic combustible has a direct effect on lamp reliability, containment, light output and uniformity thereof, and output timing characteristics. It has been found that powders of various metals differ appreciably in their abilityto attenuate the phosphorous-oxidizer reaction and in their ability to ignite the shreded metallic combustible within the flashlamp. Metal powders that are relatively superior with regard to one function may be quite inferior with regard to the other. Sensitivity and reliability of the fulminating material both decrease as metal powder content increases. This is a general behavior for all kinds of metal powder, although the relative fall-off of sensitivity and reliability with increasing metal content differs from one metal to another.

Zirconium metal powder has been adopted on an industry-wide basis as the material of choice for use in the primer of electrically fired, filament type flashlamps. Zirconium was therefore used in the first fulminating materials for percussive flashlamps. It was found, however, that problems were encountered with either reliability or light output and timing, and that no manipulation of the formula gave completely satisfactory results.

Additional testing showed that powdered boron gave significant attenuation of the phosphorus-oxidizer reaction and did so at a weight percentage that did not seriously affect the impact sensitivity of the mixture. Large scale testing of boron type primers showed an inherent weakness in that system the reliability of shred ignition 'by the fulminating material discharge was distinctly inferior to that provided by zirconium powder. Accordingly, compromise blends of zirconium and boron powders were next used and found to be advantageous over either zirconium or boron alone.

Further research showed titanium powder to be an improvement over zirconium-boron blends with respect to shred ignition reliability, especially for those lamps having a lower than average quantity of fulminating material. As an added benefit, titanium powder provided a significantly lower settling rate than zirconium in the liquid fulminating material slurry. Titaniumbased fulminating materials have now been used in percussive flashlamps for several years; lamp reliability and light output have been very good.

Recently it has been found that the light. output per unit weight of shredded combustible burned can be increased by either chopping the shreds into short, straight lengths, or by multiply bending the former long shreds into small, crumpled balls or wads. Both of these changes offer greater manufacturing economy and permit more light output from a given size vessel. However, both short, straight lengths and crumpled wads are relatively mobile within the lamp vessel when compared to the former long shreds. When used in percussive flashlamps especially, such shreds are particularly susceptible to relocation and compacting by the fulminating material discharge. Burning of compacted shreds is inefficient and gives rise to both low and variable light output. The degree of fulminating material attenuation attainable through the use of titanium metal powder is therefore marginal for use with the new, more efficient types of shredded combustible.

Another development that has rendered titanium metal-based'fulminating materials marginal in performance has been the sale of certain camera models which are highly critical to the timing characteristics of the light output from percussive flashlamps. In particular, the so-called rise time (which is the time it takes for the lamp to attain a specified intensity of output) tends to be too fast, with the associated possibility of photographic underexposure with those lamps that are somewhat faster than average. In effect, part of the light output is generated before the camera shutter is sufficiently open to make use of that light.

The timing characteristics of percussive flashlamps may be slowed down (increased rise and peak times) by increasing the ratio of metal powder to phsophorus in the fulminating material. However, the degree of fulminating material attenuation now required cannot be obtained by this method without some sacrifice in product reliability.

In view of the foregoing, one of the principal objects of this invention is to provide an improved fulminating material for percussive flashlamps that gives controllably delayed rise times and peak times so that the lamp light output characteristics may be better matched to the shutter timing requirement of given camera models.

Another object is to provide attenuated fulminating materials that do not disadvantageously relocate the shredded metallic combustile within the flashlamp and which thereby enhance light output uniformity.

A further object is to provide a fulminating material attenuated sufficiently to make possible elimination of the deflector bead on the anvil wires of percussive fiashlamps so as to effect a reduction in manufacturing cost.

These and other objects, advantages and features are attained, in accordance with the principles of this invention, by the use of metal hydride powders as the flame transport and attenuating agent in the fulminating material of percussive flashlamps. More specifically, we have found that zirconium hydride, and titanium hydride to an even more pronounced degree, attenuate the phosphorus-chlorate reaction far more than the pure metals do. This is known in fulminating material formulations that are otherwise identical. By substituting titanium hydride for titanium powder, for example, lamp peak and rise times can be extended by a factor of two or more.

The use of metal hydride powders, and in particular titanium hydride, in fulminating material for percussive flashlamps permits attainment of desirable slower lamp timing characteristics and at the same time allows sufficient phosphorus content to insure lamp reliability. The degree of fulminating material attenuation that can be realized with this invention is sufficient that it makes good photometric output possible without a deflector bead on the anvil of percussive flashlamps. Such bead elimination affords a significant reduction in manufacturing costs.

Titanium hydride powder gives a greater combined degree of attenuation and reliability than does any material previously used in percussive flashlamp fulminating materials. Zirconium hydride is somewhat less effcctive as an attenuating agent than titanium hydride and, because of its higher density, settles out more rapidly from fluid suspensions. From the standpoint of settling stability in fulminating material slurries, titanium hydride offers advantages over titanium metal because of its lower density (3.8 vs. 4.5).

An important alternative is the use of combinations of, for example, titanium hydride and titanium metal powders in percussive flashlamp fulminating materials. Such combinations permits adjustment of lamp timing characteristics to any value lying between those for the pure separate components. Combinations of zirconium with its hydride or with titanium hydride may also be used. The latter combination is particularly effective in those situations where particle settling is not a prime consideration. Titanium hydride contributes its outstanding attenuation characteristics and zirconium its superior ability to effect shred ignition.

In the specific embodiment of the invention illustrated in the accompanying drawing, the FIGURE is an elevational view partly in section of a percussive-type phototlash lamp. The lamp comprises a length of glass tubing defining an hermetically sealed lamp envelope 2 constricted at one end to define an exhaust tip 4 and shaped to define a seal 6 about aprimer 8 at the other end thereof. THe primer 8 comprises a metal tube 10 and a wire anvil 12 coated with a charge of fulminating material 14. A combustible such as filamentary zirconium 16 and a combustion-supporting gas such as oxygen are disposed within the lamp envelope. The wire anvil 12 is centered within the tube 10 and held in place by a crimp 18 just above the head 20 of the anvil. Additional means, such as lobes 22 on wire anvil 12, are also used to aid in stabilizing and supporting it substantially coaxial within the primer tube 10 and insuring clearance between the fulminating material 14 and the inside wall of the tube 10. A refractory bead 24, fused to the wire anvil 12 just above the inner mouth of the primer tube It), eliminates burnthroughs and functions as a deflector to deflect and control the ejection of hot particles of fulminating material from the primer tube. As discussed hereinbefore, head 24 may be eliminated when using sufficiently attenuated fulminating materials in accordance with the invention.

By way of example, a fulminating material for percussive flashlamps in accordance with the principles of this invention may be formulated as follows. The anvil wire is initially dipped into an aqueous slurry having the following dried composition (percent by weight): 36.15 percent titanium hydride powder, 2.5 micron; 36.15 percent titanium powder, 2.5 micron; 24.1 percent red phosphrous; 1.4 percent hydroxyethyl cellulose as a binder; 1.2 percent sodium lignin sulfonate as a chemical dispersing agent; 0.2 percent sodium Z-ethylhexyl sulfate as a wetting agent; 0.1 percent N-(3-chloroallyl) hexaminium chloride as a bactericide; and 0.7 percent magnesium oxide and sulfur (10:1 blend). The addition of a small amount of sulfur has been found to improve shelf life and impact sensitivity of red phosphorus based fulminating materials, and the magnesium oxide maintains the mixture slightly alkaline. The water content of this slurry is adjusted to give the desired coating thickness The coating is then dried and dipped into an aqueous solution containing 25 percent by weight of dissolved sodium chlorate. Upon drying, the resulting coating is a highly sensitive and reliable fulminating material for percussive flashlamps.

A group of percussive flashlamps of the type shown in the FIGURE and containing as fulminating material 14 the formulation described in the preceding paragraph were tested against a control group of lamps which were identical except for employing pure titanium as the combustible metal powder component in the fulminating material instead of 50 percent titanium and 50 percent titanium hydride. The average rise time for the test lamps was 4.4 milliseconds, as compared to 3.3 milliseconds for the control lamps; the average peak time of the test lamps was 9.2 milliseconds, as compared to 7.6 milliseconds for the control lamps; and the average light output in zonal lumen seconds from 0-25 milliseconds was 452 as compared to 484 for the control lamps. Hence the hydride-containing test lamps exhibited a 33 percent increase in rise time and a 21 percent average increase in peak time, while the fulminating material attenuation reduced light ouput by only 6 percent.

As previously discussed, lamp timing characteristics hafnium or boron powder can be used in combination with the hydrides of titanium or zirconium. In addition, hafnium hydride can be used as an alternate hydride, although it is considerably more expensive.

may be adjusted by varying the combinations of tita- 5 Wh t w l i i nium hydride and titanium metal powders in the fulmi- 1. A photoflash lamp comprising: nating material. This effect is illustrated by the followan hermetically sealed, light-transmitting envelope; ing test data for percussive lamps in which the fulminata quantity of filamentary combustible material 1 ing material was formulated using a 3:1 ratio of hydride r d i hi id envelope; and metal powders to phosphorus, and a 25 percent so- 10 a combustionupporting gas i id v l lution of sodium chlorate: and a primer secured to and extending from one end Average Average Light Output in Peak Time Rise Time Zonal Lumen Seconds TiH Ti (msecs.) (msecs.) (0-25 msecs.)

The ratio of metal hydride or metal and metal hyof said envelope and in communication therewith, dride to red phosphorus may be varied from about 1:1 said primer including a charge of percussionto 8:1 on a weight basis. The combined weight of metal sensitive fulminating material having a powdered hydride, metal (if used), and red phosphorus may commetal hydride as one of its components. prise from about 80 percent to nearly 100 percent of 2. The lamp of claim 1 wherein said metal hydride the dried composition excluding oxidizer. The oxidizer comprises titanium hydride, zirconium hydride, or a may be incorporated in a second operation as decombination thereof. 1 scribed. or it can be stirred into an aqueous mixture 3. The lamp of claim 2 wherein said fulminating maprior to application. If applied by the described imbibterial further contains powdered zirconium or powing process, the concentration of the solution used may dered titanium, be varied from about 10 percent to 50 percent, or the 4. The lamp of claim 1 wherein the principal compoupper limit of solubility for the chosen oxidizing nents of said fulminating material are a fuel, an oxiagent(s). Below about 10 percent, reliability is unacdizer, a powdered metal hydride and a binder. ceptable. The exact optimum percentage is a function 5, The lamp of claim 1 wherein the principal compoof duration of immersion and the nature of the oxidants nts f said fulminating material are red phosphorus, used. For example, mixtures of sodium chlorate with n idi a bi der, nd a combustible metallic pow- Potassium Chlorate Potassium P chlorate, or with der comprising titanium hydride, zirconium hydride or potassium dichromate have been tested; however, a soa combinatign h f, lution of sodium chlorate alone is preferred. If the oxiv 6, Th l f l i 5 h i id t lli powder dizihg agent is to be Stirred directly into the aqueous additionally contains titantium or zirconium. fulminating material slurry, it should be incorporated 40 7 Th l f l i 5 h i th r ti f th d to the extent of 5 t0 5 0 Perceht y Weight of the weight of said metallic powder to said phosphorus is bebined other ingredients. 1 tween about 1 to 8.

Accordingly, although the invention has been de- 8, Th lamp f claim 5 wherein said oxidizer is soscribed with respect to a specific embodiment, it will be di hl te, 1 appreciated that modifications and changes may be 9. The lamp of claim 5 wherein the composition of made by those skilled in the art Witho t dep r ing o said fulminating material further includes relatively the spirit and scope of the invention. For example,'the small quantities of chemical dispersing agent, a wetting combustible metallic powder component of the fulmiagent, a bactericide, sulfur, and magnesium oxide. nating material may also comprise combinations of powdered titanium with zirconiumhydride. Further,

Claims (9)

1. A photoflash lamp comprising: an hermetically sealed, light-transmitting envelope; a quantity of filamentary combustible material located within said envelope; a combustion-supporting gas in said envelope; and a primer secured to and extending from one end of said envelope and in communication therewith, said primer including a charge of percussion-sensitive fulminating material having a powdered metal hydride as one of its components.

2. The lamp of claim 1 wherein said metal hydride comprises titanium hydride, zirconium hydride, or a combination thereof.

3. The lamp of claim 2 wherein said fulminating material further contains powdered zirconium or powdered titanium.

4. The lamp of claim 1 wherein the principal components of said fulminating material are a fuel, an oxidizer, a powdered metal hydride and a binder.

5. The lamp of claim 1 wherein the principal components of said fulminating material are red phosphorus, an oxidizer, a binder, and a combustible metallic powder comprising titanium hydride, zirconium hydride or a combination thereof.

6. The lamp of claim 5 wherein said metallic powder additionally contains titantium or zirconium.

7. The lamp of claim 5 wherein the ratio of the dry weight of said metallic powder to said phosphorus is between about 1 to 8.

8. The lamp of claim 5 wherein said oxidizer is sodium chlorate.

9. The lamp of claim 5 wherein the composition of said fulminating material further includes relatively small quantities of chemical dispersing agent, a wetting agent, a bactericide, sulfur, and magnesium oxide.

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