US2868003A

US2868003A - Photoflash lamp

Info

Publication number: US2868003A
Application number: US639959A
Authority: US
Inventors: Warren F Albrecht
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1957-02-13
Filing date: 1957-02-13
Publication date: 1959-01-13
Anticipated expiration: 1976-01-13
Also published as: CH363233A

Description

W. F. ALBRECHT PHOTOFLASH LAMP Filed Feb. 15, 1957 Jan. 13, 1959 lnven liow". Warren E. Atbvech t, by ya: A,

IT" His A t vneg.

United States PatentOv PHOTOFLASH LAMP Warren F. Albrecht, Euclid, Ohio, assignor to General. I

Electric Company, a corporation of New York My invention relates to photographic flash lamps of the type comprising a sealed bulb or envelope containing a combustion-supporting atmosphere and a charge of combustible material which is ignited by an ignition means comprising a fulminating primer.

In the presently available commercial flash lamps the ignition means includes a fine tungsten filament which is heated to incandescence, usually by a dry cell battery, to ignite the primer which in turn ignites the combustible material, the said combustible material usually consisting of a shredded foil of aluminum. While lamps of that type give good results under proper conditions, yet there exist certain difliculties such as failure of the lamp to fire if the battery should be weakened or run down or if there should be relatively poor contact in the circuit, as between the lamp base and its socket, for instance.

It is therefore an object of my invention to overcome the aforesaid diflficulties by providing a flash lamp and ignition system wherein the filament is dispensed with. It is a further object to provide a filamentless type flash lamp which is completely reliable in operation even fro-m an electrical power source possessing very little energy It is a still further and particularly desirable object to provide a flash lamp which can be flashed reliably by the low energy output of a piezoelectric crystal.

Generally speaking, it has been proposed heretofore to provide a filamentless type photoflash lamp. In one such lamp containing a filling of combustible foil, a pair of electrodes were arranged in fixed spaced relation and a fulminating substance was disposed in the gap therebetween to be ignited by an arc discharge formed between the electrodes by application of a high voltage current from a transformer. It has also been proposed to provide a flash lamp with a single electrode coated with a dielectric and with a primer composition and flashed by a potential of some 10,000 to 20,000 volts to produce a spark discharge to ignite the primer and the combustible foil.

Suchprior art lamps require the application of a substantial amount of electrical energy for reliable flashing of the lamp, and it is a further object of my invention to provide an improved flash lamp construction which is reliable in operation from a source of substantially lower electrical energy level and which does not require a precise fixed electrode spacing.- Further features and advantages of my invention, including novel features of construction, will appear from the following description of species thereof.

In accordance with one aspect of my invention, I provide a flash lamp comprising a bulb or envelope containing a combustion-supporting atmosphere and a combusin tible metallic material such as shredded foil, and a pair of internal electrodes at least one of which is provided with a primer composition and wherein the combustible material is arranged to provide a conducting path between the electrodes whereby a power surge will form small arcs between an electrode and the combustible material through the primer to thus ignite the primer and,

Patented Jan. 13, 1959 through it, the combustible materiaL. The current flows in a path from one electrode, in an are through its primer coating to the combustible material and, by conduction through the foil, to the other electrode or, in case the second electrode is also provided with a primer coating, then to the said primer coating and in an are through said coating to the second electrode, thus completing the circuit.

For a further understanding of the invention, reference may be had to the following detailed description and to the drawing wherein:

Fig. 1 is a side view, in section, of a flash lamp of unique double-ended construction comprising my inven tion and an electrical operating circuit therefor;

Fig. 2 is a fragmentary section of a'slightly modified construction; and a 1 Fig. 3 is an elevation of a single-ended type of lamp embodying the invention. 7

Referring to Fig. 1, the lamp shown therein is of a double-ended construction which is made practicable for manufacture on a commercial basis by the absence of a filament. The lamp comprises a radiation-transmitting bulb 1 preferably of glass and of tubular form. The ends 1 of the bulb are provided with'r educed neck portions 2 to which are hermetically sealed, preferably by direct fused metal-to-glass seals, metal terminals or contact members 3, here illustrated as slightly dished or concave discs of a metal or alloy capable of sealing to glass, for instance a chrome iron alloy where the bulb 1 is of the usual high expansion glass employed in the'lamp art. Thereis attached to each of the terminals 3, for example by welding or brazing,-a' wire electrode 4 which extends into the interior of the bulb and may be made of any suitable metal such as iron, copper, aluminum, nickel, etc.

One of the electrodes 4 is coated with a porous primer 5 which may be of the same composition as that employed generally in the conventional filament type flash lamps. Such primers generally comprise a porous mix ture of a readily ignitable metallic powder such as zirconium or a mixture of zirconium with magnesium, and an oxidizing agent such as potassium perchlorate, bonded together by a suitable binder such as nitrocellulose. By way of example, a suitable primer composition may consist of, by weight, 90% zirconium and 10% potassium perchlorate formed as a suspension in a solution of nitrocellulose in amyl acetate and having a: viscosity about 24 centipoises x grams per cubic cm; In a typical example,

a half inch long electrode carried a total weight of about .00437 gram of the primer.

The bulb 1 contains a filling of a loose mass of combustible material 6, preferably in the form of shredded aluminum foil such as that employed in conventional lamps. The bulb also contains an atmosphere of combustion-supporting gas, preferably oxygen at a suitable pressure which may be below or above atmospheric. In smaller bulb sizes the oxygen pressure may be some 1200 millimeters.

The lamp shown in Fig. 2 is essentially like that shown in Pig. 1 but with a modified form of terminal 3 which is cup shaped and has its edge or rim embedded in the thickness of the neck portion 2- of the bulb 1.

The lamp shown in Fig. 3 is -of a single-ended type comprising a glass bulb 7 of conventional butt seal construction wherein a pair of lead-in wires or electrodes 8 extend into the bulb through the walls'thereof' and are held in spaced relationship by 'a glass bea'd9 fused thereto. The portion of each electrode 8 above the head 9 is coated with a primer 10 which may be of the composition referred to above in connection with Fig. '1.

In order to prevent short-circuiting of the electrodes 8 by the metallic foil 11, the portions of the electrodes within the bulb and below the head 9 are provided with an electrically insulating or dielectric coating indicated at 12. Conveniently, the dielectric coating 12 may be of a borate composition which is conventionally applied to the leads or electrodes 8 to assist in forming a good fused'sea'l with the glass bulb 1. The electrodes may be composed of conventional dumet wire which is a copper-sheathed nickel-iron core wire. The borate coating isremoved from'the portions of the'electrodesgabove the bead 9, or at least from the extremities thereof, before application of the primer 10 thereto. The bulb 7 is filled with a combustion-supporting gas and may be provided with a base.13 having a .shell contact 14 and amend contact lS to which are connected the respective lead wires or electrodes 8.

It is an essential feature of my invention that the combustible foilfforms a conducting path between the electrodes from which the foil 'is physically separated only by the normally insulating porous primer coating on one or both electrodes. Thus, in Fig. l, the foil 6 is in direct contact with the right-hand electrode 4 and with the primer coating on the left-hand electrode 4. In Fig. 3, the foil 11 is in engagement with the primer coatings on both electrodes 8. i

The lamp is flashed by a power surge from a source 16 of relatively high voltage (say 200 to 500 volts) and short duration (say'20 to 100 microseconds). The voltage appearing across the terminals 3 (Fig. 1) forms small arcs in completing a current path inside the lamp. This path starts from one electrode 4 (say the left-hand one, arcing through the primer coating 5 to the foil 6 and through the foil to the .other electrode 4, thus completing the circuit. The small arc or arcs thus formed ignite the primer 5 which ignites the foil 6 to flash thelamp. In the lamp of. Fig. 3thepath is from one electrode 8, arcing through the primer coating 10 thereon to the foil 11 which conducts thecurrent to the primer coating 10 on the other electrode v8, and arcing through that primer to the said other electrode to complete the circuit and flash the lamp.

A significant advantage of this construction is that there need be no definite fixed spacing between the .electrodes, thereby eliminating the need for accuracy and making entirely feasible the mass production of such lamps on a commercial basis. The absence of a filament also makes practicable the production of doubleended lamps of the type shown in Fig. 1 which lend themselves particularly well to use in magazine type feeding or loading equipmentemployed with a camera.

A particularly significant advantage of the lamps disclosed herein is that they are capable of being flashed reliably when a piezoelectric crystal isemployed as the energy source as indicated at 16 in Fig. 1. The lamps may be flashed successfully when the power source 16 is a battery-transformer combination or a static electricity charge, butit is especially advantageous that they can be flashed successfully when employing a source of such low energy level (in the order of microwatts) as that supplied by a piezoelectric crystal, thereby completely eliminating the need for a battery with its attendant inconvenience and disadvantages. To flash the lamp, the crystal 16 -is given a sharp blow to cause it to emit a momentary voltage of steep wave front. While Rochelle salt crystals may be employed, I prefer to employ a crystal of barium titanate which may yield a voltage of some 200 to 1000 volts for a duration of a few microseconds with a total energy in the order of microwatts. A barium titanate crystal of about inch diameter and flrinch thick yielding a potential of about 450 volts has been employed satisfactorily for this purpose.

It will be noted that the gap between the

electrodes

4 or 8 is much too large to sustain a discharge directly therebetween through the gaseous atmosphere in the bulb when employing a piezoelectric crystal as the power source. Inorder tosustain a discharge directly between the electrodes from a piezoelectric crystal source, the electrode spacing would have to be of the order of inch; obviously, it would be inordinately difficult to maintain such spacing on a commercial mass production basis. Neither is it feasible to flash any of the lamps heretofore proposed and of which the applicant is aware, whether of the type containing a filament or of the arc type, by employing a piezoelectric crystal as the source of power. In the case of the filament type lamp, the energy level of the surge from the crystal is too low to heat the filament to a sufficiently high temperature to ignite the primer, and in the case of the arc type lamps the energy level islikewise too low to form an arc in the constructions heretofore proposed. It is therefore essential for this purpose to employ the construction disclosed herein where the combustible foil is arranged to form a conducting path or bridge between a pair of internal electrodes.

In the lamp shown in Fig. 1, it is preferable to coat the entire length of the one electrode 4 with the primer 5. However, if desired, the primer may be applied on only a portion of the length of the electrode, preferably the innermost end portion remote from the terminal 3, and in that event the remainder of the electrode must be coated with an insulator or dielectric to avoid shortcircuiting of the two electrodes 4 by the metallic foil 6. Such insulating or dielectric coatings may consist of an oxide of the metal of the electrode, for instance a copper oxide coating on a copper electrode, or other suitable dielectric coatings such as the borate coating 12 in the Fig. 3 lamp or a coating formed by a smoke deposit from a flame burning a mixture of boric acid and Synasol. Synasol is a water white liquid composed of about 100 parts denatured ethyl alcohol, 5 parts ethyl acetate and one part aviation gasoline.

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

l. A photographic flash lamp comprising a sealed radiation-transmitting bulb, a pair of spaced metallic electrodes extending into said bulb, one of said electrodes having substantially its full length within the bulb coated with electrically insulating material, at least a portion of said insulating material consisting of a primer, a loose mass of metallic combustible material substantially filling said bulb and in contact with both the primer on said one electrode and with the other electrode and forming an electrically conducting path therebetween for formatron of a spark discharge between said one electrode and the combustible material through said primer upon appllcatlon of a high voltage current to said electrodes, and a combustion-supporting atmosphere in said bulb.

2. A photographic flash lamp comprising a sealed rad1at1on-trans-mitting bulb, a pair of spaced metallic electrodes extending into said bulb, .one of said electrodes having substantially its full length within the bulb coated with electrically insulating primer, a loose mass of metalcombustible material substantially filling said bulb and in contact with both the primer on said one electrode and wlth the other electrode and forming an electrically conductlng path therebetween for formation of a spark discharge between said one electrode and the combustible material through said primer upon application of a high voltage current to said electrodes, and a combustionsupporting atmosphere in said bulb.

3. A photographic flashlarnp comprising a sealed ramatron-transmitting bulb, a pair of spaced metallic electrodes extending into said bulb, both said electrodes havingsubstantially their full lengths within the bulb coated with electrically insulating material, at least a portion of said insulating material consisting of a primer, a loose mass of metallic combustible material substantially filling said bulb and in contact with the primer onbothsaid electrodes and forming an electrically conducting path therebetween for formation of spark discharges between said electrodes and the combustible material through said primer upon application of a high voltage current to said electrodes, and a combustion-supporting atmosphere in said bulb.

4. A photographic flash lamp comprising a sealed tubular radiation-transmitting bulb, a pair of spaced metallic electrodes extending into said bulb from the opposite ends thereof, one of said electrodes having substantially its full length Within the bulb coated with electrically insulating material, at least a portion of said insulating material consisting of a primer, a loose mass of metallic combustible material substantially filling said bulb and in contact with both the primer on said one electrode and with the other electrode and forming an electrically conducting path therebetween for formation of a spark discharge between said one electrode and the combustible material through said primer upon application of a high 5. A photographic flash lamp comprising a sealed tubular glass bulb, a pair of disc-like metallic terminals fusionsealed directly to the edges of respective openings in the opposite ends of said bulb, a pair of metallic electrodes secured to respective ones of said terminals and extending into the bulb, one of said electrodes having substantially its full length within the bulb coated with electrically insulating material, at least a portion of said insulating material consisting of a primer, a loose mass of metallic combustible material substantially filling said bulb and in contact with both the primer on said one electrode and with the other electrode and forming an electrically conducting path therebetween for formation of a spark discharge between said one electrode and the combustible material through said primer upon application of a high voltage current to said electrodes, and a combustionsupporting atmosphere in said bulb.

References Cited in the file of this patent UNITED STATES PATENTS