Method And Apparatus For Indirect Electrical Ignition Of Combustible Powders

Abstract

A method and apparatus for the ignition of combustible powders using transparently shielded sources of high intensity light pulses is described. Preferably, low actuating voltage, one shot or consumable photoflash lamps are used to generate a light pulse which is absorbed by the combustible powders and produces ignition. Particularly described is a flashbulb connected to a flashing circuit and a secondary circuit in the flashing circuit for intermittently or continuously conductively monitoring the firing status of the bulb prior to flashing. Particularly preferred combustible powders are nitrocellulose and/or black powders which because of their black color are particularly light absorptive. A photoflash igniter device for practicing the method is particularly described. The igniter and method are particularly useful for generating gas pressure waves which can be used for mass movement and/or forming.

Description

BACKGROUND OF THE INVENTION

The present invention relates to an igniter for combustible powders. In particular, the present invention relates to the use of transparently shielded high intensity light pulses preferably those generated by chemical reactions initiated at low voltage to ignite combustible powders.

The prior art, such as illustrated by U. S. Pat. Nos. 3,642,304 and 3,695,179 shows electrical igniters wherein the electricity directly causes the ignition of a detonatable powder using an electrical spark or heated wire. Such devices do not provide a means for easily and safely continuously monitoring the continuity of the firing circuit because of the danger of causing a premature ignition of the powder.

The effect of light in heating solids is shown in Nelson, L.S., Intense Rapid Heating With Flash Discharge Lamps Science, Volume 136, No. 3513, (April 1962) and U. S. Pat. No. 3,175,030 and 3,271,220. The discussion therein is directed to reusable rare gas, such as xenon, type flash lamps, requiring a relatively high transient high voltage for firing.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an electrical ignition means which provides for continuous conductive monitoring of the electrical circuit without risk of premature or unwanted ignition of the combustible powder. These and other objects will become increasingly apparent to those skilled in the art by reference to the following description and the drawing.

SUMMARY OF THE DRAWING

FIG. 1 is a schematic view of the method of the present invention particularly illustrating the firing of a flashbulb to ignite a combustible powder maintained in contact with the bulb by a covering.

FIG. 2 illustrates a flashbulb with a powder containing ring attached so that the powder is separated a small distance from the bulb.

FIG. 3 illustrates powder in two positions on the inside flashbulb cover and with an outer cover over the bulb.

FIGS. 4 and 4a illustrate a flashbulb disposed on the outside of a cylindrical glass tube with the powder positioned on the inside of the tube adjacent the bulb.

FIG. 5 illustrates a flashbulb with a transparent film interposed between the bulb and the combustible powder.

FIG. 6 illustrates a burnable material positioned above the powder.

FIG. 7 shows a low voltage battery circuit for continuously monitoring the conductivity of a flashbulb circuit of FIG. 1.

FIG. 8 is a schematic view showing a type of an igniter system for air bags where the gas from the ignition of an explosive directly expands the bag.

FIG. 9 is a schematic view showing an air bag system where the igniter actuates a frangible valve connected to a high pressure gas source.

FIG. 9a is a cross sectional view of the frangible valve shown in FIG. 9.

FIG. 10 is a schematic view showing an aperture shield between a light source and a barrel and projectile system.

DETAILED DESCRIPTION OF THE INVENTION

In particular the present invention relates to the method of igniting combustible powders which comprises: providing a finely divided light absorptive combustible powder in spaced, transparently shielded separation from an electrically conductive means for generating a high intensity light pulse which has a duration of less than about one second; and providing a voltage above the threshold, thereby exposing the combustible powder to the high intensity pulse so that the powder is ignited. Further, the present invention relates to the article of manufacture useful as an igniter which comprises: an electrically conductive transparently shielded means for generating a high intensity light pulse of less than one second duration; a finely divided light absorptive combustible powder adjacent the surface of the shield opposite the means for generating the light pulse so as to be light ignitable; and means for holding the powder in position adjacent the shield so as to be light absorptive prior to generation of the light pulse. As will be apparent from the following description, it is the light and not the heat from the generation of the light pulse which ignites the combustible powder.

The preferred one shot or consumable light flash generating means, such as flashbulbs, used in the present invention generate light in the visible and ultravoilet spectrums. The bulbs are usually constructed with a fine wire magnesium element inside a glass bulb containing air or oxygen enriched air fitted to a press or screw metal base. Two terminals inside the bulb are connected to the magnesium wire, one terminal being connected to the side walls of the base and the other to a conductive pin at the center of the base. The terminals are insulated from each other. The bulb is provided with a plastic covering which prevents the glass bulb from shattering. The plastic covering can be omitted in situations where glass high velocity particles from pressure waves are not a problem or where they are desirable. With the flash cubes, the transparent plastic covering can be removed and multiple firings (four bulbs at once can be used.

The bulbs or other light transmissive shielding means can have magnesium or aluminum powder bonded onto a high resistive conductor which heats the powder for firing. Other compounds which generate high intensity light pulses in the visible spectrum upon chemical reaction and which permit continuous conductive monitoring of the circuit without firing can be used. Usually the firing voltage for flashbulbs is less than (5) volts and preferably above (1) volt. Numerous variations will occur to those skilled in the art. A reactive gas environment can be used with the magnesium or aluminum, particularly a highly reactive oxidizing agent (such as oxygen). This results in a more intense light pulse or flash.

The rare gas flash lamps can be used in the method and apparatus of the present invention and are well known to those skilled in the art although they are not preferred because of the much greater voltage requirement for firing. Such lamps are shown in U. S. Pat. No. 3,175,030 and have the advantage of being reusable; however, they would have to be shielded from the combustible powders used in the method and apparatus of the present invention such as by a shutter to prevent damage. Small lamps for photographic purposes operate on 110 volt A.C. sources and are relatively inexpensive by comparison to general purpose rare gas flash lamps.

The combustible powders are preferably light absorptive or are coated with light absorptive chemicals. Black powder and nitrocellulose powders are sufficiently light absorptive without any coatings. It is contemplated for instance that the magnesium powders alone or in combination with ammonium nitrate could be ignited using the method of the present invention. Other powdered explosives can be ignited in the same manner.

Examples I and II illustrate the use of a black combustible powder which is very light absorptive of its color.

EXAMPLE I

Referring to FIG. 1 a conventional plastic coated round transparent photoflash bulb 10 measuring about 3.8 cm long by about 12 cm in diameter (Sylvania-Focal Plane 26) was used. Inside the bulb 10 were fine magnesium wires 10a connected to two terminals. The flashbulb 10 was of the socket metal side 11 press base 12 type firing at 3 volts or more and having an intensity of 20,500 lumen second upon firing. Black powder 13 (FFF, DuPont) was ground to a fine flour-like powder. The center portion of the adhesive surface of a semi-transparent tape 14 about 4 cm long was coated with the ground black powder 13 and then attached around part of the circumference of the bulb 10. The bulb 10 was placed in an adaptor for the side 11 and base 12 and then fitted into a conventional aluminum case, ceramic light bulb holder with a long heavy duty two-wire 15 and 16 electrical cord attached. A conventional 110 volt AC to 15 volt DC transformer (not shown) was used to provide a DC voltage for triggering the flashbulb through the electrical cord terminals 17 and 18. Continuity of the flashbulb circuit was determined with a low voltage ohmmeter across terminals 17 and 18. There was very little resistance. The bulb 10 with the powder 13 attached was then flashed using the 15 volts DC which produced a detonation or explosive noise from the ignition of the black powder 13. The plastic surface of the bulb 10 was melted from the ignition of the powder 13 and from the heat from the flashing of the bulb 10; however, the fired bulb 19 was not broken apart, and the tape 14 adhered to the surface of the fired bulb 19.

EXAMPLE II

The procedure of Example 1 was repeated without grinding the FFF black powder and the powder ignited.

In Example I, the black powder which is more finely divided is easier to ignite because more light energy is absorbed by individual particles. As can be seen from Example II much larger sized particles (FFF) will also ignite.

When the powder was provided in spaced relation from the outside surface of the bulb, ignition depended upon the particle size of the powder and the spacing as can be seen from the following Examples III, IV and V.

EXAMPLE III

Referring to FIG. 2, the procedure of Example I was repeated except that the powder 21 was separated from a bulb 22 by placing it about 0.6 cm from the outer circumference surface of the bulb 22. This was accomplished by using a 0.6 cm by 2.5 cm inside diameter ring 23 covered by cardboard 24 on the bottom fixed to the ring 23 with the ground powder 21 loosely dispersed on the cardboard 24 inside the ring 23. The ring 23 was taped 25 to the surface of the bulb 22. Upon flashing of the bulb 22 the powder 21 ignited with a detonation sound. The ring 23 and cardboard 24 separated from the bulb 22 but the bulb 22 was not broken. The bulb 22 had a conventional base 26, magnesium wires 27, glass envelope 28 and plastic protective covering 29.

EXAMPLE IV

The procedure of Example III was repeated with the FFF black powder 21 which did not ignite.

EXAMPLE V

The procedure of Example III was repeated with the ground powder 21 about 2.54 cm from the bulb 22 and it did not ignite.

The clear bulbs transmit the most light, but blue bulbs of much smaller size work as well for ignition of the combustible powders. Illustrative is the following Example VI.

EXAMPLE VI

The procedure of Example I was repeated with smaller blue oblong flashbulbs measuring about 3.2 bu 7.6 cm in diameter (M-2 Sylvania). As before, the powder was taped with semi-transparent tape to the surface of the bulb. Upon flashing the powder ignited with a detonation sound. The bulb was not broken.

In order to demonstrate that other light absorptive combustible powders could be ignited, the procedure of Examples I and VI were repeated with nitrocellulose gun powder. Illustrative are the following Examples VII and VIII.

EXAMPLE VII

The procedure of Example I was repeated with the clear FP-26 flashbulb and with nitrocellulose powder (16 gauge shotgun disc shaped) taped to the bulb. The powder ignited upon flashing of the bulb but did not produce a detonation sound.

EXAMPLE VIII

The procedure of Example VII was repeated with the M2 blue flashbulb and again the nitrocellulose powder ignited without a detonation sound.

As will be apparent from Examples VII and VIII compared with Examples I to VI, the black gun powder is ignited more vigorously than the nitrocellulose powder. Illustrative is the following Example IX.

EXAMPLE IX

The procedure of Example I was repeated with a mixture of FFF black and nitrocellulose powders, about equal parts by volume, taped to the surface of the bulb. It was found that there was a loud detonation sound.

In order to enhance the absorption of light by the powder, black elastic vinyl electrical tape was used to completely cover the bulb with the powder next to the bulb surface. Illustrative is the following Example X.

EXAMPLE X

Referring to FIG. 3, using the procedure of Example I, equal parts by volume of black and nitrocellulose powders 30 were taped 31 with black vinyl elastic tape, which is light absorptive because of its color, to the top 32 and side 33 surfaces of the bulb 34. The bulb 34 was then wrapped completely with the elastic tape 35. Upon ignition the powders 30 detonated and it was found that the tape 35 covering was separated from the bulb 34 without tearing and that the metal base 36 had separated from the bulb 34 but the bulb 34 was otherwise intact because of the elastic nature of the tape 35.

In order to demonstrate the effect of the light alone, without the heat from the plastic covering due to flashing of the bulb, the flash of light was directed to the powder through a curved piece of glass. Illustrative is the following EXAMPLE XI.

EXAMPLE XI

Referring to FIG. 4, the procedure of Example I was repeated except that the F-P 26 bulb 37 was taped 38 in contact with the outside surface of a glass jar 39 with the powder 40 adhered with black tape 41 to the inside of the jar 39 about 10 cm in diameter and with about 0.3 cm wall thickness. The powder 40 was equal parts by volume black powder and nitrocellulose. The black powder was ground to flour. It was found that the powder was ignited without a detonation sound. Where the bulb 37 was placed on the inside of the curved jar 39 and the powder 40 on the outside (not shown) the diffusion of the light pulse by the jar 39 walls prevented ignition, probably because the reverse curvature of the jar 39 diffused the light away from the powder.

It was thought that some light focusng means around the flashbulb would make the ignition of the powder more energetic. Illustrative is the following Example XII.

EXAMPLE XII

As shown in FIG. 4a, the procedure of Example XI was repeated, except that a ring of polished aluminum 42 was provided around the bulb 37 and extending outward from the jar 39. Upon flashing of the bulb 37 the powder 40 inside the jar 39 ignited without a detonation sound but with an apparently shorter ignition duration.

Other barrier materials of thinner cross-section allowed more light to go to the powder. Illustrative is the following Example XIII.

EXAMPLE XIII

Referring to FIG. 5, the procedure of Example X was repeated except that a thin clear vinyl film 43 was interposed between the powder 44 and the bulb 45 and all were taped to the surface of the bulb 45. Upon flashing, the ignition of the powder produced a detonation sound without burning of the clear vinyl film.

The rate of ignition of the combustible powders is illustrated by the following Example XIV.

EXAMPLE XIV

The almost complete instantaneous ignition of the powders was shown by placing a white piece of paper 47 above the powder 48 using the procedure of Example X with the covering 49 on the bulb 50. It was found that upon detonation the paper 47 was largely unburned. Where there was not a detonation, as with the nitrocellulose powders alone, there was evidence of some burning but even in this instance, the burning was not substantial. The effect of the light is very fast where all of the powder is exposed to the light under confined conditions.

In order to demonstrate that it was not the heat from the bulb that was igniting the combustible powder, the light from the flash was shielded in a manner allowing heat transfer to the powder. Illustrative is the following Example XV.

EXAMPLE XV

The procedure of Example 1 was repeated except that a single layer of black vinyl tape was placed on the outside surface of the bulb so as to form a light barrier to powdered FFF black powder positioned on the tape with a second tape covering. Upon flashing of the bulb, the powder did not ignite.

FIG. 7 shows a circuit for continuously monitoring the conductivity of the circuit of FIG. 1. Thus a battery 51 of low voltage, for instance, less than the three volts firing voltage is provided in electrical parallel along with a meter 52 such as a voltmeter. A switch 53 is provided with a high firing voltage battery 54 which can be in the form of a conventional inertia actuated sensing device such as shown in U. S. Pat. No. 3,552,768, 3,618,117 and 3,571,539. Other variations will be obvious to those skilled in the art.

FIG. 8 illustrates one variation of a direct air bag expansion system using the gases from the combustion of a powder to fill the air bag. In particular a flashbulb 60 is electrically connected as in FIG. 7 at terminals 17 and 18. The base 61 of the bulb 60 is positioned in a slot holder 62 in a canister or container 63. A combustible powder 64 is packed around the bulb 60. A diaphragm or thin film (such as vinyl) 65 is sealed to the inner walls 63a of the canister 63. The wall 66 of the canister 63 has openings or orifices 67 for passage of the expanding gas from the ignition of the powder 64. On the downstream side of the openings 67 is a flared open ended housing 68 for an air bag 69 (shown in its collapsed condition). In operation, the bulb 60 flashes, the powder 64 ignites and fills the cavity 70. The diaphragm 65 reaches the outer wall 66 of the canister 63 and ruptures at the orifices 67 releasing the gas to the bag 69. The above system is similar to that shown in U. S. Pat. No. 3,695,179. Numerous variations will occur to those skilled in the art.

FIGS. 9 and 9a illustrate one variation of the indirect air bag expansion system using the explosion of the powder to open a valved, high pressure gas tank. The general system as shown in FIG. 9 includes a high pressure gas tank 71 connected by a conduit 72 to an explosively actuated valve 73. The downstream side of the valve 73 is connected by a conduit 74 to an air bag holder 75 and an air bag 76 (shown in broken lines in its expanded position). The valve 73 is explosively actuated by an igniter 77 electrically connected by leads 78 and 79 to a sensor device 80 usually of the inertial ring or pendulum type. This basic type of air bag system is shown in U. S. Pat. No. 3,642,304. Referring to FIG. 9a, the base 82 of the bulb 81 is positioned in a holder 83. A combustible powder 84 is positioned around the bulb 81 in a canister 85 having holes 86 at the end opposite the bulb 81. A larger housing 87 mounts the igniter assembly into position in valve 73. On the downstream side of the holes 86 is a chamber 88 adjacent an explosively rupturable diaphragm 89 with a ring groove 90 for separation by the explosion of the powder 84. The movement diaphragm 89 opens the valve 73 for passage of the gas in tank 71 to the air bag 76.

FIG. 10 schematically illustrates a variation wherein a metal shield 91 is provided between the light source 92 and an ignitable powder 93 with an opening 94 for light passage. The powder 93 is fitted into the base of a cartridge 95 with a bullet 96 and the cartridge 95 is provided in a barrel 97. The shield 91 is rotatable on an axis. The flashbulb 92 can be of the cube shaped type and can be of the "X" type with its own battery powder. In this case there would be four holes 94 in the shield 91. In operation the shield 91 is positioned so that the opening allows passage of light from the flashbulb 92 and then rotates to close the barrel 97. A trigger (not shown) actuates the bulb 92 and wheel 91 in the manner of an aperture of a camera. As will be seen, the system is easily adaptable to the "caseless" type cartridge 95 wherein bonded particles of powder form the cartridge 95.

Various light focusing means, such as lenses or shields, can be used to enhance the effect of the light. Such variations will be obvious to those skilled in the prior art.

Claims

I claim:

1. The method of igniting combustible powders which comprises:

a. providing a finely divided light absorptive explodable combustible powder in spaced, transparently shielded separation from an electrically conductive means for generating a high intensity visible spectrum flash light pulse upon achieving a threshold voltage which has a duration of less than about one second;

b. providing means for holding the powder in position adjacent to the shield so as to be light absorptive; and

c. providing a voltage above the threshold, thereby exposing the combustible powder to the high intensity pulse so that the powder is ignited.

2. The method of claim 1 wherein the powder comprises black powder.

3. The method of claim 2 wherein a nitrocellulose powder is mixed with the black powder.

4. The method of claim 1 wherein the powder is provided in contact with the outside surface of a conventional photoflash bulb as the conductive means for generating the light pulse.

5. The method of claim 1 wherein the conductive means for generating the light pulse is a flash bulb and wherein the powder is sealed in contact with the outside of the surface of the bulb by a sealling means.

6. The method of claim 5 wherein a light absorbing sealing means for the powder is used.

7. The method of claim 5 wherein the powder is a mixture of black and nitrocellulose powders.

8. The article of manufacture useful as an igniter which comprises:

a. an electrically conductive transparently shielded means for generating a high intensity visible spectrum flash light pulse of less than one second duration upon achieving a threshold voltage;

b. a fully divided light absorptive explodable combustible powder adjacent the surface of the shield opposite the means for generating the light pulse so as to be light ignitable; and

c. means for holding the power in position adjacent to the shield so as to be light absorptive.

9. The article of claim 8 wherein the combustible powder is a mixture of black and nitrocellulose gun powders.

10. The article of claim 8 wherein the means for holding the powder is a covering over the powder and shield so that the powder is held in contact with the outside surface of the shield.

11. The article of claim 10 wherein the powder is exploded by the light and wherein the cover is elastic and is projectable outward from the shield upon detonation of the powder.

12. The article of claim 8 wherein the powder is explodable by the light pulse and wherein a solid mass is associated with the powder such that it is movable by the explosion.

13. The article of claim 8 wherein the light pulse means includes reactive chemicals requiring a low threshold voltage for generation of the light pulse.

14. The article of claim 8 wherein the light pulse means is a photoflash bulb having a threshold voltage of less than about five volts.