US3110846A - Electrical igniter - Google Patents

Description

Nov. 12, 1963 D. A. wEDwIcK 3,110,346

ELECTRICAL IGNITER Filed June '7, 1960 svs oazmnssaad FIG. 3

033:! BSGIELLHVO DON A. WEDWICK INVENTOR.

United States Patent Olice 3,ll,8b Patented Nov. l2, l

3,ll-,346 ELECTRCAL EGNTER Don A. Wedwieir, Mount Ariington, NJ., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Filed .lune '7, 196i?. Ser. No. 34,419 4 Claims. (Si. 311-80) This invention relates to devices for iigniting thermally decomposable gas-generating charges. More specically, it is related to electrical igniters for igniting gas-generating charges in which the igniter is repeatedly utilized.

The various types of electrical igniters heretofore utilized in the explosives art have been of the perishable type. That is, for the most part, they have been one-shot devices which are usually destroyed or consumed with the explosive that they were employed to initiate. However, with the advent of blasting methods which employ reutilizable apparatus such as pressure-resistant tubes and pressure-resistant drills in conjunction with thermally de` composable gas-generating charges, the requirements of electrical igniters take on an entirely different aspect. Such electrical igniters must then be re-utilizable, capable of repeatedly resisting extremely high pressures and ternperatures, and must possess outstanding characteristics in respect to safety, reliability and longevity.

A primary object of the present invention is to provide devices meeting the aforesaid requirements. Other objects of the invention will appear hereinafter, the novel features and combinations being set forth in the appended claims.

Generally described, the present invention comprises an electrical igniter for a gas-producing cartridge especially adapted for penetration of the cartridge and repeated utilization having in combination support means, a pair of spaced longitudinal conductive members, each of which has one end extending through the support means to form a pair of electrical terminals and each of which has the other end pointed and inwardly bent in close spaced relationship to each other, and heating means bridging lthe conductive members near the inner point of transition of the inwardly bent portion of each conductive member.

A preferred embodiment of the invention has been chosen for purposes of illustration and description and is shown in the accompanying drawing wherein reference symbols refer to like parts Wherever they occur.

FIG. l is a part sectional, part elevational View of apparatus utilizing igniter means according to the invention.

FIG. 2 is an enlarged, fragmentary, part sectional, part elevational view of igniter means constructed in accordance with the invention; and

PIG. 3 is a plan view of the igniter depicted in FIG. 2.

ln FIG. l, support members l, forming a part of an automatic blasting apparatus, are rigidly secured to a cylindrical combustion chamber 2 having an aft or feed end for ingress of thermally decomposable cartridges containing gas-producing composition and a forward end of reduced diameter for the egress of pressurized gas. Threadedly secured to the combustion chamber 2 is a retainer ring 3 which in turn compressively secures a head insert ring 4 between the ring 3 and the chamber 2 with an O ring-seal Zrs providing a gas-seal therebetween. A reciprocating ring head 5 slides into the head insert ring 4 and is gas-sealed by an O ring-seal Srs. The firing head 5 is provided with a rigid, bifurcated electrical igniter 6 which is secured to the tiring head by Ia retainer nut 7 which is threaded into the firing head. A compression assembly is then provided by insulated washer S, socket connector 9, and spacers it@ each side of Teflon seal l1. This compression assembly with the seal l1 interposed between the spacers or rigid compression elements lil prevents any blow-back of high pressure gas through the ignition system since the retainer nut 7 is utilized to impart considerable precompression on the assembly to insure that the Teflon seal is sufficiently tight about the lead wires and is firmly seated to withstand the pressures generated in the combustion chamber. Although Teflon, which is a polytetrailuoroethylene resin, is preferred as the seal material, other resins and compressible sealing miaterials which are suitable for high temperature and high pressure service may be used. A compression spring l2 has one end secured to the retainer nut 7 and its other end provided with a thrust washer i3. r[he spring in its fully extended position extends to approximately the point of the igniter 6.

In operation of the device, it will be understood, of course, that the firing head S and the assembly aiiixed thereto retract into an automatic feed chamber (not shown) whereupon the points of the igniter 6 and the thrust washer 13 engage a cartridge 14 and push it forward to engage a thrust seat l5, which in turn supports a shear ring lr6. The thrust seat 15 is gas-sealed to the combustion chamber 2 by an 0 ring-seal 15m. A cartridge guide 17 affixed to the head insert ring 4- insures that the cartridge is guided to properly engage the shear ring 16. The cartridge 14 comprises a paper shell 18, a heat-resistant rupturable closure element 19 affixed to its fonvard end, a main gas-producing charge 2d, a primer charge 2l, and a penetrable tinted end crimp 18e for closing its aft or ignition end. When [the cartridge 14 is operatively positioned in the combustion chamber 2, the rigid electrical igniter 6 has been forced through the penetrable fluted end crimp lSc into the cant-ridge and has penetrated the cartridge to a depth of about 11A inches. The firing head 5 is then locked by suitable means (not shown) and the `device is ready for firing. Electric firing current is then delivered via lead wires 22 and 23 to the rigid electrical igniter `6 which ignites the ignition of priming charge 2l which in turn ignites the main gas-producing charge 2t?. This results in a self-sustained decomposition of the cartridge including its shell and when the resulting high pressure gases reach a predetermined pressure, the rupturable closure element l@ ruptures and disintegrates with Sudden release of the gases from the combustion chamber 2 via a discharge orifice 24 to perform useful work, particularly in conjunction with blasting apparatus such as that disclosed in copending application of Robert W. Lawrence and Robert l'. Shiel, Serial No. 783,867, filed December 30, 1958 and now Patent No. 3,055,648.

Referring to FIGS. 2 and 3, it rwill be noted that the igniter 6 is the igniter depicted in FIG. l which will now be described in detail. The igniter 6 has a stainless steel support member Si). A pair of stainless steel spaced longitudinal conductive members 3l and 32, respeotiveiy, extends through the support member Sil. One end of each of the longitudinal conductive members was threaded and utilized as a terminal las represented by 33 and 3d, respectively. insulating sleeves 35 and 36 were provided through the support member 3i? to insulate the conductive members 3l and 32 therefrom. Flanges 3'7 and 3S integral with conductive members 3l and 32, respectively, |were provided to engage compatible flanges on the insulating sleeves 35 and 36. A thick insulating member 39 was provided within the support member 3@ with the conductive members 3l `and 32 extending there* through. A nut and washer combination 4t) and el was provided with the nuts thereof engaging the threaded portions 33 and 34, respectively, of conductive members 3l and 32. This assembly provided a rigid construction upon tightly securing the nuts whereupon the insulating sleeves 35 and 36 and the insulating member 39 were D precompressed to form a seal resistant to high pressure gas as generated on ythe ingress side of the igniter.

The ingress end of conductive members 31 and 32 was formed by pointing and inwardly bending each of the members as represented by 42 and 43, respectively, so that the ends thereof were in close spaced relationship. Additionally, the facing surfaces 44 and 45 of conductive members 31 and 32, respectively, were finished to provide a parallel surface. A heating element 46 was provided to bridge the conductive members 31 and 32 near the inner point of transition of the inwardly bent portion of each conductive member. The heating element extended through the members and was finished flush with the outer surfaces thereof. The support member 30 was approximately 11/2 inches in diameter and l inch high. The conductive members 31 and 32 were each approximately 3A@ inch in diameter and extended from the support member 30 about 4 inches to give a penetration of about 1% inches 'within the cartridge as heretofore described. The heating element 46 was made of Nichrome V, which consists of 80% nickel and 20% chromium, and had a diameter of about 0.040 inch and was positioned near the transition point of the inwardly bent portion of the conductive members 3l and 32 which was about 3A inch from the ends thereof. The spacing between the ends of the conductive members 3'1 and 32 was about inch and the parallel facing surfaces 44 and 45 extended about 3716 inch.

With Ireference to the foregoing, it will be appreciated that although the invention has been described with reference to stainless steel as a preferred material yfor the support member and the conductive members, other high temperature-resistant materials of construction may be utilized. For example, the support means may be made of nonconductive material :such as resins or ceramics whereby it is unnecessary to insulate the conductive members therefrom. Similarly, although Nichrome V is disclosed as a preferred material for the heating means, other nickel-chromium alloys and other resistance materials may be used.

With reference to the igniter heretofore described, it will be appreciated that the igniter is capable of penetrating hard cartridge casings with hard interior substances as well as soft cartridge casings with soft interior substances or any combination thereof. It will be further appreciated that the igniter of this invention affords positive ignition when utilized with particulate or discrete packed explosive charges since the design prevents the formation of hollows about the resistance element. Still further, although the invention has been described in conjunction with automatic operation wherein the reciprocating ring head pushes the cartridge into the combustion chamber and is suitably locked without rotative movement, the igniter is particularly adapted for rotative movement in conjunction with discrete charges wherein it is desired to use a rotative breech-lock or the like.

An example of operation of the invention is given for firing a gas-generating device in accordance with the invention wherein the device in conjunction with the igniter of this invention is especially adapted and safe for coal mining as will be evident by the following. A primer charge essentially consisting of 42 grams of smokeless powder composition was packed into a llame-retardant paper container. The charge was ignited with a nonilaming initiator and did not ame in the atmosphere and would not ignite an explosive mixture of methane and air. The composition was as follows:

Nitroglycerin 15%. Nitrocellulose 20%. Nitroguanidine 51%. Cellulose acetate 7%.

Ethyl centralite 7%.

4 Calculated flame temp 2330 K. Particle size 0.053" diameter X 0.09" long.

The above composition also would not ignite or detonate when subjected to impact from 30.06 or 0.22 caliber hollowpoint bullets, or #8 electric blasting caps, or 100- pound weight dropped from a height of 10 feet on a steel plate, or standard friction pendulum tests with steel shoe and anvil. Compositions of this type were then charged into cartridges as the primer charge in conjunction with a main charge of the following composition:

Percent Ammonium nitrate 49.0 Magnesium nitrate hexahydrate 34.0 Wood our 17.0

Main charge Weight grams 360 These cartridges were initated as hereinbefore described in a combustion chamber having a volume of 156 cubic inches resulting in an average time of 4 seconds to rupture the rupturable closure after application of current was applied to the igniter. The current applied averaged 24 amperes at l2 volts for approximately 21/2 seconds. The average gas pressure generated was from about 8,000 to about 16,000 pounds per square inch which demonstrated that the igniter of the present invention was suitable for use in conjunction with pressure-resistant tubes or pressure-resistant drills or other cutting devices for the blasting of coal. Utilization of the invention in actual mine tests verified the suitability demonstrated b' the above example.

From the foregoing, it is evident that there are several factors which will influence the choice of materials to be used in combination for the most satisfactory operation for the igniters of this invention. For example, the shell may be of any suitable material such as paper, plastic sheeting, cardboard or the like and should be nonflammable or be made nonilammable by appropriate coating or other treatment. However, the shell should be thermally decomposable and substantially completely consumed during decomposition of the main charge wherein the decomposition of the shell is essentially a combustion supported by oxygen from the main charge. The penetrable, nonconductive closure for the shell may be the conventional uted crimp or the shotgun type crimp, or the like, and should be reasonably soft to accommodate penetration of the igniter. The fluted crimp is preferred since it is normally formed with a small central opening permitting easy ingress of the igniter into the cartridge. The cartridge should, of course, be moistureproof using suitable shell materials, coatings, or seals where necessary, inasmuch as ammonium nitrate which is the principal constituent of the main charge is hygroscopic. The rupturable closure for the cartridge may be made of any heatresistant, frangible material of desired strength consistent with the release of the pressurized gas at a pressure adequate for performing predetermined useful work such as the breaking of coal or other hard material. The shape of the rupturable end closure or shear disc may be varied considerably, the important thing being that it serve to form a gas-tight seal for the combustion chamber during generation of gas and thereafter rupture at a desired pressure. A partial hemispherical shape is preferred as shown in the drawing since it readily disintegrates into small particles and is easily fabricated and atiixed to the cartridge as by force-fitting, adhesive-sealing and the like. The preferred materials of construction for the rupturable closure are materials such as fiber or plastic which are nonsparking as the disintegrated particles of the closure strike the vent openings of a blasting tube, blasting drill or other metallic implement utilized for the high pressure work. It will be appreciated from the foregoing that the igniter or heating means of the invention is reciprocable and re-utilizable and should be sufficiently rigid to pierce the penetrable closure and to penetrate the primer charge or the main charge, as the case may be, within the cartridge.

The primer charges which may be used preferably contain a major proportion o-f smokeless powder. As a permissible, such primers, of course, should be nonlaming in the atmosphere and incapable of igniting an explosive mixture of methane and air. Primer charges which have been found quite satisfactory for meeting the rigorous requirements of coal mining comprise from about 10 to about 20% of nitroglycerin, from about 15 to about 25% of nitrocellulose, from about 50 to about 55% of nitroguanidine or guanidine nitrate, from about to about of cellulose acetate and from about 5 to about 10% ethyl centralite or other stabilizer, by weight, and conventionally colloided, extruded and cut to have a particle size of from about 0.03 to about 0.10 inch diameter and from about 0.01 to about 0.10 inch long. Moderants such as cryolite, potassium sulfate, barium nitrate, potassium nitrate, and the like may be added in small amount, not over about 1%, to the extent that they do not alter the principal characteristics of the primer composition which are: nonllammable in the atmosphere; will not ignite explosive mixtures of methane and air; insensitive to standard sensitivity tests, such as rifle bullets, friction, blasting caps; and consistently and reliably cause main gas-generating charges to react under pressure. The quantity of primer charge utilized may be varied depending on the amount of the main charge, with from about 30 to about 70 grams usually found suitable for use in conjunction with main charges used for blasting and similar operations. The primer charge may be conveniently packaged in a decomposable plastic bag or the like prior to placing into the cartridge or the primer and main charges may be placed in direct Contact with each other. The calculated flame temperature for the primer composition insofar as permissibility is concerned may be Varied from about 1500o to about 2500 K. It will be understood, of course, that in instances where permissibility is not a factor, other primers may be used in conjunction with the igniters of this invention and in instances where the main charge is made sufficiently heat-sensitive and prolonged ignition time tolerated, the primer charge may be dispensed with entirely.

Compositions suitable for use as the main charge comprise ammonium nitrate alone, desirably of relatively coarse granulation, or ammonium nitrate, as the principal gas-generating constituent, that is, over 40% present, with other material such as the following typical composition: ammonium nitrate 49.0% magnesium nitrate hexahydrate 34.0%, carbonaceous (nut meal, pulp, starch) 17.0%; ammonium nitrate 75.0%, calcium carbonate 25.0%; ammonium nitrate 90.0%, starch 10.0%; and ammonium nitrate 65.0%, calcium formate 34.9%, calcium stearate 0.1.%

From the foregoing, it will be seen that the igniters in accordance with this invention provide advantages heretofore not realized by the art in respect to a high degree of safety, ease of operation particularly in respect to semiautomatic and automatic operation, and economy. Furthermore, although the present invention has been described more particularly in respect to a combustion chamber suitable for utilization with automatic blasting apparatus, it may, of course, be utilized for other applications such as in conjunction with pressure-resistant blasting tubes, bolt-driving devices, catapult devices and the like where repeated tiring is desired for obtaining a source of very high pressure gas.

Still further, it will be seen that this invention may be carried out by the use of various modiiications and changes Without departing from its spirit and scope, with only such limitations placed thereon as imposed by the appended claims.

What I claim and ldesire to protect by Letters Patent is:

1. An electrical igniter which is designed to penetrate one end of a gas-producing cartridge having a soft nonconductive container and to ignite the cartridge for the production of high pressure gas in a combustion chamber, said igniter comprising in combination:

(a) a cylindrical supporting member,

(b) a pair of rigid longitudinal conductive members spaced from each other and extending through the `supporting member to form a pair of electrical terrninals at one end thereof and inwardly bent toward each other with their -facing surfaces in close parallel spaced relationship at the other end thereof to form means for ease of pene-mation of the aforesaid cartridge,

(c) precompressed insulating and sealing means disposed within the supporting member and surroundin-g the pair of electrical terminals to prevent the escape of aforesaid high pressure gas therethrough, and

(d) heating means bridging the conductive members and extending therethrough near the inner point of transition of their inwardly bent end portions whereby the aforesaid cartridge is ignited when the heating means has penetrated -thereinto.

2. The electrical igniter as dened in claim 1 in which the support means is nonconductive material.

3. The electrical igniter as `defined in claim 1 in which the support means is conductive material and each of the conductive members is insulated therefrom.

4. The electrical igniter as defined in claim 1 wherein the precompressed insulating and sealing means comprises compressible insulating and sealing material interposed between rigid compression elements.

References Cited in the tile of this patent UNITED STATES PATENTS 1,361,689 Crousaz Dec. 7, 1920 2,064,706 Wiggert Dec. 15, 1936 2,370,159 Hanley lFeb. 27, 1945 2,473,405 Zebree June 14, 1949 2,481,696 Seavey Sept. 13, 1949 2,754,757 MacLeod July 17, 1956 2,767,655 Seavey Oct. 23, 1956 2,882,820 Young Apr. 21, 1959 2,894,161 Sheheen July 7, 1959 FOREIGN PATENTS 318,233 France Oct. 10, 1902

Claims (1)

1. AN ELECTRICAL IGNITER WHICH IS DESIGNED TO PENETRATE ONE END OF A GAS-PRODUCING CARTRIDGE HAVING A SOFT NONCONDUCTIVE CONTAINER AND TO IGNITE THE CARTRIDGE FOR THE PRODUCTION OF HIGH PRESSURE GAS IN A COMBUSTION CHAMBER, SAID IGNITER COMPRISING IN COMBINATION: (A) A CYLINDRICAL SUPPORTING MEMBER, (B) A PAIR OF RIGID LONGITUDINAL CONDUCTIVE MEMBERS SPACED FROM EACH OTHER AND EXTENDING THROUGH THE SUPPORTING MEMBER TO FORM A PAIR OF ELECTRICAL TERMINALS AT ONE END THEREOF AND INWARDLY BENT TOWARD EACH OTHER WITH THEIR FACING SURFACES IN CLOSE PARALLEL SPACED RELATIONSHIP AT THE OTHER END THEREOF TO FORM MEANS FOR EASE OF PENETRATION OF THE AFORESAID CARTRIDGE, (C) PRECOMPRESSED INSULATING AND SEALING MEANS DISPOSED WITHIN THE SUPPORTING MEMBER AND SURROUNDING THE PAIR OF ELECTRICAL TERMINALS TO PREVENT THE ESCAPE OF AFORESAID HIGH PRESSURE GAS THERETHROUGH, AND

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