US3431851A - Primers for use with delay action blasting caps and process of blasting using the same - Google Patents

Description

March 11, 1969 KE ET AL 3,431,851

E WIT PRIMERS FOR US H DEL ACTION BLASTING CAPS AND PROCESS OF BLAST USING THE SAME Filed Aug. 1%67 Patented Mar. 11, 1969 12 Claims ABSTRACT OF THE DISCLOSURE Primer cartridges are provided adapted for use with nonelectric delay action blasting caps, initiated by low energy detonating cord, and comprising a cartridge for primer explosive, a receptacle in the cartridge for reception of a blasting cap, and a tubular fuse holder means made of energy-absorbing material and attached to the cartridge, so that the material of the fuse holder is interposed between the fuse and the primer cartridge wall. The tubular holder separates the fuse from the primer wall, and prevents detonation of the primer by the fuse.

This application is a continuation-inpart of Ser. No. 642,396, filed May 31, 1967.

This invention relates to primers and to primer cartridges especially designed for use with delay action blasting caps initiated by low energy detonating cord, and more particularly to primers and primer cartridges having an energy-absorbing tubular fuse holder through which the fuse passes, and attached to the outside wall separating the initiating fuse for the blasting cap from the primer container wall, and to a method of blasting using such primers, which avoids the necessity of threading or lacing the initiating fuse through the primer.

Electric blasting caps are subject to being set off by thunderstorms, stray electric currents, static electricity and RF energy, with a resulting premature explosion Consequently, for many years the explosive industry has been confronted with the hazards of electric blasting caps under these conditions.

In order to overcome this problem, but still retain the delay characteristics of electric blasting caps, 21 nonelectrical initiating system has been introduced, employing nonelectric millisecond delay blasting caps for in-hole initiation of explosives. These blasting caps provide the precise timing of electric blasting caps, but are immune to the hazards or effects of extraneous electricity. The system is composed of a length of low energy detonating fuse, with a delay element and a nonelectric blasting cap attached to one end. The other end of the detonating fuse is tied to a standard detonating fuse trunk line, which, when initiated, causes a detonating wave to travel down the low energy detonating fuse to the delay element. The delay element introduces a predetermined delay period, and then initiates the nonelectric blasting cap, thus duplicating the effect that would be obtained by the use of an electric blasting cap in the same location.

In using the system with a conventional primer containing the properly insensitive explosive, the low energy detonating fuse is laced through the cartridge, and the cap inserted in the crimped end of the cartridge. Thus, the fuse actually passes through the explosive at this point, and is intimately in contact with the explosive there. It is not possible to half-hitch the detonating fuse around the cartridge as is usual with electric blasting cap lit lead wires, since the fuse can cut off at the point of crossover.

As a consequence, the system requires that the primer used be insensitive to initiation by the low energy detonating fuse, but it must readily accept detonation from a No. 6 blasting cap. Conventional nitroglycerine-based explosives cannot be used any circumstances, since the fuse in most instances initiates this type of explosive, thus nullifying or short-circuiting the delay element before the cap.

This type of lacing also means that if the primer is used in a water-filled hole, Water can penetrate the explosive at the point where the fuse is laced through it, and depending on the type of explosive in the primer, can migrate towards the blasting cap, reach or desensitize the powder around the cap, and cause the primer to misfire.

Considerable private research has been carried out by the inventors in an attempt to overcome the ditliculty introduced by threading or lacing the fuse through the cartridge. Relatively insensitive primer explosives have been tried in cast form, such as pentolite, composition B, and trinitrotoluene. However, it was found that the low energy detonating fuse when held in close contact with the cast primer, either by taping, tying, or other means, in from 25 to of the cases would rupture the cast explosive, and cause the primers to malfunction. Cardboard or paper tubes were also inserted in the priming wells, but this step was equally unsuccessful.

In accordance with the invention, a primer cartridge is provided with tubular means for holding the detonating fuse along the outside wall of the primer while separating it from the wall sufiiciently to avoid any danger of detonating the primer, or of rupturing a cast primer explosive. This tubular fuse holder means is made of energyabsorbing material, and is attached to the outside wall of the primer cartridge. Through this holder is threaded the fuse running to the primer, so that the material of which the fuse holder is made is interposed between the primer wall and the detonating fuse. Thus, the material separates the fuse from the primer wall, and prevents detonation of the primer by the fuse. It also eliminates the necessity of threading or lacing the detonating fuse through the primer, in order to attach the fuse to the primer. The tubular means for holding the detonating fuse can be firmly attached to the cartridge, so that the fuse can be firmly atlixed to the primer.

The primers of the invention are very easily employed in in-hole initiation of explosives using nonelectric delay blasting caps. The length of low energy detonating fuse of conventional type with a delay element and the non electric blasting cap crimped to one end is simply threaded through the holding means for such fuse attached to the primer cartridge, and the blasting cap inserted in the receptacle provided therefor in the primer cartridge. The other end of the detonating fuse is tied to a standard detonating fuse trunk line. This, when initiated, causes the detonating wave to travel down the low energy detonating fuse to the delay element, which imparts a predetermined delay period in the usual Way, and then initiates the nonelectric blasting cap. The detonating wave travels safely along the low energy fuse Without affecting the primer because of the insulating effect of the separating fuse holder interposed therebetween. The result is a reliable primer for use with delay action blasting caps of all types.

The tubular fuse holder can be made of any energyabsorbing material. A tube of rubber, either natural or synthetic, will serve. will a tube of paper, or synthetic resin, such as polyethylene, polypropylene, polystyrene and polyvinyl chloride. However, the wall of the tube must be thick enough to absorb and thus insulate the primer cartridge from the detonating wave traveling along the fuse to the primer. The thickness will depend on the energy conductivity of the material; a thin layer of a relatively high energy-absorbing material can be just as effective as a thick layer of relatively low energy-absorbing material, and in either case the layer must be thick enough to insulate the fuse from the container wall, and prevent the fuse from damaging the primer. It has been determined that the wall must be at least 0.005 inch thick, and preferfably it is at least 0.01 inch thick. This is somewhat thicker than the wall of most commercially available tubes. There is no upper limit on thickness, but a thickness greater than 0.25 inch is not normally required.

A further insulating effect is obtained if the tubular holder is made of foamed or cellular material, which contains open cells and thus displays an enhanced energyabsorbing and heat-insulating effectiveness. The foam material is preferably a foamed plastic or rubbery material, such as polyvinyl chloride resin foam, polyurethane resin foam, foam rubber, foam nylon, foam polyethylene, and

foam polypropylene.

The tubular holder can be wide or narrow, and extends along the outside of the primer cartridge, generally from end to end. The holder can be attached to the wall by use of any means appropriate for the purpose, such as a tape, adhesive or bonding agent.

The tube should be of a width at least equal to the diameter of the detonating fuse, so as to insulate it fully from the cartridge wall. It can, if desired, be considerably wider than the detonating fuse, so as to provide an ample area for insulation protection. It is thought that the tube protects the primer explosive against detonation because of the insulating effect of the tube wall, and because of its compressibility, which enables it to take up some of the shock of the detonating wave traveling down the fuse.

Accordingly, the tube material should be compressible to a certain degree.

The tubular holding or holder means for attaching the detonating fuse to the cartridge can take any of several forms. A preferred embodiment is a tube, such as a spiral wound cardboard tube, extending a substantial part or all of the length of the primer cartridge. The detonating fuse can be threaded through this tube along the outside of the primer cartridge.

In another embodiment, the tubular holder means takes the form of a tubular channel, so shaped and sized that the fuse is tightly held therein in a press-fit, and is separated from the cartridge by the channel wall. The channel can have a diameter slightly less than the diameter of the fuse, so that the fuse is slightly compressed on insertion in the channel, and the resilient side walls of the channel are correspondingly thrust somewhat apart, due to the relative noncompressibility of the fuse, with a corresponding spring action tending to retain the fuse in the channel. The channel should extend over at least 180 of arc, and preferably at least 270 of are.

In still another embodiment, a channel having a plurality of loops is provided, instead of a continuous tube, through which the fuse can be threaded in running it to the blasting cap.

The tubular holder means can be circular, elliptical, or otherwise U- or ring-shaped in cross-section.

The invention is applicable to primer cartridges of all types. The primer cartridge can be made of any material, such as paper, cardboard, metal or plastic, such as aluminum, steel, iron, polyvinyl chloride, polyethylene, cel lulose acetate, and ethyl cellulose.

Any primer explosive material can be packaged in the primers of the invention, inasmuch as the explosive need not be insensitive to initiation from the detonating fuse, due to the protection afforded by the tubular holder. The explosive should be suificiently sensitive to be reliably initiated by a No. 6 blasting cap, but it can be more sensitive than this, if desired. Typical primer explosives that can be employed include pentolite, composition B, trinitrotoluene, Cyclonite, Tetryl, special explosives and blasting agent combinations, including the nitrocarbonitrates, TNT-sensitiZed-ammonium nitrate-type slurried high explosives, smokeless powdersensitized-ammonium nitrate-type slurried high explosives, nitrostarchsensitized-ammonium nitrate-type slurried high explosives, TNT-ammonium nitrate-pellet-form solid high explosives, and high explosives that include nitrostarch-sensitized-arnmonium nitrate-type semi-solid high explosives, nitroglycerine dynamites, such as the semi-gelatins, ammonia gelatins, and ammonia dynamites, pentaerythritol tetranitrate, and Cyclotol.

The drawings illustrate a preferred embodiment of the invention.

FIGURE 1 is a view in elevation, with parts cut away, of an explosive primer cartridge of the invention, showing a delay action blasting cap in position in the well provided therefor.

FIGURE 2 is a cross-section taken along the lines 2--?. of the primer cartridge of FIGURE 1.

FIGURE 3 shows the mode of attachment of the primer cartridge of the invention to a detonating fuse and delay action blasting cap for in-hole initiation.

The explosive primer of FIGURES 1 to 3 includes a primer cartridge 1 made of cardboard, equipped with a blasting cap well 2 open to the atmosphere for insertion of a blasting cap 3 with a delay element as a component part thereof. The cartridge is filled with a high explosive 4, such as pentolite, in cast or powdered form.

Attached to one side of the cartridge, and extending from end to end of the cartridge, is a polyethylene tube 6, wall thickness 0.04 inch, internal diameter 5 inch, 21 diameter sufficient to receive a detonating fuse 7 running to the blasting cap 3. This tube is attached to the cartridge by a suitable adhesive 5.

If desired, on top of the charge of primer high explosive or blasting agent combination there can be placed a booster cup containing a booster explosive. Any booster explosive can be used, preferably in cast form, such as pcntolite or composition B. If used, the detonating velocity of the booster explosive is sufficient to initiate the primer. This booster cup is also sealed in the explosive cartridge, and the blasting cap well is inserted in the booster cup for initiation of the booster.

In practice, as shown in FIGURE 3, a length of low energy detonating fuse 7, with a delay element-fitted nonelectric blasting cap 3 crimped to one end, is threaded through the tube 6, while the blasting cap is inserted in the well 2. The other end of the detonating fuse is tied via suitable connector 8, such as a J-connector, to a standard detonating fuse trunk line 10, to which can be afiixed a plurality of such primer assemblies (not shown) with blasting cap attached. The primer is then slipped into a bore hole 12.

When the detonating fuse trunk line 10 is initiated, the detonating wave travels down it, and then down each of the low energy detonating fuses 7 attached thereto, running to the delay element through the tube 6 without affecting the primer. The delay element imparts a predetermined delay period, and then initiates the blasting cap, setting off the primer.

A number of primers were prepared, of the type shown in FIGURES 1 to 3, utilizing fuse holder tubes 6 of a variety of materials. These were tested to deter-mine resistance of the primer to damage by the fuse. The Primaline PETN detonating fuse was used. A tube of plastic straw (polyvinyl chloride) wall thickness 0.008 inch, I.D. Q4 inch was compared with a Kraft paper tube, 0.012 inch wall thickness, I.D. inch and with a polyethylene tube, airline type, 0.04 inch wall thickness, LD inch. In the test, each was afiixed to the canister wall of a /3 lb. cast pentolite primer. The Primaline was then threaded through the tube. All three materials prevented the wall of the canister from being ruptured when the Primaline detonated. When the Primaline was afiixed to the wall of the primer canister without the benefit of the tubular insulator, the wall was torn, and the pentolite fractured and partially displaced from the area adjacent to the Primaline.

These data show the effectiveness of the insulating tube in preventing primer damage.

The water-resistance of the primers in accordance with the invention is greatly enhanced, because the detonating fuse is not laced or threaded through it. Consequently, the primers can be employed in water-filled holes without introducing any problem. All that is necessary is that the primer cartridge itself be water-proof, or sufficiently water resistant so that water does not have time to penetrate to and desensitize the primer before the charge is set off. The primer is sufficiently versatile to permit its use in nonelectrical delay initiation systems of conventional type, employing the usual types of fuse delay elements for nonelectric blasting caps.

Having regard to the foregoing disclosure, the following is claimed as the inventive and patentable embodiments thereof:

1. A primer cartridge especially adapted for use with nonelectric delay action blasting caps and detonating fuse, comprising a cartridge for a primer explosive having means permitting insertion of a blasting cap in juxtaposition to the primary explosive; and a tubular fuse holder means of energy absorbing material on the exterior of the cartridge for guiding a detonating fuse to the blasting cap, said fuse holder having a wall attached to the exterior cartridge wall and interposed between the dctonating fuse therein and the cartridge so as to protect the cartridge from rupture and inhibit premature detonation of the explosive in the cartridge by a detonating wave along the detonating fuse to the blasting cap, thereby ensuring that the explosive in the cartridge is detonated only after the delay introduced by the blasting cap.

2. A primer cartridge in accordance with claim 1, n which the holder means is a tube having a diameter slightly larger than the diameter of the detonating fuse.

3. A primer cartridge in accordance with claim 1, in which the holder means is a channel extending over at least 180 of are.

4. A primer cartridge in accordance with claim 1, in which the energy-absorbing material of which the tube i formed is a plastic material.

5. A primer cartridge in accordance with claim 4, in which the plastic material is a plastic foam.

6. A primer cartridge in accordance with claim 1, in which the wall of the tube is at least 0.005 inch thick.

7. A primer comprising a primer cartridge in accord-v ance with claim 1, filled with a primer explosive.

8. A primer in accordance with claim 7, in which the explosive is in cast form.

9. A primer in accordance with claim 7, in which the explosive is in powdered form.

10. In the process for blasting using a nonelectric delay action blasting cap, detonating fuse, and a primer ex plosive in a primer cartridge in which after initiation of the detonating fuse, which initiates the blasting cap, a predetermined delay occurs before the primer explosive in the cartridge is detonated, the improvement which com prises guiding the fuse to the blasting cap along the exterior of the cartridge in a tubular fuse holder of energy absorbing material with a wall of the holder interposed between the fuse and the cartridge to absorb the force of the detonating wave while the detonating wave is travelling along the fuse to the blasting cap to thereby prevent rupture of the cartridge, and, inhibit premature detonation of the primer explosive but permit the blasting cap to be detonated.

11. The process according to claim 10, in which the absorbing layer is a plastic material.

12. The process according to claim 1], in which the plastic material is a polyethylene.

References Cited UNITED STATES PATENTS 1,512,714 10/1924 Saucier 10224 2,708,408 5/1955 Sweetman 1022O 3,129,663 4/1964 Schnepfe 102-27 3,311,056 3/1967 Noddin 102-27 VERLIN R. PEND-EGRASS, Prinmry Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,431,851 March 11, 1969 Forest L. Kern et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, lines 6 to 8, "assignors to Trojan Powder Company, Allentown, Pa. a corporation of Pennsylvania should read assignors, by mesne assignments, to Commercial Solvents Corporation, a corporation of Maryland Signed and sealed this 17th day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

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