US2775200A - Priming device - Google Patents

Description

Dec. 25, 1956 R. G. GUENTER PRIMING DEVICE Filed Dec. 5, 1952 RICHARD e. GUENTER INVENTOR.

AGENT.

PRIMING DEVICE Richard G. Guenter, Lawrence, Kans., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application December 3, 1952, Serial No. 323,856

8 Claims. Cl. 102-27 This invention relates to detonating means for explosive charges and in particular to detonating devices especially adapted for use in applications where relatively insensitive explosive is employed, or where advanced temperatures are encountered which render the use of conventional blasting initiators undesirable.

In recent years there has been a trend toward the use of relatively insensitive blasting agents which contain little or no nitroglycerin and depend primarily for explosive trength upon such materials as ammonium nitrate. While these blasting agents when brought to detonation are characterized by suflicient strength for most blasting operations, they are normally not detonatable by commercially available blasting caps. In fact, the test employed to determine the sensitivity characteristics of such blasting agents is usually one in which their resistance to detonation by a No. 6 or No. 8 cap is determined.

The usual methods for detonating these explosives have involved the use of separate priming cartridges of high explosive such as tn'nitrotoluene (TNT) which are brought to detonation by means of commercial electric blasting caps. is employed which contains a base charge of about 1030 g. of pentaerythritol tetranitrate or equivalent explosive. While both of these means of initiating explosives are operable, they still necessitate the use of blasting initiators which are expensive and which are themselves considerably more sensitive to both heat and shock than the blasting agent itself. Thus, the safety for which the insensitive blasting agents were originally designed is still not always obtainable in the degree desired by the art.

Special difficulties are encountered in shooting hot holes in which the temperatures often reach a point high enough to cause premature detonation of conventional' blasting caps. A means for initiating these insensitive explosives which does not require the presence of large amounts of sensitive explosive or electric blasting caps in the borehole itself is therefore greatly to be desired.

Now in accordance with the present invention, there has been developed a means for initiating insensitive blasting agents and explosives generally which does not require the presence of either highly sensitive high explosive compositions or electric initiators of any sort in the immediate vicinity of the charge to be detonated.

Generally described, the present invention is a priming device for detonatable explosive compositions which comprises a detonatable body of compacted explosive composition containing crystalline high explosive selected from the group consisting of cyclonite (RDX) and pentaerythritol tetranitrate (PETN) and at least of nitrocellulose. In accordance with one embodiment of the invention, the compacted body is associated with detonative means. Preferably, the detonative means Alternatively a highly potent booster cap' atent PETN or RDX covered with fabric or plastic) or Cordeau (granular TNT covered with thin lead tubing containing the desired number of grains of explosive pe foot and will be disposed in detonating relationship wit the explosive body. Preferably, the fuse will be di: posed in a recess, that is, in a Well or a perforatio formed in the compacted body, although other suitabl disposition may be employed. In applications where rt sistance to heat or shock is not an important facto: blasting caps may be similarly employed as the detonz tive means. In a preferred embodiment of the invei tion, the compacted explosive body is formed into a axially perforated cylinder, the perforation extendir through at least a major extent of the length of th cylinder. With such a structure, the detonative mear employed may be disposed in or pass through the pe:

. foration.

The compacted body of explosive compositionin a cordance with this invention is readily detonated t detonating fuses of the desired strength, such as Prim: cord and Cordeau, but is highly insensitive both to shoc conditions which can normally be expected during blas ing operations and to. ignition or detonation by temper: tures usually encountered. It is usually desirable to i] corporate a small amount of stabilizer for nitrocelh lose, such as diphenylamine or Centralite, in the con positions from which the compacted body is forme The amount employed is usually in the order of .2 to .19 While this composition will normally be sufiiciently w; ter resistant for most moisture conditions encountere it is desirable in some instances to include a non-vol; tile plasticizer for nitrocellulose such as diethyl phthalat dibutyl phthalate, dimethyl phthalate, ethyl Centralit or dinitrotoluene. While varying amounts of the plasi cizer may be employed, increase in plasticizer e fects a corresponding decrease in sensitivity to de onation It has further been found that nitroglycer can be employed in amounts up to about 5% WithOl adversely affecting the thermal stability of the OV612 composition. In general, it has been found that it unnecessary to employ more than 5% of plasticizer Sll1( this amount has been found to render these compositior sufficiently resistant to water that they will shoot wit 50 grain Primacord (50 gr. PETN per foot) after daj of exposure to water at pressures as high as p. s. When employed in hot holes, the compacted bodi primed with Primacord have been found to function pro; erly without violent decomposition or premature e1 plosion at temperatures of 500 to 1000 F.

The compacted bodies are preferably made in coaxia ly perforated cylinders by extrusion 'in accordance Wi' known smokeless powder extrusion techniques. Ho ever, the compacted bodies may have any desired sha and may be molded by any desired process.

Having generally described the invention, several er bodiments will be more specifically illustrated with re erence to the accompanying drawings in which Fig. represents a longitudinal section of a cylindrical cor pacted body in accordance with the invention; Fig. is a sectional end view of Fig. 1; Fig. 3 is a part elev tional, part sectional view of the body of Figs. 1 a1 2 primed with detonating fuse; Fig. 4 is a part section: part elevational view of an explosive cartridge priml with the device of Fig. 3; Fig. 5 is a part sectional, pa elevational view of a cylindrical compacted body prim with an electric initiator; and Fig. 6 is a side elevation a borehole primed in accordance with the invention.

Referring now to the drawings in which like numbe represent similar parts, and particularly to Figs. 1 to a cylindrical compacted body 10 of exposive compo: tion in accordance with this invention is provided wi a coaxial perforation 11. Alength of detonating 11 12 is passed through the coaxial perforation 11 of tl ady 10 and is suitably secured therein. In Fig. 3, the etonating fuse is secured within the perforation by reams of a knot tied in the detonating fuse which pre-- :nts its withdrawal. .In Fig. 4, a cartridge 13 of insensitive explosive 1s nipped with a coaxial bore 14 defined by a hollow tube 5 passing concentrically through the cartridge 13. The )llow tube is indented at 16 to provide a detent means. concentrically perforated, compacted body of explosive accordance with the invention is disposed in the coial bore 14 and is prevented from passing therethrough the indentation 16 in the tube 15. Detonating fuse 12 .sses through the compaetedbody and extends cometely through the coaxial bore .14 :of the cartridge 13.

4 t be detonated at a safe distance from the borehole 23 by means of an electric initiator.

The following examples are presented to more specifically illustrate embodiments of the invention. In the table, Examples 1 to 24 illustrate different compositions for the compacted body. The water resistance of these compositions and the comparative sensitivity to detonation of Wet and dry compositions are set forth. The compacted bodies tested were in the form of coaxially 10 perforated cylinders 4 inches in length and 0.67 inch in diameter. The diameter of the perforation was about 0.27 inch. These cylinders were prepared by conventional smokeless powder compounding and extrusion techniques as hereinafter described. All compositions were stabilized he leading end of the detonatig fuse 12 passed 15 with 0.3 of diphenylamine.

Primacord Sensitivity 1 Explosive, Percent 15;, Dry Wet-45 'Lbs. Pressure for 5 Days Water RDX PET-N NO Plasticizer Gr. Gr. Gr. 60 Gr. 100 Gr. Pickup}; 30 Gr. 40 Gr. 50 .Gr. 60 Gr. 100.61.

percen 19. 7 0 DEP. S 12.25 F F PS PS S 19. 7 1 DEP- PS 7. 90 F F PS PS S 19. 7 2* DEP. PS 6. 5,2 F F PS S 19. 7 3 DEP- F 4. 67 F F PS 19. 7 4* DEP F 1. 50 F PS S 19. 7 5* DEP. F 0. 74 F F PS 19. 7 6* DEP. F 0.00 F F F 15. 7 4 DEP. F 1.16 F PS PS 10.7 4 DEP. F 5.19 F F S 24. 7 0 PS 11.87 F F PS 20.7 4DEP F 1.38 F F PS 19.7 5N.Ge PS 0.52 F PS S 19.7 5 DNT- F 1. 29 F PS 19. 7 5 TNT F 1.07 F -]?-S 19. 7 S 8.03 S 19.7 1* DEP S 9. 96 PS PS '19. 7 2* DEP- S 10. 10- PS PS 19. 7 3* DEP. S 9. 77 PS PS 19. 7 4* DEP. S 3.88 PS S 19.7 5 DEP- S 1. 90 PS -S 19.7 6 DEP- S 1.57 S 24. 7 S 5.15 PS S 29. 7. .0 S 5.09 F PS 16. 7 3 DEP. S 11.01 F PS 1 Tested by shooting with PETN Primacord 01 indicated strength. RDX-eyclonite. PETN-pentaerythritoltetranitrate. N Cnitrocellu10se.

DEF-diethyl phthalate.

N G-nitroglycerin. DNT-dinitrotoluene. TNT-trinitrotoluene.

S-'-sh'ot,hole in plate.

PS-shot, dent inplate.

*Plasticizer added to composition.

ough a centrally orificed-wooden'disk 17 which has a meter greater than 'thatof the tuber15. The leading i of the detonatingrfuse 12 is knotted to :prevent its isage through the disk 17. The priming cartridge 13 vy be lowered into a'borehole by means of the detonatfuse 12 and the compacted'priming body 10 is thus intained imposition in thecentral portion of the carle 3- n Fig. 5, a cylindrical, compacted .body 18 in accord- :e :with the invention is provided with a well19. An ctric initiator 20 is disposed in the well '19 and con- :ted to a current source (not shown) lay lead wires 21. n Fig. 6, blasting cartridges 22 are disposed in a verti- .borehole.23. The lowercartridgeZZ is primed inacdance with the invention-by disposing a coaxially perated cylindrical body 10-of explosive composition, as wn in Fig. l, in the upper portion of the cartridge. A gth of Primacord 12 passes-laterally through the carlge and-through the coaxial perforation of the comted body 10. The Primacord 12 is then tied as shown [.leads out of the'borehole. The -:remaining cartridges aredisposed .ontopof the- 1ower:primed cartridge. The e hole is "stemmed as at 25. 'The'Primacord 12 may Example v25 Field trials were conducted in'which several boreholes were loaded with commercial blasting cap insensitive blasting agent principally comprising ammonium nitrate. The temperature in these boreholes was between 400500' F. due to undergroundfires. In each hole a primer cartridge was employed similar to that shown in Fig. 4. The primer cartridge contained commercial blasting cap insensitive blasting agent. The compacted body was similar to that of Example 1 and contained 80% RDX, 19.7% NC, and 3% diphenylarnine. A 50 grain PETN Primacord was employed which was initiated at a distance from the hole by means of an electric blasting cap. After being loaded, the .holes were not fired for about '20 minutes. All holes fired normally and with no indication of any decomposition of the compactedbody in the primer cartridge.

From the foregoing examples, and especially from Examples l to 24, it will be seen that the compositionof the compacted bodies may be subject to considerable variatron. It'hasbeen found, however, that at least 15% of nitrocellulose must be employed in order to obtain a compacted'body having the requisite physical strength and to obtain the necessary extrusion characteristics. When less than 15% of nitrocellulose is employed, the bodies do not compact well and are crumbly.

The amount of crystalline explosive employed will depend on the degree of sensitivity required for the particular application. Due to the fact that PETN is more sensitive to detonation than RDX, less PETN than RDX need be used with a detonating fuse of a particular strength. Similarly, the amount and nature of the plasticizer may be varied to give the desired characteristics in terms of water resistance and sensitivity to heat and shock. For commercially available detonating fuse, it has been found desirable to employ at least 75% of RDX and at least 70% of PETN.

While cylindrical compacted bodies of RDX or PETN with nitrocellulose have been employed to specifically illustrate the invention, the invention is not so limited, since as previously indicated the compacted bodies may be of any desired shape.

The compacted bodies are easily produced by the usual smokeless powder process. In accordance with the preferred process, the nitrocellulose, Wet with 2B alcohol, is placed in a sigma-blade mixer together with the stabilizer and plasticizer, if used, the particulate explosive, acetone, and additional 2B alcohol. The ingredients are then thoroughly mixed, preferably for about 3 hours. In accordance with the preferred procedure, the composition is then extruded through a die of the desired dimensions, the perforation being formed by a die pin of a size slightly larger than the detonating fuse to be employed. The compacted, extruded bodies are dried in air at a temperature of about 120-140 F. to effect solvent removal. Alternatively, however, the paste from the mixer may be compression molded in a suitable mold and the solvent removed by drying as before. The RDX or PETN employed should be finely divided.

From the foregoing, it will be seen that the priming devices of the invention have many advantages. Devices having high heat or shock resistance may be prepared which when detonated, are highly bn'sant and capable of satisfactorily initiating insensitive blasting agents or other explosive composition. While the compacted bodies may be made in any size, small, inexpensive bodies are satisfactory. These bodies are structurally self-suflicient and require no metal or plastic shells for support. What is of great importance from the standpoint of both manufacturer and user is that the compacted bodies can be easily and economically prepared by utilizing known smokeless powder extrusion techniques and equipment. Other advantages will be apparent to those skilled in the art.

While the explosive priming device of the invention will have primary utility when used with the currently popular insensitive blasting agents, the device can also be used with more sensitive explosives if desired. In like manner, although the device has special utility for shooting hot holes, its use is not so restricted. It is intended that the scope of this invention be defined solely by th scope of the appended claims.

What I claim and desire to protect by Letters Patent is 1. As a new article of manufacture a priming devic for detonating blasting charges comprising a compacte explosive composition formed as a cylinder, the walls 0 said cylinder forming an annulus about a substantiall coaxially disposed perforation extending through at lea: a major extent of the length of the cylinder and adapte to contain a detonating means, said explosive consistin essentially of at least 75 percent cyclonite and at least 1. percent nitrocellulose to form an independent cohesiv body.

2. An article of claim 1 wherein said perforation ex tends through said cylinder.

3. An article of claim 1, wherein said detonating mean is a detonating fuse disposed in at least a portion of sait perforation in propagating relationship with said com pacted composition.

4. An article of claim 1 wherein the said compacte explosive contains not in excess of about 5 percent of nonvolatile plasticizer for nitrocellulose.

5. As a new article of manufacture a priming devic for detonating blasting charges comprising a compacte explosive composition formed as a cylinder, the walls 0 said cylinder forming an annulus about a substantiall coaxially disposed perforation extending through at lea: a major extent of the length of the cylinder and adapter to contain a detonating means, said explosive consistin, essentially of at least percent pentaerythritol tetrani trate and at least 15 percent nitrocellulose to form a1 independent cohesive body.

6. An article of claim 5 wherein said perforation ex tends through said cylinder.

7. An article of claim 5 wherein said detonating mean is a detonating fuse disposed in at least a portion of sait perforation in propagating relationship with said corn pacted composition.

8. An article of claim 5 wherein the compacted ex plosive contains not in excess of about 5 percent of nonvolatile plasticizer for nitrocellulose.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Feb. 16, 1932

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