United States Patent (19) 11 4,331,081 45) May 25, 1982 Cloutier Et Al
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United States Patent (19) 11 4,331,081 45) May 25, 1982 Cloutier et al. 3,451,339 6/1969 Precoul........................... 102/205 X (54) EXPLOSIVE BOOSTER 3,754,061 8/1973 Forrest et al. ... ... 149/105 X Inventors: Joseph A. R. Cloutier, Montreal; 3,880,080 4/1975 Cook .................... ... 102318 75 Anthony C. F. Edmonds, Mont St. 4,060,033 11/1977 Postupacket al. .. ... 102/318 Hilaire, both of Canada Primary Examiner-Peter A. Nelson 73) Assignee: C-I-L Inc., Willowdale, Canada 57) ABSTRACT 21 Appl. No.: 172,163 An explosive booster is provided for the detonation of insensitive blasting agents. The booster contains TNT 22 Filed: Jul. 25, 1980 as the sole explosive ingredient, is sensitive to blasting (51) Int. Cl. ................................................ F42B 3/00 cap initiation yet remains insensitive to impact initia 52 U.S. Cl. .................................... 102/318; 102/322; tion. The booster comprises an elongate structure hav - 102/286 ing a gradually increasing density from end to end, only 58) Field of Search ............... 102/318,322, 285, 286; the less dense end being cap sensitive. Reduced density 149/105 is accomplished by the incorporation of voids or pock 56) References Cited ets, by means of, for example, glass microspheres. Par U.S. PATENT DOCUMENTS ticulate sodium nitrate and vermiculite are included as density enhancers. 3,285,172 11/1966 Foster ............................. 102/318 X 3,288,065 11/1966 Tousley, Jr. ........................ 102/318 3,437,038 4/1969 Newman ............................. 102/38 8 Claims, 2 Drawing Figures U.S. Patent May 25, 1982 4,331,081 4,331,081 2 not greater than 1 Mg/m3 by the inclusion therein of EXPLOSIVE BOOSTER discrete voids or gaseous pockets, a booster charge may be provided which is sensitive to blasting cap initiation. This invention relates to an explosive booster used for It has been noted, however, that the detonation wave the detonation of explosive compositions which are generated by the initiation of low density TNT of 1 insensitive to detonation by ordinary blasting caps. Mg/m3 or less is of a low intensity and is not adequate Typical of such cap-insensitive explosives are, for exam for the initiation of regular or normal density cast TNT ple, ammonium nitrate/fuel oil (ANFO) mixtures and in contact with it or for the initiation of an adjacent aqueous slurry blasting agents. insensitive blasting agent. It is postulated that the den sity difference at the interface between the low density BRIEF DESCRIPTION OF THE DRAWINGS TNT and an adjacent insensitive explosive, creates an FIG. 1 is a cross section of the explosive booster with impedance discontinuity which tends to reflect away a a solid cast primer. Substantial amount of the energy of the detonation wave FIG. 2 is a cross section containing an axial tunnel in generated by the low density TNT thus preventing said primer. 15 boostering. To overcome this difficulty, the booster of A large variety of booster types are known in the the present invention comprises an elongated TNT explosives art. Most boosters employed with cap-insen casting of gradually increasing density from end to end. sitive blasting agents comprise a cast or pressed cap-sen The means by which the gradually increasing density sitive high explosive charge usually having a recess or may be conveniently created during the period of solidi well adapted to receive a blasting cap or other initiator 20 such as a length of detonating cord. Sometimes such fication and cooling of the casting of the void-contain cast or pressed boosters comprise a core of explosive ing TNT is by the incorporation in the molten TNT of which is sensitive to detonating cord or cap initiation, particulate sodium nitrate and particulate expanded which core is itself surrounded by a sheath of non-cap vermiculite and gas bubbles. The booster of the inven sensitive explosive. Such a core-and-sheath booster is 25 tion is preferably adapted for the convenient attachment disclosed, for example, in U.S. Pat. No. 3,037,452. Other or insertion of the initiating cap or detonating cord typical cast or pressed boosters are disclosed in U.S. against or within the most sensitive low density portion Pat. Nos. 3,037,453, 3,341,382, 3,371,606, 3,491,688, of the casting. The addition of particulate sodium ni 3,437,038, 3,359,902, 3,604,353, 3,604,354 and 4,009,060. trate, preferably having a grit size of less than 20 mesh In general, all of the aforedisclosed boosters are water 30 Tyler and in an amount of up to 20% by weight of the resistant and are generally insensitive to initiation from total booster, provides for an increase in the overall impact. They are, however, not without some limita density of the cast booster without reducing its sensitiv tions and disadvantages. In substantially all cases the ity or its energy output, explosives of choice for cast and pressed boosters is From computed values of detonation pressure ob trinitrotoluene (TNT) because of its relatively cheap 35 tained from TNT containing up to 20% by weight of cost and ready availability. However, since TNT is, particulate sodium nitrate, it can be observed that no except under unusual conditions, insensitive to blasting substantial reduction in detonation pressure takes place cap or detonating cord initiation, it has been necessary from that observed with unadulterated TNT. It is, to combine with the TNT an amount of another cap therefore, possible to prepare practical and useful prim sensitive explosive in order to insure initiation of the 40 ers of the type described herein without the need of any TNT. This combination may be in the nature of a sensi separately cast TNT portion. The addition of particu tive core material surrounded by the TNT sheath or it late expanded vermiculite (filter grade) to a castable may be made by placing sensitive explosive in side-by TNT/sodium nitrate mixture tends to slow the settling side abutment with the TNT. Alternatively the TNT of the sodium nitrate and any solid void-containing may be made more sensitive by mixing a sensitive mate 45 material during the period of cooling and solidification rial with the TNT to form a cap-sensitive combination. of the TNT biend. Typical of the cap-sensitive materials which may be The incorporation of the discrete voids within the combined or mixed with TNT are, for example, penta TNT casting is most easily accomplished by adding to erythritol tetranitrate (PETN) and cyclonite (RDX). the molten TNT sufficient glass microspheres to It will be obvious that the manufacture of two-com 50 achieve the desired low density and the resulting sensiti ponent boosters, of say, a PETN core surrounded by a zation. Such glass microspheres, especially in the pres TNT sheath, will be substantially more costly than a ence of particulate expanded vermiculite, tend to settle single cast or single press booster of, say, TNT alone. only very slowly as the TNT solidifies thus producing a Not only does the two-component booster require addi gradual decreasing density from top to bottom in the tional manufacturing steps but also the cost of the cap 55 final cast product. Discrete voids may also be incorpo sensitive ingredient, for example, PETN, is substantially rated in the TNT casting by the mechanical "whipping greater than the cost of an equivalent volume of TNT. in' of air or by the addition of particulate gas-generat In addition, because of the presence of cap-sensitive ing Inaterials such as, for example, sodium borohydride. PETN or the like, the manufacture and the use of the While the addition of whipped-in air or the generation multi-component booster carries with it an additional 60 of gas in situ have the obvious advantage of economy risk or hazard factor. over the use of glass microspheres, it will be appreciated A method has now been found for manufacturing a that difficulties may be encountered in providing a con cast booster comprising TNT alone as the only self. trolled distribution and sizing of whipped-in or gener explosive material which booster is sensitive to blasting ated gas bubbles. cap and detonating cord initiation, is insensitive to acci 65 A further aspect of the present invention provides for dental initiation by impact and is cheap to manufacture. a combination booster comprising a mixture of TNT It has been surprisingly discovered that by control and one other cap-sensitive solid castable explosive ling or maintaining the density of cast TNT to a value wherein the quantity of the cap-sensitive castable explo 4,331,081 3 4 sive can be substantially reduced by the incorporation tion and to maintain a constant low density throughout. in the mixture of discrete voids. After cooling, the coaxial pin was removed and the The following examples taken in conjunction with booster was detonated by means of an electric blasting the attached drawings which show in FIG. 1 a solid cast cap 14 placed within the co-axial channel or tunnel 15 TNT primer of the invention and in FIG. 2 a TNT cast and close to the interface of the low density and the primer of the invention having an axial tunnel or cap increasing density portions of the casting. On detona well, illustrate the invention. The percentage of each tion upon a one inch thick mild steel plate a crater was constituent is expressed by weight of dry material. produced indicating complete detonation at high veloc EXAMPLE 1. ity. A booster of similar dimensions but comprised of 10 unadulterated TNT could not be initiated with a similar With particular reference to FIG.