May 25, 1965 M. A. COOK ETAL 3,185,017 METHOD OF MAKING AN EXPLOSIVE BOOSTER Original Filed July 13, 1959

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INVENTORS AE1M at OOC AOWGLMS Al ACA 3,185,017 United States Patent Office Patented May 25, 1965 2 3,185,017 pressed pentolite (PETN-TNT), TNT, tetryl, tetrytol METHOD OF MAKING AN EXPLGSWE GOSTER (tetryl-TNT), cyclotol (RDX-TNT), composition B Melvin A. Cook and Dotigias E. Pack, 3: it lake City, (RDX-TNT-wax) and Ednatol (EDNA-TNT). The Utah, assig Rors to Intertanozzataia Researcia and Engi more inexpensive of these explosives are not detonatable eering Company, Inc., Saitake City, Utah, a cospera by Prinnacord, however. tion of Utah 5 Original application July 13, 1959, Ser. No. 826,539, how It has been found that PETN, PETN-TNT mixtures, Patent No. 3,637,453, dated June 5, 1932, Cisie at: RDX and cyclotol are detonated by Primacord, but their this application Oct. 24, 1960, Ser. No. 70,334 high cost and the relatively large quantities required make 2 Clairls. (C. 86-) it uneconomical to use them as boosters. O The improved boost cr of the invention generally com This invention relates to detonating means for ex prises a core of Primacord-sensitive explosive material plosives and more particularly to boosters for relatively sit trol inted by a compacted sheath of Primacord-insensi insensitive explosive compositions. This application is tive explosive imaterial of high brisance, said booster a division of our copending application Serial No. 826,539, having at cast one perforation extending through said filed July 13, 1959, now U.S. Patent No. 3,037,453. sheath and Said core adapted to receive a detonating fuse, Insensitive explosives, containing a high percentage of said core comprising a tube containing Primacord-sensitive ammonium nitrate and containing non-explosive organic explosive adjacent to and defining at least a portion of the sensitizers, have found wide application as biasting ex perimeter of said perforation. plosives. Prilled ammonium nitrate containing 94 per One embodiment of the invention is such a booster cent ammonium nitrate and 6 percent fuel oil and aqueous 20 wherein said Primacord-sensitive explosive is pentaeryth slurries of coarse TNT-ammonium nitrate are examples ritol tetranitrate contained within said tube and wherein of such insensitive explosives. Such compositions are not said Primacord-insensitive explosive is cast TNT. A detonatable by blasting caps and prior art methods for further embodiment is Stich a booster wherein said Prima detonating them include the use of dynamite or relatively cord-sensitive explosive is pentaerythritol tetra nitrate con large quantities of fine-grained TNT priners, for example, tained within said tube and said Prinacord-insensitive ex which are detonated by blasting caps or Primacord. These plosive is a cast mixture of 25 percent by weight of TNT methods suffer from the disadvantage of being expensive and 75 percent by weight of composition B. and further, dynamites, fine TNT and blasting caps are A preferred for in comprises such a bcoster wherein two very sensitive to heat and shock. perforations are provided and wherein the core comprises in modern large diameter blasting operations using high 30 a tube in a figure 8 configuration containing Primacord annonium nitrate explosives, Primacord fuse is the most sensitive explosive adjacent the perimeters of said perfora desirable detonator. The high ammonium Titrate ex tions. A1, alternative embodiment is such a booster where plosives are not dependably detonatable by Primacord, in the tube containing Prinnacord-sensitive explosive is however, and require a booster. Unfortunately, only a wound in helical fashion adjacent to and defining the few of the most sensitive explosives are consistently capa 3 5 perimeter of said perforation. ble of detonation by Primacord containing the minimum The method of the invention generally comprises sup content of PETN, e.g., about 50 grains of PETN per foot porting a rod, placing a tube containing Primacord-sensi of Primacord. Of those boosters that are operable, rea tive explosive contiguous to Said rod, compacting a sheath tively large quantities of expensive boostering composi of Primacord-insensitive explosive about said rod and tube, tions are required consistently to boostcr the ammonium : and removing said rod from said compacted sheath to nitrate explosive. provide a perforation through the sheath adapted to Accordingly, it is an object of the present invention receive a detonating fuse. A preferred method involves to provide a booster for insensitive explosives which is casting the sheath about the rod and tube. The tube of consistently detonatable by minimum PETN content Prinacoid-sensitive material may be helically wrapped Primacord. about the rod, or if two rods are provided, the tube may It is another object of the invention to provide such a be would in figure 8 fashion about said rods. booster which consistently detonates high ammonium FIGURE 1 is a view of the tube of Primacord-sensitive nitrate explosives in either the wet or dry state. explosive positioned on a pair of rods prior to compacting A further object of the invention is to provide such a the sheath of Primacord-insensitive explosive about it. booster which is inexpensive and utilizes a minimum of FiGURE 2 illustrates the casting of Primacord-insensi the expensive Primacord-sensitive materials. 50 tive explosive about the tube according to the invention. Among the other objects of the invention, one is to FiCURE 3 is a view of a finished booster made in ac provide a protected core booster in which Primacord is cordance with the invention. readily and simply threaded for use in blasting operations. FGURE 4 is a cross-sectional view of the booster of Another object of the invention is to provide a booster FGURE 3. which is much less sensitive to heat, shock, impact, friction The booster as shown in FIGURES 3 and 4 comprises and other influences causing accidental initiation than prior a compact sheath 10 of Primacord-insensitive explosive. art boosters. Within the sheath () is a tube 1 containing Primacord Another object is to provide improved methods for sensitive explosive E2 adjacent to the perforation 13. In making boosters. the embodiment shown, two holes 3 extend through the 60 booster for receiving Primacord detonating fuse and the Other objects and advantages will be apparent to those tube 1 is disposed in FIGURE 8 configuration with re skilled in the art. spect to the holes 11. We have now found that the most important factor in While the assembly may assume any desired shape, it a booster with respect to its boostering activity on in is preferred to use the cylindrical for in shown for eco sensitive explosives is its detonation pressure or brisance. nomy of material and ease of manufacture. It is pre The term "brisance' connotes shattering action which is ferred to employ two holes i3 to loop the Primacord fuse dependent on the detonation pressure. In the hydro through, although the boosters of the invention are de dynamic theory of detonation, the detonation pressure is pendably detonated by Primacord passing through only proportional to the density of the explosive and the square one hole. Accordingly, the booster may have only one of the detonation velocity. O hole with the tube disposed in helical fashion about the Examples of cxplosives of high brisance are cast or periphery of the hole. In a further modification, two 3,185, Ol? 6. t 4. holes may be used and the tribe helically disposed about with a 50 grain PETN/foot Prinnacord strand running each hole. through one hole only. Such boosters cut a clean hole As shown in FIGURES 1 and 2, a base 4 is provided through a one inch thick, 6 x 6 inch steel plate. with a pair of upstanding pins or rods 5. The tube a Similarly, we have found that one foot lengths of 200 is wound about the rods 5, the winding being in fig 5 grain PETNA foot and 400 grain PETN/foot Primacord ure 8 form, although helical winding of the tube abo, it wound in a figure 3 core yield 100% detonations when the rods may also be used. A form 16 of metal or card cast 100% TNT is used as the sheath. As a control, cast board is placed over the wound rods and molten Prima cylinders of 100% composition B without a core failed to cord-insensitive explosive 7 is pourcd into the form from yield 100% detonation with 50 grain PETN/foot Prima spout 16. After the assembly has hardened, it is rc cord threaded through both holes. moved from the base 4 to yield a booster as shown in While it is not intended to be bound by any theory, of FIGURE 3 having two perforations extending there operation, it is believed that the tube 1 of Primacord through. sensitive explosives, adjacent and peripheral to the perfo Forms 16 made of cardboard or paper are satisfactory rations, yield detonation waves that interact and rein and it has been found unnecessary to remove the form force each other to produce a high intensity shock ef from the booster in such cases. fect, thereby detonating the main booster charge 10 which An alternative method of compacting the explosive is otherwise not detonatable by Primacord. about the core comprises pressing particulate explosive in In use, a Primacord fuse, such as 50 grain PETN/foot, the form to yield a compact shaped booster. is threaded through one or more of the holes 13 and The tube 11 may be made of plastic such as polyethyl kncited to prevent the removal of the booster from the ene, vinyl chloride, vinylidene chloride, polyethylene ter fuse. The booster may be inserted in a priming cartridge ephthalate or any of the synthetic rubbers or it may be of aminenium nitrate explosive or preferably lowered by of cellulosic material such as regenerated cellulose, cellu itself into the bore hole by suspending it on the Prima lose acetate or cellulose nitrate. Additionally, Prima cord line at the appropriate position in the hole. The cord itself, which contains fine grained PETN, may be 2 5 main charge is then introduced simply by pouring the used as the tube containing Primacord-sensitive explosive. loose or slurry explosive into the hole. The Primacord The Primacord-sensitive explosive 12 contained within fuse is initiated electrically as is well known in the art. the tube is preferably fine-grained material and may be Either cast or pressed boosters may be prepared in ac PETN, REDX, amatol, tetryl and fine-grained TNT. The cordance with the invention, Cast boosters are preferred latter is Primacord-sensitive whereas coarse or cast TNT 3. because they do not crumble upon wetting or subjected to is Primacord-insensitive. If fine-grained TNT is used rough handling. Cast boosters are also less water-sensi in the tube and the sheath is cast TNT, a sufficiently heavy tive. walled tube must be used to insulate the TNT within the We have thus described novel boosters which are con tube from the heat of the molten TNT which is cast to sistently operative for boostering ammonium nitrate ex form the sheath. plosives which employ a minimum of expensive materials The Primacord-insensitive explosive forming the sheath and which are consistently detonatable by 50 grain Prima 10 may be cast or pressed TNT, composition B (59% cord. While the invention has been described in terms RDX-40% TNT-1% wax) or composition B-TNT mix of certain embodiments, these are to be considered illus tures. The above possess high brisance but are not con trative rather than limiting and it is intended to cover all sistently detonatable by Primacord containing 50 grains 40 further embodiments that fall within the spirit and scope of PETN per foot. of the appended claims. It has been found that cylindrical boosters about three We cairn: inches in diameter and two inches long provided with two 1. The method of making a booster for insensitive ex holes made in accordance with the invention consistently plosives comprising supporting a rod on a base in up detonate the insensitive ammonium nitrate explosives. 4. 5 standing relation thereto, wrapping a flexible tube con Such boosters contain about 300-400 grams of Prima taining Primacord-sensitive explosive around Said rod, cord-insensitive explosive. The tube 11 containing the copacting a sheath of Primacord-insensitive explosive Primacord-sensitive explosive i2 may contain about 5 to on said base about said rod and tube and removing said 10 grams of PETN or its equivalent. For the least sen rod and base from said compacted sheath to provide a sitive explosives in the sheath it), more Primacord-sensi perforation through the sheath adapted to receive a deto tive explosive should be used to achicve high order deto Rating fuse. nations. For example, forty boosters were prepared in 2. The method of making a booster for insensitive ex accordance with the invention, utilizing one foot lengths plosives comprising supporting a pair of rods on a base of 0.263 inch internal diameter 0,020 inch thick (wall normal thereto and parallel to each other, winding a thickness plastic tubes containing about 10 grams of 5 5 flexible tube containing Primacord-sensitive explosive PETN each). Twenty of such tubes were wound about around said rods in figure 3 configuration, casting a sheath the rods 15 in figure 3 fashion as shown in FIGURE 1 of Primacord-insensitive explosive on said base about said and twenty were wound helically on the rods 5. Ten rods and tibc, and renowing said rods and base fronn said of each of the groups were then formed into boosters cast sheath to provide perforations through the sheath by casting a cylinder 3 inches in diameter by 2 inches high GO adapted to receive a detonating fuse. from 100% TNT. Ten of each of the boosters were formed in the same manner by casting 25% TNT, 75% References Cited by the Examiner composition B. The boosters were then fired with 50 UNITED STATES PATENTS grain PETN/foot Primacord threaded through one only 1,652,961 12/27 Snelling ------102-27 of the holes. All forty of such boosters fired, giving a 2,682,220 6/54 Hagensen ------102-24 detonation percentage of 100%. 2,709,407 5/55 Lowe ------102-24 As indicated above, Primacord itself may be used as 2,757,566 8/56 Towell et al. ------86-1 the tube containing the Primacord-sensitive explosive. 2.913,982 1 1/59 Hayes ------102-24 In a series of tests, we have found that boosters made 3,037,452 6/62 Cook et al. ------102-27 from 6 inch to one foot lengths of 50 grain PETNA?oot C Primacord wound in figure 8 fashion contained within a BENJAMIN A. BORCHELT, Primary Examiner. sheath of 350 grams of cast 75% composition B, 25% TNT according to the invention yield 100% detonations ARTHUR M. HORTON, SAMUEL BOYD, Examiners.