Booster for explosive blasting agents
United States Patent [191 Cook [451 Apr. 29, 1975 I BOOSTER FOR EXPLOSIVE BLASTING AGENTS [75] Inventor: Melvin A. Cook, Salt Lake City,  
 Utah  
 [73] Assignee: Ireco Chemicals, Salt Lake City,  
 Utah  
 [22] Filed: Apr. 6, 1973 21 Appl. No.: 348,767  
 OTHER PUBLICATIONS Military Explosives, TM 9-l9l0/TO ll A-l-34, Apr. 1955, pp. 182, 183.  
 Primary Examiner-Verlin R. Pendegrass Attorney, Agent, or Firm-Robert A. Bingham [57] ABSTRACT A booster for detonating cap-insensitive explosives is provided comprising a container having a main body portion and a neck portion of smaller cross-sectional area than the main body portion and having an opening in the neck portion for introduction of a detonatingfuse-insensitive explosive charge which fills the main body portion, and a detonating-fuse-sensitive explosive charge which fills the neck portion. The booster of the present invention is conveniently prepared and handled or loaded and has inherent waterresistance even though not necessarily water-proof and though inexpensive water-soluble explosive ingre clients may be employed.  
 14 Claims, 2 Drawing Figures BOOSTER FOR EXPLO&#39;SIVE BLASTING AGENTS This invention relates to an explosive booster for detonating cap-insensitive explosive compositions such as ammonium nitrate/fuel oil and aqueous blasting agents commonly referred to as slurry blasting agents or explosives.  
  Many types of boosters have been used in the past for detonating explosive compositions. Conventional booster assemblies generally comprise a cast or pressed high explosive charge having a well, indentation or hole capable of receiving a cap, or fuse-, type primary initiator. Many variations of this general assembly are found. For instance, the high explosive charge may be in a protective container with the hole or well extending into or through the charge and separated from the body of high explosive by an extension of the container wall. Other booster assemblies comprise a compacted or cast core of detonating-fuse-sensitive explosive surrounded by a compacted or cast sheath of highly brisant detonating-fuse-insensitive explosive and having one or more wells or bores extending through the core and sheath adaptable for receiving a detonating fuse or other primary initiator. When the detonating fuse is initiated, it in turn initiates the detonating-cord-sensitive core which in turn initiates the detonating-cordinsensitive sheath. Boosters of this latter type are shown in US. Pat. Nos. 3,037,452, 3,037,453, and 3,359,902. These boosters are generally not encased by a water-tight container and therefore the cast or pressed explosive must be water-resistant, if the boosters are to be used in water-containing boreholes. ln application, boosters of this latter type can be placed singly or intermittently at appropriate spacings at or from the bottom to the top of a borehole. Such placement is accomplished by threading detonating fuse (which generally runs the length of the borehole) through the bore of the booster(s) and allowing the booster to slide down the fuse into the borehole at a proper sequence during the loading of the borehole with explosive charge. Thus, the loaded an primed borehole may consist of a series of appropriately spaced boosters threaded together by a detonating fuse downline (which may be tied at the down end to prevent the bottom booster from slipping off the line) all held firmly in place by the explosive charge, which surrounds the boosters and fills the borehole. Generally, this boostering series would be located along the axis of the explosive charge.  
  Threading boosters on a detonating fuse downline at approximate intervals during the filling of the borehole with an explosive charge is a convenient method of boostering. The booster of the present invention is conveniently loaded and thereby also provides a convenient method of boostering. The boosters of the present invention also have the beneficial attributes of boosters having a protective container.  
  The booster of the present invention comprises a container of suitable shape and material having a main body portion and an elongated neck portion. The elongated neck portion has substantially less cross-sectional area than the average cross-sectional area of the main body portion. The main body portion of the container is filled by conventional means to the base of the neck with a detonating-fuse-insensitive explosive charge which need not have any water-resistant characteristic. The neck is then filled with a detonating-fuse-sensitive explosive which is essentially water-resistant. Detonating fuse may then be wrapped or tied around the periphery of the neck so as to position the fuse in close proximity to the detonating-fuse-sensitive explosive for initiation purposes. The neck may have an outward extending lip at its opening to prevent slippage of the detonating fuse off the neck.  
  Boosters of the present invention can be easily loaded and positioned in a borehole merely by wrapping or tying a detonating fuse downline around the neck of the booster. Boosters can be attached in this manner at appropriate intervals along the length of the detonating fuse. Since these boosters are firmly attached along the detonating fuse downline, the series of boosters may be prepositioned in the borehole prior to filling with the main explosive charge rather than positioned concurrently during filling as is necessary when boosters having a bore are threaded on a fuse downline as described previously. The ability, when desired, to conveniently pre-position a series of boosters in the above manner is one of the advantages of the present invention.  
  The exact mode of attaching the detonating fuse to the booster is not overly critical and depends primarily on preference for manner of handling and loading the booster(s). For instance, a closed loop of detonating fuse having its ends embedded in the detonating-fusesensitive explosive charge could readily be used so long as close, positive contact between fuse downline and loop was maintained. This would allow loading of the boosters in the conventional threaded manner, since the detonating fuse downline could be threaded through the closed loop. Other attachment variations are possible.  
  A more detailed description of the present invention is obtained by reference to the accompanying drawings which depict representative embodiments.  
 A detailed description of the drawings is as follows:  
  FIG. 1 is a cross-sectional front view of a booster of the present invention.  
  FIG. 2 is a cross-sectional front view of a booster container of preferred shape.  
  With reference to FIG. 1, a symmetrically circular container 1 is shown having an elongated neck 5 of smaller diameter than the average diameter of the main body of the container. Container 1 is flask-shaped to a certain degree due to the truncated cone-shaped portion connecting the neck 5. This general container shape is particularly advantageous for boosters of the present invention as will be explained below. At the opening 6 at the end of the neck of the container is a lip 3. Within the container is an explosive charge 4 which is insensitive to detonation by a detonating fuse or detonating-fuse-insensitive and which fills the main body of the container to the base of the neck 5 as shown at 7. Filling the neck 5 of the container is a detonating-fuse-sensitive explosive charge 2. This fusesensitive charge functions somewhat as a plug for the container to provide water-resistance for the fuseinsensitive main body charge as will be explained below. Around the circumference of the neck are two wrappings of detonating fuse 8. These wrappings are held in place around the neck by lip 3 that acts as a barrier to impede slippage of the fuse off the neck.  
  In application, the booster shown in FIG. 1 will be appropriately positioned so as to be in direct contact with an explosive charge in a borehole. The boostering system for the charge may be a single booster or a series of spaced boosters all connected in series to the detonating fuse. A single detonating fuse downline can be easily tied or wrapped around the booster neck(s) and of the wave front and also produce a similarly expanding wave front generally along the axis of the container in the direction opposite the container opening, i.e., toward its base. In this manner the explosive energy of then the fuse and connected booster(s) can be lowered 5 the booster will be directed eesentially forward and into the borehole. Therefore, the booster or boosters outward from its base thereby constituting a specifimay be pre-positioned in the borehole prior to filling cally directed and thus concentrated boostering power with explosive charge. for the main explosive charge in the borehole. Al-  
 Once the boostering system described above is posithough the .booster power f f f l0 ward from its base, careful positioning or aligning of tioned and the borehole has been loaded with explosive f l I d f the axis of the booster within the axis of the borehole charge and the sur-roun mg area y C ear-e 9r is not critical so long as the base of the booster is enblasting, the detonating fuse is then initiated which will com ed or s nded b ex losive char 6 It is in turn initiate the detonating-fuse-sensitive high explogj j g g an X aspfar as j i d sive charge in the neck of the booster container which p g p l5 practical, the axis of the booster with that of the borewill in turn initiate the detonating-fuse-insensitive exhole so that the base of the booster faces the main of plosive charge in the main body of the container. In this the ex losive char 6 Positionin the booster in this manner, complete detonation of the booster is accomp t g b t i plished. Detonation of the booster or boosters will then mannef l l 00S ermg power 5 initiate the explosive charge surrounding the boosters transmltte, to 6 exp Oswe argej resulting in a successful explosion According to the present invention, boosters were prepared and tested and the results tabulated as shown The booster Show F 1 has a flask or below in Table l. The boosters tested comprised a a appearance whlch advantagaous for maxlmlz&#39; homogenious mix main body explosive charge consistmg a i boosfer shock a exlaoswe as ing of 60 percent air dried TNT (trinitrotoluene), and as obtaining maximum efficiency in detonation of the 40 percent AN (ammonium nitrate) m ground to a mam f Upon aetonanon the detonatmg&#39; particle size of 32 mesh or smaller. The ground AN fuse-sensitive high explosive charge 2 in the neck 5 of prms used were Monsanto An explosive charge container 1, caused by initiation of the circumferencmg containing a combination of AN and TNT is commonly dematmg fuse a detonatfon a from produced referred to in the art as amatol. The configuration of during the detonatlon reacnon Wm expand laterally the container used for the boosters tested is shown in outward and forwardfmm f charge generally 9 FIG. 2. The main body portion of the container was apthe axis of the container. This shock wave expansion proximately 4 inches in length and 2 inches in width w ll generally follow the conical shape of booster conand the container neck portion was approximately 1 1 tamer 1 which also extends i wa By inches in length and 1 inches in diameter. The trunforming the shape of the container containing the main 35 Gated cone portion of the main body portion connect booster charge (dctoatmg&#39;fuse&#39;msensftwe explos we ing the neck portion was approximately nine-sixteenths charge) the Shape of the expanding detonauon inches in length. The containers used were bell-shaped wave front, all or most of the wave front energy W11l be in order to maximize detonation efficiency and power transmitted through all or most of the explosive charge as explained above. The high explosive initiating to be initiated thereby maximizing booster detonation 40 Charge in the container neck comprised 40 to grams effic&#39;ency of a cast blend of /35 PETN (pentaerythritol tetrani- The main booster charge initiated in this manner will trate)/TNT (trinitrotoluene) A combination of PETN undergo a detonation-reaction conforming to the shape and TNT is commonly referred to as pentolite.  
 TABLE I Testing Conditions Dctonating Fuse Rcsults*** Time in Water Pressure of Configuration Results*** Water Dry (0 days) 1 turn, 18 grain PC* 1, Failed do. 2 turns, l8 grain PC 1, Punched do. 1 turn, 25 grain PC 8. Punched do. 2 turns, 25 grain PC I, Punched 1 Day 50 psi 2 turns, 25 grain PC I, Failed l, Punched l, Punched 3 Days 50 psi 2 turns, 25 grain PC 1, Punched 2, Punched (50%) 4 Days 50 psi 2 turns, 25 grain PC 2, Punched l, Dented (l%&#34;) l 1 Days 50 psi 2 turns, 25 grain 2, Failed through the plate. Percentage figure following Punchcd&#34; indicates amount of total hole formed. i.c.. 7r  
 of hole circumference.  
  The boosters tested were prepared in the following manner: the ammonium nitrate prills were uniformly mixed into and throughout molten TNT which was at a temperature of about 82 C and thereafter the fluid blend was poured into the container filling the main body portion to the base of the neck. This charge (amatol) was then allowed to solidify. Thereafter, molten pentolite at a temperature of about 82 C was cast into the neck of the container and allowed to solidify. Casting was accomplished at or as close to the solidification temperature as possible so as to eliminate, as far as possible, air holes or pockets which may form due to shrinkage of the charge upon cooling. Thus free space within the container was minimized. Casting of most of the boosters was in fact accomplished after part of the TNT had crystalized but while the charge was still easily pourable. Detonating fuse of type described in the table was then tied around the periphery of the neck of the container in the manner described in the table. Detonation results upon initiation of the detonating fuse were as shown.  
  As indicated in the table, some of the boosters were stored under water pressure of 50 psi. for various periods of time. Although no specific attempt was made to make the containers watertight, the results show that the boosters were still effective even after four days storage under such circumstances. Thus, another important advantage of the boosters of the present invention is their inherent water-resistancy even though they are not necessarily water-tight and even when a watersoluble explosive charge is used, e.g., AN is very soluble in water.  
  Visual examination of the boosters after storage indicated that water had penetrated the inside of the container and in fact had surrounded the amatol main body charge. The boosters were, however, still effective. Thus boosters of the present invention can be considered water-resistant even if not necessarily waterproof. This attribute allows their effective use in deep water-filled boreholes.  
  The inherent water-resistance of the boosters of the present invention that contain a water-soluble main explosive charge is attributed to the fact that dissolution of the soluble salt or ingredient contained within the main body explosive charge occurs only by the slow process of diffusion. The fuse-sensitive high explosive charge in the neck of the booster (which itself must not be soluble or decomposable in water) functions to restrict the diffusion path area of dissolved salt or ingredient to only that small area surrounding the periphery of the charge between the container and the charge. Thus, boosters of the present invention can be stored under water for extended periods of time without any adverse water damage since only a very small amount of soluble explosive charge will have diffused out of the container. Extended water storage, however, may cause desensitization of the charge due to water permeation throughout the entire body of the explosive charge. As shown in the table, after 11 days water storage the boosters failed to detonate. Casting or loading the boosters with explosive charge should be accomplished so as to minimize air space or voids between containerwall and charge and Within charge in order to minimize amount of water intrusion. Different oxidizing salts such as any of the alkali or alkaline earth metal nitrates or chlorates and perchlorates as well as different types or brands of the same salt can have a substantial effect on the duration of effective water-resistancy. For example, potassium and ammonium perchlorates are much less soluble than AN and would therefore provide better water-resistance.  
  Although AN is very soluble in water, it has a unique property which provides good water resistance. One important reason for the minimal amount of diffusion evidenced over extended water storage of boosters containing AN as part of the explosive charge is that AN swells in volume upon dissolution thereby increasing the pressure within the container, which would therefore tend to inhibit further dissolution and subsequent diffusion. Any oxidizer salt or or water-soluble explosive component having a similar property would be equally advantageous. Thus, even though watersoluble ingredients can be used in boosters of the present invention since only a limited degree of diffusion occurs as explained above, it is preferable to use those soluble ingredients such as AN which swell in volume upon dissolution.  
  Another major advantage of the present invention is that relative inexpensive inorganic oxidizing salts or other inexpensive ingredients can be combined in relatively high proportion with a more expensive high explosive ingredient such as TNT to form the fuseinsensitive, main body charge of the explosive. This combination results in a significantly less expensive booster than those comprised of high explosive ingredients such as TNT, RDX, PETN, and the like and mixtures of these. Less expensive ingredients such as AN function not only as a bulk filler of the booster container volume thereby reducing the amount of more expensive explosive required, but also as participating explosive ingredients which enter into the detonation reaction and provide for a more oxygen-balanced charge. The use of inorganic oxidizer salts in combination with high explosive will generally result in a lower cost/energy value than when high self-explosive is singularly used. For example, amatol having a composition of 60% TNT and 40% AN has cost/energy value of about 34 cents/million calories, whereas TNT has a similar value of about 51 cents/million calories. The preferred range of inorganic oxidizing salt would be 20 to 60 percent by weight, and correspondingly high explosive to 40 percent. The use of these inexpensive, and usually soluble ingredients is made possible by the inherent water-resistancy of the boosters as explained above.  
  The fuse-sensitive high explosive charge for the neck of the booster must not be soluble or decomposable in water in order to function as :a plug to prevent water degradation of the booster as explained above. A preferred fuse-sensitive charge is pentolite having a range of PETN of 50 to 65 percent by weight, depending upon desired sensitivity and pourability or castability, and a corresponding 50 to 35 percent by weight range of TNT.  
  The size and shape of the container can be varied to any desired degree. Although the high explosive charge contained within the neck of the container is adequate to prevent substantial water impairment over relatively extended storage periods, a cap or similar device may be placed over the neck opening to essentially prevent or impede water intrusion and impairment. The material of the container is not critical but should be durable in the environment present in the borehole and compatible with the explosive contents. Polyethylene is a preferred container since it can be easily blow molded into any desired container shape and is relatively inexpensive.  
  The invention described above offers outstanding advantages in providing a booster which is inexpensive, conveniently manufactured and applied in the field and water-resistant. Although the present invention was described in terms of using detonating fuse as the primary initiator, it is obvious to one skilled in the art that a cap primary initiator could be used to detonate the boosters with appropriate attachment to or placement in the detonating-fuse-, or cap-, sensitive explosive charge.  
  It will be obvious that modifications mentioned above and others not mentioned may be made by those skilled in the art without departing from the spirit and purpose of the invention. It is intended to cover the invention and obvious variations and modifications as broadly as the prior art permits.  
 What is claimed is:  
  1. A water-resistant booster for detonating capinsensitive explosive blasting agents comprising a. a container having a main body portion and an elongated neck portion of smaller-cross-sectional area than the main body portion and having an opening at the end of the neck portion opposite main body portion,  
 b. an at least partially water-soluble detonating fuseinsensitive explosive charge within the main body portion of said container, and  
 c. a water-insoluble detonating fuse-sensitive explosive charge substantially wholly contained within the neck portion of said container and having an outer peripheral surface which conforms to the inner surface of the neck portion throughout at least most of the charges outer peripheral surface to provide close contact therewith and thereby to allow said charge to plug said container.  
  2. A booster according to claim 1 wherein said detonating fuse-insensitive explosive is a combination of a high explosive and an inorganic oxidizing salt selected from the group which consists of alkali or alkaline earth metal nitrates, chlorates and perchlorates.  
  3. A booster according to claim 2 wherein said inorganic oxidizing salt is ammonium nitrate.  
  4. A booster according to claim 2 wherein said high explosive is trinitrotolune.  
  5. A booster according to claim 3 wherein said high explosive is trinitrotoluene.  
 6. A booster according to claim 5 wherein ammonium nitrate is present in amount of about 40 percent by weight and trinitrotoluene is present in amount of about 60 percent by weight.  
  7. A booster according to claim 1 wherein said detonating fuse-sensitive explosive is a combination of trinitrotoluene and pentaerythritol tetranitrate.  
  8. A booster according to claim 1 wherein said container is flask or bell-shaped to conform to a forward, laterally outward, expanding detonation wave front obtained upon detonation of said detonating fusesensitive explosive within the neck portion and which wave front proceeds axially through the main body portion.  
  9. A booster according the claim 1 wherein material of said container is polyethylene.  
  10. A booster according to claim 1 wherein said detonating-fuse-insensitive explosive contains a soluble ingredient which swells in volume upon dissolution in an aqueous medium.  
  11. A method of preparation of the booster of claim 1 comprising the consecutive steps of v a. filling the main body portion of said container with said detonating-fuse-insensitive explosive,  
 b. filling the neck portion of said container with said detonating-fusesensitive explosive, and  
 c. securing a detonating fuse in close proximity to said detonating-fuse-sensitive explosive.  
  12. A method according to claim 11 wherein said filling of said container with said detonating-fuse-, sensitive and insensitive explosive charges is accomplished by casting said explosive charges into said container in molten form at or close to solidification temperature of said explosive to minimize voids or free space which may result upon solidification of said explosive charges.  
  13. A method of boostering a borehole filled with cap-insensitive explosive charge using the booster of claim 1 comprising axially positioning said booster or series of said boosters into a borehole by securing said booster(s) to a detonating fuse downline at desired position or intervals along the length of the detonating fuse.  
  14. A method according to claim 13 wherein said booster or series of said boosters is pre-positioned in the borehole before the borehole is filled with the explosive charge.