Patent Publication Number: US-2003221577-A1

Title: Standalone ignition subassembly for detonators

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to pyrotechnic detonators, and more particularly, to a standalone ignition subassembly designed for incorporation into detonators.  
       [0002] The efficient use of explosives in mining operations and the demolition of structures often requires that many charges be placed in a predetermined pattern and detonated in a timed sequence. In general, timed detonation can be accomplished by detonators that use pyrotechnic delays, sequential-type blasting machines, and electronically programmable detonators. Some examples of time-delayed detonators are described in U.S. Pat. Nos. 6,173,651, 6,085,659, 6,079,332, 5,602,360, 5,460,093, 5,435,248, 4,869,170, 4,819,560, 4,730,558, and 4,712,477, the disclosures of which are hereby incorporated by reference herein.  
       [0003] Such detonators are, however, generally tailored to a specific application, thus precluding the use of interchangeable detonators for a number of applications. Hitherto, it is believed that it has not been conceived to use an interchangeable, standalone ignition subassembly to initiate a variety of detonators.  
       SUMMARY OF THE INVENTION  
       [0004] An object of the present invention is to provide a standalone ignition subassembly that can be readily incorporated into a variety of detonator shells.  
       [0005] A separate object of the present invention is to provide an ignition subassembly that is protected against vibration and the environment, so as to permit convenient handling and transportation of the subassembly. 
     
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
     [0006]FIG. 1 is a side sectional view of an embodiment of the present invention.  
     [0007]FIG. 2 is a top sectional view of an alternate embodiment of the present invention.  
     [0008]FIG. 3 is an exploded side and sectional view showing how an embodiment of the present invention such as that shown in FIGS.  1  or  2  fits into a loaded detonator shell.  
     [0009]FIG. 4 is a side view of an alternate embodiment of the present invention having an alternate outer surface to that of the embodiment shown in FIG. 3.  
     [0010]FIG. 5 is a side sectional view of an alternate embodiment of the present invention incorporating an off-the-shelf capacitor, with this embodiment inserted in a loaded shell and crimped in place with a plug.  
     [0011]FIG. 6 is a side sectional view of another alternate embodiment similar to that shown in FIG. 5, with the off-the-shelf capacitor in a different configuration. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 1    
     [0012] Referring to FIGS. 1 and 2, an ignition subassembly  8  of an embodiment of the present invention, and an alternate embodiment  8 ′, are shown. As shown in FIG. 3, such a subassembly is placed inside of a shell  40  that may contain a primary charge  36  and a base charge  38  loaded into its closed end. (A detonator shell is typically a metal cylinder 6 to 8 mm. in diameter and from 60-100 mm. in length). Subassembly  8  can then be secured in place in the shell  40 , such as by placing an elastomeric plug or the like (see elastomeric plug  46  and crimp  47  in FIGS. 5 and 6) in the open end of the shell and crimping the shell  40  to the plug, or other suitable method. Subassembly  8  may have a body portion  32  formed of an encapsulation  31  and may have ridges  57  protruding out from the outer surface of body portion  32 , so as to snugly hold subassembly  8  within the shell  40 . Such ridges  57  or other protuberances such as nubs  57 ′ shown in FIG. 4 are preferably formed to dampen vibrations to which the detonator may be subjected, generally in accordance with the teachings of U.S. Pat. No. 6,079,332.  
     [0013] The material for encapsulation  31  is preferably chosen to afford economical material and manufacturing costs, desirable electrical isolation and vibration and environmental protection for the encapsulated circuitry (including desirable modulus of elasticity, et cetera, as generally taught in U.S. Pat. No. 6,079,332), adequate physical integrity and holding and securing of the subassembly&#39;s components, and a lack of chemical volatility with other materials comprising the detonator. At least three processes may be used, including insert molding with thermoplastics, hot-melt molding (similar to glue-gun technology), and reactive injection molding (RIM, a 2-part mix and injection with low temperatures and pressures). Insert molding is a preferable technique, and preferred encapsulation materials for use in that technique are polypropylene, polyurethane, or polyethylene, although polystyrene, polyester, polyamide, and polyolefin can also be considered depending on the application. The preferred encapsulation materials for use in the hotmelt technique are polyamides, but polypropylene, polyurethane, polyester, polyolefin, EVA, acrylic, and silicone can also be considered depending on the application. The preferred encapsulation materials for use in the RIM technique are polyurethane-based materials. Some relevant teachings regarding encapsulation are also set forth in U.S. Pat. Nos. 6,079,332 and 4,869,170.  
     [0014] Although a standalone ignition subassembly according to the present invention may include any kind of suitable ignition element (e.g., matchhead-type) as long as it is hermetically sealed and protected from the environment, a header-based, or automotive airbag initiator-style, ignition element  28  is employed in the preferred embodiments shown in the Figures. As will be appreciated, such an ignition element lends itself to hermetic sealing because it includes an integral, rigid charge can and header that hermetically seals the charge in an enclosure. U.S. Pat. Nos. 6,274,252, 5,709,724, 5,639,986, 5,602,359, 5,596,163, 5,404,263, 5,140,906, and 3,971,320 are also hereby incorporated by reference herein for their disclosure concerning the construction of ignition elements based on a glass-to-metal sealed header feedthrough.  
     [0015] As shown in FIGS. 1 and 2, ignition element  28  (and  28 ′) includes a header assembly with a sealed electrical feedthrough, comprising an eyelet  10  (preferably stainless steel), insulator glass  14  (preferably a glass such as a sodasilicate, e.g.,  9010 , that is chosen to form a compression seal with the eyelet and center pin, or less preferably a matched seal), a center pin  18  (preferably an iron nickel alloy), a ground pin  20 , and an igniter wire  12  (preferably a low energy igniter wire with a diameter of 10 to 20 microns). The ignition element  28  further preferably includes a charge can  26  that is preferably metallic and hermetically sealed to the eyelet at circumferential through-weld  16 , with an ignition charge contained between the can  26  and upper surface of the header, in tight contact with igniter wire  12 . An insulator cup  27  may preferably be attached around the can  26  so that, except for female connectors  52  that protrude from the input end of the subassembly, the entire outer surface of ignition subassembly  8  consists of insulating material, thus providing electrical isolation and vibration and environmental protection to the components within. Pins are inserted and crimped within female connectors  52 .  
     [0016] In the depicted embodiment, a circuit board  24  and electronic components  25  may be provided within ignition subassembly  8 , to provide a means of triggering ignition of the ignition element based on the processing of an electrical ignition signal received by connectors  52 , which are electrically connected to a blasting machine or the like that powers the detonator. Such electronic components are well-known and preferably include means for imparting a programmable period of delay to the ignition, means for ESD and RF protection, et cetera. Circuit board  24  and electronic components  25  are preferably encapsulated together in encapsulation  31 , and connected to pins  18  and  20  at contacts  22  through soldering or other suitable connection. Referring to FIG. 2, as is well-known in encapsulated automotive airbag initiators, retention of the ignition element  28  to the encapsulation  31  may be enhanced by providing a lip  17  at the bottom of the eyelet  10 ′. The insulator cup  27 ′ may also be held within the encapsulation  31  to facilitate its retention as well, and the can may also have a lip (not shown) as another retention feature.  
     [0017]FIGS. 5 and 6 illustrate two alternate configurations for the electronics encapsulated within the alternate ignition subassemblies  8   a  and  8   b . In these configurations, an off-the-shelf cylindrical capacitor  42  is contained within the encapsulation  31 , either between the input leads  48  and circuit board  24   a  as shown in FIG. 5, or between the circuit board  24   a  and the ignition element  28  as shown in FIG. 6. As shown in FIG. 5, in order to accommodate the capacitor  42  within the diameter of the encapsulation  31  (which is determined by the inner diameter of the type of detonator shell with which the ignition subassembly is to be compatible), thin, flat flexible jumpers  44  can be provided, and the axis of the capacitor  42  slightly offset from the axis of the subassembly  8   a . Similarly, as shown in FIG. 6, flexible jumper  60  can traverse the length of capacitor  42 , and the leads to capacitor  42  can be soldered to the circuit board  24  at through-mounts (as can one or both of the ends of flexible jumper  60 ).  
     [0018] By way of example, in an embodiment like that shown in FIGS. 1 and 2, it has been found that a nickel/chromium alloy, 13 micron diameter, 0.7 mm long igniter wire, and a 50 mg ignition charge of zirconium potassium perchlorate having a height of 1.0 mm and a diameter of 4.8 mm, is capable of reliably detonating all commonly used primary charges. Preferably, a minimum suitable charge is approximately 30 mg for a configuration of this size, as a smaller charge may result in an insufficient charge thickness. A preferred all-fire voltage is 6 volts, and in this embodiment, may be delivered with a 100 microfarad capacitor included in the electronic components  25 .  
     [0019] It should be noted that although the Figures depict embodiments including electronic components that receive, process, and deliver an ignition signal, such an ignition signal may alternately be received, processed, and delivered by a number of other well-known non-electronic or partly-electronic means, such as through the use of a shock tube to deliver an ignition signal to a piezoelectric device, column fuse delays, et cetera. It is noted that this detailed description of certain embodiments herein does not imply that such alternate embodiments are not within the scope of the invention.  
     [0020] A preferred embodiment of a standalone ignition subassembly designed for ready incorporation into pyrotechnic detonators, and many of its attendant advantages, has thus been disclosed. It will be apparent, however, that various changes may be made in the form, construction, and arrangement of the parts without departing from the spirit and scope of the invention, the form hereinbefore described being merely a preferred or exemplary embodiment thereof. Therefore, the invention is not to be restricted or limited except in accordance with the following claims.