Patent Publication Number: US-2003221576-A1

Title: Detonator with an ignition element having a transistor-type sealed feedthrough

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to pyrotechnic detonators, and more particularly, to a detonator with an ignition element that includes a transistor-style sealed header feedthrough.  
       [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 subject to one or more drawbacks, however, such as the following: (1) the use of an ignition element that is difficult to manufacture to precise dimensions so as to ensure predictable performance, (2) the use of an ignition element that requires careful handling during manufacturing and thus impedes the beneficial incorporation of automated steps in the detonator assembly process, (3) the use of an ignition charge that contains lead, which presents an environmental and health hazard, (4) the use of a non-low energy ignition element, which inhibits compact design, (5) lack of reliability, and (6) costly manufacturing.  
       [0004] On the other hand, such problems are overcome or at least ameliorated in well-known glass-to-metal sealed initiators such as those currently manufactured and sold by the assignee of this patent application. Various patents also disclose other examples of glass-to-metal sealed initiators having features that address one or more of such problems, including 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, the disclosures of which are hereby incorporated by reference herein.  
       [0005] Despite the aforementioned problems and the widespread existence of such initiators, it is believed that hitherto it has not been conceived or attempted to utilize an ignition element that includes a transistor-type glass-to-metal sealed header, in a detonator for use in mining, blasting, and demolition.  
       SUMMARY OF THE INVENTION  
       [0006] One object of the present invention is to provide a detonator that incorporates a transistor-type glass-to-metal sealed header so as to overcome or ameliorate one or more of the problems enumerated above.  
       [0007] Another objective of the present invention is to provide a detonator utilizing an ignition element having a transistor-type glass-to-metal sealed header, resulting in a reliable and economical detonator.  
       [0008] Another separate and alternative objective of the present invention is to provide a detonator utilizing an ignition element that is relatively easy to manufacture to precise dimensions with known and proven manufacturing processes, resulting in a detonator having predictable performance.  
       [0009] It is another separate and alternative objective of the present invention to provide a detonator utilizing an ignition element that is sufficiently durable to permit the incorporation of useful automation steps in the detonator assembly process.  
       [0010] It is a further separate and alternative objective of the present invention to provide a detonator utilizing an ignition charge that does not contain any lead, so as to reduce hazards to the environmental and health resulting from the use of the detonator.  
       [0011] It is yet another separate and alternative objective of the present invention to provide a detonator utilizing a low energy ignition element, resulting in a detonator that may be made more compact. 
     
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
     [0012]FIG. 1 is a top sectional view of an embodiment of the present invention.  
     [0013]FIG. 2 is a partial top sectional view of the ignition element portion of the embodiment shown in FIG. 1.  
     [0014]FIG. 3 is a partial top sectional view of the ignition element portion of an alternate embodiment to that shown in FIGS. 1 and 2. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 1    
     [0015] Referring to FIGS. 1 and 2, an embodiment of a detonator according to the present invention is shown. The detonator includes a shell  40  loaded with a primary charge  36  and a base charge  38 , and an ignition subassembly  8 . (A detonator shell is typically a metal cylinder 6 to 8 mm. in diameter and from 60-100 mm. in length). Subassembly  8  is then secured in place in the shell  40  preferably by placing an elastomeric plug  46  or the like in the open end of the shell and crimping the shell  40  to the plug, or subassembly  8  can be secured using any other suitable method. Subassembly  8  may have a body portion formed of an encapsulation  31  and may be formed to snugly hold subassembly  8  within the shell  40  and dampen vibrations to which the detonator may be subjected, generally in accordance with the teachings of U.S. Pat. No. 6,079,332.  
     [0016] Alternately, an ignition subassembly similar to that of FIG. 1 (but preferably lacking encapsulation  31 ) can be directly incorporated into a shell, such as by molding it directly in the shell. Various other methods of incorporating a transistor-type header ignition element into a detonator in accordance with the present invention will be readily apparent, and the present invention does not require the use of a “standalone” ignition subassembly although one is shown in FIG. 1.  
     [0017] Turning to the specifics of the depicted transistor-type glass-to-metal sealed header ignition element  28 , it can be seen that ignition element  28  includes a header assembly with a sealed electrical feedthrough, comprising an eyelet  10  (preferably Kovar®), insulator glass  14  (preferably a glass such as a sodasilicate, e.g., 9010, that is chosen to form a matched seal with the eyelet and center pin), a center pin  18  (preferably a nickel/chromium alloy), a ground pin  20 , and an igniter wire  12  (preferably a low energy igniter wire with a diameter of 10 to 20 microns). Due to its thin profile, eyelet  10  can be stamped or cold-formed, resulting in cost savings as compared to a machining operation. Ground pin  20  and center pin  18  are preferably selected of the same material. 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  30  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 electrically isolating and providing vibration and environmental protection to the components within. FIG. 3 depicts an alternate header including a dogleg eyelet  10 ′ with an integral ground pin  19  that may be formed by stamping if the eyelet is stamped.  
     [0018] In the depicted embodiment, a circuit board  24  and electronic components  25  may be provided within the 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 FIGS. 2 and 3, retention of the ignition element  28  to the encapsulation  31  may be enhanced by providing a lip  17  (or  17 ′) at the bottom of the eyelet  10  or ( 10 ′). The insulator cup  27  may also be held within the encapsulation  31  to facilitate its retention as well.  
     [0019] By way of example, in an embodiment like that shown in the Figures, 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 with a height of 1.0 mm and a diameter of 4.8 mm is suitable. 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 may be 6 volts, and may be delivered with a 100 microfarad capacitor included in the electronic components  25  in an embodiment like that depicted.  
     [0020] 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 does not imply that such alternate embodiments are not within the scope of the invention.  
     [0021] A preferred embodiment of a detonator with an ignition element that includes a transistor-style sealed header feedthrough, 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.