Patent Publication Number: US-3878786-A

Title: Safety detonator device for detonating fusecord

Description:
United States Patent 1 Ridgeway [451 Apr. 22, 1975 SAFETY DETONATOR DEVICE FOR DETONATING FUSECORD [75] Inventor:  
 [73] Assignee: Explo-Ridgeway International Limited, St. Heliers. J ersey, Channel Islands 221 Filed: Dec.27,l973  
  211 Appl.No.:428.699  
 John Jerold Ridgeway, Paris. France [52] US. Cl. 102/27 R; l02/28 R; l02/27 F [5 l] Int. Cl. C06c 5/06 [58] Field of Search 102/27, 28  
 [56] References Cited UNITED STATES PATENTS 3.188.9l4 6/1965 Dahl 102/28 3.739.724 6/1973 Tlam 102/28 Primary E.\&#39;aminer-Verlin R. Pendegrass Attorney. Agent. or Firm-Cushman, Darby &amp;  
 Cushman [57] ABSTRACT 12 Claims. 2 Drawing Figures PATENTEUAPR22|915 FIG. 2  
 FIG. I  
 SAFETY DETONATOR DEVICE FOR DETONATING FUSECORD This invention&#39;relates to a safety detonator device for initiating detonating fusecord. in which device the initiating explosive charge is enclosed in a safety housing capable of confining theexplosive force consequent on premature ignition of the said explosive charge.  
  Detonating fusecord is widely used as a detonation transmission line in blasting operations and is commercially available, for example, under the names Primacord and Cordtex (Registered Trade Marks). It is normally detonated by means of a commercial blasting cap containing a charge of initiating explosive and. op tionally, a booster charge. These blasting caps are capable of causing grievous harm to personnel if they are accidentally ignited during handling. and for that reason, storage, handling and transporting of blasting caps is strictly controlled. Compliance with the regulations causes long delays in transporting and often precludes the timely and/or economical performance of certain blasting contracts.  
  There is therefore a demand for a detonator device for detonating cord which is safeguarded against the effects of premature ignition so that it may be safely transported by air and be generally safer to store and handle and also easy to connect to detonating cord.  
  Thus, it is an object of the present invention to improve the blasting caps for detonating cord to overcome the hazards associated with accidental ignition of the caps. A further object is to provide a convenient detonator device which is safer to store, transport and handle than the conventional blasting cap.  
  A detonator device for initiating detonating fusecord comprises a closed elongated housing having at one end a charge of initiating explosive composition capable of initiating detonating fusecord and ignition means for igniting said charge, and having in its other end an aperture through which an end of a length of detonating cord may be inserted into position in the housing for initiation by the said explosive charge. said aperture being closed by a movable valve element which is displaceable from the aperture to permit an end length of detonating cord to be inserted into the housing, the closed housing being sufficiently strong to confine the explosion energy in the event of premature detonation of the said charge of initiating explosive.  
  Conveniently, the aperture is formed axially in a plug located in the end of the housing and the valve element is a flap seated on the inner face of said plug over said aperture, the said inner face preferably being inclined to the aperture axis to facilitate the insertion of the fusecord. The flap is preferably biassed towards the aperture and the biassing means may, for example, comprise a spring such as, for example, a strip of phosphor bronze, spring steel or beryllium-copper. In a preferred embodiment the flap is located with respect to the housing by means of a hinge of spring strip material. The said plug and flap may conveniently be metal or plastics material such as nylon, polyethylene, polypropylene, polyvinyl chloride or the like. Advantageously. the flap may be formed with a sharp edge arranged to resist withdrawal of the detonating cord from the housing by biting into the side of the cord.  
  The charge of initiating explosive composition and ignition means may conveniently be those used conventionally in blasting caps. Thus, a small charge of compressed lead azide and an electric fusehead in train therewith may be located in the end of the housing with the electrical leads from the fusehead emerging through the end closure. The minimum charge of lead azide required reduces with the degree of compaction so it is advantageous to use a highly compressed charge of lead azide.  
  The invention is further illustrated by the preferred embodiment which is hereinafter described by way of example only, with reference to the accompanying drawings wherein:  
  FIG. 1 is a diagrammatical longitudinal section of a detonator device of the invention FIG. 2 is a diagrammatical longitudinal section of the device of FIG. I with a length of detonating fusecord in position for detonation.  
  The device comprises of a charge of initiating explosive composition 10 compressed in the base of a metal cup 11 in which an electric fusehead l2 enclosed in a plastics sleeve 13 is juxtaposed to the explosive charge 10. The cup 11 is inserted to an intermediate position in a metal tube 14 where it abuts an internally bevelled guide bush 15 located in one end of the tube I4 and electrical conductor wires 16 connected to the fusehead l2 are trained through a perforated plug of elastomer I7 in the other end of the tube 14, which is crimped around the plug 17. The guide bush I5 is. at its narrow internal dimension adapted to accommodate, as a sliding fit, an end length of detonating fusecord. The fusehead l2, sleeve 13, cup 11 and metal tube 14 are bonded together by a cement composition 18.  
  The bushed tube I4 is inserted as a sliding fit cement bonded into one end of a tubular housing 19 and the end of housing 19 is crimped around the crimped end of tube 14. An end plug 20 is located as a tight fit in the other end of housing l9 and the end of the housing is swaged as a plug retaining lip 21 over the end of plug 20. The plug 20 is formed with an axial aperture 22 through which a length of detonating fusecord may be readily inserted, and its inner end face is inclined to the longitudinal axis. The inner end of the aperture 22 is covered with a flap valve member 23 which (in FIG. 1) seats on the inner face of the plug 20. The valve member 23 is located by a strip spring member 24 which has one end connected to the valve member 22 and the other fixed between the plug 20 and the housing 19.  
  In the unlikely event of the initiating explosive charge 10 being accidentally detonated the explosive force tends to close the valve member 23 against its seat and the force is thereby contained within the housing 19.  
  In use for initiation of detonating fusecord, an end length of the fusecord 25 is inserted through the aperture 22, pushing aside the valve member 23 and into the guide bush 15 to contact the end of cup 11, as shown in FIG. 2.  
  In the assembly of the device the plug 20 valve member 23 and spring member 24 are inserted into the flanged end of tube 14 or alternatively the plug 20 may be inserted before the plug retaining lip 21 is formed. The metal tube 14 and its contents are conveniently first constructed and assembed as a conventional detonating cord blasting cap and the open end of the tube 14 is subsequently inserted and cemented in the housing I9.  
  The housing and its closures must be sufficiently strong to withstand the explosive force from detonation of the initiating explosive but it will be understood that the material and dimensions thereof used in theconstruction of the device may be widely varied. However. the optimum parameters can readily bedetermined by straight forwardexperiment. I  
 . As an example. in one construction of the device the explosive charge 10 is one grain (0.065 gram) of lead azide pressed in an aluminium cup 11 having an internal diameter of 0.25 inch and a wall thickness of 0.028. The tube 14 and housing 18 are of 0.028 inch thick aluminium, the housing being 0.5 inch diameter and 5 inches long. The cement composition 17 is a silicone cement. The plug 19 is an aluminium bush having an aperture 0.22 inch diameter and the valvemember is a 0. l 5 inch nylon disc in which a phosphor, bronze strip is moulded.  
 What is claimed is:  
  l. A detonator device for initiating detonating fusecord comprising a closed elongated housing having at one end a, charge of initiating explosive composition capable of initiating detonating fusecord and ignition means for igniting said charge. and having in its other end an aperture through which an end of a length of detonating cord may be inserted .into position in the housing for initiation by the said explosive charge. said aperture, being closed by an internally movable valve element which is arranged to be forced to a closed position by the force of said charge if accidentally detonatedandwhich is displaceable from the aperture to permit an end length of detonating cord to be inserted into the housing. the closed housing being sufficiently strong to confine the explosion energy in the event of premature detonation. of the said charge of initiating explosive. if  
  2. A device as&#39;claimed in claim 1 wherein aplug defining an axial apertureis locatedin said other end of the housing and the valve element comprises a flap seatedover said aperture on the inner face of said plug.  
  3. A device as.claimed in .claim lwherein the inner face of the plug is inclined to the.ax,is. v. i W  
  4. A device as claimedin claim &#39;Z wherein the flap is biassed towards said aperture. 7  
  5. A device as claimed in claim 4 wherein the biassing means comprises a spring,  
  6. A device as claimed in claim 5 wherein the spring comprises a strip of material selected from the group consisting of phosphor-bronze, spring steel and beryllium-copper 7. A device as claimed in claim 2 wherein the flap is located with respect to the housing by means of a hinge of spring strip material.  
  8. A device as claimed in claim 2 wherein the flap is made from a member of the group consisting of metal and plastics materials.  
  9. A device as claimed in claim 8 wherein the flap is made from a plastics material selected from the group consisting of nylon. polyethylene. polypropylene and polyvinyl chloride.  
  10. A device as claimed in claim 2 wherein the flap is formed with a sharp edge arranged to resist withdrawal of the detonating fusecord from the housing.  
  11. A device as claimed in claim 1 wherein the charge of initiating explosive composition comprises lead azide.  
  12. A device as claimed in claim 11 wherein the .iarge of initiating explosive composition consists of about 1 grain of compressed lead azide.  
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