Patent Publication Number: US-5427031-A

Title: Detonator primer capsule

Description:
TECHNICAL FIELD OF THE INVENTION 
     The invention relates to a detonator for explosives. Specifically, the invention relates to a primer capsule for incorporation into a detonator which is constructed such that a primer charge housed within the capsule is protected from sympathetic initiation and the output from the initiated primer charge is focused toward a small amount of base charge material contained within the capsule to provide efficient detonation of an external base charge. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to explosive detonators, and more particularly, relates to explosive detonators wherein the primer charge is protected and the output of the primer charge is focused toward the base charge providing efficient initiation. 
     There are various detonator designs known in the art which basically fall into three categories. The first category of detonators are constructed such that the primer charge is located on top of the base charge and in intimate contact with the delay element. These designs do not provide for protection of the primer charge against sympathetic detonation, nor do those designs provide for focusing of the output from the primer charge for efficient detonation. 
     A second category of detonators known in the art are constructed such that the primer charge is protected in some manner, but includes a gap between the primer charge and the delay element, and thus, reliable initiation is not obtained. Further, these designs do not provide a means to focus the primer charge output toward the base charge and thus, are inefficient. 
     The third category of detonators known in the art are common among European manufacturers and are constructed such that the primer charge is located inside the delay element which is in intimate contact with the delay element core and protected against sympathetic detonation, but these designs do not focus the primer charge output toward the base charge and thus, are also inefficient. 
     None of the known detonator designs provide (1) primer charge protection against sympathetic initiation, (2) focusing of the primer charge output for efficient base charge initiation, and (3) intimate contact between the delay element and the primer charge for reliable initiation. The present invention provides a detonator which supplies protection of the primer charge, reliable initiation and efficient use of the primer charge and base charge materials. 
     SUMMARY OF THE INVENTION 
     The invention is directed to explosive detonators having a primer capsule contained therein. The primer capsule is comprised of a top and bottom. The capsule has a channel running therethrough wherein primer charge material and base charge material are contained. The capsule top, which is pointed in shape or frustrum shaped, contains primarily primer charge material in the channel. The top has an opening centrally located therein which is in communication with the channel containing primer charge and base charge material. The top provides protection for the primer charge against sympathetic detonation. The channel in the bottom which is in communication with the primer charge contained in the top contains primer charge and a base charge material. The base charge material is less sensitive than the primer charge and is preferably packed or pressed against the primer charge. The base charge material provides protection or insulation of the primer charge against sympathetic initiation from forces directed from the bottom of the primer capsule. The channel in the top and a portion of the channel in the bottom are preferably frustro-conical or frustro-trapezoidal shaped and thus focuses the output of the primer charge toward the base charge material to provide efficient detonation of an external base material. Also, the entire channel, in the top and bottom, can be frustro-conical or frustro-trapezoidal shaped. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of the primer capsule of the present invention; 
     FIG. 2 is a perspective view of the primer capsule of the present invention; 
     FIG. 3 is a cross-sectional view of the primer capsule of the present invention loaded with primer charge and a small charge of base material; 
     FIG. 4 is a cross-sectional view of the primer capsule of the present invention incorporated into a detonator shell; 
     FIG. 5 is a cross-sectional view of the primer capsule of the present invention incorporated into an electric detonator; 
     FIG. 6 is a cross-sectional view of the primer capsule of the present invention incorporated into a non-electric detonator; and 
     FIG. 7 is a cross-sectional view of the primer capsule of the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     The invention relates to electric and non-electric detonators for explosives. Specifically, the invention relates to detonators having a primer capsule inserted therein. The primer capsule of the present invention is illustrated in FIGS. 1 and 2. Referring to FIG. 1, primer capsule 1 is comprised of top 2 and bottom 3 having hollow channel 4 running therethrough. Top 2 has a small opening 5. As shown, channel 4 is in communication with opening 5 in top 2. Preferably, top 2 is pointed or frustrum-shaped and bottom 3 is tubular-shaped. As used herein, frustrum-shaped means shaped like the part of a cone or pyramid that is formed by cutting off the top by a plane parallel to the base. Preferably, channel 4 in top 2 and for a portion in bottom 3 is frustro-conical or frustro-trapezoidal-shaped. Preferably, the remaining portion of channel 4 in bottom 3 which is not frustro-conical or frustro-trapezoidal-shaped is tubular-shaped or cylindrical. Bottom 3 has a large opening 6 in communication with channel 4 as shown in FIG. 1. Large opening 6 is provided so that channel 4 can be in direct contact with an external base charge to be detonated. Preferably, the large opening is of the same width as channel 4 in bottom 3. FIG. 2 is a perspective view of primer capsule 1 shown in cross-section in FIG. 1. 
     The primer capsule of the present invention is preferably of a single uniform construction whereby the top and bottom are constructed of the same material or materials. Examples of materials which may be used to construct the primer capsule of the present invention include, but are not limited to, steel, lead, copper and copper alloys, aluminum, zinc, thermoplastic resins, graphite, or the like and mixtures thereof. 
     The dimensions of top 2, bottom 3, channel 4, opening 5, opening 6 and generally, primer capsule 1 is dependent upon the desired application and use of the primer capsule. Generally, the primer capsule of the present invention is of such shape and construction wherein it can be easily inserted into a detonator shell to provide intimate contact or communication between the core of a delay element in the detonator shell with a primer charge contained in the primer capsule through opening 5 in top 2 of capsule 1. However, it is also contemplated that primer capsule 1 of the present invention may be used alone, i.e., not inserted into a detonator. 
     FIG. 3 illustrates a loaded primer capsule 1 of the present invention. Referring to FIG. 3, a primer charge material 7 is contained within the frustro-conical shaped portion of channel 4 in top 2 and bottom 3. A small amount of base charge material 8 is contained in channel 4 of bottom 3 and is pressed directly against primer charge 7 in channel 4. 
     The primer charge material contained inside the top of the primer capsule can be comprised of any primer charge material known in the art and includes, but is not limited to, lead azide, lead styphnate, diazodinitrophenol, and lead azide/lead styphnate mixtures. The specific primer charge material and the amount utilized depends upon the application, the desired rate of detonation, and the base charge to be initiated. 
     The small amount of base charge material 8 used in the present invention may be comprised of any known base charge material and includes, but is not limited to, such materials as PETN, RDX, HMX, or tetryl or mixtures thereof. The specific base charge material used and the amount used depends on the application, desired rate of detonation, and the base charge to be detonated. 
     Referring to FIG. 3, portion 9 of the walls of primer capsule 1 surrounding the frustro-conical portion of channel 4 containing primer charge 7 in top 2 and bottom 3 is thicker than the walls surrounding the tubular portion of channel 4 containing base charge material 8 in bottom 3. Portion 9 of the walls are of sufficient thickness to provide protection of primer charge 7 contained therein such that the primer charge material is not susceptible to sympathetic initiation from external sources. However, it is contemplated that other means of protection can be used instead of thicker walls. For example, portion 9 of the walls can be constructed of various materials which provide increased protection of the primer charge from sympathetic initiation. 
     In addition to the protective top, the primer charge is also protected from sympathetic detonation by the base charge material 8. The base charge material 8 is less sensitive than primer charge 7. Preferably, the base charge material is pressed against the primer charge such that the primer charge 7 is protected against sympathetic initiation from forces originating from the bottom of the primer capsule. 
     Channel 4 of primer capsule 1 is constructed such that upon initiation of the primer charge by a delay element through opening 5, the primer charge material reaches full velocity and shock and its output is focused upon base charge material 8 whereby efficient initiation of an external base charge is obtained. Note, while a portion of channel 4 may be frustro-conical shaped it may also be frustro-trapezoidal shaped. 
     While the drawings illustrate primer capsule 1 having a portion of channel 4 frustro-conical shaped, it should be understood that channel 4 may also be frustro-conical shaped or frustro-trapezoidal shaped throughout the entire length of primer capsule 1, i.e., from opening 5 in top 2 to the end of tubular bottom 3. In addition, though the present invention has been illustrated and described wherein the frustro-conical shaped portion of channel 4 contains only primer charge material, it is understood and contemplated that some primer charge material may be contained in the tubular shaped portion of channel 4 in bottom 3 and/or some of the base charge material may be contained within the frustro-conical shaped portion of channel 4 in top 2 or both. 
     The performance of the primer capsule of the present invention as opposed to a primer system wherein the primer charge is not protected nor is the output of the primer charge focused toward the base charge is illustrated in Table I below: 
     
                       TABLE I                                                     
______________________________________                                    
Detonator Explosive Output                                                
                  Base Charge Grams of                                    
Primer System     Weight      Sand Crushed                                
______________________________________                                    
120 mg. lead azide on top of                                              
                  780 mg. PETN                                            
                              106                                         
base charge, no confinement and                                           
no focusing                                                               
100 mg. lead azide plus 50 mg.                                            
                  600 mg. PETN                                            
                              104                                         
PETN inside primer capsule                                                
______________________________________                                    
 
    
     From the data in Table I, the primer capsule of the present invention generated 0.160 grams crushed sand per milligram of PETN, while the unconfined system generated only 0.136 grams crushed sand per milligram of PETN. The primer capsule of the present invention generated this additional output using approximately 16 percent less lead azide. 
     The data in Table II below illustrates the higher level of shock protection provided by the primer capsule of the present invention. Detonators containing primer capsules of the present invention can therefore withstand much higher shock pressures in boreholes without sympathetic initiation. 
     
                       TABLE II                                                    
______________________________________                                    
Resistance to Underwater Propagation                                      
Primer System       Pressure Tolerance                                    
______________________________________                                    
No confinement and no focusing                                            
                    8,000-9,000 psi                                       
Primer capsule of the present                                             
                    14,000-16,000 psi                                     
invention                                                                 
______________________________________                                    
 
    
     FIG. 4 illustrates the primer capsule of the present invention inserted into detonator shell 10 containing delay element 11 having a core 12 centrally located therein. The detonator primer capsule is inserted into one end of the detonator shell such that opening 5 in top 2 containing primer charge material. 7 is in direct contact with core 12 of delay element 11 which is inserted in the other end of the detonator shell. As shown also in FIG. 3 and described above, in the primer capsule of the present invention, primer charge material 7 is in direct contact with base charge material 8. 
     Detonator shell 10 as illustrated and described above, may be comprised of various materials known in the art and includes, but is not limited to, steel, lead, aluminum, copper, thermoplastic resins, graphite, and the like and mixtures thereof. Preferably, the detonator shell is of tubular construction. 
     Referring to FIG. 5, an electric detonator is shown utilizing the primer capsule of the present invention. As shown in FIG. 5, delay element 11 is inserted in one end of detonator shell 10 and primer capsule 1 is inserted into the other end of detonator 10 as shown and described in FIG. 4. An electric ignition source 14 is provided in air space 15. Air space 15 containing the ignition source 14 is provided with a plastic insulator sleeve 16. The ignition source 14 inside air space 15 is secured inside detonator shell 10 by sealing plug 17. Through sealing plug 17 run leg wires 18 which connect to ignition source 14 and to an external electrical source for ignition. 
     Primer capsule 1 of the present invention can be used in a non-electric detonator as shown in FIG. 6. Delay element 11 and primer capsule 1 are inserted into detonation shell 10 as shown in FIGS. 4 and 5 and described above. As shown in FIG. 6, a static separator 19 is provided above delay element 11. On top of the static separator 19 is provided a closure bushing 20 having a channel running therethrough containing non-electric signal tube 21. 
     FIG. 7 illustrates one embodiment of the primer capsule of the present invention wherein channel 4 is frustro-conical or frustro-trapezoidal shaped for its entire length. 
     While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by those skilled in the art to which the invention pertains.