Detonating cord and methods of making and using the same

Abstract

The velocity of detonation of an explosive such as detonating cord ( 18, 22 ) is controlled by the addition of a diluent to the explosive, e.g., to the core of the detonating cord ( 18, 22 ). An explosively inert diluent, or a diluent comprised of an explosive of lower brisance than the principal explosive comprising the core of the detonating cord, will serve to reduce the velocity of detonation. Such reduced velocity of detonation has beneficial effects in certain operations, including cleaving rock ( 10 ), wherein it is observed to significantly reduce radial cracks ( 24 ) and stickers ( 26 ) (long radial cracks) in the vicinity of the boreholes ( 12 ) in which the low-velocity detonating cord ( 18, 22 ) is functioned to cleave the rock ( 10 ). The low-velocity detonating cord also facilitates leaving behind a smoother face in cutting trenches and tunnels through rock. The method of manufacture of low-velocity detonating cord includes incorporating a suitable diluent, such as phenolic microballoons, into an explosive core of, e.g., PETN.

1 . A detonating cord comprising an elongate tubular sheath encasing a core of an explosive material comprising a first pulverulent explosive admixed with a diluent comprising explosively inert microballoons present in an amount which reduces the velocity of detonation of the detonating cord as compared to that of an otherwise identical detonating cord in which the explosive material contains no explosively inert microballoons. 
   
   
       2 . The detonating cord of  claim 1  wherein the microballoons are selected from the class consisting of glass microballoons and resin microballoons, the microballoons having a diameter of from about 10 to about 175 microns. 
   
   
       3 . The detonating cord of  claim 1  wherein the microballoons comprise resin microballoons. 
   
   
       4 . The detonating cord of  claim 3  wherein the microballoons have a diameter of from about 10 to about 175 microns. 
   
   
       5 . The detonating cord of  claim 4  wherein the microballoons comprise phenolic resin microballoons. 
   
   
       6 . The detonating cord of  claim 1  wherein the explosive material further comprises a second explosive having a lower velocity of detonation than the first explosive. 
   
   
       7 . The detonating cord of  claim 6  wherein the second explosive comprises ammonium nitrate. 
   
   
       8 . The detonating cord of  claim 1  containing from about 0.5 to 15% by weight of the diluent, based on the dry weight of the core. 
   
   
       9 . The detonating cord of  claim 8  containing from about 0.5 to 5% by weight diluent. 
   
   
       10 . The detonating cord of  claim 1  wherein the first explosive is selected from the class consisting of PETN, HMX, LINS, TNC, PYX and RDX, and mixtures of two or more thereof. 
   
   
       11 . A method of cleaving a rock formation comprising:
 drilling a plurality of substantially parallel boreholes into the formation to define between adjacent boreholes a web of rock interconnecting adjacent boreholes with each other;   placing within the boreholes at least one length of detonating cord extending along the length of the respective boreholes;   connecting the length of detonating cord to an explosive initiating device and initiating the length of detonating cord to cleave the formation;   wherein the detonating cord comprises an elongate tubular sheath encasing a core of an explosive material comprising a first pulverulent explosive admixed with a diluent comprising explosively inert microballoons present in an amount which reduces the velocity of detonation of the detonating cord as compared to that of an otherwise identical detonating cord in which the explosive material contains no explosively inert microballoons.   
   
   
       12 . The method of  claim 11  wherein the explosive material contains from about 0.5 to 15% by weight of the diluent, based on the dry weight of the core. 
   
   
       13 . The method of  claim 11  wherein the explosive material contains from about 0.5 to 5% by weight of the diluent, based on the dry weight of the core. 
   
   
       14 . The method of  claim 11  wherein the first explosive is selected from the group consisting of PETN, HMX, HNS, TNC, PYX and RDX. 
   
   
       15 . The method of  claim 11  wherein the diluent further comprises a second explosive material having a lower velocity of detonation than the first explosive material. 
   
   
       16 . The method of  claim 11  wherein the microballoons comprise resin microballoons having a diameter of from about 10 to about 175 microns. 
   
   
       17 . A method for making a detonating cord comprises the steps of preparing an explosive material by admixing a pulverulent explosive with a diluent comprising explosively inert microballoons, the diluent being present in an amount which reduces the velocity of detonation of the detonating cord as compared to an otherwise identical detonating cord in which the explosive material contains no explosively inert microballoons; and
 enclosing the explosive material within a tubular sheath to provide a detonating cord having a core of the explosive material.   
   
   
       18 . The method of  claim 17  including admixing a sufficient quantity of the explosively inert microballoons with the first explosive to provide in the core from about 0.5 to 15% by weight of the explosively inert microballoons, based on the dry weight of the core. 
   
   
       19 . The method of  claim 17  or  claim 18  wherein the first explosive is selected from the class consisting of PETN, HMX, HNS, TNC, PYX and RDX, and mixtures of two or more thereof. 
   
   
       20 . The method of  claim 17  or  claim 18  wherein the microballoons comprise resin microballoons. 
   
   
       21 . The method of  claim 20  wherein the microballoons comprise phenolic resin microbal loons. 
   
   
       22 . The method of  claim 17  or  claim 18  wherein the microballoons have a diameter of from about 10 to about 175 microns.