Explosive charge

Abstract

An explosive charge ( 1 ) comprising an elongate casing ( 2 ) with elongate grooves ( 3,4 ) running along the casing, each groove locally reducing the thickness of the casing. The grooves are distributed in two or more groups around the circumference of the casing and the edge-to-edge spacing between each adjacent pair of grooves in a group is less than the edge-to-edge spacing between each pair of adjacent groups. Detonation causes the casing to break at a pair of grooves in one of the groups and form a fragment from material between the pair of grooves, the fragment cutting an obstacle ( 28 ).

1 . An explosive charge comprising an elongate casing with elongate grooves running along the casing, each groove locally reducing the thickness of the casing, wherein the grooves are distributed in two or more groups around the circumference of the casing and the edge-to-edge spacing between each adjacent pair of grooves in a group is less than the edge-to-edge spacing between each pair of adjacent groups. 
     
     
         2 . The charge of  claim 1  wherein each group of grooves has no more than two grooves. 
     
     
         3 . The charge of  claim 1 , wherein there are no more than four groups of grooves distributed around the circumference of the casing. 
     
     
         4 . The charge of  claim 2  wherein there are no more than four pairs of grooves distributed around the circumference of the casing. 
     
     
         5 . The charge of  claim 1 , wherein the grooves are distributed in three or more groups around the circumference of the casing 
     
     
         6 . The charge of  claim 1 , wherein the edge-to-edge spacing between each groove in a group is greater than zero, so that each groove has an edge which is separated from an adjacent edge of an adjacent groove by a non-grooved portion of the casing. 
     
     
         7 . The charge of  claim 6  wherein the average angle subtended by the non-grooved portions at the centre of the casing, when viewed in transverse cross- section, is less than 5°. 
     
     
         8 . The charge of  claim 1 , wherein the average edge-to-edge spacing between the adjacent edges of each groove within a group is less than the average edge-to-edge spacing between the adjacent edges of adjacent groups by a factor of 10 or more. 
     
     
         9 . The charge of  claim 1 , wherein the grooves taper outwardly when viewed in transverse cross-section. 
     
     
         10 . The charge of  claim 1 , wherein the average angle subtended by each groove at the centre of the casing, when viewed in transverse cross-section, is less than 10°. 
     
     
         11 . The charge of  claim 1 , wherein the total angle subtended by the grooves at the centre of the casing, when viewed in transverse cross-section, is less than 90°, preferably less than 60°, and most preferably less than 30°. 
     
     
         12 . The charge of  claim 1 , wherein the casing has an internal wall and an external wall; and wherein the grooves are formed in the external wall. 
     
     
         13 . The charge of  claim 12  wherein the internal wall is substantially circular in cross-section. 
     
     
         14 . The charge of  claim 1 , wherein the casing has a threaded head end adapted to be coupled to the tail end of an adjacent charge, and a threaded tail end adapted to be coupled to the head end of an adjacent charge. 
     
     
         15 . A kit of parts comprising two or more charges according to  claim 1 , each charge having a head end adapted to be coupled to the tail end of an adjacent charge, and a tail end adapted to be coupled to the head end of an adjacent charge. 
     
     
         16 . A method of cutting an obstacle using the explosive charge of  claim 1 , the method comprising detonating explosive material in a compartment of the casing, the detonation causing the casing to break at a pair of grooves in one of the groups and form a fragment from material between the pair of grooves, the fragment cutting the obstacle. 
     
     
         17 . The method of  claim 16  further comprising coupling two or more of the charges head to tail; and detonating explosive material in each charge.