Stemming Plug

Abstract

The invention relates to a stemming plug ( 10 ) which is made from a suitably resilient plastic material and comprises two cup-shaped members ( 12,14 ) which face each other with their rims ( 22 ) in abutment and means, which extends between the centres of the base portions of the cups ( 20 ) in the plug ( 10 ), which is adapted to move the bases of the cups ( 20 ) towards each other to compress the cups ( 10 ) and cause a circumferential zone of the plug ( 10 ) on either side of the abutting faces of the cups ( 20 ) to increase in radial dimension to be brought into load bearing contact with the side of a predrilled hole ( 38 ) in which the plug ( 10 ) is to be located, in use, and to enable the bases of the cups ( 20 ) to be moved away from each other to allow the plug ( 10 ) to be withdrawn from the hole ( 38 ) in the event of a misfire of the explosive in the hole ( 38 ).

1 . A stemming plug which is made from a suitable resiliently deformable plastic material, characterised in that the plug comprises two cup-shaped members which face each other with their rim faces in abutment, a plurality of circumferentially spaced and releasably engaged socket and spigot formations in arid projecting from the abutting cup rim faces and means, which extends between the centres of the base portions of the cups in the plug, which is adapted to move the bases of the cups towards each other to compress the cups and cause a circumferential zone of the plug on either side of the abutting faces of the cups to increase in radial dimension to be brought into load bearing contact with the side of a predrilled hole in which the plug is to be located, in use, and to enable the bases of the cups to be moved away from each other to allow the plug to be withdrawn from the hole in the event of a misfire of an explosive in the hole. 
   
   
       2 . A stemming plug as claimed in  claim 1  wherein a portion of the wall of each cup shaped member from its rim is substantially cylindrical around the axis of the plug which passes through the centres of the cup bases to define the circumferential load bearing zone of the plug. 
   
   
       3 . A stemming plug as claimed in  claim 2  wherein each cup-shaped member includes a substantially cylindrical skirt which extends from the substantially cylindrical portion of its wall away from the abutting rims of the cups to surround at least a portion of the cup wall. 
   
   
       4 . A stemming plug as claimed in  claim 3  wherein the composite substantially cylindrical outer wall of the plug is divided into segments by slots which are parallel to the plug axis. 
   
   
       5 . A stemming plug as claimed in  claim 4  wherein the abutting rim faces of each of the wall segments are connected to each other by the socket and spigot formations. 
   
   
       6 . A stemming plug as claimed in  claim 5  wherein the outer surface of each of the wall segments include outwardly projecting formations for gripping the surface of a hole when the segments are brought into load bearing contact with the surface, in use. 
   
   
       7 . A stemming plug as claimed in  claim 6  wherein the gripping formations are ribs which are parallel to the segment defining slots. 
   
   
       8 . A stemming plug as claimed in  claim 4  wherein the non-cylindrical wall material of each cup-shaped member includes a line of weakness on the inside of and against the wall of the cup across each of the wall segment slots. 
   
   
       9 . A stemming plug as claimed in  claim 8  wherein the line of weakness is defined by arcuate slots with the ends of each slot being spaced from the ends of adjacent slots. 
   
   
       10 . A stemming plug as claimed in  claim 9  wherein the non-cylindrical portion of each of the cup-shaped members includes a pleat which extends from the ends of each of the arcuate slots in a direction towards the plug axis to expedite expansion of the plug in a radial direction, in use. 
   
   
       11 . A stemming plug as claimed in  claim 10  wherein the pleated wall material of each cup-shaped member is thinner than the adjacent cup wall material. 
   
   
       12 . A stemming plug as claimed in either one of  claim 10  wherein the pleats are V-shaped in cross-section, 
   
   
       13 . A stemming plug as claimed in either one of  claim 10  wherein the pleats are C-shaped in cross-section. 
   
   
       14 . A stemming plug as claimed in  claim 5  wherein the non-cylindrical portion of each of the cup-shaped members includes an aperture through which a fuse or electrical detonator conductors may be passed. 
   
   
       15 . A stemming plug as claimed in  claim 13  wherein the sockets and spigots on the rim faces of each of the cup-shaped members are so arranged that the fuse apertures in each cup-shaped member are in register with each other and to prevent rotation of the cups relatively to each other about the plug axis. 
   
   
       16 . A stemming plug as claimed in  claim 1  wherein a first of the cup-shaped members includes a holed boss in its base and the second an aperture in its base and the cup base moving means is a headed elongated element which passes axially through the plug cavity between the first and second cups with its head, which is adapted for rotation by a removable toot, bearing on the outer surface of the second cup around the aperture with a portion of its length from its unheaded end including formations which are movably engageable with complementally shaped formations in the hole in the boss of the first cup member. 
   
   
       17 . A stemming plug as claimed in  claim 16  wherein the engageable formations on the end portion of the elongated element and in the boss hole are helical thread formations. 
   
   
       18 . A stemming plug as claimed in  claim 1  wherein, a first of the cup-shaped members includes an aperture in its base around the plug axis, at least two outwardly projecting gripper formations which are attached to and project outwardly from the base of the cup to be biased towards the plug axis over the aperture and carry on their faces which face the plug axis ratchet teeth, the second cup-shaped member carries an elongated element which passes through the aperture in the first cup and between the gripper formations and carries ratchet teeth which are oppositely directed to those on the faces of the gripper formations with the directions of the ratchet teeth being such that the end of the elongated element may be pulled outwardly from between the teeth of the gripper formations to draw the cup bases towards each other to set the plug, in use, when the pulling tension on the elongated element is relaxed. 
   
   
       19 . A stemming plug as claimed in  claim 18  including two gripper formations which face each other from opposite sides of the aperture in the base of the cup and the portion of the elongated element which carries its ratchet teeth is square or rectangular in cross-section with the ratchet teeth on two opposite sides of the element while the remaining opposite sides are flat so that the ratchet teeth on the gripper formations will, when the elongated element and the cup to which it is attached is rotated through 90°, be disengaged from the ratchet teeth on the elongated element to enable the base portions of the cup-shaped elements of the plug to move away from each other to reduce the radial dimension of the plug to enable it to be removed from a predrilled hole in the event of a misfire of the explosive in the hole. 
   
   
       20 . A stemming plug as claimed in either  claim 18  wherein each of the gripper formations includes at its free arid a surface which tapers from the end of the formation inwardly towards the plug axis for releasing its ratchet teeth from those on the elongated element by means of a suitable tool.