Friction-modified wedge stemming plugs

Abstract

A stemming plug ( 10 ) for stemming a blast hole in a mine, the plug ( 10 ) comprising an active wedge-shaped member ( 12 ) having a sloping face received in sliding relationship with a matching face of a passive wedge-shaped member ( 14 ). In use, the active wedge-shaped member ( 12 ) is positioned nearest to an explosive material in the blast hole and the passive wedge-shaped member ( 14 ) is positioned further from the explosive material in the blast hole. The active wedge-shaped member ( 12 ) has a friction reducing material provided on at least part of its surface to reduce the sliding resistance of the active wedge-shaped member ( 12 ) relative to the passive wedge-shaped member ( 14 ); whereby, in use, when a shockwave from initiation of the explosive material in the blast hole encounters the active wedge-shaped member ( 12 ) it acts as a piston, sliding on the passive wedge-shaped member ( 14 ) so that both wedge-shaped members exert diametrically opposed forces against a wall of the blast hole and are locked in place.

1 . A stemming plug for stemming a blast hole in a mine, the plug comprising:
 an active wedge-shaped member having a sloping face received in sliding relationship with a matching face of a passive wedge-shaped member wherein, in use, the active wedge-shaped member is positioned nearest to an explosive material in the blast hole and the passive wedge-shaped member is positioned further from the explosive material in the blast hole; and,   the active wedge-shaped member having a friction reducing material provided on at least part of its surface to reduce the sliding resistance of the active wedge-shaped member relative to the passive wedge-shaped member;   whereby, in use, when a shockwave from initiation of the explosive material in the blast hole encounters the active wedge-shaped member it acts as a piston, sliding on the passive wedge-shaped member so that both wedge-shaped members exert diametrically opposed forces against a wall of the blast hole and are locked in place.   
     
     
         2 . A stemming plug as defined in  claim 1 , wherein the active wedge-shaped member is coated with a friction-reducing surface treatment. 
     
     
         3 . A stemming plug as defined in  claim 2 , wherein the friction-reducing surface treatment is a PTFE paint, liquid or solid friction modifier. 
     
     
         4 . A stemming plug as defined in  claim 2 , wherein the active wedge-shaped member is enclosed within a friction-reducing envelope such as a plastic sleeve, in which the envelope provides a lower coefficient of friction than the surface of the active wedge-shaped member by itself. 
     
     
         5 . A stemming plug as defined in any one of  claims 1  to  4 , wherein the passive wedge-shaped member is of greater mass than the active wedge-shaped member wherein, in use, the passive wedge-shaped member provides greater resistance to movement than the active wedge-shaped member. 
     
     
         6 . A stemming plug as defined in any one of  claims 1  to  5 , wherein the passive wedge-shaped member has a friction-increasing material provided on at least part of its surface where it contacts the wall of the blast hole to increase the sliding resistance of the passive wedge-shaped member relative to the active wedge-shaped member. 
     
     
         7 . A stemming plug as defined in  claim 1 , wherein the wedge-shaped members are formed from a single cylindrical elongate member cut through at an angle to form the pair of wedge-shaped members. 
     
     
         8 . A stemming plug as defined in  claim 7 , wherein each end of the cylindrical elongate member is substantially flat, having a surface that is substantially orthogonal to a longitudinal axis of the cylindrical elongate member. 
     
     
         9 . A stemming plug as defined in  claim 8 , wherein the cylindrical elongate member is cut through at an acute angle of between about 55° and 85°. 
     
     
         10 . A stemming plug as defined in  claim 9 , wherein the cylindrical elongate member is cut through at an acute angle of between about 75° and 85°. 
     
     
         11 . A stemming plug as defined in  claim 7 , wherein the cylindrical elongate member forms a solid core of the plug. 
     
     
         12 . A stemming plug as defined in  claim 11 , wherein the solid core is about 250 mm to 600 mm in length. 
     
     
         13 . A stemming plug as defined in any one of  claims 1  to  12 , wherein the stemming plug further comprises an outer liner having a first inner join line and a second outer join line, the inner join line being made of water-soluble material and defining a first diameter of the liner which is smaller than a second diameter defined by the second join line and is adapted to be received in the blast hole. 
     
     
         14 . A stemming plug as defined in  claim 13 , wherein the liner is made from a water-absorbent material, with suitable friction properties to provide grip in the blast hole during installation. 
     
     
         15 . A stemming plug for stemming a blast hole in a mine, the plug comprising:
 an outer liner having a first inner join line and a second outer join line, the inner join line being made of water-soluble material and defining a first diameter of the liner which is smaller than a second diameter defined by the second join line and is adapted to be received in a blast hole; and,   a pair of elongate wedge-shaped members received in sliding relationship with respect to each other within the liner, one of the wedge-shaped members having a friction reducing material provided on at least part of its surface to reduce the sliding resistance of the one wedge-shaped member relative to the other wedge-shaped member;   wherein, in use, when the plug is immersed in water it dissolves the first inner join line, and when the plug is tamped into the blast hole the liner expands to the second diameter and the wedge-shaped members slide relative to each other so as to wedge into the blast hole and block the blast hole.   
     
     
         16 . A stemming plug for stemming a blast hole in a mine, the plug comprising:
 an outer liner adapted to be received in a blast hole; and,   a pair of elongate wedge-shaped members received in sliding relationship with respect to each other within the liner, wherein one of the wedge-shaped members has less mass than the other wedge-shaped member so that under dynamic loading the lighter wedge-shaped will accelerate faster than the other, heavier wedge-shaped member; and,   wherein, in use, when the plug encounters a shockwave after initiation of an explosive in the blast hole the lighter wedge-shaped member moves relative to the heavier wedge-shaped member so as to wedge the pair of wedge-shaped members into the blast hole and block the blast hole.   
     
     
         17 . A stemming plug as defined in  claim 15  or in  claim 16 , wherein the one wedge-shaped member is an active wedge-shaped member having a sloping face received in sliding relationship with a matching face of the other wedge-shaped member, the other wedge-shaped member being a passive wedge-shaped member wherein, in use, the active wedge-shaped member is positioned nearest to an explosive material in the blast hole and the passive wedge-shaped member is positioned further from the explosive material in the blast hole. 
     
     
         18 . A stemming plug as defined in  claim 17 , wherein the active wedge-shaped member is coated with a friction-reducing surface treatment. 
     
     
         19 . A stemming plug as defined in  claim 18 , wherein the friction-reducing surface treatment may be PTFE paint, liquid or solid friction modifier. 
     
     
         20 . A stemming plug as defined in  claim 18 , wherein the active wedge-shaped member is enclosed within a friction-reducing envelope, such as a plastic sleeve, in which the envelope has a lower coefficient of friction than the surface of the active wedge-shaped member by itself. 
     
     
         21 . A stemming plug as defined in any one of  claims 17  to  20 , wherein the stemming plug further comprises an installation wedge-shaped member provided at a base of the stemming plug, and wherein the passive wedge-shaped member also has a wedge-shaped base whereby, in use, the installation wedge-shaped member is forced against the passive wedge-shaped member during installation. 
     
     
         22 . A stemming plug as defined in  claim 21 , wherein the wedge-shaped members are formed from a single cylindrical elongate member cut through at an angle to form two or more wedge-shaped members. 
     
     
         23 . A method of stemming a blast hole in a mine, the method comprising:
 filling an outer liner with a pair of elongate wedge-shaped members received in sliding relationship with respect to each other to form a stemming plug, the liner having a first inner join line and a second outer join line, the inner join line being made of water-soluble material and defining a first diameter of the liner which is smaller than a second diameter defined by the second join line and is adapted to be received in a blast hole;   providing a friction reducing material on at least part of the surface of one of the wedge-shaped members, to reduce the sliding resistance of the one wedge-shaped member relative to the other wedge-shaped member;   providing one or more of the stemming plugs to a mine site ready for use in the event that a blast hole needs to be blocked;   immersing one or more of the stemming plugs in water for a prescribed time until the water dissolves the first inner join line;   inserting the one or more wetted stemming plugs in the blast hole; and, jolting each stemming plug so that the liner expands to the second diameter and the wedge-shaped members slide relative to each other so as to wedge into the blast hole and block the blast hole.   
     
     
         24 . A method of stemming a blast hole in a mine as defined in  claim 23 , wherein the method further comprises the step of tamping the stemming plug to firmly locate the wedge-shaped members in the blast hole.