Patent Publication Number: US-6708619-B2

Title: Cartridge shell and cartridge for blast holes and method of use

Description:
This application claims foreign priority benefits under 35 U.S.C. §119 from Australian Patent Application Serial No. PQ5910 filed Feb. 29, 2000. 
     FIELD OF THE INVENTION 
     The present invention relates to a cartridge shell and a corresponding cartridge for blast holes for the purpose of fracturing hard materials. The invention further relates to a method of use of such a cartridge and in particular a method of charging blast holes with the cartridge. 
     BACKGROUND OF THE INVENTION 
     A typical cartridge shell for a blast hole is in the form of a cylindrical tube closed at both ends. Some cartridges may contain only an energetic substance while others may contain both an energetic substance and an initiator. The cartridge will be inserted to reside near the toe of a blast hole drilled or otherwise formed in a rock or other hard material to be fractured. The hole may then be stemmed with a particulate stemming material. When the energetic material in the cartridge is initiated there is a rapid generation of gas and thus a rapid build up of gas pressure near the toe of the hole. Provided that the gas generated is contained for a short period of time the resulting gas pressure may cause fractures to be propagated from the hole through the hard material. 
     The efficiency and effectiveness of this process is largely determined by factors such as the provision and quality of a gas seal formed on the side of the cartridge nearest the collar of the blast hole and the ability to hold the seal in position. Clearly if the seal is poor, gas will escape around the seal thereby reducing gas pressure as well as the rate of gas pressure increase. Further, the escaping gas has adverse effects in terms of ejecting stemming from the blast hole, generation of recoil and producing flyrock. However, even if the seal is one of high integrity, if the seal is not held firmly in place and is able to be pushed back toward the collar of the hole then the physical volume of the confined space within the hole in which the gas acts increases, thereby decreasing the gas pressure. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a cartridge shell and associated cartridge that in use may assist in alleviating the above noted deficiencies. It is a further object of the present invention to provide a method of charging a blast hole with such a cartridge. 
     According to a first aspect of the present invention there is provided a cartridge shell for use in fracturing hard materials, said shell including at least: a main body defining a volume for holding an energetic material, the body having a first and second opposite ends, the first end being generally planar and the second end being tapered to form a point or wedge-like member directed away from the first end. 
     Preferably the main body includes a line or zone of weakness adjacent to the first end. 
     Preferably the cartridge shell includes a closure device at the first end said closure device being provided with, or in conjunction with the main body defining, the line or zone of weakness. 
     Preferably the main body is provided with an opening at the first end and the closure device comprises a cap for closing said opening. 
     In one embodiment, the cartridge shell further includes an aperture at the first end through which an initiator lead passes. Preferably the aperture is formed in the closure device. 
     Advantageously, the cartridge shell includes a recess passageway on an outer surface about the first end to seat the initiator lead. 
     In an alternate embodiment the cartridge shell includes an aperture in or near the second end through which an initiator lead passes. In this embodiment the cartridge shell may include an internal recess or passageway through which the initiator lead extends. 
     Preferably the second end is provided with two or more inclined surfaces that converge toward each other in the direction from the first end to the second end. 
     However, in an alternate embodiment, the second end is in the form of a conical frustum. 
     According to a second aspect of the present invention there is provide a shell for a cartridge for use in breaking and/or fracturing of hard material by the insertion of the cartridge followed by particulate stemming material in a hole and subsequent initiation of the cartridge, the shell including at least a main body defining a volume for holding an energetic material, the body having first and second opposite ends, the second end including a surface for exerting a radial compressive force on the stemming material in use. 
     According to a further aspect of the invention there is provided a cartridge for use in fracturing a hard material, the cartridge comprising at least: 
     a cartridge shell in accordance with the first or second aspect of the present invention and a quantity of an energetic material held within the main body of the cartridge shell. 
     Preferably the cartridge further comprises an initiator disposed within the main body. 
     Preferably the cartridge further includes an initiator lead connected at one end to the initiator and passing through an aperture in the cartridge shell. 
     Preferably the energetic material is a propellant. 
     Preferably the initiator is a non-explosive initiator. 
     Preferably said cartridge includes a booster for the initiator. 
     In an alternate embodiment, said cartridge further includes one or more booster cartridges each containing a quantity of energetic material, said one or more booster cartridges connectable in an end to end fashion with said first end of said main body and with each other whereby the total quantity of energetic material contained by the cartridge is varied by connecting one or more booster cartridges to said main body. 
     Preferably said main body and each of said booster cartridges each contain no more than 10 gm of energetic material. 
     Preferably each booster cartridge has a first engaging means at a first end and a second complimentary engaging means at a second opposite end whereby the first engaging means of a booster cartridge is engageable with a second engaging means of an adjacent booster cartridge. 
     Preferably said first engaging means is received inside said second engaging means so that an outer surface of a plurality of connected booster cartridges is of substantially constant outer diameter. 
     Preferably each booster cartridge includes a substantially cylindrical body of a first outer diameter; an axial extension at said first end forming said first engaging means of a second reduced outer diameter; and, a recess at said second end forming said second engaging means, of an inner diameter less than the outer diameter of the axial extension to enable said first engaging means to fit inside said second engaging means. 
     Preferably said first engaging means and said second engaging means are relatively configured relative to each other to provide an interference fit therebetween. 
     Preferably said axial extension includes a plurality of circumferential, axially spaced apart ribs. 
     In an alternate embodiment said first and second engaging means are threadingly engageable with each other. 
     Preferably said booster cartridges are closed at opposite ends by respective webs, where said webs are combustible, or frangible, or both combustible and frangible. 
     According to a further aspect of the present invention there is provided a cartridge shell including at least; 
     a primary shell having a main body defining a volume for holding an energetic material, the main body having first and second opposite ends, the second end being tapered to reduce in transverse area away from said first end; and, 
     one or more secondary shells, each secondary shell having a generally cylindrical body for holding a volume of energetic material, said one or more secondary shells releasably connected in an end to end manner with said first end of said primary shell and with each other. 
     According to a further aspect of the invention there is provided a method of charging and stemming a blast hole in a hard material, the blast hole having a collar adjacent a free face of the hard material and a toe at the opposite end of the hole, the method including at least the steps of: 
     inserting a cartridge in accordance with the second aspect of the present invention into the blast hole with the second end of the cartridge facing the collar of the blast hole; 
     providing a particulate stemming material comprising a mixture of a dry binding agent, fines and coarse material; 
     depositing said stemming material into said hole; 
     mechanically holding the stemming in the hole. 
     Preferably said depositing step includes blowing said stemming material into said hole. 
     Preferably said method further includes the steps of blowing the stemming material into the hole to a level below the free surface of the hard material; inserting a stemming bar into the blast hole to bear at one end on the stemming material with an opposite end of the stemming bar extending from the free face of the hard material; and, mechanical holding said opposite end of the stemming bar. 
     Preferably said method includes the step of forming one end of the stemming bar with a point or wedge-like member directed away from the opposite end of the stemming bar. 
     Preferably said method further comprises the step of injecting a volume of a liquid or gel into the blast hole after insertion of the cartridge to fill any space between an outer surface of the cartridge and the hole and provide a liquid or gel layer between the second end of the cartridge and the particulate stemming material. 
     Preferably when the method is used in an underground mine having a wall in which the blast hole is formed and an opposite wall, the step of mechanically holding the stemming in the hole includes the step of operating a jack so that one end of the jack bears on the wall over the blast hole while an opposite end of the jack bears on the opposite wall. 
     According to a further aspect of the invention there is provided a stemming material for use in charging a blast hole the stemming material comprising a mixture of a dry binding agent, fines, and coarse material. 
     Preferably the binding agent is one of the group consisting of fly ash; smelter waste material; or other fines containing cementitious material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: 
     FIG. 1 is an exploded sectional view of a cartridge shell in accordance with the present invention; 
     FIG. 2 is a bottom view of an end cap incorporated in the cartridge shell; 
     FIG. 3 is a view of section A—A of FIG. 1; 
     FIG. 4 is a view of section P 1 —P 1  of FIG. 1; 
     FIG. 5 is a view of section P 2 —P 2  of FIG. 1; 
     FIG. 6 is a view of section P 1 —P 1  of a second embodiment of the cartridge shell; 
     FIG. 7 is a view of section P 2 —P 2  of the second embodiment of the cartridge shell; 
     FIG. 8 is a section view of an upper end of a third embodiment of the cartridge shell; 
     FIG. 9 is a section view of a bottom part of the cartridge shell of FIG. 1 showing the layout of an initiator and initiator lead; 
     FIG. 10 is a section view of a fourth embodiment of the cartridge shell; 
     FIG. 11 is a section view of a bottom part of a fifth embodiment of the cartridge shell; 
     FIG. 12 depicts one method of use of a cartridge made from a cartridge shell in accordance with embodiments of this invention; 
     FIG. 13 illustrates the second method of use of a cartridge incorporating the cartridge shell in accordance with embodiments of this invention; 
     FIG. 14 illustrates a further embodiment of a cartridge shell/cartridge; 
     FIG. 15 is a sectional exploded view of a secondary shell depicted as FIG. 14; 
     FIG. 16 is a cross-sectional view of a secondary cartridge of FIGS. 14 and 15; and 
     FIG. 17 is a plan view of a closure disc incorporated in the shell/cartridge shown in FIGS.  14  and  15 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1-5 depict a first embodiment of the cartridge shell  10 . The cartridge shell comprises a main body  12  defining a volume  14  for holding an energetic material (not shown). The main body  12  has a first end  16  and an opposite second end  18 . The first end  16  is generally planar and in effect forms a planar base for the shell  10 . The second end  18  however is tapered to form a point or wedge-like member  20 . 
     The tapering of the second end  18  is configured so that an area of the second end  18  measured in a plane transverse to a longitudinal axis of the main body  12  reduces in a direction to the first end  16  to the second end  18 . Thus, with reference to FIGS. 4 and 5, the area of the second end  18  in plane P 2  is reduced in comparison to the area measured in plane P 1 . 
     The second end  18  can take one of a number of different specific shapes. In FIGS. 1,  4  and  5  it is seen that the second  18  is in the form of two inclined surfaces  22  and  24  that converge toward each other. However, in an alternate embodiment the second end  18  can be in the form of a conical frustum. This is depicted in FIGS. 6 and 7 which illustrate a transverse section of the second end  18  through planes P 1  and P 2  respectively. In yet a further embodiment depicted in FIG. 8, the second end  18  is in the form of a chisel point. Of course other shapes are possible such as, but not limited to, three, four or five sided prisms. 
     Ideally the main body  12  and the second end  18  would be formed integrally and from a plastics material. However it is possible for the second end  18  to be made separately from the main body  12  and if so, the two components can then be attached together. The main body  12  will conveniently be in the form of a cylindrical tube as depicted in FIG. 3 showing section A—A of FIG.  1 . 
     Main body  12  has an opening  26  at the first end to allow filling of the shell  10  with an energetic material. A closure in the form of a cap  28  is provided for insertion into and closure of the opening  26 . The cap  28  is press/interference fitted into the opening  26 . This forms a line or zone of weakness at the first end  16 . 
     An aperture  30  is formed centrally through the cap  28  to allow an initiator such as an electric match  32  (see FIG. 9) to be pushed into the main body  12 . A lead  34  from the match  32  passes through aperture  30  for coupling with an electric power source. 
     In an alternate embodiment depicted in FIG. 10 the outer surface  36  of the shell  10  near the first end  16  is provided with a recess  38  for seating the initiator lead  34 . The recess includes a first length  40  provided on the main body  12  and a second length  42  provided in the cap  28 . The cap  28  is orientated when inserted into the main body  12  so that the lengths  40  and  42  of the recess  38  are in alignment. When the electric match  32  is inserted through the aperture  30  the lead  34  can be seated in the recess  38  to provide it with some protection from accidental damage or cutting when the shell  10  is inserted into a blast hole. In a further variation the length  40  of the recess  38  can be extended along the main body  12  to at least a point where the wedge-like member  20  commences. 
     In a further variation depicted in FIG. 11, the aperture  30  is placed in the point or wedge-like member  20  rather than in cap  28 . In this embodiment the shell  10  can also be provided with an internal passageway  35  through which the lead  34  passes to deposit the initiator  32  near the first end  16  inside the main body  12 . 
     FIG. 12 illustrates one method of use of the shell  10 . The volume  14  of the shell  10  is filled with an energetic substance such as a propellant to form a cartridge  10   c . The cartridge  10   c  is inserted into a blast hole  46  formed in hard material  47  with first end  16  first so that the first end  16  is adjacent a toe  48  of the hole. Accordingly the second end  18  faces or is directed toward a collar  50  of the hole. Next, a quantity of particulate stemming material  52  is placed in the hole  46 . Typically this will be done by blowing. The stemming material  52  is blown into the hole  46  to a level below the free face  54  of the hard material  47  in which the hole  46  is formed. The stemming  52  is then mechanically held in the hole  46 . 
     In the embodiment of FIG. 12 the mechanical holding is achieved by inserting a stemming bar  56  into the hole  46  so that one end  58  of the stemming bar rests on the stemming  52  and an opposite end  60  of the stemming bar extends from the free face  54 . A cup  62  is placed over and cradles end  60 . An opposite side of the cup  64  is formed with a planar base and supports an acrow prop  66 . The acrow prop  66  is extended in length or otherwise jacked so that its opposite end  68  abuts a wall  69  disposed opposite the free face  54 . 
     By connecting lead  34  with an electrical power source, the initiator  32  generates a high temperature flame to initiate the propellant or other energetic material within the cartridge  10   c . The gas generated upon initiation initially bursts through the main body  12  about the line of weakness formed by the coupling of the cap  28  to the main body  12 . The increase in gas pressure can tend to force the cartridge  10   c  toward the collar  50  of the hole  46 . As this occurs, the point or wedge-like member  20  acts on the stemming  52  to increase the radial compressive force on the stemming material in an annular-like region between the peripheral of the second end  18  and the adjacent portion of the surface of hole  46  thereby increasing the sealing effect of the stemming material  52 . The stemming material  52  is prevented from blowing out of the hole  46  by action of the mechanical retention provided by the stemming bar  56  and acrow prop  66 . 
     The sealing effect of the stemming material  52  is enhanced by forming the stemming material  52  from a mixture of a dry binding agent, fines, and coarse material. It has been found that fly ash is a particularly beneficial binding agent and the mixture containing fly ash has a tendency to set when blown under pressure into the hole  46 . The binding agent and fines comprises particulate solids of mesh size less than about 1 mm. The coarse material within the stemming aggregate contains particles of mesh size up to about 6 mm. Binding agents other than fly ash can be used in the stemming material such as waste products from smelters, or fines containing cementitious material. 
     In an alternate method for stemming the hole  46 , after the cartridge  10   c  has been inserted into the hole a volume of a liquid or gel  70  is inserted into the hole  46  to fill any space between the outer surface of the cartridge  10   c  and the surface of the hole  46  and provide a liquid or gel layer  72  between the particulate stemming material  52  and the cartridge  10   c . The gel  70  assists in sealing the hole  46  to prevent the escape of gases upon initiation of the energetic material held within the cartridge  10   c . In all other respects, the method depicted in FIG. 13 is the same as that depicted in FIG.  12 . 
     The use of the stemming material  52  either by itself or in conjunction with the liquid/gel  70  provides a seal of high integrity that substantially limits the escape of gas. The mechanical retention of the stemming by use, in these embodiments, of the stemming bar  56  and the acrow prop  66  prevents the stemming  52  being displaced toward the collar of the hole  50  thus maintaining relative constant the volume of the hole  46  within which the gas operates. 
     FIGS. 14 and 15 depict a shell  10 ′ and corresponding cartridge  100   c  in accordance with a further embodiment of the present invention. The cartridge  100   c  is in effect a stackable cartridge comprising a shell  10  in substantial accordance with that depicted in FIG. 1, although with a body  12  of shorter length, and two secondary cartridges  102   a  and  102   b  (hereinafter referred to in general as “secondary cartridges  102 ”). Different embodiments of the cartridge  100   c  can include either a single secondary cartridge  102  or more than two secondary cartridges  102 . The shell  10 , when containing energetic material constitutes primary cartridge  10   c.    
     Each secondary cartridge  102  contains a quantity of energetic material (not shown) and is formed so as to be connectable in an end to end fashion with the first end  16  of the main body  12  and with each other. In this way, the total quantity of energetic material contained by the cartridge  100   c  can be varied by connecting one or more secondary cartridges  102  to the main body  12 . This has substantial ramifications in terms of transportation and storage of energetic materials. For example, by forming the body  12  and the secondary cartridges  102  to contain no more than 10 gm of energetic material, a 50 gm cartridge can be constructed by connecting together a single body  12  and four secondary cartridges  102 . However the individual body  12  and cartridges  102  can be transported separately as “10 gm cartridges” potentially under less stringent requirements than a single 50 gm cartridge under the UN Safety Classification regarding the transportation of such goods. 
     Each secondary cartridge  102  has a first engaging means  104  at one end and a second complimentary engaging means  106  at a second opposite end. This enables the first engaging means of one secondary cartridge (e.g. engaging means  104  of secondary cartridge  102   b ) to engage with the second engaging means of an adjacent secondary cartridge (e.g. second engaging means  106  of booster cartridge  102   a ). 
     Each secondary cartridge  102  has an outer shell  108  which includes a substantially cylindrical body  110  with the first engaging means  104  being in the form of an axial extension  112  at the first end of the cartridge  102 . The extension  112  is formed with an outer diameter less than the outer diameter of the cylindrical body  110 . The second engaging means  106  is in the form of a recess  114  formed at an opposite end of the cylindrical body  110 . 
     The outer surface of the axial extension  112  is circumscribed by two axially spaced protrusions  116 . The protrusions  116  have a saw tooth like profile, as can be seen most clearly in FIG.  15 . 
     The inside surface of each recess  114  is likewise circumscribed by two axially spaced apart ridges or ribs  118 . 
     As is further apparent from FIG. 15, the inner diameter of the recess  114  is greater than the inner diameter of the cylindrical body portion  110  of the shell  108  creating an annular seat  120  therebetween. The recess  114  is created by inserting a closure disc  122  into the end of the shell  108  to sit against the annular seat  120 . A further ridge or rib  124  is formed about the inside surface of the recess  114  at locations spaced from the annular seat  120  by a distance approximately equal to the thickness of the periphery of the disc  122 . Further, the ridge  124  and disc  122  are dimensionally related so that the ridge  124  sits behind the disc  122  and effectively holds the disc  124  against the seat  120 . The disc  122  is made from a combustible material such as plastics, paper or cardboard. 
     When assembling the cartridge  100   c , the shells  108  are held in a vertical disposition with axial extension  112  down, and energetic material poured in through recess  114  to maximum level up to the annular seat  120 . The closure disc  122  is then inserted past ridges  118  and  124  to be held against the annular seat  120 . 
     To connect two secondary cartridges  102  together, the axial extension  112  of one cartridge is pushed into the recess  124  of an adjacent cartridge. During this process, the protrusions  112  click past the ridges  118  until the forward end of the extension bears against the disc  120 . In this position, the ridges  118  are effectively seated with a snap fit behind respective protrusions  116 . The end most secondary cartridge  102   b  of the cartridge  100   c  is closed with an end cap  28  identical to that described in relation to FIGS. 1 and 10. 
     A longitudinal groove  126  is formed along the outside surface of cartridge  100   c /shell  10 ′ having a separate length on each of shell  10  and shells  108  of cartridges  102   a  and  102   b . The groove  126  seats lead  34  provided with an electric match  32  which is inserted into the end cap  28 . Prior to the insertion of the end cap  28 , a hole is pierced through the disc  122  in cartridge  102   b  through which the match  32  can be inserted. 
     In order to assist in the alignment of the separate lengths of groove  126  on both the shell  10  and shells  108 , the outside surface of each extension  112  and the inside surface of each recess  114  is provided with a flat. The flat is depicted as item  128  on the axial extensions  112  in FIG.  14 . Corresponding flats (not shown) are provided on the inside surface of each recess  114 . 
     In order to allow insertion of the closure disc  122  into the recess  114 , the disc  122  is also provided with a flat  130 . 
     To facilitate coupling of the primary cartridge  10   c  with the booster cartridge  102   a , shell  10  is also modified in comparison to that depicted in FIG. 1 by the incorporation of a recess  114  to receive the extension  112  of secondary cartridge  102   a . The recess  114  in the primary cartridge  10   c  is of the same form and configuration as that described and depicted in relation to the secondary cartridges  102  and is closed by a disc  122 . 
     Now that embodiments of the present invention have been described in detail it will be apparent to those skilled in the relevant art that numerous modification and variations may be made without departing from the basic inventive concepts. For example in the method depicted by FIGS. 12 and 13, instead of mechanically holding the stemming  52  within the hole  56  by use of an acrow prop  66 , different mechanical devices can be used such as for example, a weight or massive object, or placing say the bucket of an excavator over the collar  50 . In a further variation, second end  18  of the shell  10  can be formed with a circumferential rebate  74  as depicted in FIG. 14 for seating one end of a sleeve or tube  76 . The tube  76  is filled with the stemming material  52 . Tube  76  ideally would be made from a thin walled easily frangible and/or pliable material such as paper, thin plastics, rubber or cardboard. Indeed the shell  10  could also be made of such materials. In this event the tube  76  and/or shell  10  can be radially expanded to press against the wall of hole  46  and eliminate any free volume within the hole when subjected to axial compression forces provided by the acrow prop  66  or other mechanical retention device. End  58  of stemming bar  56  can be press fit into the opposite end of the tube  76  to allow one step insertion of the cartridge  10   c , stemming material  52  and stemming bar. 
     Also, end  58  of the stemming bar can be formed with a point, taper or wedge-like member  78  as shown in phantom in FIGS. 12 and 13 to assist in the radial spreading and compaction of the stemming material  52  against the sides of the hole  46  thereby increasing the sealing effect. 
     With reference to the embodiment shown in FIGS. 14-16, as an alternative to the snap type fit between the primary cartridge  10   c  and secondary cartridges  102 , other types of couplings can be used. For example, in the simplest form, the axial extension  112  and recesses  114  can be relatively configured to provide an interference fit. In other alternatives, complimentary screw threads can be formed on the outer surface of the extension  112  and the inner surface of the recess  114 . In yet a further variation, a bayonet type coupling can be provided. 
     In addition, the closure discs  122  can be replaced by a frangible and/or combustible webs. 
     In addition, it is possible for the closure disc  122  or web to be placed at the end of shell  108  distant the axial extension  112 . In order to then allow for engagement of an adjacent cartridge  102 , the cartridges  102  will be filled with a quantity of energetic material less than their volume providing an air space to accommodate the inserted axial extension  112 . 
     Also, in FIG. 14, a single electric match  32  is shown at the end of lead  34  for insertion into the end cap  28 . However, it is possible for multiple electric matches or other initiators to be incorporated. For example, one or more additional electric matches can be coupled with a lead  34  via branch leads and sandwiched between the closure disc  122  and axial extension  112  of adjacent coupled primary shell and secondary shell, or to adjacent coupled secondary shells. 
     All such modifications and variations are deemed to be within the scope of the present invention the nature of which is to be determined from the above description and the appended claims.