Patent Publication Number: US-2007107617-A1

Title: Detonator assembly

Description:
BACKGROUND OF THE INVENTION  
      This invention relates generally to a detonator assembly and is also concerned with a method of installing a plurality of detonators in a plurality of respective boreholes.  
      It is known to make use of electronic detonators, which are individually programmable, to establish a blasting configuration. Each detonator is assigned a unique identity number and is connected in parallel to a trunk cable. As each detonator is uniquely identified it is possible to address a chosen detonator and program desired blasting information into the detonator.  
      In a different connection technique a plurality of detonators are connected to one another in a daisy-chain configuration. In this arrangement the detonators are addressed in sequence with a given detonator being placed in a programming mode while the other detonators are in a non-programmable mode. Certain benefits are associated with a daisy-chain arrangement although one disadvantage arises from the need to make a connection between each detonator in the sequence and the following and preceding detonators. This aspect and the capability of being able to insert a detonator to a variable depth inside a borehole, give rise to a requirement that two variable lengths of cable must be associated with each detonator viz. a first cable length to go down a first borehole and a second cable length to go from the first borehole to an adjacent, second borehole. In dealing with the cables associated with each of a large number of detonators, the cables can become entangled with one another and errors can arise in configuring a blasting sequence.  
      Another aspect which should be addressed is that each detonator should be packaged in a way which facilitates the use of automated manufacturing and testing processes, which readily allows for handling and transport, and which enables each detonator to be labelled so that it complies with applicable regulations and legislation.  
     SUMMARY OF INVENTION  
      The invention provides a detonator assembly which includes a first cable coil with first and second ends, a second cable coil with third and fourth ends, a detonator connected to the first end of the first cable coil, a first connector connected to the second end of the first cable coil and to the third end of the second cable coil, and a second connector connected to the fourth end of the second cable coil and wherein a first variable length of cable, extending from the first end, can be drawn from the first cable coil without materially moving the first connector and a second variable length of cable, extending from the fourth end, can be drawn from the second cable coil without materially moving the first connector.  
      The first cable coil may be provided in the form of a first tubular roll. The first end may be inside the first tubular roll. Similarly the second cable coil may be provided in the form of a second tubular roll and the fourth end may be inside the second tubular roll.  
      The detonator assembly may include a confinement structure of any appropriate type for maintaining the cable in the required coiled configuration.  
      The first connector may be accessible without opening or removing the confinement structure. The first connector may for example be positioned on an outer side of the confinement structure.  
      The second and third ends of the cables, which are connected to the first connector, are preferably integrally connected and at no time are separable from each other. These ends may extend out of the confinement structure.  
      The confinement structure may be in the form of a housing which includes a first compartment for the first cable coil. A second compartment may be provided inside the housing for the second cable coil. At least one divider may be positioned between the compartments. Preferably the first and second cable coils are separated by at least two dividers. Each divider may be provided in any appropriate way and preferably each divider abuts at least one recessed formation which extends from an outer surface of the housing into an interior of the housing.  
      The confinement structure may be circular cylindrical or in the form of a parallelepiped. In one embodiment the confinement structure is in the form of a housing which is made from a relatively rigid material, and the housing has four relative large sides and two relatively small sides which form opposed ends of the housing.  
      The housing may be made from any suitable material and maybe made from a rigid material such as cardboard which may be corrugated or a similar bio-degradable material.  
      The first and third ends of the cables may extend through respective apertures in the smaller sides of the housing.  
      In a preferred form of the invention the confinement structure is made from flexible sheet material. The sheet material may extend around the cable coils and may have a composition which allows the sheet material to be shrunk onto the coils. This type of sheet material is known in the art.  
      Each cable coil may be positioned inside a respective enclosure which, in turn, is located inside the confinement structure. The enclosure may comprise flexible sheet material such as plastic film. Each cable coil may comprise a plurality of windings arranged in overlying layers around a hollow core.  
      The windings may be arranged so that they form a circular cylindrical shape. The first end may extend from an innermost winding of the first cable coil, facing the respective hollow core. This allows the cable to be withdrawn from the first cable coil without removing the first coil from the confinement structure.  
      The fourth end may be similarly configured with respect to the second cable coil.  
      The invention also provides a method of forming a cable coil assembly which includes the steps of drawing cable from a supply source and winding a single coil of a first predetermined length around a first former, severing the cable so that the single coil is separated at a first end from the supply source, and forming a first cable coil by winding cable, of a second predetermined length which is shorter than the first length, drawn from the single coil, commencing at the first end, around a second former, and thereby simultaneously forming a second cable coil of a length which is substantially equal to the difference between the first and second lengths.  
      The single coil may be formed by winding the cable in a first direction around the first former and the first coil may be formed by winding cable drawn from the single coil in a second direction around the second former, wherein the first direction is opposite to the second direction.  
      The first cable coil may be positioned so that it is co-axial with the second cable coil.  
      The invention also provides a method of installing a plurality of detonators in a respective plurality of boreholes in a daisy-chain configuration which includes the steps, for each borehole, of drawing a first length of cable from a first cable coil in confinement structure, positioning a first detonator which is connected to a first end of the first length of cable at a predetermined depth inside the respective borehole, drawing a second length of cable from a second cable coil inside the confinement structure and connecting a first connector which is at a junction of the first and second coils, at the confinement structure, to a second connector which is at an end of a respective second length of cable associated with a first borehole.  
      The method may include the step of connecting a respective second connector at an end of the second length of cable, associated with the respective borehole, to a respective first connector at a second borehole. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention is further described by way of examples with reference to the accompanying drawings in which:  
       FIG. 1  schematically depicts a plurality of detonators which are located in respective boreholes and which are connected to each other in a daisy-chain configuration;  
       FIG. 2  is a cross sectional view of a detonator assembly according to the invention;  
       FIGS. 3 and 4  are perspective views of the detonator assembly of  FIG. 2  illustrating different aspects thereof;  
       FIG. 5  is a schematic side view of a detonator assembly according to the invention with a housing thereof fully opened;  
      FIGS.  6  to  8  show the detonator assembly in different stages of manufacture;  
       FIGS. 9, 10  and  11  illustrate steps in the winding of cable coils for use in a detonator assembly according to one form of the invention;  
       FIG. 12  is a perspective view of a detonator assembly according to a variation of the invention;  
       FIG. 13  is a side view in cross section of the detonator assembly in  FIG. 12 ; and  
       FIG. 14  is similar to  FIG. 1 , depicting the use of a plurality of the detonator assemblies in  FIG. 12 , in a blasting system. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT  
       FIG. 1  of the accompanying drawings illustrates schematically a plurality of boreholes  10 A,  10 B . . .  10 N which are drilled in the ground  12  using conventional techniques. A respective detonator  14 A,  14 B . . .  14 N is placed in each borehole. A first length  16 A,  16 B . . .  16 N of cable extends from the respective detonator to a respective first connector  18 A,  18 B . . .  18 N which is positioned at surface, and a respective second length  20 A,  20 B . . .  20 N of cable extends between adjacent pairs of connectors  18 A and  18 B,  18 B and  18 C, . . .  18 N- 1  and  18 N.  
      As indicated in the preamble to this specification practical problems arise, when making a daisy-chain arrangement of the type shown in  FIG. 1 , in that the lengths  16  and  20  of the cables are variable. If standard lengths of cable are connected, beforehand, to a connector  18  then once a detonator  14  is placed in a borehole a first excess portion of cable can lie at the mouth of the borehole while, once a connection is made between a connector  18 A and a following connector  18 B, a second excess length of cable can lie on the surface between the boreholes. The invention is aimed at addressing at least this type of problem.  
       FIG. 2  illustrates a detonator assembly  30  according to the invention. The assembly includes a cable confinement structure which is formed by a housing  32  which is of parallelepiped form which, as is more clearly shown in  FIGS. 3 and 4 , has four relatively large rectangular sides and opposed ends  34  and  36  which are smaller than the larger rectangular sides. The housing  32  is made from a corrugated cardboard blank  38  generally of the type shown in  FIG. 5  which is formed with lines of weakness and cut-outs so that the blank can be folded into the configuration shown in  FIGS. 3 and 4 . At three of its longitudinal corners  40 A,  40 B and  40 C respectively, portions of the blank can be forced inwardly to form right angled recess formations  42 A,  42 B and  42 C respectively. As is shown in  FIG. 2  end portions  44  and  46  of the blank abut these formations, on an inner side of the housing, and thereby divide the housing interior into three compartments  50 ,  52  and  54  respectively.  
       FIG. 4  illustrates further details of the recessed formation  42 C which extends a substantial portion of the width of the respective side, designated  56 . A relatively large rectangular window  58  is formed in a base of the recessed formation. A rectangular cardboard insert  60 , which has a centrally located relatively small rectangular window  62 , is locatable in the recessed formation  42 C.  
      FIGS.  9  to  11  illustrate successive stages in the manufacture of two coils of cable from a single length of cable  66 . A large drum  68  of the cable  66  is mounted to suitable support structure  70 . The cable  66  is passed over suitable pulleys and rollers  72  and  74  respectively and is wound in a first direction  76  about a first former  78 . A predetermined length of cable, say 40 metres long, is wound onto the former  78  to form a single coil  80 . A first end  82  of the cable is positioned inside an interior of the coil. Thereafter the coil is severed by means of a set of knives  84 . The cable is then wound onto a second former  86  in a direction  88  which is opposite to the first direction  76 . The cable is drawn from the single coil  80  for this purpose. In this way, as is shown in  FIG. 11 , a first coil  90  is formed with a predetermined length of cable of, say, 30 metres and a second coil  92  is formed with a predetermined length of, say, 10 metres. The first coil has a second end  94  which is integrally connected to an end  96  of the second coil (referred to herein as the third end). A free end of the coil  92  designated  98 , and referred to herein as the fourth end, is positioned inside an interior of the second coil.  
      As is shown in  FIG. 2  the first and second coils, which are coaxially aligned, are inserted into the compartments  50  and  54  respectively. The end portions  44  and  46 , which act as dividers, have slits  99  through which parts of the cable section  100  between the coils (effectively the integrally joined ends  94  and  96  shown in  FIG. 11 ) can pass. The cable section  100  is then looped through the window  58 , as is shown in  FIGS. 4 and 5 . The first end  82  of the first coil is passed through an aperture  104  in the end  34  of the housing while the fourth end  98  of the second coil is passed through an aperture  106  in the end  36 .  
      Referring particularly to  FIGS. 7 and 8  a first connector  110  is crimped onto the cable section  100  without severing this cable i.e. the first and second coils are at all times integrally connected to each other. A label  112  is attached to the cable adjacent the first connector. A second connector  114  is attached to the fourth end of the cable. A detonator  116  of conventional design which is suited for daisy-chain connections is attached to the first end  82  of the cable.  
      The end  82  is looped, as is shown in  FIGS. 2 and 8 , and the detonator  116  is inserted into the compartment  50  so that it lies inside the hollow interior of the first coil  90 . The fourth end  98  is folded over an external surface of the housing and is coupled with a press fit to the first connector  110 . The cardboard insert  60  is then manipulated so that the connectors  110  and  114  pass through the window  62  together with the label  112 . The insert is then pushed into the recessed formation  42 C (see  FIG. 4 ) so that the connectors are contained within the recessed formation. Thereafter a preformed tubular sleeve  120 , of rectangular cross-section, is placed over the housing to envelope the four larger sides. The sleeve is pre-printed with information which relates to the detonator and which is prescribed by regulation and legislation. The sleeve has slits  122  which define a rectangular section  124  which can be folded inwardly to nestle in the recessed formation  42 B so that the sleeve is thereby kept in position on the housing.  
      When the detonator assembly is to be used it is transported to a blast site and allocated to a particular borehole  10 . A tab  136  on the sleeve is pulled to tear the sleeve free from the housing or, alternatively, the sleeve is torn only enough to expose the connector set. The connectors  110  and  114  are then detached from each other. The detonator  116  is extricated from the interior of the housing. Cable is drawn from the first coil  90  so that the detonator can be inserted to a predetermined depth inside the borehole. It is pointed out in this respect that the detonator  116  shown in  FIG. 7  corresponds to a detonator  14  shown in  FIG. 1 . The length of cable between the detonator and the housing  32  is designated by the reference numeral  16  in  FIG. 1 . A predetermined length of cable, corresponding to the length  20  shown in  FIG. 1 , is drawn from the second coil. This enables the connector  114  to be connected to a corresponding first connector  110  at an adjacent borehole  14 B, as is shown in  FIG. 1 .  
      As each length of cable  16  and  20  is drawn from the housing the position of the first connector  110  is not materially altered. Excess cable not required for making connections between adjacent boreholes is left in the housing.  
      By mounting two coils inside the housing multiphase manufacturing steps are made possible. The housing, with its contents, can be moved or indexed through sequential automated manufacturing processes. The detonator and the connectors can be tested while secured within the packaging.  
      The outer sleeve is preferably pre-printed with deployment instructions and safety information as may be stipulated by local and international legislation. The sleeve is kept in position, relatively to the housing, by means of the folded portion  124  which engages with a corresponding recess  42 B.  
      The recessed formations  42 A and  42 B facilitate handling of the housing for they provide convenient handgrips.  
      The detonator  116  is preferably stored as is shown in  FIG. 2 , within the confines of the first coil  90 . This, together with the partitioned packaging design, provides a substantial amount of separation of detonators which are in a plurality of detonator assemblies. The detonator can be removed from the housing without undue handling of the housing.  
      FIGS.  12  to  14  illustrate a detonator assembly  30 A, according to a variation of the invention, which bears substantial similarities to the detonator assembly  30 . Consequently, where relevant, like reference numerals are used to designate like components.  
      First and second coaxially aligned coils  90  and  92  respectively, which are slightly spaced from each other, are formed using any suitable technique. Each cable coil has a plurality of windings  150 ,  152  around a corresponding hollow core  90 A,  92 A, and has a circular cylindrical shape. The cable coils are linked by a cable section  100  to which a connector  110  is crimped. An end  82  of the first coil is connected to a detonator  116  -which is positioned inside the hollow core  90 A of the first coil. An end  98  of the second coil, accessible from the hollow core  92 A of the second coil, is connected to a connector  114  which can be mated to the connector  110 .  
      The coils  90  and  92  are separately wrapped in a suitable sheet material, e.g. a cling-wrap plastic material  160  and  162 , and the coils are then held in a fixed relationship to each other by means of a confinement structure which comprises a shrink wrapping  164  which has openings  166  and  168  at opposed ends of the assembly through which the detonator  106  and the connectors  110  and  114  can respectively be accessed.  
       FIG. 14  is similar to  FIG. 1  and depicts a blasting arrangement which is established through the use of a plurality of the detonator assemblies  30 A. For the sake of convenience reference numerals which are the same as those in  FIG. 1  are used to designate like components.  
      The detonator assembly  30 A is used in substantially the same way as the detonator assembly  30 . The wrapping  164  is cheaper than the housing  32  and, apart from the access openings  166  and  168 , is waterproof.  
      In the preceding description the cable coils  90  and  92  are linked by the integral cable section  100 . Although this is a preferred form of construction it is not essential for the respective end portions of the cable coils could be interconnected through the use of a suitable connector  110 , which is also designed to engage with a connector  114 .  
      The detonator assembly provides a means of connection between detonators inside the same blast hole or in sequential blast holes, by permitting sufficient cable to be withdrawn from the housing. Unused cable remains securely within the packaging and the likelihood of cable knots or damage occurring is reduced.  
      The invention has been described with reference to the use of a single detonator in each borehole. Similar techniques can be employed to make connections between two or more detonators in a single borehole, if required.