Patent Publication Number: US-2009229338-A1

Title: Crimping of detonators

Description:
THIS INVENTION relates, broadly, to the crimping of detonators for detonating explosives. More specifically, the invention relates to a device and a method for crimping the mouth of a metal detonator housing around an initiating element such as a shock-tube, fuse or electrical lead protruding into the housing. 
     According to the invention, there is provided a device for crimping the mouth of a metal detonator housing around an initiating element protruding into the housing through the mouth, the device comprising
         a pair of opposed jaws, at least one which is movable relative to the other and is reciprocally mounted so that at least one of the jaws is reciprocally movable alternately towards and away from the other jaw to successively bring the jaws tightly into contact with each other and then to space the jaws apart from each other;   a plurality of toothed segments arranged side-by-side in series on each jaw, at least some of the segments being moveable and at least some of the segments of each jaw being located in one or more cavities provided therefor in the jaw, each segment having a pair of side faces whereby the segment abuts an adjacent segment when the jaws are tightly in contact with each other so that the segments of the jaws together form a segmented ring, the side faces of each segment converging from a broad radially outer end of the segment towards a toothed radially inner narrow end of the segment, each segment thereby having a tapering shape when viewed in a direction parallel to the axis of the ring, with the teeth of each segment being parallel to said axis;   a resiliently stressable biasing element provided between each adjacent pair of segments in a jaw, the biasing element acting to space the segments of the pair apart when the jaws are spaced apart from each other and acting to permit the segments, in response to movement of the moveable segments arising from the closing of the jaws, to abut against one another in series when the jaws are tightly in contact with each another, to form the segmented ring, the ring defining, at its centre, a passage having a toothed cross-sectional outline provided by the toothed narrow ends of the segments for holding a crimped mouth of a detonator, the mouth having been crimped by the toothed inner ends of the segments in response to radially inward movement of the segments caused by the tight closing of the jaws.       

     Each jaw may have the same number of segments. The number of segments in each jaw may be selected by routine experimentation, bearing in mind difficulties in obtaining a desirably circular toothed passage when the jaws are tightly closed, when there are too few segments, and difficulties associated with expense and complexity of construction, when there are too many segments. 
     The number of segments in each jaw may thus be in the range of 2 to 8, more preferably 3 to 5, and conveniently 3. 
     More particularly, each jaw may have an odd number of segments, for example 3, 5 or 7, the preferred number again being 3, so that there are, in each jaw, a central segment and one or more additional segments on each side of the central segment. 
     At least one segment in each jaw, for example the central segment, may be fixed and hence immovably connected or integral with the remainder of its associated jaw, with a cavity being provided in the jaw on each side of the fixed segment for receiving one or more movable segments. 
     Alternatively, all of the segments may be movable, being in the nature of movable inserts, a single cavity being provided in each jaw for receiving the inserts, in which cavity the inserts are located. 
     Each cavity may provide one or more abutment faces for abutting respectively against the broad ends of the movable segments. The abutment faces may be flat and the broad ends of the movable segments may have radially outwardly facing surfaces which are also flat. Each abutment face and the radially outer surface of the associated segment may be provided with a radial projection which projects into an associated tangential slot, relative to the ring. The projection may be a radially outward projection from the outer surface of the broad end of the segment and the tangential slot may be provided in the abutment face of the recess, or in principle vice versa, with the projection projecting radially inwardly from the abutment face of the recess and the tangential slot being provided in the outer surface of the broad end of the segment. 
     When there is an odd number of segments in each jaw, however, there need be no slot and projection acting between the outer surface of the broad end of the central segment and the associated abutment face, the abutment face and outer surface of the central segment instead respectively being provided with opposed sockets, and a biasing member such as a coil spring under axial compression or an elastomeric block under similar axial compression, being located in the opposed sockets and spanning the interface between the outer surface of the broad end of the central segment and the abutment face, the compression of the biasing member acting to urge the outer face of the central segment away from the associated abutment face. 
     Each biasing element may be an elastomeric block which is held captive in a cavity provided therefor in the side face of one of the segments of the pair of segments between which it acts. The elastomeric block may project tangentially outwardly from its cavity relative to the axis of the ring, when the jaws are spaced apart from each other, the block thereby acting to space apart the segments of the pair, and is compressed and forced into its associated cavity by the side face of the other segment of the pair when the jaws are tightly in contact with each other. Each elastomeric block may be cylindrical in shape, being located in a correspondingly part-cylindrical cavity having an axis which is parallel to the axis of the ring. 
     Each jaw may comprise a more or less elongated rectangular flattened bar, conveniently of metal, the bar being longer than it is wide and wider than it is thick, so that it has a pair of major faces spanning its length and width, a pair of side edge faces spanning its length and thickness, and a pair of end edge faces spanning its width and thickness, the bars abutting against each other, by means of a pair of opposed side edge faces thereof, when the jaws are in the tightly closed condition. In this case the cavities holding the respective series of segments may be more or less semi-regular-polygonal indentations into the respective opposed side edge faces of the bars, the indentations extending from one major face of the bar to the other. The axes of the polygons may be parallel to the axis of the ring, and each cavity may in turn also extend from one major face of the bar to the other. Each major face of each bar may be enclosed by a cover plate, which acts to hold the segments and biasing elements in place against axial movement thereof in the direction of the ring axis. 
     The device may include a guide pin protruding from at least one of the segments, into a complementary guide slot in the cover plate which abuts that segment. Typically, each of the segments may be provided with such a guide pin, with each guide pin then located in its own complementary guide slot. 
     The jaws may further be provided respectively on their side edge faces which abut when the jaws are tightly in abutment, with a guide pin and an opposed tubular guide socket, the pin entering the socket when the jaws approach each other, and leaving the socket when the spacing between the jaws is increased sufficiently, as the jaws leave each other. 
     In use, a succession of detonator housings are moved intermittently in series along a path extending between the jaws, in a direction perpendicular to the axis of the ring, with their associated initiating elements in place, optionally held there by a resiliently flexible sleeve or ferrule located coaxially between the mouth of the detonator housing and the initiating element, the detonator housings being aligned parallel to the ring axis, while the jaws are spaced apart, with each detonator housing being placed between the jaws and coaxially aligned with the ring axis, before the jaws are moved together into tight abutment with each other to clamp the detonator housing mouth between the jaws by means of the segments, the segments moving radially inwardly towards the ring axis to crimp the mouth of the detonator housing around the initiating element. 
     The invention accordingly extends to a method of crimping the mouth of a metal detonator housing around an initiating element, the method including the steps of:
         moving a succession of detonator housing in series intermittently along a path extending between a pair of opposed jaws, the detonator housings being in turn located in a stationary condition between the jaws; and   moving the jaws into abutment with each other to grip a mouth of the stationary detonator housing located therebetween by means of toothed segments mounted on the jaws which, when the jaws are tightly in abutment with each other, form a segmented ring defining, at its centre, a passage having a toothed circumferential outline,       

     the segments being arranged simultaneously to move radially inwards towards and into contact with the mouth of the housing located between the jaws as the jaws approach each other, to crimp the housing against the initiating element by the time the jaws are in tight abutment with each other, the detonator housing being coaxially aligned with the axis of the ring and the detonator housings being moved in succession, while the jaws are spaced apart, in a direction perpendicular to the ring axis, the jaws being moved apart after the mouth of each detonator housing has been crimped, to allow the succeeding detonator housing to be moved into its stationary condition between the jaws, before the jaws are again moved together to crimp the mouth of said succeeding detonator housing. 
     In accordance with the method, moving the jaws into abutment may be against a bias which acts to space the segments apart from one another and to space the segments radially outwardly, automatically to enlarge the ring, as the jaws move apart. 
     It is a feature of the invention that it allows the series of detonator housings intermittently to be moved, typically in a straight line, along a path extending between the jaws and perpendicular to the ring axis, while the jaws are reciprocated in synchronisation with the intermittent movement of the detonator housings, between a tightly abutting condition with their segments located around a crimped detonator housing mouth, and a condition spaced apart to allow subsequent movement of the detonators along the path, thereby permitting low crimping cycle times, as short as about 2 s or less, for the crimping of each detonator housing mouth. 
    
    
     
       The invention will now be described, by way of non-limiting illustrative examples, with reference to the accompanying diagrammatic drawings, in which: 
         FIG. 1  shows a sectional plan view of a device in accordance with a first embodiment of the invention, in a direction parallel to the axis of its ring of segments, with its jaws spaced apart; 
         FIG. 2  shows a view corresponding to  FIG. 1 , with the jaws tightly in abutment; and 
         FIG. 3  shows an exploded three-dimensional view from the bottom and side, of a device in accordance with a second embodiment of the invention. 
     
    
    
     Referring to  FIGS. 1 and 2 , reference numeral  10  generally designates a device in accordance with a first embodiment of the invention for crimping the mouth of a metal detonator housing (not shown). The device  10  comprises, broadly, a pair of opposed elongate-rectangular hardened mild steel jaws  12 ,  14 , having a length of 120 mm, a width of 40 mm and a thickness of 20 mm. The jaws thus have 120×40 mm 2  major faces, 120×20 mm 2  side edge faces designated  16 , and 40×10 mm 2  end edge faces designated  18 . In the drawings, the jaws  12 ,  14  are viewed face-on to their major faces and are shown with their major faces co-planar, one face  16  of the jaw  12  being opposed to one face  16  of the jaw  14 , the opposed faces  16  being shown tightly in abutment at  20  in  FIG. 2 , and spaced apart by a spacing “S” in  FIG. 1 . 
     In the present example, the jaws  12 ,  14  are reciprocably mounted on a hydraulic reciprocating mechanism (not shown) arranged to reciprocate them simultaneously between a closed condition, shown in  FIG. 2 , and a fully open condition in which they are spaced apart sufficiently to allow a series of detonator housings to be crimped to pass between the jaws in a direction parallel to their edge faces  16 . The direction of reciprocation is normal to the faces  16  and is shown by arrow  22 , and the direction of movement of the detonator housings is shown by arrow  24 . 
     It is to be noted that in  FIG. 1  the jaws  12 ,  14  are not shown fully spaced apart, but only partly spaced apart, the jaws in their fully spaced-apart condition permitting a succession of detonator housings to pass therebetween in the direction of arrow  24 , midway between their opposed side edge faces  16 , without being interfered with by the guide pin  26  (described hereunder) provided on the jaw  12 . In other examples, the jaws may be movable by a pneumatic reciprocating mechanism or by a mechanical reciprocating mechanism such as a crank; and it will be appreciated that in other examples only one of the jaws  12 ,  14  need reciprocate, the other being stationary. 
     In the present example, the detonator housings are carried past the jaws  12 ,  14  by a conveyor mechanism (not shown) situated below the jaws  12 ,  14 , the edge faces  16 ,  18  being vertical and the major faces being horizontal, with the detonator housings projecting upwardly from the conveyor mechanism to present their mouths at a desired elevation between the opposed side edge faces  16 . The conveyor mechanism moves a succession of detonator housings intermittently in the direction of arrow  24  when the jaws  12 ,  14  are sufficiently spaced apart, and holds the detonator housings stationary at other times. Only one detonator housing at a time will be located between the opposed jaw faces  16 , the spacing between, and/or speed of movement in the direction of arrow  24  of, succeeding detonator housings moved by the conveyor mechanism being selected accordingly; and the movement of the detonator housings in the direction of arrow  24  will be appropriately synchronised with the reciprocation of the jaws  12 ,  14  so that the detonator housings are moved in the direction of arrow  24  only when the jaws  12 ,  14  are sufficiently spaced apart, and are held stationary at other times, particularly when interference with detonator housing movement by the pin  26  arising from too close a spacing between the jaws  12 ,  14  is possible. 
     As shown in the drawings, the pin  26  is held captive in a passage  28  in the jaw  12 , by a screw  30  which screws axially into the inner end of the pin  26  and engages with a tapped extension  32  of the passage  28 . The jaw  14  is in turn provided with a passage  34  which receives the part of the pin  26  which projects from the jaw  12 , when the jaws  12 ,  14  are sufficiently closely spaced from each other, to guide accurate movement of the jaws into face-to-face abutment of their side edge faces  16 . 
     Each jaw  12 ,  14  is provided, in its side edge face  16  which faces the other jaw, with a semi-regular-hexagonal indentation  36  (see  FIG. 1  in particular) which is broadly C-shaped and provides three abutment faces  38 , namely a central abutment face and a pair of lateral abutment faces respectively on opposite sides of the central abutment face. The faces  38  are flat and are directed radially inwardly towards the axis  40  of the hexagon of which they form part. Each of the lateral abutment faces  38  is provided with a slot  42 . Each slot  42  is located midway between the major faces of the associated jaw  12 ,  14  and extends in a tangential direction relative to the associated axis  40 . Each central abutment face is provided with a centrally positioned passage  44  which receives a sleeve  46  as described hereunder (see  FIG. 2 ). 
     Three hardened mild steel segments  48  are provided in each indentation  36 , namely a central segment and a pair of lateral segments on opposite sides of the central segment. Each segment  48 , when viewed in a direction parallel to the axes  40 , is broadly equilateral-triangular in outline, having a broad end  49  which is radially outermost, for abutment against an associated abutment face  38 , a pair of side faces  51  for abutment against adjacent segments  48 , and a toothed inner narrow end  53 , having teeth which extend parallel to the axes  40 , the abutment in question taking place when the jaws  12 ,  14  are in abutment, as shown in  FIG. 2 . The broad ends  49  of the lateral segments  48  remain at all times, however, in abutment with the lateral abutment faces  38  having the slots  42 . 
     Each of the lateral segments  48  has an insert  50  screwed into a tapped socket in the broad end  49  of the segment  48 , the insert  50  providing a projection which projects radially outwardly, relative to the associated axis  40 , from the broad end of the segment  48 , into the associated slot  42  in the associated abutment face  38 . Location of this projection in the associated slot  42  holds the lateral segments  48  captive in the associated indentation  36 , the lateral segments in turn holding the respective central segments  48  captive in said indentations  36 . One side face of each segment  48  is provided with a part-cylindrical cavity  52  which holds a cylindrical rubber biassing element in the form of a cylindrical block  54  press-fitted into the cavity  52 . 
     As shown in  FIG. 1 , each sleeve  46  contains a coil spring  56  under compression, each sleeve  46  projecting into a socket  58  provided therefor in the central segment  48  associated with the central abutment face  38  having the passage  44  receiving said sleeve  46 . Each sleeve  46  thus projects from the socket  58  in the associated central segment  58 , into the associated passage  44  in the associated abutment face  38 , being a press fit in the socket  58 , but being slidable in the passage  44 . The coil spring  56  acts against segment  48  at the inner end of the socket  58 , and against a plug  60  held in an extension of the passage  44  by a grub screw  62 . The springs  56  are omitted from  FIG. 2  for ease of illustration. 
     Two plastics cover plates are provided to cover the major faces respectively of each jaw  12 ,  14 . Minor projections of the lower cover plate can be seen in  FIG. 1  at  64 . The cover plates are bolted to the jaws  12 ,  14  by bolts  66  provided with washers  68 , the positions of the bolts  66  and washers  68  being illustrated schematically. The cover plates act to enclose the segments  48  to prevent unwanted movement of the rubber blocks  54  and the segments  48  in the direction of axes  40 , while protecting against the ingress of dirt. 
     It will be appreciated that, when the opposed faces  16  of jaws  12 ,  14  are in tight abutment at  20  as shown in  FIG. 2 , the broad end  49  of each central segment  48  abuts its associated abutment face  38 , the side faces  51  of adjacent pairs of the segments  48  all being in abutment and the rubber blocks  54  all being under lateral compression and forced laterally into their respective cavities  52 . The axes  40  will coincide and the segments  48  will form a segmented ring around a central axis, also designated  40  in  FIG. 2 , provided by the coinciding axes  40  of  FIG. 1 . When the opposed abutting faces  16  of the jaws  12 ,  14  move apart, the springs  56  push the central segments away from their respective abutment faces  38 , and the rubber blocks  54  push adjacent pairs of segments  48  apart, as shown in  FIG. 1 . It will be appreciated that, in  FIG. 2 , the ring of toothed radially inner narrow ends  53  of the segments  48  combine to form a central passage around the central axis  40 , their teeth being parallel to said axis  40 . 
     In use, as mentioned above, the conveyor mechanism, when the jaws  12 ,  14  are sufficiently spaced apart, successively and intermittently moves the detonator housings into position, in the direction of arrow  24 , to place them at the position of the central axis  40  shown in  FIG. 2 , with the projections of the inserts  50  being located at the ends of their respective slots  42  which are closest to the opposed edge faces  16  of the jaws  12 ,  14 , and with the rubber blocks  54  spacing the side faces of the segments  48  apart. When the jaws are moved together, with the detonating housing held stationary and coaxial with the central axis  40 , engagement of the lateral segments  48  of the jaw  12  with the lateral segments  48  of the jaw  14 , via the two rubber blocks projecting into the space “S” between the jaws  12 ,  14 , compresses the various rubber blocks  54  and forces them into the associated cavities  52 , while bringing the side faces of the segments  48  into abutment. Simultaneously therewith, the springs  56  are compressed to bring the broad ends of the central segments  48  into abutment with their associated abutment faces  38 ; and the lateral segments  48  slide along their respective abutment faces  38  until the projections of their inserts  50  are at the ends of their associated slots  42  furthest from the opposed faces  16  of the jaws  12 ,  14 , at which stage the situation shown in  FIG. 2  is reached, with the opposed faces  16  in abutment. 
     It will be appreciated that, as the jaws  12 ,  14  move together, as described above, the toothed radially inner narrow ends of the segments  48  converge axially inwardly towards the axis  40  and towards one another, until they form the substantially circular central passage shown around the central axis  40  in  FIG. 2 . When they reach the mouth of the detonator housing located coaxially with the central axis  40 , said toothed radially inner ends act to crimp the mouth of the housing around the initiating element (and any sleeve or ferrule holding the initiating element) projecting in the housing. When the jaws  12 ,  14  are subsequently moved apart, the rubber blocks  54  act automatically to space the side faces of the segments  48  apart in each jaw  12 ,  14 , while the springs  56  automatically move the central segments  48  away from their respective abutment faces  38 , the projections of the inserts  50  of the lateral segments  48  moving back to the ends of the associated slots  42  closest to the opposed faces  16  of the jaws  12 ,  14 , the outer ends of the lateral segments  48  sliding along their respective abutment faces  38 . 
     Referring to  FIG. 3 , reference numeral  100  generally designates a device in accordance with a second embodiment of the invention, for crimping the mouth of a metal detonator housing (not shown). 
     Parts of the device  100  which are the same as, or similar to, those of the device  10  of  FIGS. 1 and 2 , are indicated with the same reference numerals. 
     In the device  100 , the pin  26  in the jaw  12  and the complementary passage  34  in the jaw  14 , have been dispensed with. 
     The device  100  includes upper cover plates  102 ,  104  and lower cover plates  106 ,  108 . Bolts  66  protrude inwardly from the lower cover plates  104 ,  108 , through passages  110  in the jaws  12 ,  14 , and engage threaded sleeves  112  protruding inwardly from the upper cover plates  102 ,  104 . 
     The device  100  also includes a guide pin  114  protruding from each of the segments  48 , with each guide pin nestling or located movingly in a guide slot  116  provided in one of the lower cover plates  106 ,  108 . The guide pins  114  and guide slots  116  ensure accurate and consistent movement of the segments  48 . 
     It is a feature of the invention that the simple reciprocating movement of the jaws  12 ,  14  (arrow  22 ), and the simple intermittent movement of the detonator housings along their path between the jaws  12 ,  14  (arrow  24 ) allow rapid cycle times for the crimping of individual detonator housing mouths, expected to be of the order of 2 s or less. 
     Finally, it is to be noted that, although in the examples shown in the drawings the detonators are described as moving in the direction of arrow  24 , in other examples they can move in a direction perpendicular or normal to the direction of arrow  24 , and parallel to the direction of arrow  22 . In this case the jaws  12 ,  14  will not only be reciprocated towards and away from each other in the direction of arrow  22 , but will also be indexed simultaneously in a direction parallel to the direction of arrow  24  into crimping stations in which they can reciprocate towards and away from each other, and out of said crimping stations in a direction parallel to the direction of arrow  24 , to allow subsequent movement of the series of detonators, in a direction parallel to the direction of arrow  22 .