Abstract:
A tamping device ( 10 ) for plugging an open end of a blasting hole used in a mine blasting application comprising an expandable sleeve ( 20 ) having a bore. The sleeve is configurable between circumferentially expanded and circumferentially retracted positions. An actuation member ( 40 ) having a head section ( 41 ) is at least partially locatable inside the expandable sleeve. The head section and the expandable sleeve are adapted in order for relative longitudinal movement between the head section and the expandable sleeve, to cause the sleeve to be manipulated from the retracted position to the expanded position.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a tamping device for plugging or tamping an aperture, and more particularly, but not exclusively, to a tamping device for plugging an end of a blasting hole used in a mine blasting application. 
       BACKGROUND TO THE INVENTION 
       [0002]    Mine blasting activities form an important part of the mining process and industry. In one mine blasting application, typically used for underground blasting, a blasting hole is drilled at an ore face into an ore body to be blasted. An explosive charge is subsequently inserted from an open end of the hole into the hole and is positioned at a blind end of the hole. When the explosive charge is detonated, high-pressure shock waves and high-pressure gases propagate back towards the open end of the blast hole. It is advantageous to trap these high-pressure gases inside the blast hole, as the high-pressure gases assist in breaking the ore into smaller particles. A number of methods have therefore in the past been proposed to block or plug the open end of a blasting hole. 
         [0003]    In a first method, a resilient bag is filled with clay, whereafter the bag, and thus the clay, is soaked, causing the bag and clay to expand and to form a plug in the hole. However, proper sealing is often not obtained using this solution, because for example, of insufficient soaking time. As the soaking process takes an undesirably long time, users of this device often elect rather to install more than one bag filled with clay to obtain better sealing, instead of waiting for the proper expansion and the sealing of the bag, thus also reducing the cost efficiency associated with this method. 
         [0004]    A further tamping device comprises an expandable sleeve arrangement, where the sleeve includes a circumferential knife-edge type contact area, which is outwardly displaced upon installation of the tamping device. The fact that the contact area is of a knife-edge circumferential configuration limits the sealing force that can be obtained using the sealing device. Also, special installation tools are required, which are prone to being displaced, thus rendering the device unusable. 
         [0005]    A further solution is to fill a rubber sleeve with sand once the sleeve has been installed in the blasting hole. This solution is however not suitable for vertical drilling applications. 
         [0006]    It should also be noted that a permanent type of plug arrangement would not suffice, as explosive charges sometimes misfire, and the blasting hole should thus be accessible in order to remove the charge to remedy the problem. 
       OBJECT OF THE INVENTION 
       [0007]    It is accordingly an object of the invention to provide a tamping device that would at least partially alleviate the above-mentioned disadvantages. 
         [0008]    It is furthermore an object of the invention to provide a tamping device, which would be an alternative to existing tamping devices. 
       SUMMARY OF THE INVENTION 
       [0009]    According to the invention there is provided a tamping device, suitable for use in plugging an open end of a blasting hole, the tamping device comprises:
       an expandable sleeve having a bore, the sleeve being manipulatable between a circumferentially expanded position and circumferentially retracted position;   an actuation member having a head section;   the head section being at least partially locatable inside the expandable sleeve; and   the head section and expandable sleeve being adapted in order for relative longitudinal displacement between the head section and the expandable sleeve to cause the sleeve to be manipulated from the circumferentially retracted position to the circumferentially expanded position.       
 
         [0014]    Preferably, the sleeve remains stationary, and the actuation member is displaced relative to the sleeve. More particularly, the actuation member may be longitudinally displaced relative to the sleeve. 
         [0015]    The actuating member may be displaced by exerting a tensile force thereon. The tensile force may be exerted by pulling a handle of the actuation member, and may alternatively be exerted by a biasing means, for example a spring. Alternatively, complementary threads may be provided on the actuation member and the sleeve, and the actuation member may be displaced by rotating the actuation member relative to the sleeve. 
         [0016]    There is provided for an outer surface of the head section and an inner surface of the sleeve to be tapered relative to one another. 
         [0017]    Preferably, the sleeve may have a tapered bore. 
         [0018]    The sleeve may define a plurality of spaced slots extending longitudinally from a distal end of the sleeve to divide the sleeve in a plurality of gripping members. The gripping members are at least partially resilient, and are radially outwardly manipulatable relative to the actuation member, thus rendering the sleeve expandable. 
         [0019]    Each gripping member preferably has a planar inner surface. An outer surface of each gripping member may be arcuate and serrated. 
         [0020]    The sleeve may be made of plastic, and more particularly is made of a resilient material. A longitudinal, elongate groove is provided in the sleeve, more particularly in an outer surface of the sleeve, for receiving a detonator cord. 
         [0021]    The sleeve may comprise a retaining formation for retaining the actuation member relative to the sleeve. The retaining formation may be C-shaped when viewed in plan, and may include at least two opposing resilient arms. 
         [0022]    The head section of the actuation member is preferably tapered when viewed in cross-section. The head section may include a plurality of planar outer surfaces when viewed in plan. More particularly, the head section is configured and dimensioned to compliment the bore of the sleeve. The head section may be hexagonal in cross-section. 
         [0023]    The actuation member also includes a stem section extending from the head section. There is provided for the stem to be tapered and for the tapering angle to be less than 5°; preferably about 1°. The stem section locates inside the retaining formation, and the retaining formation engages the stem section as the stem section is displaced relative to the retaining formation, due to the tapered configuration of the stem section. 
         [0024]    There is provided for the tapered stem section to be of self-locking configuration relative to the retaining formation. 
         [0025]    The actuation member also includes a handle section. 
         [0026]    The handle section is configured substantially transverse to the stem section. 
         [0027]    The stem section includes a zone of reduced diameter at a junction with the handle section. The zone of reduced diameter may be in the form of a circumferential groove. 
         [0028]    There is provided for the handle section to become detached from the stem section at the zone of reduced diameter when a predetermined tensile or pulling force is applied on the handle section. 
         [0029]    There is provided for the tamping device to be self-locking when the explosive is detonated, in that high-pressure gasses will exert a force on the head section of the actuation member in order to further longitudinally displace the head section, so as to further manipulate the expandable sleeve to the circumferentially expanded position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    A preferred embodiment of the invention is described by way of a non-limiting example, and with reference to the accompanying drawings in which: 
           [0031]      FIG. 1  is a perspective view of a tamping device in accordance with the invention; 
           [0032]      FIG. 2  is a cross-sectional side view of the tamping device in  FIG. 1 ; 
           [0033]      FIG. 3  is a cross-sectional view taken through line A-A of  FIG. 2 ; 
           [0034]      FIG. 4  is a cross-sectional view taken along line B-B of  FIG. 2 ; and 
           [0035]      FIG. 5  is a cross-sectional view of the tamping device of  FIG. 1 , with the sleeve having been displaced to the circumferentially expanded position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    Referring to the drawings in which like numerals indicate like features, a non-limiting example of a tamping device in accordance with the invention is indicated by reference numeral  10 . The tamping device comprises an expandable sleeve  20 , a retaining member  30 , and an actuation member  40 . 
         [0037]    The expandable sleeve  20  is of substantially tubular configuration and defines slots  21  extending longitudinally from a distal end of the sleeve to divide the sleeve into gripping elements  22 . The gripping elements  22  are resilient, and can pivot relative to a base  23  of the sleeve  20  at another end of the sleeve, so as to render the sleeve radially outwardly manipulatable or circumferentially expandable. Serrations  24  are provided on the outer surface of the gripping elements  22 , and ensure proper contact between the sleeve and a surface of a blasting hole in which the tamping  10  is to be used. A bore  25  of the expandable sleeve is of tapered configuration. As can best be seen in  FIG. 4 , the gripping elements  22  have planar inner faces  26 , which are adapted to complement an outer surface of the actuation member as described below. An outer perimeter of the sleeve  20  is substantially circular when viewed from an end thereof, and an inner perimeter of the sleeve  20  is substantially hexagonal when viewed from an end thereof. 
         [0038]    A retaining formation  30 , shown in  FIG. 3 , at the base  23  of the sleeve  20 , comprises a base  31  from which two arcuate retaining extensions  32  extend. The arcuate retaining extensions  32  form a substantially C-shaped retaining formation, and are at least partially resilient in order to retain the actuation member  40  as described herein below. 
         [0039]    The actuation member  40  includes a head section  41 , a stem section  42  and a handle  43 . The head section  41  of the actuation member has a tapered outer surface  41 . 1 , which abuts the tapered inner surface  25  of the expandable sleeve  20 . The tapered outer surface  41 . 1  includes a plurality of flat surfaces that renders the head section hexagonal when viewed from an end thereof, as can best be seen in  FIG. 4 . 
         [0040]    The stem section  42  extends from the head section  41  to handle  43 . The stem section comprises a stem  42 . 1  that extends from the head section in a chamfered arrangement  42 . 2 . The stem  42 . 1  is of a tapered configuration, and more particularly tapers from a major to a minor diameter in a direction towards the handle, as shown by arrow A. The tapered stem configuration causes the stem  42 . 1  to engage the retaining member  30  when displaced in the direction of arrow A. The increasing diameter causes the resilient retaining extensions  32  to be spaced apart, thus resiliently applying an inward force on the stem  42 . 1 . The taper of the stem  42 . 1  is small enough to render the stem  42 . 1  self-locking relative to the retaining member  30 . Preferably, the taper would be less than 5° and more preferably in the vicinity of 1°. The stem section  42  also includes a zone of reduced diameter in the form of a circumferential groove  42 . 3  provided towards the handle  43 , When a predetermined tensile force is applied onto the handle  43 , the handle will become separated at the circumferential groove  42 . 3  for the purposes described hereinbelow. 
         [0041]    In use, the tamping device  10  is located inside a blasting hole to be sealed, the expandable sleeve in a circumferentially retracted position and with the actuation member  40 , in particular the head section  41 , being at least partially displaced away from a bore of the expandable sleeve  20 . Once the tamping device  10  has been located at a desired position, a pulling force is exerted by an installer on the handle  43 , which is transmitted via the stem section  42  to the head section  41  of the actuation member  40 . As a result, the actuation member is longitudinally displaced relative to the expandable sleeve  20 , and the relative tapered configuration between the sleeve  20  and the head section  41  causes the expandable sleeve  20  to be manipulated from a circumferentially retracted position to a circumferentially expanded position, as is shown in  FIG. 5 . More particularly, the resilient gripping members are forced outwardly and abut the inner wall of the blasting hole in which the device is used. The serrations  24  provided on the gripping members  22  ensure proper engagement between the sleeve and the blasting hole. A detonator cord (not shown) used in the application is located inside an elongate groove  27  provided in the tamping device, and the detonator cord is therefore not compressed during the actuation of the tamping device  10 . When a predetermined tensile or pulling force is applied by an installer to the handle  43 , the handle  43  becomes detached from the stem section  42  at the circumferential groove  42 . 3 . The broken off handle hence serves as an indicator to an inspecting party that the tamping device has been properly installed in that a sufficient tensile force has been applied to the tamping device, and that the sleeve  20  has been sufficiently expanded. 
         [0042]    The tamping device is now ready to be used, and will provide a temporary seal when the explosive charge, not shown, is detonated. The initial high-pressure shock wave from the explosion will exert a further force on a larger face  41 . 3  at a distal end of the head section  41  of the actuation member  40 , acting as a piston, and which will momentarily increase the sealing integrity of the tamping device  10 , before the ore body disintegrates. 
         [0043]    In the case of a misfire of the explosive charge, the tamping device  10  can be removed by applying a oppositely directed force onto the stem section  42  which will reverse the process as described above. 
         [0044]    It will be appreciated that the above is only one embodiment of the invention, and that there may be many variations without departing from the spirit and the scope of the invention. For example, only the bore of the sleeve, alternatively only the outer surface of the head section may be tapered, provided that there is a relative taper between the head section and the sleeve. Also, the head section as well as the sleeve may be of many different cross-sectional profiles and does not need to be hexagonal as shown in this embodiment. The outer surface of the sleeve may also be of many different configurations, and any irregular surface may be provided instead of the serrations shown in this embodiment.