Abstract:
A hydraulic cable tensioning device having a main body and tensioning yoke formed from aluminum and being capable of delivering 5,000 psi to tension a cable bearing a barrel and wedge assembly such as in a mine roof bolt or a cable truss. The body defines a pair of cavities which each receive an elongated member bearing a piston which together act as dual action hydraulic cylinders. A cable receiving bore defined in the body receives a cable gripping member to grip the cable while the tensioning yoke pushes against the barrel and wedge assembly in response to forces from the hydraulic cylinders.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Serial No. 60/088,095 entitled “Hydraulic Cable Tensioner”, filed Jun. 5, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to hydraulic cable tensioners, more particularly, to a portable, lightweight hydraulic cable tensioning device for use in tensioning mine roof cable bolts and cable trusses. 
     2. Prior Art 
     Hydraulic cable tensioners have been used to apply tension to a length of installed cable having one fixed end such as a conventional cable bolt having a barrel and wedge assembly or a cable truss having a length of cable terminating with a barrel and wedge assembly. Tension is applied to the installed cable between the barrel and wedge assembly and the fixed end of the cable by pulling on the free end of the cable while urging the barrel and wedge assembly towards the fixed end of the cable. 
     FIG. 1 depicts a conventional cable tensioning unit U formed of three separate steel cylinders, two being hydraulic cylinders HC coupled together via a yoke Y and a central cylinder CC which receives the cable to be tensioned. Hydraulic fluid is fed to the hydraulic cylinders HC via hydraulic lines L and manifolds M from a remote hydraulic fluid supply unit located at a mining machine. The steel unit U is heavy, typically weighing about eighty pounds, and must be held in one place by one operator at the location of the cable bolt or cable truss to be tensioned while a second operator located at the mining machine operates the controls for the hydraulic fluid delivered to the unit U. 
     The maximum hydraulic pressure applicable to the unit U is about 2,500 psi resulting in tensioning of an installed cable by about eight tons. This conventional cable tensioner is cumbersome due to its weight and need for two people to install and operate the unit. 
     Accordingly, a need remains for a hydraulic cable tensioning device which may be readily portable and held overhead by one individual as well as operated at the location of the cable bolt or cable truss to be tensioned. 
     SUMMARY OF THE INVENTION 
     This need is met by the hydraulic cable tensioning device of the present invention which is used to induce tension in a cable, the cable having one end fixed to a structure and a free end bearing an attachment assembly. The device includes (1) a unitary body defining a cable receiving bore and an elongated cavity, (2) a cable gripping member received within the cable receiving bore, (3) an elongated member received within the cavity and having a first end extending out of the body, (4) a piston slidably fitted within the cavity and fixed to a second end of the elongated member, thereby defining a first chamber on one side of the piston and a second chamber on an opposite side of the piston and (5) a yoke attached to the first end of the elongated member, the yoke defining a bore aligned with the cable receiving bore and having an abutment surface. The body is preferably formed from aluminum. 
     When a cable having one end fixed to a structure and a free end bearing an attachment assembly is received in the bore and the piston is urged towards the yoke, the cable gripping member grips the cable while the elongated member moves out of the cavity thereby urging the abutment surface against the attachment assembly and tensioning the cable between the attachment assembly and the fixed end of the cable. Preferably, the body defines a pair of elongated cavities positioned on opposite sides of the bore, each cavity receiving an elongated member with a piston slidably fitted within the cavity and fixed to one end of the elongated member, thereby defining a first chamber on one side of each piston and a second chamber on an opposite side of each piston, with the yoke being fixed to the elongated members. The piston is moveable towards the yoke when pressure within the first chambers is greater than pressure within the second chambers. The pressure in said first chambers is up to about 5,000 psi. The device further includes a pair of hydraulic fluid supply lines and the body further defines (i) a first passageway in fluid communication with one hydraulic fluid supply line and the first chambers and (ii) a second passageway in fluid communication with the other hydraulic fluid supply line and the second chambers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a cable tensioning unit of the prior art; 
     FIG. 2 is a perspective view of a hydraulic cable tensioning device made in accordance with the present invention with cross-section lines III—III passing from a yoke end to a first end of the cable tensioner device; and 
     FIG. 3 is a reversed cross section view of the hydraulic cable tensioner depicted in FIG. 2 taken along lines III—III, with the yoke end oriented in relation to direction X and the front end. in use with a cable bearing a barrel and wedge assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For purposes of the description hereinafter, the terms “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom” and derivatives thereof shall relate to the invention as it is oriented in the drawing figures. However, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the invention. Hence, specific dimensions and other physical characteristics related to the embodiments disclosed herein are not to be considered as limiting. 
     The hydraulic cable tensioning device  2  of the present invention is illustrated in FIGS. 2 and 3 and is configured for use with a length of cable C having an attachment assembly A typically including a barrel B and a plurality of wedges W received therein. The cable C may be a galvanized steel multi-strand cable conforming to ASTM designation A 416 entitled, “Standard Specification for Steel Strand Uncoated Seven Wire for Prestressed Concrete.” One end of the cable C is installed in a structure (not shown), such as rock strata or a portion of a mine roof cable truss, and thus is fixed to that structure. The attachment assembly A is positioned on the cable intermediate the fixed end of the cable C and a free end (commonly referred to as a pigtail) of the cable. The attachment assembly A may act as a loading bearing mechanism (for a mine roof bolt) or as a holding mechanism (in a cable truss). The hydraulic cable tensioner  2  is configured to apply tension in the cable C between the fixed end of the cable C and the attachment assembly A. 
     The hydraulic cable tensioning device  2  includes a unitary body  10  which defines a cable receiving bore  12  extending the length of the body  10  and a pair of elongated cavities  14 . A cable gripping member  16  is received within the cable receiving bore  12 . The cable gripping member  16  includes an externally threaded sleeve  18  and a plurality of gripping members or tapered wedges  20 . The sleeve  18  has an internally tapered inner surface shown at  22  which cooperates with the tapered surfaces of the wedges  20 . A first spacer  24 , a pair of springs  26  and a second spacer  28  are received within the cable receiving bore  12  between the wedges  20  and a first end  29  of the body  10 . A cap  30  having an aperture therethrough is threaded into the first end  29  of the body  10 . 
     An elongated member  32  is received within each of the elongated cavities  14 . A piston  34  slidably fitted within each cavity  14  surrounds a narrowed end portion of each elongated member  32  and is fixed thereto via washers  36  and a locking nut  38  threaded onto the elongated member  32 . In this manner, the portions of the body  10  defining the cavities  14  act as piston receiving members. A groove is defined in an inner surface of the piston  34  and receives an o-ring  42 . A pair of first channels are defined in an outer surface of each piston  34  and each receive a wear band  46 , preferably formed of rubber or other pliable material. A groove is also defined in the piston outer surface and receives a dynamic seal  48 . Each piston  34  divides the cavity  14  into a first chamber  50  and a second chamber  52 . The o-ring  42  and the dynamic seal  48  prevent leakage of fluid between the first and second chambers  50  and  52 . The wear bands  46  minimize any damaging effect that the pistons  34  may have on the body  10  when the pistons  34  slide through the cavities  14  as described below. 
     The elongated cavities  14  terminate in a pair of openings in the body  10  which each receive a collar  56 . A groove defined in an outer surface of the collars  56  receives an o-ring  60 . A groove is defined in an inner surface of the collars  56  and receives a wiper ring  64 . A pair of second channels also are defined in each of the collar inner surfaces. One of the second channels receives a back-up sealing ring  66 , a dynamic seal  68  and a wear band  70 , preferably formed of rubber or other pliable material. The other of the second channels also receives a wear band  70 . The o-ring  60  and the dynamic seal  68  prevent leakage of fluid out of the second chamber  52 . The wiper ring  64  and back-up sealing ring  66  function to prevent extraneous fluid or particulate matter from entering into the cavity  14 . The wear bands  70  minimize any damaging effect that the collars  56  may have on the elongated members  32  when the elongated members  32  slide through the collars  56  as described below. 
     A face plate  72  covers the second end of the body  10  and portions of the collars  56 . The face plate  72  defines a first aperture  74  aligned with the cable receiving bore  12  and pair of second apertures  76  aligned with the cavity openings. Handle  75 , preferably integrally formed, extends from the face plate  72 . As shown in FIG. 2, a plurality of fasteners  77  such as screws extend through mating holes defined in the face plate  72  and the body  10  to secure the face plate  72  thereto. 
     The tensioner  2  further includes a yoke  78  which is coupled to the elongated members  32  via a pair of pins  80 . The yoke  78  defines a threaded aperture  82  aligned with the cable receiving bore  12  in the body  10 . A tubular insert  84  is threaded into the yoke aperture  82 . One end  86  of the insert  84  extends towards the body  10  and the other end of the insert  84  extends in an opposite direction and includes an enlarged portion  88 . The outside diameter of the enlarged portion  88  is sized to be about the same as the outside diameter of the barrel B of the attachment assembly A. An inner sleeve  90  is received within the enlarged portion  88 . The sleeve  90  has an outside diameter which is sized to be about the same as the outside diameter of the wedges W of the assembly A. A spring  92  surrounds one end of the sleeve  90 , and the sleeve  90  includes a radial rib  94  against which the spring  92  bears. A set screw  96  may be threaded through the insert on an opposite side of the rib  94  from the spring  92 . 
     A centralizing member  98  surrounds the insert end  86  and is fixed thereto via set screws  100  extending through the centralizing member  98 . The centralizing member  98  further includes a sleeve  104  having an inner diameter sized and configured to receive the sleeve  18  therein. The sleeve  104  functions to prevent fluid or particulate matter from entering the cable receiving bore  12  when the yoke  78  and the centralizing member  98  move away from the body  10  as described below. 
     The body  10  further defines a pair of branched passageways (not shown) in fluid communication with the first and second chambers  50  and  52 . One passageway communicates with the first chambers  50  and a port  106  defined in a surface  108  of the body  10 . The other passageway communicates with the second chambers  52  and a port  110  defined in the body surface  108 . Hydraulic fluid supply lines  112  and  114  are connected to the ports  106  and  110 , respectively, via suitable fittings  115 . The hydraulic fluid supply lines  112  and  114  are closely coupled to a hydraulic fluid control unit  116  with actuating levers  118  and  120  for delivery and removal of hydraulic fluid. Although not shown in the drawings, additional hydraulic fluid lines are also connected to the control unit  116  from a main hydraulic fluid source. The body  10  further includes a handle  122 . 
     The hydraulic cable tensioning device  2  may be used to induce tension in a cable mine roof bolt or a cable in a truss. For tensioning a cable bolt, the bolt is installed in a bore hole in a mine roof either in a vertical, horizontal or angled orientation with resin cartridges in a conventional manner. A bearing plate having an aperture therethrough is slipped over the cable bolt. A barrel and wedge assembly is positioned on the free end of the cable bolt so that the barrel and wedge assembly urges the bearing plate against the mine roof. The cable bolt is sufficiently long that a length of cable (e.g., two feet) extends out of the barrel and wedge assembly into the mining chamber. The cable bolt is rotated to destroy the resin cartridges and mix the resin. Once the resin is mixed sufficiently, it is allowed to set. After the resin sets, the cable bolt may be tensioned by operation of the hydraulic cable tensioning device  2 . 
     The free end of the cable C is passed through the insert  84  with inner sleeve  90  and spring  92 , the centralizing member  98  and into the cable receiving bore  12 , through the sleeve  18  and wedges  20 , the first spacer  24 , springs  26  and second spacer  28  and out through the cap  30  until the barrel B abuts the end of the insert  84  and the wedges W abut the end of the inner sleeve  90 . The wedges  20  grip the cable C within the cable gripping member  16 . Hydraulic fluid is fed through the passageways into the body and into the first chambers  50  by actuating the lever  118 . As the hydraulic fluid fills the first chambers  50 , the pressure in the first chambers  50  becomes greater than the pressure in the second chambers until the pistons  34  and elongated members  32  fixed thereto are forced to move in the direction of arrow X shown in FIGS. 2 and 3. Movement of the elongated members  32  causes the yoke  78  and the insert  84  with the inner sleeve  90  to likewise move in the direction of arrow X. By abutting the barrel and wedge assembly A against the ends of the insert  84  and the inner sleeve  90 , respectively, the barrel B and wedges W are prevented from moving relative to each other during tensioning and the entire attachment assembly A moves in the direction of arrow X. The wedges  20  are also urged in the direction of arrow X until they lock against the tapered inner surface  22  thereby gripping the cable C and preventing the cable C from moving in the direction of arrow X. The force applied by the elongated members  32  and yoke  78  is counteracted by the gripping force of the cable gripping member  16  to induce tension in the cable C. 
     When the desired tension has been applied to the cable C, the flow of hydraulic fluid to the first chambers  50  is ceased. Hydraulic fluid is fed through the passageways in the body and into the second chambers  52  by actuating the lever  120 . As the hydraulic fluid fills the second chambers  52 , the pressure in the second chambers  52  becomes greater than the pressure in the first chambers  50  which forces the pistons  34  and elongated members  32  to move in a direction opposite to that of arrow X. The yoke  78  likewise moves in the direction opposite to arrow X, and the end  86  of the insert  84  travels back until it abuts the ends of the wedges  20  and ultimately knocks the wedges  20  away from the cable C so that the hydraulic tensioning device  2  may be removed from the cable C. Hydraulic fluid remaining in the first and second chamber  50  and  52  may then be drained. 
     The hydraulic cable tensioning device  2  may be used to tension the end of a cable in a cable truss such as disclosed in U.S. Pat. No. 5,836,720, incorporated herein by reference. When used with a cable truss, a length of cable is extended through a splice tube or the like and a barrel and wedge assembly is installed on the free end of the cable extending from the splice tube and adjacent thereto. The hydraulic cable tensioning device  2  is operated in a similar manner to its use in tensioning a cable bolt. 
     The hydraulic cable tensioning device  2  of the present invention is preferably made of aluminum with the exception of certain of the smaller components such as the sleeve  18 , wedges  20 , spacers  24  and  26 , cap  30 , insert  84 , and inner sleeve  92 , which are preferably formed of steel to prevent wear thereof. The body  10  is preferably formed of a unitary piece of aluminum. By the use of aluminum for the body  10 , the weight of the hydraulic cable tensioning device  2  is greatly reduced from the weight of the hydraulic tensioners of the prior art and typically is about twenty pounds. The design of the simple, unitary body  10  renders the hydraulic cable tensioning device  2  relatively easy to manufacture and assemble. A single mining operator can readily hold the hydraulic cable tensioning device  2  overhead and simultaneously operate the hydraulic levers  118  and  120  at the location of the cable C to be tensioned. The need for a second operator is avoided because one person can install and operate the hydraulic cable tensioning device  2 . The hydraulic cable tensioning device  2  is thus more portable and safer to use overhead in the mining environment than the heavy, cumbersome hydraulic tensioners of the prior art. 
     In addition, the unitary block design of the hydraulic cable tensioning device of the present invention allows for delivery of a much higher hydraulic pressure and concomitant greater tensioning than the prior art tensioners. It has been found that hydraulic pressure of about 5,000 psi may be applied to the hydraulic cable tensioning device of the present invention resulting in about sixteen tons of tensioning force applied to the cable. 
     It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Such modifications are to be considered as included within the following claims unless the claims, by their language, expressly state otherwise. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.