Abstract:
A concrete reinforcement cable tensioner ( 10 ) has a cable gripper ( 60 ) with its base end ( 87 ) mounted to a flange ( 18 ) which is secured to the tensioning cylinders ( 12, 14 ) by abutting a shoulder on the outside of the cylinders ( 12, 14 ). An auxiliary retraction spring ( 94 ) is contained in a tubular handle ( 86 ) which is fixed to the flange ( 18 ) and the spring ( 94 ) acts on a rod ( 92 ) which extends beyond the handle ( 86 ) and has its distal end fixed to a yoke ( 104 ) which connects the piston rods ( 30 ) of the cylinders ( 12, 14 ) and on which a seat ( 108 ) for bearing against the concrete slab is mounted. The base ends ( 24 ) of the tensioning cylinders ( 12, 14 ) are hydraulically connected by a manifold ( 16 ) which is common to the cylinders ( 12, 14 ) and binds the base ends ( 24 ) of the cylinders ( 12, 14 ) together.

Description:
This claims the benefit of U.S. Provisional Patent Application No. 60/037,635 filed Jan. 17, 1997. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a hydraulic cylinder operated device for tensioning reinforcement cables in green concrete. 
     DISCUSSION OF THE PRIOR ART 
     Concrete is sometimes reinforced with braided wire cables, sometimes referred to as wire rope. For example, a grid of such cables may be placed in a concrete form, the concrete poured and allowed to set into a semi-cured state, referred to as green concrete, and while green the cables, which extend beyond the concrete slab, are tensioned so that they are under a tensile stress, thereby exerting a compressive load on the slab. The cables extend all the way through the slab and beyond the side edges of it, so that they may be grasped by the tensioning mechanism. Typically, one end of each cable is anchored to the slab at one side edge and the other end is grasped by the hydraulic tensioning device. 
     Such tensioning devices typically have two hydraulic cylinders with a gripping mechanism fixed to the cylinders for grasping the cable and a seat secured to the piston rods of the cylinders for bearing (directly or indirectly) against the side edge of the concrete slab so that a tension of a high magnitude can be exerted on the cable. A seat which mates with the tensioning tool is typically cast into the side edge of the concrete where the cable comes out and the cable extends through the seat and through a grommet in the seat which only permits one way movement of the cable through the grommet. In other words, when the cable is being tensioned the cable can move through the grommet, but when the cable attempts to move backwardly through the grommet back into the slab, the grommet engages the cable and tightens around it to prevent such reverse movement and consequent reduction in the tensile force on the cable. Tensioning devices for performing this operation, seats and grommets are all well known. 
     In the currently existing tensioning devices, a significant length of cable must be extended past the side edge of the slab where the tensioning device is operated to be grasped by the device. If the cable length extending beyond the side edge of the slab is less than that required by the tensioning device to grip the cable, for example if the cable is cut too short, or if when pouring the concrete a worker steps on the cable, thereby pulling it back through the seat which is cast into the slab, an extension cable may need to be assembled to the end of the cable so that it can be grasped by the tensioner. This can be a very tedious and time consuming process, involving several hours of additional labor. 
     In addition, speed is of the utmost importance in tensioning cables. Typically, a tensioner operator may do nothing but tension cables. The operator may be paid per pull, i.e. per cable tensioned, so the operator wants to tension each cable as quickly as possible. For long cables, the tensioning device may stroke several times for each cable. Thus, the speed of operation of the tensioning device is important. 
     The extension speed of the tensioner is determined by the flowrate of hydraulic fluid to the tensioner, which is to a certain extent at least under the control of the operator. However, for single acting cylinders the retraction speed of the tensioner is determined by the cylinders and particularly by the springs inside the cylinders which act to return them. In addition, since a tensioner of this type is constantly being handled by the operator, it is important that the tensioner be easy to use, handle, move and supply hydraulic fluid to. Since these tensioners are also used on construction sites, they must also be rugged. 
     SUMMARY OF THE INVENTION 
     The invention provides a concrete reinforcement cable tensioner which addresses the above described needs. Thus, as in prior art concrete reinforcement cable tensioners, a tensioner of the invention has one or more hydraulic cylinders, a cable gripper mounted to the cylinders for gripping a cable and a seat for bearing directly or indirectly against the concrete, so that the gripper and the seat can be separated under a hydraulically generated force to apply tension to the reinforcement cable. However, a tensioner of the invention is improved, in one aspect, in that the gripper is mounted to each of the cylinders by a flange which engages a shoulder of each of the cylinders. Thus, the gripper can be mounted in such a manner so that the length of cable required to protrude from the green concrete slab is reduced, i.e., a shorter grip length is required, which can obviate the time consuming process of having to extend a cable which does not extend beyond the slab far enough for the prior art tensioners to grip it. In this aspect, the gripper is mounted to the flange at a base end of the gripper, i.e., the end of the gripper which is closest to the base ends of the cylinders, which reduces the grip length by at least the thickness of the flange. 
     In another aspect, a tensioner of the invention is further provided with a spring external to cylinders for biasing the device to a retracted position. Such a spring is in addition to the usual retraction springs inside the cylinders, and therefore helps speed up retraction of the device, which reduces the time needed for each cable pull. 
     In another aspect, the spring is contained in a handle of the tensioner. The handle is preferably a tube, in which the spring is contained, and the spring is a compression spring which acts between a flange of an auxiliary spring rod and a cap of the tube. The rod extends through a hole in a cap of the tubular handle and is fixed at its distal end to the piston rods of the cylinders, for example, through a yoke which connects the piston rods and to which is mounted the seat. 
     In another aspect, the device has multiple cylinders and the base ends of the cylinders are hydraulically connected by a manifold which is common to the cylinders. Multiple ports at various locations can be provided in the manifold to permit a choice of places in which to establish a hydraulic connection with the manifold to connect a pump with the device. Those ports of the manifold which are not used to connect a pump to the cylinders are plugged. 
     These and other objects and advantages of the invention will be apparent from the detailed description and from the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a cable tensioner of the invention shown in a retracted position; 
     FIG. 2 is a perspective view of the tensioner of FIG. 1 shown in an extended position; 
     FIG. 3 is a top plan view of the tensioner of FIG. 1; 
     FIG. 4 is a front plan view of the tensioner of FIG.  1  and also illustrating a jaw retaining spring (the jaw retaining spring is also illustrated in FIGS. 5 and 6 but is not shown in FIGS. 1-3 for purposes of illustration); 
     FIG. 5 is a sectional view from the plane of the line  5 — 5  of FIG. 6; 
     FIG. 6 is a sectional view from the plane of the Line  6 — 6  of FIG. 5; 
     FIG. 7 is a front top perspective view of an assembly of a cable gripper and mounting flange of the tensioner of FIGS. 1-6; and 
     FIG. 8 is a top plan view of gripper jaws for the tensioner of FIGS. 1-6 at a stage of manufacture prior to being cut apart. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A concrete reinforcement cable tensioner  10  of the invention includes a pair of single acting cylinders  12  and  14  which are bound together at their base ends  24  by a manifold  16  and are bound together at a point between their base ends  24  and rod ends  22  by a gripper mounting flange  18 . Each cylinder  12  and  14  is shouldered at the position where the flange  18  resides, indicated at  20 , so that the outer diameter of each cylinder  12  and  14  is greater between shoulder  20  and rod end  22  than it is between shoulder  20  and base end  24 . The flange  18  has holes  19  in it sized to slide over the smaller diameter portions of the cylinders  12  and  14  but not over the larger diameter portions, so that flange  18  abuts shoulders  20  and is prevented thereby from moving any closer to the rod ends  22 . Set screws  26  in the flange  18  secure the flange  18  against the shoulder  20 . 
     The cylinders  12  and  14  are conventional (except for being stepped in outside diameter as described above) single acting cylinders. The rod  30  of each cylinder  12  and  14  is hollow (i.e. tubular) and an extension spring  32  having one end fixed to the closed end  34  of the rod  30  and the other end fixed to the base end  24  of the housing  36  of each cylinder  12  and  14 . The connections between the extension spring and the respective rod  30  and housing  36  are conventional, not shown in detail, and could be provided by any suitable means. For example, in one type of connection a connector is screwed into each end of the extension spring, and each connector is pinned to the respective rod  30  or housing  36 . 
     The base ends  24  of the cylinders  12  and  14  are in hydraulic fluid communication with one another via manifold  16 . Each cylinder  12  and  14  has a single base end port  40  which is in fluid communication through an O-ring  42  with a port  44  formed in the manifold  16 . The ports  44  are in fluid communication with one another by passageways formed within the manifold  16  including a pair of transverse passages  46  (FIG.  5 ), one for each port  44 , and a lateral passageway  48  which extends lengthwise all the way through the manifold  16  and connects the passages  46 . 
     The ends of the passageways  46  and  48  are tapped and are either plugged with a threaded plug or receive a threaded hydraulic connector, to provide a total of four possible positions in which to supply hydraulic fluid to the device  10 , two of which are at the ends of passageway  48  and the other two of which are at the ends of the two passageways  46 . 
     The manifold  16  is bolted to the base ends  24  of the cylinders  12  and  14  by bolts  50  which extend through holes  52  in the manifold  16  that are threaded into holes  54  in the base ends  24 . A gripper  60  of generally conventional design (except for the end at which it is anchored to the cylinders  12  and  14 ) includes a gripper housing  62  of the general shape shown in FIG.  7  and wedge shaped gripper jaws  64  which slide on angled surfaces within the gripper housing  62 . Only the jaw  64  on the right side of the gripper housing  62  is illustrated in full lines in FIG.  5  and only the right jaw  64  is illustrated in FIG. 7 for purposes of illustration. The jaw  64  on the left side in FIG. 5 is shown in phantom, it being understood that in operation both the left and right jaws would be provided. Plates  73  are welded or otherwise affixed on the bottom side of housing  62  to help support the jaws  64  inside the housing  62 . 
     The inside surfaces of the jaws  64  are serrated so as to grip a cable, as is well known. The serrated jaws  64  grip the cable and the tension generated in the cable when the device  10  is extended tends to move the jaws  64  toward the end  65  (hereafter referred to as the rod end) of the housing  62  which is closest to the rod ends  22  of the cylinders  12  and  14 , which because of the wedge shape and angled surfaces  71  inside the housing  62  increases the strength of the grip exerted on the cable by the jaws  64 . 
     The jaws  64  are retained in the housing  62  and biased into the position shown in FIG. 5, in which they are fully open, by a jaw retaining spring  66  (FIGS.  4 - 6 ). The spring  66  is essentially a steel rod which is looped and bent as indicated. The two legs  69  of the spring  66  extend through slots  67  in the flange  18  and the end of each leg  69  is threaded into the corresponding jaw  64 . When the jaws  64  move together, the spring  66  exerts a force on them which tends to return them to the home (disengaged) position shown in FIG.  5 . 
     The serrations inside the jaws  64  can be made by forming a trapezoidally shaped block  70  of the form shown in FIG. 8, which is equal to the two jaws  64  put together (plus the kerf along central axis  76  which is created when the two jaws  64  are cut apart). The block  70  is bored and tapped with the holes  72  into which the legs  69  of spring  66  are threaded. The block  70  is also bored and tapped with a through bore  74 , which is of a diameter approximately equal to the cable diameter. The block  70  is then cut apart along axis  76  to make the two jaws  64  (which cut removes the material in the kerf). The serrations on the concave inner sides  63  of the jaws  64  are provided by the screw threads of bore  74 , to grip the cable. 
     As best shown in FIG. 5, a cable channel  80  which opens downwardly extends for the full length of the device  10  to permit engagement with the cable and passage of the cable through the device  10 . The gripper housing  62  is bolted to the gripper mounting flange  18  by four bolts  82  (only one shown in FIGS.  1  and  2 ), which extend through holes  85  in the flange  18  and are threaded into tapped holes  83  in the base end  87  of the housing  62  (which includes plates  73 ), which is the end of the housing  62  closest to the base ends  24  of the cylinders  12  and  14 . 
     The bolts  82  also secure a handle mounting flange  84  to the gripper mounting flange  18 . The handle mounting flange  84  is welded to a tubular handle  86  which extends longitudinally with respect to the tensioner  10 , parallel to the central axis of the tensioner  10  and above the cylinders  12  and  14 . The handle  86  is closed at its base end by a cap  88 , which may be vented to permit air to enter the handle  86 , and is closed at its rod end by a cap  90  having a central hole through which an auxiliary spring rod  92  extends for sliding movement relative to the cap  90 . 
     The spring rod  92  is biased into the retracted position by a compression spring  94 . A flange or plunger  96  is fixed at the base end of the rod  92  for the base end of the spring  94  to bear against and the rod end of the spring bears against the cap  90 . The rod end of the rod  92  is secured by a screw  98  to a flange  100  which is bolted by bolts  102  to a yoke  104  that is bolted to both rods  30  via bolt holes  91  (FIG.  5 ). Alternatively, the rod end of the rod  92  could extend through the flange  100  and be threaded so as to be secured by a nut to the flange  100 . Thus, as the device  10  is extended, the spring  94  becomes compressed so as to bias the rod  92  into the retracted position. 
     The bolts  102  also secure a plunger manifold  106  to the yoke  104 . A seat  108  is bolted on the opposite side of the yoke  104  from the manifold  106 . As shown in FIG. 5, a plunger  110  is reciprocable in the seat  108  and is biased in an extended position by a pair of springs  112  which are contained in bores  114  in the plunger manifold  106 . The springs  112  are compression springs which act between the plunger manifold  106  and a flange  116  of the plunger  110  so as to bias the plunger  110  in the extended position relative to the seat  108 . The end of the plunger  110  acts against the face of the grommet which holds the cable under tension in the concrete slab. When the cable is pulled through the grommet by the device  10 , the grommet acts against the end face of the plunger  110  to move it into a retracted position in which the grommet permits the cable to slide relative to it so that the cable can be tensioned. However, the plunger  10  maintains a biasing force on the grommet tending to move the grommet into the engaged position in which it bites into the cable and holds the cable under tension. 
     As an alternative, the springs  112  can be replaced with hydraulic plungers or pistons and hydraulic pressure applied to the back side of the plungers via ports  120  in the plunger manifold  106  so as to positively seat the grommet so that the engagement of the grommet with the cable is made fast after a tensioning operation.