Implements or apparatus for applying pushing or pulling force – Pipe or rod jack – Tie rod tensioner
Reexamination Certificate
1999-07-14
2001-05-01
Scherbel, David A. (Department: 3723)
Implements or apparatus for applying pushing or pulling force
Pipe or rod jack
Tie rod tensioner
C029S452000
Reexamination Certificate
active
06224036
ABSTRACT:
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.
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patent: 4746096 (1988-05-01), Donnell et al.
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patent: 716195 (1968-12-01), None
patent: 961759 (1957-03-01), None
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patent: 2091230 (1972-01-01), None
Gordon William J.
Prince George T.
Applied Power Inc.
Quarles & Brady LLP
Scherbel David A.
Shanley Daniel
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