GB2546768A

GB2546768A - Self aligning strand jack mounting

Info

Publication number: GB2546768A
Application number: GB1601568.7A
Authority: GB
Inventors: Frederick Stokes Kevan; Conrad Stokes Andrew
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-01-28
Filing date: 2016-01-28
Publication date: 2017-08-02
Also published as: GB201601568D0

Abstract

A self-aligning mounting for a strand jack 1 has at least one axis of rotation allowing the strand jack to align itself in the direction of the load 5. The axes of rotation 13a, 13b are positioned at the point of entry/exit of the strands and are normal to the axis of the jack 3. The mounting may be a trunnion or a gimbal. The jack may be mounted on a cylindrical or spherical surface or it may be mounted in a cradle 12 suspended from a pin or pins above the main body of the jack.

Description

Title

Self-Aligning Strand Jack Mounting

Background

Strand jacks are well known and are used to tension strands of wire, such as cables and reinforcement bars, and to move loads. Usually they are used to apply tension to the strands, drawing them progressively through the jack but they can also be used to lower a load under the influence of gravity in a controlled manner by paying out the strands in a reverse direction to the norm. The strands are commonly high tensile steel of 15 mm to 18 mm in diameter.

For a strand jack to function correctly without causing a reduction in capacity or damage to the jack components or to the strands, it is essential that the axis of the jack is aligned with the load vector, the direction of pull. So long as the load vector does not change direction significantly during the operation of the jack, the jack can be aligned at the outset using all manner of devices such as wedges. However, if the load vector changes direction significantly during an operating cycle, damage and or failure will result when the magnitude of the load is high.

This can be overcome by known means such as mounting the jack on a platform that can be tilted but such a device must be powered by external means as it will not be self-aligning. Such mechanisms require control or some sort and so are inherently at a greater risk of failure or malfunction. A self-aligning strand jack mounting is highly desirable for use when the load direction will change during operation and is of high magnitude, as it reduces the risk of malfunction, failure or damage. Small magnitude loads, such as that due to the self-weight of the strands, can usually be accommodated without significant damage and it is only the proportionally higher magnitude loads which occur during tensioning or when under load that are of concern and which are addressed by the present invention.

Statement of invention

To overcome this problem the present invention proposes a self-aligning strand jack mounting that includes one or more points or axes of rotation located on the opposite side of the exit face of the jack to the side where the load is applied. The exit face is the plane normal to the axis of the jack where the load strands are no longer constrained by the jack components. It is advantageous that the centres of rotation are as remote from this face as is practical in order to increase the moment arm and thus the torque available to overcome resistance to rotation due to friction, etc.

Advantages

It will be possible to use a strand jack for a purpose that includes a change of direction of the load vector during the loaded cycle without the need to recourse to a control mechanism.

Introduction to drawings

Figure 1 shows a vertical elevation of a strand jack [Ϊ] supported on a firm, flat surface [2] with an axis [3] is shown being used to tension a number of strands @ that are loaded in a direction [5] that aligns with the with the jack axis [3]. This is a satisfactory operating mode.

Figure 2 shows the same jack [Ϊ] viewed from below the supporting surface [2] and identifies the point of exit of a strand @ from the jack [β].

Figure 3 shows the same jack orientated with it is axis |3] horizontal and supported on a vertically inclined, firm, flat surface [2] such as a wall.

Figure 4 shows the jack [Ϊ] supported on a firm, flat surface [2] with an axis [3] being used to tension a number of strands @ that are now loaded in a direction |t] that does not align with the jack axis [3]. This can result in a very tight bend radius in the strands [§| resulting in damage or malfunction.

Figure 5 shows the jack |l] as in figure 4 but viewed from below.

Figure 6 shows the same strand jack [Ϊ] suspended in a trunnion [9] at a distance 10| from the point of exit. Rotation of the jack about the trunnion axis [IT] is possible.

Figure 7 shows the jack [I] as in figure 6 but in a different elevation and with the jack [I] rotated about the trunnion axis [TT] relative to the supporting face [|| such that its axis [3] is aligned with load vector [5].

Figure 8 shows a strand jack [Ϊ] mounted in a frame [12] that is part of a mechanism with two axes of rotation |l3a| and |l3b| between the jack and the mechanism support face [1¾. This also shows the large radius bend [Ϊ5] that might occur in the free, unloaded ends of the strands.

Detailed description

This invention can be achieved by; altering the interface between the jack [I] and the support surface [2] from flat to cylindrical, for rotation within a plane, or spherical for rotation in any direction; or by mounting the jack [I] on or in a device that can rotate about a pin or trunnion [§, for rotation within a plane, or a pair of pins for rotation about two axes |l3a| and |l3b|, or one or more gimbals for rotation about two or three orthogonal axes; but in all instances these axes or points of rotation are remote [ϊο] from the point of exit of a strands from the jack § and on the opposite side of this point |β| to the side where the load vector [5] is applied.

For clarity, a distinction must be made between the large radius bend [Ϊ5| that might occur in the free, unloaded ends of the strands due to their self-weight and the tight radius bends that will occur in the loaded ends [§] if the load is not aligned with the axis of the jack. The former [Ϊ5| can be easily mitigated for and or accepted without damage, malfunction or loss of capacity whereas the latter [δ] cannot.

Claims

1. A self-aligning mounting for a strand jack that includes one or more points or axes of rotation located on the opposite side of a plane, located at the point of exit or entry of the loaded strands from or to the jack and normal to the axis of the jack, to the side where the load is applied.

2. A self-aligning mounting for a strand jack according to claim 1, in which the jack is mounted in a trunnion.

3. A self-aligning mounting for a strand jack according to claim 1, in which the jack is mounted in one or more gimbals.

4. A self-aligning mounting for a strand jack according to claim 1, in which the jack is mounted on a cylindrical surface with freedom of rotation about an axis.

5. A self-aligning mounting for a strand jack according to claim 1, in which the jack is mounted in on a spherical surface with freedom of rotation about two or more axes.

6. A self-aligning mounting for a strand jack according to claim 1, in which the jack is mounted in on a cradle suspended from a pin above the main body of the jack and with the pin orthogonally aligned with the axis of the jack.

7. A self-aligning mounting for a strand jack according to claim 6, in which the pin is in turn suspended from another pin that is orthogonally aligned with both the first pin and the axis of the jack.