US3638909A

US3638909A - Gripping means

Info

Publication number: US3638909A
Application number: US89386A
Authority: US
Inventors: Herbert Oliver Richard Dew
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-11-13
Filing date: 1970-11-13
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01

Abstract

In a gripping means comprising a gripping jaw, or a pair of gripping jaws, mounted in a slot in a support means, said slot having an open mouth into which an object to be gripped can be entered for engagement by the gripping jaw or jaws and opposed plane walls converging towards said open mouth, the or each gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that the gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface and spring means is provided normally urging the outer portion of the inwardly facing surface of the or each gripping jaw in a direction towards the object to be gripped. The gripping means is particularly suitable for use in withdrawing piles from the ground. It may also be used in quickrelease shackles and tensioning devices.

Description

United States Patent Dew [ Feb. 1, 1972 [54] GRIPPING MEANS [72] Inventor: Herbert Oliver Richard Dew, Ross, George Street, Hintlesham, Ipswich, England [22] Filed: Nov. 13, 1970 [21] Appl. No.1 89,386

[52] US. Cl. ..254/29 A, 24/263 SW [51] Int. Cl ..E2lb 19/00 [58] Field of Search ..254/29, 29 A; 24/263 R, 263 BW,

24/263 SB, 263 C, 263 HW, 264

Primary Examiner,Andrew R. Juhasz Assistant Examiner-David R. Melton Attorney-Michael S. Striker [5 7] ABSTRACT In a gripping means comprising a gripping jaw, or a pair of gripping jaws, mounted in a slot in a support means, said slot having an open mouth into which an object to be gripped can he entered for engagement by the gripping jaw or jaws and opposed plane walls converging towards said open mouth, the or each gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that the gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface and spring means is provided normally urging the outer portion of the inwardly facing surface of the or each gripping jaw in a direction towards the object to be gripped.

23 Claims, 8 Drawing Figures PATENTED FEB 11972 3.838.909 sumac? 3 BY 0% L A 7" TQRNE Y Pmmmrw 1m 3.538.909 SHEETZUF 3 BY d/M/ 6% A TTUWWE Y Wmmrm 1m 3.633.909

sum 30f 3 ATTONEY GRIPPING MEANS This invention relates to a gripping means of thekind comprising one gripping jaw or a pair of gripping jaws mounted in a support means and movable into a position to engage an object to be gripped. In particular, but not exclusively, the invention relates to a means for gripping a pile which has been driven into the ground, so that by exerting a tractive force on the gripping means the pile can be withdrawn from the ground.

For removing a pile which is embedded in the ground, it is known to employ a gripping means comprising a support means having an open-ended slot therein. This slot has a pair of opposed walls which are plane and inclined at an acute angle A to one another, these walls converging towards each other in the direction away from the bottom ofthe slot. Within the slot there is mounted a pair of gripping jaws of generally wedge shape, the wider ends of the gripping jaws being disposed near to the bottom of the slot and the outwardly facing and inwardly facing surfaces of each jaw being inclined to one another at an angle approximately equal to A/2.

With such a gripping means, it will be appreciated that if the wedge-shaped gripping jaws are moved more deeply into the slot while their outwardly facing surfaces are maintained in contact with said inclined walls of the slot then the spacing apart of the inwardly facing surfaces of the gripping jaws will be increased. Conversely, if the gripping jaws are moved in the direction away from the bottom of the slot, their inwardly facing surfaces will be brought closer together until eventually they abut one another.

In use of the above described gripping means for removing a pile from the ground, the support means is lowered onto the upper end portion of the pile with the open mouth of the slot facing downwards, so that the upper end portion of the pile enters the slot and is received between the pair of gripping jaws. If an upwardly directed force is now exerted on the support means, for example employing a crane, the gripping jaws move relatively to the support means in the direction causing the inwardly facing surfaces of the jaws to grip the pile. As the upwardly directed force on the support means increases, the gripping jaws grip the pile more and more tightly due to the wedging action between the outwardly facing surfaces of the gripping jaws and the inclined walls of the slot. By a suitable choice of the angle A, the grip exerted on the pile can be sufficiently great for the pile to be withdrawn from the ground when the support means is raised. In general, the smaller the angle A is, the greater will be the grip exerted on the pile by .the gripping jaws.

When the pile has been withdrawn, however, it is usually an extremely difficult and tedious task to release the gripping jaws from the pile, and in general the smaller the angle A is, the greater the difficulty becomes.

Increasing the angle A will facilitate release of the gripping jaws from the withdrawn pile, but as the angle A is increased the risk of slipping occurring between the pile and the gripping jaws during the pile-withdrawing operation is also increased. This increases the time taken to withdraw a pile and results in damage both to the pile and to the gripping jaws.

An object of the present invention is to provide an improved gripping means of the kind referred to.

According to one aspect of the invention, a gripping means comprising a gripping jaw mounted in a slot in a support means said slot having an open mouth into which an object to be gripped can be entered for engagement by the gripping jaw and opposed plane walls converging towards said open mouth, is characterized in that the gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that the gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface, and spring means normally urging the outer portion of the inwardly facing surface of the gripping jaw in a direction towards the object to be gripped.

In this specification the terms outer" and inner when used in relation to surfaces or ends of the gripping jaw mean, respectively, surfaces or ends lying close to or remote from said open mouth of the slot when the gripping jaw is wholly within the slot.

Preferably, there are two gripping jaws in the slot and according to this aspect of the invention a gripping means comprising a pair of gripping jaws mounted in a slot in a support means, said slot having an open mouth into which an object to be gripped can be entered for reception between the gripping jaws and opposed plane walls converging towards said open mouth, is characterized in that each gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that each gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface, and spring means normally urging the outer portions of the inwardly facing surfaces of the gripping jaws towards each other.

The slot is the support means may be open ended. A hole communicating with the slot may extend right through the support means with the axis of the hole passing through the open mouth of the slot, so that an object to be gripped can, if necessary, extend right through the support means.

Preferably, the cross-sectional shape of the gap between the opposed walls of the slot, in planes perpendicular to the axis of the slot, are rectangular.

The inwardly facing surface of the or each gripping jaw may be lined with material to improve their frictional grip and/or prevent damage to the object to be gripped.

Preferably, the spring means comprises a leaf spring and in the case of a gripping means with two jaws the leaf spring has two limbs each limb being interposed between one of said opposed walls of the slot and the inner and outer portions of the outwardly facing surface of a respective gripping jaw. The leaf spring may consist of a single leaf or a plurality of nested leaves.

When the gripping means according to the invention is used as a pile-withdrawing device, the angle B is made equal to or substantially equal to half the angle A at which the opposed walls of the slot converge and the angle A preferably is from 18 to 23. When the angle A is 18, a suitable value for the angle C is from 1 1 to 14, preferably 12.

Various embodiments of gripping means in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which FIG. 1 is a schematic sectional elevation of a first embodiment of a gripping means intended for use in withdrawing a pile from the ground,

FIG. 2 is a sectional view taken on the line II-II of FIG. 1, except that the right-hand half of this Figure shows a modified construction of a support means and a gripping jaw associated therewith, 5

FIG. 3 is a view similar to FIG. 1, but showing the gripping jaws in a different position compared with FIG. 1,

FIGS. 4 and 5 are views similar to FIGS. 1 and 2, respectively, of a second embodiment of a gripping means intended for use in withdrawing a pile from the ground, FIG. 5 being a sectional view taken on the line V-V of FIG. 4 except that the right-hand half of FIG. 5 shows a modified construction of a support means and a gripping jaw associated therewith,

FIG. 6 is a schematic sectional elevation of a third embodiment of a gripping means intended for use in withdrawing a pile from the ground,

FIG. 7 is a schematic sectional elevation of a quick-release shackle incorporating a gripping means, and

FIG. 8 is a schematic sectional elevation of a tensioning device incorporating a gripping means.

The gripping means shown in FIG. 1 and the left-hand half of FIG. 2 comprises a support means 1, for example a forged steel block, having an open-ended slot 2 formed therein. The slot 2 has opposed, accurately machined plane walls 3, 4 which are inclined to one another at an angle A and converge towards the open mouth 5 of the slot. The walls 3, 4 are symmetrically disposed with respect to a plane WW disposed at right angles to the plane of the paper and at right angles to the plane surface 6 ofthe support means 1. Furthermore, the walls 3, 4 are disposed so that the cross-sectional shape of the gap between the walls, in planes perpendicular to the axis of the slot, is rectangular. The support means 1 is provided with any suitable means (not shown) for example an apertured lug or shackle, by means of which it can be lifted by a hoisting device, for example a crane.

Within the slot 2 are two

identical gripping jaws

7, 8 of double wedge shape. The outwardly facing surface of each of these jaws has a recess 16 formed therein, the bottom of the recess being formed by a plane outer portion 9 and a plane inner portion 10, the plane portion 9 being inclined to the plane portion 10 at an obtuse angle D. The inwardly facing surface of each of the

jaws

7, 8 has a plane outer portion 11 and a plane inner portion 12, these two portions being inclined to one another at an obtuse angle E. The portions 9 and 10 of the outwardly facing surfaces and the

portions

11 and 12 of the inwardly facing surfaces of the jaws are accurately machined. The angles D and E are chosen such that the acute angle B between the surface portions 9 and 12 is equal to A/2 and the acute angle C between the surface portions 10 and II is greater than A/2. Furthermore, the lengths of the portions 9-12 are chosen such that the vertex F of the angle D is closer to the surface 6 than the vertex G of the angle E.

A leaf spring 13 bent into substantially U-shape is mounted in the slot 2 with its limb l4 interposed between the jaw 7 and the wall 3 and its limb 15 (shown partly broken away in FIGS. 1 and 2) interposed between the jaw 8 and the wall 4, these limbs being received in the recesses 16 formed in the outwardly facing surfaces of the jaws. Although the spring 30 is shown as having a single leaf, it will be appreciated that it can have a plurality of rested leaves.

FIG. 1 shows the situation when the support means I is lowered on to a pile 17 which it will be assumed has its lower end portion (not shown) embedded in the ground. The upper end portion of the pile enters the slot 2 between the

gripping jaws

7, 8 and the latter are held by the spring 13 in the position in which the outer portions 11 of the inwardly facing surfaces of the jaws engage the pile. If now the support means 1 is raised by a force acting in the direction of the arrow X the jaws rotate against the action of the spring limbs l4, l5 and the inner portions I2 of the inwardly facing surfaces of the jaws grip the pile and the outer portions 9 of the outwardly facing surfaces of the jaws force the spring limbs l4, 15 against the walls 3, 4, respectively of the slot 2, see FIG. 3. The effective wedge angle of the jaws 7, Sis now the angle A/2 and continued upward movement of the support means 1 results in the gripped pile being withdrawn from the ground.

When the pile 17 has been withdrawn from the ground, the spring 14 reasserts itself and rocks the

jaws

7, 8 back to their positions shown in FIG. 1. The effective wedge angle of the jaws is now greater than the angle A/2, so facilitating release of the pile from the gripping means.

In the embodiment shown in the drawing the angle A is equal to 18, the angle B is 9 and the angle C is 12.

The right-hand portion of FIG. 2 shows a modified form of support means 1a and an associated jaw 8a of modified crosssectional shape. The jaw 8a differs from the jaw 8 in that it has outwardly facing flanges 18 which are received in relieved portions 19 of the support means la to prevent lateral movement of the jaw in the slot 2. The jaw 7 would, of course, be similarly modified.

In the gripping means of FIGS. 1 to 3, the vertex F of the angle D is always closer to the surface 6 then the vertex G of the angle E. This is essential in the case ofa gripping means in which easy return of thejaws from the position of FIG. 3 to the position of Flg. l is required after use of the gripping means, for example when the gripping means is employed for withdrawing piles. In some applications of the gripping means according to the invention, however, an overcenter gripping action is desirable. This is achieved in the gripping means of FIGS. 1 to 3 by shaping the jaws so that in the FIG. 1 position the vertex F is closer to the surface 6 than the vertex G, but that in the FIG. 3 position the vertex G is closer to the surface 6 than the vertex F. To enable this to occur, a recess is provided in each of the walls 3 and 4, these recesses being so dimensioned as to allow local deflection 0f the

spring limbs

14, 15 intermediate their ends. A suitable recess for this purpose is shown in dotted lines in the wall 3 in FIG. 1, this recess being designated by the numeral 20.

The gripping means shown in FIGS. 4 and 5 are similar to those shown in FIGS. 1-3, except that the leaf spring 13 of FIG. 1-3 is replaced by a pair of springs 13a, 13b made from steel rod of circular cross section. These springs 13a, 13b are located in recesses 21 in the jaws 7, 8 (or 8a). It will be appreciated that in this embodiment of the gripping means the outwardly facing plane surface portions 9a and 10a of the jaws 7, 8 (or 8a) make direct contact with the slot walls 3, 4, respectively. These embodiments of the gripping means are suitable for applications where metal seizure between the jaws and the walls of the slot is highly improbable.

The gripping means described above with reference to FIGS. 1 to 5 all have two gripping jaws, but it will be appreciated that one of the jaws may be omitted to provide a gripping means with a single jaw. One embodiment of such a gripping means is shown in FIG. 6 and is a modified form of the gripping means of FIGS. 1 to 3. Parts of the gripping means of FIG. 6 which are similar to those of the gripping means of FIGS. 1 to 3 have been designated by the same reference numerals with the addition ofa prime. In FIG. 6 the support means 1 has an open-ended slot 2 formed therein. The slot 2 has opposed, accurately machined plane walls 3, 4 which are inclined to one another at an angle A and converge towards the open mouth 5 of the slot. The wall 4' is disposed parallel to a plane WW disposed at right angles to the plane of the paper and at right angles to the plane surface 6 of the support means 1. Furthermore, the walls 3, 4 are disposed so that the cross-sectional shape of the gap between the walls, in planes, perpendicular to the axis of the slot, is rectangular. The support means 1 is provided with any suitable means (not shown) for example an apertured lug or shackle, by means of which it can be lifted by a hoisting device, for example a crane.

Within the slot 2 is a gripping jaw 7 of double wedge shape. The outwardly facing surface of the jaw 7 has a recess 16' formed therein, the bottom of the recess being formed by a plane outer portion 9' and a plane inner portion I0, the plane portion 9 being inclined to the plane portion 10 at an obtuse angle D. The inwardly facing surface of the jaw 7 has a plane outer portion 11' and a plane inner portion 12, these two portions being inclined to one another at an obtuse angle E. The portions 9 and 10 of the outwardly facing surface and the portions 11' and 12 of the inwardly facing surface of the jaw are accurately machined. The angles D and E are chosen such that the acute angle B between the surface portions 9 and 12 is equal to A and the acute angle C between the

surface portions

10 and 11 is greater than A. Furthermore, the lengths of the portions 9-12 are chosen such that the vertex F of the angle D is closer to the surface 6' than the vertex G of the angle E.

A leaf spring 13 bent into substantially U-shape with

limbs

14 and 15 is mounted in the slot 2' with its limb 14 (shown partly broken away in FIGS. 1 and 2) interposed between the jaw 7 and the wall 3 this limb being received in the recess 16.

The manner of operation of the gripping means of FIG. 6 is similar to that of FIGS. 1 to 3.

The gripping means described above with reference to FIGS. 1-6 are intended primarily for withdrawing piles from the ground. It will, however, be appreciated that the same gripping means can be employed for lifting objects and transporting them from one place to another. When it is intended to use the gripping means for lifting fragile or easily damaged objects, for example sheets of glass, it is desirable to line the inwardly facing surfaces of the jaws 7, 8 (or 8a) with a soft material, for example rubber.

FIG. 7 illustrates the employment of the gripping means of FIGS. 4 and 5 in a quick-release shackle intended for pitching sheet piles into position preparatory to pile driving. Some existing quick-release shackles for this purpose require a hole to be drilled in each pile adjacent to the end which is uppermost during the pile-driving operation, the shackle being engaged with the pile using this hole. The quick-release shackle shown in FIG. 7 avoids the necessity for drilling each pile.

The quick-release shackle shown in FIG. 7 includes a support means lb,

jaws

7, 8 and springs 13b similar to either of the gripping means of FIGS. 4 and 5. A hole 25 in the support means lb communicates with the slot 2 and houses a block 26 provided with ratchet teeth 27 on its external surface. A spring-loaded detent 28 slidably mounted in the support means lb engages the ratchet teeth 27. A screw-threaded rod 29 is threadedly engaged in a bore 30 passing through the block 26, the axes of the bore 30 and the hole 25 being substantially coincident and disposed substantially in the plane of symmetry W-W of the slot 2. Externally of the support means 1b the rod 30 is provided with a handwheel 31. Inside the slot 2, the rod 30 is connected to a member 32 provided with projections 33, 34 which engage the inner ends of the

jaws

7, 8 respectively. The support means lb is provided with an arm 35 by means of which the support means can be connected to a hoisting device, for example to the hook of a crane.

In use of the quick-release shackle shown in FIG. 7, the

jaws

7, 8 are engaged with the end portion of a pile l7 and the jaws are then moved in the direction of the arrow Y, by the rotation of the handwheel 31, so as to grip the pile. The ratchet and detent mechanism 27, 28 allows the shackle to accommodate piles of different thickness. When the

jaws

7, 8 are gripping -'the pile, the support means is lifted by means of a hoisting device (not shown) connected to the arm 35, and the pile is pitched vertically into the desired position. Any fouling of the pile on other objects, or any upward thrust exerted on the pile, during this pitching procedure does not cause any slackening of the grip of the

jaws

7, 8 on the pile, since the member 32 acts as a stop means to limit movement of the

jaws

7, 8 into the slot 2. When the pile is pitched in the desired position the shackle is released by withdrawing the detent 28 from the ratchet teeth 27 and then lowering the shackle, so enabling the jaws to rock on their vertices F and then moves more deeply into the slot 2 and thus release their grip on the pile.

It will of course, be appreciated that the gripping means of FIGS. 1-3 may be used, instead of the gripping means of FIGS. 4 and 5, in the quick-release shackle of FIG. 7, the member 32 and/or the spring 13 being suitably shaped so that they do not interfere with each other.

FIG. 8, illustrates a tensioning device which includes the gripping means of FIGs. l-3. In this device a support means 10, which houses the

jaws

7, 8 and the leaf spring 13, is slidably mounted in a casing 40 and at its end remote from its surface 6 the support means is provided with a screw-threaded adjustment means in the form of screw-threaded rod 41. The axis of the rod 41 lies substantially, in the plane of symmetry -W of the slot 2 and the support member is slidable in the casing 40 in a direction parallel to the axis of the rod 41. The rod 41 passes through a boss 42 on an end cover 43 of the casing 40 and receives a nut 44 externally of the casing. Between the nut 44 and the boss 42 there is arranged a thrust bearing 45 surrounding the rod 41. A handle 46 is provided on the nut 44 for the purpose of facilitating turning of the nut. An indicating device 47, shown purely schematically, is connected to the free ends ofthe limbs l4, l5 ofthe spring 13 for the purpose of indicating the separation of the ends of these limbs.

In FIG. 8 the tensioning device is shown employed in tensioning a rod 48, for example a reinforcing rod in a concrete object 49. The rod 48 has a screw-threaded portion 50 which receives a nut 51. A washer 52 is interposed between the nut 51 and the object 49. Adjacent to the screw-threaded portion 50, the rod 48 has an axially extending integral end portion 53.

In use of the tensioning device shown in FIG. 8, the portion 53 of the rod 48 is introduced between the

jaws

7, 8 and a flanged end 54 of the casing is applied against the object 49. The support means 1c is then moved in the direction away from the object 49, by rotation of the nut 44. During the initial stages of rotation of the nut 44 the support means 10 moves relative to the spring 13 so that the inner ends of the spring limbs engage against the walls of the slot 2. At the same time the

jaws

7, 8 grip the rod portion 53 and apply a tensile force to the rod 48. As rotation of the nut 44 is continued, the

jaws

7, 8 gradually force the

spring limbs

14, 15 apart as the tensile force exerted on the rod 48 increases. The indicating device 47, which measures the separation of the free ends of the

spring limbs

14, 15 is calibrated in terms of the load exerted on the rod 48. When the indicating device 47 shows that rod 48 has been tensioned to the desired degree, the nut 51 is tightened against the object 49 and then the tensioning devices released by turning the nut 44 in the direction allowing the support means 10 to approach the object 49. It will be appreciated that the maximum load indicated by the device 47 is achieved before the outer ends of the

springs

14, 15 bear against the walls of the slot 2.

What is claimed is:

1. A gripping means comprising a gripping jaw mounted in a slot in a support means, said slot having an open mouth into which an object to be gripped can be entered for engagement by the gripping jaw and opposed plane walls converging towards said open mouth, characterized in that the gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that the gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface and in that spring means is provided normally urging the outer portion of the inwardly facing surface of the gripping jaw in a direction towards the object to be gripped.

2. A gripping means comprising a pair of gripping jaws mounted in a slot in a support means, said slot having an open mouth into which an object to be gripped can be entered for reception between the gripping jaws and opposed plane walls converging towards said open mouth, characterized in that each gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that each gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface, and spring means normally urging the outer portions of the inwardly facing surfaces of the gripping jaws towards each other.

3. A gripping means according to claim 2, in which the cross-sectional shape the gap between the walls, in planes perpendicular to the axis of the slot is rectangular.

4. A gripping means according to claim 3, in which the inner and outer portions of the outwardly facing surface of the or each gripping jaw have plane surface portions.

5. A gripping means according to claim 2, in which the spring means comprises a leaf spring having two limbs, each limb being interposed between one of said opposed walls of the slot and the inner and outer portions of the outwardly facing surface ofa respective grippingjaw.

6. A gripping means according to claim 5, in which the leaf spring consists ofa single leaf or a plurality of nested leaves.

7. A gripping means according to claim 2, in which a hole communicating with the slot extends right through the support means, the axis of the hole passing through the open mouth of the slot.

8. A gripping means according to claim 2, in which the angle B is made equal to or substantially equal to half the angle A at which said opposed walls of the slot converge.

9. A gripping means according to claim 8, in which the angle A is from 18 to 23.

10. A gripping means according to claim 9, in which the angle A is l8, the angle B is 9 and the angle C is from 1 1 to l4.

11. A gripping means according to claim 10, in which the angle C is 12.

12. A pile-withdrawing means comprising a gripping jaw mounted in a slot in a support means, said slot having an open mouth into which a pile to be withdrawn from the ground can be entered for engagement by the gripping jaw and opposed plane walls converging towards said open mouth, characterized in that the gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that the gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface and in that spring means is provided normally urging the outer portion of the inwardly facing surface of the gripping jaw in a direction towards the pile to be withdrawn.

13. A pile-withdrawing means comprising a pair of gripping jaws mounted in a slot in a support means, said slot having an open mouth into which a pile to be withdrawn from the ground can be entered for reception between the gripping jaws and opposed plane walls converging towards said open mouth, characterized in that each gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that each gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface, and spring means normally urging the outer portions of the inwardly facing surfaces of the grippingjaws towards each other.

14. A pile-withdrawing device according to claim .13, in which said support means is provided with an apertured lug or shackle by means of which the support means can be lifted by a hoisting device.

15. A uick-release shackle comprising a gripping jaw mounted in a slot in a support means, said slot having an open mouth into which an object to be hoisted can be entered for engagement by the gripping jaw and opposed plane walls converging towards said open mouth, and means on the support means enabling connection of the support means to a hoisting device, characterized in that the gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that the gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface and in that spring means is provided normally urging the outer portion of the inwardly facing surface of the gripping jaw in a direction towards the object to be hoisted.

16. A quick-release shackle comprising a pair of gripping jaws mounted in a slot in a support means, said slot having an open mouth into which an object to be hoisted can be entered for reception between the gripping jaws and opposed plane walls converging towards said open mouth, and means on the support means enabling connection of the support means to a hoisting device, characterized in that each gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that each gripping jaw has the inner portions ofits inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface, and spring means normally urging the outer portions of the inwardly facing surfaces of the grippingjaws towards each other.

17. A quick-release shackle according to claim 16, comprising an adjustable stop means carried by the support means, which stop means limits the movement of the jaws in the direction away from said open mouth of the slot.

18. A quick-release shackle according to claim 17, in which said adjustable stop means is releasably carried in the support means.

19. A quick-release shackle according to claim 18, in which the adjustable stop means is releasably carried in the support means by a detent and ratchet mechanism.

20. A tensioning device comprising a casing, a support means slidably mounted in the casing, a gripping jaw mounted in a slot in said support means, said slot having an open mouth into which an object to be tensioned can be entered for engagement by the gripping jaw and opposed plane walls converging towards said open mouth, and means for adjusting the position of the support means in the casing, characterized in that the gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that the gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface and in that spring means is provided normally urging the outer portion of the inwardly facing surface of the gripping jaw in a direction towards the object to be tensioned.

21. A tensioning device comprising a casing, a support means slidably mounted in the casing, a pair of gripping jaws mounted in a slot in a support means, said slot having an open mouth into which an object to be tensioned can be entered for reception between the gripping jaws and opposed plane walls converging towards said open mouth, and means for adjusting the position of the support means in the casing, characterized in that each gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that each gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface, and spring means normally urging the outer portions of the inwardly facing surfaces of the gripping jaws towards each other.

22. A tensioning device according to claim 21, comprising screw-threaded adjustment means for adjusting the position of the support means in the casing.

23. A tensioning device accordin g to claim 21, comprising a

Claims

5. A gripping means according to claim 2, in which the spring means comprises a leaf spring having two Limbs, each limb being interposed between one of said opposed walls of the slot and the inner and outer portions of the outwardly facing surface of a respective gripping jaw.

6. A gripping means according to claim 5, in which the leaf spring consists of a single leaf or a plurality of nested leaves.

9. A gripping means according to claim 8, in which the angle A is from 18* to 23* .

10. A gripping means according to claim 9, in which the angle A is 18*, the angle B is 9* and the angle C is from 11* to 14* .

11. A gripping means according to claim 10, in which the angle C is 12* .

13. A pile-withdrawing means comprising a pair of gripping jaws mounted in a slot in a support means, said slot having an open mouth into which a pile to be withdrawn from the ground can be entered for reception between the gripping jaws and opposed plane walls converging towards said open mouth, characterized in that each gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that each gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface, and spring means normally urging the outer portions of the inwardly facing surfaces of the gripping jaws towards each other.

14. A pile-withdrawing device according to claim 13, in which said support means is provided with an apertured lug or shackle by means of which the support means can be lifted by a hoisting device.

15. A quick-release shackle comprising a gripping jaw mounted in a slot in a support means, said slot having an open mouth into which an object to be hoisted can be entered for engagement by the gripping jaw and opposed plane walls converging towards said open mouth, and means on the support means enabling connection of the support means to a hoisting device, characterized in that the gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that the gripping jaw has the inner portion of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface and in that spring means is provided normally urging the outer portion of the inwardly facing surface of the gripping jaw in a direction towards the object to be hoisted.

16. A quick-release shackle comprising a pair of gripping jaws mounted in a slot in a support means, said slot having an open mouth into which an object to be hoisted can be entered for reception between the gripping jaws and opposed plane walls converging towards said open mouth, and means on the support means enabling connection of the support means to a hoisting device, characterized in that each gripping jaw has an inwardly facing surface comprising inner and outer portions inclined to one another at an obtuse angle and an outwardly facing surface comprising inner and outer portions also inclined to one another at an obtuse angle such that each gripping jaw has the inner portions of its inwardly facing surface inclined to the outer portion of its outwardly facing surface at an angle B which is smaller than the angle C between the outer portion of its inwardly facing surface and the inner portion of its outwardly facing surface, and spring means normally urging the outer portions of the inwardly facing surfaces of the gripping jaws towards each other.

23. A tensioning device according to claim 21, comprising a tension-indicating device.