GB2126981A - Improvements in or relating to grab bucket apparatus - Google Patents

Abstract

A grab (1) comprises a pulley system-type opening and closing mechanism having a standing block (5) and a running block (9) in the grab body (2) and actuated by two cables, whereby the first or suspension cable (17) is connected to the running block (9) and the second or pulley cable has one end anchored to a fixed part of the grab (1). A fixing arrangement comprises a means for fixing the suspension cable to the running block and which is constituted by a yoke (19), mounted so as to pivot about its point of fixing (20) to the said block and a means of guiding the pulley cable, which is integral with the yoke and which is constituted by a stirrup (21) and a pulley (22). The fixing arrangement acts to bring whichever of the two cables is taut into alignment with the vertical axis of symmetry of the grab. <IMAGE>

Description

SPECIFICATION Improvements in or relating to grab bucket apparatus Field of Invention The present invention relates to grab bucket apparatus, and concerns a suspension arrangement for a grab or grab bucket and also a grab or grab bucket apparatus incorporating such a suspension arrangement. The invention relates particularly to a suspension arrangement for a grab of the twin cable type, that is a grab having a suspension cable and a pulley cable for manipulating purposes.

Background to the Invention Grabs or grab buckets are used for excavating generally vertical shafts, holes or troughs in the ground, for example for the purpose of producing cast walls from successive panels. However, with known suspension devices used for these grabs it is not possible to produce a shaft having rectilinear, vertically sided walls, and this leads to deficiencies at the junction between individual panels with the result that it is not possible to obtain a cast wall in the ground which has adequate sealing and appearance characteristics.

The problem arises because with the known suspension devices for grabs or grab buckets it is not possible to check the position of the grab or grab bucket either during the descent of the grab into the shaft, or during the closing of the shells or troughs of the grab, in view of the fact that the device does not make it possible to position the taut manipulating cable along the vertical axis of symmetry of the grab or grab bucket.

It is accordingly an object of the present invention to solve these problems by proposing a grab or grab bucket of the twin cable type, which makes it possible to obtain a balanced suspension of the grab or grab bucket, no matter which cable is in taut condition.

The Invention According to the present invention there is provided a suspension arrangement for a grab or grab bucket comprising a pulley system-type opening and closing mechanism which is operated by two cables, a first or suspension cable being connected to the running block for the pulley system and a second or pulley cable one end of which is anchored to a fixed part of the grab or grab bucket, the arrangement comprising means for fixing the suspension cable to the running block said fixing means being pivotally mounted for pivotal movement relative to the running block about a fixing point, and means for guiding the pulley cable, the guide means being fixed relative to the fixing means to pivot therewith, the arrangement acting to maintain the two cables spaced from one another, and acting to bring either the suspension cable or the pulley cable respectively into alignment with the vertical axis of symmetry of the grab when the respective cable is in taut condition.

Thus, the forces exerted on the grab are applied along its vertical axis of symmetry and consequently make it possible to obtain a perfectly balanced suspension of the grab, during both lowering and digging operations. Thus, it is possible to check the position of the grab, during its lowering into the shaft and during the closing of the shells or troughs.

The fixing means preferably comprises a yoke mounted so as to pivot about a fixing spindle secured to the running block, and preferably also so as to pivot about a fixing spindle connected to the end of the suspension cable, the guidance means being constituted by a stirrup fixed to a lateral side of the yoke.

In order to permit a better guidance of the pulley cable, a sheath or pulley is preferably mounted so as to rotate freely in the aforementioned fixing yoke, the guidance means or stirrup maintaining the pulley cable in contact with said pulley.

Moreover, two guide rollers are desirably mounted on the running block of the grab, one on each side of the vertical axis of symmetry, in order to keep the pulley cable in the axis of symmetry of the grab and consequently bring about a new guidance point of the pulley cable in the axis of symmetry of the grab.

The arrangement according to the invention makes it possible to maintain the spacing of the two manipulating cables of a grab or a grab bucket, and by the pivoting of the means for fixing the suspension cable to the running block of the pulley system the cable is brought into the taut position in the axis of symmetry, leading to a perfectly balanced suspension of the grab or grab bucket without any risk of the two cables tangling.

The invention also relates to an apparatus more particularly intended for the excavation of vertical shafts in the ground, which comprises a grab or grab bucket equipped with a suspension arrangement in accordance with the present invention.

One preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 a side elevation, with parts broken away, illustrating a grab or grab bucket in an open position and incorporating a suspension arrangement according to the present invention; Figure 2 a view similar to Figure 1 showing the grab in a closed position; and Figure 3 a view diagrammatically illustrating the excavation of vertical shafts for producing a cast wall in the ground with a grab according to the invention.

Detailed Description of the Drawings Figures 1 and 2 illustrate a grab or grab bucket 1 of the twin cable type, comprising a fixed grab body 2 supporting a mechanism for the opening and closing of shells or troughs 3 of grab 1 , the shells 3 being mounted so as to pivot about two rotation shafts 4 supported by the grab body 2.

The mechanism for opening and closing the grab or grab bucket in the illustrated embodiment is constituted by a pulley system comprising a first standing block 5 fixed in the grab body 2 and a second running block 9 arranged for movement in the longitudinal direction of grab body 2.

The standing block 5 comprises a yoke 6 mounted in fixed manner on grab body 2 and supporting two pulleys 7, 8, e.g. sheaves, the rotation shafts 4 of the shells 3 being advantageously fixed to the lower end of yoke 6.

The running block 9 comprises a yoke 12 carrying two pulleys 13, 14 mounted symmetrically with respect to the vertical axis of symmetry 15 of the grab.

Each corner of the yoke 12 is equipped with a caster 10 which moves on rolling and guiding surfaces 11 fixed to grab body 2 in order to guide the movement of block 2 in a direction parallel to the vertical axis of symmetry of the grab.

The running block 9 is connected to shells 3 by arms 16, in the form of rods, in order to bring about the opening or closing of said shells by the displacement of block 9 in the grab body 2.

Moreover, and as can be seen in Figures 1 and 2, the rotation axis of pulleys 8, 7 is located in the vertical plane of symmetry of grab 1.

The pulley system is actuated by two cables, namely a first or suspension cable 1 7 connected to the running block 9 and a second or pulley cable 1 8 passing round pulleys 7, 8, 13, 14, one end of the second cable being fixed to the grab body 2.

The suspension cable 17 is fixed to yoke 1 2 of running block 9 by a fixing means constituted by a yoke 1 9 mounted so as to pivot about its fixing point 20 to yoke 12, and a guidance means 21 in the form of a stirrup, for maintaining the pulley cable 1 8 in a spaced apart position with respect to suspension cable 1 7. It is to be noted that fixing point 20 is also in the vertical axis of symmetry of grab 1, this axis also including the centre of gravity of the grab. The arrangement also comprises a pulley or roller 22 mounted in yoke 1 9 and cooperating with a stirrup 21 for guiding cable 18 and for maintaining it in a spaced apart position with respect to suspension cable 1 7.

Yoke 1 9 is connected to a suspension cable 1 7 by a fixing device pivoting about a fixing spindle 23 and in the form of a yoke-like member 24.

Pulleys 7, 8, 13, 14, 22 are preferably sheaves or grooved wheels in order in this way to permit a better guidance of the pulley cable 1 8. However, these pulleys can also be wheels with smooth surfaces in the form of rollers, while still being within the scope of the invention.

Finally, the arrangement includes two guide pulleys or rollers 25, 26 mounted on yoke 12 of block 9, one on each side of the vertical axis of symmetry 1 5 of the grab in order to guide the pulley cable and in this way form a second guidance point for said cable in order to maintain it in the axis of symmetry.

The operation of the suspension arrangement according to the invention can be clearly gathered from Figures 1 and 2. Thus, in Figure 1 which shows the grab in the open position, the pulley cable 1 8 is in the slack position, whilst the position cable 1 7 is in the taut position This brings about the pivoting of yoke 1 9, bringing it into alignment with the vertical axis of symmetry 1 5 of grab 1. Thus during the lowering of grab 1 into a vertical shaft, the grab is positioned automatically, under the action of its own weight, so that it is perfectly vertical.

When the shells 3 come into contact with the bottom of the vertical shaft 27, as illustrated in Figure 3, the suspension cable 1 7 is slackened, whilst the pulley cable 18 is pulled taut in order to bring about the closing of the shells 3. Tensioning of cable 1 8 automatically brings about the pivoting of yoke 1 9 through the action of cable 1 8 on pulley 22. Stirrup 21 brings cable 18 into the axis of symmetry of the grab and holds it there.

The cable is also held in this axis of symmetry by the second guidance point, formed by roller 26, as illustrated in Figure 2. Thus, throughout the shell closing operation, the force exerted on grab 1 is directed into its vertical axis of symmetry and consequently brings about no unbalance of said grab.

Thus, the suspension arrangement according to the invention brings about a balanced suspension of grab 1, in view of the fact that the cable on which a force is exerted is still located in the vertical axis of symmetry of the grab. Moreover, this arrangement makes it possible to obviate the risk of the two manipulating cables 17, 1 8 being entangled and consequently makes the operation of a grab or grab bucket more reliable.

As a result, it is possible to obtain by use of a grab or grab bucket apparatus incorporating a suspension arrangement according to the invention and as described hereinbefore, shafts which are vertical and rectilinear along their two orthogonal planes, so that walls cast on the ground with successive panels can be obtained.

Thus the wall obtained has a very good appearance and sealing properties, in view of the fact that the panels are aligned.

Clearly, the embodiment described hereinbefore has been given by way of example only, and the form of the pulley system, the number of pulleys, the device for guiding and displacing block 9 in body 12, etc can be modified in various ways.

Claims (7)

1. A suspension arrangement for a grab or grab bucket comprising a pulley system-type opening and closing mechanism which is operated by two cables, a first or suspension cable being connected to the running block for the pulley system and a second or pulley cable one end of which is anchored to a fixed part of the grab or grab bucket, the arrangement comprising means for fixing the suspension cable to the running block, said fixing means being pivotally mounted for pivotal movement relative to the running block about a fixing point, and means for guiding the pulley cable, the guide means being fixed relative to the fixing means to pivot therewith, the arrangement acting to maintain the two cables spaced from one another, and acting to bring either the suspension cable or the pulley cable respectively into alignment with the vertical axis of symmetry of the grab when the respective cable is in taut condition.

2. An arrangement according to claim 1, wherein the fixing means comprises a yoke mounted so as to pivot relative to a fixing spindle secured to the running block, the guidance means being constituted by a stirrup fixed to a lateral side of the yoke.

3. An arrangement according to claim 2, wherein the yoke is mounted so as to pivot relative to a fixing spindle connected to the end of the suspension cable.

4. An arrangement according to claim 2 or 3, wherein a pulley is mounted so as to rotate freely in the fixing yoke, the stirrup maintaining the pulley cable in contact with said pulley.

5. An arrangement according to any one of the preceding claims, wherein two guide rollers are mounted on the running block on either side of the vertical axis of symmetry of the grab, in order to form a second guidance point for the pulley cable in the vertical axis of symmetry of the grab.

6. A suspension arrangement for a grab or grab bucket, substantially as herein described with reference to, and as shown in, the accompanying drawings.

7. A grab or grab bucket apparatus for excavating vertical shafts, incorporating a suspension device in accordance with any one of the preceding claims.