GB2094393A

GB2094393A - Flexible coupling between inner and outer concentric member

Info

Publication number: GB2094393A
Application number: GB8107056A
Authority: GB
Original assignee: PERNAS CHARTER MANAGEMENT SDN
Current assignee: PERNAS CHARTER MANAGEMENT SDN
Priority date: 1981-03-06
Filing date: 1981-03-06
Publication date: 1982-09-15
Also published as: NL8200930A; AU8110782A; GB2094393B; DE3207762A1

Abstract

A flexible coupling has an outer bush 2, an intermediate bush 3 and an inner bush 1 coaxially located within one another. One layer 4 of elastomeric material is disposed between and bonded to bushes 1 and 3, and another layer 5 of elastomeric material is disposed between and bonded to bushes 2 and 3. Radial projections 7, 9 on flanges 6, 8 of the bushes 1, 2 and axial projections 10 on bush 3 can interengage to limit relative rotation of the bushes. The coupling can be employed for pivotally linking buckets of a dredge bucket chain. <IMAGE>

Description

SPECIFICATION Flexible coupling This invention relates to flexible couplings which may be used for coupling dredge buckets.

Dredgers are used in many parts of the world in numerous tasks which involve dredging material from the sea bed, river beds, lake beds and the like. The nature of these tasks is such that the dredge buckets which are used to bring up the material are subjected to very difficult working conditions from the silt, sand and gravel, for example, through which the buckets have to travel. Dredge buckets are connected in a continuous chain, there being a rotatable joint between each adjacent pair of buckets. The chain is driven by passing the buckets over a top tumbler which is driven, the tumbler generally having six or seven flat surfaces which bear against the flat underside of each bucket and which therefore transmit the driving force to the bucket chain in the same manner as a sprocket and chain.A six sided tumbler requires a rotation of 600 between adjacent buckets, and maintenance procedures on the dredger and its equipment require a further rotation of some 1 50, thus requiring a total rotational capability of 750 between adjacent buckets.

The rotatable joint between adjacent buckets generally takes the form of a metallic bush, usually manufactured in two halves out of austenitic manganese steel, attached within the back eye of one dredge bucket and a pin, usually of forged, or possibly cast, nickel-chrome-molybdenum steel, passing through the front eyes of the adjacent dredge bucket. Because of the construction of the bush, only one half thereof is subjected to wear, the non-wearing half being welded to the bucket back eye and'the wearing half being secured in position by mild steel wedges. The pin is formed with an L-shaped head and is secured in the bucket front eyes by means of a mild steel wedge which prevents the pin from rotating in the bucket front eyes.

The pin thus rotates within the bush without any form of lubrication and the joint is subjected to the abrasive action of the materials through which the buckets pass. This causes rapid wear of the rotating metal surfaces and necessitates regular replacement of the wearing half of the bushes and of the pins. Economically, this replacement is undesirable, but no better alternative has so far been proposed. Moreover, as the bearings wear, but before they are replaced, play develops in the bearings and the length of the bucket chain increases.The result of this is that the buckets, as they pass over the top tumbler, no longer fit exactly to the flats of the tumbler, thus causing wear on the bucket bases and on the tumbler flats and it is therefore necessary to attach packings to the tumbler, which involves manoeuvring large sheets of steel into place on the top tumbler and increases the down-time of the dredger.

According to the present invention there is provided a flexible coupling which comprises: an inner bush, an outer bush, and an intermediate bush, the three bushes being substantially coaxial and the intermediate bush being located radially between the inner bush and the outer bush; a first layer of elastomeric material positioned radially between the inner bush and the intermediate bush, the first elastomeric layer being bonded to the inner and intermediate bushes; a second layer of elastomeric material positioned radially between the intermediate bush and the outer bush, the second elastomeric layer being bonded to the intermediate and outer bushes; and interlocking projections arranged between the three bushes to limit the rotation of the inner bush relative to the intermediate bush and to limit the rotation of the outer bush relative to the intermediate bush, thereby limiting the rotation of the outer bush relative to the inner bush.

Such a construction eliminates metal-to-metal rotational contact between the bucket pin and the bucket eyes, indeed metal-to-metal rotational contact is completely eiiminated except for minor non-load bearing areas between the sides of adjacent bushes. Moreover, excessive stresses in the elastomeric material are also avoided because of the rotational limitations on all three bushes, thus avoiding shear failure in the elastomeric material.

In addition, when the flexible couplings are incorporated in a dredge bucket chain, the lower rate of wear avoids to a large extent elongation of the bucket chain and thus the top tumbler no longer requires periodic packing.

The first and/or the second elastomeric layer may be made of rubber.

The interlocking projections may comprise one or more radially inwardly extending projections formed on the outer bush, one or more radially outwardly extending projections formed on the inner bush, the radially outwardly extending projection(s) overlapping the radially inwardly extending projection(s), and one or more axially extending projections formed on the intermediate bush, the axially extending projection(s) extending between the radially inwardly extending projection(s) and the radially outwardly extending projection(s).

In one embodiment, four equispaced projections are formed on the inner bush and on the outer bush, and eight equispaced projections are formed on the intermediate bush, each projection on the intermediate bush being located between a projection on the inner bush and a projection on the outer bush. The projections may each have an arcuate extent of 12210.

The invention also relates to a dredger having a continuous bucket chain, each bucket having a pair of front eyes and a back eye for receiving a bucket pin, wherein a flexible coupling as hereinbefore defined is located in each of the front eyes and in the rear eye, the pin passing through the inner bushes of each of the couplings.

Preferably, an O-ring is arranged between adjacent bushes which are rotatable relative to one another.

A seal may be provided to prevent the ingress of abrasive substances into the pivot joint.

When the flexible couplings are used in a dredge bucket chain it may be useful to preload the couplings by rotating them through a predetermined angle prior to inserting them in the bucket chain. For example, the couplings in the bucket front eyes may be preloaded 11-410 clockwise and the coupling(s) in the bucket back eye may be preloaded 11-410 anticlockwise.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will fluw be made, by way of example, to the accompanying drawings in which: Figure 1 is an end view of a flexible coupling in accordance with the present invention; Figure 2 is a partial section through a diagrammatic representation of a joint between two dredge buckets incorporating the flexible coupling of Figure 1; and Figure 3 shows, on a larger scale, the detail X in Figure 2.

As can be seen from the drawings, the flexible coupling of the present invention requires a minimum of modifications to the components already in use.

The flexible coupling comprises an inner bush 1 for engagement with a bucket pin 20, an outer bush 2 for engagement with a bucket front eye 21 or with a bucket back eye 22, and an intermediate bush 3. Between the bushes 1 and 3 there is disposed a first layer 4 of elastomeric material, such as rubber, and between the bushes 2 and 3 there is disposed a second layer 5 of elastomeric material which may be the same as or different from the elastomeric material of the first layer. The two layers of elastomeric material are securely bonded to the bushes 1, 2 and 3.

At each end of the inner bush 1 there is formed a radially outwardly extending lip 6 which has four equispaced radial projections 7 formed thereon.

The projections 7 each cover an arc of 12 2210.At each end of the outer bush 2 there is formed a radially inwardly extending lip 8 which has four equispaced radial projections 9. The projections 9 extend between the projections 8 and each cover an arc of 12210. At each end of the intermediate bush 3 there are formed eight equispaced axial projections 10, each of which projections covers an arc of 12210. The projections 10 extend into the gaps between the projections 7 and 9.

The projections 7, 9, 10 form an interlocking rotation limiting device which limits the rotation of the inner bush relative to the intermediate bush and which limits the rotation of the outer bush relative to the intermediate bush, and thus prevents excessive stresses being applied to the elastomeric layers. Reference to Figure 1 will show that a rotation of 100 clockwise is possible for each projection 7 before it contacts a projection 10, and that a similar rotation of 100 anticlockwise is also possible. Simiiarly, a rotation of 100 clockwise is possible for each projection 9 before it contacts a projection 10, and a similar rotation of 100 anticlockwise is also possible.

Thus, the outer bush may be rotated 200 clockwise and 200 anticlockwise relative to the inner bush, making a total rotation of 400.

As can be seen from Figure 2, a flexible coupling is arranged in each bucket front eye, and two flexible couplings are arranged in the bucket back eye. The bucket pin 20 passes through all four couplings, but in this embodiment is arranged to be rotatable to the bucket front eyes. Thus, the relative movement between two adjacent buckets 30, 31 is 400 due to the couplings between the front eyes and the pin and 400 due to the couplings between the pin and the back eye, making a total of 800.

Figure 3 shows that an O-ring seal is arranged between at least those bushes of adjacent couplings which rotate relative to one another.

In practice, because a rotation of 600 is required in one direction, whereas a rotation of only 1 50 is required in the other direction, the flexible couplings are preloaded in such a way that the couplings in the bucket front eyes are preloaded 1 1 4 in a clockwise direction and the couplings in the bucket rear eye are preloaded 1 1 4 in an anticlockwise direction. Thus, with two adjacent buckets horizontal, the total preload in the flexible couplings amounts to 2230. In other words, for all the flexible couplings in any one joint to return to their neutral position, which is iliustrated in Figure 1, a movement of the buckets 2230 would occur, thus producing an angle of 1 57710 between the bases of the adjacent buckets.The additional movement to complete 600, i.e. an angle between the buckets of 1200, is 1 8430 in each flexible coupling which is 1 4 less than the maximum available movement. In the opposite direction, a total movement of 1 50 is required, which is 730 for each coupling. In addition to the preload, this represents a total movement of 18430 in each coupling, which is again 1- less than the maximum available movement. There is, therefore, 2 2 reserve movement available in the joint, 110 for each coupling, over and above that required in each direction, producing a total reserve movement of 50.

Whilst it is not shown in the drawings, a seal may be provided to keep, as far as possible, abrasive material away from the flexible couplings.

Such a seal may, for example, be in the form of a rotating seal between the bucket front eyes and the pin, or it may be in the form of a cover over the pin.

A further feature which is not shown in the drawings is that the inner and outer bushes are secured in a non-rotatable manner to the pin and to the bucket eyes, respectively. This securing may be achieved, for example, with the aid of a key arranged between the two adjacent members, or by means of a compression joint which, when tightened, creates sufficient friction to prevent rotation.

Whilst the flexible coupling described with reference to the drawings has been designed primarily for use with civil-type dredgers, such as those which are used for tin mining, the coupling may be used in other applications. Naturally, where different degrees of rotation are required, the arc through which the projections 7, 9, 10 extend may be varied. However, it is important to note that the inner, intermediate and outer bushes will always be interlocked in one way or another to prevent overloading of either of the elastomeric layers.

Claims

1. A flexible coupling which comprises: an inner bush, an outer bush, and an intermediate bush, the three bushes being substantially coaxial and the intermediate bush being located radially between the inner bush and the outer bush; a first layer of elastomeric material positioned radially between the inner bush and the intermediate bush, the first elastomeric layer being bonded to the inner and intermediate bushes; a second layer of elastomeric material positioned radially between the intermediate bush and the outer bush, the second elastomeric layer being bonded to the intermediate and outer bushes; and interlocking projections arranged between the three bushes to limit the rotation of the inner bush relative to the intermediate bush and to limit the rotation of the outer bush relative to the intermediate bush, thereby limiting the rotation of the outer bush relative to the inner bush.

2. A flexible coupling as claimed in claim 1, wherein the first and/or the second elastomeric layer is made of rubber.

3. A flexible coupling as claimed in claim 1 or 2, wherein the interlocking projections may comprise one of more radially inwardly extending projections formed on the outer bush, one or more radially outwardly extending projections formed on the inner bush, the radially outwardly extending projection(s) overlapping the radially inwardly extending projection(s), and one or more axially extending projections formed on the intermediate bush, the axially extending projection(s) extending between the radially inwardly extending projection(s) and the radially outwardly extending projection(s).

4. A flexible coupling as claimed in claim 3, wherein four equispaced projections are formed on the inner bush and on the outer bush, and eight equispaced projections are formed on the intermediate bush, each projection on the intermediate bush being located between a projection on the inner bush and a projection on the outer bush.

5. A flexible coupling as claimed in claim 4, wherein the projections each have an arcuate extent of 12-210.

6. A dredger having a continuous bucket chain, each bucket having a pair of front eyes and a back eye, respectively coupled with the back eye and the pair of front eyes of the buckets in front and behind, wherein a flexible coupling as claimed in any preceding claim is located in each of the front eyes of a bucket and in the back eye of the bucket in front, a bucket pin passing through the inner bushes of each of the couplings.

7. A dredger as claimed in claim 6, wherein an O-ring is arranged between adjacent bushes which are rotatable relative to one another.

8. A dredger as claimed in claim 6 or 7, wherein a seal is provided to prevent the ingress of abrasive substances.

9. A dredger as claimed in claim 6, 7 or 8, wherein the couplings are preloaded by rotating them through a predetermined angle prior to inserting them in the bucket chain.

10. A dredger as claimed in claim 9, wherein the couplings in the bucket front eyes are preloaded 11- lao clockwise and the coupling(s) in the bucket back eye are preloaded 1 14 anticlockwise.

11. A flexible coupling substantially as hereinbefore described with reference to the accompanying drawing.

1 2. A dredger substantially as hereinbefore described with reference to the accompanying drawing.