GB2042456A - Telescopic crane - Google Patents

Abstract

A crane with a jib having telescopic parts (10, 11, 12) and a jib head (13) on the upper most part (12) has two sets of stationary sheaves (16, 23). One set (16) is mounted on the jib head (13), but the second set (23) is mounted at the top of the bottom jib part (10). The hoist rope (15) is reeved through both sets of sheaves (16, 23) and through sheaves (21) in the lifting block (17). With this arrangement, when the jib is retracted, which is when the crane can lift its maximum load, only part of this load is transmitted to the jib head (13). In consequence the head (13) can be made lighter and this makes it possible to increase the maximum lifting capacity of the crane. When the jib is extended so that the crane can only lift lighter loads, the hoist rope (15) is reeved through some of the sheaves (21) in the lifting block (17) and through the sheaves (16), the sheaves (23) being missed out. <IMAGE>

Description

SPECIFICATION Telescopic crane This invention relates to cranes of the kind having a telescopic jib comprising a bottom part and one or more upper parts which fit telescopically one within the other, a stationary set of sheaves mounted on or adjacent a jib head at the upper end of the inner or innermost part, a set of movable lifting sheaves having a lifting device, such as a hook, and a hoist rope which has one end fixed and is reeved around the sheaves in the stationary and movable sets.

In such cranes, it is necessary to construct the jib head on the inner or innermost telescopic part to withstand the maximum crane lifting capacity, which exists only when the telescopic jib is retracted. The reason for this is that in all the telescopic conditions, the entire crane load is trasmitted to the crane through the jib head. The jib head, is thus over-designed and heavier than necessary for very many loading and working conditions where the telescopic jib is fully or partially extended. The excess weight of the jib head has the effect of reducing the load carrying capacity of the cranes as a whole. Also, in known telescopic cranes, lifting blocks are used which, on account of the varying number of sheaves in the blocks and the consequent different forms of construction, cannot be standardized.

The object of the present invention is to avoid the aforementioned disadvantages and provide an improved telescopic crane with a telescopic jib, which, in use, has a more favourable distribution of weight and loading of the jib and which with a jib of the same dimensions has an increased lifting capacity when the jib is partially or fully extended.

To this end, according to this invention, in a crane of the kind initially described, a second set of stationary sheaves is mounted on the bottom jib part or on an upper jib part other than that which carries the jib head and the hoist rope is reeved around the set of movable sheaves and around both sets of stationary sheaves.

Thus, the concept underlying the present invention is to reduce the load carried by the jib head thus making it possible to reduce the weight of the jib head below that necessary to withstand the full load capacity of the crane when the telescopic jib is retracted, and this is done by transferring a portion of the crane load via the second stationary set of sheaves directly to the bottom jib part or another jib part below the uppermost. As a consequence of the reduction in weight of the jib head and the manner in which the load is transferred to the jib, the lifting capacity of the crane when the telescopic jib is partially or fully extended can thus be increased by comparatively sim ple means. Not only can the invention be put into effect in new telescopic cranes, but existing telescopic cranes can easily be converted to incorporate the present invention.

Preferably, the second set of stationary sheaves is constructed as a unit and is secured to the upper end of the bottom jib part.

This form of construction is especially simple and effective. It is however alternatively possible to secure the second set of sheaves not to the bottom jib part but to an intermediate telescopic part, when there is one and it is desirable to do so for constructional or operational reasons. As a further possibility, the second set of sheaves can be sub-divided for specific purposes into at least two separate units, which are attached at different positions to the bottom jib part and to at least one intermediate telescopic part. For example, in the case of two units, one can be attached to the upper end of the bottom jib part and the other to the upper end of the lowermost telescopic part.

In essence, the stationary set of sheaves can be sub-divided into any number of sets which can be secured in any desired manner to the reduced-weight jib head and to other parts of the jib. The particular division of the set will depend upon the particular operating requirements. A simple example, which can be used for most purposes, is characterized in that the stationary set of sheaves is divided into two sets containing equal numbers of sheaves.

Preferably, the second set of stationary sheaves is detachably fixed to the jib part. As a result, the second set can be fitted, changed or removed in a manner to suit the particular operating requirements of the crane.

In one especially favourable embodiment, the second set of stationary sheaves is formed as a unit and the set of movable sheaves and/or the first set of stationary sheaves comprise a similar unit. Such a standardised construction as a unit makes possible more economical manufacture and calls for less storage, since, for example, a number of units can be combined with one another in order to make up sets of sheaves of larger dimensions, for example, the movable set of lifting sheaves, the total number of sheaves in which is normally equal to the total number of stationary sheaves. The second set of stationary sheaves can also, if necessary, be composed of a plurality of units. Further, the unit principle of construction can be employed also for the stationary set of sheaves which remains on the jib head.

Preferably, the unit comprises a set of sheaves disposed on a pivot shaft and two securing arms one at each end of the shaft. A unit comprising three sheaves has for practical purposes been found especially suitable, for example for use in a telescopic crane where the stationary sheaves are to be in two sets of equal numbers. Two units combined can then form the movable lifting block. Favourable conditions are obtained in use if the securing arms are members which are pivotally attached to a part about which the arms can pivot about axis parallel to the shaft. For this purpose the securing arms have, at their free ends, in the simplest case, aligned bores, through which for example a pin can be inserted.

In one practical form of embodiment, the jib part on which the second set of stationary sheaves are mounted has a projection to which the securing arms of the unit are pivotally attached. This makes possible rapid and easy attachment of the unit to the telescopic jib.

The invention thus leads, by the dividing of the stationary sheaves into two or more sets and by the resultant reeving of the hoist rope through both sets and through the movable sheaves, to a considerable reduction in weight of the jib head, which brings about an increase in the lifting capacity of the telescopic crane in the to .partially or fully extended telescopic state. X view view of the stepped lifting capacity of a telescopic crane, the set of sheaves uppermost on the telescopic part comprising the jib head is constructed at the maximum lifting capacity of the crane, only to take part of the load. The other part of the load is directly transferred from the second set of stationary sheaves to the bottom jib part and/or to an intermediate telescopic part. The movable lifting block itself is of course constructed to take the total load.

An example of a crane constructed in accordance with the invention will now be described with reference to the accompanying diagrammatic drawings in which: Figure 1 is a side view of the upper end of a conventional telescopic jib of a crane, with blocks comprising six sheaves fixed to the jib head, and a lifting block also comprising six sheaves, the jib being retracted; Figure 2 is a view of the jib shown in Fig.

1, but with the jib extended and provided with a lifting block having only three sheaves; Figure 3 is a side view of the upper end of the jib of a crane in accordance with the invention, the jib being retracted and having a block with three sheaves fixed to the jib head, a second block with three sheaves fixed to the upper end of the bottom jib part, and a lifting block having two sets each of three sheaves; and, Figure 4 is a side view of the jib shown in Fig. 3 when extended and with the second block removed and the lifting block shown in Fig. 3 replaced by one having only a single set of three sheaves.

Corresponding parts of the crane shown in the various Figures of the drawings have the same reference numerals. In the conventional crane shown in Figs. 1 and 2, a telescopic jib consists of a bottom jib part 10, an intermediate upper telescopic part 11, and of an innermost or uppermost telescopic part 1 2 carrying a jib head 1 3. On the jib head a guide sheave 1 4 is rotatably mounted and, over it, a hoist rope 1 5 extending from a winding drum, not shown, is guided. At the forward end of the jib head 13, remote from the guide sheave 14, a block forming a stationary set of six sheaves 1 6 is mounted.Associated with the stationary set of sheaves 1 6 is a movable set of sheaves 1 7 in a lifting block, which hangs from the lifting rope 1 5 and, in the example shown in Fig. 1 likewise comprises six sheaves. When modified as shown in Fig. 2 a movable set of sheaves 1 7 comprising three sheaves is provided. A lifting hook is fixed to the lifting block for the load to be attached.

In the conventional crane, the jib head 1 3 must be constructed to withstand the full lifting capacity of the crane, since the head has to carry the entire load when the jib is retracted and the lifting capacity is greatest.

When the jib is partially or fully extended so that the crane has only a reduced lifting capacity, the jib head 1 3 is therefore overdesigned, which means that it has a weight greater than necessary and this leads to a reduction in lifting capacity. In every case, the jib head and the stationary set of sheaves must, in conventional telescopic cranes be capable of accepting the maximum crane load. The lifting rope 1 5 is connected at one end to the winding drum, not shown, and is fixed at its other end to a point 19, which in the conventional cranes is on the jib head.

The telescopic jib of the crane in accordance with the present invention also consists as shown in Figs. 3 and 4, of a bottom jib part 10 an intermediate upper telescopic part 11, and of an innermost or uppermost telescopic part 1 2 carrying a jib head 1 3. On the jib head, a guide sheave 14 is rotatably mounted and a lifting rope 15, extending from a winding drum, not shown, is guided over the sheave 1 4. At the forward end of the jib head 13, furthest from the guide sheave 14, a set of three sheaves 1 6 is mounted and this is only a portion of the total number of stationary sheaves, as will be explained later.

As shown in Fig. 3, there is once again in the lifting block a movable set of sheaves 1 7 and a load hook 18 is attached to the block, which hangs from the lifting rope 1 5 one end of which is secured at a point 1 9. The lifting block 1 7 is associated with the stationary set of sheaves 1 6 on the jib head 1 3 and also with a second, separate set of stationary sheaves 20. This separate set of sheaves 20 which forms a second stationary block, is constructed in the form of a unit 21, which is detachably pivotally mounted on the free or upper end of the bottom jib part 10. The unit 21 has a shaft 22, three sheaves 23 rotatably mounted on the shaft 22, and two securing arms 24.The arms have at their free ends mutually aligned bores through which the unit 21 can be detachably pivoted, for example to a projection 25 on the bottom jib part 10.

The movable sheaves 1 7 consist, as shown in Fig. 3, of two units 21 which are connected by their securing arms 24 to a connecting member 26 in the form of a hook suspension. Thus the hoist rope 1 5 is reeved around six sheaves of the lower block and around two sets of sheaves of the two-part stationary set of sheaves. In the example illustrated in Fig. 3, the jib head 13, on account of the halving of number of sheaves which it carries, has to be constructed to withstand only one half of the maximum lifting capacity of the crane in comparison with the jib head of the conventional crane, since the unit 21 attached to the bottom jib part 10 transfers half of the load directly to the bottom jib part 10. In contrast, the lifting block must of course be constructed for the full lifting capacity.In the present example, for reasons of simplicity and economy of maintenance of stocks, the lifting block is formed by combining two units.

Fig. 4 merely illustrates that the crane in accordance with this invention can also be adapted for use in a conventional manner, that is without dividing the load between different parts of the telescopic jib. As shown in Fig. 4 the unit 21 is removed from the projection 25 of the bottom jib part 10, and the lifting block consists of only one unit 21 with a load hook 1 8 fixed thereto. Thus, when the crane is used in this way which is only suitable for loads well below the maximum capacity, the entire load is transferred to the jib head 1 3.

Instead of the example illustrated in Fig. 3, the sheaves of the stationary set of sheaves can be separated into groups in virtually any desired manner and to suit particular operating conditions. Similarly, a further sub-division of the separate set of sheaves 20 is also possible, in that one or more of the sheaves may be fixed, for example, to the bottom jib part 10 and one or more may be fixed to the intermediate telescopic part 11. Instead of this, the entire part set of sheaves 20 can alternatively be attached to the intermediate telescopic part 11.

Moreover, attachment to other, intermediate telescopic parts, when these are provided is also possible. The units 21 can of course have less than or more than three sheaves, and also the sheaves remaining on the jib head 1 3 may consist of one or more units 21. Thus numerous variants can be carried out within the scope of the present invention and the construction of the crane can be adapted to the relevant operating requirements. In every case, however, the result is achieved that the weight of the jib head can be reduced and the maximum crane lifting capacity can be increased.

Claims (9)

1. A crane having a telescopic jib comprising a bottom part and one or more upper parts which fit telescopically one within the other, a stationary set of sheaves mounted on or adjacent a jib head at the upper end of the inner or innermost part, a set of movable lifting sheaves having a lifting device, and a hoist rope which has one end fixed and is reeved around the sheaves in the stationary and movable sets, wherein a second set of stationary sheaves is mounted on the bottom jib part or on an upper jib part other than that which carries the jib head and the hoist rope is reeved around the set of movable sheaves and around both sets of stationary sheaves.

2. A crane according to Claim 1, in which the second set of stationary sheaves is formed as a unit and is attached to the upper end of the bottom jib part.

3. A crane according to Claim 1 or Claim 2, in which the two sets of stationary sheaves contain equal numbers of sheaves.

4. A crane according to any one of Claims 1 to 3, in which the second set of stationary sheaves is detachably fixed to the jib part.

5. A crane according to any one of Claims 1 to 4, in which the second set of stationary sheaves is formed as a unit and the set of movable sheaves and/or the first set of stationary sheaves comprise a similar unit.

6. A crane according to Claim 5, in which the unit comprises a set of sheaves disposed on a pivot shaft and two securing arms one at each end of the shaft.

7. A crane according to Claim 6, in which the unit has three sheaves.

8. A crane according to Claim 6 or Claim 7, in which the securing arms are members which are pivotally attached to a part about which the arms can pivot about axes parallel to the shaft.

9. A crane according to any one of Claims 6 to 8, in which the jib part on which the second set of stationary sheaves are mounted has a projection to which the securing arms of the unit are pivotally attached.

1 0. A crane according to Claim 1, substantially as described with reference to Fig. 3 of the accompanying drawings.