Boom Sheave Assembly

Abstract

A boom sheave assembly is provided wherein a sheave shaft is supported by a plurality of struts which are loaded substantially only in tension. The boom sheave assembly is pivotally mounted to position a beam, strong in bending, in alignment with the direction of the forces applied to a load implement.

Description

With the advent of cranes capable of lifting substantial loads, it is necessary to increase the load handling capacity of the boom sheave assembly. Typical boom sheave assemblies for less heavily loaded booms comprise a plurality of sheaves mounted on a sheave shaft with the opposite ends of the sheave shaft mounted on the boom. The most elementary approach taken by the prior art to increase the load bearing capacity of a boom sheave assembly has been to increase the size of the sheave shaft to handle the larger loads.

Along with the trend to greater crane capacities, it has been the practice to increase the number of lines between the boom sheave assembly and a traveling block. There have consequently been more sheaves mounted on the sheave shaft thereby necessitating a longer shaft to accommodate the additional sheaves. Longer sheave shafts have aggravated the bending of the shaft. It will be apparent that increasing the diameter of the sheave shaft to accommodate greater loads and particularly to accommodate greater bending loads, has obvious practical limits.

One approach of the prior art to minimize bending of the sheave shaft is to support the sheave shaft intermediate the ends thereof by one or more cantilevered struts. Since these struts of the prior art extend between the sheaves, the struts must be relatively narrow and consequently cannot have a substantial flange thereon imparting substantial resistance to bending. Since a cantilevered mounting is a relatively weak securement for a strut of this nature, this approach of the prior art has not been altogether satisfactory.

This invention comprises a boom sheave assembly having a beam parallel to the sheave shaft, which is strong in bending, with the sheave shaft being secured thereto by a plurality of depending struts which are loaded substantially only in tension. The beam is pivotally mounted on the crane boom so that load forces applied to the sheaves pivot the beam to position the same coplanar with the direction of the applied loads.

It is an object of this invention to provide a boom sheave assembly of maximum strength consistent with low weight.

Another object of the invention is to provide a boom sheave assembly wherein a sheave shaft is supported intermediate the ends thereof by a plurality of struts stressed substantially only in tension.

A further object of the invention is to provide a boom sheave assembly comprised of a beam to position the same in alignment with forces applied to the sheaves.

Still another object of the invention is to provide a crane having a boom thereon equipped with a sheave assembly of the aforementioned type.

IN THE DRAWINGS:

FIG. 1 is a side elevational view of a high capacity crane equipped with a boom sheave assembly of the invention;

FIG. 2 is an enlarged side elevational view of the boom sheave assembly of FIG. 1;

FIG. 3 is a front view of the boom sheave assembly of FIG. 2, certain parts being broken away for clarity of illustration; and

FIG. 4 is a cross-sectional view of the boom sheave assembly of FIGS. 2 and 3 taken substantially along line 4--4 of FIG. 3 as viewed in the direction indicated by the arrows.

Attention is directed to FIG. 1 wherein there is illustrated a crane 10 having a boom 12 pivotally mounted to a carrier 14. The carrier 14 is supported by an underlying ring 16 and is secured to an upper works 18 for rotation therewith. Interconnecting the boom 12 and the carrier 14 are suitable boom stops 15 which act to prevent elevation of the boom 12 beyond a predetermined angle with respect to the underlying ground surface. This type of crane is described in more detail in the application of Daniel E. Beduhn, Ser. No. 704,488, filed Feb. 9, 1968, now U.S. Pat. No. 3,485,383 and assigned to the assignee of this application.

Secured to the free end of the boom 12 is a boom sheave assembly 20 made in accordance with this invention. A load line 22 is operatively connected to a drum 24 on the upper works 18 and is reeved through the sheave assembly 20 to an implement 26 illustrated as a traveling block. The path of the load line 22 is defined by a plurality of guide sheaves 28 as is customary.

Referring to FIGS. 2-4, the boom sheave assembly 20 comprises as major components a load supporting beam 30, mounting means 32 for securing the assembly 20 to the boom 12, a sheave shaft 34, a plurality of sheaves 36 and a plurality of struts 38 securing the shaft 34 to the beam 30.

The beam 30 is illustrated as a deep rectangular box having walls 40, 42, 44, 46 secured together by suitable weldments 48. The ends of the box beam 30 are closed by end caps 50, 52 secured by weldments 54. The beam 30 consequently has a major axis of bending strength 56 disposed on a radius of the sheave shaft 34 and a minor axis of bending strength 58 perpendicular to the major axis 56. Although a rectangular box beam is illustrated, it will be apparent that a square box beam, an I-beam, a T-beam, a tube or any other structural member strong in bending may be used.

Referring to FIGS. 2 and 3, the mounting means 32 is illustrated as comprising a pair of arms 60, 62 secured adjacent opposite ends of the beam 30 and providing a pair of socket forming members 64, 66. The members 64, 66 are aligned with a pair of complementary socket forming members 68, 70 provided at the top of the boom 12 with a pair of pins 72, 74 securing the socket forming members 64, 66, 68, 70 together. Suitable means, such as cotter keys or the like, may be provided to retain the pins 72, 74 in position. The members 64, 66 define a pivot axis spaced from the shaft 34, the importance of which will be explained hereinafter. It will be seen that the mounting means 32 not only constitutes means for mounting the beam 30 and the assembly 20 on the boom 12, but also constitutes means for pivotally mounting the beam 30 and the struts 38 in a manner more fully described hereinafter.

Each of the sheaves 36 comprises a suitable bearing 76 rotatably mounting the sheave 36 on the shaft 34. Suitable lubrication connections 78 may be provided for the bearings 76. Annular sealing plates 80 are secured to the hub of the sheave 36 and operate to retain lubricant in the bearing 76. The plates 80 also act as bearings to accommodate any relative rotation between adjacent abutting sheaves 36. As will be apparent from the insuing description, the plates 80 also act as a bearing between the struts 38 and the sheaves 36 adjacent thereto.

As shown best in FIGS. 3 and 4, the struts 38 are secured at the upper end thereof to the beam 30. The lower end of each strut 38 provides an aperture 82 closely receiving the sheave shaft 34. A pair of end fittings 84, 86 captivate the shaft 34 in the apertures 82 of the struts 38. Suitable connections 88 affix the end fittings 84, 86 to the ends of the shaft 34. The generally circular end fittings 84, 86 are provided with a straight segment 90, 92 which cooperate with an abutment 94, 96 affixed to the outer struts 38. It will be apparent that the segments 90, 92 and the abutments 94, 96 prevent rotation of the shaft 34.

Since the sheave shaft 34 is supported at a number of spaced locations along the length thereof, the deflection of the shaft 34 in bending is substantially reduced. It will be noted that the struts 38 depend from the beam 30 and are free from features which would induce substantial bending forces therein.

When the crane 10 is hoisting a load in a purely vertical direction, the forces applied to the shaft 34 resolve into a vertical force vector 98 shown in FIG. 2. It will be apparent that the stresses resulting in the struts 38 are substantially only tensile in nature. It will also be apparent that the loads applied to the beam 30 are in alignment with the major axis of bending strength 56. It will be further apparent that when the angle of the boom is changed, as is common in crane operation, the boom sheave assembly 20 will remain vertical with the load in line with the major axis of the beam 30.

It will be apparent that the crane 10 is called upon to handle other than purely vertical loads, for example when a load is rotated about the axis of the upper works 18 or when a load is lifted from a location other than immediately below the boom top. The forces applied to the shaft 34 resolve into a non-vertical force vector 100 which radially extends from the shaft 34. Since the pivot axis defined by the members 64, 66 is spaced from the shaft 34, a counter clockwise moment is induced in the boom sheave assembly 20 to rotate the beam 30, the struts 38 and the shaft 34 to align the force vector 100 with the beam 30, the struts 38 and the shaft 34. Without the movable connection provided by the mounting means 34, it will be apparent that the force transmitted to the struts 38 would not be substantially only in tension but instead would include a substantial bending force thereby converting the struts 38 into cantilevered beams. Since the struts 38 are substantially weaker when mounted as a cantilevered beam rather than as a pendant support, it will be seen that the capacity of the boom sheave assembly 20 would be substantially reduced. In a similar fashion, the forces applied to the beam 30 would no longer be in alignment with the major axis of bending strength 56 thereby decreasing the load bearing capacity of the beam 30 and consequently detracting from the capacity of the boom sheave assembly 20. It will accordingly be apparent that the movable connection provided by the mounting means 32 is of significant utility.

Claims

I claim:

1. A crane comprising

a boom;

means for elevating the boom with respect to an underlying surface including means for preventing elevation of the boom beyond a predetermined angle with respect to the underlying surface;

a boom sheave assembly comprising a shaft having an axis; a plurality of sheaves thereon; a beam above the shaft; a plurality of depending struts, connecting the beam and the shaft, substantially wholly supporting the shaft and stressed substantially only in tension in response to a load applied to the shaft; and means connecting the beam and the boom for pivotally mounting the sheave assembly on the boom; the pivotal mounting means including arms extending from the beam and cooperative pivotal connections, between the arms and the boom, defining a pivot axis positioned between the beam and the shaft axis;

a load line reeved over the sheaves; and

an implement operatively connected to the load line and movable with respect to the sheave assembly for handling a load.

2. The crane of claim 1 wherein the arms and the struts reside on a common radius relative to the shaft.

3. The crane of claim 2 wherein the beam, shaft and pivotal connections reside substantially in a common plane.

4. The crane of claim 1 wherein the plurality of struts includes struts at opposite end portions of the shaft and at least one intermediate strut connected to the shaft between two of the sheaves.