Crane Boom Having Universally Swiveled Wear Pads

Abstract

The lower wear pads of multi-section telescoping crane booms comprise assemblies located on the forward end and bottom of each boom section. Each such assembly consists of a support housing for a pair of laterally spaced wear pad units and within the support housing are retainer means for each wear pad unit. Each unit includes low friction wear pad elements for direct frictional engagement with the bottom face of the next innermost boom section and spherically curved universally self-adjusting seating means for the wear pad elements.

Description

With the development of increasingly large telescoping crane booms having great lifting capacity and the use of a greater number of telescoping sections in such booms, important problems are encountered in connection with the bearing means between boom sections which directly absorb the exceedingly heavy stresses caused by loading the boom. Friction between telescoping boom sections can be minimized by the use of rollers, but rollers have the disadvantage of localizing and increasing stresses because they are essentially line contact devices. Generally speaking, wide surface flat wear pads have proven more advantageous for the bearing means between telescoping boom sections because they have the ability to distribute the stress over a considerable area and their greater friction is utilized advantageously in resisting longitudinal forces on the boom tending to cause it to retract under load. However, there are other factors which detract from the efficiency of wear pads and these factors include inherent longitudinal bending and misalignment due to canting or cocking of adjacent boom sections. Such factors tend to cause the wear pads to wear unevenly and to have the stresses concentrated at the corners of the pad elements, thereby robbing them of their inherent advantages compared to rollers.

For these and other similar reasons, there is a definite need in connection with large telescoping crane booms for some ready means to enable the flat wear pads to adjust themselves automatically to the various conditions inherently present which cause misalignment of the boom sections during operation. Such self-adjusting means must be practical, efficient in operation and not excessively costly and must be adaptable to telescoping boom structures without causing extensive modification or redesigning thereof. It is the principal objective of the present invention to provide a universally self-adjusting wear pad means for telescoping crane booms which will satisfy all of the above criteria in an economical and efficient manner and without adding significantly to the complexity or cost of the boom. Other features and advantages of the invention will be apparent during the course of the following description.

BRIEF DESCRIPTION OF DRAWING FIGURES

FIG. 1 is a fragmentary side elevation, partly in section, of a multi-section telescoping crane boom equipped with self-adjusting wear pad means embodying the invention;

FIG. 2 is an enlarged transverse vertical section taken on line 2--2 of FIG. 1;

FIG. 3 is a fragmentary plan view, partly in section and partly broken away, showing the wear pad means; and

FIG. 4 is an enlarged longitudinal vertical section taken on line 4--4 of FIG. 2.

DETAILED DESCRIPTION

Referring to the drawings in detail wherein like numerals designate like parts, in FIG. 1 there is shown a fragmentary part of a plural section telescoping crane boom, such as a hydraulically operated boom, having telescoping sections 10, 11 and 12. While the wear pad means of the invention is adaptable to a variety of boom configurations, the invention has been illustrated in connection with a boom whose telescoping sections are trapezoidal in transverse cross section. This particular shape has the advantage of enabling the laterally spaced wear pads on the front and bottom of each boom section to be placed directly under the side walls of the next innermost boom section so as to directly receive the load forces and greatly eliminate transverse bending stresses which effect booms of other cross sectional shapes where it is not possible to locate the wear pads directly under the side webs.

As shown, the boom mid-section 11 comprises upwardly converging side webs 13 whose lower ends are welded to lower side longitudinal relatively heavy reinforcing bars 14, interconnected transversely by a lower horizontal web 15. The next outermost boom section 10, such as another mid-section or base section of the boom, is similarly constructed and includes upwardly converging side web 16 and an interconnecting bottom horizontal web 17, the latter having large rectangular notches 18 in its forward corners to accommodate the self-adjusting wear pad units constituting the invention.

Each lower wear pad assembly embodying the invention comprises a support housing 19 in the form of a sturdy transverse channel member secured by welding to the particular boom section at its forward end and bottom. More particularly, the member 19 forms a part of the customary reinforcing collar 19' which surrounds the forward end of each boom section. The member 19 directly underlies the forward end portion of bottom web 17 and has its opposite end portions located beneath the notches 18. Reinforcing end plates 20 are welded to the ends of the support housing 19 to close these ends and the plates 20 at their tops are tied directly to the side walls of boom section 10 for rigidity as shown in FIG. 2.

Inwardly of the end plates 20 and below and on opposite sides of the lower bars 14 of boom section 11 are pairs of parallel spaced rigid retainer plates 21, all securely welded to the support housing 19 and integrated therewith. The vertical parallel retainer plates 21 extend transversely across the channel-like housing 19 from front-to-back thereof directly under the lower web 17 and under the notches 18.

Between each pair of retainer plates 21, near and above their bottoms and welded securely thereto, is a hardened steel bearing block 22 having a concave spherically curved seat 23 formed in its top. Freely resting upon each spherical seat 23 is a hardened steel swivel plate 24 whose lower face is convex and spherically curved to match the curvature of the seat 23. Resting freely on top of each swivel plate 24 is a preferably steel pad retainer block 25 which is rectangular and elongated so as to extend substantially for the full distance between the forward and rear sides of support housing 19, FIG. 4. Referring to FIGS. 2 and 3, the elements 24 and 25 have their opposite sides spaced slightly from the vertical plates 21.

The pad retainer blocks 25 each have a pair of relatively shallow rectangular recesses 26 in their upper faces receiving removably therein a pair of rectangular wear pads 27, each having a flat upper face for direct frictional contact with the lower faces of bars 14. The wear pads 27 are preferably fiberglass reinforced nylon plate elements impregnated with graphite and sold under the name Nylatron. Other similar types of materials may be employed in some instances.

By virtue of the above-described arrangement, the wear pads 27 have the ability to adjust themselves universally on the spherical seats 23 so as to remain in full surface contact with the bars 14 regardless of changes in angularity of the latter due to canting of the boom sections 11 and 10 as depicted in FIG. 1. This canting or cocking is caused to increase somewhat as the telescoping boom sections approach the outward limits of their extension because of the inherent clearances between sections of the boom. The range of self-adjustment of the pads 27 will always be sufficient to accommodate maximum misalignment or canting between adjacent boom sections. Friction is minimized and wear on the pads 27 is minimized with the invention.

It will be understood that additional wear pad or bearings means is provided on the rear end and upper side of each boom section which is received telescopically in another boom section. The upper wear pad means may be of any known or preferred type and is not shown herein.

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

Claims

I claim:

1. In a telescoping crane boom, first and second telescoping boom sections having bottom surfaces disposed in close proximity to each other, means forming a support housing for laterally spaced wear pad units on the forward end and bottom of the first boom section, said support housing located beneath the bottom surface of said first boom section, laterally spaced spherically curved universally self-adjusting bearing means in said support housing and located below the bottom surface of the first boom section, and wear pad devices resting on said universally self-adjusting bearing means and extending upwardly through apertures in the bottom surface of said first boom section and engaging the bottom surface of said second boom section in complete seating engagement as the angularity between said first and second boom sections changes during telescopic movement of the second boom section.

2. The structure of claim 1, and said bearing means in said support housing comprising bearing block elements having top spherically curved recesses, means anchoring the bearing blocks to said support housing below said bottom surface of said first boom section, coacting self-adjusting spherically curved swivel devices on said bearing blocks, and flat faced wear pad elements on the swivel devices frictionally engaging said bottom surface of said second boom section.

3. In a telescoping crane boom, first and second telescoping boom sections, means forming a support for laterally spaced wear pad units on the forward end and bottom of the first boom section comprising a reinforcing collar on the forward end of said first boom section including a transverse channel member connected beneath the bottom surface of said first boom section, laterally spaced spherically curved universally self-adjusting bearing means secured within opposite end portions of said channel member and located below the bottom surface of the first boom section, and wear pad devices resting on said universally self-adjusting bearing means and extending upwardly through apertures in the bottom surface of said first boom section and engaging the bottom surface of the second boom section disposed in close proximity to the bottom surface of the first boom section.

4. The structure of claim 3, and said bearing means comprising fixed bearing blocks within the opposite end portions of the channel member and having top spherically curved seats, spherically curved swivel plates engaging said seats and adapted to swivel freely thereon universally, and wear pad devices resting on the tops of said swivel plates and underlying said bottom surface of said second boom section.

5. The structure of claim 4, and each wear pad device comprising a wear pad retainer block having plural retainer recesses in its top face, and a corresponding number of wear pads mounted within the retainer recesses.

6. The structure of claim 5, and said wear pads comprising plate-like elements having flat top faces.

7. In a telescoping crane boom, first and second telescoping boom sections having bottom surfaces in close proximity to each other, means forming a support for laterally spaced wear pad units on the forward end and bottom of the first boom section including a transverse channel member extending across and below the bottom surface of the first boom section at its forward end, laterally spaced bearing block elements having top spherically curved recesses, pairs of spaced upstanding plates fixedly secured within the transverse channel members near the opposite ends thereof anchoring the bearing block elements to said support below the bottom surface of the first boom section, coacting spherically curved universally self-adjusting swivel devices on said bearing blocks, and flat faced wear pad elements on the swivel devices extending upwardly through apertures in the bottom surface of said first boom section above said pairs of spaced upstanding plates and frictionally engaging said bottom surface of the second boom section.