Traversing hoists – Boom or mast – Extensible by sliding sections
Reexamination Certificate
2001-07-27
2002-12-31
Brahan, Thomas J. (Department: 3652)
Traversing hoists
Boom or mast
Extensible by sliding sections
C212S270000
Reexamination Certificate
active
06499612
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to lifting devices, such as cranes or the like, and more particularly to a boom assembly comprised of a plurality of telescoping boom sections and corresponding interchangeable wear pads for reducing the friction during the relative telescoping movement.
BACKGROUND OF THE INVENTION
Various types of telescoping booms or boom assemblies for use in cranes or other lifting devices are known in the art. Typically, the boom assembly includes a plurality of nested tubular sections, with each outer section having a larger cross-sectional size than the next-adjacent inner section to permit the desired relative telescoping movement. In the typical arrangement, the proximal end of the outermost boom section is pivotally mounted on a turntable, and the distal end of the innermost section carries one or more sheaves or equivalent structures for supporting the hoisting cable or the like. Friction-reducing structures, such as wear pads, shoes (also known as “slippers”), or like structures formed of a wear-resistant material with enhanced tribological characteristics are normally provided between the adjacent boom sections to provide support and reduce friction during the relative telescoping movement. A basic example of such an arrangement is shown in Kidde's U.S. Pat. No. 5,829,606 to Erdmann.
In recent years, the general direction of progress in the art has been away from a conventional boom section formed having a square or rectangular cross-sectional profile, as shown in the '606 patent, and towards a boom section having a cross-sectional profile that is at least partially rounded. As should be appreciated, a boom section with a partially rounded profile requires less material to manufacture and is thus lighter in weight. In addition to reducing weight and conserving material, it has been discovered that a boom section with a partially rounded profile is able to resist equal or greater bending stresses than the square or rectangular counterpart. Representative examples of proposals for modem telescoping boom assemblies including having partially rounded boom sections are found in Grove's U.S. Pat. No. 6,108,985 to Paschke et al., Kidde's U.S. Pat. No. 5,884,791 to Vohdin et al., and Liebherr's European Published Patent Application 0 583 552. In particular, each of these references discloses a boom assembly including a plurality of telescoping boom sections, each having a rounded lower portion defined by a plurality of non-equidistant, non-equiangular breaks.
Despite the advantages generally afforded by the partially rounded profiles formed by breaks of the type disclosed in these references, a significant, but heretofore unrecognized problem arises with regard to the corresponding wear shoes or pads used to reduce the friction between the lower front ends of the boom sections during telescoping movement. In particular, since the angle forming each break and the distance between adjacent breaks is substantially different, a plurality of different sizes and shapes of wear pads are required for engaging one or more of the different length segments (“flats”) created. This problem is further compounded by the fact that different sizes of wear pads are required for supporting the various different sizes of nesting boom sections. For example, in the boom assembly disclosed in the Grove '985 patent, at least three different types of wear “slippers” are required for positioning between the lower front ends of each adjacent pair of telescoping boom sections. In the case where three telescoping boom sections form the boom assembly, at least six different types of wear slippers must be kept on hand or in inventory; for four boom sections, at least nine different types of wear slippers are required; and telescoping boom assemblies formed of five boom sections require at least twelve different types of wear slippers.
As should be appreciated, the requirement for having multiple types of non-interchangeable wear pads is disadvantageous, since it increases the cost from both the manufacturing and production standpoint. An associated consequence is the need for the crane operator to keep the various different types of wear pads on hand at the job site, in case there is an immediate need for replacement. Even in the case where the wear pads are inspected between jobs and replaced if excessive wear is observed, the manufacturer of the crane must still keep a ready supply of the different types of replacement wear pads available throughout the service life of the crane or other lifting device using such a boom assembly. This not only increases the amount of inventory and the associated expense that must be borne by the crane manufacturer (and ultimately passed on to the crane operator), but it also creates deleterious inventory management and control problems. The net result is an increase in the overall manufacturing and operational cost of the crane or other lifting device having a boom assembly with several different types of non-identical wear pads or shoes for supporting the lower front end of each adjacent boom section during telescoping movement.
Accordingly, a need is identified for an improved boom assembly and a corresponding arrangement of friction or wear-reducing structures that address and overcome the foregoing limitations of the prior art arrangements. In particular, the telescoping sections forming the boom assembly would have the desirable partially rounded profile for reduced weight, enhanced stiffness and added strength, but would be adapted for receiving a plurality of interchangeable wear pads along the rounded portion. As a result, the need for keeping different types of wear pads on hand for supporting each boom section and by engaging the rounded portion would be eliminated, and an improved boom assembly would be provided, especially in terms of reduced manufacturing and operational expense.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, a boom assembly for a crane or other lifting device is provided. The boom assembly is comprised of at least two adjacent telescoping boom sections. A first of the telescoping boom sections includes a rounded portion formed by a plurality of substantially equiangular breaks. A plurality of substantially identical wear pads are also provided as part of the assembly for reducing friction between the adjacent boom sections during telescoping movement. In use, each wear pad is positioned adjacent to one of the breaks relative to the first boom section and supported by a matching second, adjacent telescoping boom section. Hence, the wear pads not only reduce friction in the desired manner, but also are freely interchangeable. Advantageously, this eliminates the need for keeping a plurality of different types of non-identical replacement wear pads on hand such as for positioning between the lower front ends of adjacent boom sections, either at the job site or in the inventory kept by the manufacturer at a remote location.
In one embodiment, each of the plurality of breaks formed in each side of the lower portion of the first boom section are equidistant from each other. Additionally, at least a portion of the outer surface of the first boom section on either side of each break is substantially flat. To ensure that intimate contact is established with the corresponding boom section, including the flat segments between the adjacent breaks, each substantially identical wear pad is provided with a contoured engagement surface. This contoured engagement surface is preferably substantially V-shaped to match the shape of the corresponding outer surface of the boom section. However, the use of other equivalent shapes or contours capable of achieving the desired friction-reducing engagement is also possible.
Normally, the boom is formed of three or more nested telescoping boom sections, each identical in shape and increasing in cross-sectional size from the innermost to the outermost boom section. In the case of an innermost boom section having a sma
Harrgington Daniel L.
Murphy Shannon J.
Brahan Thomas J.
King & Schickli PLLC
Link-Belt Construction Equipment Co. L.P. , LLLP
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