Abstract:
A hoist ring assembly adapted to be arc welded directly to an object to be lifted. A hoist ring mount is provided with the assembly having a generally radially extending flange portion integral with the proximal end of a generally cylindrically bearing portion. The perimeter of the flange portion is welded directly to an object to be lifted by means of a peripheral weld boundary. The bearing portion has a circumference. The length of the peripheral weld boundary is greater than the length of the circumference, thereby reducing stresses applied across the weld while maintaining the load capacity of the assembly after welding. A conventional lifting loop is pivotally mounted to a collar member. The collar member is rotatably mounted on the cylindrical bearing portion of the hoist ring mount. The lifting loop assembly, comprising the lifting loop and the collar member, is detachably mounted on the welded-in-place hoist ring mount. This attachment may be through an internal or external threaded mount, or a quick release detent-locking element configuration.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/297,287 filed Jun. 11, 2001. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates in general to hoist ring assemblies and, in particular, to a weld mounted hoist ring assembly with a flanged bushing, wherein the perimeter of the flange is welded directly to the surface of an object to be lifted. 
   2. Description of the Prior Art 
   Various hoist ring assemblies had been proposed previously. Typically, such hoist ring assembles were designed to threadably engage an object to be lifted. For example, the hoist ring assemblies in Tsui et al U.S. Pat. No. 5,848,815, in Tsui et al U.S. Pat. No. 4,705,422, in Tsui et al U.S. Pat. No. 4,641,986, in Tsui U.S. Pat. No. 5,405,210, and in Wong et al U.S. Pat. No. 4,570,987 all had a protruding mounting screw for threadably engaging an object to be lifted. Generally, to accommodate such prior screw mounted hoist ring assemblies the object must be drilled and tapped to the appropriate thread size and depth before installation. Importantly, it is critical for safety purposes that the depth of the threaded hole is sufficient to provide the proper amount of thread engagement for the hoist ring screw. If the depth is insufficient, catastrophic failure may occur. Thus, hoist ring assemblies with protruding mounting screws are generally unsatisfactory for use in situations where the thickness of the object to be lifted is insufficient to provide enough thread engagement, or, as in watercraft, where holes in the object are undesirable. 
   Previous expedients proposed for the weld mounting of hoist rings involved a conventional stud welding operation to affix a stud to a metal object. The welded stud replaced the conventional threaded mounting screw. See Sawyer et al. U.S. Pat. No. 5,586,801. The strength of a mounted hoist ring assembly depends in significant part on the mounting structure bearing firmly and uniformly on the load. Any misalignment of a welded mounting stud would prevent this and greatly weaken the mounted assembly. Any weakening of the object by the heat or imperfection of the welding operation is unpredictable so a safety limit for the capacity of the assembly can not be reliably established. The quality of the weld has a great impact of the strength of the system. The weld is concentrated at the end of the stud in a small area, so the loads are likewise concentrated in this small area. The weld mounting of hollow retainer plates for load anchors with limited movement had been proposed. See Smith et al. U.S. Pat. No. 3,831,532. 
   Previously, difficulties had been anticipated in attempting to weld mount hoist ring assemblies directly to objects to be lifted. Welding had been believed to introduce uncertainty into the resulting load capacity of a hoist ring. For instance, the heat added during welding may destroy the underlying strength of the system. The characteristics of the object have an influence on the strength of the weld. It had been proposed to supply pre-drilled and tapped mounting plates for use with conventional screw mount hoist ring assemblies. These mounting plates were welded directly to the surface of the object to be lifted. The hoist ring assemblies were then threadably mounted to the welded plates. However, due to the wide variety of hoist rings assemblies and their associated lift ratings, a large inventory of various sized, pre-drilled and tapped plates was found to be necessary. Maintaining such an inventory is not only undesirable, but also increases the chances of mismatching an incorrect plate size or capacity for a given hoist ring assembly. Such mismatches are undesirable and can result in catastrophic failure. 
   Thus, there is a need to provide hoist ring assemblies capable of lifting heavy objects having relatively thin surfaces or surfaces that should not be perforated for attaching the assemblies. There is also a need for such assemblies to be self-contained thereby eliminating the chances of mismatching separately provided threaded plates with conventional screw mount hoist ring assemblies. Those concerned with these problems recognize the need for an improved self-contained hoist ring assembly, one capable of being welded directly to an object to be lifted. The design of the weld must be such that the strength of the resultant weld is reliably and predictably greater than the underlying load rating of the hoist ring assembly so that the weld does not reduce the load rating capacity of the hoist ring assembly. 
   BRIEF SUMMARY OF THE INVENTION 
   A preferred embodiment of the weld mount hoist ring assembly according to the present invention comprises a hoist ring mount adapted to be welded to the surface of an object to be lifted. The hoist ring mount has a generally radially extending flange portion integral with the proximal end of a bearing portion. The bearing portion is adapted to detachably accept a lifting loop for rotational and pivotal movement. The flange portion has an obverse face that is adapted to being positioned flat against the surface of the object to be lifted. The opposed reverse face of the flange is adjacent the generally cylindrical surface of the bearing portion of the mount. The obverse and reverse faces are joined at their peripheries by a perimeter portion. 
   The perimeter portion provides a peripheral weld boundary, which is adapted to being arc welded to the surface of the object. Arc welding minimizes the amount of heat that is applied to the hoist ring mount. The bearing portion includes a peripheral bearing boundary. The length of the peripheral weld boundary is greater than the length of the peripheral bearing boundary in order to reduce the stresses applied to the weld when the object is lifted. The flange also serves to space the collar member from the weld so that it is free to rotate about the bearing portion. The peripheral weld boundary is generally at least one and one quarter, and, preferably, at least about twice to three and one half or more times greater than the length of the peripheral bearing boundary. The length of the weld boundary, as determined by the length of the perimeter portion, is such that it eliminates the weld as being the weak link in establishing the load capacity of the assembly. Even if there is an imperfection in the weld, there should be enough good weld to support the load. Placing the heat of the weld out on the perimeter of the flange away from the body of the mount protects the body from unpredictable heat induced property changes. Also, since it is known that the perimeter portion will be subjected to heat, the worst case for heat induced weakening of the flange portion can be taken into consideration in designing safety factors into the mount. Increasing the length of the perimeter portion, or the thickness of the flange, or both can usually compensate for the effect of heat induced weakening. 
   Hoist rings are generally designed to withstand loads of up to five times their rated capacity. Typically, the weakest link in the system is the pivoting structure or the mounting structure, and they typically fail in shear. The strength of the weld, assuming an average weld, and the worst case for heat induced weakening of the flange portion, should be such that it exceeds the rated load of the hoist ring by a factor of at least about 5.1, and, preferably at least about 5.5. For example, the design strength of a weld for a hoist ring with a rated load of 10,000 pounds should be at least 51,000 pounds. 
   Preferably, the hoist ring mount is arc welded to the surface of an object to be lifted with the remaining parts of the assembly temporarily removed. This minimizes the heat to which the various rotating and pivoting parts are subjected during the welding process. After welding, the parts are re-assembled and the object is ready for lifting. The hoist ring mount can be adapted for use with a wide variety of different hoist ring assemblies. 
   To acquaint persons skilled in the pertinent arts most closely related to the present invention, a preferred embodiment of a weld mounted hoist ring that illustrates a best mode now contemplated for putting the invention into practice is described herein by, and with reference to, the annexed drawings that form a part of the specification. The exemplary weld mounted hoist ring assembly is described in detail without attempting to show all of the various forms and modifications in which the invention might be embodied. As such, the embodiments shown and described herein are illustrative, and as will become apparent to those skilled in the arts, can be modified in numerous ways within the scope and spirit of the invention, the invention being measured by the appended claims and not by the details of the specification. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention provides its benefits across a broad spectrum of hoist ring assemblies. While the description which follows hereinafter is meant to be representative of a number of such applications, it is not exhaustive. As those skilled in the art will recognize, the basic apparatus taught herein can be readily adapted to many uses. It is applicant&#39;s intent that this specification and the claims appended hereto be accorded a breadth in keeping with the scope and spirit of the invention being disclosed despite what might appear to be limiting language imposed by the requirements of referring to the specific examples disclosed. 
     Referring particularly to the drawings for the purposes of illustration only and not limitation: 
       FIG. 1  is an exploded perspective view of a prior art drilled and tapped weld block used in conjunction with conventional screw-type hoist ring assembly. 
       FIG. 2  is a perspective view of the prior art weld block of  FIG. 1  after being arc welded to the surface of an object to be lifted. 
       FIG. 3  is an exploded perspective view of a preferred embodiment of a hoist ring mount according to the present invention wherein an internal thread is provided for rotatably and pivotally attaching a lifting loop assembly to the mount. 
       FIG. 4  is a perspective view of the embodiment of  FIG. 3  after the peripheral boundary of the radially extending flange portion of the hoist ring mount has been arc welded to the surface of an object to be lifted. 
       FIG. 5  is a partial cross-sectional side elevational view of a preferred embodiment. 
       FIG. 6  is an exploded perspective view of the preferred embodiment shown in FIG.  5 . 
       FIG. 7  is a partial cross-sectional side elevational view of another preferred embodiment. 
       FIG. 8  is an exploded perspective view of the preferred embodiment shown in FIG.  7 . 
       FIG. 9  is an exploded perspective view of a preferred embodiment wherein a quickly detachable lifting loop assembly includes a detent element for engagement in an annular groove in the hoist ring mount. 
       FIG. 10  is a perspective view of an embodiment of a hoist ring mount according to the present invention wherein an externally threaded mounting member is provided. 
       FIG. 11  is a cross-sectional view of a further embodiment of the present invention wherein a circular disk is rotatably trapped within an annular cavity formed between a generally hat-shaped member and a threaded cap. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings, like reference numerals designate identical or corresponding parts throughout the several views. 
   In  FIGS. 1 and 2  there is shown at  11  a pre-drilled and threaded mount plate of the prior art to be used in conjunction with conventional screw mount hoist ring assemblies. The pre-drilled and threaded mount plate  11  is welded to the surface  13  of object  15 , as shown in FIG.  2 . The pre-drilled and threaded mount plate had been believed necessary to provide a sufficient thread engagement for conventional hoist ring assemblies when, for example, the thickness of the surface of the object is too thin. For example, a one inch hoist ring assembly rated to lift 10,000 pounds requires a thickness of about one inch in the object to be lifted in order to provide enough thread engagement. Objects having less than this thickness had previously been believed to require the predrilled and threaded mount plate  11 . Providing pre-drilled and threaded mount plates for use with conventional screw mounted hoist ring assemblies has many disadvantages. A large inventory of various sizes and thickness of such threaded plates must be maintained to satisfy a wide variety of lifting applications. Such an inventory creates the possibility of selecting the incorrect plate for a given application, which can result in catastrophic failure. These and other difficulties are overcome according to the present invention. 
   Referring particularly to  FIGS. 5 through 8 , there is illustrated generally at  10  a weld mount hoist ring assembly of the present invention. The weld mount hoist ring assembly  10  comprises a hoist ring mount  12  that is to be welded directly to the surface  13  of an object  15 . The purpose of the assembly is to lift object  15 . 
   Referring particularly to  FIGS. 3 and 4 , the hoist ring mount  12  has a generally radially extending flange portion  14  that is integral with a bearing portion  16 . Flange portion  14  includes obverse face  15  and opposed reverse face  17 . Reverse face  17  is adjacent external bearing surface  20 . The obverse face  17  of flange portion  14  is placed directly on the surface  13  of the object  19 . The obverse and reverse faces of flange portion  14  are peripherally joined by a perimeter portion. The perimeter portion, as shown particularly in  FIG. 4 , is welded in place on the surface  13  of object  15  by peripheral weld boundary  18 . 
   As shown, for example, in  FIGS. 3 and 4 , the hoist ring mount  12  includes a bearing portion  16  that includes an external bearing surface  20  and internal threaded portion  38 . External bearing surface  20  is adapted to rotatably and pivotally mount a lifting loop assembly between its proximal end, where the flange portion  14  is mounted, and its distal end where the internal threaded portion  38  opens. An axis extends between the proximal and distal ends. The internal threaded portion  38  is adapted to threadably receive the mounting screw of a conventional hoist ring assembly. External bearing surface  20  is circumscribed by a peripheral bearing boundary  24 . It has been found advantageous in this preferred embodiment that the length of the peripheral weld boundary  18  be, for example, at least approximately the length of the peripheral bearing boundary  24 . This distributes the stresses in the weld when a lifting load is applied. In addition, this separates the area of the weld on the flange from the bearing portion of the mount so the heat from the welding process does not adversely effect the material of the bearing portion. The length of the peripheral weld boundary  18  should be at least sufficiently greater than the peripheral bearing boundary  24  to provide a weld that is at least as strong as the other elements of the assembly. Although the shape of the peripheral weld boundary is illustrated as being generally circular, other shapes can be used, for example oval, square, polygon, and the like. 
   A preferred embodiment of the present invention is shown particularly in  FIGS. 7 and 8  wherein the hoist ring mount is adapted with parts of a hoist ring assembly as disclosed in Tsui et al. U.S. Pat. No. 4,705,422, which Tsui et al. patent is hereby incorporated herein by reference. This embodiment includes lifting loop  26  in pivotal engagement with a collar member  28  via pins  30 , which pins are retained in place by retainer clips  32 . A load washer  34  and retainer screw  36  are provided. The retainer screw engages the internal threaded portion  38  of hoist ring mount  12  and is tightened down against the load washer  34 . The bearing portion of the collar member  28  between its distal and proximal ends along axis  52  is slightly longer than the thickness of collar member  28 . With the retainer screw  36  fully tightened in internal threaded portion  38 , the collar member  28  is left free to rotate about the bearing portion of hoist ring mount  12 . Flange portion  12  provides for the separation of the collar member  28  from the weld. The weld is thus prevented from interfering with the rotation of collar member  28 . The reverse face of flange portion  12  is provided with a raised boss against which the mating face of collar member  28  turns. Importantly, the torque settings for the retainer screw  36  are less critical than for an equivalent sized prior art screw mount hoist assembly, because the shear stresses are not localized across the screw. Also, unlike conventional screw mounted hoist rings, if the obverse face of flange  14  is not exactly flat against the surface of the load, it is generally of no significant concern, because the loads are transmitted through the weld. Unexpectedly, it has been discovered that the weld mount hoist ring of the present invention, as compared to an equivalent size prior art screw mount hoist assembly, requires a lower installation torque setting and can support greater lifting loads. 
   Installation of the embodiment of  FIGS. 7 and 8  is achieved by removing screw  36  to free the hoist ring mount  12  from the lifting loop assembly. The entire lifting loop assembly, including the lifting loop and the collar member, is removed from mount  12 . The hoist ring mount  12  is then arc welded along its perimeter portion to the surface of the object. This assures the parts of the assembly, other than the hoist ring mount  12 , are not effected in any way by the heat of the welding process. The ability to disassemble the hoist ring mount from the lifting loop assembly thus contributes significantly to the safety of the system. The parts of the lifting loop assembly are then re-positioned about the hoist ring mount, screw  36  is installed and brought to its appropriate torque value. 
   Another embodiment of the present invention is shown particularly in  FIGS. 5 and 6 . In this embodiment the hoist ring mount  12  is adapted for use with the parts of the hoist ring assembly as disclosed in Tsui U.S. Pat. No. 5,405,210. This Tsui et al. patent is hereby incorporated herein by reference. In this embodiment, the hoist ring assembly  10  includes a forged hoist ring or lifting loop  40  having two integral stub shaft members  42  pivotally engaged in retainer recesses  44  of a collar member  46 . A retainer screw  48  and load washer  50  complete the assembly as the retainer screw engages the internal threaded portion  38  of the hoist ring mount  12 . The lifting loop assembly rotates generally about axis  52 . The reverse face of the flange portion  14  is configured with a grooved boss. The grooved boss serves to engage and retain the enlarged ends of the stub shaft members  42 . The collar member  46  rotates about the bearing member  16  and lifting loop  40  pivots about stub shaft members  42 . 
   In the embodiment illustrated particularly in  FIG. 9 , a hoist ring mount indicated generally at  12  includes a generally radially extending flange portion  14 , the reverse face  17  of which is integral with the proximal end of generally circular bearing member  16 . The obverse face  19  of flange portion  14  is adapted to being positioned against the surface of an object that is to be lifted. The obverse face  15  is joined to reverse face  17  through a peripheral portion. This peripheral portion is adapted to being welded to the surface of the object. For the purposes of illustration, the length of the peripheral portion has been illustrated as being less than about twice the circumference of the bearing portion. It will be understood that the length of the peripheral portion can be made  2  or  3  or more times the circumference of the bearing portion, as may be desired. The lifting loop assembly resembles that depicted in  FIGS. 7 and 8  except that a first end of a generally C-shaped detent element  54  is pivotally attached to the distal face of collar member  28  for movement in a plane that is generally normal to the longitudinal axis of the system. The throat  58  of C-shaped detent element  54  is positioned to move between an engaged and an unengaged configuration with a locking element in the form of annular groove  56  in bearing portion  16 . A pin  60  is provided for insertion through the second end of C-shaped detent element  54  and Into the body of collar member  28  when throat  58  is engaged with annular groove  56 . Pin  60  retains the detent element in engaged position with the locking element. The collar member  28  is free to rotate around the bearing portion  16 , and the lifting loop  26  is free to pivot about pins  30 . The throat  58  remains engaged with the locking element as the collar member rotates. Freeing pin  60  from engagement with collar member  28  permits the detent element to disengage from the locking element. The lifting loop assembly can then be removed from the hoist ring mount. When a quick hand releasable pin is used, the lifting loop assembly can be removed and replaced without the use of any tools. The bearing portion  16  has the advantage of being solid. Other lifting loops, such as, for example, that illustrated in  FIGS. 5 and 6  can also be used with quick disconnect detent and locking elements. 
   The hoist ring mount embodiment of  FIG. 10  is similar to that of  FIG. 3  except that an external threaded portion  62  is provided for the mounting of the lifting loop assembly. A nut, not illustrated, is drawn down against a thrust washer to hold a lifting loop assembly on the hoist ring mount. 
   The hoist ring mount of  FIG. 11  is a generally hat-shaped member having an annular flange  68  that is welded at  66  to the surface of a substrate  64 . A centrally located threaded stud  74  is threadably engaged with a cap member  70 , which together with a generally annular disk  76  and stem  72  forms a lifting loop assembly. Generally annular disk  76  is rotatably trapped in a cavity that is formed between the opposed end of threaded stud  74  and the inner end of cap member  70 . Stem  72  projects from generally annular disk  76  through the end of cap member  70 . Eye  78  is adapted to receive a clevis pin to which a lifting loop is mounted. 
   In the embodiments, which have been selected for purposes of illustration, the hoist ring or lifting loop is capable of continuous swivel about a longitudinal axis  52  and can also pivot approximately 180 degrees. The present invention can easily be adapted for use with a wide variety of lifting loop assemblies. 
   What have been described are preferred embodiments in which modifications and changes may be made without departing from the spirit and scope of the accompanying claims. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.