Abstract:
A sling system comprises a plurality of sling units each including a synthetic fibrous sling and a roller unit which has one or more spool-shaped rollers. The system provides for lifting a load in equilibrium and maintaining the load in that position or be rotated or tilted between horizontal and vertical positions. The system provides for a plurality of attachment points of the sling units to the load, and the sling units and may be set up as a single array or a multiple array depending on the type of load being lifted, transported and positioned. Endless and continuous loop synthetic slings and multiple roller units are used in sling units and provide for uniform and equal distribution of the load throughout the sling system. The spool-shaped rollers may be molded of a rigid plastics material with each roller having end flanges to confine the synthetic sling.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    When performing a lift in the hoisting and rigging industry, it is often desired that the load be in equilibrium so that each connection point at the load carry an equal part of the weight at all times to prevent overloading of the lifting components or prevent undesirable stresses on the load. In some applications, not only is it necessary to keep the load points in equilibrium, it is necessary to rotate or tilt the load from a horizontal position to a vertical position. Commonly, this task is accomplished by using wire rope or cable slings and large metal pulleys. In order to maintain the wire cable capacity, the ratio between the diameter and type of cable and the diameter of the pulley is referred to as a D/d ratio where “D” is the diameter of the pulley and the “d” is the diameter of the cable. By international standards for existing technology, this ratio ranges from 12-15. For example, a one inch diameter cable would require a pulley having a minimum diameter of twelve inches. Wire cables and their associated pulleys are commonly made of steel or some other metal which results in the cables and pulleys being extremely heavy and cumbersome. One form of cable and pulley rigging system is produced by Meadow Burke and illustrated on their website of MeadowBurke.com. 
         [0002]    Multi-strand synthetic fiber slings are commonly manufactured in two styles. In an eye to eye style, the sling is made with a continuous fiber core, and at each end the fibers are equally split, placed in a protective cover and sewn together. A continuous loop style is made similar, but the fibers are separated for the entire loop, creating a continuous endless loop, and the fibers are placed within a protective sleeve. Both of these styles are usually made in two different configurations, either single path or twin path. The single path has one or several continuous fibers looping around for a predetermined number of times depending on the required strength. The twin path has two separate paths of one or more continuous loops in isolated paths, and a protective cover is sewn lengthwise around the twin paths. 
         [0003]    Flat type synthetic slings are manufactured in many styles. They are a woven fabric type materials that can be sewn together in plies to increase strength and are supplied in variable widths. They can be eye to eye with either sewn or attached metal ends, or a reverse eye which changes orientation of the eye in relationship to the body. They also can be sewn together to create a continuous loop type sling. Such slings are generally used for lighter loads. Examples of synthetic fiber slings are disclosed in U.S. Pat. No. 4,850,629, No. 5,492,383, No. 5,836,631, No. 6,508,051, No. 7,658,423, No. 7,661,737 and No. 7,669,904. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention is directed to a rigging or sling system for carrying and positioning a heavy load and wherein synthetic fibrous sling units are connected to the load in a plurality of places so that balance and equilibrium are obtained. In accordance with the invention, each unit has a synthetic sling directed over a roller so that the load is distributed through the sling to the roller. As the load is rotated or tilted, the sling shortens on one side while lengthening on the other side, and the corresponding angle of the sling to the load will change accordingly while maintaining equal loading at the attachment points to the load regardless of the angle of the slings with respect to the load. The sling units may be arranged in a single or multiple arrays, and each sling unit is attached to the load at two points. This allows for unlimited arrays in both the horizontal and vertical directions. For example, a two by two array of horizontal connection points to the load requires two roller and associated sling units, and the rollers are connected to a lifting device such as a crane hook or a load beam attached to a crane hook. In this configuration, a load can be lifted, and each attachment point will have an equal portion of the load based on its relationship to the center of gravity of the load. By increasing the number of sling units in a vertical direction, the number of attachment points can be increased, while evenly distributing the load. Thus, an array of four by two sling systems requires two primary rollers and four secondary rollers, whereas a four by four array requires two primary rollers, four secondary rollers and eight tertiary rollers. 
         [0005]    The present invention provides for sling systems of different configurations with rollers for using slings having a single path, a twin path or a combination. An eye to eye type synthetic sling requires only a single roller unit with the sling passing over the roller and having two eyes attached to the load. A continuous endless loop sling unit requires multiple roller units, one end unit at each point of connection to the load and one double roller unit between the end units. After a load is lifted where all connection points to the load are at the same level, only a small force is required to tilt the load to a position where the connection points are located with one over the top of the other thereby placing the load in a vertical position while maintaining an equal force at each connection point to the load. If desired, a locking mechanism may be used with any of the rollers so that the load is stabilized from further rotation. This can be done either manually, automatically or by a predetermined stop on the sling. 
         [0006]    A sling system constructed in accordance with the present invention provides a number of advantages over existing sling systems. For example, the sling units provide for a significant weight reduction by using lightweight synthetic slings which are more flexible and permit a significant lower roller diameter to sling thickness ratio. The substantially lighter weight sling system, including the lighter weight and smaller diameter rollers, may be as much as 80% lighter and is also safer, easier and faster to install and further results in less likelihood of an injury to an operator. The sling system also provides for better distribution of the loads due to the fact that length tolerances are better controlled using synthetic slings which have less stretch under load and are able to maintain their required lengths after many uses. The synthetic sling and roller system of the invention further provides for a substantial cost savings over currently used sling systems. 
         [0007]    Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a sling system constructed in accordance with the invention and showing its use for lifting, transporting and tilting a heavy object in the form of a precast reinforced concrete wall panel; 
           [0009]      FIG. 2  is an enlarged fragmentary perspective view of the portion of the sling system shown in circle  2  of  FIG. 1 ; 
           [0010]      FIG. 3  is an enlarged fragmentary perspective view of the portion of the sling system shown in circle  3  of  FIG. 1 ; 
           [0011]      FIG. 4  is an enlarged fragmentary perspective view of the portion of the sling system shown in circle  4  of  FIG. 1 ; 
           [0012]      FIG. 5  is an enlarged fragmentary perspective view of the upper portion of the sling system shown in circle  5  Of  FIG. 1 ; 
           [0013]      FIG. 6  is an elevational view of the portion of the sling system shown in  FIG. 4 ; 
           [0014]      FIG. 7  is a fragmentary vertical section taken generally on the line  7 - 7  of  FIG. 6 ; 
           [0015]      FIG. 8  is a side elevational view of the portion of the sling system shown in  FIG. 6 ; 
           [0016]      FIG. 9  is a vertical section taken generally on the line  9 - 9  of  FIG. 8 ; 
           [0017]      FIG. 10  is a perspective view of a sling system constructed in accordance with another embodiment of the invention for lifting and transporting a heavy object such as a precast concrete tower section; 
           [0018]      FIG. 11  is an enlarged fragmentary perspective view of the sling system within the circle  11  in  FIG. 10 ; 
           [0019]      FIG. 12  is an enlarged fragmentary perspective view of the sling system shown in the circle  12  of  FIG. 10 ; 
           [0020]      FIG. 13  is a fragmentary perspective view of a roller shackle and sling assembly as shown in  FIG. 3 ; and 
           [0021]      FIG. 14  is a vertical section of the shackle and sling assembly, taken generally on the line  14 - 14  of  FIG. 13 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    Referring to  FIG. 1 , a sling system  20  constructed in accordance with the invention is ideally suited for lifting, transporting and tilting a heavy object such as a horizontal reinforced concrete panel  22  which is commonly precast on a horizontal concrete floor and later lifted, tilted to a vertical position and positioned to form a wall panel for a single or multi-story tilt-up building. However, a sling system constructed in accordance with the invention may be used for lifting and maneuvering any form of heavy object with the aid of a lifting device such as a mobile crane. In accordance with the invention, a plurality of upper sling units  25  are used to connect an adaptor member or plate  28  to a horizontal elongated spreader beam  30 . The adaptor plate  28  has a slot or opening  32  ( FIG. 2 ) for receiving a crane hook (not shown), and the spreader beam  30  ( FIG. 5 ) is preferably formed of square tubular metal or steel has horizontally spaced adjustment holes  34 . Each of the sling units  25  includes a continuous and endless loop flexible sling  40  in the form of a flexible synthetic fibrous sling having a cross-sectional width substantially greater than its cross-sectional thickness when directed over a roller. One form of sling material which has provided satisfactory results is manufactured by Lift-All Company, Inc. in Landisville, Pa. and sold under the trademark TUFLEX. This continuous loop synthetic fibrous sling commonly uses a tubular flexible jacket which encloses an intermediate portion of the sling, and forms lifting eyes at opposite end portions of the sling or the jacket may be omitted. 
         [0023]    Each of the sling units  25  also includes a double roller assembly or unit  45  ( FIGS. 1 &amp; 2 ) which connects each endless loop sling  40  to the lift plate  28  or other sling to interface with a single or duplex type crane hook. Each of the double roller units  45  includes a housing formed by a pair of side plates  48  ( FIGS. 2 ,  4  &amp;  6 - 9 ), and the side plates are rigidly connected by a set of shafts  52  and  54 . Each of the shafts has opposite end portions of reduced diameter and is secured to the side plates  48  by snap-type retaining rings  56  ( FIG. 9 ) or other forms of fasteners. The shaft  52  supports a cylindrical bearing  58  which is secured to a spool-like roller  60  preferably molded of a rigid plastics material with the bearing  58  as an insert. As shown in  FIG. 9 , the roller  60  has a generally cylindrical center portion  62 , but may be convex or concave, which integrally connects opposite end flanges  64  of larger diameter so that the flexible sling  40  is captured and confined by the roller and opposite edge surfaces of the sling do not contact the side plates  48 . 
         [0024]    Another spool-like roller  70  ( FIG. 9 ) is constructed the same as the roller  60  but is smaller in diameter and is also molded with a metal bearing  74  as an insert within the roller  70 . As shown in  FIG. 7 , the lower roller  70  is sufficiently smaller than the upper roller  60  so that portions of the endless sling  40  may loop or extend substantially 180 degrees around each of the rollers  60  &amp;  70 . As shown in  FIG. 2 , the upper end portions of the side plates  48  are connected to the lift plate  28  by a cross-pin  78  extending through a bearing  79  within the plate  28  and secured by a cotter pin. 
         [0025]    Referring to  FIG. 5 , opposite end portions of each of the two endless synthetic slings  40  are connected to the spreader beam  30  by a pair of adjustable brackets  85  each including a pair of parallel spaced side plates  87  having a pair of cross-pins  88  or bolts extending through aligned holes within the side plates  87  and the spreader beam  30 . A vertical plate  92  is rigidly connected to each pair of side plates  87  by cross-pins  93  or bolts, and a single roller shackle  95  ( FIGS. 5 &amp; 13 ) connects each plate  92  to the endless synthetic sling  40 , as shown in  FIG. 5 . As shown in  FIG. 13 , each of the shackles  95  includes a pair of flat or formed side plates  97  having lower end portions with aligned holes receiving a cross-pin or bolt  99 . The bolt  99  also extends through an aligned hole within the vertical plate  92  and receives a nut  102  and retaining cotter pin  103 . The upper end portions of the side plates  97  receive a cross-pin  106  ( FIG. 14 ) which receives a spool-like roller  60  around which a longitudinal portion of the sling  40  extends about 180 degrees. 
         [0026]    As apparent from  FIG. 1 , as a result of the pair of sling units  25 , including the endless synthetic slings  40  and their connections to the lift plate  28  and the spreader beam  30  by the double roller units  45  and the single roller shackles  95 , any load on the spreader beam  30  is uniformly distributed or equalized on each leg of each endless loop synthetic sling  40  with the spreader beam  30  remaining horizontal at all times when being lifted by a crane hook connected to the adaptor plate  28 . This permits the use of a lighter weight tubular spreader beam. 
         [0027]    Referring to  FIG. 1 , a set of four sling units  115  extend downwardly from the spreader beam  30  in parallel spaced planes perpendicular to the spreader beam. Each of the units  115  also includes an endless loop synthetic fibrous sling  120  which is constructed substantially the same as the endless loop sling  40  except longer in length. Each of the flexible slings  120  is connected to each of the adjustable brackets  85  ( FIG. 5 ) by a downwardly projecting welded plate  92 , a U-shaped shackle  121  and a double roller unit  45 . The lower end portions of each endless loop sling  120  receives an upper spool-like roller  70  ( FIG. 9 ) which is supported by the upper end portions of the side plates  48  of a double roller unit  45 . The upper or top roller  70  on each unit  45  is rotatably supported a cross shaft  122  ( FIG. 9 ) including a handle member  124  secured to one end portion of the shaft which has an opposite end portion receiving a retaining cotter pin  126 . 
         [0028]    Referring again to  FIG. 1 , each of the double roller units  45  with a top roller  70  connected to an endless loop sling  120 , also receives a lower sling unit including an endless loop synthetic fiber sling  140  which is constructed substantially the same as the endless loop slings  40  &amp;  120 , except that the sling  140  is longer in length, and there are eight sling units. As shown in  FIG. 3 , each of the lower end portions of each sling  140  is connected by a single roller shackle  95  to an attachment member  145  having a base plate  148  secured by anchor members (not shown) welded to the plate  148  and projecting downwardly into the precast reinforced concrete panel  22 . A vertical projection or plate  151  is welded to the base plate  148  and has a cross hole which receives a shackle bolt  99  as shown in  FIG. 13 . 
         [0029]    Referring to  FIG. 10 , a sling system constructed in accordance with the invention may also be used for lifting and transporting a heavy object such as a cylindrical tower section  165  used for erecting a vertical tower for supporting a wind turbine. In accordance with this embodiment, a sling system  170  comprises a pair of sling units each including a flexible endless loop synthetic fiber sling  175  which extends over the roller  60  of a single roller shackle  95  ( FIG. 12 ) having side plates  97  receiving a cross-bolt or pin  99 . The cross-pin  99  extends through an inverted U-shaped non-roller shackle  178  having opposite end portions connected to the lift plate  28  by a cross-bolt  181  extending through a bushing  182  within the lift plate  28 . The lower end portions of each sling  175  have conventional end loops or eye portions  184  ( FIG. 11 ) each of which receives a cross-pin  187  of a non-roller shackle  190 . 
         [0030]    Each of the shackles  190  has side plates  192  pivotally connected by laterally aligned cross pins  194  extending into a swivel ring or collar  196  which rotates about the axis of a screw  197  connected to a tower bracket  198 . The bracket  198  has horizontal base flanges secured to the tower section  165  by a pair of bolts  201  threaded into anchor tubes or fittings  203  embedded in the upper end portion of the tower section  165 . As apparent from  FIGS. 10 &amp; 12 , the roller shackles  95  and the synthetic slings  175  provide for evenly distributing or equalizing the load or weight of the tower section  165  or other heavy object and significantly reduce the weight of the sling system  170 . The tower section  165  may be shipped with a horizontal axis and by use of the sling system  170 , including the swivel shackles  190 , and be rotated by a crane to a vertical position with a vertical axis, as shown in  FIG. 10 . 
         [0031]    As apparent from the drawings and the above description, a sling system constructed in accordance with the present invention provides desirable features and advantages. For example, the sling system provides all of the advantages referred to in above paragraph [0006]. The sling system of the invention is also modular in that any number of combinations of components may be used with the synthetic slings, including a single roller unit, a double roller unit, and non-rolling and rolling shackles. 
         [0032]    While the sling systems herein described and their method of use constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to the precise forms of sling systems described, and that changes may be made therein without departing from the scope and spirit of the invention as defined in the appended claims.