US 3776585 A
A sling particularly adapted for use in hoisting heavy objects. The sling is formed in a predetermined length and has loops at each end for connection to the hoisting equipment or for looping the sling about the load which is to be hoisted. The sling comprises a synthetic fabric, which according to the invention is woven in three plies in which each ply comprises chain warps extending throughout the length of the ply, the plies being interconnected both by the filling yarns and by connecting binder warps. The chain warps, the connecting warps and the filling yarns are composed of filaments of the same synthetic fiber. The connecting warps interlace the outer ply on one side with the central ply and interlace the outer ply on the other side with the central ply so that the connecting binder warps on one side do not extend through the entire thickness of the fabric. The binder warps on each side pass around each weft of the central ply as well as around each weft of the outer ply to provide a firm interconnection of the plies. In the event of damage to the webbing, for example by reason of fraying through or other failure of the ply on one side of the webbing, the damaged ply does not destroy the integrity of the remaining two plies which are otherwise undamaged. The failure of the sling at the point of damage is postposed, and the likelihood of the load coming loose from the hoisting equipment is substantially reduced.
Description (OCR text may contain errors)
United States Patent 1 Bridgehouse SYNTHETIC FIBER SLING CONSTRUCTION  Inventor: Scott Bridgehouse, Leola, Pa.
 Assignee: Lift-All Company, Inc., Manheim,
22 Filed: Sept. 15, 1972 21 Appl. Nb; 289,542
 US. Cl. 294/74, 139/411  Int. Cl. B66c l/l2  Field of Search 294/74; 139/408, 139/409, 411, 412, 383 R  References Cited UNITED STATES PATENTS 2,985,480 5/1961 Otley 294/74 R25,406 6/1963 Byme 139/412 X 3,464,459 9/1969 Ballard 139/383 R 3,296,062 1/1967 Truslow 139/426 R 2,423,910 7/1947 Snow 139/409 3,530,904 9/1970 Ballard 139/383 R OTHER REFERENCES Nylon Sling, Wear-flex Corporation, Page 1 Primary Examiner-Evon C. Blunk Assistant Examiner-James L. Rowland Att0rney-Dexter N. Shaw et al.
[ 7 ABSTRACT A sling particularly adapted for use in hoisting heavy objects. The sling is formed in a predetermined length and has loops at each end for connection to the hoisting equipment or for looping the sling about the load which is to be hoisted. The sling comprises a synthetic fabric, which according to the invention is woven in three plies in which each ply comprises chain warps extending throughout the length of the ply, the plies being interconnected both by the filling yarns and by connecting binder warps. The chain warps, the connecting warps and the filling yarns are composed of filaments of the same synthetic fiber. The connecting warps interlace the outer ply on one side with the central ply and interlace the outer ply on the other side with the central ply so that the connecting binder warps on one side do not extend through the entire thickness of the fabric. The binder warps on each side pass around each weft of the central ply as well as around each weft of the outer ply to provide a firm interconnection of the plies. In the event of damage to the webbing, for example by reason of fraying through or other failure of the ply on one side of the webbing, the damaged ply does not destroy the integrity of the remaining two plies which are otherwise undamaged. The failure of the sling at the point of damage is postponed, and the likelihood of the load coming loose from the hoisting equipment is substantially reduced.
6 Claims, 3 Drawing Figures I SYNTHETIC FIBER SLING CONSTRUCTION The present invention relates to hoisting equipment and has particular application to hoisting slings.
When using slings for hoisting components of heavy equipment and the like, it is important to maintain a close inspection of the sling material in order to avoid using a sling which might rupture and fail during hoisting. Since hoisting equipment is used in areas where workers must be present, any failure of the sling which would allow the load to fall uncontrolledly creates danger to the working people present in the hoisting area.
Various techniques have been tested for reducing the possibility of failure of the slings, including the provision of special strands in the sling which when they become worn expose a visible signal which is observed by the workers to indicate that that particular sling should be retired from use.
It has also ben porposed to strengthen the sling by incorporating into the sling fabric reinforcing strands of wire cable or the like. Although such a reinforcement provides a degree of safety, it also impairs the flexibility of the sling fabric and the ability of the sling fabric to conform to the shape of the load. The use of the wire reinforcement in the webbing construction has the effect of utilizing the webbing as a cover element for the wire reinforcement and when the cover is damaged, the wire reinforcement is exposed which may cause loss of gripping effect on the load and may cause the wire reinforcement to damage the load.
Despite the precautions of periodic inspections of the slings, as well as the presence of wear signals in the sling, there is a tendency for the workers to delay the replacement of the sling, particularly when the replacement slings are not immediately available at the time when the first signs of wear are observed.
With conventional slings, as soon as one of the components of the sling fabric is broken or otherwise fails, the construction of the fabric is such that the entire fabric is weakened and the entire sling fails. Thus, when the sling is brand new, and not subjected to any substantial wear, inadvertent damage to the sling, for example by sharp objects, may rupture a component of the sling fabric and cause premature failure of the sling at that point. Thus, regardless of the care and caution exerted by the working people, sling failure is a substantial danger to the work force at any location where material is being hoisted by the use of slings and the like.
With the foregoing in mind, the present invention provides an improved sling construction which reduces the danger to which the working people are exposed in the area where the sling of the present invention is used.
More particularly, the present invention provides a sling construction in which damage to one of the components of the sling does not automatically cause failure of the entire sling, but the load-carrying ability of the sling is maintained, although at a reduced level.
In particular the present invention provides a sling in which the sling fabric comprises a three-ply woven construction which consists of weft yarns interwoven with chain warps confined to each ply. The plies, in turn, are interconnected by connecting binder warps which connect the outer plies to the central ply. The warp yarns of the fabric construction being rigid, i.e. non-bulk and the weft yarns being bulked.
All of the objects of the invention are more fully set forth hereinafter with reference to the accompanyint drawing wherein:
FIG. 1 is a plan view of a sling embodying the present invention;
FIG. 2 is a longitudinal sectional view through the sling weave construction embodied therein as indicated by the lines 2-2 in FIG. 1; and
FIG. 3 is a transverse sectional view of the weave construction as indicated by the lines 3-3 of FIG. 1.
With reference to the drawing, the sling illustrated in FIG. 1 comprises a length of narrow fabric webbing which is folded back on itself at each end and sewn together to form sling eyes at each end which permit the sling to be connected to the hoisting equipment, and also permit the sling to be looped into itself to form a load-engaging noose. In the present instance, the sling comprises a single length of webbing wherein the free ends of the webbing are along the length of the sling between the loops forrned at each end. For the purpose of description, the loop bights of the sling are designated l1 and 12. On one side of the sling, the webbing fabric is in a continuous run 13 extending continuously from one bight 11 to the other bight 12. On the other side of the sling, the webbing fabric is provided with a double thickness by reason of the two end portions as indicated at 15 and 16 respectively. The runs of webbing 13, 15 and 16 are sewn into face-to-face engagement along their length of overlap by stitching indicated at 17 and 18. In the form of sling shown in FIG. 1, the end portions 15 and 16 are sewn to the continuous run 13 so as to form flat eyes in the bights 11 and 12. An alternate form of loop, i.e. the twisted loop, may be formed by sewing the webbing ends to the continuous run by twisting each end on its axis prior to being sewn. Where it is desired to use the sling with hooks, cables or other equipment, metallic fittings may be secured in the bight at one or both ends. Other standard sling arrangements may also be employed, including the fabrication of the sling into an endless loop having bights at both ends.
In accordance with the present invention, the webbing of the sling is of an improved fabric construction which provides a safety factor which delays failure of the entire sling when one of the components of the fabric fails, due to wear or to severance by harsh handling. As shown in FIGS. 2 and 3, the fabric construction is a three-ply construction. The upper ply of the fabric consists of weft elements 21a which are interwoven by chain warps 22 and 23, in the present instance in a plain weave construction. The central ply comprises weft elements 21b and central chain warps 24 and 25, likewise in the present instance interwoven with a plain weave construction. The bottom ply likewise consists of elements 210 and chain warps 26 and 27. In each ply, the weft elements and the chain warps make up a selfsustaining fabric which will retain its integrity apart from the other plies.
The three plies are integrated, as shown into a composite fabric, not only by weft elements 21a, 21b and 210, which are parts of a continuous weft strand 21 as shown in FIG. 3, but also by means of additional connecting binder warps 29 best shown in FIG. 2 which interweave between the upper and middle plies and connecting warps 31 which interweave with the central and lower plies. As shown in FIG. 2, the binder warps on one side of the composite fabric pass around each weft component of the outer ply and around each weft component of the central ply alternately. As shown in FIG. 2, in the present instance, the weft components of the outer plies are offset between the weft components of the central ply.
In each sling, all of the textile components of the sling are of the same fiber. Thus the weft elements 21, the chain warps 22, 23, 24, 25, 26 and 27, and the connecting warps 29 and 31 as well as the thread used in the stitching 17 and 18 are of the same fiber. In a nylon sling, all of the yarns and threads are nylon, in a polyester sling, all of the yarns and threads are polyester, etc.
In accordance with the invention, the warps of the fabric constructon are all rigid, continuous-filament, synthetic yarns, i.e. synthetic yarns which have not been textured or otherwise treated to become stretch or bulked yarns. The rigid synthetic yarns are flexible in the sense of being capable of bending along their axis but are rigid in the sense that they cannot be extended except by actual stretching of the filamentary components of the yarn. To insure maximum flexibility laterally, thereby assuring conformability of the webbing to the load, the warp elements are preferably multifilament yarns having a soft twist therein. The weft elements on the other hand, are bulked yarns. The bulked yarns are characterized by the fact that they are multifilament and that the individual filaments of the yarn are crimped, pigtailed, entangled or otherwise distorted so as to produce an enlarged cross section in the filament bundle. By incorporating such bulk yarn into the weft elements, the elements resist raveling in the event of rupture of one of the components of the fabric construction. Although it is preferred to use a continuous filament synthetic yarn in the weft, multifilament yarns having discontinuous filaments have been employed without substantial loss of effectiveness as far as strength and durability are concerned. However, the tactile and visual characteristics of the webbing are affected by the choice of continuous or discontinuous filamentary material. In the present instance, continuous filamentary material is preferred.
While a particular embodiment of the present invention has been illustrated, the invention is susceptible to various modifications. Not only is arrangement of the webbing in the sling variable as noted above, but also the weave construction may be varied without departure from the invention. For example, although a plain weave has been illustrated in each of the plies, other weave forms may be used alone or in combination and the mode of connecting the outer plies to the center ply may be varied by altering the pattern of the connecting warps. The present construction has the same warp and weft density in all three plies, but the densities may be varied to accommodate the construction to special uses. Furthermore, if desired, signal yarns may be incorporated into the weave construction, for example as special warps, as additional weft, or by coding selected warps in the central ply to signal when the sling has been subjected to sufficient wear or hard usage to justify replacement.
The integrity of the sling is maintained by use of the construction of the present invention in the event of damage to the weave, for example through wear or damage to the warps in the outer ply. The destruction of one of the outer plies and particularly if the ply is damaged across the full width of the webbing, although the integrity of the outer ply may be destroyed by de struction of the components, the integrity of the remaining two plies remains substantially unimpaired so that the strength of the sling is not lost completely. With prior art multi-ply webbing, in the event of destruction of one ply, the remaining plies tend to delaminate and, after separation are subject to premature rupture by reason of the excessive strains placed on the delaminated plies. The construction whereby the connecting binder warps are confined to only two of the three plies insures against delamination of the entire plied structure in the event of damage to the connecting warps. In this fashion, the synergistic effect of the laminated plies is retained. It has been found that the slings made in accordance with the present invention exhibit substantially greater durability and the lengths of webbing are less subject to damage during the sewing operation in fabricating the webbing into the slings. Furthermore, since a safety factor is obtained by the fact that the integrity of the sling is retained even after destruction of a single ply in the outer surface, the slings may be used for less strenuous requirements after the sling shows the first signs of wear.
Modifications to the illustrated embodiment of the invention have been suggestd, and the invention is not limited to the specific embodiments illustrated and described. Other changes and modifications may be made therein and thereto in the scope of the following claims.
1. A sling for use with hoisting equipment, comprising a length of fabric webbing having means forming a loop or bight at each end thereof, said fabric webbing comprising a three-ply fabric construction having in each ply weft components and chain warps interconnecting said components to form a self-sustaining fabric construction therein, said plies being interwoven by connecting binder warps, each binder warp being interwoven with one ply at the surface of said webbing by passing around each weft component in said ply and with the central ply by passing around each weft component in said ply whereby said binder warp is confined to only two of said plies, each of said chain and binder warps being a rigid, continuous-filament, synthetic yarn, each of said weft components being a bulked, multifilament, synthetic yarn.
2. A sling according to claim 1 wherein said warps are multifilament yams.
3. A sling according to claim 2 wherein said weft components consist of a bulked, continuous filament yarn.
4. A sling according to claim 1 wherein said sling comprises a single length of webbing having its end portions folded back to overlie itself to form loops at each end, said overlaid portions being sewn together by thread composed of the same synthetic fiber as the warp and weft yarns.
5. A sling according to claim 1 wherein said chain warps and weft elements in each ply comprise a plain weave, the warp and weft densities in all of the plies being substantially equal.
6. A sling according to claim 1 in which all of the warps and weft components consist of the same synthetic fiber.