IE44112B1 - Improvements relating to load supports - Google Patents

Description

Thia invention relates to supports for loads to be lifted, and particularly to slings and to bags for transporting bulk material, for example comminuted material.

Hammock-type slings are known which comprise a 5 rectangular sheet of material, the two ends of which are folded over along straight lines and stitched to form a tunnel at each end of the sling. A lifting loop extends through each tunnel and the two loops can be engaged by lifting equipment to lift the sling together with a load placed on the sling. As the lifting force is applied it is found that the sling material at the ends of the sling is bunched into the centre and the edges of this material are more highly stressed than the centre. This limits the lifting capacity of the sling. targe hags Foi· transporting bulk quantities of powdered or granular material are now commonly used, such - 2 bags usually having a square base from which four walls extend upwardly. The upper edges of the fabric of the walls are folded over along straight lines and are stitched to form tunnels and a drawstring passes through the tunnels and is enclosed thereby except at the four corner points of the bag. At these corners the drawstring forms lifting loops by way of which the bag may be lifted.

As with the sling, the material of the bag walls bunches towards the centre of each wall and the edges of the walls are more highly stressed than are the centres.

According to the present invention a support for a load to be lifted comprises a fabric support member on or in which a load may be placed, the member having edges whcih are folded to a shape which is concave away IS from the body of the member, the folded-over part of each folded edge being stitched to the body of the member to form a tunnel, and a lifting sling extending through each tunnel and forming a lifting loop or loops.

Thus, a hammock-type sling according to the invent2θ ion comprises a rectangular length of material each end of which is folded to a shape which is concavfi away from the body of the sling, each folded-over part being stitched to the main body of the sling to form a tunnel, and lifting slings extending one through each tunnel and formed into loops by way of which the sling can be lifted. The stitching lines may each follow a concave shape substantially parallel to the folded edge - .1 44112 of the material., may follow a different concave shape or may simply be a straight line across the width of the material.

A bag according to the invention, for containing bulk material , has a wall structure extending upwardly from a base, the upper edge of the wall structure having parts which are folded to shapes which are concave away from the body of the bag, each folded-over part being stitched to the main body of the wall structure to form a tunnel, and a lifting sling in the form of a drawstring extending through each tunnel and exposed to form lifting' loops* Again the or each stitching line may be. straight or of concave shape and may be substantially parallel to tlie respective folded edge.

In each case the part of lifting si ing in the tunnel, ivhen a load is applied, takes up a concave shape similar to that of the edge of the material, rather than following a straight edge of the material as in slings and bags known prior to the invention. Xt is found that as the material bunches when a lifting load is applied to the loops, the stress distribution over the width of the material is very much more even, so that the lifting capacity or factor of safety of a sling or bag according to the invention is higher than that of previously known slings or bags.

In one form of the invention the edge of the material - 4 4 4 H 2 i.ss folded to a continuous, substantially uniform concave curve, and held to that curve by suitable stitching. In an alternative form a number of transversely-shaped cuts are made extending longitudinally of the material to form a plurality of flaps, which arc individually folded to give the required concave shaped edge. The flaps are secured by a number of parallel lines of stitching which may conveniently run parallel to the shape of the concave edge.

JO for any given size of bag or sling which is to be used for a given load there i.s an optimun shape for each edge which gives virtually equal stress distribution across the whole of the width of tlie fabric. This optimun shape may be determined empirically as will be described later.

The invention is particularly suited to slings and bags of woven material, for example polypropylene, which can readily be stitched and which has the required loadbearing properties.

The invention will be. better understood from the following description of specific embodiments thereof, read in conjunction with the accompanying drawings in which: figure 1 shows part of a sling according to the prior art; figure 2 shows the equivalent part of a first embodiment of a sling according to the invention; - 5 44113 Figure .3 is a perspective view ol' a second embodiment of a Sling according to the invention.

Figure 4 is a perspective view of a bag according to the invention; and Figure 5 is a diagram illustrating how an optimum shape can be determined.

Figure 1 shows one end of a known hammock type sling comprising a length of fabric 1, the end of which is folded along a straight line and is stitched at 2 to form a tunnel. A lifting loop 3 extends through the tunnel and is engageable by lifting equipment. As a lifting force is applied the edges of the fabric become very highly stresses and tlie sling fails by tearing across the fabric from one edge.

IS Figure 2 shows the corresponding end of a sling according to the invention, comprising a length of fabric 4 the end of which is folded over along a concave curve and stitched at 5 to form a tunnel. The stitching lines extend substantially parallel to the concave curve of the edge. Again, a lifting loop 6 extends through the tunnel and is engageable by lifting equipment. In this case, however, the fabric is substantially evenly stressed across its width and the sling fails by tearing in the body of the fabric rather than from one edge. Tests with identical pieces of fabric constructed as shown in Figures - 6 44112 and 2 have shown that the failure load of a fabric formed as shown in Figui'e 2 is from 30# to 50$ higher than that shown in Figure 1.

Figure 2 shows an ideal form of tunnel which is formed by folding the edge of the material to an accurate, substantially uni form concave curve, and holding the material by appropriate stitching. Figure 3 shows an embodiment of sling and illustrates a simple method of obtaining a sufficiently close approximation to the ideal curve. The sling is shown in the use position before lifting, and comprises a length of woven polypropylene 7 on which is placed a load 8, the ends of the sling being drawn up about the load. Straps 9, 10 extend across the top of the load and are joined by a buckle 11 of the type which allows the straps to be tightened and prevents the tension being released.

Identical tunnels, 12, 13 respectively, are formed at each end of the sling, and only tunnel 12 will he described in detail. To form this tunnel two transversely-spaced longitudinally extending cuts 14j 15 are made in the material to divide tin· end into three flaps 16 to if?.

The centre flap 17 is folded about a line substantially perpendicular to the longitudinal edge of the material, and the outer flaps 16 and lk are folded about lines that are inclined at equal and opposite angles to the fold line of flap 17. All three, flaps are stitched, to the „ 7 44113 body of the sling by a number of parallel rows of stitching 19 which extend substantially parallel to tho fold lines of the flaps. A lifting loop 20 is passed through the tunnel 12 and a similar lifting loop 21 is passed through the tunnel 13. The load is lifted by engaging the two lifting loops with appropriate lifting equipment and it is found that, due, to the concave shaped edges, the tension is spread substantially evenly across the full width of the material of the sling. to For slings of different sizes and different capacities the concave shapes of the edges of the material may differ from that shown. Furthermore it is not essential to form the tunnels hy making three flaps at the ond of each bag and any number of flaps can be used, with all flaps preferably being of equal width.

Referring now to Figure 4 this shows a bag for containing bulk material, the hag having a square base 22 from which four walls 23 to 2b extend upwardly. The upper edge of each wall is formed with a tunnel 27 to 3θ respectively produced by cutting individual flaps in the material and folding and stitching these in the manner already described for· the sling shown in Figure 3· Tho upper parts of the walls of the bag are separated from each other by cuts such as 31 and the material around the lower end of each cut is bound by a pad 32 of material stitched to the bag to reinforce the juncture between adjacent walls. A drawstring 33 extends through the tunnels in each of the walls and is formed into loops 34 to - 8 4 4112 in thi· spaces formed by the cuts at the corners of the bag. The bag is lifted by engaging the loops with lifting equipment and as with the sling it is found that the lifting load is distributed substantially evenly across the full width of each side of the bag. figure 4 shows a square-bottomed bag, but the invention Figure 5 shows a method whereby the optimum shape lor tlie edge of the material can be plotted. The Figure shows a rectangular outline having a width w equal to the fabric width, and a height h equal to the free length of fabric in tlie loaded sling or bag to be lifted. By free longth is meant that length oi' fabric which lies above the level of the load and is thus not restrained from movement by the Load. The rectangular outline is divided into a number of equal widths by lines A-A^ etc., with a centre line G -fJ . With compasses at centre A an ai*c of radius ib is drawn to intersect the centre line at Ii. The compasses are tlr-n moved to centre 13 and set to a radius equal to the distance from Ii to ll, an arc being drawn to intersect line B-B1 at 1. The compasses are moved to centre C and set to a radius equal to the distance from C to I!, an arc heeing drawn fo intersect l ine f-C at .1. Points K, 1 and M are - 9 44113 established in a similar manner. The curve joining ii, M, L>, K, .1, 1, Λ1 is then the ideal curve Per the edge of tin: material and will result in maximum uniformity ol' stress transmission to the material. The curve will be Pound to become shallowcx· as the value of h increases

Claims (9)

1. ]. A support for a load to be lifted comprising a fabric support member on or in which a load may be I>1 accd, the member having edges which are folded to a 5 shape which is concave away from tho body of the member, the folded-over part of each folded edge being stitched to the body of the member to form a tunnel, and a lifting sling extending through each tunnel and forming a lifting loop or· loops. 1(l

2. A support according to claim 1, in which each si.itching line follows a concave shape substantially parallel to tho respective folded edge of the material.

3. · A support according to claim 1 or claim 2 in which, at edges of the material to be folded, a number 15 of transversely spaced cuts are made, extending longitudinal Jy of tbe material to form a plurality of flaps, which arc individually folded to give the concave edge.

4. - A support according to claim 3 in which two cuts arc made in each edge to be folded to form three flaps, 20 tho centre flap being folded about a line substantially perpendicular to the longitudinal edge of the material, and the outer flaps being folded about lines that are inclined at equal and opposite angles to the fold line of tiie centre flap. 25

5. Λ hammock-type sling comprising a rectangular length of material, each end of which is folded to a 44113 shape which is concave, away from the body of the sling, each folded-over part being stitched to the main body of the sling to form a tunnel, and lifting slings extending one through each tunnel and formed into loops by way of which the sling can be .lifted.

6. A hammock-type sling substantially as described herein with reference to Figure 2 or Figure 3 of the accompanying drawings.

7. · Λ bag for containing bulk material, the bag having a wall structure extending upwardly from a base, the upper edge of the wall structure having parts which are folded to shapes which are concave away from the body of the bag, each folded-over part being stitched to the main body of tlie wall structure to form a tunnel, and a lifting sling in the form of a drawstring extending through each tunnel and exposed to form lifting loops.

8. A bag according to claim 7 in which the wall structure comprises four walls extending upwardly from a rectangular base, the upper edge of each wall being folded to concave shape and stitched to the main body of the respective wall to form a tunnel, a single drawstring extending through al l. four tunnels and being exposed to form lifting loops, one at each junction between two adjacent wails.

9. · A bag for containing bulk material, substantially as described herein with reference to Figure 4 of the 4 4112 accompanying drawings.