EP0000838B1

EP0000838B1 - Flexible bulk container

Info

Publication number: EP0000838B1
Application number: EP78300256A
Authority: EP
Inventors: Allan Macfarlane Sandeman; James Duncan Bell
Original assignee: Tay Textiles Ltd
Current assignee: Tay Textiles Ltd
Priority date: 1977-08-06
Filing date: 1978-08-07
Publication date: 1981-12-23
Also published as: CA1095470A; DE2861452D1; ATA567278A; FI61169B; FI61169C; PT68389A; EP0000838A1; AT382582B; FI782410A; US4207937A

Description

This invention relates to a flexible bulk container.
Such containers may be used in the storage and transport of materials in granular, powder and other particulate form, such as chemicals, foodstuffs, cement and so forth. The containers are generally in the form of large bags or sacks. They are often required to carry loads of up to one tonne or more, and there should desirably be a considerable safety margin above this working load.
The containers are frequently made from woven fabric, for example woven polypropylene or another suitable synthetic material. In many instances there will be seams between adjacent portions of the container and it has been found that in use these can become regions of high stress concentration so that there is an increased tendency of the fabric to tear adjacent the seams. It is also known to attach lifting loops or the like to the main body of the container, and the points of attachment may similarly become regions of high stress concentration.
Various methods have been proposed for reinforcing a container in regions of potentially high stress concentrations, but many of these proposals involve the use of additional reinforcing material and an increased number of manufacturing steps. This may increase the time and cost of production, which can be undesirable, particularly if the containers are intended to be disposable.
In Japanese Utility Model 48-62246, there is disclosed a flexible bulk container of woven fabric having side walls and a closed bottom, the warp threads of the fabric constituting the side walls extending up the container and there being a region of a side wall in which the strength of the warp per unit width is greater than that over at least the major part of the remainder of the side wall. The particular bag disclosed in this Japanese Utility Model is woven using a circular loom and reinforcement is provided by regions of crammed warp threads to which the lifting loops are simply stitched. Whilst this has the advantage of reinforcement inherent in the woven fabric, a circular woven bag is not always desirable and it is frequently desirable to have joins between fabric portions for example to make a bag of square cross-section from a number of panels.
Thus viewed from one aspect a container in accordance with the present invention is characterised by a joint extending along two fabric portions constituting the side walls adjacent selvedges thereof, there being a greater strength warp region adjacent to and terminating at the respective selvedges of the portions where they are joined together, and the lifting means being attached to the side walls in such region.
Thus it is possible to both reinforce a seam and the point of attachment of lifting loops with a simple construction which is nevertheless effective.
The container may be made from a plurality of fabric panels or from a single strip of fabric suitably folded, different parts of which constitute fabric portions. It is generally desirable that higher warp strength regions are provided adjacent both selvedges of a fabric panel or strip.
Advantageously, the container may be designed so that as many of its seams as possible extend along selvedges, or at least those seams which will be subjected to the highest stress concentration in use.
In a construction employing a plurality of fabric panels, which for ease of manufacture may be of constant width, the panels may be joined to one another along their selvedges to form an open top bag-like structure with the seamed selvedges extending generally vertically. One such concentration may comprise three portions, one of which is U-shaped, the other two being connected across the ends of the U-shaped portion, the curved bight of which forms the bottom of the container.
It will be appreciated that in such an arrangement reinforced regions can extend up the side walls and across the base of the container. This is useful in itself and provides advantages over the disclosure in Japanese Utility Model 48-62246. Thus viewed from another aspect a container in accordance with the present invention is characterised in that it consists of three woven fabric portions one of which is substantially U-shaped and forms first and second side walls and the base of the container, the warp threads of such portion extending between the first and second side walls and across the base, and the remaining two of which are connected across the ends of the U-shaped portion and form third and fourth side walls, each of said portions including a region of greater warp strength extending the length thereof, the lifting means being attached to said regions.
Joining of fabric portions may be by any suitable means such as welding or stitching. For example, stitching may be applied as a continuous helix, each convolution penetrating the higher warp strength regions. Alternatively, parallel rows of stitching can be inserted through the higher warp strength regions.
The lifting means, such as fabric loops, may be stitched or otherwise fastened to the regions of higher warp strength.
Although in preferred containers the higher warp strength regions are adjacent seams, regions of higher warp strength could be provided between the selvedges, for example in the middle of a panel portion, so as to facilitate the attachment of lifting loops, straps and so on, at locations other than adjacent seams.
Such positioning of higher warp strength regions independently of seams is itself advantageous, and is applicable to a container having no suitable seams, for example, a container having a seamless main body portion.
Such a container may comprise a main body portion in the form of a seamless tube the warp threads of which are parallel to the axis of the tube, the regions of higher strength warp being spaced around the periphery of the tube, the tube being closed at one end and lifting means such as loops being fastened at the other end of the tube to the higher strength warp regions.
The body portion may be closed at the bottom end by fitting a circular bottom piece to the body portion and attaching it thereto e.g. by stitching the sides together.
The body member presents no longitudinal seams which would be weak points, and is simple to form due to the reduced number of sewing operations.
Lifting loops for example may be fastened to containers in accordance with the invention by attaching the ends of the strips of loop material to flanges on the container which may for example be radially projecting and formed by pinching together the regions of the container with higher warp strength, the loop ends being attached to the opposite outside faces of the pinched portions. An arrangement combining the use of flanges and reinforced warp regions is desirable in itself and provides advantages over the disclosure in Japanese Utility Model 48-62246. Thus viewed from a still further aspect a container in accordance with the present invention is characterised in that there is formed from a region of higher warp strength a flange of at least double thickness material extending from a side wall of the container and the lifting means are attached to such flange.
In an alternative although not preferred arrangement opposite ends of a strip of material to form a loop may be fastened to the inside and the outside surfaces of the container.
The higher strength warp regions could be provided by using a higher density of warp threads, by using higher tenacity warp threads, or by a combination of the two. Warp threads of lower tenacity may be formed as flat polypropylene tape, and those of higher tenacity as twisted polypropylene tape R.E.F. (roll embossed film) yarns or high tenacity multi-filament yarns. In a preferred construction, whilst the lower tenacity threads are flat tape, the higher tenacity threads are e.g. R.E.F polypropylene yarns or circular cross-section filaments. The two types of thread may be of different materials, for example the lower tenacity threads being of polypropylene and the higher tenacity threads of polyester or nylon.
It will be appreciated that by means of the suitable disposition of higher warp strength regions, it is possible to provide reinforcement at the point of attachment of lifting means such as a loop, by means which are inherent in the production of fabric of the container, and the design of the container itself. Of course, for additional strength, it is possible to combine the use of higher warp strength regions with other means of reinforcement.
Woven fabric for use in constructing the container may for example be in the form of a strip having stronger warp regions adjacent each selvedge, or elsewhere as appropriate, or for example in the form of a tube woven on a circular loom, with suitable regions of higher strength warp.
Aside from reinforcing the lifting loops or the like, and seams in some embodiments, the stronger warp regions may be employed to provide reinforcement along other lines of stress.
Two embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which:-

Fig. 1 is a perspective view of a container in accordance with the invention;
Fig. 2 is a view of part of the seam between two fabric panels in the container; and
Fig. 3 is a perspective view of a second embodiment of a container in accordance with the invention.

Referring now to the drawings, in Fig. 1 there is shown a flexible bulk container for carrying up to 1 tonne of material, possible with a safety factor of at least five times this weight. The container includes a bag portion 1, to which are attached four lifting loops 2. The bag is of woven fabric, for example, woven polypropylene although polyethylene terephthalate, rayon nylon and so forth could be used. A preferred fabric construction is 5.9 x 4.7 threads per cm woven polypropylene tape of 222.2 tex. The fabric may be sealed by a coating of polypropylene, or by laminated polyethylene.
The loops 2 are preferably webbing e.g. woven polyethylene terephthalate approximately 5 cm wide.
The bag 1 comprises three pieces of fabric, namely a substantially "U"-shaped portion 3, forming two sides and the base of the bag, and two rectangular pieces 4 and 5 forming the other two sides of the bag. The fabric pieces are arranged with their warp threads running vertically up the sides of the bag. The pieces are joined by stitching along seams, e.g. a blanket stitch using polypropylene yarn. The selvedges of the fabric pieces 3, 4 and 5 run vertically along the seams, apart from at the base of the bag. Stitching 6 is provided around the top of the bag, to prevent fraying of the fabric. The seam construction and method of attachment of the loops to the bag is shown more clearly in Fig. 2. The two pieces of fabric 3 and 4 are stitched together along seam 7, by polypropylene yarn 8.
The loop 2 has two legs 9 and 10. The fabric adjacent the seam 7 is pinched together, to form a flange, and the legs 9 and 10 are stitched to the flange, straddling it. Each stitch passes through the legs 9 and 10 of the loop and the two thicknesses of bag fabric.
Although not shown, adjacent the selvedge of the fabric pieces the weft threads are turned back, for example a distance of 1.27 cm. This can provide a degree of reinforcement adjacent the seam. Additionally however, and in accordance with the invention, strengthening is obtained by means of a higher strength density of warp threads. For example, in regions generally marked 11 and 12, adjacent the selvedge of fabric pieces 3 and 4 respectively, where the loop 2 is attached there is a higher density of warp threads, i.e. the threads are packed closer together, and/or warp threads of higher strength are used. Thus, over the majority of the bag, the warp threads could be polypropylene tape having a tenacity of perhaps 353.2 to 529.8 mN tex-1. In regions such as 11 and 12, adjacent selvedges, the warp threads could be polypropylene R.E.F. yarns having a tenacity of 441.5 to 618.1 mN tex-1 or multi-filament polypropylene yarns. The widths of the regions 11 and 12 are such as to accommodate the legs of the loop, and they run the length of the selvedges.
In Fig. 3, there is shown another embodiment of the invention, in which the container comprises a one-piece, tubular main body portion 13, to which is stitched a circular base 14. Four loops 2 are attached to the top of the bag, spaced equidistantly around it. At the point of attachment of a loop 2, the bag fabric is pinched to form a flange adjacent the top of the bag. The legs of the loop straddle the flange and are stitched thereto as in the previous embodiment.
The points of attachment of the loops 2 are in regions 15 of higher strength density warp threads, the warps threads extending vertically up the bag. The higher strength density may be obtained as described earlier. In other respects, for example regarding the materials used, the bag is similar in construction to those described earlier.
It will thus be seen that there is provided a container which, whilst simple in construction, has improved strength and reliability, and in which lifting stresses, when the container is lifted by the loops, are transmitted down the container by reinforced regions. The method by which the fabric of the bag is manufactured, and the bag is constructed, allow for greater productivity.
We have found that a particularly advantageous arrangement combines the use of R.E.F. yarns with a "cramming" effect, in the regions adjacent the selvedges. Thus R.E.F. polypropylene warp yarns are woven in pairs; to assist in the weaving process it is then advantageous for the warp yarns to pass over and under two weft threads at a time. The resultant container has a considerably improved strength, and is capable of carrying up to between 8 and 10 tonnes.

Claims

1. A flexible bulk container of woven fabric having side walls (3, 4, 5) and a closed bottom (3), the warp threads of the fabric constituting the side walls extending up the container and there being a region (11) of a side wall (3) in which the strength of the warp per unit width is .greater than that over at least the major part of the remainder of the side wall to which region lifting means (2) are attached, characterised in that there is a joint (7) extending along two fabric portions (3, 4) constituting the side walls adjacent selvedges thereof, there being a greater strength warp region (11, 12) adjacent to and terminating at the respective selvedges of the portions (3, 4) where they are joined together, and the lifting means (2) being attached to the side walls in such regions.

2. A container as claimed in claim 1, characterised in that the greater strength warp regions (11, 12) adjacent the joint (7) are formed into a flange of at least double thickness material extending from the side walls (3, 4) the lifting means (2) being attached to such flange.

3. A container as claimed in claim 2, characterised in that the lifting means (2) comprises a loop having two legs (9, 10), the legs being stitched to the flange.

4. A container as claimed in claim 1, 2 or 3, characterised in that it consists of three fabric portions (3, 4, 5) one of which (3) is U-shaped so as to form first and second side walls and the base of the container, and the remaining two of which (4, 5) are connected across the ends of the U-shaped portion so as to form third and fourth side walls, there being greater strength warp regions (11, 12) extending along each of said three portions adjacent both selvedges thereof.

5. A container as claimed in claim 4 characterised in that lifting means (2) are provided at each of the four corners of the container.

6. A flexible bulk container of woven fabric having side walls (3, 4, 5; 13) and a closed bottom (3; 14) the warp threads of the fabric constituting the side walls extending up the container and there being a region (11, 12; 15) of a side wall (3, 4; 13) in which the strength of the warp per unit width is greater than that over at least the major part of the remainder of the side wall, to which region lifting means (2) are attached characterised in that there is formed from said region (11, 12; 15) a flange of at least double thickness material extending from the side wall (3, 4; 13) and the lifting means (2) are attached to said flange.

7. A container as claimed in claim 6, characterised in that the lifting means (2) comprises a loop having two legs (9, 10) connected to the flange by stitching.

8. A container as claimed in claim 7 charac-_' terised in that the legs (9, 10) of the loop (2) straddle the flange.

9. A container as claimed in claim 6, 7 or 8 characterised in that the flange is formed by an outwardly pinched region (15) in a continuous fabric portion (13).

10. A flexible bulk container of woven fabric having side walls (3, 4, 5) and a closed bottom (3), the warp threads of the fabric constituting the side walls extending up the .container and there being a region (11, 12) of a side wall (3, 4, 5) in which the strength of the warp per unit width is greater than that over at least the major part of the remainder of the side wall to which region lifting means (2) are attached characterised in that the container consists of three woven fabric portions (3, 4, 5) one of which (3) is substantially U-shaped and forms first and second side walls and the base of the container, the warp threads of such portion (3) extending between the first and second side walls and across the base, and the remaining two of which (4, 5) are connected across the ends of the U-shaped portion and form third and fourth side walls each of said portions including a region (11, 12) of greater warp strength extending the length thereof, the lifting means (2) being attached to said regions.

11. A container as claimed in claim 10 characterised in that each of said portions (3, 4, 5) includes a pair of said greater warp strength regions (11, 12) on opposite sides thereof.

12. A container as claimed in any preceding claim characterised in that the warp threads in the or each region (11, 12; 15) of greater warp strength are of a higher strength than elsewhere.

13. A container as claimed in claim 12 characterised in that the warp threads in the or each region (11, 12; 15) of greater warp strength are roll embossed film polypropylene yarns and the warp threads elsewhere are polypropylene tape.

14. A container as claimed in any preceding claim, characterised in that the warp threads in the or each region (11, 12; 15) of greater warp strength are more closely packed together than elsewhere.

15. A container as claimed in claims 14 and 13 characterised in that the roll embossed film yarns are woven in pairs and pass over and under two weft threads at a time.