WO1994019259A1

WO1994019259A1 - Flexible containers

Info

Publication number: WO1994019259A1
Application number: PCT/GB1994/000369
Authority: WO
Inventors: Jeffrey Robin Caldwell-Nichols; Alastair Mcdonach
Original assignee: Some Guys Limited; University Of Strathclyde
Priority date: 1993-02-24
Filing date: 1994-02-24
Publication date: 1994-09-01
Also published as: GB9303709D0

Abstract

A flexible container (2) comprising a body (3) with lifting handles (4) is provided with an indicator panel (10) which ruptures at a lower tensile loading than for the remainder of the container to provide a visual indication of historic excessive loading. The panel (10) is formed of material woven into the body (3) but of different tensile characteristics and different colour characteristics.

Description

FLEXIBLE CONTAINERS

This invention relates to large capacity flexible containers that are suitable for storage and transport of various goods, particularly dry goods of powdered or granular type.

Such containers are often referred to as flexible intermediate bulk containers (FIBCs) , and they typically have a capacity in the range from 0.25 - 2.0 m³ and are rated safe for loads of half a tonne up to three tonnes. They are made of flexible material which must be of adequate strength for lifting of the filled containers by engaging one or more handles or loops at the top. The usual material is woven synthetic plastics, for example woven tapes of polypropylene and requires to have tensile properties greater than is required for the safe working load, for example, by a factor of 5, in order to accommodate transient stresses and strains imposed during use by acceleration and impact forces. Thus, for a 3 Tonne load the container is capable of withstanding forces of up to 15 Tonnes(f). This is the maximum load rating of the container.

Containers of this type may be divided into two principal groups, being distinguished by the method of forming their lifting handles or loops. The first group have their lifting handles formed from extensions of the container wall, to be called 'integral' loops. The second group have their lifting handles formed from separate pieces, normally webbing, which are then sewn to the container body, to be called 'attache ' loops.

All FIBCs are top lifted at some stage by their handles, and most are top lifted many times. There has been no design feature built into any FIBC that allows for an easy assessment of the condition of the FIBC, with regard to its ability to be lifted safely when filled. This is a particular problem with FIBCs that are reused many times. Assessment of their condition can only be done by individual inspection and close assessment.

According to the present invention a flexible container having a container body with lifting handles is formed of a flexible material of sufficient strength to provide the container with a predetermined maximum load rating, characterised in that the container is provided with at least one panel of material whose tensile properties are such that the panel will fail when the container is subjected to a loading which is a predetermined fraction of said maximum load rating, said panel when failed providing a visible indication of the failure and being arranged such that the structural integrity of the container is essentially maintained.

Preferably the flexible material is woven and the panel is formed of threads woven into the flexible material for example in substitution for selected threads of the flexible material. The flexible material may be formed of flat polypropylene tapes and the panel threads may also be flat polypropylene tapes but of lower tensile properties. It is preferred that the panel threads, in tape form, overlie the tapes of the flexible woven material. For example the warps of the weave may consist of the two overlying tapes whilst the wefts of the weave consist only of single tapes being those of the greater tensile properties.

Preferably the threads of the panel are a different colour from the woven flexible material so that upon failure, the rupture or failure of the panel threads is highly visible exteriorly of the container.

By way of example if the container is designed to have a predetermined rated safe loading of say 3 tonnes and a safety factor of 5 it would normally be used with loads of up to 3 tonnes and repeatedly reused quite safely. The panel threads in this case would be designed to fail at 11.25 tonnes (i.e. 75% of the maximum load rating) thereby, if failed, indicating that the container has been subjected to excessive treatment and must be handled carefully for the remainder of its useful life. It will be appreciated that the 75% figure given above is merely exemplary. Any conventient figure can be selected.

The panel may be located in either or both of the container body and the lifting handle.

By virtue of the present invention a flexible container is provided with a visible indication of any previous excessive loading.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Fig. 1 illustrates one form of flexible container in accordance with the present invention;

Fig. 2 illustrates a detail of the Fig. 1 container

Figs. 3 and 4 depict the results of strain loading at different locations around the periphery of a typical container;

Figs. 5 and 6 illustrate different forms of flexible containers in accordance with the present invention.

As shown in Fig. 1 a flexible container 2 comprises a container body 3 with a lifting handle 4 which is of the integral lifting loop type. The container body 3 is formed of close-woven tapes of polypropylene and the fabric is edge seamed top and bottom, as at 5, to provide structural integrity. The top seam 5 is normally covered by a sleeve which defines the shape of the handle 4. A heat cut slit or aperture 6 is provided beneath the handle to permit filling and lifting of the container 2. Typically the body 3 is made of 250 cm circumference tubing with warp and weft tapes each 3 mm wide, having a Tex value of 170 and a strain at break value of 22%. Typically the edge seaming 5 is provided by polypropylene threads which may be formed of a bundle of narrow gauge tapes also with a strain at break value of 22%. In accordance with the present invention the container 2 is additionally provided with at least one panel 10 of material whose tensile properties are such that the panel 10 will fail or rupture at a lower loading than for the container body 3. The preferred arrangement, as shown in Fig. 2, is that the panel 10 is formed by a plurality, say 10, of individual polypropylene tapes 8 each 3 mm wide, having a Tex value of 200 and a strain at break value in the range of 3 to 8%, more preferably in the range 3 to 6%. The tapes 8 are woven into the base fabric of the body 3 such that they overlie, piggy-back fashion, the tapes 9 of the base fabric. In the interests of clarity Fig. 2 shows only three tapes 8 which are of different width from the tapes 9. Tapes 8 may extend only in the warp direction,i.e. from the handle 4 to the base of the body 3 but may also or alternatively extend circumferentially or peripherally in the weft direction if so desired. Because the tapes 8 effectively form part of the body 3 they are bound in at each end by the edge seaming 5 so that they are subjected to the same degree of loading as the tapes 9 of the base fabric when the container 2 is in use.

The panel 10 of the warp tapes 8 may be located at any circumferential location on the container body 3 but for a given load of fill material in the container 2 the strain imposed on the tapes 8 depends upon their particular circumferential location. This is illustrated in Figs. 3 and 4 where the container 2 has a slit or aperture 6 underneath and extending transverse to the handle 4 and has three exemplary panels 10 at peripheral locations 11A, 11B and 11C. The resultant strain/load graphs are shown in Fig. 4 for the three peripheral locations. Greatest strain is imposed at location 11C adjacent the slit under the handle 4 whilst least strain is imposed at location 11A which is essentially aligned with the handle 4. Thus if there is only a single panel 10 the tensile strength properties of its tapes require to be selected for the panel location in order to fail at a predetermined fraction of the maximum load rating of the container. Alternatively if there are say three or four mutually-spaced panels 10 (as shown in Fig. 1) they can be arranged with different tensile strength properties either individually to fail at the same predetermined fraction of the maximum load rating or to fail at different predetermined fractions of the maximum load rating.

It will of course be understood that in the production of polypropylene tapes the standard procedure is to extrude the polymer into a thin sheet which passes over a series of blades to slit the sheet into an array of side-by-side tapes. The tape array is then passed through an oven and drawn to provide longitudinal molecular orientation. Typically the tapes 9 of the base fabric are drawn with a draw ratio of 7:1 or 8:1 to provide their tensile strength properties whereas the tapes 8 of the panel 10 are drawn with a draw ratio of about 15:1 and additionally may be subjected subsequently to mechanical fibrillation in order to generate pin points of mechanical weakness to the tape throughout its length. Variation of the draw ratio and the degree of mechanical fibrillation permits tailoring of the tensile properties of the tapes 8 of the panel 10.

The tapes 8 of the panel 10 are preferably of a different colour from the tapes 9 of the basic fabric and when they fail due to overloading they burst or rupture and snake back from the rupture point towards the end scanning 5 resulting in a series of visible loops of tapes 8 appearing as protrusions from the base fabric of body 3. They are therefore highly visible. Additionally the ruptured ends of the tapes 8 become fibrillated which enhances visibility.

Fig. 5 illustrates an alternative form of the container 2 which has corner attached lifting loops 12 made of webbing material. The preferred position of the panels 10 for maximum strain loading is illustrated as being in alignment with the loops 12 at or adjacent the seaming 5. It will be understood that in this embodiment the container body 3 can be formed of several, e.g. five, woven pieces seamed together.

Fig. 6 illustrates a further alternative form of the container 2 which has cross corner attached loops 13 made of webbing material. The preferred position of the panels 10 for maximum strain loading is illustrated as being in alignment with the -ends of the loops 13. In this embodiment the body 3 may either be made of woven tubing or of woven pieces seamed together as at 5.

Claims

- 1 - CLAIMS

1. A flexible container having a container body with lifting handles is formed of a flexible material of sufficient strength to provide the container with a predetermined maximum load rating, characterised in that -he container is provided with at least one panel of material whose tensile properties are such that the panel will fail when the container is subjected to a loading which is a predetermined fraction of said maximum load rating, said panel when failed providing a visible indication of the failure and being arranged such that the structural integrity of the container is essentially maintained.

2. A flexible container as claimed in claim 1, characterised in that the flexible material is woven material and the panel is formed of one or more threads woven into the flexible material.

3. A flexible container as claimed in claim 2, characterised in that the flexible woven material is formed of flat polypropylene tapes and the panel threads are flat polypropylene tapes of lower tensile properties than the tapes of the flexible woven material and arranged to over-lie the tapes of the flexible woven material.

4. A flexible container as claimed in any preceding claim, characterised in that there are a plurality of panels with different tensile properties such that different panels will fail at different predetermined fractions of said maimum load rating.

5. A flexible container as claimed in any preceding claim, characterised in that the panels are formed in the container body.