EP0111852A2

EP0111852A2 - Flexible container for transport and storage of bulk material and a method for its manufacture

Info

Publication number: EP0111852A2
Application number: EP83112416A
Authority: EP
Inventors: Anders Juel; Olaf Strand
Original assignee: Norsk Hydro ASA
Current assignee: Norsk Hydro ASA
Priority date: 1982-12-10
Filing date: 1983-12-09
Publication date: 1984-06-27
Also published as: PT77801B; DK566983A; NO824157L; DK566983D0; FI834476A; EP0111852A3; NO151279C; CA1215001A; TR22005A; FI69436C; FI834476A0; NO151279B; PT77801A; FI69436B; ES285028U; ES285028Y

Abstract

The present invention relates to a flexible container for transport and storage of bulk material and a method for its manufacture. The container shall endure the strains it is exposed to during a drop test in the bursting zone having a radial bursting effect. The container (1) consists of a hose-formed piece of material which upper part is joined with its central part (12) by joints (8) which form an angle 0°<x<90°, preferably 30°<x<60° with the longitudinal direction of the material. The joints (8) can be in the form of a V or W and the extreme point (B) if preferably above the bursting zone (9). The container (1) can be made from a flattened hose-formed piece of material which is cut in two symmetrical parts (1) along a line cut a, a', b', b where the lines a, a' and b', b form an angle 0°<x<90° with the longitudinal axis of the material and the line (a'-b') > 0 is vertical in the middle of the piece of material (1) on both sides of the folded line (1). The upper part of the piece of material (1) is folded over the line (2) and joined with the part (12) along cut lines for forming lifting loops (5). The container combines the requirements to high tensile strength and high resistance to strain in the bursting zone (9).

Description

The present invention relates to flexible containers for transport and storage of bulk material, especially pulverant or granular material. The invention also comprises a method for manufacture of such a container.
The container comprises integrated lifting loops, filling opening, a central part and a bottom section. The container can be equipped with an inner liner of impervious material.
There are today several modifications of flexible containers of the above stated type. Regarding containers having integrated lifting loops, reference is made to the applicant's patents GB 1.475.019 and US 4.136.723. Flexible containers according to these patents are preferably made from one piece of woven material, for instance flat woven or round woven polypropylene.
According to the first mentioned patent, the container's lifting loops are formed from a doubled piece of material in form of a closed loop which is a continuous integral alongation of the piece of material which forms the container itself. The total width of the lifting loops is substantially equal to the container's circumference. The container's Bottom is formed by joining together the lower part of said piece of material. According to the US patent, several flaps at the lower part of the material are made, and by joining these together in a special way a double bottom is formed.
The latter patent comprises also a flexible container made from round woven material and where the container's height is in the longitudinal direction of the material. In this case the container's top is joined together or closed by lashing and is lifted by means of a clamping hook, straps with a running knot or the like, whereby its lifting strength is weakened, as the strength of the material no longer can be utilized maximally during lifting of the container.
The above mentioned flexible containers have achieved extensive utilization, for instance because of their simple construction which at the same time gives high strength as the strength of the material itself in the vertical or horizontal direction can be maximally utilized, however only in one direction at the time. When such a container is made from round woven material, it has also substantially larger strength in the horizontal direction along the container's circumference than containers having one or several side seams in their longitudinal direction, but the lifting strength becomes less than for containers made from flat woven material.
For some applications there are, however, special requirements regarding the container's strength. Thus it is required that containers for transport of dangerous material shall endure falling from a certain height against a plane floor or the like without being ruptured. The container shall be carried through a so-called drop test if it shall be used for transport and storage of this type of bulk material. During the drop test the lower part of the flexible container will be exposed to especially high strain along the circumference, as one will have a radial bursting effect perpendicularly.on the container's vertical axis when the container is exposed to this drop test. In the following text this zone will be defined as the bursting zone, which usually can extend from the container's bottom and upward to about half of its height in filled condition. How large part of the container will be exposed to this extra strain, depends on the properties of the material to be transported.
Too weak containers will rupture in the bursting zone when they are exposed to the drop test. Flexible containers having one or several side seams will generally have a lower strength in the bursting zone than containers made from round woven material because the basic material is weakened along the circumference of the side seams. It is, however, possible to make containers meeting these requirements of the drop test by overdimensioning the quality of the material for making the container, but such a large overdimensioning will not be very economic.
From the applicant's Norwegian patent No. 143.399 it is known to put a hose-formed or round woven piece of material outside the container having side seams as reinforcement in order to obtain an acceptable result during the drop test. Placement of the hose-formed piece of material around the container does, however, require extra labour. Such a belt may also cause problems during emptying of the container.
The object of the present invention was to arrive at an improved flexible container having integrated lifting loops and which had a cylindrical part which could endure the strain the container would be exposed in the bursting zone during a drop test. Said container should at the same time have the same advantages regarding high lifting strength and strong bottom construction for distributing the strain on the container in a favourable way.
A further object was to arrive at a construction which would allow application of round woven material, as application of round woven material has certain advantages, for instance during manufacture.
The inventors first considered the relative importance of the advantages and disadvantages of the known flexible containers in order to sort out which properties had to be improved and if this could be done without sacrificing reduction of the container's positive properties. One of the most important advantages of the previously mentioned container having integrated lifting loops, is their high lifting strength. It was row surprisingly found that by manufacturing the container in a special way from a hose-formed material, it could be obtained containers having high strength in the bursting zone at the same time as they had lifting loops with sufficiently high lifting strength.
A flexible container according to the invention was made from a hose-formed material which was cut at one of its ends such that a substantial part of the cutting deviated from the longitudinal and transveral direction of the material, i.e. the woven material's warp and weft. The hose-formed material was folded transversally and the edges of the cuts were joined together, for instance ty seaming, such that a container was formed having integrated lifting loops in its upper part and a cylindrical part between the lifting loops and a bottom section which was formed as known per se, for instance according to US 4.136.723.
The most important feature of the flexible container according to the invention is the way it is joined together in order to form lifting loops and connect them with the cylindrical part of the container. The joints are characterized by forming an angle x with the lengthwise direction of the hose-formed - material (warp of the woven material). It was found that the angle x should have a value between 0° and 90°, as x = 0⁰ corresponds to a container having one or several side seams, x = 90° corresponds to a container having one or several joints transversally to the longitudinal direction of the material, for instance sewn lifting loops. The lifting strength of the container is reduced corresponding to the difference between the strength of the woven material and the strength of the joints. The strength of the material is normally reduced by strain transversally of the joining _direc- tion with 50-70% when there is a seam in the woven material. By choosing an angle x less than 90° the length of the joints will be increased such that the imposed weakening, by cutting the material and then joining it together again, to a great extent will be counteracted. Using an angle x = 45°, one will thus get a length of the joint which is about 40% longer than when x = 90⁰ if the seam has the form V between the edges of the lifting loops. Assuming that the strength of the joints is 60% one-should expect a total strength of 60 x 1,4 = 84% for a container according to the invention. Because the joints can hardly be made with exactly the same elastic properties as the material and the forces which the joints are exposed to are not perpendicular to these, shear forces are introduced which can reduce somewhat that gained by having larger lengths of the joints. By correctly choosing the way of joining together the material, the reduction because of shear strains is substantially less than that gained by increasing the length of the joints, such that one can expect that a container according to the invention will have a strength between that of containers having x = 90° (joined lifting loops) and x = 0° (joints in the container's sides).
The special features of the invention are as defined in the following patent claims.
The construction of the flexible container and the method for its manufacture will be further explained below with reference to the drawings.

Fig. 1 shows a basic piece of material for making two flexible containers.
Fig. 2 shows one of the basic materials from fig. 1 folded transversly.
Fig. 3 is a 3-dimensional drawing of a container made by joining together a basic material according to fig. 2.
Fig. 4 shows a basic material doubled and readycut.
Fig. 5 shows folding of a basic material in fig. 4.
Fig. 6 shows the basic material in fig. 4 folded transversly.
Fig. 7 is a 3-dimensional drawing of a container made from the basic material in fig. 4.
Fig. 8 shows an alternative way of cutting a basic piece of material for making two flexible containers.

In fig. 1 is shown two round woven basic materials (1) from a hose-formed material which is cut along the lines a, a', b' and b and where the cutting lines a, a' and b' b form angles x with the warp in a round woven material. The cutting lines a'-b' will contrary to this follow the weft in the material. In the basic material (1) there can be made a cut across the folding line (2) for a central filling opening (3). The cuts (4) will make it possible to form a double bottom such as described in US 4.136.723. Before joining together the upper part of the container with its cylindrical part (12) it is advantageous to fold out the material (1) such as shown in fig. 2. Thereupon the basic material (1) is folded over the folding line (2) as long as necessary for getting the joints of a, a' to overlap with b, b', and lifting loops (5) are formed. The lowest point (B) in the V-formed joint (8) lies preferably above the bursting zone (9) as shown on fig. 3. The points at the extremes of the V-formed joint (8) are designated (B^I). The joints can be made by seaming, gluing, melt3ng the joints together or in any other suitable way. The container's bottom is made as known per se.
The container can also be made by making the cut line a'-b' equal to 0, i.e. the piece of material (1) is cut directly from a to b. The joints are thereby drawn into the top of the lifting loops (5) and cuts corresponding to the length of the lifting loops must be made in the basic material (1). The container can also be made by prolonging the cut lines a'-b' beyond the crossing of a, b' with b, b' as shown by the dotted line (11) on fig. 1, in order to prolong the opening (6) and thereby the lifting loops.
The container can also be made with shortened openings (6) for the lifting loops by continuing the joints from a', b' (fig. 2) and a'', b'' (fig. 6) in the direction of the folding line (2) such that one obtains side joints in the upper part of the central section of the container.
The container can also be made by letting the cut lines a, a', b, b' form curves or joined pieces of cuts which form angles with the longitudinal direction of the material different from the angle x as long as the joining line between the cut lines' starting and end point forms an angle x with the longitudinal direction of the material piece (1) and the cut lines substantially cover each other after being folded over the folding line (2).
_Fig. 4 shows a round woven basic piece of material, double folded as shown in fig. 5, with folding lines (10). Said piece of material is then cut up in the same way as shown in fig. 1. When the basic material (1) is folded out again after having been cut up along the lines a, a', b' b', it will be in the form shown in fig. 6. When the flaps above the folding line (2) are folded around this one and joined along the cut lines, one will obtain a joining line (8) in the form of a W with the extreme points at (B") and its lowest points at (B). Fig. 7 shows a container made from the material shown in fig. 4 and with joining lines (8) for formation of lifting loops (5). As can be seen from fig. 7, this container is not shown with a central filling opening. Such a container can be filled with bulk material through one of the side openings (6), but it can also be equipped with a central filling opening (3). Also for containers according to fig. 3 bulk material can be filled through the side openings (6) and application of a central filling opening (3) can be avoided.
By making the flexible container in this way one obtains equally long seams (8) as when it has V-form, but the lowest point (B) of the seams (8) will not extend as far down on the cylindrical part (12), and there is no risk that the seam (8) gets down into the bursting zone (9).
As shown in fig. 8 one might also make the flexible container by cutting the line a'-b' upward on the basic material (1) such that both parts of the cut lines a, b' and b, b' become positioned on each side of the folding line (2).
The joint (8) will then occur on each of their sides of the lifting loop (5) such that the lowest point (B) or (B', B'') of the joints (8) will not extend as far down on the cylindrical part (12) that there is any risk that the joint (8) get down into the bursting zone (9).
By varying the length of the line a'-b' the lowest point (B) can be kept at a constant height above the bottom (7) for such containers by varying the relation between length and width when applying V- or W-formed joints (8) having a constant angle x.
It has been found advantageous to make the container with joints (8) such formed that the angles x are in the area 30°<x<60° and where the lowest point (B) of the joints becomes positioned at about half the height of the container when it is filled, however, the whole joint shall preferably be positioned above the bursting zone (9). The invention is, however, not limited to these values, because, among other things, the flowability of the material which shall be filled in the container will influence on the point for the largest bursting effect during the drop test. The flowability will also influence on the angle the container's walls will form with the container's vertical centre line when the container is lifted with its lifting loops joined in a lifting hook. The distribution of strain in the flexible container will accordingly vary with the type of material filled into it. Therefore it will be advantageous to adjust according to the flowability of the material which shall be transported in the container.
In order to determine the strength of a container according to the invention relatively known containers, some comparing tests were carried out. Flexible containers I and II according to the applicant's US patent No. 4.136.723 which has x = 0°, flexible containers III and IV having x = 90° and flexible containers V-VIII according to the invention with x = 40° were filled with 6-50 kg flowable material and exposed to a static stretch test until rupture.
The containers III-VIII were made from round woven material, and the containers I and II were made from flat woven material, all made from polypropylene tape of 170 tex with 34 tapes per 10 cm in both warp and weft. All the test containers were made in the same dimension such that they contain equally many tapes in the container's longitudinal direction and had a bottom construction according to the above mentioned _US patent. For comparing the test results, the results of a flexible container according to said US patent were used as reference and is here = 100%. Tensile strength was measured in k_N, and average value for the tensile strength is given for to containers of each type.
As can be seen from the table, containers having lifting loops joined such that x = 90° (containers III and IV) have their lifting strength almost halved (53%) because of the seam, and this was also expected. Containers V and VI according to the invention can contrary to this be exposed to 76% of the strain which the container without a seam in the lifting loops can endure. Containers VII and VIII are containers of the same type as V and VI, but having other elastic properties in the joints. On the average these can be exposed to 85% of the strain. It can clearly be seen from the tests that the new construction makes it possible to expose a filled container according to the invention for larger tensile forces than flexible containers with sewn lifting loops (x = 90⁰), while it on the other side can be exposed to less strain, but close up to that of a flexible container with integrated lifting loops with joints in the sides (x = 0) (containers I and II).
It was then carried out drop tests on containers corresponding to containers I-VIII. The containers were also now filled with 650 kg flowable material and was tested at drops of 50 cm and 80 cm. When the container ruptures during the test that is stated with Yes in the table. When it gets through the test without rupturing, it is stated with No.
As can be shown from the table, the known containers I and II rupture in the side seams only at a drop height of less than 50 cm, while the flexible containers III and IV with sewn lifting loops and having x = 90°, and the flexible containers V-VIII according to the invention all can endure being dropped from at least 80 cm against a rigid surface or floor without rupturing.
The tests show that a filled flexible container according to the invention has high tensile strength as it can be exposed to-strains very close to that which a flexible container having integrated lifting loops without seam (x = 0°) can endure, and at the same time it can endure the same strains during drop tests as a flexible container of hose-formed material and sewn lifting loops with x = 90°.
The flexible container according to the invention combines not just the requirements to high tensile strength and high strains in the bursting zone, but it is also simple to manufacture and it does not require more material than containers to which it is compared here. One has also obtained a new container which has a high lifting strength and a strength in the bursting zone which fulfils the drop test requirements.

Claims

1. Flexible container (1) for transport and storage of bulk material, comprising integrated lifting loops (5), filling opening (3 or 6), a central part (12) and a bottom section (7), characterized in that the container consists of a hose-formed piece of material which upper part is joined with its central part (12) by means of joints (8) which form an angle x with the longitudinal direction of the hose-formed material, as x lies between 0°<x<90° and that its lower part of the hose-formed material is joined as known per se for formation of the bottom section (7).

2. Flexible container according to claim 1, characterized in that the joints (8) are in the form of a V or W, which lowest point (B) preferably is positioned above the bursting zone (9) which is that part of the container that is exposed to the largest strain when a filled container is exposed to a vertical fall against a plane surface.

3. Flexible container according to claims 1 and 2, characterized in that the joints (8) form the angle 30°<x<60° with the longitudinal direction of the hose-formed piece of material and that the extreme points (B' B'') of the joints are positioned at the lower edge of the side opening (6) for the lifting loops (5).

4. Flexible container according to claims 1 and 2, characterized in that the extreme points (B' B'') of the joints (8) are positioned above the lower edge of the side openings (6) for the lifting loops (5).

5. Method for manufacturing of flexible containers according to claims 1 to 4. characterized in that a hose-formed piece of material is laid flat, possibly first folded at least once in its lengthwise direction, whereupon it is cut in two symmetrical pieces (1) along a cut line a, a', b', b, where the lines a, a', b', b form an angle 0°<x<90° with the longitudinal axis ot the piece of material and the line a'-b', which is larger than or equal to 0 forms a vertical line parallel with said axis and is positioned in the middle of the piece of material (1) on both sides of a folding line (2) and that the upper part of the cut up material piece (1) is folded over the line (2), whereupon the upper part is closed by a joint (8) along the cut lines for forming lifting loops (5) and that the lower part of the piece of material (1) is closed as known per se.

6. Method according to claim 5, characterized in that in the piece of material (1) there is made cuts for a central filling opening (3) and cuts (4) in its lower part for formation of flaps for making a double bottom (7)..

7. Method according to claims 5 and 6, characterized in that a hose-formed piece of material (1) first is folded double along folding lines (10), whereupon two symmetrical pieces (1) are cut out along a cut line a, a', b', b, whereupon the piece of material (1) is folded out and its upper part is folded over the line (2) and joined with the central part (12) in a W-formed joint (8).

8. Method according to claims 5 to 7, characterized in that by cutting up the piece of material (1) there are formed lines a'-b' having a length corresponding to twice the length of the side opening (6).

9. Method according to claims 5 to 7, characterized in that the piece of material (1) is formed such that the line a'-b' < twice the length of the opening (6) and that in the extension of this line there is made a cut (11) for obtaining the desired length of the openings (6).

10. Method according to claims 5 to 7, characterized in that the piece of material (1) if formed such that the line a'-b' gets a length larger than twice the length of the opening (6) and the distance between the lower edge of the opening (6) and the extreme points (B',B'') of the joints (8) are joined together.