Reinforced flexible container

A reinforced flexible container unit includes a flexible container having an upper section with lifting loops, a filling opening, a container bottom, and a central section formed by side walls extending from the container bottom to the upper section. The central section has a height portion extending upwardly from the container bottom and adapted to be contacted by bulk material when the container is filled with such bulk material. A reinforcing belt or belts are positioned to extend around the entire circumference of the central section of the container at least at a lower portion thereof adjacent the container bottom. The belt or belts have an open lower end and do not cover or enclose the container bottom. The belt or belts have a total width of from one-third of the height portion of the central section of the container equal to the height of such height section.

BACKGROUND OF THE INVENTION 
The present invention relates to a reinforced flexible container for 
transportation and storage of bulk material. The container comprises a 
conventional flexible container which can be made from woven textile 
fibers, laminated plastics or textile coated with plastic or the like. It 
comprises a bottom section, a central section and an upper section with 
lifting loops, and it can also be equipped with an inner sack of 
impervious material. The lifting loops can be integral parts of the 
container itself, but may also comprise separate loops or lifting straps 
secured to the container. 
Several types of such containers for transportation of bulk material are 
used today. Some of these known containers are used only once, while 
others can be used several times. Among such known flexible containers are 
those described in British Pat. No. 1,431,582, published Apr. 7, 1976; and 
in British Pat. No. 1,475,019, published June 1, 1977, U.S. Pat. No. 
4,136,713. 
The container according to the above U.S. patent is preferably equipped 
with an inner sack of impervious material, and preferably the upper 
section of the container comprises integrated lifting loops and a central 
filling opening. The special feature of this container is that its bottom 
section consists of at least two pairs of equally wide flaps which are 
direct extensions of the container walls, and that such flaps are joined 
at their lower edges such that the joints thereby formed cross each other 
at one point. This bottom construction has by dynamic testing been found 
to endure greater strains than the bottom construction according to the 
above mentioned British Pat. No. 1,475,019. 
For certain applications however, conventional flexible containers do not 
meet the requirements regarding container strength. For transportation of 
dangerous material like ammonium nitrate for instance, it is required that 
the container shall endure a specified drop against a plain floor, etc. 
without rupturing. By example, Verkehr der Bundesrepublik Deutschland, 
i.e. the authorities of the German Federal Republic, require that flexible 
containers having a volume of 250-1250 liters shall endure a drop of 1.2 
meter when they are filled with pulverent, dangerous materials. References 
made to "Amtsblatt der Bundesministers f ,uml/u/ r Verkehr der 
Bundesrepublik Deutschland", No. 6, page 254-259, of Mar. 31, 1976 volume 
30, published in Bonn, Germany. In this application dangerous material 
means that classified as such in packaging group 3 by the 
Intergovernmental Maritime Consultative Organization (IMCO). 
The disadvantage of the known flexible containers is that they burst just 
above the bottom when dropped, in filled condition, against a floor etc. 
Tests have shown that most of them burst already when the drop height is 
only 0.3 meter. 
SUMMARY OF THE INVENTION 
The main object of the present invention is to provide flexible containers 
which may be employed for transportation and storage of dangerous 
material. Another object is to provide such container by just reinforcing 
known flexible containers without substantially changing their basic 
construction or method of manufacture. 
Reinforcing known containers by increasing the weaving density or the 
thickness of the fabric has proved to be expensive for making containers 
that could endure a drop height of 1.2 meter. In addition to increasing 
weaving density and/or thickness of the fibres, this method also requires 
that the seams be reinforced. 
The inventors have developed a simple method of obtaining sufficiently 
strong flexible containers without altering the basic construction of 
known containers. 
The special feature of the invention is that a flexible container is 
equipped with at least one belt around its central section and that the 
belt or belts have a total width which maybe as much as the height of the 
bulk material in the filled container. Preferably such belt width 
corresponds to 1/3-2/3 of the height of the bulk material of the filled 
container, and the belt is than placed around the lower part of the 
container. 
The belt or belts can be made from the same material as the container 
itself, and preferably the belt is formed of round woven textile material. 
The belt can, however, also be made by joining together a piece of woven 
textile material. 
The belt can also consist of a wide strap with tightening means such that 
the strap is secured around the container subsequent to the filling of the 
container. 
The invention also includes a flexible container equipped with several 
narrow belts. The same reinforcement is then obtained with a total width 
of the belts somewhat less than the width necessary with a single belt. 
The application of several belts is, however, in most cases more expensive 
and labour consuming. 
The most preferred performance of the invention is to place a round woven 
belt around the container before filling. During the filling operation the 
container walls will be pressed against the belt and keep it in the right 
position. Optionally, the belt can be secured flexibly to the container by 
means of, for instance, tape or threads through the belt and the container 
wall.

DETAILED DESCRIPTION OF THE INVENTION 
One example of a reinforced flexible container according to the invention 
is schematicly shown in FIG. 1. Around the container 1 there is a belt 2. 
Threads 3 for securing the belt 2 are shown, even though they are not 
necessary. FIG. 2 shows a round of tubular woven belt 2. 
The most essential advantage of the invention is that it makes it possible 
in a very simple way to reinforce conventional flexible containers when 
that is necessary. This means that flexible containers can be manufactured 
for different purposes by the same method and equipment and only those 
containers that must endure drop strain have to be equipped with a belt 
and this is preferably done immediately before filling the container. 
Accordingly, a reinforced flexible container is attained without altering 
the basic construction of the container itself. 
Another advantage of the invention is that it can be applied to several 
types of flexible containers. A further advantage of the invention is that 
the belt can be used for marking purposes, as informative label, etc. 
EXAMPLE 
Flexible containers according to U.S. Pat. No. 4,136,723 were filled with 
800 kilos of bulk material (NPK-fertilizer prills) and exposed to varying 
drop tests. Three such containers were not equipped with belts, while 
three such containers were equipped with belts of woven polypropylene 
having the same weaving density and fibre thickness as the container 
itself. A circular belt was made from a piece of woven polypropylene 
joined together by zigzag seams. Such belts are somewhat weaker than round 
woven belts made from the same material. The width of the belts were 2/3 
of the height of the bulk material in the filled containers. The belts 
were thread around the containers immediately before filling. 
The following table shows the test results: 
TABLE 
______________________________________ 
Container 
without Container 
belt with belt 
Drop height 
1 2 3 4 5 6 
______________________________________ 
0.10 m 
0.20 ok ok ok 
0.30 R R R 
0.40 
0.50 ok ok 
0.60 
0.70 
0.80 ok ok ok 
0.90 
1.00 
1.10 
1.20 ok ok,ok.sup.x 
ok German Limit 
1.30 
1.40 
1.50 ok ok ok 
1.60 R 
______________________________________ 
Each container without a belt burst at the second drop which was 0.3 meter 
high. Two of the reinforced containers were exposed to four drop tests and 
were still completely intact, marked ok in the table. One of the 
reinforced containers was dropped five times and burst at the fifth drop 
which was 1.6 meter high, marked R in the table. 
It was proved during the tests that by equipping a conventional flexible 
container with a belt, it was reinforced such that it could endure for 
instance several drops of more than 1.2 meter, contrary to a conventional 
container without the best which burst at a drop of 0.3 meter. The 
containers first burst at the side seams just above the bottom of the 
containers. If stronger belts than those in the above example are used, 
the reinforced containers will endure drops of even more than 1.6 meter.