EP2387629B1 - Method for manufacturing transport and storage bulk bags and bag obtained by the method - Google Patents

Description

Technical area

The present invention relates to a method of manufacturing bags for transporting and storing bulk goods, and the bag obtained by the method.

State of the art

Bags for the transport and storage of bulk goods, also called "big bags", are generally made with woven polypropylene cloths, which can be rolled or not. The most common method for making such bags is to sew several pieces of fabric together so as to form a rectangular parallelepiped.

Canvas used for this purpose can be made by means of flat loom. However, flat looms are relatively rigid machines in their conditions of use and expensive, which implies a high cost of the canvas. This is why, for a little more than a decade, it has been proposed to produce bags using tubular fabrics made by so-called circular looms that are less expensive than looms flat, the pieces to be sewn together to form the bag being constituted by sections of tubular fabric flattened so as to form flat double thickness canvas coupons having for width half of the circumference of the tube. A first advantage of the use of a double fabric is that it allows a canvas of 75 to 125 grams per square meter to be used where a single fabric of 150 to 250 grams per square meter would have been used. This is an obvious economic advantage because, in general, the production of the same fabric tonnage of x grams per square meter is less expensive than that of the same tonnage of fabric of 2x grams per square meter. Another important benefit resulting from using a double canvas is that the canvas double significantly reduces the risk of tearing or piercing the bag, especially in case of abrasion, the double fabric is more resistant to friction and ramming than a simple canvas. In fact, assuming that the outer thickness is deteriorated in one place, the inner thickness remains capable of supporting only the entire load (it should be specified in this respect that the safety coefficient which must be respected for big bags is 5 to 1).

As regards the seaming of the cloth pieces together for the formation of the bag, one-needle or two-needle sewing machines, of the type described in the patent applications, are generally used. GB-A-2,301,087 , JP-A-2004 033548 or JP-A-2005 118400 . In the case of two-needle machines, the needles work in parallel, generally at a distance of the order of 0.5 to 1 centimeter, so as to achieve two parallel seams that increase the strength of the assembly. An example of such a machine is shown schematically in the figure 3 .

Big bags are used for storing, handling and transporting various goods, with nominal weights in the order of 250 to 3,000 kilograms. These goods are often in the form of more or less fine powders.

Due to the perforation of the fabric pieces when sewing them to form the bag, there is a risk of escape of the powder through the seam holes, even in the case of rolled fabrics. To remedy this drawback, hitherto, various methods or methods have been used, such as, for example, inserting a sheath made of polyethylene or other plastic material inside the bag, or the use thereof. special fibrous sewing threads of the "flock" type combined with traditional sewing threads, or the application of felt on the seams. However, none of these solutions has been fully satisfactory. Inserting a sheath into the bag is a delicate additional operation. On the other hand, the sheath slows the filling of the bag and may block the filling if its insertion into the bag is not perfect. In addition, the sheath may pollute the goods contained in the bag at the time of its emptying. Ultimately, depending on the nature of the powders to be transported, polyethylene sheaths can be expensive, which significantly increases the cost of manufacturing the bag. Likewise, the aforementioned combinations of yarns are imperfect solutions which do not provide sufficient sealing for very fine powders. In addition, because of their fibrous nature, these son may pollute the contents of the bag and constitute a significant danger of contamination.

Disclosure of the invention

The object of the present invention is to propose a method for manufacturing bags for transporting and storing bulk goods that makes it possible to overcome the drawbacks mentioned above, and in particular to achieve an almost perfect seal with powders, without insertion of a sheath into the bag and without resorting to floss-type yarns or the addition of felt.

To this end, the present invention relates to a method of manufacturing bags for the transport and storage of bulk goods in which is used a fabric cut into several pieces which are then assembled to each other by means of seams, characterized in that the seams are made by means of a sewing machine having at least two needles working in line one behind the other so that the stitching point of the second needle is made on the thread of the seam stitch made by the first needle, so as to cover the perforation made by the first needle and so that the perforation performed by the second needle is performed through said yarn clogging and said perforation by said thread.

It also relates to a bag for the transport and storage of bulk goods obtained by this method and a sewing machine for carrying out the method characterized in that it comprises at least two needles arranged to work one behind the other and alternately.

Other important features of the invention are the subject of the dependent claims and are discussed below.

Brief description of the drawings

• la figure 1 est une vue en perspective d'un exemple schématique de cinq pièces de toile destinées à être cousues entre elles pour former un sac selon l'invention;
• la figure 2 est une vue en perspective d'un exemple schématique de trois pièces de toiles destinées à être cousues entre elles pour former un sac selon l'invention;
• la figure 3 est une vue en perspective schématique partielle d'une machine à coudre conventionnelle à deux aiguilles travaillant en parallèle;
• la figure 4 est une vue en perspective schématique partielle d'une machine à coudre à deux aiguilles selon l'invention, les deux aiguilles étant agencées pour travailler en séquence l'une derrière l'autre; et
• la figure 5 est une vue schématique en coupe verticale le long d'une couture destinée à assembler deux pièces de toile pour la formation d'un sac selon l'invention.

The following description is given by way of non-limiting example. It refers to the drawing where:

• the figure 1 is a perspective view of a schematic example of five pieces of fabric to be sewn together to form a bag according to the invention;
• the figure 2 is a perspective view of a schematic example of three pieces of fabric to be sewn together to form a bag according to the invention;
• the figure 3 is a partial schematic perspective view of a conventional two-needle sewing machine working in parallel;
• the figure 4 is a partial schematic perspective view of a two-needle sewing machine according to the invention, the two needles being arranged to work in sequence one behind the other; and
• the figure 5 is a schematic vertical sectional view along a seam for assembling two pieces of fabric for the formation of a bag according to the invention.

Detailed description of the embodiments of the invention

The bags according to the invention are preferably made with pieces consisting of sections of tubular fabric flattened so as to form double-thickness flat canvas coupons having width half of the circumference of the tube. Such pieces of cloth are for example represented at Figures 1 and 2 .

On the figure 1 there can be seen a first piece 1 which will serve as the bottom of the bag, as well as four lateral pieces 2, which may be square or rectangular, and one of whose dimensions is equal to one of the sides of the piece 1. coins 1 and 2 are presented as they will be assembled, their assembly being performed by sewing, as will be described later, along virtual lines 4, represented in broken lines at the figure 1 , parallel to the sides of parts 1 and 2.

In the example shown in figure 2 , there is recognized a first part 5, intended to constitute both the bottom of the bag and two opposite side walls, and two complementary parts 6, intended to form the other two side walls of the bag. Of course, many other combinations of parts are possible for the realization of a bag according to the invention.

The essential idea of the manufacturing method according to the invention is to sew the pieces of fabric together with a sewing machine with two needles, but where the two needles no longer work in parallel, but one behind the other. An example of such a machine is shown schematically in the figure 4 . Such a machine can be made by modifying a conventional machine of the type shown in FIG. figure 3 . As mentioned above, with the machine of the figure 3 , the two needles A and B work in parallel, generally at a distance of 0.5 to 1 centimeter, so as to achieve two parallel seams 7 and 8. The modification is therefore obtained by rotating the support of the needles by 90 degrees and by adapting the machine, so that after modification of the machine, the two needles A ', B' work one behind the other in the direction 10, at distances of equivalent stitches, but alternately and not more simultaneous, for sewing along a single line 9. The second needle perforates the fabric in the middle of the stitch of the first needle, so as to cover both the stitch and the perforation of the first needle, as will be described in more detail below.

The realization of the seam for the formation of a bag according to the invention will be better understood if one refers to the figure 5 .

We have shown figure 5 the state of progress of a seam 9 using the needles A 'and B' of the figure 4 for the assembly of two pieces of fabric 1 and 2, such as those represented for example in the figure 1 . The needle A 'makes stitches using two threads 11 and 12, while the needle B' uses two threads 13 and 14. At the stage of sewing shown in FIG. figure 5 the first needle A 'has finished making the stitching point 15 after having perforated the cloths at the position 17. At this moment, the second needle B' is put into action and its perforation takes place through the thread 11 constituting the stitching point 15 of the first needle. Said perforation performed by the second needle B 'is thus clogged by the thread 11 of the stitching point 15 made by the first needle A'. On the other hand, the yarn 13 covers the stitching point 15 as well as, of course, the previous stitching point, both made by the needle A '. Therefore, the wire 13 also covers the previous perforation 16 of the first needle A '. In addition, because of the use of fabric parts 1 and 2 of double thickness, the sewing takes place through the two layers of fabric. At the time of sewing, the outer fabric 1 'slides slightly with respect to the inner fabric 1 ", which contributes to the obstruction of the perforation of the seam.

Bags made according to the process of the invention have a degree of sealing much greater than conventional bags. This degree of tightness can be further improved by using, for sewing, multifilament yarns having a textured structure and in particular having an elongation of 30 to 35%.

The bags according to the invention can advantageously be made from pieces of flattened tubular fabrics comprising conductive wires.

Claims (7)

1. Method for manufacturing bags for the transport and storage of bulk goods wherein use is made of fabric cut into several pieces, which are then assembled together by means of seams, characterised in that said seams are made using a sewing machine comprising at least two needles, namely a first needle (A') and a second needle (B'), operating in line one behind the other in one and the same direction (10) so as to form a seam along a single line (9), and in that the needles (A', B') are controlled so as to work alternately, and at equivalent stitch distances, such that the second needle (B') perforates a thread (11) sewn beforehand by the first needle (A') before perforating the fabric.
2. Method according to claim 1, characterised in that said pieces of fabric are sections of tubular fabric which are flattened so as to form lengths of flat double-thickness fabric.
3. Method according to one of the preceding claims, characterised in that the second needle (B') perforates the fabric in the middle of the stitches produced by the first needle (A').
4. Method according to one of the preceding claims, characterised in that multifilament threads with a textured structure are used.
5. Bag for the transport and storage of bulk goods obtained according to the method of one of claims 1 to 4, formed by sewing together a plurality of pieces of fabric (1, 2, 3, 4, 5, 6), characterised in that at least two seams joining two adjacent pieces of fabric (1, 2) are superposed in a single line (9), the stitches of said seams being substantially of the same length and being offset such that the perforations separating each of the stitches of each of the seams are filled by a thread forming the other seam.
6. Bag according to claim 5, characterised in that it is made of flattened tubular pieces of fabric comprising conductive threads.
7. Sewing machine for implementing the method according to one of claims 1 to 4, characterised in that it comprises at least two needles (A', B') which are arranged to work one behind the other in one and the same direction (10) and alternately.

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