GB2103576A - Method of manufacture of a bulk material transport bag - Google Patents

Abstract

In the manufacture of a bulk material transport bag 11, the method of joining two adjacent side wall panels 19, 21 for the bag and mounting a lifting loop 29 at the top corner formed by the two side wall panels comprises, in sequence, the steps of folding back and stitching a terminal strip to form an integral vertical open-ended edge pocket 51 on each panel, stitching the fold edges of the two panels together at 67 in overlapping relation, inserting the legs 31 of a lifting loop into the open top ends of the pockets in the two panels, and applying zig-zag loop anchor stitching 71 across the upper portions of the pockets, to the full length of the lifting loop leg inserts. <IMAGE>

Description

SPECIFICATION Method of manufacture of a bulk material transport bag Background of the Invention The use of large fabric bags for transporting bulk quantities of powdered or granular material, bags which can be lifted by material handling equipment having hooks or tines, is well known in the art. Bags of this type are shown in U.S. Patents 3,961,655 and 4,010,784 issued to Frank Nattrass and Peter Johnson Nattrass. The bags shown in these patents each have four lifting loops attached to the top of the bag by gathering or bunching the bag fabric at each of four spaced locations.Each leg of a loop is secured to the fabric of the bag by folding a section of the fabric to a substantially S-shaped configuration extending from the top toward the bottom of the bag to form three overlying thicknesses of fabric and the leg is inserted between two of the three fabric layers. The resulting assembly is stitched together to anchor the loop to the bag. This construction, while strong and commercially succesful, has the disadvantage that the top of the bag is smaller than the cross sectional area of the lower portion of the bag, which may inhibit filling of the bag and reduces the overall capacity.

A stronger bag construction having the added advantage of an open top as large as the lower part of the bag, is disclosed in the co-pending application of Peter J. Nattrass, Serial No. 159,833, filed June 16, 1980. In that bag construction the vertical edges of each adjacent pair of side panels are folded back and the panels are joined by a seam stitched through the fold edges. The tops of the folded portions of the side panels are used to form pockets that receive the end portions of the legs of a lifting loop, which is anchored to the bag by zig-zag anchor stitching extending for the full height of the lifting loop leg end portions. The sequence of operations performed in manufacturing this bag can be of substatial importance as regards the cost of the bag and its strength and durability.

Summary of the Invention It is a principal object of the present invention, therefore, to provide a new and improved method of manufacture of a bulk material transport bag, particularly the bag of the aforesaid Nattrass application and modifications thereof, which method minimizes the cost of manufacture and provides optimum strength and durability for the bag.

Accordingly, the invention relates to the manufacture of a bulk material transport bag of the kind comprising a plurality of generally rectangular side wall panels joined to and extending upwardly from a bottom wall panel, each vertical side wall panel edge being folded back on itself to form an elongated terminal strip, the fold edges of adjacent side wall panels being joined by a seam, and a plurality of lifting loops being secured to the top corners of the bag in pockets formed by the top portions of the side wall panel terminal strips.The invention comprises the improved method of joining two adjacent side wall panels to each other and to a lifting loop including the following steps in the recited sequence: A. folding a terminal strip along the vertical edge of each panel back on itself, and stitching the free edge of the terminal strip to the side wall panel to form a vertical, open-ended edge pocket; B. aligning the fold edges of the two panels in overlapping relation to each other and stitching them together to form a seam joining the two panels, the stitching of step B being spaced from the stitching of step A, on each panel, by a distance sufficient to allow insertion of a lifting loop leg into the open end of the portion of the pocket remaining therebetween; C. inserting the legs of a lifting loop into the open top ends of the pockets in the two panels; and D. applying zig-zag anchor stitching to the upper portion of each vertical edge pocket to anchor each loop leg in place, the anchor stitching on each panel extending for the full width of the pocket in that panel and for a height at least about equal to the length of lifting loop leg disposed in the pocket.

Brief Description of the Drawings Figure 1 is a perspective view of a bag manufactured by the method of this invention; Figure 2 illustrates an initial stage in the manufacture of the bag of Fig. 1; Figure 3 illustrates an intermediate stage in the manufacture of the bag of Fig. 1; Figure 4 illustrates the finishing stages in the manufacture of the bag of Fig. 1; Figure 5 is a perspective detail view, partly in cross section, of one top corner of the bag of Fig. 1; Figure 6 illustrates a modification of the finishing stages of manufacture; and Figure 7 illustrates a further modification of the finishing stages of manufacture.

Description of the Preferred Embodiments Fig. 1 of the drawings shows a bulk material transport bag 11 manufactured in accordance with one embodiment of the invention.

The bag 11 includes a body of generally rectangular horizontal cross section having four side wall panels 15, 17, 19 and 21 and a bottom wall panel 23, all formed of a high tensile strength woven fabric. Each panel is rectangular in shape and is connected to all adjacent panels to form a body of essentially constant cross section from the bottom wall 23 to the open top 25.

A lifting loop 29 is installed in each top corner of the bag 11. Each lifting loop is a length of strong webbing that affords a pair of legs 31 joined by a bight portion 33. The lower ends of the legs 31 are attached to the side walls of the bag body as described below.

Vertically extending seams 35, 36, 37 and 38 are formed at the four vertical corners of the bag body. Two horizonatally extending seams 34 and 39 are formed at opposite sides of the bottom wall panel at the juncture of the side wall panels 1 5 and 1 9 with the bottom wall 23. The seams 34-39 are all substantially the same in construction; indeed, the seams 37, 38 and 39 are preferably continuous, as are the seams 34, 35 and 36.

The present invention relates to an improved method of joining any two adjacent side walls of the bulk material transport bag to each other and to one of the lifting loops 29. This method comprises the following steps in the recited sequence, as applied to the joining of the side wall panels 19 and 21 along the seam 37 and the mounting of a lifting loop 29 thereon.

A. Initial Stage, Fig. 2 As the first step in joining the two side wall panels 1 9 and 21, each of the panels is folded back upon itself along a vertical edge, affording the terminal strips 55 and 57. The terminal strip 55 of panel 1 9 is then stitched, along its free edge, by the stitching 53 to form an open-ended edge pocket 51 that will be vertical when assembly of bag 11 is completed. Similarly, the free edge of terminal strip 57 is stitched to the body portion of panel 21, by the stitching 59, to form a vertical open-ended edge pocket 61.

B. Intemediate Stage, Fig. 3 After the vertical edge pockets 51 and 52 are formed as in Fig. 2, the fold edges 63 and 65 of panels 19 and 21 are aligned in overlapping relation to each other as shown in Fig. 3. The fold edges 63 and 65 are then stitched together by the stitching 67 to form the seam 37 joining these two panels. The seam stitching 67 of this intermediate stage of manufacture is spaced from the pocket stitching 53 and 59 by a distance W that is sufficient to allow opening of the two pockets 51 and 61 for insertion of one of the lifting loop legs 31 into the open end of each pocket.

C. Initial Finishing Stage, Fig. 4 Following the sewing of seam 37, Fig. 3, panels 19 and 21 are spaced apart as shown in Fig. 4 and the two legs 31 of a lifting loop are inserted into pockets 51 and 61. A substantial portion of each lifting loop leg should be inserted into each pocket. Typically, the length of the inserted portion is of the order of ten inches.

D. Final Finishing Stage, Figs. 4 and 5 Zig-zag anchor stitching 71 is now applied to the upper portion of each of the two pockets 51 and 61 to anchor each of the loop legs 31 in place in the top corner portion of the bag. The anchor stitching 71 for each panel extends for the full width of the pocket in that panel, as shown in Figs. 4 and 5.

Furthermore, the anchor stitching 71 should extend for a height at least about equal to the length of the portion of the lifting loop leg that has been inserted into the pocket, as shown in Fig. 1. A double zig-zag anchor stitching pattern, as shown in Figs. 1 and 5, is preferred.

Fig. 6 illustrates a modification of the finishing stages of the invention that affords some added strength at the top of seam 37 where the lifting loop legs 31 are joined to the bag corner. As shown in Fig. 6, the fold edges 63 and 65 may be folded back parallel to one of the panels 1 9 and 21 so that the anchor stitching 71 binds the fold edges flat to one of the panels.

Fig. 7 illustrates another modification of a method of joining two adjacent side wall panels 19 and 21 to each other and to the legs 31 of the lifting loop. In this instance, the modification is directed to the manner in which the fold edges 63 and 65 of the two panels are aligned with each other in the intermediate step B. Here, the two panels are disposed in opposed relation to each other for overlapping of the two fold edges and application of the seam stitching 67. As in the arrangement of Fig. 6, the anchor stitching 71 is applied from side to side, in zig-zag manner, across both of the terminal strips 55 and 57, simultaneously.

In all of the different embodiments of the method of the invention, the cloth elements constituting the bag panels and the lifting loop legs are easily maintained in flat condition for convenient and rapid sewing. Manipulation of the elements being joined to each other is mimimized. At each stage of manufacture, for any sewing operation, the sewing machine operator need control no more than two individual elements. Thus, the manufacturing cost is effectively held to a minimum.

Nevertheless, the resulting bag structure has the high'/ desirable attributes of improved strength and durability.

In particular, the completed bag displays substantially greater strength and durability when subjected to a drop test than previously known bags, as long as an adequate width of fabric is folded back for the terminal strips 55, 57. In a typical construction, using eight ounce babric for the bag and 400 pound/ inch tape for the loops 29, with terminal strips at least three and one-half inches in overall width, the bag can be dropped three feet while holding one ton without damage to the bag fabric.

For both the seam stitching 67 and the pocket stitching 53 and 59, double lines of stitching are shown in the drawings. However, it should be recognized that single lines of stitching may be employed in either instance, provided the stitching is strong enough.

Claims (3)

1. In the manufacture of a bulk material transport bag of the kind comprising a plurality of generally rectangular side wall panels joined to and extending upwardly from a bottom wall panel, each vertical side wall panel edge being folded back on itself to form an elongated terminal strip, the fold edges of adjacent side wall panels being joined by a seam, and a plurality of lifting loops being secured to the top corners of the bag in pockets formed by the top portions of the side wall panel terminal strips, the improved method of joining two adjacent side wall panels to each other and to a lifting loop comprising the following steps in the recited sequence:: A. folding a terminal strip along the vertical edge of each panel back on itself, and stitching the free edge of the terminal strip to the side wall panel to form a vertical, open-ended edge pocket; B. aligning the fold edges of the two panels in overlapping relation to ech other and stitching them together to form a seam joining the two panels, the stitching of step B being spaced from the stitching of step A, on each panel, by a distance sufficient to allow insertion of a lifting loop leg into the open end of the portion of the pocket remaining therebetween; C. inserting the legs of a lifting loop into the open top ends of the pockets in the two panels; and D. applying zig-zag anchor stitching to the upper portion of each vertical edge pocket to anchor each loop leg in place, the anchor stitching on each panel extending for the full width of the pocket in that panel and for a height at least about equal to the length of lifting loop leg disposed in the pocket.

2. The improved method of joining two side wall panels of a bulk material transport bag to each other and to a lifting loop, according to Claim 1, in which the fold edges of the two panels are aligned with the two panels in full overlapping relation, in step B, and subequently opened up to extend away from each other in step D.

3. The improved method of joining two side wall panels of a bulk material transport bag to each other and to a lifting loop, according to Claim 1 or Claim 2, in which the anchor stitching is applied with the two panels flattened across the seam such that the anchor stitching extends continuously back and forth across both pockets.