WO2010086794A1

WO2010086794A1 - A device and a method for making a double fold

Info

Publication number: WO2010086794A1
Application number: PCT/IB2010/050348
Authority: WO
Inventors: Amit Kumar Lohia
Original assignee: Lohia Starlinger Limited
Priority date: 2009-01-29
Filing date: 2010-01-27
Publication date: 2010-08-05

Abstract

The present invention is related to operations where a fabric (1a) or a bag made from it is folded before it's either stitched or heat welded into a seam. The present invention provides a device that forms a double fold in flexible sheet materials (1a) in a single continuous automated process. The device accepts the running sheet material which passes through an arrangement of mechanical parts such that the double-fold formed is of uniform width, without irregularities such as creases, and operates independently of type of fabric. This facilitates effective stitching or sealing of the fold and in turn a more effective seam or a joint. The invention is useful in making double folds in any flexible sheet material or fabric such as those used in the garment industry or in paper product industry, or the sheet rubber or sheet plastic industries and similar other industries.

Description

A Device And A Method For Making A Double Fold

Field of invention

The present invention is related to automated bag making operation or operations where a fabric or a bag made from it is folded before it's either stitched or heat welded into a seam. In particular the invention is related to a device for double folding fabrics or bags made using them.

Background of Invention Folding of fabric prevents loosening of fabric strands and adds to the integrity of the seam, therefore it is a common practice to fold the fabric ends to be stitched. The seams that have the fabric edge completely hidden - that is seams formed by doubly folding the fabric - are superior to seams made on singly folded fabric.

The common approach for double fold formation in the bag-making industry is to form two single folds in succession, the second of the single folds forming over the first single fold. It is difficult to maintain uniform fold- width in this process as the fabric tends to unfold due to its flexibility. The fabric also tends to slip out of grip of the folding device due to its softness. The folds formed using conventional methods, therefore, are unreliable and lead to inferior quality seams that are much dependent on the fabric type and quality. Deviations in the width and quality of the folds also potentially results into loss of material. The bags manufactured with seams produced by conventional methods are poor in appearance and finish quality.

There is therefore a need to provide an apparatus and a reliable method to form double folds of uniform width at the seams of polyolefin woven fabrics to be used in automatic bag making machines.

It is also noticed that similar need exists in other industries where fold making is necessary, eg garment making, paper products, sheet rubber and sheet plastic products.

Objects and advantages of the invention

Accordingly one object of the present invention is to provide an apparatus and a reliable method to form double folds of uniform width at the seams of polyolefin woven fabrics, particularly of a tubular form, to be used in automatic bag making machines.

A further object of the present invention is to provide an apparatus and a reliable method to form double folds of uniform width in any flexible fabric such as those used in the garment industry or in paper product industry, or the sheet rubber or sheet plastic industries.

One of the advantages of the present invention is that it is compact. Another advantage of the present invention is that it results in folds of uniform fold width across the seam length as well as complete extension of second fold leg within the double fold.

A further advantage of the present invention is that the folds produced are uniform in their thickness and without pleats or wrinkles or any other similar flaws.

Summary of the invention:

The present invention provides a device that forms a double fold in flexible sheet materials in a single continuous automated process. The device accepts the running sheet material which passes through an inventive arrangement of mechanical parts such that the double-fold formed is of uniform width, and without irregularities such as creases, and operates independently of type of fabric. This facilitates more effective stitching or sealing of the fold and in turn a more effective seam or a joint. The invention is useful in making double folds in any flexible sheet material or fabric such as those used in the garment industry or in paper product industry, or the sheet rubber or sheet plastic industries and similar other industries.

Brief description of figures :

Figures 1 to 7: Isometric views of the double folder of the present invention Figure 7A - top view of the assembled double folder of the invention Figure 8: Positioning of second guide Figure 9: Cross section AA representing entry of the fabric into the device (and showing the onset of the first fold formation)

Figure 10: Cross section BB showing near-completion of first fold formation Figure 11 : Cross section CC showing onset of the depression in fabric Figure 12: Cross section DD showing second fold being developed

Figure 13 : Cross section EE showing formation of completed double fold

List of Parts:

1 - Direction of fabric advance 8 A - First gap; 8C - Second gap IA - Fabric 8B - upstream end FAl of folder

2 - Difference in levels of first and angle second bases 9 - Mounting block

3 - First folder bracket 10 - First guide 3A - First base 1OA - Wall element

4- Second folder bracket 1 OB - Base element

4A - Second base 1OC - First arm; 10Ca -

4B - Upstream end FB2 of second downstream part of first arm base 1OD - Second Arm

5 - First wall; 5A - Recess 1 OE - Upstream end FG 1 of first

6 - Second wall guide; 1OF - Slit

7 - Spacer bush 11 - Second guide

8 - Folder angle HA - first angle θ 1 IB - second angle θi 13B - Upstream end TGl of top

11C - Bottom edge BEl of the guide second guide 14 - Hanger bracket

12 - Bottom guide 15 - Mandrel

12A - Upstream end BGl of the 15A - MEl bottom guide 16 - Folder block

12B - Downstream end BG2 of the 16A - Upstream end FB 1 of Folder bottom guide Block

13 - Top guide 16B - Interface between the

13 A - Top guide wall mandrel and the folder block

Description of the invention:

The present invention discloses a device through which a fabric advances such that an edge of the fabric is folded into a double fold formation so that the folded fabric can be taken for seam forming. For the ease of the description, the invention is defined to have two ends, namely and upstream end and a downstream end. The upstream end is where the fabric needing to be folded enters the invention and the downstream end is where it exits it. The direction of fabric advance (1) is indicated in Figures 2 to 5.

Figure 1 shows an exploded view of the entire invention taken from downstream side (in respect of the fabric movement). Figure 2 also shows a view of the assembled invention from its upstream end with many parts of the device in view. Figure 3 shows yet another view of the assembled device. As shown in Figure 1, a first folder bracket (3) and a second folder bracket (4) are provided. The first folder bracket (3) has a first wall (5) and a first base (3A) and the second folder bracket (4) has a second base (4A) and a second wall (6). The brackets (3 and 4) are such positioned and held together securely with the help of spacer bushes (7), at least one in number, preferably two or more, so as to form a space within their corresponding walls (5 and 6) within which the rest of the components of the present invention are accommodated. The bases (3 A and 4A) and the walls (5 and 6) are either formed separately and joined together fixedly, or formed integrally, to form the shape of the brackets (3 and 4).

The bases of both folder brackets (3 and 4) are preferably flat and their relative positioning is such that the level of the bottom surface of the second base (4A), as can be seen from Figures 9 and 10, is raised above the level of the bottom surface of the first base (3A). The difference in levels (2) is maintained such that it allows accommodation and movement of the fabric throughout its passage through the device.

As is evident from figures 1 to 7, many of the components of the invention are in an elongated shape and for the ease of description these parts are also referred to in terms of their upstream and downstream ends as appropriate.

As seen from Figures 1 and 4, the upstream part FB2 (4B) of the second base (4A) also serves as a folder angle (8). The shape of the upstream end FAl (8B) of the folder angle (8) is such that it facilitates the fabric entry into the device without any obstruction, preferably the end FAl (8B) being lifted up gradually. Preferably a taper is also provided in the horizontal plane so that the fabric has an unobstructed entry into a first gap (8A) (see Figure 9) that is provided between the side of the folder angle (8) and the first wall (5).

As shown in Figures 1 and 6, a folder block (16), which is preferably an elongated block, is provided. As shown in figures 6 and 7, it is fixedly attached to the second base (4A). A second gap (8C) (see Figure 10) of same width as that of the first gap (8A) is maintained between the side face of the folder block (16) and the first wall (5). The upstream end FBI (16A) of the folder block (16) is shaped such that the entry of the fabric past itself is obstruction- free. Preferably the upstream end FBI (16A) of the folder block (16) being machined to provide tapers or rounded shape as shown in figures 5 and 7.

As seen from Figure 1, two further parts, namely a first guide (10) and a second guide (11) are provided. The first guide (10) has a wall element (10A) and a base element (10B), the wall element (10A) being fixedly but adjustably attached to the first wall (5). The base element (10B) of the first guide (10) has a slit (10F) which splits the base element (10B) into a first arm (10C) and a second arm (10D). As can be seen from Figures 1, 5, and 7, the downstream part (lOCa) of the first arm (10C) slopes down in downstream direction. As can be seen from Figures 1 and 6, the second guide (11), which is in the form of flat plate, is positioned so that its bottom edge BEl (11C) is situated within the slit. As seen from Figure 8, which represents the top view of the invention, and also from figures 9 and 10, which represent cross sections taken through the invention, the second guide (11) is placed preferably at a first angle (1 IA) in the range from 1 ° to 10 °; alternatively, the second guide (11) is placed parallelly with the first wall (5). The bottom edge (HC) of the second guide (11) preferably slopes gradually downwards in the downstream direction (see Figures 8, 9 and 10), the second angle (HB) of the slope being in the range of 1° to 10 °. and at some point the bottom edge (HC) of the second guide (11) goes below the level of the slit such that a depression in the passing fabric is made. The second guide (11) is attached, preferably fixedly using a mounting block (9), to the second wall (6) in a manner such that the second guide (11) is adjustable in its own plane. The position of the mounting block (9) on the second wall (6) is preferably adjustable in the direction of the fabric movement. The preferred shapes of the first guide (10) are seen in Figures 4, 5, and 8.

As seen from Figure 5, the upstream part of the base element (10B) of the first guide (10) is in a tapered shape, increasing in width in the downstream direction, and its end FGl (10E) near the upstream end FBI (16A) of the folder block (16) is machined or smoothened to facilitate unobstructed and continued passage of the fabric. In the preferred embodiment of the invention a recess (5A) is provided into the inside face of the first wall (5) such that the upstream end FGl (10E) of the first guide (10) is tucked away in the recess.

As seen in Figure 1 a bottom guide (12) is provided, which is preferably of an elongated shape, more preferably a strip. As seen in Figure 5, its upstream end BGl (12A) is lifted up gradually and overlaps sloping part of the first arm (10C). This arrangement creates a gap between BGl and first arm (10C) which in turn makes for an unobstructed entry of the progressing fabric to the underside of the bottom guide (12). As seen from Figure 1, the bottom guide (12) increases in width, preferably gradually, in the direction of the fabric progress. The bottom guide (12) is so profiled that its downstream end BG2 (12B) is preferably at the same level as the level of the sewing platform. The bottom guide (12) is attached to second wall (6), preferably with the help of at least one hanger bracket (14), preferably three, in a fixed but adjustable manner.

As seen from Figure 1 a mandrel (15) which is in an elongated shape is provided, preferably a strip, and is preferably attached to the folder block (16), preferably fixedly. As seen from Figure 6, in the preferred embodiment, the mandrel is situated into a recess formed into the folder block (16). Alternatively, the mandrel (15) may be attached to the first wall (5). The mandrel (15) is preferably of a tapered shape, increasing in width with the direction of the fabric passage. As seen from Figure 6, the upstream end MEl (15A) of the mandrel (15) is positioned in a manner that the interface (16B) between the mandrel (15) and the folder block provides a smooth transition for the fabric's passage when the fabric passes past the first and second guides (10 and 1 1) and over the juncture between the folder block (16) and the mandrel (15). This is achieved by making the top surface of the mandrel (15) preferably level with the top surface of the folder block (16). In an embodiment of the present invention, the top surface of the mandrel (15) at its upstream end MEl (15A) may be lower than the top surface of the folder block (16) at their meeting point.

The tapering mandrel (15) and the tapering bottom guide (12) are placed on top of each other in a manner similar to how two arms of a typical pair of scissors are positioned in a pair of scissors, with a gap is maintained between the bottom surface of the mandrel (15) and the top surface of the bottom guide (12) so as to allow the passage of fabric between them. This is evident from figure 5 and also from Figures 9 (cross section AA) and 12 (cross section DD).

As shown in Figure 1, a top guide (13), which is in an elongated shape is provided, preferably a strip. The top guide (13) is provided with means, preferably a top guide wall (13A), to attach it fixedly but adjustably to the first wall (5) (see Figure 5). As seen from Figure 5, the width of the top guide (13) preferably increases along the direction of the fabric passage. The upstream end of the top guide, TGl (13B), is lifted up gradually. This creates a gap between the bottom surface of the top guide and the top surface of the second arm (10D) so as to facilitate unobstructed entry of the folded fabric between the bottom surface of the top guide (13) and top surface of the mandrel (15). It is important to provide this gap as it is situated at a point where the fabric is folded into a second fold by entering in between the mandrel and the bottom guide. The chances of the fabric bulging up are substantial and the arrangement of TGl ensures that the potentially bulged up fabric doesn't get caught but advances smoothly.

The length of the mandrel (15) and the top guide (13) is such that it permits full fold formation, which in turn depends on the speed of passage and the type of the fabric.

The folder block (16) is provided with a tapered shape to its downstream part such that it facilitates accommodation of the growing width of the bottom guide (12). The gaps between the bottom guide (12) and the mandrel (15) and that between the mandrel (15) and the top guide (13) is preferably maintained such that the double fold formed is of uniform thickness.

The magnitude of the space between the first and second walls (5 and 6) is maintained uniform, using at least one spacer bush (7), preferably two, at value that depends on the width of the fold that needs to be formed; the greater the width, the greater the space. The overall lengths of the various parts making up the invention are more or less independent of the type of fabric being used. However, the maximum widths of the various parts making up the invention are dependent on the width of the fold needing to be formed; the greater the width of the fold, the greater the maximum widths. The slopes at which the various parts are lifted up, as appropriate, are provided such that adequate clearance is provided for unobstructed passage of the fabric. The clearances depend on the type of the fabric, the stiffer the fabric the greater the clearance required. The positions of the spacer bushes (7) are any positions that allow the first and the second walls (5 and 6) to be held together securely without obstructing the flow of the fabric.

The edges and ends of the various parts making up the invention are smoothened and rounded off in order to facilitate unobstructed passage of the fabric.

Operation of the device of the present invention:

Figures 9-11 show cross sections taken through the assembled device at various stages. It shows the fabric position and illustrates how fold formation takes place as the fabric advances through the device.

The device assembled in accordance with the foregoing description (see Figure 7A) is placed in line of the moving fabric, preferably on a flat surface, which is at the level of the sewing platform in the case of a sewing machine used for stitching a seam. As shown in Figure 6, owing to the tapering shape of the upstream end FBI (16A) of the folder block (16) and also that of the upstream end FGl (10E) of the first guide (10), the advancing fabric or a bag made from it enters the first gap (see Figure 9). It is entered in a manner that provides sufficient width of the fabric which can be turned into a double fold. The advancing fabric or the bag made using it is folded by the first guide (10) to form the first fold (see Figure 10). The relative positioning of the folder block (16) and the tapering part of the first guide (10) is such that the fabric is kept taught as it gets folded into 1^st fold.

As the fabric advances further, the increasing width of the first guide (10)'s tapering portion increases the width of the 1^st fold. Preferably once the first fold has attained its full width, the second guide (11) makes a depression into the folded fabric (see Figure 11). The folded fabric with a depression advances further to enter the zone of overlap of the bottom guide (12) and the mandrel (15), which are positioned in the shape of arms of a typical pair of scissors. (This is apparent from Figures 9 to 12.) This relative positioning of the mandrel (15) and the bottom guide (12) ensures that the fabric already shaped into the 1^st fold is gradually pushed into the gap between the mandrel (15) and the bottom guide (12) thus beginning to form a second fold (see Figure 12), the width of the second fold increasing gradually as the folded part of the fabric gets gradually pushed towards the first wall (5) by the taper in the bottom guide (12). The relative tapers in the mandrel (15) and the bottom guide (12) (see Figure 5 and Figure 12) also ensure that the fabric is maintained taught and snug with the surfaces around which it is folded, during the process of the fold formation. The maximum widths of the mandrel (15) and the bottom guide (12) are such that the second fold attains its maximum width before the fabric leaving the device.

A top guide (13), which is attached to the first wall (5), is provided over the mandrel (15) so that the fabric, which has a tendency to curl up, is held securely, while the fold formation progresses. The relative positioning of the bottom guide (12), the mandrel (15) and the top guide (13) is such that the double fold formed is uniform in width and also in its thickness (see Figure 13). The fact that the fabric remains taught during all stages of the fold formation and the gradual nature of the fold formation ensures that there are no undesired creases or kink sin the folds formed. The folds formed at the end of the fold formation are of uniform width and depth.

The folded fabric that leaves the mandrel (15) arrives at the level of the sewing platform.

It is evident from the foregoing description that the present invention offers the following advantages: that the device is compact that it results in folds of uniform fold width across the seam length as well as complete extension of second fold leg within the double fold that the folds produced are uniform in their thickness and without pleats or wrinkles or any other similar flaws. The device of the present invention is useful in forming double folds in a variety of fabrics such as any flexible fabrics such as rubber, metal foils, plastics; cotton, wool; polyolefin woven fabrics, and any composite materials made using these materials, and the like. The device is also useful in making double folds in fabrics themselves or in the articles made using these. For example, bags made using any of the above fabrics, which are typically used for storage of grains, raw materials such as cement, need to be folded before seams are stitched. The present device is therefore useful in the bag-making industry.

It is also evident from the foregoing description that the present invention comprises following items;

1. A device for making a double fold, said device comprising: a first folder bracket (3), a second folder bracket (4), said brackets having provided with corresponding bases and walls, namely a first base (3A) and a second base (4A), and a first wall (5) and a second wall (6), said walls positioned to form a uniform space between them;

at least one spacer bush (7), preferably two or more, said plurality of spacer bushes (7) attached to said walls (5 and 6) in a manner that securely holds said walls at a uniform distance from each other;

bottom surface of said first base (3A), preferably flat, being raised above the level of bottom of said second base (4A); a folder angle (8) being provided at the upstream end of the device, the shape of said folder angle (8) being such as to facilitates the fabric entry into the device without any obstruction, preferably the upstream end FAl (8B) of said folder angle (8) being lifted up gradually, and said folder angle (8) being provided with a tapered shape at the beginning so that the fabric has an unobstructed entry into a first gap that is provided between the side of said folder angle (8) and said first wall (5);

a folder block (16), preferably in an elongated shape, being provided and fixedly attached to said second base (4A) such that a second gap of at least the same width as that of said first gap is maintained between the side face of said folder block (16) and said first wall (5); the upstream end FBI (16A) of the folder block (16) is shaped such that the entry of the fabric past itself is obstruction- free, preferably the upstream end FBI (16A) of said folder block (16) being provided a smooth or rounded shape;

a first guide (10) and a second guide (11) are provided; said first guide (10) has a wall element (10A) and a base element (10B), said wall element (10A) being attached to said first wall (5), and said base element (10B) has a slit which divides said base element (10B) into a first arm (10C) and a second arm (10D), and wherein the downstream part of the first arm (10C) slopes down in downstream direction; a second guide (11), which is preferably in the form of flat plate, is positioned so that its bottom edge (HC) is situated within the slit, such that when viewed from the top, the second guide (11) is placed either parallely with the first wall (5), or alternatively at an angle in the range from 1 ° to 10 °, and such that the bottom edge (HC) of the second guide (1 1) preferably slopes gradually downwards in the downstream direction, the slope being in the range of 1° to 10 °, and further such that at some point the bottom edge (1 Ic) of the second guide (11) goes below the level of said slit; said second guide (11) is attached, preferably fixedly but adjustably to said second wall (6) using a mounting block (9);

the upstream part of said base element (10B) increases in width in the downstream direction and its end FGl (10E) near the upstream end FBI (16A) of the folder block (16) is preferably smoothened;

a recess being provided into the inside face of the first wall (5) such that the upstream end FGl (10E) of the first guide (10) is tucked away in the recess;

a bottom guide (12) is provided, preferably of an elongated shape, more preferably a strip, such that its upstream end BGl (12A) is lifted up gradually and overlaps said first arm (10C); said bottom guide (12) increases in width, preferably gradually, in the direction of the fabric progress, and said bottom guide (12) being so profiled in its longitudinal dimension that its downstream end BG2 (12B) is preferably at the same level as the level of the sewing platform; said bottom guide (12) being attached to second wall (6), preferably with the help of at least one hanger bracket (14), preferably three, in a fixed but adjustable manner;

a mandrel (15), which is preferably in an elongated shape is provided, preferably a strip; the upstream end MEl (15A) of said mandrel (15) being positioned in a manner that it preferably forms a level or smooth transition surface along with top surface of said folder block (16);

said mandrel (15) preferably increasing in width with the direction of the fabric passage, said mandrel (15) preferably being attached to said folder block (16), preferably fixedly and preferably situated into a recess formed into the folder block (16);

the tapering said mandrel (15) and the tapering bottom guide (12) are placed on top of each other in a manner similar to two arms of a typical pair of scissors and such that a gap is maintained between the bottom surface of said mandrel (15) and the top surface of bottom guide (12);

a top guide (13), which is in an elongated shape is provided, preferably a strip; said top guide (13) being provided with means to attach it adjustably to said first wall (5), the width of the top guide (13) preferably increasing with the direction of the fabric passage. 2. A device for making a double fold as described in item 1 further wherein a recess is provided into the inside face of the first wall (5) such that the upstream end FGl (10E) of the first guide (10) is tucked away in the recess.

3. A device for making a double fold as described in any of items 1 and 2 wherein when said device is viewed from the top, said second guide (11) is placed parallelly with said first wall (5).

4. A device for making a double fold as described in any of items 1 to 3 wherein when said device is viewed from the top, said second guide (11) is placed at a first angle (HA) with said first wall (5).

5. A device for making a double fold as described in items 4 wherein said first angle (1 IA) is in the range between 1° to 10 °.

6. A device for making a double fold as described in any of items 1 to 4 wherein when said device is viewed from side, the bottom edge (HC) of said second guide (11) is placed at a second angle (HB) with the horizontal.

7. A device for making a double fold as described in item 6 wherein said second angle (1 IB) is in the range between 1 ° to 10 °.

8. A device for making a double fold as described in any of items 1 to 7 wherein when said device is viewed from side, said second guide (11) is placed such that at some point the bottom edge (HC) of the second guide (11) goes below the level of said slit.

9. A device for making a double fold as described in any of items 1 to 8 such that the relative positioning of the folder block and the tapering part of the first guide (10) is such that the fabric is kept taught during its passage over tapering part of said first guide (10). 10. A method of making a double fold comprising the steps of a. providing a device for making double fold as described in any of claims l to 9, b. entering the advancing fabric or a bag made using it into said first gap c. folding said fabric around said first guide (10) to form a first by ensuring that said fabric is kept taught as it gets folded into said first fold d. making a depression into folded area of the advancing fabric e. advancing said folded fabric with a depression while gradually pushing it into the gap between said mandrel and said bottom guide (12) f. continually advancing the fabric carrying two folds such that the folded part of the fabric is gradually pushed towards the first wall (5) due to the taper in the bottom guide (12) thereby increasing the width of the second fold gradually as said fabric advances, whereby the second fold attains its maximum width before the fabric leaving the device.

While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. It must be realized that modifications and variations are possible based on the disclosure given above without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.

Claims

Claims:

1. A device for making a double fold, said device comprising: a first folder bracket, a second folder bracket, said brackets having provided with corresponding bases and walls, namely a first base and a second base, and a first wall and a second wall, said walls positioned to form a uniform space between them;

at least one spacer bush, preferably two or more, said plurality of spacer bushes attached to said walls in a manner that securely holds said walls at a uniform distance from each other;

bottom surface of said first base, preferably flat, being raised above the level of bottom of said second base;

a folder angle being provided at the upstream end of the device, the shape of said folder angle being such as to facilitates the fabric entry into the device without any obstruction, preferably the upstream end FAl of said folder angle being lifted up gradually, and said folder angle being provided with a tapered shape so that the fabric has an unobstructed entry into a first gap that is provided between the side of said folder angle and said first wall;

a folder block, preferably in an elongated shape, being provided and fixedly attached to said second base such that a second gap of at least the same width as that of said first gap is maintained between the side face of said folder block and said first wall; the upstream end FB 1 of the folder block is shaped such that the entry of the fabric past itself is obstruction-free, preferably the upstream end FBI of said folder block being provided a smooth or rounded shape;

a first guide and a second guide are provided; said first guide has a wall element and a base element, said wall element being attached to said first wall, and said base element has a slit which divides said base element into a first arm and a second arm, and wherein the downstream part of the first arm slopes down in downstream direction;

a second guide, which is preferably in the form of flat plate, is positioned so that its bottom edge is situated within the slit, such that when viewed from the top, the second guide is placed either parallely with the first wall, or alternatively at an angle in the range from 1 ° to 10 °, and such that the bottom edge of the second guide preferably slopes gradually downwards in the downstream direction, the slope being in the range of 1° to 10 °, and further such that at some point the lower edge of the second guide goes below the level of said slit; said second guide is attached, preferably fixedly but adjustably to said second wall using a mounting block; the upstream part of said base element increases in width in the downstream direction and its end FGl near the upstream end FBI of the folder block is preferably smoothened;

a recess being provided into the inside face of the first wall such that the upstream end FGl of the first guide is tucked away in the recess;

a bottom guide is provided, preferably of an elongated shape, more preferably a strip, such that its upstream end BGl is lifted up gradually and overlaps said first arm; said bottom guide increases in width, preferably gradually, in the direction of the fabric progress, and said bottom guide being so profiled in its longitudinal dimension that its downstream end BG2 is preferably at the same level as the level of the sewing platform; said bottom guide being attached to second wall, preferably with the help of at least one hanger bracket, preferably three, in a fixed but adjustable manner;

a mandrel, which is preferably in an elongated shape is provided, preferably a strip; the upstream end MEl of said mandrel being positioned in a manner that it preferably forms a level or smooth transition surface along with top surface of said folder block;

said mandrel preferably increasing in width with the direction of the fabric passage, said mandrel preferably being attached to said folder block, preferably fixedly and preferably situated into a recess formed into the folder block;

the tapering said mandrel and the tapering bottom guide are placed on top of each other in a manner similar to two arms of a typical pair of scissors and such that a gap is maintained between the bottom surface of said mandrel and the top surface of bottom guide;

a top guide, which is in an elongated shape is provided, preferably a strip; said top guide being provided with means to attach it adjustably to said first wall, the width of the top guide preferably increasing with the direction of the fabric passage.

2. A device for making a double fold as claimed in claim 1 wherein a recess is provided into the inside face of the first wall such that the upstream end FGl of the first guide is tucked away in the recess.

3. A device for making a double fold as claimed in claim 1 wherein when said device is viewed from the top, said second guide is placed parallely with said first wall.

4. A device for making a double fold as claimed in claim 1 wherein when said device is viewed from the top, said second guide is placed at a first angle with said first wall.

5. A device for making a double fold as claimed in claim 1 wherein said first angle is in the range between 1 ° to 10 °.

6. A device for making a double fold as claimed in claim 1 wherein when said device is viewed from side, the bottom edge of said second guide is placed at a second angle with horizontal.

7. A device for making a double fold as claimed in claim 1 wherein said second angle is in the range between 1 ° to 10 °.

8. A device for making a double fold as claimed in claim 1 wherein when said device is viewed from side, said second guide is placed such that at some point the lower edge of the second guide goes below the level of said slit.

9. A device for making a double fold as claimed in claim 1 such that the relative positioning of the folder block and the tapering part of the first guide is such that the fabric is kept taught during its passage over tapering part of said first guide.

10. A method of forming a double fold comprising the steps of a. providing a device for making double fold as described in any of claims l to 9, b. entering the advancing fabric or a bag made using it into said first gap, c. folding said fabric around said first guide to form a first by ensuring that said fabric is kept taught as it gets folded into said first fold, g. making a depression into folded area of the advancing fabric , h. advancing said folded fabric with a depression while gradually pushing it into the gap between said mandrel and said bottom guide, i. continually advancing the fabric carrying two folds such that the folded part of the fabric is gradually pushed towards the first wall due to the taper in the bottom guide thereby increasing the width of the second fold gradually as said fabric advances, whereby the second fold attains its maximum width before the fabric leaving the device.