METHOD AND MACHINE FOR FORMING FLEXIBLE BAGS WITH SPECIAL BOTTOM

Abstract

A flexible bag comprising a first wall and a second wall superposed over the first wall, the walls being connected to each other along their longitudinal edges by two gussets. As per a bag formation process, successively: the bag is closed with a flap extending from one of the walls and held on the other wall to form a closed end of the bag; the first wall of the bag is gripped at a predetermined distance from the closed end with the lower grippers and the second wall by the upper grippers and the walls are separated to form a side on the gussets; the second wall is released by the upper grippers and the closed end is folded by a folding device on to the second wall, thus making the bottom.

Claims

1. A process for forming flexible bags, the bag comprising a first wall and a second wall superposed over the first wall, the walls being connected to each other along their longitudinal edges by two gussets, whereby successively: the bag is closed to form a closed end of the bag opposite to the open end; at a predetermined distance from the closed end of the bag the first wall is gripped by the lower grippers mounted on a lower support and the second wall by the upper grippers mounted on an upper support and the walls are separated by means of the grippers; the second wall is released by the upper grippers and the closed end is folded by the folding device on to the second wall forming a first crease extending on to the first wall between the lower grippers, a second crease extending on to the second wall between the ends of the sides, and a third crease entering into the second wall symmetrically with the end of the bag with respect to the second crease, thus making the bottom delimited between the first and second creases; the process being characterised by the fact that when the grippers are separated, a side is formed on the gussets extending from one wall to the other.

2. The process of claim 1 whereby a pressing system presses on to the second wall after the upper grippers are released.

3. The process of claim 1, wherein a separation is maintained between the second wall and the first wall over at least part of the width of the bag and over its entire length in order to create a channel to supply air from the open end to the closed end.

4. The process of claim 1, wherein bags closed by the flap are formed initially, and stacked and then unstacked to make the bottom.

5. The process of claim 1, wherein the formation of the bottom is accomplished in line with the formation of the bag.

6. The process of claim 1, wherein the predetermined distance between the closed end and the first crease, respectively the second crease is more or less equal to the depth of the gussets.

7. A machine for manufacturing flexible bags, the bag comprising a first wall and a second wall superposed over the first wall, the walls being connected to each other along their longitudinal edges by two gussets, one end of the bag being closed, the machine being characterised by the fact that it comprises a reception system for receiving a series of bags moving in a main direction parallel to the longitudinal edges, with the closed end leading, a lower support for supporting two lower grippers, the lower grippers being arranged to grip the first wall at a predetermined distance from the closed end of the bag, an upper support for supporting upper grippers, the upper grippers being arranged to grip the second wall at a predetermined distance from the closed end of the bag, the upper support and the lower support being arranged to separate the lower grippers from the upper grippers to form a side on the gussets extending from one wall to the other, a folding device to fold the bottom on to the second wall by forming a first crease extending on to the first wall between the lower grippers, a second crease extending on to the second wall between the ends of the sides, and a third crease entering on to the second wall symmetrically at the end of the bag with respect to the second crease.

8. The machine as per of claim 7, in which the lower and upper supports are respectively lower and upper contrarotating cylinders.

9. The machine of claim 8, characterised by the fact it comprises a pressing system for pressing on the second wall after the upper grippers are released and which comprises a ruler extending in the direction of a generatrix of the upper cylinder, and an actuating system for extracting the ruler from the upper cylinder during the folding phase and then retracting it.

10. The machine of claim 7 in which the folding device is made by a folding cylinder configured to squeeze the bag against the lower support.

11. The machine of claim 7 in which the lower support and/or the upper support comprise(s) a suction system to suck respectively the first and/or second wall so as to separate them before being gripped by the grippers.

12. The machine of claim 11 in which the suction system extends upstream of the upper support over a sufficient length to create at least one channel to feed air from the open end of the bag to the closed end.

13. The machine as perof claim 12 in which the suction system comprises a strip permeable to air mounted in a loop and against which the second wall of the bag is sucked, the strip being driven to advance at the same speed as the bag.

14. The machine of claim 7, wherein the machine comprises a creasing station to mark the walls of the bag as per a first marking at a predetermined distance from the closed end and as per a second marking at the same predetermined distance from the first marking.

15. The machine of claim 14 in which the creasing station comprises a creasing cylinder and a counter-cylinder mounted contrarotating in parallel with each other, the creasing cylinder comprises two blades extending along two generatrixes and protruding from the surface of the cylinder, the counter-cylinder comprising a soft surface.

Description

DESCRIPTION OF THE FIGURES

[0029] Other characteristics and advantages of the invention will emerge clearly from the description below given as an indication and non-exhaustively, referring to the appended drawings amongst which:

[0030] FIG. 1 is a schematic side view of a machine according to one of the invention's accomplishment modes;

[0031] FIG. 2 is a perspective view of a flat bag before transformation as per the invention's process;

[0032] FIG. 3 is a view similar to FIG. 2 of the bag after it has undergone a step to form the sides;

[0033] FIG. 4 is a view similar to FIG. 2 of the bag during a folding phase;

[0034] FIG. 5 is a side view of the bag in FIG. 2 at the end of the folding phase;

[0035] FIG. 6 is a perspective view of the open bag standing upright ready to be filled;

[0036] FIG. 7 is a view similar to FIG. 1 as per a second accomplishment mode;

[0037] FIG. 8 is a view similar to FIG. 2 after accomplishment of the creasing as per the second accomplishment mode.

DETAILED DESCRIPTION

[0038] A machine for manufacturing flexible bags, as per a first accomplishment mode and such as illustrated schematically in FIG. 1, comprises a conventional bottom-forming station 1 whose detailed description is not given here. On leaving the bottom-forming station 1, a flat bag 2 is provided, bag 2 comprising as shown in FIG. 2 a first wall 21 and a second wall 22 superposed over the first wall 21. Walls 21, 22 are connected to each other along their longitudinal edges 23 by two gussets 24. One end 20 of the bag 2 is closed by a flap 25 extending from the first wall 21 and bonded on to the second wall 22. The bag 2 is shown with a tab 26 that prolongs the first wall 21 beyond the end of the second wall 22 at the opposite end to the closed end. However, the invention also applies to the case where the tab 26 prolongs the second wall 22 or, more generally speaking, whatever the shape of this end.

[0039] The machine also comprises a reception system 3, a lower support 4, an upper support 5 and a folding device 6.

[0040] The reception system 3 is designed to receive a series of bags 2 moving in one main direction parallel to the longitudinal edges coming from the bottom-forming station 1, with the closed end 20 leading. The reception system 3 makes it possible to move the bags 2 one by one at regular intervals to the next step.

[0041] The lower support is in the shape of a lower cylinder 4 mounted in rotation. The lower cylinder 4 supports two lower grippers 41, the lower grippers 41 being arranged to grip the first wall 21 of bag 2 presented by the reception system 3 at a predetermined distance from the closed end 20 of bag 2. The lower grippers 41 are aligned on the same generatrix of the lower cylinder 4. The upper support is in the shape of an upper cylinder 5 mounted in rotation in the opposite direction to that of the lower cylinder 4. The upper cylinder 5 supports the upper grippers 51 which are arranged to grip the second wall 22 at the predetermined distance from the closed end 20 of bag 2. To achieve this, the lower 41 and upper 51 grippers are opposite each other without any angular offset. The upper grippers 51 are aligned on the same generatrix of the upper cylinder 5. The walls are gripped when the grippers are at the level of the collar between the lower and upper cylinders 4, 5.

[0042] To facilitate the gripping by grippers 41, 51, the upper and lower cylinders 4, 5 comprise a suction system 8, for sucking respectively the first and second wall 21, 22 so as to separate them before being gripped by grippers 41, 51. This suction system comprises two lower chambers 81 and two upper chambers 82 opposite each other upstream of the upper support 5 and, for each chamber 81, 82, an air-permeable strip 83, 84 mounted in a loop. The permeable strip 83, 84 is placed against chamber 81, 82 in front of an opening in it and is driven to advance at the same speed as the bag. The strip 83, 84 has for example a row of holes running down its middle. Chamber 81, 82 is placed under negative pressure by a system, not shown, so that the second wall 22 of the bag is sucked against the strip 84 of the upper chamber 82 and the first wall 21 of the bag is sucked against the strip 83 of the lower chamber 81. The length of the chambers 81, 82 is sufficient to ensure that, when the grippers grip the upper and lower walls 21, 22, a channel feeding air is created from the open end 21 of the bag going to the closed end 20 by separating the walls owing to the suction against the strips 83, 84. Preferably, chambers 81, 82 are placed to suck the edges of walls 21, 22 at the level of the gussets 24.

[0043] The upper support 5 and the lower support 4 are arranged to separate the lower grippers 41 from the upper grippers 51. The separation is obtained by the continued rotation of the lower and upper cylinders 4, 5 in such a way that the distance between the grippers 41, 51 increases. A side 27 is thus formed on each of the gussets 24 extending from one wall to the other.

[0044] The machine also comprises a pressing system 7 for pressing against the second wall 22 after the upper grippers 51 have been released. The pressing system 7 comprises a ruler 71 extending in the direction of a generatrix of the upper cylinder 5, and an actuating system to extract the ruler 71 from the upper cylinder 5 during the folding phase and then retract it.

[0045] The folding device 6 is designed to fold the bottom on to the second wall 22. The folding device 6 consists of a folding cylinder 6 configured to squeeze the bag 2 against the lower cylinder 4 while rotating in the opposite direction to the lower cylinder 4.

[0046] The machine implements a process to form a special bottom on the flat bags 2.

[0047] Once one of the ends of bag 2 has been closed in the bottom-forming station 1 by a flap 25 extending from one of the walls 21 and bonded on to the other wall 22, in a manner known per se, bag 2 is advanced in a transport direction by the reception system 3, the longitudinal edges 53 of bag 2 being parallel to the transport direction Fl, towards the collar between the upper and lower cylinders 4, 5, which are contrarotating. The closed end 20 of bag 2 protrudes from the collar and the suction system tends to separate the first wall 21 from the second wall 22. Furthermore, a channel is created inside the bag along each edge to allow the bottom to communicate with the opening of the bag. The lower and upper grippers 41, 51 are actuated to grip respectively the first and second wall 21, 22 at a predetermined distance from the closed end 20 of bag 2. Thus, grippers 41, 51 enter into the space delimited by the gussets 24. They hold the first wall 21, respectively the second wall 22, on the lower cylinder 4, respectively upper cylinder 5.

[0048] As the lower and upper cylinders 4, 5 continue to rotate, the walls are separated by grippers 41, 51 to form one side 27 on the gussets 24 extending from one wall to the other 21, 22, as shown in FIG. 3. The cavity thus created is filled with air from the open end passing through the air supply channels. The upper grippers 51 are then commanded to release the second wall 22. The ruler 71 on the pressing system 7 is deployed to press against the second wall 22 once the upper grippers 51 have been released, as shown in FIG. 4.

[0049] The bag 2 continues its trajectory towards the folding cylinder 6 to fold the closed end 20 of bag 2 on to the second wall 22 forming a first crease 281 extending on to the first wall 21 between the lower grippers 41, a second crease 282 extending on to the second wall 22 between the ends of the sides 27, and a third crease 283 entering on to the second wall 22 symmetrically with the end of the bag 2 with respect to the second crease 282, thus making the bottom 29 delimited between the first and second creases 281, 282. The distance between the closed end 20 and the first crease 281, respectively the second crease 282 is more or less equal to the depth of the gussets 24.

[0050] When using bag 2, you can open it at the open end by separating the first and second walls 21, 22, to obtain a shape as shown in FIG. 6. Depending on the nature of the material bag 2 is made of, it can stand upright on its bottom 29 created as per the process. The material may be paper, plastic film or a woven thermoplastic material.

[0051] In a variant that is not shown, we start by forming bags closed by flap 25, then stack them and unstack them to make the bottom 29. An unstacking system replaces the bottom-forming station 1 and feeds the reception system 3 with the bags one by one.

[0052] The action of the pressing system 7 is not essential, depending on the behaviour of the material used to make the bags. The third crease 283 can be formed naturally by the folding action.

[0053] As per a second accomplishment mode of the invention, shown in FIG. 7, the machine is distinct from the first accomplishment mode in that it comprises a creasing station 9 that marks the walls of the bag and facilitates its shaping. The creasing station 9 is placed upstream of the suction system 8 and comprises a creasing cylinder 91 and a counter-cylinder 91. These two cylinders 91, 92 are mounted to rotate in parallel with each other and are contrarotating. The creasing cylinder comprises two blades 911, 912 extending along two generatrixes and protruding from the surface of the cylinder 91. The counter-cylinder 92 has a soft surface, made for example with a rubber coating, at least opposite the blades 911, 912.

[0054] In operation, the peripheral speed of the cylinders 91, 92 is the same as that of the advancing bags. The blades 911, 912 successively squeeze the bag 2 against the counter-cylinder 92 and thus make two marks on each bag. Preferably, the first marking corresponds to the first crease 281 and to the second crease 282, whereas the second marking anticipates the third crease 283, as shown in FIG. 8. The preferential distance between the first marking and the edge of the closed end is equal to the depth of the gussets. The preferential distance between the second marking and the edge of the closed end is equal to twice the depth of the gussets. The rest of the operation is similar to what has been described earlier.