GB2053861A

GB2053861A - Method and installation for cutting off and stacking bags, and in particular plastic bags

Info

Publication number: GB2053861A
Application number: GB8018774A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-06-12
Filing date: 1980-06-09
Publication date: 1981-02-11
Also published as: IT1129089B; FR2458498B1; FR2458498A1; DE3021868A1; IT8067911A0

Abstract

Before the cutting operation at 16, a first pressing means 37 is applied on the pile of bags 36, and after the cutting operation, a second pressing means 38 is moved from under the bag on top of the pile and applied to the top of the pile, the first pressing means is raised up, and a new length of bags is placed on the pile by causing it to pass between the first and second pressing means. <IMAGE>

Description

SPECIFICATION Method and installation for stacking bags, and in particular plastic bags The invention relates to a method and installation for stacking bags, and in particular plastic bags.

The production of plastic bags starts from a roll of a tubular strip which is heat-welded and cut at regular intervals, transversely to its length.

Two methods are used, the first one consisting in continuously unwinding the strip and in alternatively moving the heat-welding and cutting members so that they effect the said heat-welding and cutting operations whilst moving in the same direction and at the same speed as the strip, the second method consisting in moving the strip intermittently over a length corresponding to the size of one bag and in actuating the heat-welding and cutting members during the periods when the strip is not moving.

The first method requires a complex and fragile installation and has a low output considering that it is limited by a relatively slow speed of displacement of the heat-welding and cutting members, because of their inertia and of the mechanical requirements.

The second method gives a higher output due to the poor amplitude of movement of the heatwelding and cutting members, but a problem remains to be solved as regards the stacking of the bags delivered by such a machine.

Indeed, because of the fast rate of production, the suppleness, the lightness of the material constituting these bags and of the static electricity that it contains, the bags delivered are not stacking in a perfect pile when they are released from the installation, so that lengthy manipulations are necessary which often require the stoppage of the installation.

It should also be noted that the stacked bags tend to adhere to one another by their heatwelded end, this tendency being all the greater than the walls of the bags are thick, (high thermal inertia) and that the rate of production is fast.

It is a particular object of the invention to overcome these drawbacks and to propose to this effect a method for stacking bags such as plastic bags, wherein the tubular strip of plastic material, moved intermittently, is heat-welded and cut at regular intervals in order to form bags which are stacked in a pile on a support, method whereby, before the cutting operation, a first pressing means is applied on the pile of bags, and after the cutting operation, a second pressing means is moved from under the bag on top of the pile and applied to the top of the pile, the first pressing means is raised up, and a new length of bags is placed on the pile by causing it to pass between the first and second pressing means.

According to another characteristic of the invention, the second pressing means is moved from under the cut edge of the bag on top of the pile, in order to be applied on top of said pile along the cut edge of the bags.

According to yet another characteristic of the invention the heat-welding tongs are closed simultaneously to the application of the first pressing means on to the pile.

The invention further relates to an installation for carrying out the aforesaid method, which installation comprises a device intermittently supplying a tubular plastic strip, heat welding tongs, and means for cutting the tubular strip, all of which are movable perpendicularly to the direction of displacement of the said strip, and a support receiving the stacked bags, said installation further comprising two pressing means to be applied alternatively on the top face of the pile, one of said means being constantly applied on the pile.

The present invention is therefore applicable to the setting up of an installation for producing plastic bags, which installation works at a high output rate (for example 1 50 bags per minute) and delivers said bags in a perfect pile, each pile being composed of a specific number of bags, whatever their dimensions or the nature of the material constituting them, the said installation being of a relatively low cost, reliable, and easily adaptable to different sizes of bags.

The invention will be more readily understood, on reading the following description with reference to the accompanying drawings, in which: Figure 1 is a diagrammatical illustration of an installation assembly according to the invention; Figure 2 is a front view of the cutting device; Figure 3 is a lefthand view of Figure 2 which shows in particular the drive mechanism of the cutting device.

This installation is fed from a roll of tubular strip or sheath of plastic material 1 passing through two drums 2 and 3 which drums unwind the strip in continuous manner.

Said strip is thereafter interlaced on the transverse pins 4 of two supports 5 and 6 one of which 5 is fixed whilst the other 6 is mounted to pivot in 7 against the action of elastic return means.

The strip then goes through two pairs of drums 7, 8, 9 and 10 which are driven in rotation intermittently, the difference of movement between the continuous unwinding by the drums 2 and 3 and the intermittent displacement by the drums 7 and 8 being absorbed, by the support 6 which pivots about the point 7 whilst keeping the strip 11 constantly stretched.

The drums 7 and 9 are driven in intermittent rotation by a hydraulic motor 12 and by means of brakes mounted on the axis of the said drums so as to deliver at each rotation a length of strip which corresponds to a dimension (generaily the length) of the desired bag.

Said strip length passes first of all between the two elements 1 3 and 14 which constitute the heat-welding tongs the element 14 of which is vertically movable to come and press on and heatweld the two faces of the tubular strip.

Then the said strip passes under the cutting device which consists (see Figures 2 and 3) of a blade 1 5 with two cutting side edges 15, and 152, said blade being integral with an endless belt 16 which is stretched over three pulleys 1 7, 1 8 and 19, the said endless belt 1 6 being driven in alternate displacement so that the blade 15, which is guided in its displacements by the slide 20 cuts across the strip at each displacement.

The endless belt 1 6 is driven by way of a driving shaft 21 turning continuously and by two pinions 22 and 23, each one of which is associated to an electromagnetic clutch device 24 and 25.

The axes 17, and 18, of the pulleys 17 and 18 which traverse a support 26 are respectively connected to the clutch devices 24 and 25.

With these devices, is obtained an alternate displacement of the strip 1 6 of the blade 15 starting from the continuous rotation of the shaft 21 by alternatively actuating the clutch device 24 and 25 so that the pinions 22 and 23, meshing into each other, drive the pulleys 17 and 18 in a reverse rotation.

Each strip length which is delivered by the drums 9 and 10 passes between the heat-welding device 13, 1 4 at the height of the cutting blade 1 5, settles on the upper side of an endless belt 27 which will constitute the support for the pile of bags being formed.

Said endless belt 27 is stretched by three drums 28, 29 and 30 mounted on a chassis moving vertically in the direction of the double arrow 31 so as to be placed either in a high position during the stacking up operation, or in a low position to evacuate the pile of bags.

In this last position, the drum 30 comes into contact with the periphery of a drum 32 which drum is itself in contact with an endless removal belt 33 stretched by two drums 34 and 35.

The upper side of this endless belt 33 is situated on the same level as the upper side of the belt 27 when this is in its lower position, so as to be able to take over the pile of bags as soon as the endless belt 27 is, in its lower position, driven away by the drum 32 in the same direction and at the same speed as the endless belt 33.

On the pile 36 of bags being formed, are alternatively applied two pressing members 37 and 38, which, when the strip length has been delivered, are situated, the one 37 above the said strip length, and the other 38 beneath, the said last pressing member being, at this stage of the functioning, applied against the upper face of the pile 36 along the cut edge of the bags.

This installation functions as follows: When a length of bag is delivered by the strip 11, the pressing member 37 comes in 37, in resting contact on the upper face of the pile, whereas simultaneously, the element 14 of the heat-welding tongs moves towards the element 13 to carry out the heat welding of the two faces of the tubular strip.

During the descending movement of the member 37, said latter stretches the strip length situated between it and the heat-welding tongs, then one of the clutch devices 24 or 25 is actuated in order to move the blade 1 5 transversely to the strip and in parallel to the line of welding produced.

One completed bag is then separated from the strip.

Then, the pressing member 38 is lifted in 381 above the level of the cutting blade 1 5 and comes down again whilst resting against the upper face of the bag which it presses against the pile of bags being formed.

During these movements, the pile of bags-is held-in the position 37, by the pressing member 37, and at the end of these movements, the pile of bags is held both by the pressing member 37 and by the pressing member 38 which is applied thereon along the cut edges.

The functioning cycle then ends with the lifting up of the pressing member 37 so that the drums 7 and 9, driven by the hydraulic motor 12, can deliver a new length of bags.

The synchronized movement of the heatwelding element 14, of the blade 1 5 and of the pressing members 37 and 38 is obtained by a motor, and for example by means of a cam-shaft, said motor being in turn controlled by a contactor which is switched off during the periods where the drums 7 and 9 are stopped.

In the same way, the synchronized displacement of the endless belt 27 is obtained by way of a preselection meter 39 which totalises the number of intermittent actuations of one of the movable parts of the installation and for example the number of actuations of the pressing member 38.

Thus, by totalising the number of actuations of the pressing member 38, the meter 39 totalises the number of stacked bags in order to lower the endless belt 27 and to remove the pile with a preselected number of bags.

Said meter 39 is also connected to the braking system of the drums 7 and 9, in order to prevent the intermittent rotation of these drums whilst the belt 27 is not in the high position, namely throughout the whole period of removal of a pile of bags.

The release of the pile of bags by the vertical displacement of the belts 27 can be obtained by other relative movements and for example by rolling the pressing members 37 and 38 or by pivoting the endless belt 27 about the axis of the drum 30. In this case, the belt 33 can be placed at the same level as the belt 28, the belt 27 being driven by the belt 33 by the displacement of the connecting drum 32.

The devices according to the invention can also be used in order to prevent the stacked bags from adhering together on the side of their heat-welded edge. To this effect, (see Figure 1) a second pair of pressing members 40 and 41 is provided, which members are actuated so that, before the cutting operation, the first pressing member is lifted in 401 whereas after the cutting operation, the pressing member 41 is lifted in 411 to detach the bag on top of the pile along the welded edges, and then lowered on the top of the pile. Said pressing members 40 and 41 are preferably synchronously driven with the members 37 and 38 and they are adjustable in the direction of arrow F in order to permit the control of their position in relation to the length of the bags.

The said members 40 and 41, provided that they are connected with the endless belt 38, can comprise a further lifting device actuated when the belt 27 is lowered, in order to allow the removal of the pile of bags. Said lifting device of course will not be necessary if the pressing members 40 and 41 are connected with the belt 27 and, in such a case, in view of the short length of the said belt 27, the pressing members 40 and 37 can become one.

Claims

1. Method for stacking bags and in particular plastic bags consisting in heat-welding and cutting at regular intervals a tubular strip of plastic material which is moved intermittently, to form bags which are stacked in a pile on a support, wherein before the cutting operation, a first pressing means is applied on the pile of bags, and after the cutting operation, a second pressing means is moved from under the bag on top of the pile and applied to the top of the pile, the first pressing means is raised up, and a new length of bags is placed on the pile by causing it to pass between the first and second pressing means.

2. The method of claim 1 , wherein the second pressing means is moved from under the cut edge of the bag on top of the pile, in order to be applied on top of said pile along the cut edge of the bags.

3. The method of claim 1, wherein the second pressing means is moved from under the heatwelded edge of the bag on top of the pile, in order to be applied on top of said pile along the heatwelded edge of the bags.

4. The method of claim 1 , wherein the heatwelding tongs are closed simultaneously to the application of the first pressing means on to the pile.

5. Installation for carrying out the method of any one of the preceding claims, comprising a device intermittently supplying a tubular plastic strip, heat-welding tongs, and means for cutting the tubular strip, all of which are movable perpendicularly to the direction of displacement of the said strip, and a support receiving the stacked bags, said installation further comprising two pressing means to be applied alternatively on the top face of the pile, one of said means being constantly applied on the pile.

6. The installation of claim 5, wherein the support is constituted by a support which is movable towards an endless belt for the removal of the piles of bags, the support being controlled by a pre-selection meter which is in turn actuated by a movable heat-welding, cutting and pressing member.

7. The installation of claim 5, wherein the cutting member is constituted by a blade with two cutting edges, which moves alternatively across the tubular strip.

8. The installation of claim 6, wherein the blade with two cutting edges is secured to an endless belt stretched over at least two pulleys, the axes of which are connected to pinions meshing in together via gear means, one of said pinions being driven intermittently into rotation.

9. The installation of claim 5, wherein two pairs of first and second pressing means are provided one along the cut edge of the bags of the pile of bags, and the other, along the heat-welded edge.

10. A method for stacking bags substantially as hereinbefore described with reference to the accompanying drawings.

11. An installation for stacking bags, constructed and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.