WO1983000116A1

WO1983000116A1 - Heat sealing apparatus

Info

Publication number: WO1983000116A1
Application number: PCT/AU1982/000105
Authority: WO
Inventors: Electronic Equipment Pty. Ltd. Orion
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-07-06
Filing date: 1982-07-06
Publication date: 1983-01-20
Anticipated expiration: 1984-01-06
Also published as: EP0082858A1

Abstract

Un dispositif de scellement thermique comprend un rouleau (3) monté de manière à pouvoir tourner autour de son axe longitudinal (A-A), un organe de scellement thermique (14) monté de manière rotative et définissant lors de l'utilisation un chemin circulaire de mouvement, excentrique par rapport au chemin de mouvement de la périphérie du rouleau (3), et des organes (2, 4) servant à déplacer une bande (6) d'un matériau plastique. Lors de l'utilisation, l'organe de scellement thermique (14) exécute un mouvement périodique interposé entre le rouleau (3) et la bande (6) et ne présente aucune vitesse relative sensible ni par rapport à la bande (6) ni par rapport au rouleau (3) de manière à sceller la bande (6).A thermal sealing device comprises a roller (3) mounted so as to be able to rotate about its longitudinal axis (AA), a thermal sealing member (14) mounted in a rotary manner and defining in use a circular path of movement , eccentric with respect to the path of movement of the periphery of the roller (3), and members (2, 4) serving to move a strip (6) of a plastic material. In use, the heat sealing member (14) performs a periodic movement interposed between the roller (3) and the strip (6) and exhibits no significant relative speed either with respect to the strip (6) or by relative to the roller (3) so as to seal the strip (6).

Description

"HEAT SEALING APPARATUS"

The present invention relates to a heat sealing apparatus for the sealing of polymeric materials. In particular, the present invention relates to a heat sealing apparatus for use in the manufacture of plastic bags.

In one known type of apparatus for forming bags from a web of tubular plastics material, the web is fed past a rotating drum and a heat sealing device is positioned adjacent the drum so that the web passes therebetween. The heat sealing device reciprocates between a first position and a second downstream position relative to the direction of movement of the web. The heat sealing device includes a sealing head which is controlled to contact the web when the speed of the heat sealing device is approximately the same as that of the web of plastics material.

There are two principal disadvantages with this type of heat sealing apparatus. First, the use of a heat sealing device which approaches the side of the tubular plastics material which is remote from the rotating drum causes an undersirable tensioning of the plastics material when the sealing head contacts the plastics material. Second, the throughput of the apparatus is dependent on the speed at which it is possible to reciprocate the heat sealing device. One object of the present invention is to provide an improved heat sealing apparatus for forming bags which alleviates the disadvantages of the known type of apparatus described in the preceding paragraph. According to the present invention there is provided a heat sealing apparatus comprising, a roller mounted for rotation about its longitudinal axis, a heat sealing means mounted for rotation and in use defining a circular path of movement which is eccentric to the path of movement of the periphery of the roller, and means for moving a web of plastics material, whereby in use said heat sealing means periodically moves interposed between the roller and the web and has no substantial relative velocity relative to either the web or the roller to thereby seal said web.

Preferably the heat sealing means comprises a plurality of lengths of wire, each length of wire being coupled, at each end, to a respective rotatable drum, and each length of wire being selectively operable to rotate about the circular path of movement to be interposed between the roller and the web.

Preferably the apparatus comprises adjustment means which are operable to change the orientation of each length of wire relative to the axis of the roller. Preferably the means for moving the web comprises the roller and a nip roller associated therewith.

Preferably the apparatus further comprises biasing means to bias the web of plastics material into contact with the roller. Preferably the biasing means comprises a continuous belt mounted to spaced rollers with the belt being spaced from the roller to define a gap therebetween.

One preferred embodiment of the present invention is now described with reference to the following drawings in which:

Figure 1 is a schematic view of a heat sealing apparatus formed in accordance with the present invention, Figure 2 is a perspective view of one side of a heat sealing assembly forming part of the heat sealing apparatus shown in Figure 1,

Figure 3 is a sectional view along the line X-X in Figure 2, and Figure 4 is a schematic view of the embodiment shown in Figures 2 and 3.

In Figure 1 is shown a heat sealing apparatus, which comprises a feed roller 2, a take-up roller 4 and a heat sealing assembly 8. A web 6, of plastics material is fed from the feed roller 2, through the heat sealing assembly 8 and is wound on the take-up roller 4. The heat sealing assembly 8 is arranged to extend generally transverse to the web, and periodically seals the web as the web moves through the assembly. The web is preferably a tube so that the sealed lines define bottoms for plastic bags.

Figures 2 and 3 illustrate one side of the heat sealing assembly 8 shown in Figure 1. The other side of the heat sealing assembly is identical to the side shown and has not been included in Figures 2 and 3 in order to simplify the description.

The heat sealing assembly 8 comprises a roller 3 which is supported by a hollow fixed shaft 5. A drive shaft 7 is located within the fixed shaft 5 and is coupled to a drive means (not shown) which rotates the roller 3 about the longitudinal axis A-A of the roller.

A gear 9 is mounted adjacent the end of the drive shaft 7 and meshes with a ring gear 11 which is mounted to the inner surface of the roller 3. A support member 13 is secured to the ring gear 11 and is mounted to the fixed shaft 5 via a centrally mounted bearing 17. A collar 15 is mounted on the fixed shaft 5 to restrict the axial movement of the support member 13 along the length of the fixed shaft 5.

The heat sealing assembly 8 further comprises a biasing means 10 which biases the web of plastics material 6 against the periphery of the roller 3. The biasing means 10 comprises three rollers 39, 45 and 47 which extend coaxially to and are spaced equidistant from the roller 3. An endless belt 43 extends around the rollers 39, 45 and 47. The web of plastics material 6 fits snuggly in the gap 12 between the belt 43 and the roller 3, and when the roller 3 rotates the web is moved through the gap 12.

In an alternative arrangement the biasing means comprises the roller 39 alone which acts as a nip roller and bears directly against the web of plastics material.

The heat sealing assembly 8 further comprises a heat sealing means 14 which includes two sealing wires 19 and 21 which are mounted for rotation about the periphery of roller 3. The path of movement 61 (see Figure 4) of the sealing wires as shown in

Figure 3 is eccentric to the periphery of the roller and passes through the gap 12 and between the roller 3 and the web of plastics material 6.

The sealing wires 19 and 21 are connected to sealing wire carriers 49 and 51 respectively which are pivotally mounted to respective annular support members 31 and 33. The support members 31 and 33 are connected to drums 23 and 25 respectively. The drum 23 is mounted on bearings 27 for rotation about the fixed shaft 5, and drum 25 is mounted on bearings 29 for rotation about the drum 23. Drums 23 and 25 are concentric and rotate about axis B-B which, as can be seen in Figure 4, is positioned between the axis A-A of the fixed shaft 5 and the axis C-C of the drive shaft 7.

As can best be seen in Figure 2, the sealing wire carriers 49 and 51 are substantially identical and each comprises a coil spring 53 which is mounted to a frame 55. The frame 55 includes a pin 57 which pivotally mounts the carrier member to the respective support member 31 and 33 so that the orientation of the sealing wire relative to the axis A-A of the roller 3 can be altered. The frame 55 also includes an adjustment means (not shown) which controls the extent to which the carrier member is able to pivot. The sealing wire associated with each carrier member is connected to the coil spring 53 which maintains the sealing wire in tension. A certain amount of slack sealing wire is provided wrapped around the coil spring to accommodate variations in the length of sealing wire required when the carrier member is pivoted to change the orientation of the sealing wire.

The heat sealing apparatus further comprises a drive means (not shown) which rotates the drive shaft 7 about the axis C-C and the drums 23 and 25 about the axis B-B.

An electric brake (not shown) constrains the drums 23 and 25 in a rest position 59 (see Figure 4) remote from the roller 3, and a clutch arrangement (not shown) on the drive means is operable to release the brake.

A pulse sensing device 49, diagrammatically shown in Figure 4, is mounted upstream of the roller 3 and controls the clutch arrangement. The pulse sensing device 49 periodically disengages the clutch, whereby one of the sealing wires 19 and 21 rotates about the path of movement 61. In use of the heat sealing apparatus the drive means rotates the drum 3 about its longitudinal axis A-A, and a web of plastics material is passed through the gap 12 between the roller 3 and the endless belt 43. In response to a signal from the pulse sensing device 49, the clutch arrangement releases the brake and the drum 23 is driven about the axis B-B. As a consequence the sealing wire 19 rotates along the path of movement 61 between the roller 3 and the web of plastics material 6. The sealing wire 21, at this stage is constrained in the rest position. It can be appreciated that the circumferential speed of the sealing wire 19 is slightly greater than the circumferential speed of the roller 3 since the diameter of the path of movement 61 of the sealing wire 19 is larger than the diameter of roller 3. However, when the sealing wire 49 moves into the gap 12 between the roller 3 and the endless belt 43 and contacts the outer periphery of roller 3 the friction between the outer periphery of the roller and the sealing wire causes the sealing wire to rotate at the same circumferential speed as the roller 3. Thus, as the sealing wire 19 passes through the gap 12 there is no relative velocity between the sealing wire and the roller 3. There is also no relative velocity between the sealing wire 19 and the web of plastics material 6. As the sealing wire 19 and the web of plastics material 39 move in unison the sealing wire heat welds together the two sides of the tube so as to form transverse join lines 50 (see Figure 1) which define the bottoms of bags. The rotational speed of roller 3 and the duration of the contact between the roller 3 and the web of plastics material 6 are selected so that the seal is completed before the web moves from the gap 12.

As the sealing wire 19 rotates around the path of movement 61 the sealing wire 21 is released for rotation by the clutch arrangement in response to a signal from the pulse sensing device. The sealing wire 21 rotates around the path of movement 61 and seals the web of plastics material 6 at a section on the web which is upstream from the section previously sealed by the sealing wire 19. During the time the sealing wire 21 rotates about the path of movement 61 the sealing wire 19 returns to the rest position 59.

The emlxdiment of the present invention has been described in relation to the use of two sealing wires. However, it should be appreciated that any number of sealing wires could be used depending on the particular application of the apparatus.

The present invention has been described in relation to the use of an endless belt 43 which biases the web of plastics material against a section of the outer periphery of roller 3. It should be appreciated that any other suitable alternate arrangements could be used. It should also be appreciated that the length of the gap defined between the endless belt and the roller 3 is variable depending on the requirement that the sealing of the tubular plastics material be completed whilst the web is in the gap.

The present invention has been described in relation to the heat sealing of plastics bags. It should be appreciated that the present invention is applicable to any application which requires the heat sealing of polymeric materials. For example, the apparatus could be used in connection with the heat sealing of polymeric laminates.

Modifications may be made to the invention without departing from the spirit and scope thereof which includes every novel feature and combination of novel features described herein.

Claims

THE CLAIMS : -

1. A heat sealing apparatus comprising, a roller mounted for rotation about its longitudinal axis, a heat sealing means mounted for rotation and in use defining a circular path of movement which is eccentric to the path of movement of the periphery of the roller, and means for moving a weB of plastics material, whereby in use said heat sealing means periodically moves interposed between the roller and the web and has no substantial relative velocity relative to either the web or the roller to thereby seal said web.

2. A heat sealing apparatus as claimed in claim 1, wherein the heat sealing means comprises a plurality of lengths of wire, each length of wire being coupled, at each end, to a respective rotatable drum, and each length of wire being selectively operable to rotate about the circular path of movement to be interposed between the roller and the web.

3. A heat sealing apparatus as claimed in claim 1 or claim 2, further comprising adjustment means which are operable to change the orientation of each length of wire relative to the axis of the roller.

4. A heat sealing apparatus as claimed in any one of the preceding claims, wherein the means for moving the web comprises the roller and a nip roller associated therewith.

5. A heat sealing apparatus as claimed in any one of the preceding claims, further comprises biasing means to bias the web of plastics material into contact with the roller.

6. A heat sealing means as claimed in claim 5, wherein the biasing means comprises a continuous belt mounted to spaced rollers with the belt being spaced from the roller to define a gap therebetween.