HEAT SEALING APPARATUS

Abstract: A heat sealing apparatus comprises a roller (3) mounted for rotation about its longitudinal axis (A-A), a heat sealing means (14) mounted for rotation and in use defining a circular path for movement which is eccentric to the path of movement of the periphery of the roller (3), and means (2, 4) for moving a web (6) of plastics material. In use, the heat sealing means (14) is adapted for periodic movement interposed between the roller (3) and the web (6) and has no substantial relative velocity relative to either the web (6) or the roller (3) to thereby seal the web (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, where¬ by 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 therebetwee . 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 inven¬ tion, 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 OMPI 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 equidis¬ tant from the roller 3. An endless belt 43 extends around the rollers39, 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. I J UREATΓ OMPI 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 shaf 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 ith 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 -fυREAlr OMPI 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 circum¬ ferential 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 circum¬ ferential 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) OMPI -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 com- pleted 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 inclu¬ des 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, where¬ by 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. - ια - 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. - '

Inventors: KOCSIS JOSEPH LUDVIC, KOCSIS, JOSEPH, LUDVIC
Applicants: ORION ELECTRONIC EQUIP, ORION ELECTRONIC EQUIPMENT PTY. LTD.
Application year: 1982
Main classification: B29C27
IPC codes: B29C65, B31B19