GB2030514A

GB2030514A - Plastics sheet material welding apparatus and method

Info

Publication number: GB2030514A
Application number: GB7830507A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-07-20
Filing date: 1978-07-20
Publication date: 1980-04-10
Also published as: GB2030514B

Abstract

In a welding method involving the use of directly applied heat to obtain the welding of plastics sheets (10), the sheets are moved continuously past means (26) for the longitudinal welding thereof and past welding tool (34) forming part of welding assembly (14) and the arranged so as to be reciprocable in both the direction of movement of the continuously moving sheets and transversely to these sheets so that intermittent transverse welding of the plastics sheet materials is obtained. <IMAGE>

Description

SPECIFICATION Plastics sheet material welding apparatus and method This invention relates to methods and apparatus for the welding of plastics sheet materials.

The applicant herein has undertaken a substantial amount of work in the development of a technique of welding together superimposed sheets of plastics material by the use of heat which is transferred to a welding surface applied to one of the sheets of plastics materials from a heat source, both the welding surface and the heat source being in heat transfer relationship with a finger or bar of substantial length which allows the heat source to be kept at a substantial distance from the sheet materials and shielded with respect thereto. The welding surface is heated to a temperature which is about or only a little above the melting point orflow point temperature of the plastics materials and the welding surface is maintained in contact with those materials for a sufficient time for sufficient heat to be transferred for welding to take place.

In accordance with the present invention there is provided a method of welding sheets of plastics materials comprising passing superimposed sheets thereof in a continuous movement along a path, applying a heated welding surface to one of said sheets, and moving said surface and sheets together along said path, removing the welding surface from the sheets and moving the welding surface in a direction opposed to the direction of movement of the sheets, and repeating the steps of movement of the welding surface during the continuous movement of the sheets so as to make successive welds.

The present invention is particularly applicable to transverse welding, that is the creation of welds which extend in a direction at right angles to the direction of movement of the superimposed sheets.

In a preferred embodiment of the invention in which the welding surface is utilised to produce transverse welds, the method includes the step of simultaneously providing a longitudinal weld in the sheets which longitudinal weld may or may not intersect the transverse weld.

Furthermore, in a further preferred aspect of the invention, the superimposed sheets have different transverse dimensions so that the longitudinal edges thereof are spaced in the transverse sense. In this way, it is possible to produce articles, such as bags, which have lips.

Furthermore, in accordance with preferred aspects of the invention, the superimposed sheets of plastics materials can be cut transversely during or after the transverse welding step so as to provide completed articles. Alternatively, the welded sheets can be wound up and transferred to alternative apparatus for the transverse cutting which may be required.

In accordance with the invention also, there is provided apparatus for the welding of plastics sheet materials comprising supply and takeup means and guide means for establishing a path for the continuous movement of two superimposed sheets of such materials, a heatable welding surface and means for selectively imparting movement to the welding surface both towards and away from said sheet movement path and both in and against the direction of movement of the said superimposed sheet along said movement path.

Preferably, the welding surface is arranged to extend transversely to the movement path.

Preferably also, the surface is a bar fixed to a support capable of executing some of said movements. In this case the welding surface may be an extreme surface of a welding bar which is hinged to the support, the support extending transversely of the movement of path, and the support itself performs the movement towards and away from the movement path while the hinged welding bar executes the movements in and against the direction of movement of the superimposed sheets. Alternatively, the welding surface may be a surface of a welding bar which extends transversely of the movement path and is mounted in the support for reciprocal movement with respect to said movement path. The support itself again is then able to execute the movements towards and away from the movement path.

In the case of the hinged bar, the heating means may be mounted on the support and in heat transfer relationship with the welding bar. In the case of the reciprocating welding bar, the heating means may be secured directly to the welding bar.

The apparatus may be arranged so that the heating means adopts a desired position with respecs to the path of movement of the sheet materials. In a preferred arrangement of the apparatus the heating means lies below the movement path. This enables the temperature within the apparatus to be reduced to a minimum vatue since heat transfer is more easily obtained when it is in an upward sense.

Preferably, the welding bar is arranged to lie substantially at right angles to the sheet being welded.

The heating means could be arranged either above or below the path of movement or the path of movement itself could be at an angle other than the horizontal and the heating means and the welding surface arranged accordingly.

In a preferred arrangement of the apparatus, a welding means for executing a longitudinal weld in the direction of movement of the sheet materials in incorporated.

It is also possible to incorporate a transverse cutting mechanism which may be located between two sets of feed rolls and the apparatus may be arranged so that a cut edge passes to the second set of feed rolls.

Two embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic and schematic side view of apparatus in accordance with a first embodiment of the invention.

Figure 2 is a side view to an enlarged scale and also schematic and diagrammatic of a part of the apparatus of Figure 1; Figure 3 is a diagrammatic and schematic side view of apparatus constructed in accordance with a second embodiment of the invention Figure 4 is a side view to an enlarged scale and schematically and diagrammatically represented of a part of the apparatus of Figure 3; and Figure 5 is a top plan view of the part of the apparatus of Figure 3 shown in Figure 4.

With reference to the embodiment of the apparatus shown in Figures 1 and 2, there is shown a framework 1 which provides supports 2, 3, for supply rolls 4, 5 of sheets of plastics materials which are guided by way of guide rolls 6 and pinch feed rolls 7 in superimposed relationship to a takeup roll 8 mounted on a support 9. In their passage from the guide roll 6 to the pinch rolls 7, the sheets 10 follow a substantially horizontal path of movement spaced slightly above a worktable 11.

Transverse welding means for the sheets 10 comprise a support 12 pivotally supported by one end thereof on a pivot means 13 secured to the table 11 and carrying a welding assembly 14 at its other end. A bolster 15 is secured to the table 11 below the path of movement of the sheets 10 in a position adjacent to the welding assembly 14. A return spring 16 acts between the worktable 11 and the support 12 and urges the support 12 and the associated welding assembly away from the table 11 about the pivot axis of the support 12.

A drive motor 17 is mounted on the frame with an associated reduction gear drive and has an output pulley 18. Drive belts 19 and 20 transfer drive respectively from the output pulley 18 to the takeup roll 8 (in this case via a slipping clutch) and to the pinch rolls 7. A further drive belt 21 is connected to a drive mechanism for the transverse welding assem buy which comprises a drive wheel 22 which acts as a crankshaft and carries a connecting rod 23 pivoted at a point 24 on the periphery of the wheel 22 and at a point 25 on the support 12 lying intermediate the pivot axis and the welding assembly.

Means for longitudinally welding the superimposed sheets 10 are schematically illustrated at 26.

Such means are described in co-pending British Patent Application No.4289/77.

In Figure 2 there is illustrated to an enlarged scale and schematically the welding assembly 14. A sub-support 30 is mounted by struts 31 onto the end of the main support 12. The sub-support 30 extends the whole width of the path of movement of the sheets 10 and is composed of a material of good heat transfer. An electrical resistance heating element 32 is secured to the upper surface of the sub-support 30 and in heat transfer relationship therewith. The sub-support 30 has a depending extension 33 whose lower edge is hingedly connected to a welding bar 34 which is substantially coextensive with the sub-support 30 and the heating element 32.The lower surface of the welding bar 34 is covered by a sheet 35 of silicone rubber material and the surface of this silicone rubber material which is coextensive with the lower edge surface of the welding bar 34 forms the welding surface which contacts the sheets. A stop member 36 is mounted across the end of the main support 12 and the welding bar 34 is resiliently held against the stop 36 by means of a spring 37 acting between the bar 34 and the flared ends 38 of screws passing through the welding bar 34 into the stop 36. Heat shielding means 39 extend coextensively with the sup-support 30 and are secured to the main support 12. The heat shielding means may have the form of aluminium foil or sheets.In operation of the apparatus described above in accordance with the method of the invention, superimposed sheets 10 are drawn from the supply rolls 4 and 5 over the guide rolls by means of the pinch rolls 7 and taken up on roll 8. The drive comes from drive motor 17 by way of the drive belts 19 and 20. Longitudinal welding, that is in the direction of movement of the sheets 10, occurs by operation of the longitudinal welding means 26. The drive belt 21 transfers drive to the wheel 22 and the connecting rod 23 therefore causes the support 12 to pivot about the pivot axis provided by the pivot means 31 to cause the welding assembly 14 to move towards and away from the path of movement of the sheets 10 and the bolster 15.This movement causes the surface of the silicone rubber sheet 35 which is coextensive with the lower edge of the welding bar 34 to contact the superimposed sheets 10 passing over the bolster 15. The contact of the sheets 10 with the surface of the silicone rubber is sufficiently forceful to cause the welding bar to be entrained by the sheets and to move with the sheets in the direction of movement thereof towards the pinch rollers 7. This movement takes place against the compressive action of the return spring 37. On continued rotation of the drive wheel 22 the connecting rod causes the support 12 to move upwardly with respect to the worktable 11 and this movement combined with the action of the return spring 16 causes the welding bar to lift away from the path of movement of the sheets 10 and the welding surface thereof to become separated from the sheets 10.The spring 37 now returns the welding bar to its rest position against the stop 36.

The electrical supply to the electrical resistance element 32 is controlled so that the temperature of the lower edge or welding surface of the welding bar 34 is kept only slightly above the flow point or melting point temperature of the sheets of plastics materials, or the lowest melting point temperature thereof where the materials are of different melting points. The duration of the welding operation is dependent upon the particular geometric configuration of the drive wheel 22, the connecting rod 23 and the support 12 and so on and the respective ratios imparted by the drive pulley 18 and the associated drive belts and pulleys. The pitch of the successive transverse welds is also dependent upon the geometric configuration and can readily be changed by adoption of a new such configuration.

Turning now to the construction shown in Figures 3, 4 and 5 of the accompanying drawings, there is shown, instead of a hinged construction as in Figures 1 and 2, a construction in which the welding bar is reciprocal in the end of the support.

The construction shown in Figures 3, 4 and 5 comprises a main frame 101 which has a worktable 102 and provides supports for supply rolls 103 and 104 of superimposed sheets 105 of plastics material as well as supports for a guide roll 106 and two sets 107, 108 of pinch rolls. The guide roll 106 and the pinch rolls 107, 108 determine a path of movement for the superimposed sheets 105 which extends generally parallel to the horizontal worktable 102.

A pivot support 109 for a support arm 110 for a welding assembly 111 is mounted about midway along the worktable 102 and provides a pivot axis 112 for the arm 110.

With reference to Figures 4 and 5 which are enlargements of the welding assembly 111 respectively in side view and top plan view, a welding bar 115 is secured to slide blocks 116 togetherwith an electric resistance heating element 117 and a support bar 118. The slide blocks 116 at each end of the supports 110 are mounted in guide slots 119 in the end members of a housing assembly 120 secured by bolts and nuts 121 to the support arm 110. Control springs respectively 122 and 123 act between the up-stream wall of the housing 120 and the blocks 116 and between the downstream wall of the housing 120 and the blocks 116. The spring 123 is stronger than the spring 122 so that the slide blocks 116 are urged towards their up-stream position in the slots 119.

In this embodiment of the invention the welding assembly 111 is located between two sets of pinch rolls. Below the path movement between the pinch rolls is a bolster 130 whose upper surface is generally coextensive with the path of movement of the superimposed sheet 105 and the nips of the two sets 107,108 of pinch rolls.

Drive for the lever arm 110 is provided by a connecting rod 131 having one end pivotally connected to the lever arm 110 and its other end carrying a pin which is located in the groove of a grooved cam 132. The apparatus is driven by a single motor 133 which has appropriate pulley and belt drive to the cam 132 and to the pinch rolls 107, 108.

In this embodiment of the apparatus a longitudinal welding assembly 134 is mounted up-stream of the transverse welding assembly 110.

The welding bar 115 in this embodiment is formed as a cutting and welding tool. Its lower surface is so constructed that on application to the welding sheet the tool serves to provide both a transverse weld and a transverse cut centrally of the weld and extending over the whole width of the sheets passing over the bolster 130. A receiving tray 140 is located below the outlet from the set 108 of pinch rolls.

In operation of the apparatus illustrated in Figures 3,4 and 5, an electrical supply is connected to the resistance heating element 117 and the temperature of the welding bar 115 is controlled so as to be sufficient for the satisfactory welding and cutting of the materials to be fed through the apparatus. The superimposed sheets 105 of plastics materials are fed through the pinch rolls 107 and across the bolster 130 into the pinch rolls 108 as well as through the longitudinal welding device 134. The superim posed sheets 105 have different transverse widths and are so guided that two longitudinal edges thereoof are in alignment and the welding apparatus 134 is provided to weld these two edges together.

The other edges of the sheets 105 are therefore transversely spaced with respect to each other to provide a lip formation to the finished articles.

The drive motor 133 is now set in operation to cause the two sets of pinch rolls to feed the superimposed sheets through the machine. The cam 132 is also set in motion which causes the support arm 110 to pivot about its axis 112 in timed relation to the movement of the feed materials through the apparatus. On every downward stroke of the support arm 110 the lower edge of the welding bar 115 presses the superimposed sheets against the bolster, which has a friction-reducing surface, and is entrained by the sheets 105 as they move across the bolster 130, the support blocks 116 sliding in the slots 119 against the action of the springs 123. The springs 122 serve to provide a supportforthe siideblocks during this movement.The welding bar both executes a weld transversely of the sheets and severs the sheets centrally of this transverse weld.

The duration of the contact with the sheets is timed to be sufficient to allow the welding and serverance to take place and the cam 132 then lifts the welding bar away from the bolster 130. The leading edge of the plastics sheet materials is then progressed over the bolster 130 by the pinch rolls 107 to be taken up again by the pinch rolls 108. The pinch rolls 108 may have a slightly faster speed than the pinch rolls 107 in order to produce a slight tension in the sheet materials. The bag, welded on three sides and having a lip, is deposited in the receiving tray 140.

The process in accordance with the invention is repeated with every revolution of the cam 132 in timed relationship to the movement of the sheets to the apparatus.

The longitudinal welding assemblies 26 and 134 utilised in the two illustrative embodiments incorporate a heated block upwardly from which extends a welding fingerthe upper tip of which serves as a welding surface. A resilient pad is mounted above the movement path and urges the superimposed sheets together and against the welding surface. The temperature of the welding surface is held at a value a little above the melting point temperature of the sheet materials.

Details of the two illustrative embodiments may be interchanged between them and the number of welding tools used can be related to the particular design or arrangement of articles to be formed from two superimposed sheets.

Claims

1. A method of welding sheets of plastics materials comprising passing superimposed sheets thereof in a continuous movement along a path, applying a heated welding surface to one of said sheets and pressing said sheets together, and moving said surface and sheets together along said path, removing the welding surface from the sheets and moving the welding surface in a direction opposed to the direction of movement of the sheets, and repeating the reciprocating movement of the welding surface during the continuous movement of the sheets so as to make successive welds.

2. A method according to claim 1 which is a method of transverse welding creating welds which extend in a direction at right angles to the direction of movement of the superimposed sheets.

3. A method according to claim 2 further including the step of simultaneously providing a longitudinal weld in the sheets which longitudinal weld may or may not interesect a transverse weld.

4. A method according to claim 2 or claim 3 in which the superimposed sheets have different transverse dimensions so that the longitudinal edges thereof are spaced in the transverse sense.

5. A method according to any one of claims 2 to 4 wherein the superimposed sheets of plastics material are cut transversely during or after the transverse welding step so as to provide completed articles.

6. A method according to any one of claims 2 to 4 wherein the welded sheets are wound up and transferred to alternative apparatus for any transverse cutting which may be required.

7. Apparatus for the welding of plastics sheet materials comprising supply and takeup means and guide means for establishing a path for the continuous movement of two superimposed sheets of such materials, a heatable welding surface and means for selectively imparting relative movement of the welding surface and said sheet movement path and movement of the welding surface both in and against the direction of movement of the said superimposed sheets along said movement path.

8. Apparatus according to claim 7, wherein the welding surface is arranged to extend transversely to the movement path.

9. Apparatus according to claim 7 or claim 8 wherein said welding surface is constituted by the free edge of a welding bar hingedly mounted on a support.

10. Apparatus according to claim 9 including heating means for heating said welding bar.

11. Apparatus according to claim 9 or claim 10 further including a bolster arranged on the other side of said path of movement from said welding surface.

12. Apparatus according to claim 7 or claim 8 wherein the surface is constituted by a bar mounted on to a support capable of executing some of said movements.

13. Apparatus according to claim 12 wherein the welding surface is an extreme surface of a welding bar which is hinged to the support, the support extending transversely of the movement of path, and the support itself performs a movements towards and away from the movement path while the hinged welding bar executes the movements in and against the direction of movement of the superimposed sheets.

14. Apparatus according to claim 12 wherein a surface of a welding bar which extends transversely of the movement path and is mounted in the support for reciprocal movement with respect to said movement path, and the support itself again is arranged to be able to execute the movement towards and away from the movement path.

15. Apparatus according to claim 13 wherein the heating means is mounted on the support and in heat transfer relationship with the welding bar.

16. Apparatus according to claim 14wherein heating means is secured directly to the welding bar.

17. Apparatus according to any one of claims 7 to 16 wherein heating means for the welding surface lies below the movement path.

18. A method of welding sheets of plastics materials as hereinbefore described with reference to the accompanying drawings.

19. Apparatus for welding sheets of plastics materials as hereinbefore described with reference to the accompanying drawings.