GB2044168A

GB2044168A - Process for producing corrugated thermoplastics sheet

Info

Publication number: GB2044168A
Application number: GB8006709A
Authority: GB
Original assignee: DOLEPORT Ltd; Imperial Chemical Industries Ltd
Current assignee: DOLEPORT Ltd; Imperial Chemical Industries Ltd
Priority date: 1979-03-06
Filing date: 1980-02-28
Publication date: 1980-10-15
Also published as: BE898916Q; GB2044168B

Abstract

A process and apparatus is described for producing a corrugated thermoplastics sheet in which a flat sheet 1 successively heated by heaters 2,3,4, (5) in a first position along one or more parallel spaced bands across its width and moved linearly into a second position where the heated portions are deformed by male and female formers 6,7 to the required corrugated profile, the procedure being repeated until the whole of the required length of the sheet has been corrugated. <IMAGE>

Description

SPECIFICATION Process for producing corrugated thermoplastics sheet This invention relates to a process for producing a corrugated thermoplastics sheet.

In general, a corrugated thermoplastics sheet is produced by an extrusion process in which the thermoplatics material, in a plastic condition, is extruded through a suitably shaped die. Inevitably, because of the high cost of the die, the process is only suited to long production runs.

It is also known to produce a corrugated thermoplastics sheet from a flat thermoplatics sheet by heating the whole surface of the sheet until the sheet is sufficiently plastic to allow it to be moulded and moulding the sheet, for example by a vacuum forming process, to produce a plurality of corrugated profiles on the sheet. The nature of the moulding process used causes considerable thinning of the sheet within the corrugations and this inevitably weakens the sheet.

According to the present invention we provide a process for producing a corrugated thermoplastics sheet, the process comprising the following steps: (1) providing a flat thermoplastics sheet, (2) moving the sheet linearly into a first position at which a marginal portion of the sheet is selectively heated along one or more parallel spaced bands extending across the sheet until the sheet within the bands is rendered plastic, (3) moving the sheet linearly into a second position where (a) that portion of the sheet which had been selectively heated when the sheet was in the first position is deformed, between the male former and a female former, one or both of which has the shape of the required corrugated profile, at locations corresponding to the spaced bands across which the sheet had been rendered plastic and simultaneously (b) another portion of the sheet, adjacent to the portion which has been selectively heated, is selectively heated above one or more parallel, spaced bands extending across the sheet until the sheet within the bands is rendered plastic, (4) moving the sheet linearly into a third position where (a) that portion of the sheet which had been deformed when the sheet was in the second position is located on a male projection or female cavity having a similar shape to the required corrugated profile and simultaneously (b) that portion of the sheet which had been selectively heated when the sheet was in the second position is deformed, between a male former and a female former, one or both of which has the shape of the required corrugated profile, at locations corresponding to the spaced bands across which the sheet had been rendered plastic and simultaneously (c) another portion of the sheet, adjacent to the portion which, in the second position of the sheet, had been selectively heated, is selectively heated along one or more parallel, spaced bands extending across the sheet until the sheet within the bands is rendered plastic, (5) repeating step (4) until corrugations are provided along the whole length of the thermoplastics sheet except in a marginal portion thereof, said marginal portion then being selectively heated along one or more parallel spaced bands and then being moved linearly into a position corresponding to the aforesaid second position as in step (3) where the said marginal portion is deformed between a male former and a female former, one or both of which has the shape of the required corrugated profile, at# locations corresponding to the spaced bands across which the sheet has been rendered plastic.

In each of steps (2), (3), (4) and (5) of the process of the invention, the sheet may be selectively heated over one, two, three, four or more parallel, spaced bands extending across the sheet until the sheet within the bands is rendered plastic. Preferably the sheet is selectively heated over at least three, and more preferably at least four, such spaced bands.

Also we prefer that in steps (2), (3), (4) and (5) of the process, the sheet is heated from above preferably by moveable heaters which can be moved into contact with the sheet (for heating the sheet) or.out of contact with the sheet as required. The use of moveable heaters offers a convenient way of altering the heating cycle in relation to the deforming cycle.

We-also provide an apparatus for producing a corrugated thermoplastics sheet, the apparatus comprising in combination, and in line, (1) a heating unit adapted to selectively heat a flat thermoplastics sheet over one or more parallel bands extending across the sheet, (2) a unit for deforming the sheet at locations corresponding to the heated bands on the sheet, said unit consisting of a male former and a female former, one or both of which has the shape of the required corrugated profile, (3) a male projection orfemale cavity having the same shape as the required corrugated profile.

In preference in the apparatus of the invention, the heating unit is located above the thermoplastics sheet so that heat can be applied to the upper, rather than lower, surface of the sheet. We have found that by locating the heating unit in this position the thermoplastics sheet can be heated along welldefine bands.

In a preferred apparatus the heating unit is adapted to m-ove vertically in relation to the sheet, from a position where it is out of contact with the sheet to another position where it is in contact with the sheet.

The apparatus of the invention can, of course, be used to carry out the above described process.

Alternatively, however, the apparatus can be used in a modified two-stage process in which, in the first stage, one half of the sheet is provided with corrugations and then, after rotating the sheet through 1 80t in the plane of the sheet, in the second stage, the other half of the sheet is provided with corrugations.

One embodiment of the process and the apparatus of the invention will now be described with the aid of the accompanying drawings in which: Figures 1 to 3 illustrate, diagrammatically, steps 2 to 4 of one embodiment of the process of the invention, and Figure 4 illustrates the profile of a number of corrugations on the corrugated sheet produced in the process illustrated in Figures 1 to 3.

Figures 5 to 7 illustrate, diagrammatically, steps 2 to 4 of another embodiment of the process of the invention, and Figure 8 illustrates the profile of a number of corrugations on the corrugated sheet produced in the process in Figures 5 to 7.

In Figure 1 a marginal portion of a flat polyvinyl chloride sheet (1) has been moved into a first position at which it is selectively heated from above along three parallel spaced bands by three (2, 3, 4) of the four bar heaters (2, 3, 4, 5) until the sheet within the bands is rendered plastic. It should be noted that the leading edge of the sheet can be positioned at any location between heaters 4 and 5.

The sheet is now moved linearly into a second position depicted by Figure 2 where the sheet is deformed between a male former (6) having a trapezoidal cross-section and a matched female former (7). It will be noted that the sheet is deformed at three locations corresponding to the spaced bands over which the sheet had been rendered plastic when the sheet was in the first position.

Also in Figure 2 it will be seen that another portion of the sheet is being simultaneously heated from above along four parallel spaced bands by the four bar heaters.

After the sheet has been deformed it is moved into a third position depicted by Figure 3 where that portion of the sheet which has been deformed is located over a male projection 8 having a similar shape to the male former. The sheet is cooled in contact with the male projection.

Also in Figure 3 it will be seen that the portion of the sheet which had been selectively heated when the sheet was in the second position is now being deformed at four locations corresponding to the spaced bands on the sheet.

Furthermore in Figure 3 it will be seen that another portion of the sheet is being simultaneously heated from above along four parallel spaced bands by the bar heaters.

The process step illustrated in Figure 3 is repeated along the length of the sheet until the whole sheet is corrugated. However, it will be realised that eventually, once the last portion of the sheet has been heated and moved between the male and female formers, the heating step will not need to be carried out.

The embodiments of the process illustrated in Figures 5 to 7 follows closely the embodiment illustrated in Figures 1 to 3, the main difference being that when the sheet is moved into the first position it is selectively heated from above along four parallel spaced bands by the four bar heaters.

Consequently when the sheet is moved linearly into a second position it is capable of being deformed at four locations in contrast to the sheet which had been heated in the process step depicted in Figure 1 which was only capable of being deformed at three locations. Because of this the corrugated profile which is obtained (see Figure 8) is slightly different to the profile obtained (see Figure 4) by the process illustrated in Figures 1 to 3.

An important feature of the apparatus used in this invention is that the spacing of the bar heaters corresponds to the relevant dimensions of the male former. In the drawings, therefore, it will be seen that the pairs of bar heaters, 2 and 3, and 4 and 5 respectively, are spaced a distance 'x' apart corres ponding to the length of the sloping sides of the trapezoidal shaped male former. Also bar heaters 3 and 4 are spaced a distance 'y' apart corresponding to the length of the top side of the male former.

Furthermore it should be noted that the distance 'z' between bar heater 5 and the nearest edge of the male former, and between the adjacent edges of the male former and the male projection, corresponds to the spacing between the corrugations on the final sheet.

The process and apparatus of the invention may be used with any suitable thermoplastics sheet based on such materials as polyvinyl chloride, polymethyl methacrylate, polycarbonate and acrylo nitrile-butadiene-styrene.

Claims

1. A process for producing a corrugated thermo plastics sheet, the process comprising the following steps: (1) providing a flat thermoplastic sheet, (2) moving the sheet linearly into a first position at which a marginal portion of the sheet is selectively heated along one or more parallel spaced bands extending across the sheet until the sheet within the bands is rendered plastic, (3) moving the sheet linearly into a second position where (a) that portion of the sheet which had been selectively heated when the sheet was in the first position is deformed, between a male former and a female former, one or both of which has the shape of the required corrugated profile, at locations corresponding to the spaced bands across which the sheet had been rendered plastic and simultaneously (b) another portion of the sheet, adjacent to the portion which has been selectively heated, is selectively heated above one or more parallel, spaced bands extendings across the sheet until the sheet within the bands is rendered plastic, (4) moving the sheet linearly into a third position where (a) that portion of the sheet which had been deformed when the sheet was in the second position is located on a male projection or female cavity having a similar shape to the required corrugated profile and simultaneously (b) that portion of the sheet which had been selectively heated when the sheet was in the second position is deformed, between a male former and a female former, one or both of which has the shape of the required corrugated profile, at locations corresponding to the spaced bands across which the sheet had been rendered plastic and simultaneously (c) another portion of the sheet, adjacent to the portion which, in the second position of the sheet, had been selectively heated, is selectively heated along one or more parallel, spaced bands extending across the sheet until the sheet within the bands is rendered plastic.

(5) repeating step (4) until corrugations are provided along the whole length of the thermoplastics sheet except in a marginal portion thereof, said marginal portion then being selectively heated along one or more parallel spaced bands and then being moved linearly into a position corresponding to the aforesaid second position as in step (3) where the said marginal portion is deformed between a male former and a female former, one or both of which has the shape of the required corrugated profile, at locations corresponding to the spaced bands across which the sheet has been rendered plastic.

2. A process as claimed in claim 1, wherein, in each of steps (2), (3), (4) and (5), the sheet is selectively heated over at least three spaced bands.

3. A process as claimed in claim 2, wherein, in each of steps (2), (3), (4), and (5), the sheet is selectively heated over at least four spaced bands.

4. A process as claimed in any one of claims 1 to 3, wherein the sheet is heated from above by means of heaters which may be moved into contact with the sheet or out of contact therewith as required.

5. A process according to claim 1 substantially as hereinbefore particularly described, with reference to the accompanying drawings.

6. An apparatus for producing a corrugated thermoplastics sheet the apparatus comprising in combination, and in line, (1) a heating unit adapted to selectively heat a flat thermoplastics sheet over one or more parallel bands extending across the sheet, (2) a unit for deforming the sheet at locations corresponding to the heated bands on the sheet, said unit consisting of a male former and a female former, one or both of which has the shape of the required corrugated profile, (3) a male projection or female cavity having the same shape as the required corrugated profile.

7. An apparatus as claimed in claim 6, wherein the heating unit is located above the thermoplastics sheet.

8. An apparatus as claimed in claim 7, wherein the heating unit is adapted to move vertically in relation to the sheet, from a position where it is out of contact with the sheet to another position where it is in contact therewith.

9. An apparatus according to claim 6 substantial ly as hereinbefore particularly described, with reference to the accompanying drawings.

10. A corrugated thermoplastics sheet whenever produced by a process as claimed in any one of claims 1 to 5 or by means of an apparatus as claimed in any one of claims 6 to 9.