GB2123336A

GB2123336A - Clamping of thermoplastic sheets in moulding apparatus

Info

Publication number: GB2123336A
Application number: GB08318377A
Authority: GB
Inventors: Gunther Kiefer
Original assignee: Adolf Illig Maschinenbau GmbH and Co KG
Current assignee: Adolf Illig Maschinenbau GmbH and Co KG
Priority date: 1982-07-08
Filing date: 1983-07-07
Publication date: 1984-02-01
Also published as: DE3225533A1; GB2123336B; DE3225533C2; FR2529825A1; FR2529825B3; GB8318377D0

Abstract

Moulding apparatus, for the deforming of sheets of thermoplastic material, comprises a moulding station, a combined heating and charging station, and a transport device for transport of the sheets between the stations. The sheet side edges which are transverse to the transport direction are clamped in the heating station. The clamping is effected by clamping strips (24, 26) the strips extending transversely to the transport direction and being fastened to a frame of the apparatus or to the guides of the transport device. One clamping strip (26) is pivotable between open and closed positions. <IMAGE>

Description

SPECIFICATION Clamping of thermoplastic sheets in moulding apparatus The present invention relates to moulding apparatus and has particular reference to the clamping of thermoplastic sheets in such apparatus.

DE-GM 8005873 discloses moulding apparatus in which a heater is incorporated in a moulding station and brings a thermoplastic plastics sheet to deformation temperature. Additionally, a preliminary heater, which heats the sheet to a temperature below the deformation temperature, is incorporated in the charging station in order to reduce the cycle time.

Heating in the charging station for deformation temperature is not possible, since the sheet contracts at its two unclamped side edges.

Apparatus is described in DE-GM 7301 715 in which heating of the sheets to deformation temperaturn takes place in a heating station in front of the moulding station. For the avoidance of lateral contraction, the sheet is clamped all round, for which purpose a frame is mounted on the heater at the underside of the sheet and the heater is displaceable in height.

It is disadvantageous in this construction that the frame on the heater as well as a counter-frame are format parts and must be changed to another format on resetting of the apparatus. This is timeconsuming and expensive. Afurther disadvantage is that a relatively large gap between the heater and the sheet must be bridged over by the frame, as the infrared radiant heaters employed usually have to be spaced from the sheet by a certain amount in order that uniform heating can take place. A heater, which is to be moved in two directions, becomes heavy due to the large frame.

Problems also arise from heating of the lower frame due to its connection with the heater and thereby undesired heating of the sheet edge occurs.

There is therefore a need for apparatus in which preferably the final heating of a sheet can take place externally of the moulding station substantially without heating up of the sheet edges, without format parts being needed and without the heating being made unnecessarily difficult by clamping equipment. The mode of construction of the clamping equipment should make it possible for a heating station and a charging station to be combined into one station so that the advantages of a compact mode of construction can be maintained.

According to the present invention there is provided moulding apparatus comprising heating means for heating sheets of thermoplastic plastics material in a heating station, moulding means for differential pressure moulding of the heated sheets in a moulding station, transport means for transporting the heated sheets from the heating station to the moulding station, and elongate clamping elements extending transversely to the direction of transport between the stations and arranged in the region of the heating station to clamp each sheet at edge portions thereof during heating by the heating means, at least one of the clamping elements being movable.

In a preferred embodiment, the apparatus comprises a moulding station, a charging station, a heating station, a transport device connecting the individual stations, as well as a sheet feed which can take the sheets from a stack and introduce them into the transporting device and/or a roll take-up with transverse cutting equipment for cutting a web from a roll into individual sheets. Clamping strips, which extend transversely to the transport direction, are connected with a frame of the apparatus or with the transport device and are arranged in the region of the heating station or the combined heating and charging station, the rim of the sheet being clamped in between the strips during the heating and at least one clamping strip being constructed to be pivotable.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Figure 1 is a front elevation of moulding apparatus embodying the invention; Figure 2 is a longitudinal sectional view of a charging and heating station of the apparatus; and Figure 3 is a cross-section of the charging and heating station.

Referring now to the drawings, there is shown in Figure 1 moulding apparatus comprising a moulding station 1, a heating and charging station 2 and, optionally also, a roll take-up 3. The moulding station 1 is constructed in accordance with the general principles of a sheet moulding machine and includes a vertically movable table 4 for a mould 5, a fixed clamping frame 6, a movable clamping frame 7 and, optionally also, a stretching aid 8. Arranged in the heating and charging station 2 is a lifting device 9, which comprises a drive 10, transverse strips 11 and suckers 12. The suckers 12 can be temporarily brought into communication with a vacuum source.

The respective uppermost sheet of a stack 13 can be lifted off by the device 9.

Also provided in the heating and charging station 2 is at least one horizontally displaceable heater 14.

A second heater can be provided if needed.

Extending between the station 2 and the station 1 is a cyclically operable transport device 15 consisting of two transport chains 17, which engage oppositely disposed side edges of a sheet 16 and which run in guides 18, the chains being driven by a motor 19.

Mounted on the underside of the guides 18 in the region of the station 2 are tilting strips 20, which can be pivoted by drives (not shown) so that a sheet can be lifted into place. Rigid counter strips 21 are provided in place of the tilting strips 20 in the region of the moulding station 1, the strips 21 being secured by screws.

In order to also clamp in the sheet 16, which is clamped in the station 2, at its transversely extending side edges during the heating so as to avoid constriction of these edges, clamping equipment is provided in this station and is, as illustrated, connected with a frame 22 of the station 2 or to the guides 18. The clamping equipment comprises two carriers 23, which extend transversely to the trans port direction and to which upper clamping strips 24 are rigidly fastened. At the lower end, the strips 24 preferably carry cooling tubes 25, which are connected to a source of a cooling medium. The tubes 25 extend down as far as the plane of the sheet.

Disposed opposite the strips 24 are clamping strips 26, which are each arranged to be pivotable about a rotational centre 27. Each rotatable centre 27 is formed by a shaft 28 retained in bearings 29 at a respective one of the carriers 23. Mounted on each shaft 28 is a toothed wheel 30, which meshes with a respective toothed rack 31 driven by a respective piston-cylinder unit 32. The units 32 themselves are connected with the carriers 23. In the pivoted-up state, shown in chain-dotted lines in Figure 2, the clamping strips 26 are disposed above the plane of the sheet 16 so that the transport of the sheet is not obstructed.

Different sheet sizes can be accommodated by the apparatus after appropriate re-equipment. An adaptation in transverse direction is effected through movement of the guides 18 towards or away from each other. In order to avoid the need to adapt the clamping strips 24 and 26 during each width resetting, which would of course be possible, these strips are kept shorter than a certain sheet width, since this is adequate in most cases. Thus, with reference to spacing A of each transport chain and guide from the adjacent ends of the clamping strips, as shown in Figure 3, it is always possible to move the guides 18 together by the amount 2 x A.

In order to make possible an adaptation to the sheet length in the transport direction, the carriers 23 are so connected with the frame 22 that they can be displaced in the transport direction. Clamping devices or elongate holes are possible means of enabling such displacement. It is, of course, also possible to fasten the carriers 23 in suitable manner on the guides 18 so that a lateral displacement of the guides 18 is possible after loosening of clamping screws.

When very large width ranges are to be covered by the apparatus and the transport device as a result must be transversely resettable over a wide range, two or three interchangeable sets of clamping strips 24 and 26 can be provided or, if needed, wider clamping strips can be adapted to the version for the least sheet width.

In the illustrated embodiment, the heating and charging stations are combined, which offers advantages with respect to space and costs. A separate charging station can, of course, be arranged upstream of a separate heating station, which may provide advantages in connection with addition of exchange magazines for the sheet stacks.

When processing from a roll is selectably possible with the apparatus, which is particularly advantageous for thinner sheets, then a film web 33 is drawn from a roll 34 on the take-up 3 and is cut by a transverse cutter 35 into sheets, which are transported and processed in like manner to the initially separate sheets in the stack 13.

In use of the apparatus, either a sheet 16 is lifted from the stack 13 by the device 9 and introduced into the transport device 15, or a portion of the web 33 is drawn from the roll 34, cut to provide a sheet and then transported into the heating and charging station 2. The two clamping strips 26 pivot closed and the sheet is clamped transversely between the strips 24 and 26 and longitudinally in the transport device 15. The heater 14 moves over the sheet and heats this to deformation temperature.

The sheet is then transported into the moulding station 1, clamped in place therein, and deformed in known manner by means of the mould 5 and through differential pressure, vacuum or compressed air. The next sheet 16 is heated during the deformation so that this can be transported into the station 1 and deformed without waiting time after the removal of the finished moulded part 36 from the mould.

Claims

1. Moulding apparatus comprising heating means for heating sheets of thermoplastic plastics material in a heating station, moulding means for differential pressure moulding of the heated sheets in a moulding station, transport means for transporting the heated sheets from the heating station to the moulding station, and elongate clamping elements extending transversely to the direction of transport between the stations and arranged in the region of the heating station to clamp each sheet at edge portions thereof during heating by the heating means, at least one of the clamping elements being movable.

2. Apparatus as claimed in claim 1, comprising feed means for feeding sheets from a stack to the transport means.

3. Apparatus as claimed in either claim 1 or claim 2, comprising feed means for feeding a sheet material web from a roll to the transport means and transverse cutting means for cutting the fed web into sheets.

4. Apparatus as claimed in any one of the preceding claims, wherein the clamping elements are connected to a frame of the apparatus.

5. Apparatus as claimed in any one of claims 1 to 3, wherein the clamping elements are connected to guide means of the transport means.

6. Apparatus as claimed in any one of the preceding claims, wherein a respective pair of the clamping elements is provided for clamping each of two opposite edge portions of each sheet, the clamping elements of each pair being mounted on a single mounting member and one of the clamping elements of each pair being mounted to be pivotable between a closed position in which it is co-operable with the respective other clamping member to clamp the sheet and an open position at which it is disposed entirely above a plane in which such sheet is disposed in the heating station.

7. Apparatus as claimed in any one of the preceding claims, wherein one of the clamping# elements is provided with cooling means.

8. Apparatus as claimed in any one of the preceding claims, wherein the length of the clamping elements is smaller than a predetermined length of such sheet edge portions.

9. Apparatus as claimed in any one of the preceding claims, wherein the or each pivotable clamping element is connected to a shaft which is provided with a toothed wheel drivably meshing with a rack.

10. Moulding apparatus substantially as hereinbefore described with reference to the accompanying drawings.