GB2101927A - Moulding apparatus - Google Patents

Abstract

Vacuum moulding apparatus includes a compressed air moulding tool for the deformation of a heated sheet of thermoplastics plastics material, the tool comprising a base platen (9) with a deep-drawing mould (8), a head platen (11) with a pressure bell (10), and a reducing frame (12). Locking pins (15) are connected with the base platen (9) and co-operable locking elements (16) with the head platen (11). Passages (17) for the pins (15) are provided in the frame (12) and are closable by pivotable flaps cooperating with seals (26). <IMAGE>

Description

SPECIFICATION Moulding apparatus The present invention relates to moulding apparatus, and has particular reference to a moulding tool, for the deformation of a heated thermoplastic plastics material film by means of compressed air, which can be incorporated in a vacuum moulding machine.

Vacuum moulding machines usually comprise two clamping frames for the clamping of a sheet of plastics material, a heater, a vertically movable moulding table for the reception of the deepdrawing mould, a vacuum pump, and an upper table or a bridge for carrying means to facilitate stretching of the sheet. The clamped sheet is heated and sucked by vacuum against the deep-drawing mould.

There are certain parts which, due to the nature of the constituent material, thickness of the material and/or the structure of the parts, are not deformable by vacuum or else are vacuum deformable only with difficulty, so that over pressure must be used. For this purpose, there are compressed air moulding machines with a pressure bell at the upper table and locking elements between the upper table and the moulding table. Such a machine must be constructed to be more rigid than a vacuum moulding machine, since high forces must be absorbed.

DE-OS 2 142997 shows equipment of this type. The locking equipment in this equipment belongs to the machine and is quite complicated and thereby expensive. As a result and because of the more difficult mode of construction, the entire machine is consequently more expensive than a machine which is provided only for vacuum deformation.

In practice, the predominant number of parts to be deep-drawn from plastics sheeting can be produced through vacuum deformation. A deep-drawing operatop will thus as a rule acquire vacuum moulding machines, namely mass-produced machines which are advantageous in cost and different deep-drawing moulds with appropriate reducing frames for adaption to the respective part size.

If a deep-drawing operatorwith vacuum moulding machines should receive an order for parts which would have to be produced by compressed air moulding, then problems arise. The purchase of a compressed air moulding machine would usually not be worthwhile and compressed air moudling is not possible with the vacuum moulding machine.

There is accordingly a need for a compressed air moulding tool which can be incorporated in a mass-produced vacuum moulding machine and allows use of air support of plastics sheeting during the heating, while for preference a commerically available type of locking equipment should be usable.

According to the present invention there is provided moulding apparatus comprising a base platen provided with a deep-drawing mould element, a head platen provided with means defining a pressure chamber, securing means arranged on the platens to secure the platens together, and a support frame disposed between the platens to support a sheet of heated thermoplastics plastics material for deformation to the shape of the mould element with the selectable use of underpressure and of overpressure in the chamber, the support frame being provided with passages for passage therethrough of the securing means and with openable closure means for closure of the passages.

In a preferred embodiment, the moulding tool is provided with the securing means which in the closed setting becomes effective between the actual deep-drawing mould element and the pressure chamber or the upper tool part. In order to provide a simple construction, it is proposed to provide in the frame, which belongs to the moulding tool, passages with movable flaps, through which a respective locking pin can be guided. The flaps serve for closing the passages during support of the plastics material sheet during a heating operation in conjunction with a blow box of the vacuum moulding machine.

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 section through the moulding station of a vacuum mould machine according to the said embodiment; Figure 2 is a cross-secton of the machine on the line B-B of Figure 1; and Figure 3 is a cross-section on the line A-A of Figure 2.

Referring now to the drawings, there is shown a vacuum moulding machine for the receiption of a moulding tool, the machine comprising a frame 1, a blow box 2, a moulding table 3 with a drive 4 for the vertical movement thereof, an upper heater 5, possibley a lower heater 6, a vertically movable clamping frame 18 and a bridge 7 with drive 27 and guides 28. The upper and lower heater can be moved rearwardly out of the moulding station.

A compressed air moulding tool is incorporated into the vacuum moulding machine and comprises a deep-drawing mould 8 mounted on a base plate 9, a pressure bell 10 mounted at a head plate 11 and an adapted reducing frame 12 with a support 13 and a sealing rubber 14. For production, the base plate 9 is fastened on the moulding table 3, and the head plate 11 with the bridge 7 and the reducing frame 12 on the blow box 2.

In order to absorb the forces arising due to the pressure build-up during moulding, upwardly projecting locking pins 15 are fastened in the base plate 9 and project into locking units 16 when the moulding tool is closed. The locking is, for preference, effected hydraulically in a known manner. Such locking units 16 are commercially available for purchase and have diverse principles of operation.

In order that the locking pins 15 can be introduced into the locking units 16, passages 17 are provided in the frame 12. In order that the plate 19 can be suppoted by air during the heating of a clamped plastics sheet 19 so that it does not sag, each passages 17 is closed off by a flap 20. The flaps 20 are constructed to be pivotable and a piston-cylinder unit 21 can be so mounted that it can move two such flaps. A seal 26 is arranged between each flap 20 and the frame 12.

An example of the arrangement of the passage 17 with the flaps 20 and the piston-cylinder units 21 is shown in Figure 2. The clamping frame 18 of the vacuum moulding machine consists of a locally fixed cross-stay 22, a longitudinal stay 23 settable in its spacing, and stays 24 which can be adapted in terms of format. The clamping frame 18 can be displaced in height by lifting equipment (not shown).

In use, a sheet 19 of thermoplastic plastics material is laid onto the frame 12, the clamping frame 18 is moved downwardly and the sheet 19 is clamped in place as a result. The heaters 5 and 6 advance and heat the sheet 19 to deformation temperture and then move back. The pressure bell 10 is lowered and the flaps 20 are opened. A preliminary suction of the plate 19 through application of vacuum at a connection 25 is possible. The deep-drawing mould 8 is then moved upwardly and a mechanical preliminary stretching of the sheet 19, or movement into the preliminarily vacuum-deformed bubble, takes place.

After the closing and locking of the deep-drawing mould 8 and pressure bell 10, compressed air is supplied through the connection 25 and the sheet 19 is brought by this means into overall contact with the mould 8. Subsequently, the compressed air is allowed to escape, the locking is released and the mould table 3 and bridge 11 are moved apart. After opening of the clamping frame 18, the finished part can be removed and a new sheet 19 be laid in. Before the new heating of the new sheet 19, the flaps 20 are closed.

In modification of the illustrated embodiment, it is of course possible to mount the locking pins 15 at the head plate 11 and the locking elements 16 at the base plate 9.

Claims (6)

1. Moulding apparatus comprising a base platen provided with a deep-drawing mould element, a head platen provided with means defining a pressure chamber, securing means arranged on the platens to secure the platens together, and a support frame disposed between the platens to support a sheet of heated thermoplastics plastics material for deformation to the shape of the mould element with the selectable use of underpressure and of overpressure in the chamber, the support frame being provided with passages for passage therethrough of the securing means and with openable closure means for closure of the passages.

2. Apparatus as claimed in claim 1, the securing means comprising locking pins connected to the base platen and co-operable locking elements con nected to the heat platen.

3. Apparatus as claimed in either claim 1 or claim 2, the closure means comprising pivotable flaps.

4. Apparatus as claimed in claim 3, comprising piston-cylinder means operable to pivot the flaps.

5. Apparatus as claimed in claim 4, wherein a plurality of pairs of the flaps are provided for closure of the passages, the piston-cylinder means comprising a respective piston-cylinder unit operatively connected to the flaps of each pair.

6. Moulding apparatus substantially as hereinbe.

fore described with reference to the accompanying drawings.