GB2121349A

GB2121349A - Moulding apparatus for moulding thermoplastic sheet material

Info

Publication number: GB2121349A
Application number: GB08312405A
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: 1982-05-29
Filing date: 1983-05-06
Publication date: 1983-12-21
Also published as: GB8312405D0; FR2527508B3; FR2527508A1; DE3220416C2; DE3220416A1; GB2121349B

Abstract

Moulding apparatus for deformation of plates or film web portions of thermoplastic material comprises a moulding station, a charging station and transport means connecting these stations. In such an apparatus, it should be possible, through appropriate construction of clamping frames (6, 7) in the moulding station, to mould articles with a planar clamping edge without distortion so that this edge does not have to be removed, but is part of the finished article. As a result, material and an additional operating step can be saved. This is achieved by recessing a sharp knife band (26) into and around a lower one (6) of the clamping frame, while the upper clamping frame (7) is formed at the underside by a pipe (28) which conducted a heated medium. <IMAGE>

Description

SPECIFICATION Moulding apparatus for moulding thermoplastic sheet material The present invention relates to moulding apparatus for moulding thermoplastic sheet material, especially plates or film web portions of thermoplastic plastics material by means of differential pressure.

Apparatus of this kind-may comprise a charging station and a moulding station, which are connected by transport means. When film web portions are to be processed, a roll take-up and a transverse cutting knife are provided at the start of the transport means.

DE Utility Model 78 01 084 discloses apparatus of this type. Articles deep-drawn by this apparatus all have a clamping edge, which is the outer region of the thermoplastic plate clamped between two clamping frames.

This region is wavy, since it has a lower temperature than the deformed inner region.

Moreover, it distorts during deep-drawing, since it is drawn inwardly to different degrees (sliding between the clamping frames) so that the longitudinal edges of the edge portions are not straight.

It is therefore usual in practice to trim the edges of the moulded article, which is very expensive, as this edge has the original plate thickness and a trimming saw cut must subsequently be deburred at both sides. In the case of parts such as refrigerator internal containers with substantial stretching and plate thickness, the trimming effort is high as is the material waste, as the clamping edge must after all be added to the finished part.

In order to provide secured gripping of the clamped edges and to prevent them from sliding during stretching, it has been proposed in DE Utility Model 74 11 776 to lay a saw belt into the upper clamping frame. However, no sealing effect is then possible there, which is not required in the case of this apparatus for the reason that the saw belt is incorporated in the upper clamping frame. A sealing rubber, which achieves this effect, is provided in the lower clamping frame.

Such a saw belt on its own does not, however, solve the problem of the distortions which arise through the temperature differences between the edges and the plate centre.

There is accordingly a need for moulding apparatus which allows production of articles preferably having a narrow, planar and straight outer edge, at which no trimming is required, and wherein a secure sealing between a lower clamping frame and sheet material to be deformed is provided during, for example, vacuum deformation.

According to the present invention there is provided moulding apparatus for moulding thermoplastic sheet material, comprising an upper and a lower clamping frame in a moulding station of the apparatus for clamping of thermoplastic sheet material therebetween and means in the moulding station for heating and pressure moulding of the clamped sheet material, the lower clamping frame being provided with a cutting edge to cut into the clamped sheet material in the zone of clamping thereof and-the upper clamping frame being provided with means to heat the clamped sheet material in the clamping zone.

In a preferred embodiment, apparatus for selectable deformation of plates or film web portions of thermoplastic synthetic material through differential pressure comprises a moulding station with moulding table, a heater and two clamping frames, a charging station and transport means extending between moulding station and charging station. A smooth sharp cutting tape is let into the lower clamping frame and duct means, such as a pipe, which serves for the conduction of a tempered medium and which is connected with a heating circuit, is arranged in the upper clamping frame. Duct means, such as a pipe, for a tempered medium can also be provided at the lower clamping frame. Moreover, apart from the heating circuit, a cooling circuit can be provided and can be selectably connected through valves with the pipes.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic longitudinal view of moulding apparatus embodying the invention; Fig. 2 is a cross-section of the apparatus in the region of a moulding station thereof; Fig. 3 is a view, to an enlarged scale, of the region of a clamped edge of sheet material in the moulding station; and Fig. 4 is a diagram of a heating circuit and a cooling circuit for heating and cooling such sheet material.

Referring now to the drawings, there is shown moulding apparatus comprising a moulding station 1, a charging station 2 and, optionally, a roll take-up 3. The moulding station 1 includes a vertically movable table 4 for the reception of a deep-drawing mould 5, a fixed lower clamping frame 6, a movable upper clamping frame 7, a heater 8 and, optionally, a stretching aid 9.

When the apparatus operates with plates of thermoplastics material, a plate stack 10 is pushed into the charging station 2. A lifting device 11, consisting of the pneumatic piston-cylinder unit 12, a carrier 13 and vacuum suckers 14 fastened thereto, lifts the uppermost plate and leads it into transport equipment 15, which extends between the charging station 2 and the moulding station 1. The transport equipment is composed of guides 1 6 for transport chains 17 with entraining members 18 and a correspondingly shaped counter strip 19. The transport chains 17 are deflected by deflecting wheels 20 and 21 and extend parallelly each to the other so as to engage at two oppositely disposed edges of a plate 27 from the stack 10. A motor 24 serves for the intermittent drive of the transport equipment.

When the apparatus is to be operated with portions from a roll of film web, such a roll 22 is placed in the roll take-up 3 and the free end portion of the film web is introduced into the transport equipment 15. After a predetermined length of advance, the portion drawn from the web is severed by a transverse cutter 23 and then transported to the moulding station 1.

With reference to Fig. 3, the lower clamping frame 6 is provided with a groove 25 and an encircling cutting belt or band 26 is let into and fastened in this groove. The band cross-section illustrated in Fig. 3 is constant all the way round and the band has a sharp cutting edge at the side facing the plate 27. The cutting edge protrudes slightly above the upper edge of the clamping frame 6 and consequently cuts sealingly into the edge of the constituent material of the plate, especially when this is heated.

The upper movable clamping frame 7 at the contact area with the plate 27 consists of an encircling, thin-walled pipe 28, which conducts a flow of a heated medium. Through this mode of construction, a very rapid temperature transition from the medium to the plate edge is achieved.

A heating circuit for the pipe 28 is illustrated in Fig. 4. A heating device 40 heats a heattransferring medium (water, oil, emulsion) and causes it to be conducted through ducts 33 and 34 to the pipe 28 and back again. In a development, it is proposed to connect, parallelly to the heating circuit, a cooling circuit which consists of a cooling device 35 and ducts 36 and 37. In this case, valves 29 to 32 are incorporated into the ducts 33, 34, 36 and 37 so that heating or cooling of the pipe 28 can take place as desired.

The purpose of this is to bring the clamped edge of the plate 27 to an increased temperature in order to obtain the least distortion, i.e. the frame 6 is so heated during the heating of the plate 27 that the plate edge becomes warm as well. When the article has been deep-drawn and is cooling, the edge is also cooled down in that the cooling circuit is substituted for the heating circuit. In this manner, distortion of the film edge may be largely prevented, although good results can also be achieved without the cooling circuit. Further influencing of the plate 27 is possible by, for example, stopping the feed of warm medium during the cooling-down process of the article.

In addition, a pipe 41, which conducts flow(s) in analogous manner to the pipe 28, may be mounted at the lower clamping frame 6 to extend around this frame. In this manner, a more rapid heating/cooling of the plate edge is made possible.

The apparatus operates as described in the following: When the apparatus operates from the plate stack, the uppermost plate is raised by the lifting device 11 and introduced in the transport equipment 15. This brings it into the moulding station 1, where it is clamped between the clamping frames 6 and 7, heated by the heater 8 and, after the raising of the table 4, deformed with the help of vacuum by the deep-drawing mould 5.

The finished article 39 is cooled down, removed from the mould and transported out of the moulding station. The upper clamping frame 6 is heated at least during the heating of the plate 27 and, optionally also, cooled during the cdoling of the article 39.

When the apparatus operates from the film roll, this is divided by the transverse cutter 23 into blanks and these are processed in like manner.

Claims

1. Moulding apparatus for moulding thermoplastic sheet material, comprising an upper and a lower clamping frame in a moulding station of the apparatus for clamping of thermoplastic sheet material therebetween and means in the moulding station for heating and pressure moulding of the clamped sheet material, the lower clamping frame being provided with a cutting edge to cut into the clamped sheet material in the zone of clamping thereof and the upper clamping frame being provided with means to heat the clamped sheet material in the clamping zone.

2. Apparatus as claimed in claim 1, comprising transport means extending between a charging station and the moulding station for selectably transporting plates of plastics material or portions of a film web of plastics material.

3. Apparatus as claimed in either claim 1 or claim 2, wherein the cutting edge is provided by a cutting band recessed into the lower clamping frame.

4. Apparatus as claimed in any one of the preceding claims, the means to heat at the upper clamping frame comprising duct means for conducting a heated medium, the duct means being incorporated in circuit means for the medium.

5. Apparatus as claimed in any one of the preceding claims, wherein the lower clamping frame is provided with further means to heat the clamped sheet material in the clamping zone.

6. Apparatus as claimed in claim 5, the further means to heat comprising duct means for conducting a heated medium.

7. Apparatus as claimed in either claim 4 or claim 5, the or each duct means being incorporated in circuit means for a cooling medium and being controllable by valve means to conduct the cooling medium in place of the heated medium.

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