GB2031326A

GB2031326A - Heating and transporting a web of film of thermoplastic synthetic material

Info

Publication number: GB2031326A
Application number: GB7926955A
Authority: GB
Original assignee: Adolf Illig Maschinenbau GmbH and Co KG
Current assignee: Adolf Illig Maschinenbau GmbH and Co KG
Priority date: 1978-09-27
Filing date: 1979-08-02
Publication date: 1980-04-23
Also published as: FR2437281A1; DE2841944B1; FR2437281B1; GB2031326B; DE2841944C2

Abstract

In a process for automatic thermal moulding of a thermoplastic synthetic material, a web of film of the synthetic material is transported by entraining members travelling along two guide rails (12) past a heating station to a moulding station. To counteract wrinkling of the web due to thermal expansion, the guide rails (12) are divergent during normal operation. When the web is cool, such as at the start of the process or during an operational interruption, the guide rails (12) are movable to be parallel so as not to expand the unheated web. The moving of the guide rails (12) is effected by means of a threaded spindle (14) carrying two threaded sleeves (19) to each of which is fixed a piston. A double-acting cylinder associated with each piston is connected to the respective guide rail (12) for moving it under the influence of pressurized fluid. <IMAGE>

Description

SPECIFICATION Method of heating and transporting a web of film of thermoplastic synthetic material and automatic thermal moulding apparatus for carrying out the method The present invention relates to a process in the heating and transporting of a web of film of thermoplastic synthetic material in an automatic thermal moulding device as well as the automatic thermal moulding apparatus for the performance of the process. Through this automatic thermal moulding device, a web of film, is drawn off from a roll, transported in steps, heated, and shaped into containers by means of differential pressure.

These containers can be stamped out of the web of film in the shaping station or in a succeeding station.

It is known from German Patent Application No. 14 54 994 to tension a web of film during heating and transporting in the region of the heating station by providing divergent guide rails.

Through this measure, the formation of waves caused by the thermal expansion of the film is counteracted. A strong expansion of the material arises most of all in the processing of film of polypropylene.

These divergent transport rails however entail problems, such as when one must switch off the machine while loaded with film web, be it because of operational disturbances, intervals, or the end of the roll. The tensioned, warm film then cools down since the heating in these cases is switched off.

As a result of cooling-down, the film web contracts, which is however only possible to a small degree since it was free of folds through tensioning in the warm state. Very high tensile stresses now arise in the web of the film and the tension transfers to its retaining or entraining members and to the guide rails for these retaining members. The consequence can be tearing of the web of film out of the clamping point, bending and damaging of parts of the transport system or bending of the retaining members.

The same tensile stresses arise when a new web of film is to be introduced into continuously diverging transport sections. The gripping of the edges of the film takes place with the film cold.

When the guide rails now move outwardly, this means a stretching of cold film, which entails similar disadvantages. A transport arrangement with parallel and diverging guide rails, as is illustrated in DT-OS 14 54 994, requires some effort and is therefore expensive concerning the drive of both the transport chains.

According to the present invention there is provided a process for heating and transporting a web of film of thermoplastic synthetic material in an automatic thermal moulding apparatus, the process comprising a starting operation comprising the steps of drawing the web of film off a roll, transporting the web between two spaced transport guide means to a heating zone, heating a length portion of the web and simultaneously or subsequently causing the transport guide means to move from a parallel position to be devergent thereby to tension the heated length portion; a normal procedure comprising the steps of transporting the web between the divergent transport guide means and reshaping the web by differential pressure downstream of the heating zone; and a shut-down operation comprising the step of detensioning the web by reversing the movement of the guide means prior to or during the cooling of the heated web.

An automatic thermal moulding apparatus for the performance of the above process comprises a roll holder, means to draw the web film off a roll, entraining means to transport the web between the transport guide means, means to heat the web in a heating zone, displacement means actuable in coordination with the starting operation and the shut-down operation to cause the transport guide means to move between a parallel and a divergent position thereof, and means to reshape the web by differential pressure.

Preferably the transport guide means comprises two guide rails to guide said means to entrain the web, and the displacement means comprises two threaded sleeves each arranged on a threaded spindle, two pistons each fixed to a respective one of the threaded sleeves, and two cylinder units each co-operating with a respective one of the pistons and each pivotally connected to a respective one of the guide rails.

An embodiment of the invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Fig. 1 shows an automatic thermal moulding device embodying the invention, Fig. 2 is a plan view onto guide rails of the device and, Fig. 3 is a section through a device for splaying of rails.

Referring now to the drawings, an automatic thermal moulding device comprises a base frame 1, a roll holder 2 for the reception of a film roll 3, a transport arrangement 4 for the intermittent transporting of a film web 5 drawn off the roll 3, a heater 6 and a moulding station 7. The moulding station 7 is also a stamping station, the residue of the film being reeled up. A moulding tool is incorporated in the moulding station 7 and the stroke motion of a lower table 10 with a lower part 8 of the moulding tool takes place through a cam disc 9. These are driven through a drive gear 11.

The transport arrangement 4 comprises guide rails 12, which extend longitudinally to both sides of the film web 5. Their spacing issettable by means of threaded spindles 13 and 14 and adaptable to the respective width of film.

Transport chains 15 within themselves known means for the retention of the web of film run in the guide rails 12. These can be pointed straps or clamping members of any suitable structure. The drive of the transport chains 15 takes place selectably from an individual drive 1 6 or from the drive 11 through rotation of the main shaft 17.

This carries the driving wheels 18 for the transport chains 15.

A threaded spindle 14 carries two threaded sleeves 19 and 20 of which one threaded sleeve displays a righthand thread and the other a lefthand thread each corresponding to a respective thread on the threaded spindle 14. A piston 20 is rigidly fastened on to each threaded sleeve 19. Extending around each piston 20 is a cylindrical pipe 21, which is closed by two covers 22 and 23 and forms a pneumatic double acting cylinder. Connected with the covers 22 and 23 is a bolt 24, which projects into a bore in a receiving socket 25. This socket is connected directly with guide rails 12. All covers 22 and 23 display bores 26 and 27 so that compressed air can be fed to the cylindrical pipe 21 on either side of the piston 20.

An adjustable and locatable abutment 28 is arranged on each threaded sleeve 19 and serves for the variation of the stroke from 0 up to a maximum value which is given by the constructional dimensions.

Illustrated in Figs. 2 and 3 is the case, in which the guide rails 12 extend parallel to one another.

In this setting, a new web of film is introduced into the transparent arrangement and guided up to below the heater 6. When the film web 5 has been heated to deformation temperature and undergone expansion, compressed air is passed into the bores 27. Thereby parts 21, 22, 23, 24, and 25 move and thereby guide rails 12 move outwardly in the direction shown by the arrows in Fig. 3. The film web 5 is tensioned and the folds are smoothed. In this manner, the guide rails 12 assume the position indicated by chaindotted lines in Fig. 2. The degree of the splaying can be adjusted by the abutment 28 between 0 and the maximum value.

Compressed air can also be fed to the bores 27 during the heating of the clamped-in section of film web to move the guide rails outwardly in accordance with the extension. It is possible to incorporate a pressure reducer 29 into the feed duct to the bores 27 so that the pressure in the cylinder and thereby the force, by which the film web 5 is retained under bias during heating, is adjustable.

Overlooking can thus be avoided and the tensioning takes place continuously as does the extension.

During the running of the machine, the guide rails 12 remain in the chain-dotted position. When the automatic thermal moulding device must be switched off for any reason, the heater moves rearwardly out of the region of the transport arrangement and the clamped-in film web 5 cools down.

Simultaneously with the switch off or gradually during the cooling down, compressed air is fed into the bores 26, the guide rails 12 thereby moving inwardly and again assuming a parallel position. Tensile stresses on film web 5, transport parts and entraining members of the transport chains 15 are avoided.

When the automatic thermal moulding device is restarted, the guide rails 12 remain in their position until heating-up occurs and then move outwardly before the deformation process starts or else compressed air is fed to the bores 27 at the start of the heating up.

The above process for the heating and transporting of a web of film has the advantages that the splaying of the transport rails can be utilized fully, whilst however, no disadvantages due to tensile forces on cooling down of the clamped-in web of film arise on operational interruptions.

Claims

1. A process for heating and transporting a web of film of thermoplastic synthetic material in an automatic thermal moulding apparatus, the process comprising: a starting operation comprising the steps of drawing the web of film off a roll, transportion the web between two spaced transport guide means to a heating zone, heating a length portion of the web and simultaneously or subsequently causing the transport guide means to move from a parallel position to be divergent thereby to tension the heated length portion; a normal procedure comprising the steps of transporting the web between the divergent transport guide means and reshaping the web by differential pressure downstream of the heating zone: and a shut-down operation comprising the step of detensioning the web by reversing the movement of the guide means prior to or during the cooling of the heated web.

2. A process as claimed in claim 1, wherein the normal procedure comprises the further step of stamping out shaped articles.

3. A process as claimed in either claim 1 or claim 2 and substantially as hereinbefore described with reference to the accompanying drawings.

4. An automatic thermal moulding apparatus for the performance of the process as claimed in claim 1 ,the apparatus comprising a roll holder, means to draw the web of film off a roll, entraining means to transport the web between the transport guide means, means to heat the web in a heating zone, displacement means actuable in coordination with the starting operation and the shut-down operation to cause the transport guide means to move between a parallel and a divergent position thereof and means to reshape the web by differential pressure.

5. An apparatus as claimed in claim 4, the transport guide means comprising two guide rails as guide said means to entrain the web, and the displacement means comprising two threaded sleeves each arranged on a threaded spindle two pistons each fixed to a respective one of the threaded sleeve, and two cylinder units each cooperating with a respective one of the pistons and each pivotally connected to a respective one of the guide rails.

6. Apparatus as claimed in claim 5 comprising displaceable abutments each mounted to a respective one of the threaded sleeves for steplessly setting the limiting of magnitude of the divergence.

7. An apparatus as claimed in either claim 5 or claim 6, comprising means to supply pressurised fluid selectively through inlets of the cylinder units, the supply means including a pressure reducer.

8. An automatic thermal moulding apparatus as claimed in any one of claims 4 to 7 and substantially as hereinbefore described with reference to the accompanying drawings.