FR2474387A1 - Tools for making large thermo:formed mouldings - using residual mould cavity pressure to develop forming pressures against compression mould face - Google Patents

Abstract

Large thermoformed mouldings are made by clamping thermoplastic sheet (4) on to a mould cavity tool having a broad rim, heating the sheet to its thermoforming temp. and then partly evacuating the mould cavity prior to forming the sheet by applying a compression mould tool. The residual air vol. is set to be slightly greater than the residual cavity vol. after the introduction of the compression tool, so that compression of the residual air raises the cavity pressure sufficiently to apply the sheet closely to the compression tool face. Used esp. for making large mouldings, e.g. boat hulls, container panels, partitions, garden ponds, work benches, electroplating baths etc. Avoids need to use large compressors to achieve same effect by vacuum forming or by pneumatic bag consolidation where large moulding surface areas are involved. The consolidation pressure rises progressively as the compression tool enters the cavity.

Description

 The subject of the present invention is a process for the compression forming of plastic sheets of large dimensions and all thicknesses, and more particularly a process for thermoforming which is self-regulating continuously in a single operation, as well as the apparatus and products resulting therefrom. .

 Vacuum and / or pressure forming devices are known. These devices require booster compressors that are all the heavier, bulky and expensive, the larger the final product requested.

Compared with these known devices, the present invention proposes to describe a simple and efficient process, making it possible to produce thermoforming devices for parts of dimensions equal to or greater than the large dimensions reached so far, and this without additional compressors and in all reliability.

 According to the process, the pressure necessary for the shaping of the plastic sheet is obtained by the impression to be molded during its penetration inside a hollow enclosure, in which a defined volume of initial air is trapped in a controlled manner by said sheet.

 We will understand the method by describing an embodiment of an apparatus using said method; device given without limitation and shown schematically in the accompanying figures.

 Figure I shows the device in the high position.

 The impression to be molded and its crew sufficiently above the hollow tank, closed in a sealed manner by the plastic sheet to be molded; to allow the passage by and from a radian heating device.

Figure z shows the same elements in the lower position with the impression pressed into the tank and the molding completed.

Figure I highlights a team consisting of a footprint 5 secured to a support 6, hinged mounted above a frame 7 provided with a return device and in connection therewith. This crew is animated by a jack 10 carried on a gantry not shown. We also see a hollow tank I with a flat upper outer edge 2, forming an annular support, a plastic sheet 4 is placed above the edge 2 and kept tightly sealed using a frame, . The width of the edge 2 is greater than that of the frame 3; which allows the frame 7 of the crew to bear on the part of the edge 2 remaining free; at the time of the compression operation by lowering the crew, said frame 7 stops at the upper edge of the tank, while the imprint continues to descend and to penetrate inside the tank. The central opening of the frame 7 is adjusted so as to allow the passage of the impression with the minimum intermediate clearance. The return device of the support 6 solidAire of the imprint 5, is provided using a column mounting 8 and springs 9; said springs work in thrust. The ends of the columns 8 are flared, forming stop stops 12.

LU frame 7 E on the effect of preventing the material from bouncing and bursting along the periphery during the compression operation; thus avoiding a significant cause of @einit,
During penetration of the cavity into the tank, the air trapped in celic @@@ changes from an initial pressure PI to
a much larger presslon @ @ @@@ aqssurane, aqssurane the molding of the fenille, as illustrated in figure 2.

 The process of @@@ mage seion the invention therefore essentially consists of @ @@@ priming the sheet which one wishes to form, directly by the residual air trapped in the tank on defined vo, by means of the 'imprint itself, the compression being contionally cnoissant and proportional to the depth of the penetration stroke of the imprint coming into external support on said sheet.

Pxéelablement 5 the final sompression, one carries out the series
nte of operation
positioning of the sheet 4 above the tank 2;
sound of the latter in a sealed manner with respect to the edge 2
using the holding pad
- heating of the sheet to the forming temperature at
using a removable or movable radian device, worn on a charict or other known transfer means; that is maintained above the sheet until the appearance of a beginning of bending; the heating element is then removed.

- we decompress by means of a valve or an ana device
organ I- housed in the lateral opening B3 provided on the
tank; said valve being simply referenced, but
not shown, because c1 is a means known per se g up
that 'the sheet takes a hollow shape, of, depth
(residual) planned so that the volume of trapped air
remaining is then substantially equal to the volume of leempreinu
you necessarily by excess.

- all that remains then is to carry out the forming by
compression as just described.

 It is during this latter operation that the forming by gradually increasing controlled compression is carried out in full.

 To the aforementioned advantages one can add that of a saving of energy, and a saving of time.

The major interest of the process being to open a new way of obtaining large parts, it follows that the fields of application are numerous.

Here are some examples
- Hull and wings of a glider
- Decorative panels; false ceilings ; pre-molds for
barriers or bases in the building - Windsurfing for several people; (big
length) - Garden ponds; Laboratory tables - Containers for acids, and / or other chemicals or
industry - Building and Public Works Industries, Chimi
aeronautics, nautics, automobiles, etc, etc ...

Claims (1)

Claims 1 - Compression forming process for sheets of ma  large plastic parts, characterized by  what it is a) to trap an initial volume of air V inside of a tank I, of appropriate dimensions, using the sheet that you want to mold, pressing it against the outer and flat edge L, provided for this purpose by means of a  box 5; the width of edge 2 being greater than the width  geur of said frame 3  b) bringing said sheet to the forming temperature, b using a removable radian heating element, coming  place by transfer over the sheet during time required, then removed; the right temperature is reached when the sheet to be molded begins to bulge; at this moment and very quickly we decompress trapped air by opening an In valve and then closing it,  when the leaf reaches, such a hollow shape, that the volume V 'of trapped air is barely known  less than the volume of the impression to be molded  c) finally, this volume V ′ of air is compressed by its pressure of  PI start at final pressure P2, with P2 C PI; the pres final pressure P2 being significantly higher than the pressure  PI; this final compression operation decomposing  in two parts: first we bring frame 7 of the crew resting on the parts of the sheet are  located above the edge 2 area of the res tank  free tee; second, by continuing to lower  the crew, we make the footprint inside  of the tank; which has the effect of compressing quickly  and gradually the air whose pressure can ter until "n" fols its initial value, thus ensuring the  perfect final shaping of the sheet under the acticn of a uniform thrust exerted at the same time in all the directions and sew all nails 2-Forming apparatus using the method of claim  I, characterized on @e that it comprises: a tank I provided with a flat edge 2 and one; love 2nd tightening ~ designed to hold  the sheet to be molded in sealed support at its upper part re, said tank comprising a pressure relief device,  Preferably arranged laterally, opening and closing  instant re, and a mold carrier crew placed above  of the tank, actuated by jacks carried on a gantry  said cylinders having the effect of lowering the crew  vertically in the tank; said covering comprising  a support 6 secured to a footprint 5 mounted so articulated with respect to a movable frame 7 using tubes guides 8 and springs 9; the frame 7 being adjusted in fa  lesson in letting the imprint pass through its center; this frame  to prevent unwanted blunting with sheet breakdown at the time of the final operation this com1ression g and the springs 8 being intended to bring back the support 6 secured to the imprint 5 at their position, initial with respect to said frame 7; during the return crew at its high starting position. use of devices according to claim 2. large mold elements resulting from the - New industrial products and more particularly