CA1067386A - Method and apparatus for fabricating flat objects - Google Patents

Abstract

TITLE OF THE INVENTION
METHOD AND APPARATUS FOR FABRICATING

ABSTRACT OF THE DISCLOSURE

The invention concerns a method and a press arrangement in which a panel is compressed between two heated plates of a press, and in which a vacuum is created between the two plates of the press during compression, one of the plates being flexible along one direction, wherein the curved flexible plate is applied to the panel to be pressed so that it contacts the panel on an elongated surface near a generatrix, the air pressure in the press around the panel is gradually lowered while the flexible plate is progressively developed to shape it into planar form, pressure is exerted on more and more surface starting from the surface of initial pressure so as to exert pressure over the entire surface of the flexible plate in order to shape it into planar form when the desired low pressure is attained.

Description

~L067386 BACKGROUND OF_'rHE INVl~N~ION

Field of the Invention ,~ . ' ---' . ''' 'rhe invention concerns a method and arrangement for control of a press for fabricating flat objects such as laminated panels having at least one surface layer of thermoplastic or thermosetting material. It is aimed more especially at presses usable for laminates, the top and/or bottom layer of which is finished, ï. e. obtained by transformation of a liquid by polymeri-zation. ~his procedure is different from and more difficult and delicate to carry out than the simple gluing together of several thicknesses of material impregnated with binder, glue or plastic resin.
.`,, '. : :' Description of the Prior Art , . . _ - -.
. ~ Methods involving thermpplastic materials or ones thermo-settable from the liquid state are known. In such methods, the object is compressed between the two plates of a heated press, one of the plates being fixed and the other, usually the upper one, ; 15 being movable vertically with respect to the first.
In such methods, there is great diEficulty in removing `~! air trapped between the laminations during pres.sing. Various , ~ methods have been proposed for doing this.

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.. . .. . .: . ' In one of ~m,the press has sea.ling fla.nges around its periphery.
. When the plates approach one a.nother, the space between them becomes sealed off and the air is pumped out to produce as low . a pressure as possible so a.s to induce the release from the sur-. face of the softened plastic material the air trapped in it at . atmospheric pressure. l~hese methods have not proved satis-; factory since the vacuum produced inside the press causes too A rapi d a forceful clamping of the plates aga.inst each-}~which . impedes the esca.pe of air.
In another known method, the press has one rigid plate while the other is flexible in one dimension. The flexible plate, which rnay be of slightly supple sheet steel, possibly reinforced in one direction by pa.rallel' straight rigid elements, is brought into contact, while curved, along a generatrix, preferably centra.l. The flexible plate . . Unbent . ~ 15 is then progressively~to yield a planar shapesoas to increase .i ~ the contact surface. In spite of the magnitude of the pressures used, these methods have not been satisfactory. Examination of the surface :
s~ of the products obtained reveals numerous a.ir bubbles in the mass of the plastic. Not only is the surface not smooth, which causes it to attra. t dirt a makes it more difficult to clean, but the struotural : _3_ '''''' :' . .
, solidity of the product is affected.
Also, the high pr~sures used only permit the realization of compact high density panels. With these methods and arrangements it is nct possible to produce an insulating panel with a porous layer.
It has also been attempted in the past to combine two methods, i. e. to use a press, one plate of which is flexible, the two plates having a sealing joint around their periphery, with means being provided to evacuate the space between the plates when the plates are sufficiently close to one another to make the seal effective.
Desirable results have not been possible thus far because if the vacuum is high enough, the flexible plate flattens out against the . laminate and impedes the escape of occluded alr.The means for forcing the flexible plate, which in practice is always the upper one, against the object to be fabricated consist of a multitude of jacks, hydraulic or pneumatic, of which only certain ones acting along the line of initial contact of the plate with the object, generally along an axis of symmetry of the plate, assure the reflexing of the plate and support it in the raised position of the press.

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...,, , . .. , ~6~738~i It has been found in operation that it is difficult to perfectly synchronize the set of lifting jacks. It has been found further that the upper plate can assume positions skewed with respect to its normal orientation so that binding of some jacks can occur with the result that their connections to the upper plate can break.
The procedures utilizing means for producing a vacuum also have the serions drawback of the difficulty of opening the press. When the vacuum inside the press is broken, the air can~
not penetrate between the plates which remain tightly clarnped together and it takes enormous forces to pull them apart. More-over, darnage to the laminated product can result. In addition, the synchronization of the set of jacks during the refle~ing displacement is more difficult the larger the forces with the result that there frequently occurs a binding of the jacks, accompanied by the drawbacks indicated above.

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.: It is therefore a goal of the present invention to offer a method and an arrangement which permit making low density panels under moderate pressures in just one operation without ; 5 leaving air trapped in the surface layers of the panels. -.~ ~ It is another goal of the present invention to remedy the .- . drawbacks noted above and to offer a method and an arrangement permitting easy removal of the product from the press and reflex-. ~ ~ ing of the upper plate without the risk of binding.
~.................... The foregoing and other objects are attained in accord-10 ance with one aspect of the present invention, through the provision : of a method and a press arrangement in which a panel is com-pressed between two heated plates of a press, and in which a vacuum is created between the two plates of the press during compression, one of the plates being flexible along one direction, ' ~ 15 wherein the curved flexible plate is applied to the panel to be pressed so that it contacts the pa.nel on an elongated surfa.ce near a generatrix, the .air pressure In the press around the panel is gradually lowered while the flexible plate is progressively developed to shape it into planar form, pressure is exerted on more and mor ~rface starting from the suriace oi inltial . .
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~0~i7386 pressure so as to exert pressure over the entire surface of the flexible plate in order to shape it into planar form when the desired low pressure is attained.
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BRIEF DESCRIPTION OF 'IHE DRAWINGS

Various objects, features and attendant advantages of the present invention will be more fully appreciated as the same ~ becomes better understood from the following detailed descrip-.;, .
tion of the present invention when considered in connection with ; the accompanying drawings, in which:
`~ Figure 1 is a schematic view in perspective of a press ; 10 equipped with a control arrangement according to the inventlon, Figure Z is a partial transverse sectlon of another f` ~ ~ ~ embodiment of the invention, and ~
Figure 3 is a schematic viewin perspective of the stabillz-atlon system of the upper plate.

~ DETAILED DESCRIPTION OF TEIE PREFERRED EM~ODIMENTS

15~ ~ ~ E~eferring now to the drawings, wherein like reference numerals designate identical or oorresponding parts throughout ; ~ the several views, and more particularly to Figure 1 thereof, the press of the invention has a lower platell which is flat and ?'~ rigid and an upper plate 12 which is flexible in one dimen~ion.
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106~3~6 In numerous application, a rectangular shape will be of interest and the upper plate will be chosen to be flexible about generatrices oriented along the length of the plate. Thus, the upper plate is reinforced by the rigid straight profiles. 13, 14, 15, 16 and 17, the numbers being selected as a function of the width of the press and the pressures which must be exerted. The lower plate has a peripheral seal 18, thick enough, or inflatable, to mate with the edge of the upper plate, which can be provided with suitable ~ facing for realizing a seal around the space between the two .~ 10 plates. Orifices 19, l9', 19" are provided on the circumference of the lower plate and are connected by line 20 to a suction pump 21. Obviously the arrangement could be different without going beyond the bounds of the mvention. For-example, the orifices ~; ; for evacuation could be on the upper plate, etc. The plates may have heating elements, steam or electric, of any suitable type, - ~ depending on local resources and the temperatures to be attained.
The displacements and deformations of the upper plate are controlled by the rows of jacks 22, 23, 24, 25 and 26, each .~
row comprising a certain number of jacks, for exarnple 26A, 26B, 26C, ZdD, et ~peced on lines along the length of thc press.

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The number of jacks across the width, i. e. the number of rows, is selected depending on the width of the press, and according to the invention, will be at least three and preferably five or more depending on the width of the laminated panels to be made.
In the example shown in the figure, each row of jacks corresponds to a reinforced profile of the upper plate. Obviously, there may ; ~ be a larger number of profiles and it is preferablei in any case, - that the rod of a jack act on the plate at right angles to a profile.
;~ In the present form or embodiment, all the jacks are ; l0 double acting pneumatic jacks and their upper ends in each row are connected to conduits, 32 in row 22, 33 in row 23, 34 in ~` row 24, 35 in Fow 25 and 36 in row 26. In the example chosen, `~ there is an odd number of rows and there is thus a central row and on each side there are equal numbers of rows symmetrically s 15 disposed. The invention is obviously appl1cable with an evennumber of rows of jacks. As will be seenJ two symmetrically disposed rows function together, This is why the conduits 32 ,.i'.,~: ~ .
and 3~6 connect to a single conduit 42 and the conduits 33 and 35 connect to a single conduit 43. ~he condu1ts 42, 43 and 34 ~ ~ are controlled by the vahes 45, 43 and 47 re=pectively, so that . . .
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they can be connected to a source 48 of fluid under pressure or opened to the atmosphere at 49J 50J 51. The valves 45J 46 and 47 are servovalves, solenoid valves, pneumatic, mechanical or other type valves and are controlled by way of lines 53 54 and 55 by any convenient means, electric, pneumatic, mechanical linkages or the like. lhe valves 45 and 46 are connect-ed through manometer 56 and conduit 57 to the interior of the press, for example, by way of conduit 20. The valve 47 is controlled by manual control 58.
To simplify the figure for the sake of clarity, the supply and purge lines of the lower ends of the jacks have not been shown.
According to the present invention, the arrangement ; functions as follows. An object to be pressed, such as a laminated slab covered on its upper surface, and possibly on ~ its lower surface also, with liquid resin polymerizable by heat is placed on the lower plate ll. The plates are suitably heated.
` ~ The manual control 58 is then actuated, the effect of whlch is to .~ open valve 47 and feed the central line of jacks 24 by way of conduit 34J the upper plate taking a convex shape as shown in figure 1. The a e 12 descends until the portion at right angle~

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10673~16 to the central profile 15 touches, over its entire length, the panel lying on plate 11. ~he descent of plate 12 is then stopped.
'rhe height of band 18 is such that, with the curvature of plate 12, it will make contact in this position with the edges of plate 12 and the seal realized. The p~mp 21 is then activated to begin the progressive evacuation of the interior of the press, and this, in accordance with the invention, at a well-measured rate, not too fast, so as not to induce too rapid deformation of plate 12, which would prevent the escape of air If forced too quickly against the laminate. ~he vacuum pump may be started j manually or by a position detector 60 which signals the stopping -: of the jacks 2a, in their low position. ~ Since the press may handle liaminated Fallels of different thicknesses, it may be advantageous to use a pneumatic sensor connected to the purging conduit of the lower end of jack 24. During the descent, an overpressure ~i due to leakage maintains a certain overpressure in the conduit.
When the jack stops moving, the overpressure in the cbnduit falls to zero in 2 second. The pressure sensor then gives a ~ignal whlch s ~t, the vaouum _ p 21 ~'~ , . ' '' ,.
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106738~i Because of the progressive evacuation of the interior of the press, the upper plate flattens out gently, being retained by the peripheral joint and the lateral jacks. ~he plate acts as a debubbler, forcing the air towards the exterior.
When the pressure is lowered to a certain level, for example by a 30% drop, the manometer 56 gives an order to open valve 45 to apply pressure to the jacks of the intermediate rows 23 and 25, Finally, when the pressure inside the press . is lowered again, for example to 50%~ the manometer 56 causes valve 49 to open applying pressure to the ja~ks in the outer rows 22 and 26. The upper plate becomes practically flat, all the ~ jacks pushing on the plate so that it fits against the frame of `~ ~ the mold.
~With the arrangement described above, the pressure due to evacuation is about 500 g/cm2; and that e~erted by the jacks alone is of the order of 1. 2 to 1. 5 kg/ cm2- ~hus, a total of about 1. 8 kg/cm2 is exerted on the panel. Such pressures permit limiting the crushing of the panel, while obtaining, because of the gradual way in which the pressure is applied, a perfect surface free of defects. In particular, it is possible to obtain : : ~ .

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panels having a porous or cellular layer without crushing.
These panels can have many uses, as, for example, the sides of containers, insulating or not, and can advantageously replace aluminum or steel sheet, being just as resistant, and also lighter and more insulating and less expensive.
The empl~yment of the invention has been described with regard to a form of realization which makes use of a mano-meter for controlling the valves of the jacks. This device is not however, indispensable; what is important is the synchronization of the lowering of the air pressure with the successive descents of the rows of jacks, from the center to the outside. Thus, with a vacuum pump of known characterlstics, and for a press of given dimensions it is po sible to know with sufficlent ;
precision the time variation of the pressure Ln the press and ? 15 program the descents of the rows of jacks accordingly. Inanother version, the jacks can descend successively, the `~ ~ stopping of one row at the end of its travel initiating the descent of the neighborlng row wi-th the help of a pneumatic sensor, ~?~ providsd thatt'.~e times of descent of the jacks are preset, by choosing the actuating pressure, so as to stagger the descents :

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of the rows of jacks in time to follow the lowering of the air pressure.
According to the invention, the surface of contact of the flexible plate is essentially proportional to the lowering of the pressure inside the press. Thus, it is similar to what is obtained if the descent of rows 23 and 24 is initiated when the pressure has been lowered by 30% and the descent of the outer rows is initiated when the pressure has been lowered 50%.
In a variant of the realization of the inventlon, shown ` 10 in partial transverse section in Figure 2, theré is placed, between the upper plate 12 and the laminated product 61, a sheet of supple rubber of given thickness. This technique permits an even more gradual application of pressure. As a variation, the sheet of rubber could be replaced by an inflatable cushion, These variations are particularly advantageous in .
the case of fabricating nibbed panels as shown in Figure 2.
The lower plate 63 of ~the press has cavitiee, hollows or the like 64 forming nibs 65 on the panel 61.
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~ 6'7386 Whatever the means used to synchronize the descent and flattening of the upper plate with the lowering of the pressure, it is difficult to synchronize the displacements of the jacks.
In accordance with the invention, means are provided to maintain the upper plate horizontal on the average. Figure 3 shows the arrangement which exerts a retracting force on the upper plate if its position cleviates from the horizontal. The system utilizes a torsion bar 71 mounted free to rotate on the supports 72 attached to the frame of the press. The bar 71 may rotate freely but its direction i~s held I0 fixed. The bar is connected to plate 12 at its two ends by two levers 73>
74 articulated at 75, 76 on two lmks 77, 78, themselves articulated at 79.
80 on the plate 12, at two points sufficiently far from the median line 24 ~, ~ of plate 12, along which the jacks 2*~, 24B, 24C, and 24D are disposed. It ;
' ~ is seen that if the axis 24 of plate 12 tilts with respect to the horizontal, lS the links 77 and 78 will impart a differential rotation to levers 73 and 74 which will devélop torsion in the bar 71. The torsion will exert a reaction which tends to bring plate 12 level again. The articulations 75,76, 79 and 80 may be swivel joints, to permit a slight inclinationof plate 12, or simple articulations with sufficient play to allow a sLight tilt of the plate.
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~ ' , .... ~- ' ~06~381fi Once lowered, the jacks remain pressurized during the time necessary or treatment of the panel. When the heating under pressure is concluded, the upper plate is raised in the following manner.
The evacuation line 20 is opened to the atmosphereO
Ambient air penetrates to the periphery of the press. The pressure is allowed to build up. Then the jacks in the outer rows 22 and 26 are raised to pull the edges o the press apart.
` When the edges are sep~*ated, the jacks in the adjacent rows 23 and 25 are raised. Following this, the jacks in the central row 24 are raised. To this end, some of the jacks can have end-of-travel detectors which sense when the liEting of a r ~ jack is completed and give the command for raising one or ~ ~ ~ , . ~
more other rows. These detectors can be simple mechanical 15 ~ devices since the raised positions of the jacks do not depend on the thickness of the panels treated.
In known methods, where the vacuum is maintained during the entire processj it has not been possible to obtain satisfactory surfaces. ~ ;

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The condition of the surface obtained and the solidity of the ' material obtained confer exceptional qualities on the panels which can be produced at a competitive price, owing to the , method of the invention, which, among other things, explains ~`' 10 the commercial success encountered.
Obviously, numerous modificatians and variations of :
the present invention are possible in light of the above teachings.
~` ~ It i6 therefore to be understood that within the scope of the sppended claIms the invention may be practiced otherwise than as specifically described herein.

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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of pressing during heating of a lamin-ated panel having at least one surface layer of thermoplastic or thermosettable material which is in a liquid or flowable state at one stage during heating and pressing and wherein the panel is pressed between upper and lower pressing plates of a press, characterized in that the upper pressing plate is flexible in one direction and is lowered toward the lower pressing plate by rows of jacks acting thereon, the rows of jacks consisting of a central row or rows of jacks and outer parallel rows of jacks symmetrically disposed on opposite sides of the central row or rows of jacks, comprising lowering the flexible upper plate toward the lower plate while reducing air pressure between the plates by evacuat-ing air peripherally from around the panel, determining the reduction of air pressure between the plates and continuing the lowering of the upper flexible plate as a function of the reduction of air pressure, the upper plate contacting the panel first along a central area of contact across the panel as a result of actation of the central row of jacks and then contacting the panel progressively outwardly on oppos-ite sides of the central area as a result of successive actua-tion of progressively outwardly rows of jacks on each side of the central row or rows of jacks.

2. A method as in claim 1, in which the area of con-tact of the upper pressing plate with the panel during lowering of the upper pressing plate is substantially proportional to the lowering of the pressure within the press.

3. A method as in claim 1, wherein a flexible sheet of rubber or an inflatable cushion is interposed between the upper pressing plate and the panel being treated.

4. A press for pressing during heating of laminated panels which have at least one surface layer of thermoplastic or thermosetting material which is in liquid of flowable state at one stage during heating and pressing comprising a rigid lower pressing plate and an upper pressing plate which is flexible along a direction of the generatrices, rows of jacks disposed parallel to the generatrix direction to lower the upper flexible plate downwardly towards the lower plate, the rows of jacks comprising a central row or rows of jacks and outer parallel rows of jacks symmetrically disposed on opposite sides of the central row or rows of jacks, and means to actuate the rows of jacks to lower the flexible upper plate against the panel first in a curved shape along a central feneratrix and then progressively into planar shape, means disposed around the periphery of the lower plate to form a seal between the upper and lower plates when suffic-iently close together, and means peripherally around the lower plate for lower-ing air pressure between the plates, and control means dependent upon the lowering of air pres-sure between the plates to sequentially actuate rows of jacks progressively outwardly from the central row or rows of jacks wherein progressive outward pressing of the upper pressing plate against the panel is proportional to the lowering of air pres-sure between the plates.

5. A press as in claim 4, wherein the control means includes a manometer for constantly measuring air pressure be-tween the plates and switch means for actuating sequential rows of jacks.

6. A press as in claim 4, the control means compris-ing pressure sensor means connected to certain of the jacks to exhaust these jacks to the atmosphere to permit detection of the end of travel of a jack and for generating a signal and means lowering of other jacks from upon detection of this signal, the timing of successive descent of rows of jacks producing a prog-ressive flattening into a planar shape of the flexible upper plate while the air pressure inside the press is gradually lowered.

7. A press as in claim 4, further comprising end-of-travel detector means for initiating successive retraction of rows of jacks starting from the outside of the press and work-ing towards the center, the completion of the lifting of one row of jacks initiating the lifting of an adjacent inner row of jacks.

8. A press as in claim 4, further comprising a tor-sion bar for preventing the upper pressing plate from tilting with respect to the lower pressing plate, the torsion bar being rotatably mounted on supports attached to framing of the press with two ends of the torsion bar being fixed to levers connected by links at two points on the press.