Laminating apparatus Sandwich elements have been commonly used in buildings and in ships for many years. They were first used in the form of thin concrete layers separated by an iso- lating layer, the core. Very often there was a mechan- ical connection between the concrete layers because the core usually could not transfer the forces neces- sary for holding the element together. Later sandwich elements were introduced in which the surface layers were made of thin layers, e. g. sheet-metal or lami- nate. With thin and flexible surface layers, a need arose for rigid cores which were able to transfer forces. This need could be met with cellular plastics, but the need, especially for fire protection and sound isolation, led to mineral wool becoming an important core material.

To make the mineral wool core rigid enough it is some- times sufficient to increase its density. However it is more customary to change instead the orientation of the fibres in the core so that the main direction of the fibres is orthogonal to the surface plane. Using such a fibre orientation, allows the board to with- stand deformation better when it is loaded orthogo- nally to its plane compared to a mineral wool core that is not reoriented. Reorientation can be carried out using a so called lamina technique, i. e. the nor- mal hardened mineral wool boards are divided into nar- row strips, which are rotated 90° around their own axis and assembled in a new sheet-type construction.

Other techniques for carrying out the reorientation

also exist.

Development has since moved towards using sandwich elements in which e. g. sheet-metal is used as a sur- face layer not only in partition walls as before, but also in outer walls and roofs. This has placed much higher demands on the quality of the elements, in terms of both appearance and especially strength char- acteristics, while at the same time the dimensions of the elements also increased many times over previous dimensions.

The principle of manufacturing sandwich elements of this kind is described in WO 98/42503.

The glue that attaches the core to the surface layers is preferably of a thermosetting type, but it may also be self-curing or hardened by some other means, e. g. ultrasound. In a press operation, if needed during heating or other procedure, the surface layers are attached to the mineral wool layers and the glue is cured. When manufacturing sandwich elements, the pressing measure is usually controlled by being car- ried out against a stopping block which defines the distance between the pressing plates and thereby the thickness of the element during the pressing.

This method can give a poor result when using thin sheet-metal, with faults such as rough surface layers and weak glue joints. Functionally this causes visual problems, because even small roughness in the form of ripples and bosses are clearly visible, especially on

totally smooth elements. The strength also deterio- rates, which usually is not permissible. To eliminate these problems, the amount of glue, the thickness of the surface layers, the density of the mineral wool layer, the binding agent concentration etc. has been increased or the surface has been additionally machined. Additional glue and binding agent contents result however in inferior fire properties. Another fact is that the product will be much more expensive, and, besides, the result is often not good enough or predictable. Not the least serious problem is, that more expensive measures have to be taken also on ele- ments which have no obvious weaknesses.

In the light of this, extensive and thorough studies and experiments have been made, which have given rise to the invention according to WO 98/42503. According to this publication, the pressing, when needed under heating, is not carried out against a stopping block to a predetermined thickness, but by using a pressure within a predetermined range, Pmax-Pmin/the size of which is determined by the included components, the mineral wool laminas, the surface layers and the glue.

In this case both the terminal points of the interval are determined by two different phenomena: the lower limit for the pressing pressure being the lowest pres- sure needed so that no adhesion breakage will occur; the upper limit being determined by how much the core material withstands while retaining its structural properties.

An important problem remains in this known method,

i. e. how the pressing pressure can be kept locally within these limits over the press platen. The problem is accentuated by the reorientation of the mineral wool core, which causes systematical variations be- tween different parts of the core, irrespective of the system used to achieve reorientation. One reason for this is the strength requirement of the element. The core construction must not be destroyed by overpress- ing, but, on the other side the attachment of the top layer must be guaranteed. The visual appearance of the element is also of importance since the human eye is disturbed by even very small bosses on the surface of the element.

Yet another problem with the pressing method lies in the flatness and parallelness of the press platens.

Usually the structures are huge, sizes of up to 15 m2 not being unusual, and the demands often include a requirement that deviations from smoothness and parallelness shall be less than 0,2 mm. The press platens are usually also heated and problems espe- cially arise with traditional presses in which the displaceable press platen often becomes slightly bent.

The invention solves the aforesaid problems with a method and an apparatus according to the accompanying patent claims.

When thin surface layers, e. g. made of sheet-metal, must be attached to a core made of reoriented mineral wool in a sandwich element, according to the invention a laminating apparatus is used in which at least one

of the press platens is flexible and is acted on by many power units, the influence of which can be con- trolled individually or in groups, it then being pos- sible to control the pressing pressure in different parts of the press platen and keep it within the aforesaid limits Pmax-Pmin- In the simplest embodiment the other press platen is fixed and flat.

Before pressing is performed, the power units are usu- ally adjusted so that the flexible press platen be- comes flat and preferably also parallel to the other press platen. For this purpose the power units may be double-acting.

In some applications it is preferable that both press platens are flexible and separately acted on by sev- eral power units, the influence of which during the pressing can be controlled individually or in groups.

Then the press platens can be formed, in the first instance with a curved cross-section. Both press plat- ens must then be bent in the same direction and by the same amount. The element then becomes accordingly curved or dome shaped, which may be desirable in cer- tain applications. Partly these dome shaped elements give an architectonic effect, partly the dome shape means that smaller deviations from an otherwise regu- lar plane will not be as clearly visible as in the case of a flat element.

In a normal case the influence of the power units shall be controlled in such a manner that both flexi- ble press platens becomes both parallel to each other and flat. As aforesaid, the aim can be elements, which have curved cross-sections and in these cases the press platens must anyway be parallel.

By continuous pressing, the optimal curing of the glue may require the press platens to be flat but conver- gent or divergent.

For an optimal glue effect it is necessary for the press platens to exert a pressure against the press object within predetermined limits, in which the lower limit is determined by the lowest pressure, Pmin, which is needed so that when tearing apart the connec- tion, adhesive failure will not occur, and the upper pressure, Pmax, is determined by the condition that the proportionality limit of the core material not shall be reached.

The limits are, at their broadest, Pmax and Pmin re- spectively, but they may also, when the practical pos- sibilities in a specific case allow, be set so that the range becomes smaller, e. g. so that the lower press limit becomes Pmin + 0,25 * (Pmax-Pmin) and the upper press limit becomes Pmax-0,25 * (Pmax- Pmin). In most cases it is both possible and desirable to accelerate the curing of the glue during the press- ing action by heating from one or both of the press platens depending if there are surface layers on one or on two sides. Other types of accelerating effect

can also be considered depending on the character of the glue.

It is understood, that if there are surface layers on both sides of the core, the heating or other curing accelerating influence must also be double sided, oth- erwise it is enough if it comes from that side where the surface layer is situated.

This potential acceleration allows a somewhat slower glue to be chosen, which makes the process less sensi- tive to disturbances, while maintaining productivity, because the glue is rapidly cured when the press ob- ject already is situated between the press platens.

Another way of utilizing heated press platens is to cool the surface layers and/or the glue to strongly retard the curing of the glue until it is correctly situated in the press.

Yet another way to accelerate the curing of the glue is to preheat the surface layer or layers, which can be done by blowing in warm air, by infrared heating or, when the surface layers are made of metal, by in- ductive heating.

Irrespective of how the accelerating of the curing is done it may be advantageous to be able to adjust it over the surface of the platen or platens respec- tively. It is also preferable, in the case of heated platen or platens, to be able to detect the tempera- ture of the platen or the platens and how the tempera-

ture is distributed.

The heating of the surface platens may also be made in a separate step before they are fed into the press.

This will also achieve other benefits because internal tensions and respectively changed dimensions of the surface layers by the heating can be dissolved and smoothened.

From many points of view it is advantageous that the press object is transported continuously through the press, partly because a higher production speed can be achieved and partly because elements can also be pro- duced which are longer than the press or vice versa, allowing the press to be kept short.

Continuous production is possible in two ways, either by preparing separate press objects of certain length before the pressing or by preparing a continuous press object. In both cases, these are then taken continu- ously into, through and out of the press. To achieve continuous production in a press with press platens it is required that the press object be placed between two belts. For a press object that is taken through the press to be subjected to a pressure, the distance between the press platens must be less than the com- bined thickness of the press object and the belts in an unloaded condition.

The invention also concerns a press for connecting surface layers and a core in an element where the sur- face layers and the core are brought together to a

press object after adding a glue layer between the surface layers and the core and then applying a pres- sure between two press platens. The press according to the invention is characterized in that at least one of the press platens is flexible and is acted on by sev- eral power units, which have been arranged between the press platen and a fixed supporting structure so that they can produce forces that can be transferred from the fixed supporting structure to this press platen, and the influence of which can be controlled individu- ally or in groups.

The power units may be of a pneumatic or hydraulic type, e. g. simple flexible tubes or cushions, but also proper piston-cylinder apparatuses. There are also other possibilities. Thus the power units may be threaded spindles or eccentrics, or they may be of electro-mechanical type.

The flexibility of the press platen can not be stated exactly, but it must be so flexible that its form can be changed considerably with those forces that the power units can produce. On the other side the press platen must be rigid enough to prevent too sharp bends arising in the surface layer of the press object.

These must in turn be adapted to the properties of the press object. To one versed in the art it is probably possible in an actual case to use a few simple calcu- lations and experiments to determine both the capacity of the power units and within which limits the flexi- bility of the press platen must lie. A good rule for the calculations is that the height and respectively

the depth of the bends should be at most one thousand of its diameter.

The supporting structure against which the power units must act may be a platen or a framework made of beams or corresponding.

If the power units are elongated, e. g. they are pres- sure hoses, it is preferable that every or possibly every pair of them is controlled separately. If the power units are not elongated, but are arranged in rows, it is preferable that every such row is con- trolled separately.

The controlling must be adapted to the type of power unit used. If they are hydraulic, the adjustment is naturally performed by controlling the pressure of the pressure medium that feeds them. If the power units are of a different type, the size, and sometimes also the direction of the power with which they act on the flexible press platen, must be measurable, e. g. with some kind of detectors.

In a press it is normally preferable that the other press platen is smooth, preferably also stationary.

The flexible press platen including its power units may then with preferably a control apparatus be made smooth and/or parallel to the other press platen.

Such a control apparatus may be more or less self-act- ing. To make the flexible press platen smooth, its deviation from smoothness is only measured in the sim-

plest case and the force with which the different power units act on the platen is then varied so that the deviations are sufficiently counteracted.

Such a measurement can be made with dial gauges, elec- trical detectors or with optical, preferably laser optical, systems. The measuring can also be made with a calibrated press object which before the process is started is taken into the press and makes the setting easier.

In a press according to the invention both press plat- ens may be flexible and both can be acted on by sev- eral power units, which are arranged between these and fixed supporting structures in such a way that they can produce forces which can be transferred from the fixed supporting structures to the press platens and the influence of which can be controlled individually or in groups, and that the press is such constructed that the power units can make the press platens paral- lel and/or smooth.

To be able to ensure an optimal gluing action it is required that the pressure that is acting on the press object in the press can be read and manually or auto- matically be kept within those limits which one in advance has have been able to determine for the compo- nents in question.

The power units may be elongated with a length which corresponds to the dimension of the flexible press platen in one direction. The elongated power units may

be tubes. If cushions or hydraulic cylinders are se- lected instead, it is a beneficial to place these in rows. It is convenient that the elongated pressure units or rows of individual pressure units are arranged transversely to the flexible press platen, because the typical need is to eliminate its bending longitudinally. In many cases some other design is more advantageous, e. g. a herringbone pattern. If a controlled bending of the press platen is preferable, and preferably so that it gets a curved cross-section, the elongated power units or rows of power units must instead be arranged in the longitudinal direction of the press platen.

Usually it is preferable to accelerate the curing of the glue in some way when the press object is already situated between the press platens in the press by heating. Then it is required that one of the press platens or both are heated, e. g. with a circulating heating medium. Which medium is chosen depends mainly on the temperature the press platen or press platens shall obtain. This in turn depends on the properties of the glue and on the need to accelerate the process.

To be able to rapidly change to another thickness of the press object, it is preferable that the supporting structure, or in the case of two flexible press plat- ens, at least one of the supporting structures is ar- ranged to take different positions, e. g. defined by stopping blocks. The supporting structure can be a framework which with hydraulic cylinders can be lifted from and lowered against the stopping block. A series

of stopping blocks can be used for different produc- tion situations or rather such stopping blocks may be used that easily can be adjusted for different produc- tion situations.

To allow the flexible press platen or press platens to change form without a net pressure arising against the press object, the power units must be double-acting so that they can not only apply repulsive forces but also attractive forces.

The invention is advantageously applicable to a situa- tion where the core material is made of mineral wool, preferably lamina oriented or otherwise reoriented to give better resistance against pressure loads orthogo- nally to the main plane of the core. Mineral wool cores of a lamina type and structures with properties of the same kind show namely to a very high degree that problematical picture which the invention starts from, especially if the density is relatively low, as it should be for economical reasons. Choosing mineral wool as core material is often due to the fact that it is cost-efficient, perpetual and shows good fire prop- erties.

Other core materials may, however, be appropriate in special applications, e. g. polystyrene cellular plas- tic and phenolic cellular plastic.

Example As a typical case an example is shown of continuous

pressing in a press with a working length of 5 m. The upper press platen of the press was flexible while the lower was rigid. The power units between the flexible press platen and its supporting structure was 16 tubes which extended across the press platen with a spacing of 330 mm. They were two and two connected to a hy- draulic system with an individual pressure control to every tube pair. Both press platens had an internal system of bores in which water of temperature 92 °C flowed, which gave the press platens a temperature close to the press surfaces of 85,5 °C.

The press object was transported through the press with two conveyor belts. By pressing against a cali- brating element the pressure in the different tube pairs was adjusted so that the flexible press platen was flat and parallel to the other press platen at a pressing pressure of 30-40 kPa.

The press object was a core of laminate oriented min- eral wool of rockwool type with a density of 90 kg/m3, the values of the density is normally for this case 70 -120 kg/m3, commonly 90-100 kg/m3. The binding agent concentration was in the example 2,5 %. It is normally 2-4 %. The press object included a plastic coated steel plate layer on both sides. The thickness of the plate was 0,5 mm on one side and 0,6 mm on the other side.

In the example the length of the press object (a fu- ture sandwich element) was 7 m and the width was 1,2 m. Lengths of 6-10 m are typical, but the element

may also be more than 10 m long. The width is normally 0,8-1,2 m.

Between the sheet-metal layer and the core was a glue layer which consisted of a two-component polyurethane glue of about 175 g/m2.

For this press object, the appropriate pressures were Pmin = 25 kPa and Pmax = 50 kPa. The curvature of the element was <0,2 mm/m and the adherence between the surface layer and the core was adequate over all sur- face of the element. The pressure of the flexible press platen against the press object was set to 35 kPa, after which the pressing pressure in the power units situated on different positions over the press platen was controlled so that possible local devia- tions from this value stayed within the aforesaid limit values.

Figure texts The invention will be described in detail with the aid of figures 1-4.

The principle of the invention will be illustrated with reference to figure 1.

The diagram in figure 1 is a graphical representation of one embodiment according to the invention. The straightening of the flexible press platen has been made with power units, i. e. the press platen has been calibrated before the press operation, after which the

press object in principle can be pressed with a prede- termined pressure all over its area. Possible local deviations from this pressure will then be kept within the limits PmaX-Pmin by controlling the power units individually or in groups.

Figures 2a, 2b, 3 and 4 are all diagrammatic represen- tations of different embodiments of the apparatus ac- cording to the invention. Figures 2a and 2b show cross-sections while figures 3 and 4 show longitudinal views.

Figure 2a shows two columns (1) which are connected by an upper piece (2) and a lower press platen (3). An upper framework (4) is pressed by hydraulic cylinders (5) against adjustable stopping blocks (6). In connec- tion with the upper framework (4) there is an upper, flexible press platen (7) which by power units (8) is pressed against the press object (9).

Figure 2b shows a corresponding apparatus, but with that difference that the flexible press platen (7) here is arranged in connection with a lower framework (10) and is pressed from this against the press object (9) by the power units (8).

In figure 3 reference number (15) represents a con- veyor with driving rollers on which a press object (9), a future sandwich elements (23), lies. The press object consists of an upper surface layer (12) and a lower surface layer (13) between which there is a core of reoriented, e. g. lamina oriented, mineral wool

(14). Between the surface layers and the core there are layers of glue, which are not shown in the figure.

The press itself consists of a framework with columns (1) and an upper piece (2). In the lower part of the frame a lower press frame (16) is assembled. On this there lies a press bed (17) and a press platen (3).

Over the press platen (3) extends a conveyor belt (18). The conveyor belt (18) extends further over two rollers (19). The lower part of the belt is supported by supporting rollers (20).

In the upper part of the framework an upper press frame (21) is suspended in double-acting hydraulic cylinders (22). From the upper press frame a flexible press platen (7) is suspended from power units (8).

The adjustable stopping blocks (6) rest against the lower press frame (16) and are so placed that they can meet the upper press frame (21) when this is pressed down by the hydraulic cylinders (22).

This press works so that the hydraulic cylinders (22) first lift the upper press frame (21) with the flexi- ble press platen (7) connected to it to such a level that the distance between this and the lower press platen (16) is bigger than the combined thickness of the press object and the conveyor belt (18). Next the press object (9) is taken, by means of the conveyor (11) and the conveyor belt (18), between the lower press platen (3) and the flexible press platen (7).

Next the hydraulic cylinders (22) press down the upper

press frame (21) against the stopping blocks (6), af- ter which the power units (8) further press the flexi- ble press platen (7) against the press object with controlled pressures.

After the pressure has acted for the time needed for the glue to cure, the upper press frame is again raised, once the pressure from the power units has ended, so that the press object (9), which has now become a sandwich element (23), can be fed out. This takes place with the conveyor belt (18) out on the conveyor (24) at the same time that a new press object (9) is fed in from the other side.

Figure 4 shows an apparatus according to the invention which is intended for the continuous pressing of a continuous press object. A continuous core (14) of laminate oriented mineral wool is moved forward on a roller line. From two rollers, which are not shown in the figure, comes an upper (12) and a lower (13) sur- face layer made of plastic-coated steel plate down and respectively up against the continuous core. Before the surface layers are brought together with the core, the space between these is injecte with a glue layer (27) from nozzles (28).

The, in this case continuous, press object (9) thus formed is taken with the conveyor belt (15) towards the press in between the lower belt (18), with its driving and turning rollers (19) and its supporting rollers (20), and the upper belt (29) with its driving and turning rollers (30) and supporting rollers (31).

The press itself consist of a framework with a column (1) and an upper piece (2). In the lower part of the frame is a lower press frame (16) mounted. On this lies a press bed (17) and a press platen (3).

In the upper part of the framework there is an upper press frame suspended from double-acting hydraulic cylinders (22). From the upper press frame suspends a flexible press platen (7) from power units (8). The driving and turning rollers (30) of the upper belt are mounted into brackets (32) projecting from the press frame (21).

The adjustable stopping blocks (6) rest against the lower press frame (16) and are placed so that they can meet the upper press frame (21) when this is pressed downwards by the hydraulic cylinders (22).

The apparatus according to figure 4 is thus intended for continuous operation. When the press object (9) between the belts (28,29) comes in between the lower press platen (3) and the upper flexible press platen (7) it is subjected to a pressure which causes a cer- tain compression. At the same time the surface layers are heated by both the press platens, which are heated by warm water that circulates in bores, not shown in the figure, in the press platens. During the simulta- neous effect of the pressure and heating, the glue is cured and converts the press object into a sandwich element (23) which is fed out on the conveyor (24).

Because, in the shown embodiment, it is a question of continuous production, the product is later cut into

pieces of suitable length. This cutting apparatus is not included in the invention and is also not shown in the figure.

The apparatus according to figure 4 can also be used for pressing prepared discontinuous press objects, the length of which consequently does not depend on the press length of the laminating apparatus. The prepared press objects may be longer than the press, but they may also be shorter and may then be fed in closely after each other.