The object of the invention is a method -which enables one to glue bent laminated plates in a new way. The bent laminated plates are herein defined as plates glued to a new bent or curved shape from originally straight layers. These plates are for example seat plates of chairs glued from veneers and shaped according to the human body.

Previously known and generally used methods to produce bent laminated plates have been to press and glue plates to the desired shape between two rigid mold halves using the normal system of hydraulic cylinders to produce a press¬ ing force. Between mold halves an intermediate sheet made from some elastic material, normally rubber, lias, been used to eliminate the influence of minor shape errors and to make glueing pressure even. . _. Previously known glueing procedures have several dis¬ advantages. Most harmful is the fact that they cannot be used in production of such kinds of bent plates which have some part of the profile parallel to the pressing direction. One of the other disadvantages when using older me- thods in glueing is that only the average glueing pressure is known. The real pressure distribution on surface to be glued id unknown and normally surfaces perpendicular to the direction of the pressing force are exposed to greater pressure than surface parts diagonal to the direction of the pressing force. This has an unfavourable effect on the quality of the product and it causes extra loading to the primary structure of the tooling system. The glueing force must be chosen according to that part of surface which is exposed to the smallest amount of pressure. Further disadvantages have been difficulties in adjust¬ ment of the glueing pressure. Because the pressure dis*- _* tribution is not known and difficulties in heat transmission through the elastic sheet to the surface to be glued when the use of such heat is necessary. Another disadvantage is increasing the spot, forces needed to achieve a required

glueing pressure when glueing large surfaces) this leads to the increased cost of the hydraulic components needed for the tooling system.

All of the disadvantages of the present methods men- tioned above can be eliminated by the invention described in this application using the new and simple technics.

Characteristic to this invention is the fact that in the glueing method you can find two clearly separate phases, both of them having separate structural parts in the mold system used in this method. The bending of the layers to be glued close to the desired shape and the actual glueing is performed separately using separate structural parts and separate sources of force.

The most important advantage offered by this invention is that when using the new method you can produce such kinds of laminated sheets which have some part or parts of sheet parallel to the direction of the pressing force.

Furthermore the price of the tools needed in the glue¬ ing process will be lower, than the price of the present tools because the use of high pressure hydraulics is not neces¬ sary. Furthermore, automation of the glueing process re¬ quired in case of mass production is easy when the new method is used because the same liquid can be used for pressuriz¬ ing and for heating as well. The control of the liquid pres- sure and temperature in automation is known to be simple.

The new method enables the use of a constant accurately controlled glueing pressure and temperature which indisput¬ ably improves the consistent quality of the product. The main characteristics of the invention are described in claim 1. The method mentioned in this application is demon¬ strated in the enclosed drawings by a mold system using the method. Also one commonly used 'old' method is included in the drawings in order to make clear the main differences. Figure 1 shows a cross section of the commonly used mold system where straight, with glue treated layers 2 are to be pressed to completed product 1 using mold halves 3 and 5 actuated by spot forces F. Intermediate elastic sheet 4 evens the pressure. Using this method the angle A can not

be smaller than 4... degrees. The smaller the angle A is the worse the sides are "exposed to pressure"..

Figure 2 presents.as a cross section an example of one tooling system using the method mentioned in this appli- cation, especially the first phase of the glueing process. Figure 3 presents a cross section of the same type of mold when the bending phase has been completed.

Figure 4 is a cross section of the same mold when the glueing pressure has been "switched on". Figure 5 shows as a side view an example of one sup¬ porting frame type and mold attitude when straight sheets to be glued have been put to their places.

Figure 6 shows as a side view the same frame when the bending phase has been completed and the glueing pressure can be or has been "switched on".

The working principle of the glueing mentioned in this application and the main structure og one tooling system are demonstrated by figures 2-6 as follows.

Glue treated straight sheets 8 have been put on the stationary mold half 13 to glueing position in order to make product 6. The structure of stationary mold half con¬ sists of perforated sheet 12, glueing membrane 11, gaskets 10 and gasket tighteners 9« Hole diameters D of perforated sheet 12 do not need to be constant along the width of perforated sheet. By variation of diameters D you can adjust the sequence of pressure influence as desired. Both mold halves are filled with liquid. Liquid of upper movable mold half is used to heat the mold and liquid of cower stationary mold half to heat and pressurize the mold. Steel is the most convenient material to make mold halves 7 and 13 and per¬ forated sheet 12 too. Membrane 11 can be for instance a thin brass sheet or some other suitable metal membrane provided that the width of membrane between gaskets 10 is the same one in both working phases described in figures 3 and 4. This situation can be achieved by choosing correct shape to perforated shhet 12 compared with mold half 7« If some elastic membrane material is used, above mentioned shapes do not need to be dimensionally very accurate.

First phase of the method bending, of layers is in this case performed by pushing the upper mold half 7 _. using for instance link mechanism 15 activated by threaded rod l6, against the lower mold half so that desired mutual position of mold has been reached and so that arms of mechanism 15 are "locked" as shown in the figure 6.. The force G needed in this bending phase is only a part of force H caused by glueing pressure. During testing of mold system the ratio of forces G and H was measured to be about- 1/20. Testing was made by glueing three veneers together to curved shape.

Thickness of ready laminate was 3 nun. The fact that, force G is small compared With force H enables the use of simple and cheap mechanism to perform the bending phase.-

The other phase of method, glueing sheets 8 together is to be performed in this example by pressurizing the liquid in the stationary mold half 13 to desired pressure P ₁ for instance using low pressure hydraulic pump. If heat is needed in glueing procedure, pressurizing liquid can be heated to desired temperature electrically. The additional force H is in this example carried by link mechanism 15 and frame structure 14. ^*

The two phase glueing method can be used to several purposes, especially when the plate to be produced has some parts of surface parallel to pressing force H. From several possibilities to use the method following ones should be mentioned: production of curved plywood sheets, production of bent plates by glueing resin-based sheets together and manufacturing of curved resin-wood laminates.