EP1854622B1

EP1854622B1 - Multidaylight press for bonding flat elements, particularly for the hot or cold bonding of veneers, laminates or the like on sandwich, chipwood, honeycomb panels or the like and for producing plywoods, chipwood panels and the like

Info

Publication number: EP1854622B1
Application number: EP20070008939
Authority: EP
Inventors: Fabrizio Azzimonti; Gastone Girardini
Original assignee: ORMAMACCHINE SpA
Current assignee: ORMAMACCHINE SpA
Priority date: 2006-05-12
Filing date: 2007-05-03
Publication date: 2011-03-02
Anticipated expiration: 2027-05-03
Also published as: EP1854622A3; ITMI20060946A1; EP1854622A2; ES2361340T3; DE602007012788D1

Description

The present invention relates to a high-productivity multidaylight press for bonding flat elements, particularly for the hot or cold bonding of veneers, laminates or the like on sandwich or hollow core, chipwood, honeycomb panels or the like and for producing plywoods, chipwood panels and the like.
Presses with multiple stacked platens, also known as multidaylight presses, have long been known and used extensively in the woodworking industry and provide a plurality of processing daylights, thus allowing to press simultaneously a number of flat elements, such as for example panels on which the facing elements to be bonded have been arranged beforehand, which is equal to the number of the daylights with which such presses are provided.
In the best-known embodiment, such presses are constituted by a framework which supports a plurality of stacked platens and corresponding presser means, which act on the platens in order to clamp them together after they have been loaded by interposing between them the panels and the flat elements with the corresponding facing elements to be pressed.
In this type of presses, the presser means are a single set for all the daylights and the pressure is accordingly applied simultaneously to all the loaded panels.
Since the preparation of the panels by positioning thereon the facing elements previously spread with adhesive usually requires a shorter time than that required for the drying of the adhesive once such elements have been loaded into the press, the operators assigned to this operation accordingly remain unproductive while waiting for the completion of the drying cycle of the adhesive of the loaded panels.
Another drawback of this type of presses is the fact that in nearly all cases the bonding processes are performed while hot, and the panels cannot be inserted individually in the respective daylights because the adhesive would react even before loading is completed; it is thus necessary to use a multiple loader.
This apparatus is usually constituted by a structure provided with a number of stacked loading belts which matches the number of daylights of the press and can move vertically in order to first allow to load each individual belt at one level and be subsequently arranged so that all the belts are at the height of the corresponding platen of the press.
Each individual panel is thus prepared in a first preparation belt, and the panel is transferred to a belt of the multiple loader, proceeding in succession until the load is complete; then all the panels are loaded simultaneously into the press by simultaneous actuation of all the belts of the multiple loader.
It is evident that this apparatus affects considerably the final costs of the system, also in view of the fact that it is necessary to provide at the output a similar apparatus, a multidaylight unloading unit, which can receive the previously pressed panels in output from the press during the new loading process; such panels must then be necessarily handled individually again for transport and for subsequent processes.
Accordingly, the final dimensions of the system are as much as five times the size of the press proper and are due to: an individual preparation belt, the multidaylight loading unit, the press body, the multidaylight unloading unit, and the individual unloading unit where the panels parked on the multidaylight unloading unit are taken individually.
An apparatus thus conceived, in addition to being bulky, complicated, expensive, and, as mentioned earlier, not particularly productive, suffers still another drawback which further limits its production possibilities. Due to the preparation time of the various panels and to the time required for the various transfers of said panels, it is in fact necessary to limit the working daylights of the press, which are usually four in number, at the most five, on penalty of the drying of the adhesive on the panels before they are introduced into the press. Indeed, when facing panels with veneering, usually having a thickness of 0.5-0.6 mm, due to the sudden curling caused by the absorption of the moisture that is present in the adhesive, which occurs as soon as it comes into contact therewith, it is not possible to prepare and consequently press more than two panels for each load.
In order to obviate all this and make the systems more productive, a type of multidaylight presses has become commercially available which, differently from the presses described above, allows independent opening and closure of one daylight while keeping the others under pressure. Such presses allow to eliminate downtimes, since during the steps for opening, loading, unloading and closure of each individual daylight the other daylights are kept under pressure. In this manner, by proceeding progressively and in succession with the loading of the different daylights, once the last daylight has been loaded and one returns to the first daylight, such first daylight has remained under pressure for the time required to achieve the bonding of the panel. Such presses have allowed to increase productivity considerably with respect to traditional multidaylight presses.
Presses that allow to open and close independently the different daylights can be traced back to two different types: a first type, disclosed for example in EP-384958 , and a second type, disclosed for example in Italian patents IT742525 and IT1218248 .
The press disclosed in EP-384958 comprises a plurality of stacked platens, which are structurally self-supporting and are connected one another by lateral hydraulic presser cylinders, and in which the flat elements to be pressed are interposed between two contiguous platens which delimit a daylight.
Substantially, a press of this kind can be likened conceptually to several single presses stacked together, in which the presser cylinders are applied directly to the platens on two facing front sides and mutually connect in each instance two contiguous platens. Such platens can therefore perform a vertical translational motion with respect to each other. In this configuration, excluding the first and last platens in order of height, each intermediate platen is in the condition of being shared by two stacked daylights. Each intermediate platen in fact acts as an upper platen for the underlying daylight, with its lower face, and as lower platen for the overlying daylight, with its upper face.
Although it achieves the purpose for which it was conceived, this press suffers certain problems.
In this press, the hydraulic cylinders required to put the machine under pressure are multiplied by the number of designated daylights and, considering a number of daylights which usually ranges from eight to ten, the expenditure of such means is evident.
Moreover, since the presser cylinders are arranged laterally to the platens, such platens, in order to be able to contrast the flexing forces, which are increased considerably by the force application distance, must be provided with thicknesses which are more than twice those required by a traditional application with pressure distributed equally on the platen, with a consequent considerable increase in the power required to heat them, due to the considerable mass increase.
Another complication which is inherent to this embodiment is constituted by the considerable weight difference which affects the presser cylinders of the different daylights of the press; the lowest cylinders, the ones of the first daylight from the bottom, in fact must bear all the weight of the overlying cylinders and platens, which gradually decreases as one rises toward the last daylight.
It should be considered that for certain processes, such as for example in the production of lightweight sandwich panels, the mere weight of platens structured in this manner is excessive, hence the need to provide the machine with a plurality of independent hydraulic circuits not only as actuation controls, as is anyway indispensable and required in order to manage the daylights autonomously, but in which the pressures of each individual circuit also must be determined by taking into account the weight of the overlying structures, with the practical result that for each daylight the corresponding battery of cylinders has to work at a different pressure than that of the batteries of cylinders of the other daylights.
The situation becomes even more complicated and practically impossible to handle reliably and precisely whenever it is necessary, and this occurs regularly due to the inevitable compression of the panel during the pressing step, to recover pressure in order to return it to the preset values inside an individual daylight.
All this leads to an extremely complicated machine which is critical in its normal operation and also economically expensive.
Moreover, this type of press entails that the loading height of each individual daylight cannot ever be determined beforehand, since it is variable as a function of the thickness of the loaded panels. Because of this fact, it is necessary to wait for the last daylight that is loaded to be closed and pressurized before it is possible to actuate the loader to place it at the correct working height for the subsequent load. This entails a waste of time which, despite appearing scarcely significant for an individual load, on the order of five or six seconds, in any case causes the loss of three or four panels for each working hour.
In the press according to patent IT742525 and according to patent IT1218248 , the different daylights are all closed and subjected to pressure simultaneously and it is possible to open, for loading and unloading, and then close sequentially each individual daylight without theoretically changing the pressure that acts on the flat elements that are inserted in the other daylights.
This press is composed of multiple superimposed platens, which are contained in a framework provided with hydraulic presser cylinders which act on the first upper platen. The pressure applied to the first upper platen is transferred to the entire stack of platens as occurs in a traditional multidaylight press.
In turn, the framework is inserted in an additional fixed containment frame, inside which it can slide vertically by way of appropriately provided movement means.
Opening devices are installed in a fixed position, on two opposite sides of the containment frame, and form a sort of clamps, each constituted by two superimposed beams whose length is equal to the larger dimension of the platens, such beams having, at one end, a system of fluid-operated actuation cylinders which open or close them vertically, and being contoured, at the other end, so that they can be inserted between any pair of contiguous platens where they engage appropriately provided reference seats.
The opening devices are pivoted to the fixed frame and can move laterally in order to allow the vertical sliding of the entire movable framework when they are spaced one another or be inserted between the platens when they are close one another.
The hydraulic actuation cylinders of these clamps are partly constituted by hydraulic balancing cylinders, which can be connected to the same circuit as the hydraulic presser cylinders so as to balance the pressure applied by the hydraulic presser cylinders. In addition to these, the hydraulic actuation cylinders of the clamps comprise hydraulic or pneumatic cylinders for opening/closing which can be actuated independently.
Furthermore, the hydraulic connections between the presser cylinders and the clamp actuation cylinders are provided so that while the presser cylinders are extended, i.e., with the stem out, the clamp actuation cylinders are closed, with the stem retracted into the corresponding cylinder.
The operating cycle of a press of this kind begins when all the daylights, formed by the various platens stacked so as to form a pack, are closed and kept under pressure by the presser cylinders installed in an upward region in the movable framework and rigidly coupled thereto, said cylinders applying their thrust downwardly from above; the clamps are closed and kept in a position in which they are spaced from the framework.
The movable framework which contains the platens under pressure is made to slide vertically within the fixed frame until the second platen from the top reaches the height of the loading belt; once it has reached this level, the clamps are moved to the position in which they are closer to the framework, in which, because of their configuration, they are inserted between the first two stacked platens.
At this point, the hydraulic or pneumatic cylinders for opening/closing the clamps are actuated and move the two beams of the clamps into contact with the two platens to be mutually spaced. Once contact has been established, the hydraulic balancing cylinders are connected to the circuit which supplies the hydraulic presser cylinders. From this point onward, the hydraulic or pneumatic opening and closure cylinders simply transfer oil from the presser cylinders to the balancing cylinders, moving mutually apart the two platens affected by the loading with a reduced force.
The panel is then loaded by means of a translating belt system which is constituted substantially by a framework provided with a conveyor belt, which after receiving the panel, is inserted fully within the daylight of the press along the entire lengthwise dimension of the platen; then, during the return step, the belt is turned in the opposite direction with respect to the return direction so that the panel is deposited onto the platen within the daylight.
During the insertion step, in subsequent loading operations, the previously pressed panel is also unloaded simultaneously and is expelled by pushing by the translational motion of the translating belt, said panel being conveyed onto a belt or roller bed arranged at the output of the press.
Once the loading operation has been completed, the hydraulic or pneumatic opening-closure cylinders are actuated in the opposite direction, so as to again transfer the oil to the presser cylinders and thus produce the mutual approach of the previously spaced platens and disengage the clamps from the two platens.
The clamps are then moved to the external position and the movable framework is again made to slide until the second daylight from the top reaches the loading level, from which the cycle resumes as described above. One proceeds in this manner until the last daylight is loaded, and one then returns to the first loaded daylight.
Even this type of press is not devoid of problems.
Although the press is in theory able to allow to open one daylight without altering the pressure applied to the flat elements inserted in the other daylights, in practice the transfer of oil from the presser cylinders to the balancing cylinders, despite balancing the thrusts, once it has reached equality, has the effect of canceling out the pressure applied between the platens. Moreover, in order to be able to open a daylight it is necessary to add the thrust required to lift all the overlying platens and overcome the inevitable friction created by their movement; this entails that during this step, which generally lasts 20-25 seconds, the pressure applied to the flat elements inserted in the other daylights increases considerably.
The pressure applied by the clamp to lift the overlying mass, by resting in practice on a platen, is in fact necessarily transmitted to all the underlying platens and the same occurs for the overlying platens.
The pressure increase that occurs during this step is not negligible and substantially changes the operating parameters, if one considers that the weight of a platen is usually approximately 1,500 kg and that usually the machines are provided with eleven platens in order to obtain ten daylights.
Moreover, this pressure is constantly variable from one daylight to another, since it is determined by the number of overlying platens, which increases or decreases constantly.
In order to solve the problem, additional hydraulic cylinders have been installed in the movable framework and are connected diagonally every two or three platens with compensation functions in order to avoid applying completely the weight of the platens, with the consequence of greater complexity, so much that this type of press currently is the most complex commercially available one.
Because of this complexity, spare parts are not often commercially available and at the slightest anomaly only the specialized personnel of the manufacturer is capable of acting to restore its correct operation. This problem is a severe limitation for a high-output machine in which every machine downtime heavily affects final production.
Moreover, a press of this kind is scarcely flexible in its use, since a press with ten daylights necessarily has to perform the entire cycle of the ten loads provided unless one acts heavily on its components, since in its operation, which is based on a sequential cyclic pressure transfer, the pressure can be always and only the same for all the flat elements being processed and it is not possible to process, within a cycle, a flat element which requires pressing parameters that differ from the others, since the opening of the daylights is determined by the stroke of the clamp actuation cylinders, which is fixed, invariable and equal for all the daylights.
GB-A-995590 discloses a multidaylight press as defined in the preamble of claim 1, but wherein the engagement between the stop elements and the intermediate platen is a simple rest engagement.
The aim of the present invention is to provide a multidaylight press which is capable of overcoming the problems and obviating the drawbacks mentioned above with reference to the multidaylight presses of the known type.
Within this aim, an object of the invention is to provide a press which is structurally simple and in which it is possible to adjust precisely the pressure applied to a flat element inserted in one daylight independently of the position of said daylight and therefore of the weight of the overlying platens and flat elements.
Still another object of the invention is to provide a press which allows to operate, in a same work cycle, with pressures which differ among daylights.
Another object of the invention is to provide a press which can work without problems on flat elements such as panels or the like having different thicknesses.
This aim and these and other objects, which will become better apparent hereinafter, are achieved by a multidaylight press for bonding flat elements, as defined in claim 1.
Further characteristics and advantages of the invention will become better apparent from the description of a preferred but not exclusive embodiment of the press according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a schematic perspective view of the press according to the invention in an operating condition;
Figure 2 is a schematic front elevation view of the press in the same operating condition shown in Figure 1;
Figure 3 is a side elevation view of the press in the same operating condition shown in the preceding figures;
Figure 4 is an enlarged-scale view of a detail of Figure 1;
Figures 5 to 13 are schematic front elevation views of the operation of the press according to the invention.

With reference to the figures, the press according to the invention, generally designated by the reference numeral 1, comprises a framework 2 which supports: a fixed platen 3, a movable platen 4 which is parallel to the fixed platen 3 and can move on command toward and away from the fixed platen 3, and at least one intermediate platen 5, which is arranged between the fixed platen 3 and the movable platen 4 and is parallel thereto.
The at least one intermediate platen 5 divides the space between the fixed platen 3 and the movable platen 4 into at least two daylights 6, which are adapted to accommodate the flat elements 10 to be pressed.
In the embodiment shown, there are seven intermediate platens 5, which divide the space comprised between the fixed platen 3 and the movable platen 4 into eight daylights 6, without altering the fact that the number of intermediate platens 5 and consequently the number of daylights 6 can vary according to the requirements.
The press according to the invention comprises first connection means 7, which are rigidly coupled to the framework 2, and second connection means 8, which are rigidly coupled to the movable platen 4. Each intermediate platen 5 is provided with locking means 9, which can engage on command the first connection means 7 in order to rigidly couple the corresponding intermediate platen 5 to the framework 2 or the second connection means 8, in order to rigidly couple the corresponding intermediate platen 5 to the movable platen 4, or can be disengaged both from the first connection means 7 and from the second connection means 8, as will become better apparent hereinafter.
The press according to the invention further comprises presser means 11 for pressing, with a preset pressure, the movable platen 4 toward the fixed platen 3 in order to press the flat elements 10 inserted in the daylights 6.
The fixed platen 3, the movable platen 4 and the intermediate platens 5 preferably have a rectangular plan shape, are arranged horizontally and the movable platen 4 is arranged above the fixed platen 3.
Advantageously, the press according to the invention comprises means for compensating for at least part of the weight of the movable platen 4 and of the intermediate platens 5 which bear on the flat elements 10 inserted in the daylights 6.
The first connection means 7 comprise fixed bars 13, which lie at right angles to the planes of arrangement of the platens 3, 4, 5, i.e., vertically, and are fixed to the fixed platen 3 and are thus rigidly coupled to the framework 2. Preferably, there are four fixed bars 13: two are fixed to one longer side of the fixed platen 3 and two are fixed to the opposite longer side of the fixed platen 3. The fixed bars 13 rise vertically and laterally with respect to the longer sides of the intermediate platens 5 and of the movable platen 4 and are fixed at their upper end to the framework 2.
The locking means comprise first clamps 14, which are mounted on the intermediate platens 5 so as to face, with their arms, two opposite faces of the fixed bars 13. Said first clamps 14 are preferably hydraulically operated and can engage or disengage on command the fixed bars 13.
The second connection means 8 comprise movable bars 15, which are connected to the movable platen 4. The movable bars 15 are arranged laterally with respect to the platens 3, 4, 5 and lie at right angles to the platens 3, 4, 5. More particularly, in this case also, there are four movable bars 15: two are fixed to a longer side of the movable platen 4 and two are fixed to the opposite longer side of the movable platen 4. The movable bars 15 rise vertically and laterally with respect to the longer sides of the intermediate platens 5 and cross, so that they can slide vertically, appropriately provided guides 16 connected to the fixed platen 3.
The length of the movable bars 15 is substantially equal to at least the sum of the thicknesses of the platens 3, 4 and 5 and of the thicknesses of the flat elements 10 to be inserted in the daylights 6, plus the play required to insert a flat element 10 in the corresponding daylight 6.
The locking means comprise second clamps 17, which are mounted on the intermediate platens 5 so that their arms face two opposite faces of the movable bars 15. Said second clamps 17 are preferably hydraulically operated and can engage or disengage on command the movable bars 15.
The presser means 11 comprise hydraulic power cylinders 18, preferably of the single-acting type, which are mounted on the framework 2 and act with the stem of their piston, which is oriented at right angles to the platens 3, 4, 5, i.e., vertically, on the movable platen 4.
The press according to the invention comprises means 19 for opening and closing the daylights 6. Said opening-closing means 19 are adapted to produce a movement of the movable platen 4, together with the movable bars 15 and the intermediate platen or platens 5 rigidly coupled to the movable bars 15 by means of the second clamps 17, toward or away from the fixed platen 3 and the intermediate platen or platens 5 rigidly coupled to the fixed bars 13 by means of the first clamps 14 for closing or opening the daylight 6 delimited on one side by the fixed platen 3 or by an intermediate platen 5 rigidly coupled thereto and on the other side by the movable platen 4 or by an intermediate platen 5 which is rigidly coupled thereto.
The opening-closure means 19 comprise hydraulic opening-closure cylinders 20 of the double-acting type which are interposed between the framework 2 and the movable platen 4.
The means for compensating the weight of the movable platen 4 and of the intermediate platens 5 rigidly coupled thereto comprise means, constituted by components provided in the hydraulic supply circuit of the hydraulic opening-closure cylinders 20, for feeding a pressurized liquid into the hydraulic opening-closure cylinders 20 so as to apply, by means of said hydraulic opening-closure cylinders 20, to the movable platen 4 and to the intermediate platen or platens 5 rigidly coupled thereto by way of the second clamps 17, an upward force which is correlated to the weight to be compensated, as will become better apparent hereinafter.
Although the press according to the invention, with the components described above, is already capable of operating correctly, achieving the intended aim and objects, in order to allow to load and unload the flat elements 10 to be pressed at a same height level, as provided with the use of loading and/or unloading devices, for example of the translating belt type currently commercially available, the framework 2 is preferably supported, so that it can slide vertically, by a supporting structure 21, and there are movement means 22 which can be actuated in order to produce the vertical movement of the framework 2 in order to arrange the daylight 6 to be loaded or unloaded at a preset level, which corresponds to the working level of the loading and/or unloading device.
The movement means 22 comprise hydraulic movement cylinders 23 of the single-acting type, which are interposed between the supporting structure 21 and the framework 2.
The translational motion of the framework 2 with respect to the supporting structure 21 can be controlled by means of sensors or detectors of a known type, not shown for the sake of simplicity, so as to ensure the positioning of the daylight 6 to be loaded or unloaded at the selected height level with high precision.
The coupling between the framework 2 and the supporting structure 21 can be performed by means of appropriately provided sliding blocks 24 and the parallel configuration in the translational motion of the framework 2 with respect to the supporting structure 21 can be ensured by providing vertical racks 25 which are fixed to the framework 2 and mesh with pinions 26 which are connected to the supporting structure 21.
The press can further comprise, in a per se known manner, means for heating the different platens with corresponding heating manifolds 27.
Operation of the press according to the invention is as follows.
For the sake of greater clarity, the intermediate platens 5 of the press are designated, starting from the top, also with the reference letters A, B, C, D, E, F, G in addition to the reference numeral 5 which is used equally for all of said platens in Figure 2 and in Figures 5 to 13.
A possible operating cycle of the press is described hereafter in order to clarify the concept on which the invention is based, without altering the fact that in practical operation said cycle can be changed according to requirements.
For the sake of greater clarity, in Figures 5 to 13 the clamps 14, 17, when activated, have been shown in broken lines.
Assuming that the cycle begins when the machine is empty, the first clamps 14 are disengaged from the fixed bars 13 and the second clamps 17 are disengaged from the movable bars 15. In this manner, the platens 3, 4, 5 are fully packed together (Figure 5). In this condition, the hydraulic power cylinders 18 are actuated and press between them the platens 3, 4, 5 and, once the intended pressure has been reached, the first clamps 14 arranged on the intermediate platens A-G are activated and thus the hydraulic power cylinders 18 are deactivated (Figure 6). However, the pressure is in practice canceled out only in the daylight 6 located between the movable platen 4 and the intermediate platen A but remains in all the underlying daylights 6, which are kept locked by the first clamps 14 closed on the fixed bars 13 which are rigidly coupled to the framework 2.
A height reader, such as for example an encoder, an optical ruler or another known type of detection system, interposed for example between the movable platen 4 and the framework 2, stores in this condition a zero level.
The hydraulic opening-closure cylinders 20 are then actuated and lift the movable platen 4 and, with it, the movable bars 15 which are rigidly coupled thereto and slide freely within the second clamps 17. As a consequence of this lifting, the first daylight 6, delimited in an upward region by the movable platen 4 and in a downward region by the intermediate platen A, is opened by an extent which is controlled by means of the height reader starting from the zero level, such as to allow the insertion in the first daylight 6 of the device for loading a flat element 10 to be pressed (Figure 7).
The entire framework 2 is simultaneously made to slide within the supporting structure 21 by means of the hydraulic movement cylinders 23, and the intermediate platen A, which is locked to the underlying platens, is moved to the loading height of the loading device.
A loading sequence is preferred which begins with the first daylight 6 located at the upper end of the plurality of daylights 6 and reaches progressively the daylight 6 arranged at the lower end, since it is convenient to perform positioning of the framework 2 in a rising direction, since the incidence of the effect caused by the inertia of its weight is negligible during movements; moreover, subsequent repositioning, once the load has been completed, can be performed quickly by gravity, controlling carefully only the final slowing step.
With the machine raised and the first daylight 6 open, a flat element 10 is inserted in the open daylight 6 (Figure 8) by using for example a device of the translating belt type described earlier, and then said daylight 6 is closed by actuating, in the opposite direction with respect to the preceding direction, the hydraulic opening-closure cylinders 20.
In this step, as well as in the steps for closing the underlying daylights 6, the action of the means for compensating at least part of the weight of the movable platen 4 and of the intermediate platens 5 which bear on the flat elements 10 inserted in the daylights 6 is utilized. These compensation means comprise a maximum-pressure valve which is arranged on the branch of the hydraulic circuit that feeds the hydraulic opening-closure cylinders 20 in the opening direction, i.e., the chamber formed in said cylinders and arranged on one side of the corresponding piston. This maximum-pressure valve, which performs a balancing function and is referenced hereinafter as a balancing valve, is set to the pressure required to bear the weight of the movable platen 4 and of the intermediate platens 5 as a whole. This pressure is constantly maintained in the circuit even during the step for closure of the daylights 6, which is achieved by applying an opposite pressure to the branch of the circuit that supplies the chamber of the cylinders that is arranged on the opposite side of the corresponding piston. In this manner, the pressure is increased on the side of piston that is fed through the balancing valve until the set value of said valve is exceeded, said valve discharging oil from the circuit, allowing the descent of the platen while keeping constant at all times the pressure inside the circuit.
This operation is simplified by the placement of the hydraulic opening-closure cylinders 20, which is performed so that the stem of the piston passes through the chamber of said hydraulic cylinders which is fed to open the daylights while the chamber arranged on the opposite side of the piston, which is fed to open the daylights 6, is not affected by the stem of the piston. The difference in cross-section between said two chambers allows to obtain a higher thrust for descent, using a pressure which is lower than the pressure that occurs in the ascent circuit.
When the movable platen 4 moves, as detected by the height reader, the thrust pressure is stabilized and kept constant by an electronic pressure regulator which acts on the circuit. The weight of the movable platen 4 in this manner is practically nonexistent; minimal pressure values, which exceed the balance condition, are in fact sufficient to achieve its downward movement.
Once the step for closing the first daylight 6 is completed, with the movable platen 4 in contact with the inserted flat element 10, the daylight 6 is pressurized by actuating the hydraulic power cylinders 18 which act on the movable platen 4; then, once the selected pressure value has been reached, the second clamps 17 (Figure 9) arranged on the intermediate platen A are activated and the first clamps 14 arranged on said intermediate platen A are deactivated. At this point, the pressure in the hydraulic power cylinders 18 is canceled and the height reader is reset; then the daylight 6 is opened, said daylight being delimited in an upward region by the intermediate platen A and in a downward region by the intermediate platen B, while the framework 2 is moved with the intermediate platen B to the loading height.
Owing to the fact that the first clamps 14 of the intermediate platen A, which kept it compacted with the underlying platens with the framework 2, have been deactivated, the intermediate platen A, rigidly coupled to the movable bars 15 connected to the movable platen 4 by the activation of the second clamps 17 arranged thereon, is raised together with said movable platen 4, keeping closed and under pressure the overlying daylight 6 in which the previously loaded flat element 10 is inserted, until a space is again created, between the intermediate platen A and the intermediate platen B, which is sufficient to allow the insertion of the loading device (Figure 10).
During all the steps of the opening of the daylights 6, the balancing valve cited above is bypassed since it would not be possible, once the last daylight 6 arranged at the lower end of the plurality of daylights 6 has been loaded, to open said daylight and lift the platens; this operation in fact requires a thrust which is greater than the balancing pressure, equal to the weight of said platens.
With this refinement, the excess pressure, however, does not affect at all the flat elements 10 being processed, since the platens between which said flat elements 10 are inserted are locked with the second clamps 17 to the movable bars 15 which are rigidly coupled to the movable platen 4 and consequently are moved without being subjected to any stress.
The daylight 6 arranged between the intermediate platen A and the underlying intermediate platen B is loaded and the operation for closing the daylight is repeated as described earlier (Figures 11 and 12).
The weight managed in descent is doubled, but it is still perfectly compensated since only the thrust required to generate the discharge of the balancing valve changes, and does so automatically, said valve being set so as to bear the weight of all the platens: the more said platens increase, the more the closure thrust pressure decreases, but the weight applied by the plurality of overlying platens to the underlying daylight 6 remains constant and practically nil.
Operation continues as already described earlier, i.e., after the required pressure has been reached on the inserted flat element 10 by means of the actuation of the hydraulic power cylinders 18, the second clamps 17 of the intermediate platen B are activated, rigidly coupling it to the overlying platens, and the first clamps 14 are deactivated, disengaging it from the underlying platens. In this manner it is possible to raise the platens which are kept under pressure and locked on the movable bars 15 which are connected to the movable platen 4 and open the daylight 6 delimited in an upward region by the intermediate platen B and in a downward region by the intermediate platen C (Figure 13), and so forth up to the daylight 6 arranged at the lower end of the plurality of daylights 6.
Once loading of the press has been completed, the framework 2 is again made to descend with the daylight 6, arranged at the upper end of the plurality of daylights 6, i.e., delimited by the movable platen 4 and by the intermediate platen A, to the loading level, from which the sequence for opening and closing the daylights 6 is resumed, unloading the first flat element 10 loaded previously, which has remained under pressure for the time required for the drying of the adhesive.
In practice it has been found that the press according to the invention fully achieves the intended aim, since it is structurally simple and solves the problem of the weight of the platens that bears on the flat elements inserted in the daylights, allowing to process without problems flat elements which have limited mechanical strength.
An additional advantage of the press according to the invention is that it allows to work, in a same loading cycle, with different pressures from one daylight to another, since the platens that delimit a daylight are kept locked and are not affected by the pressure applied to pressurize flat elements inserted in other daylights.
Yet another advantage of the press according to the invention is that it is possible to process flat elements with thicknesses which can vary over a very wide range and may be different from one daylight to another, optionally renouncing, in the case of substantially thick flat elements, to the use of some daylights.
The press thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may further be replaced with other technically equivalent elements.
In practice, the materials used, as well as the dimensions, may be any according to requirements and to the state of the art.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

A multidaylight press for bonding flat elements, particularly for the hot or cold bonding of veneers, laminates or the like on sandwich, chipwood, honeycomb panels or the like and for producing plywoods, chipwood panels and the like, comprising a framework (2) which supports: a fixed platen (3), a movable platen (4) which is parallel to said fixed platen (3) and can move on command toward or away from said fixed platen (3), and at least one intermediate platen (5), which is arranged between said fixed platen (3) and said movable platen (4) and is parallel thereto; said at least one intermediate platen (5) dividing the space between said fixed platen (3) and said movable platen (4) into at least two daylights (6), which are adapted to accommodate the flat elements (10) to be pressed; there being provided first connection means (7), which are rigidly coupled to said framework (2), and second connection means (8), which are rigidly coupled to said movable platen (4); said intermediate platen (5) being provided with locking means (9) which can engage on command said first connection means (7) in order to rigidly couple said intermediate platen (5) to said framework (2) or said second connection means (8) in order to rigidly couple said intermediate platen (5) to said movable platen (4), or can disengage from both said first connection means (7) and said second connection means (8); presser means (11) being further provided in order to press, with a preset pressure, said movable platen (4) toward said fixed platen (3) in order to press the flat elements (10) inserted in said daylights (6), characterized in that said first connection means (7) comprise fixed bars (13) which are arranged laterally to said platens (3, 4, 5) and lie at right angles to the planes of arrangement of said platens; said locking means (9) comprising first clamps (14), which are arranged on said at least one intermediate platen (5) and can engage on command said fixed bars (13), and in that said second connection means (8) comprise movable bars (15), which are connected to said movable platen (4) and are arranged laterally to said platens (3, 4, 5) and lie at right angles to the planes of arrangement of said platens; said locking means (9) comprising second clamps (17) which are arranged on said at least one intermediate platen (5) and can engage on command said movable bars (15).
The multidaylight press according to claim 1, characterized in that said fixed platen (3), said movable platen (4) and said at least one intermediate platen (5) are arranged horizontally with respect to the ground whereon said framework (2) rests.
The multidaylight press according to claims 1 and 2, characterized in that said movable platen (4) is arranged above said fixed platen (3).
The multidaylight press according to one or more of the preceding claims, characterized in that it comprises means for compensating at least part of the weight of said movable platen (4) and of said at least one intermediate platen (5) which bears on the flat elements (10) inserted in said daylights (6).
The multidaylight press according to one or more of the preceding claims, characterized in that said presser means (11) comprise hydraulic power cylinders (18) which are mounted on said framework (2) and act with the stem of their piston, oriented at right angles to said platens (3, 4, 5), on said movable platen (4).
The multidaylight press according to one or more of the preceding claims, characterized in that it comprises a plurality of intermediate platens (5) which divide the space between said fixed platen (3) and said movable platen (4) into a plurality of daylights (6) which are adapted to accommodate the flat elements to be pressed.
The multidaylight press according to one or more of the preceding claims, characterized in that it comprises means (19) for opening and closing said daylights (6); said opening-closing means (19) being adapted to produce a movement of said movable platen (4), together with said movable bars (15) and the intermediate platen or platens (5) coupled to said movable bars (15) by means of said second clamps (17), toward or away from said fixed platen (3) and the intermediate platen or platens (5) rigidly coupled to said fixed bars (13) by means of said first clamps (14) for closing or opening the daylight (6) delimited on one side by said fixed platen (3) or by an intermediate platen (5) which is rigidly coupled thereto and on the other side by said movable platen (4) or by an intermediate platen (5) which is rigidly coupled thereto.
The multidaylight press according to one or more of the preceding claims, characterized in that said opening-closure means (19) comprise hydraulic opening-closure cylinders (20) which are interposed between said framework (2) and said movable platen (4).
The multidaylight press according to one or more of the preceding claims, characterized in that said compensation means comprise means for introducing a pressurized fluid into said hydraulic opening-closure cylinders (20) for applying, by means of said hydraulic opening-closure cylinders (20), to said movable platen (4) and to the intermediate platen or platens (5) rigidly coupled thereto by means of said second clamps (17) an upward force which is correlated to the weight to be compensated.
The multidaylight press according to one or more of the preceding claims, characterized in that said framework (2) is supported, so that it can slide along a vertical direction, with respect to the ground, by a supporting structure (21), means (22) being provided for moving said framework (2) vertically with respect to said supporting structure (21) in order to position one of the daylights (6) at a preset height.
The multidaylight press according to one or more of the preceding claims, characterized in that said movement means (22) comprise hydraulic movement cylinders (23) which are interposed between said supporting structure (21) and said framework (2) and are oriented so that their axes are vertical with respect to the ground.
The multidaylight press according to one or more of the preceding claims, characterized in that said hydraulic power cylinders (23) are constituted by single-acting cylinders.
The multidaylight press according to one or more of the preceding claims, characterized in that said hydraulic opening-closure cylinders (20) are constituted by double-acting hydraulic cylinders.
The multidaylight press according to one or more of the preceding claims, characterized in that said hydraulic movement cylinders (23) are constituted by single-acting hydraulic cylinders (23).
The multidaylight press according to one or more of the preceding claims, characterized in that said compensation means comprise a maximum-pressure valve which is arranged on the branch of the hydraulic circuit that supplies said hydraulic opening-closure cylinders (20) in the direction for opening the daylights (6), i.e., the chamber of said hydraulic opening-closure cylinders which is arranged on one side of the corresponding piston; said maximum-pressure valve being set to the pressure required to bear the weight of said movable platen (4) and of said intermediate platens (5) as a whole; said pressure being maintained constantly in the hydraulic circuit even during the closure of the daylights (6) performed by applying an opposite pressure to the branch of the hydraulic circuit that feeds said hydraulic opening-closure cylinders (20) in the direction for closing the daylights (6), i.e., the chamber of said hydraulic opening-closure cylinders (20) which is arranged on the opposite side of the corresponding piston.
The multidaylight press according to one or more of the preceding claims, characterized in that said hydraulic opening-closure cylinders (20) are arranged so that the stem of the piston passes through the chamber of said hydraulic opening-closure cylinders (20) which is fed to open the daylights (6).