US3498349A - Press for gluing an endless mat of piled veneers - Google Patents

Description

PRESS FOR GLUING AN ENDLESS MAT OF FILED VENEERS Filed Oct. 24, 1967 10 w/owooooooo/f/goxk i: amour/mucus 9 ,2 7 OPERAT/N' I q 2 CONVEYOR WM/W/QV/Q/W/V/W A /AW/ United States Patent 3,498,349 PRESS FOR GLUING AN ENDLESS MAT OF PILED VENEERS Olli Heikinheimo, Helsinki, Finland, assignor to Plan-Sell Oy, Helsinki, Finland, a corporation of Finland Filed Oct. 24, 1967, Ser. No. 677,532 Claims priority, application Finland, Oct. 21, 1966, 2,792/ 66 Int. Cl. B27d 3/04 US. Cl. 144--281 4 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a press for gluing an endless mat of piled veneers, comprising heated press platens forming at least one pressure space, means for discontinuously feeding said mat of veneers into said pressure space, and, after a pressing step, out of the same, said press platens having on the side adjacent to the incoming mat of veneers extensions consisting at least on their veneer engaging surfaces of a material having poor heat conducting properties.

BACKGROUND OF THE INVENTION Gluing of plywood is at present usually carried out in multiple hot presses, piles of suitable thickness consisting of dry and glued veneers being fed into their pressing spaces either in a pre-pressed state or otherwise, whereafter a pressing step, emptying of the press, and its filling with fresh piles take place as repeated steps. Experiments have further been carried out for gluing an endless mat of piled veneers as a discontinuous operation in a hot press, but these experiments have not been successful. The reason for this poor result has been the circumstance, that outside the edges of the hot press platens, in the pile at the incoming side, the hot water vapours from the press will condense in the glue joints thus causing the glue to be diluted and to be absorbed into the wood material, so that the glue joints at this point, when they subsequently reach the hot press, will no longer bind the glued and dry veneers together. In addition the heating efiect of the hot press platens extends some distance toward the incoming side, so that the glue for this reason tends to bind prematurely without pressure.

It has further been suggested to glue an endless piled mat in a platen press with a single pressure space, having a reciprocating movement. In this case the press platens start moving from their initial position in the travel direction of the piled mat with a velocity equal to that of the mat while pressing the mat therebetween, to open at the end of their travel and then commence their return movement. This method has however been successful only in the case of piled mats of three layers, particularly in the case of slab boards. In the gluing of a multilayered veneer pile the above mentioned process is too fast for the glue joints in the middle portion of the pile to have time to be sufiiciently heated to provide a strong glue joint. If the process on the other hand is slowed down enough for all the glue joints to have time to be sufficiently heated, the above described problems of water condensation and undesirable heat effect will again present themselves at the incoming side outside the edge of the press.

SUMMARY OF THE INVENTION The above mentioned drawbacks have been eliminated in the hot press according to the invention which permits discontinuous gluing of an endless multi-layered mat of piled veneers without causing the formation of weaker or completely unglued areas in the glue joints. The press according to the invention comprises press platens form- 3,498,349 Patented Mar. 3, 1970 istics. Said pre-pressing plates are adapted to be pressed against the mat of piled veneers with a pressure not higher than the pressure exerted by the actual press platens, and are so dimensioned that viewed toward the incoming side of the mat of piled veneers they cover at least a substantial portion of the area over which the effect of the hot press platens extends. According to a preferred embodiment of the invention the pre-pressing plates consist of wood but it is to be understood that the invention is not restricted to that embodiment. Thus other materials with low heat conducting characteristics capable of resisting the temperature involved can be employed.

It is also not necessary that the pre-pressing plates en tirely consist of poorly heat conducting material, it being sufiicient that their surfaces engaging the piled mat are of such material. The pressure exerted by the pre-pressing plates according to the invention must, as already stated, not exceed that exerted by the actual press platens, and it must be at least high enough to prevent the condensation of the hot water vapour from the press, so as not to permit the condensed water to dilute the glue in the glue joints outside the actual press to cause excessive absorption of the glue into the veneers. Simultaneously the piled mat is under pressure at the area subjected to the effect of the hot press platens. Thus is achieved a continuous glue joint without discontinuities in the mat of piled veneers.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing FIG. 1 shows schematically a hot press for discontinuous pressing of endless mats of piled veneers provided with press platen extensions in accordance with the invention on the feeding side' of the press. FIG. 2 shows a fragmentary view of a modified embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawing 1 designates a hot press having a base 2, a lower press platen 3, an upper press platen 4, a top 5 and for example hydraulic means 6 for the closing and opening of the upper press platen 4. The lower and upper press platens are provided with coils 7 and 8 respectively for a heating medium. On one side of the press 1 there is provided means for feeding a length of a mat of piled veneers 10 discontinuously in between press platens 3 and 4, and upon completion of a press cycle a corresponding length forward out of the press. Said means is here shown as an endless belt conveyor 9. Starting and stopping means for such a conveyor belt are old and well known in the art, and the particular structure of the mechanism for intermittently advancing the mat is not part of the present invention. It will be obvious to those skilled in the art that the proper selection of time relays, micro-switches etc., can easily be made to produce synchronized movements of the press and feeding means so that the mat is advanced while the press is open, and the belt stops when the press is about to close. On the opposite side of the press 1 there is shown a roller conveyor 11 for supporting the outcoming veneer and carrying it forward.

In accordance with the invention press platens 3 and 4 are on the side facing the feeding conveyor 9 provided with extensions 12 and 13 respectively consisting of a material having poor heat conducting properties. In the embodiment of FIG. l'said extensions are shown as solid pieces of wood. In FIG. 2 there. is shown a modified emmodiment where the press platen extensions comprise a metallic support 14 and 15 respectively and a surface layers 16 and 17 respectively of a material having poor heat conducting properties, advantageously wood. Between the supports 14 and 15 and the lower and upper press platens 3 and 4 respectively there is provided a layer 18 and 19 respectively of heat insulating material.

The invention is further illustrated by the following examples.

Example 1 Discontinuous pressing was carried out in a conventional platen press employing three different mats of piled veneers, A, -B, and C, and conventional glue application, pressure and temperature. The dimensions of the experimental boards were 50 cms. by 160 cms. and the board A had 3 veneer layers, the board B had 5 layers while the board C had 7 veneer layers. The pressing times were 4 and 3 minutes for board A, 6 and 5 minutes for board B, and 7 and 6 minutes for board C. After the pressure periods the joints were examined at the areas having been situated outside the press platens before the actual hot pressing of these areas, the findings of the examinations being as follows- Board A: Drying in one joint and drying in the outer edge and absorption in the middle of the other joint (water vapour penetrated the joint), with a pressing time of 4 minutes. Drying at the outer edge and absorption at the inner edge of one joint and the reverse in the other joint with a pressing time of 3 minutes.

Boards B and C: Water vapour penetrated outside each pressure area and caused complete absorption in the inner joints. The boards were bulging at the middle.

The experiments demonstrate that acceptable though not good results can be obtained with the three layer boards while the boards with more layers present unbound areas in the joints.

Example 2 Discontinuous pressing was carried out with veneer piles of seven layers in similar conditions as in Example 1, employing, however, as extensions to the actual press platens, metallic cooling plates measuring about 10 cms. in the direction of feeding, between which the pile of veneers was tightly pressed adjacent the press platens. With board D the cooling plates were used without water circulation. With board E water was circulated at a temperature of 40 C. With board F water was circulated in the cooling plates at a temperature of 60 C. The results were as follows 'Board D: Moisture condensed on the cooling plates moistening the adjacent surface veneers, in addition to which obvious absorption could be observed in the pile at the area of the cooling plates.

Board E: A distinctive boundary between the press platen and the cooling plates could be observed in the resulting board. At the area of cooling plates, particularly at the middle portion thereof, obvious glue absorption could be observed. Abundant water condensed on the cooling plates, to be absorbed into the surface veneers.

Board F: The boundary between the press platens and the cooling plates was clearly observable in the resulting board. At the edges of the board the glue was dried and the middle portion showed absorption.

The experiments demonstrate that by utilization of cooling plates as extensions to the press platens the gluing result can somewhat be improved with respect to discontinuous pressing without cooling plates. Satisfactory results can however not be obtained by this method.

Example 3 Discontinuous pressing operations were carried out using the procedure of Example 2 with the exception that between the cooling plates and the'pile of veneer layers were employed consisting of thin pine board and measuring about 10 cms. in the feeding direction. The resulting board was good and the boundary between the actual press platens and the cooling plates could scarcely be, detected. No moisture condensation occurred at the surfaces of the cooling plates. Moisture had however penetrated the middle glue joint resulting in absorptionthere.

Example 4 With a seven layered pile of veneers discontinuous pressing was carried out in similar conditions as in Example 1 with the exception that as extensions to the actual press platens on the feeding side pre-pressingplates were provided, consisting of pine wood and measuring about 6 cms. in the feeding direction, the pile of veneer being pressed tightly by means of the pre-pressing adjacent the press platens. In the resulting board the glue joints were good and no boundary at all could be observed at the site of the boundary surface between hot and cold.

The above described comparative tests show that the hot press according to the invention permits discontinuous gluing of an endless mat of piled veneers with good results.

The invention is of course not restricted to the gluing of an endless mat of piled veneers but is as well applicable to the gluing of slab board, slat board, particle board, and fibre board produced by the dry method.

I claim:

1. A press for gluing an endless mat of piled veneers, comprising press platens forming at least one pressure space, platen heating means and drive means for the press, means at one side of the platens for feeding a mat of piled veneers discontinuously into said pressure space, and after a pressing step, out of the same, pro-pressing plates being provided at the feeding side as extensions adjacent to the press platens, said pre-pressing plates consisting at least at their surfaces, of a materal having poor heat conducting characteristics.

2. A press as in claim 1, said pre-pressing plates extending in the direction from which the mat is fed substantially as far as the heating effect of said heating means extends.

3. A press as in claim 1, said pro-pressing plates being essentially comprised of wood.

4. A press as in claim 1, said pre-pressing plates comprising a metallic support and a veneer engaging surface layer of wood.

References Cited UNITED STATES PATENTS 2,532,419 12/1950 Payzant 144-281 3,243,054 3/1966 Peterson 14428l X 3,321,353 5/1967 Zelnick 156-583 X FOREIGN PATENTS 492,920 4/ 1954 Italy.

GIL WEIDENFELD, Primary Examiner US. Cl. X.R. l0093; 156583

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