FR2463668A1 - METHOD AND APPARATUS FOR DRYING PLASTER SHEET FOR PLATE BACK - Google Patents

Abstract

THE INVENTION CONCERNS THE WOODEN INDUSTRY. PROCESS FOR DRYING A VENEERING SHEET3, INCLUDING SOFTENING OPERATIONS WITH AT LEAST ONE ROLLER 15, FORMING AN ANVLUM AND ONE SOFTENING ROLLER16, BY FORMING NUMEROUS SMALL CRACKS IN THE SHEET TO INCREASE THE INTERVAL OF ELASTICITY DIRECTION SENSITIVELY PERPENDICULAR TO THE GRAIN, AND COMPRESSION OPERATIONS DURING DRYING. APPLICATION TO THE MANUFACTURING OF PLYWOOD.

Description

1 2463668

  The invention relates to a method and apparatus for drying

  a plywood veneer sheet and more particularly

  Proudly a drying process that minimizes or virtually eliminates the cracking of the resulting leaf

usually such treatment.

  The known processes for manufacturing plywood

  carry out a drying operation of the veneer sheets, in order to

  from a dryer. But once dried, the veneer

  suffer from concentric cracks, irregularly localized

  which makes their quality poor, even if it was very good before drying. The cracked portions of the leaves

  should be cut and rejected, which is a waste

  and reduces the production yield of these leaves.

  To solve this problem, it was attempted, but only in a minority portion of this industry, to first form a veneer sheet softened by a large number of slits

  of short length, before submitting it to the treatment of

  chage (hereinafter referred to as "process Y"). com-

  in relation to the process without softening (hereinafter

  as "process X"), the method Y makes it possible to decrease in a certain

  the tendency of concentric crackling veneers during drying, and has so far

  acceptable results. However, this technique is not fully

  satisfactorily to the extent that it does not allow the

  total reduction of cracks attributed to the treatment of

  chage. It appears that the plating cracks due to drying and commonly observed in the usual processes result from the contraction of the sheet when subjected to this treatment. When the conveying elements in a dryer include lower and upper nets, in a net dryer for example, they hinder the contraction of a sheet of

  plating, which should be done gradually during the

  chage, and promote the formation of tensions within the leaf. The leaf breaks or creaks in areas of higher concentration of tension. In view of this problem,

2. 2463668

  the relaxation process Y is intended to prevent cracking

  by decentralization of tensions in the sheet of pla-

  cage, by means of a large number of short slits, and thus reduce the tendency to burst as a whole. During the tests to determine the advantage of the asplasticized veneer sheets, it is found that the elasticity interval in which the sheet elongates without cracking, when stretched in a direction perpendicular to its grain, is bigger for them

  leaves softened only for unstretched leaves.

  The present invention aims to improve the quality of

  and yield of plywood veneer sheets by preventing or minimizing drying cracks. The method of the invention makes it possible to solve the problems mentioned above, originating from the drying operation in industry

  plywood, which suffers from a shortage of

  in logs. The subject of the invention is also a function

  automatic operation of the drying operation and other

  subsequent processes, giving a favorable elasticity to the

veneer sheets.

  The invention will be better understood on reading the

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION In these drawings Fig. 1 is a comparative diagram of the invention and of the prior art;

  Figures 2 and 3 represent the device for

  fold, respectively in plan and face;

  Figures 4 and 5 are perspective views of

  the veneers softened; Figures 6 are large scale views of slits formed on other softened veneer sheets; Figure 7 shows a preferred embodiment of the invention;

  Figures 8 to 10 represent another embodiment of

  the invention, respectively from the side, partially from the front and partially in section; Fig. 11 is a partially cutaway plan view of Fig. 3;

  Fig. 12 is a side view of the relief device

  wrinkling of Figure II; Fig. 13 is a partial side view on a large scale of the softening device; Fig. 14 shows a variant of the embodiment of Fig. 3; Fig. 15 is a side view of another alternative. Fig. 16 is a side view of another arrangement of the device of Fig. 15; Fig. 17 is a large scale partial side view showing modified extensible elements; Figs. 18 (A) to 18 (C) - are sectional views taken along the line XVIII-XVIII of Fig. 17, showing various examples of the extensible members, and Figs. 19 and 20 are side views of a other

variant of Figure 3.

  FIG. 1 represents a comparative diagram of a process

  base of the invention. In this figure, the lines are

  relate, by way of comparison, to known drying processes X and Y, and process Z of the present invention. The reference index 100 on the ordinate, indicates a length / fiber of a veneer sheet, freshly cut in a round, in a log, in a usual manner, in a direction perpendicular to the grain (the veneer sheet having cracks on the back, but not in front, and no secondary cracks). The method X comprises the only drying operation P, the method Y comprises a softening operation Q and a drying operation P,

  and the method Z of the invention comprises a softening operation

  Q, a compression operation R and a sewing operation

  In these processes, the reference A denotes an untreated veneer sheet, having only back cracks, the reference B denotes a relaxed veneer sheet having many short slits, the reference C denotes a compressed veneer sheet. and reference D denotes a dried veneer sheet. The length of the leaves varies, as shown

  Figure 1, when treated according to the three different methods

  X, Y and Z. It is of paramount importance for the com-

  grasping the invention, to determine whether the variations of

4 2463668

  length can occur within the range of elasticity for veneer sheets. For example, according to the known method X, a veneer sheet having undergone the drying operation tends to shrink by 5% (average value) despite an elasticity range of practically 1% of the sheet A, measured experimentally. In other words, the sheet A tends to shrink by 4% beyond the yield range and, as such, is quite susceptible to cracking during drying. According to the other known method Y, the veneer sheet A is softened by a large number of short slits before drying, to obtain an expansion ratio of 2%, while

  the elasticity range then increased to almost 3.5%.

  As a result, the subsequent drying operation P

  cir A 5% leaf, which exceeds the elasticity range

  1.5%. This is less serious than in the X method, but

  however, the possibility of cracks. It therefore appears that the known methods do not allow the prevention of the possibility of cracking of the veneer sheets due to drying and that cracks always appear when the sheets are firmly retained as by attachment at their opposite ends, perpendicularly to the grain. From this point of view, the technique used to reduce the carry-over load on

  veneer was only the technique used to prevent

  expensive cracks during drying, in the various types of known dryers. This can be inferred from the fact that the most commonly used net driers, roller dryers and other dryers are commonly hot air circulating type, in which hot air is blown on

  veneer sheets to avoid their strong stress.

  The Z method of the invention comprises a compression R between the Q softening and R drying operations as shown in FIG. 1. More particularly, in this example, the dimensions of the veneer sheet A increase by stretching in the softening operation Q, decrease by compression in the operation R to give a compressed sheet C, which is then subjected to the drying operation P. The veneer

  which retains an elasticity range of 3.5%, undergoes a com-

  pressure of 2%, then is subjected to drying, at which point it begins to shrink. Compression in the sheet

2463668

  is then released, when 2 0 of the contraction of 5% are

  achieved, while the remaining 3 9 contraction are

  thought by the potential area of elasticity of 3.5% conferred on

  the veneer sheet in the softening operation. The pro-

  In this way, Z can virtually eliminate the possibility of cracking during drying by restricting contraction within the range of elasticity. Cracking can be avoided even if the dryer exerts a relatively high stress load on the veneer. In addition, the method Z of the invention opens the way for the practical use of dryers of the type putting the veneer sheets in direct contact with the heated plates and drying them effectively.

  with a relatively high stress force.

  This prevention of cracks obtained according to the

  vention, comes from the effective combination of softening and compression, with drying, in the Z process.

  The basic prerequisites for this combination are that the

  during or before drying and blending.

  during drying. With this condition, the short elasticity interval relative to the amount of the contraction

  offset by easing and compro-

  sion and, consequently, the cracks

  would produce otherwise, when the contraction exceeds the

  valle of elasticity. Flexibility can be produced without the help of

  means that significantly reduce the elasticity range, as already mentioned. Compression, if used alone, would necessarily be very high, and, in view of the difficulty presented by the compression of different types of veneer sheets, having different rates of contraction, a broad

  interval of forced compression would be necessary to

  come to all the leaves. Such a compression ratio tends to damage the leaves and this tendency is not easily

  preventable. The combination of the invention allows the two different

  ways of mutually reducing their rates

  treatment requirements, so much so that the indi-

  viduals, particularly compression, can be easily

  carried out. The present invention thus makes it possible to prevent

  easily and effectively cracking veneer sheets.

  Another advantage comes from the intrinsic combination of

  elasticity intervals provided by the compression and the

  folding. We can freely choose the global interval of elas-

  ticity, because of the combination of the determined elasticity interval (provided by compression) and the free interval

  (provided by relaxation); consequently the interval of

  chosen elasticity can compensate for any irregularity in the

  compression of the leaves and thus easily compensate for any contraction that may differ, from one area to another,

  on a sheet of veneer. Thanks to this advantage, we can easily

  offset the contraction of leaves over a wide range

  to be able to satisfy the properties of the veneer sheets.

  For example, in the process Z shown in FIG.

  holds the desired effect without any adjustment, although the rate of

  contraction can range from 2% to 5.5%.

  According to the invention, a veneer sheet can be softened and then compressed, or compressed and then relaxed,

  or compressed and relaxed at the same time. However, the

  The process of softening prior to compression is preferable to other methods because, when the softening stretches a veneer sheet as in the method Z of FIG. 1 for example, at least the stretched portion of the sheet is readily compressible. Preferred examples of the complete process using this favorable order of relaxation and

  compression are given by a process according to which

  is done before drying, then the compression is

  during drying and by a process whereby the

  wrinkling occurs during drying, followed by compres-

  if we. In the case of relaxation and compression,

  kill in reverse order or overlap, they occur

  during drying, since the compression must take place

  kill during drying, in any case. Compared to

  the ideal order, these different sequences present

  for the compression of a leaf in a direction

  pendicular to its grain or for the maintenance of the compressed state of the leaf. However, such methods can be easily conceived because the necessary compression is

  much weaker in the processes using it alone.

  The elastic properties of the plating sheets are described in detail below, relative to the preferable process.

  of relaxation, with reference to Figures 2 to 6.

  It seems that the elastic properties of the veneer sheets are due to various kinds of cracks scattered therein. By hand drawing, the cracks of a sheet are sufficiently enlarged to let the rays of visible light through. More particularly, an increased number of transmitted light rays are visible when a suitable rate of softening is applied to an untreated sheet,

  with cracks on the back. This is sufficient to ensure

  that softening increases the range of elasticity.

  It is further observed that the elasticity results from the bending, for example of narrow and elongated portions of wood finely divided by numerous cracks. FIG. 4 represents a softened veneer sheet provided with cracks or slots 2 formed independently of its grain 1 (indicating the direction of the grain), for example using a roller comprising a number of piercing elements in the form of sharp edges. Figure 5 shows another relaxed veneer sheet having slits 2 extending substantially along the grain without damaging the fibers. The tendency towards elasticity is more stably increased in the sheet of FIG. 5 whose fibers are not cut than in the sheet of FIG. 4, whose fibers are cut across. However, the sheet of Figure 5 tends to allow the slots, or enlarged by softening, to meet by turning into large cracks. From this point of view, the

  sheet of Figure 4 is desirable since

  string of slots is easy. Veneer sheet softened in either of the two ways shown, gains much more elasticity than any non-softened sheet. The subject of the present invention is a method and an apparatus which, as described hereinafter, combine the advantages of both methods.

  of flexibility to give veneers

  increased elasticity, particularly favorable.

  The method of the invention comprises primary softening and secondary softening which can be performed simultaneously with, or after, the primary softening. For primary softening, a veneer sheet is provided

  slots, distributed in a preferable configuration,

  by sharp elements or elements with

  on the periphery of a roll, suitable means may be used to form short-slots, from which cracks may be derived, In the secondary softening, slits, which tend to extend along the the

  sheet are formed by means of a device shown in

  gures 2 and 3. This process according to which one relaxes in two steps

  simultaneous or successive, abolish irregular communications

  adjacent slits and allows slit distribution similar to that of Figure 6 (a), and not that of

Figure 6 (b).

  It is of course preferable that the slots follow the configuration of Figure 6 (a), rather than that of Figure 6 (b), and even better that they extend along the grain of the

  wood. This most favorable configuration also increases the

  terval elasticity significantly.

  Figures 2 and 3 show a softening apparatus

  Newly adapted to the process of the invention. This apparatus comprises a roller 8, covered on its outer periphery with a layer of rubber-like elastic mate, and a roll 6 of smaller diameter, having a large number of recesses 7 adapted to guide elongate coil springs 4. In their operation, the rollers 6 and 8 rotate as indicated by the arrows, and clamp between them a veneer sheet 3, to send it in the direction indicated by the arrow. Pressure means (not shown), associated with the rollers 6 or 8, then exert pressure on the moving sheet 3, while the elongated coil springs 4 move in the direction of the arrow in contact with the periphery of the roll 6, under

  a relatively small radius of curvature, opening individu-

  and thus softening the sheet 3. More particularly

  Firstly, this softening apparatus implements an improved version of the so-called Elemendorf softening system, ie it uses, in combination with the Elemendorf principle, the opening actions of the external portions of the adjacent turns of each coil spring 4, which occur relatively to each other when the coil springs are guided in the curve. The device therefore lengthens the sheet 3 at its opposite ends, by forming or enlarging the

  cracks, bending and softening the sheet of pla-

  cage, with step formation, preferably small. The softening device further comprises guide elements 5 and 'for the veneer sheet and a conveyor 9 for introducing

leaf.

  It should be noted that softening "does not imply here only the formation or enlargement of a large number of small cracks allowing the drawing of a sheet

  veneer. Even if a treated leaf does not show any

  it suffices to have a large number of small cracks (including small slits pierced or formed by an instrument such as a knife) to see its increased elasticity range in a direction perpendicular to that

grain.

  The compression of a veneer sheet will be described below in connection with one embodiment of the method of

the invention.

  Fig. 7 shows a veneer treatment apparatus comprising a softening system, the major part of which consists of an anvil roll and a softener roll 16 having a large number of sharp edge members. This softening system is followed by a transfer path defined by a number of pairs of rollers 17, 17 'and 17 "and guide plates 18 each of which intervenes between the adjacent pairs of rollers. it is not always necessary to connect the transfer path to the softening system 15, 16 by a conveyor, they must be connected to each other in a manner substantially similar to that of a conveyor connection, so that an untreated veneer sheet can be relaxed in advance by the system

  easing. The transfer route, which extends

  to the softening system 15, 16 includes a deceleration zone which overlaps a length upstream of the travel path.

  transfer. This deceleration zone comprises a source of com-

  Mande 9 and a speed reduction mechanism 20 and 21, such that the second pair of rollers 17 'rotates at a speed lower than that of the first pair of rollers 17 and the third pair of rollers 17 "rotates at a speed lower than that of the second pair of rollers.

  veneer that passes through this particular area of the transport

  Filling is compressed by the pairs of transfer rollers. In the rest of the transfer path, a fourth pair of rollers

  and so on, operate at the same speed as the third

  second pair 17 "and convey the veneer sheet in the

  in its state of compression. During this time, hot air circulates in the enclosure defined by insulating walls 22, so as to dry the compressed sheet. A log 10 and a knife 11 can be connected to the softening system 15,

  16, either directly or through any

  known treatment. In this way, if the compression is

  applied to a veneer sheet that is transferred, a pass-

  transfer deceleration, using gear reducers

  speed, is defined between a certain point on the path of trans-

  fert, and another point downstream. It is clearly seen from FIG. 7 that a veneer sheet is progressively compressed by the first pair of rollers 17 to the third pair 17 ', and that it is kept in its compression state even after having passed the third pair of rollers. this allows

  compression of the sheet until its tension of com-

  The pressure disappears under the effect of drying. In this case, the operation

  Drying charge P, which uses heating means, is carried out in combination with the pressing operation R and the softening operation Q takes place substantially upstream of drying and compression, in the transfer path. Of course, the softening device may be located in the enclosure defined by the walls 22, in order to soften the sheet during

  drying. In any case, it is preferable that the system of

  is located in the deceleration zone of the

  throw, or in a position upstream of the death zone

  in order to facilitate compression and to simplify

mechanism of the device.

  It will be seen that among the systems using the methods of the invention, a continuous veneer treatment system includes a transfer path for conveying the 2463668

  sheet, a deceleration zone covering a certain length of time

  upstream of the transfer route and using

  deceleration, a localized softening system

  a suitable position upstream, also from the decelerating zone

  tion, and heating means opposed to the transfer path

  and also the deceleration zone. We can replace the

  18 in combination with the pairs of rollers, in FIG. 7, by piano strings, or other similar elongated elements, extending along the lower and upper surfaces of a veneer sheet, as long as they define the transfer path in combination with the pairs of rollers. In practice, such guide means can be omitted depending on the spacing between adjacent pairs of rollers. In addition, the deceleration zone of the transfer path is not necessarily localized in a portion

  input of the transfer path as shown, it is preferable

  that the area extends from a position where the moisture content of the sheet becomes substantially equal to 30% and causes significant shrinkage to a position of

downstream of the first position.

  Figure 8 is a side view of another veneer treatment system showing a preferred drying device. FIG. 9 represents a partial front view of this system and FIG. 10 is a sectional view along line XX of FIG. 8. The device represented is that of a heated plate type drying system, used in the method of the invention, as described above. This type of drying system has previously proved impractical because it restricts the sheet with a relatively high force and, as a result, causes visible cracks in the sheet,

  during drying. The present invention allows its use

  by applying the drying principle stated above and further improving it to promote the drying of a leaf.

being transferred.

  FIGS. 8 to 10 show a system comprising two groups of elongated multiple elements 24 and 25, for example coil springs, which are passed over several rollers 26a-26h to define a transfer path

12 2463668

  zigzag, while inserting a veneer sheet 23.

  each of the rollers 26a-2Gh comprises on its periphery annular multiple channels in which those of the elongated elements,

  closer to the roll than the sheet 23, are introduced,

  to be completely concealed. For example, as partially shown in the figure. 10, the roller 26a has

  annular channels 27a and the roller 26b comprises the annular channels

  27b. The veneer sheet 23 is thus directly clamped against the peripheral surfaces of the individual rolls. The rollers 26a 26h are individually heated with steam,

  or a similar means, from the inside and they are connected, through

  towards reducing mechanisms. 28a - 28h, to a control source 29. The rotation speed decreases progressively from the roller upstream to the roller furthest downstream from the transfer direction, thereby defining a zone of deceleration transfer. Rollers 30 rotate the direction of travel of elongate members 24

and 25.

  During operation, the rollers 26a - 26h are driven in the directions of the arrows to transfer the sheet 23 while it is being heated. At the same time, the rollers

  which rotate at successively decreasing speeds, com-

  take precedence over the sheet at the respective points of decrease from one roll to another. Cracking due to drying can therefore be reasonably eliminated by simultaneous drying and compression operations, even without softening. More effective prevention of cracking can be achieved by adjusting the speed reduction mechanisms 28a-28h to

  to adapt the deceleration of transfer to the contraction of

  its portions of the leaf. In addition, the system shown

  see leaf 23 in a desirable way. Since the elements

  elongated guides guide the sheet from one roll to another, keeping it between the rollers, the system makes it possible to overcome any possible defects in the sheet, such as decomposition points or knots, by conveying it uniformly without

  interruption and without lifting, on the heated rollers.

  This also applies to sheets of relatively small width. The system thus makes it possible to avoid any seizure of the sheet and other such accidents and is satisfactory

from a practical point of view.

13 2463668

  To comply with the drying principle of the invention,

  The softening system is placed in any suitable position, which is basically at the top of the drying device or in it. It preferably occupies a position within the deceleration zone, or a suitable position at the head of this zone, as a position independent of this zone, for introducing a sheet as shown in FIG.

  8. In practice, although not represented, the system of

  fold may be placed in the vicinity of the introducer

  8, or immediately after the turn to cut a veneer sheet located upstream, or it can be replaced by a cutting tower of the type that softens the veneer sheet during its cutting in the log. when

  it is placed in the drying zone, the softening device

  It can take the form of a softening roll, provided with piercing elements, constituted by the roller 26a in FIG. 8. According to one variant, the softening system in the drying zone can use the reducing mechanisms of speed 28a and 28b, by rotating the roller 28b at a higher speed than the roller 28a, so that these associated rollers exert light traction on a sheet placed between them,

to enlarge the cracks.

  It is not a prior necessity to use all the rollers 26a-26h of FIG. 8 to constitute the zone of

  deceleration. For example, some of the reduc-

  represented, to define a zone of deceleration

  ration by a suitable number of speed reducers and

  their associated rollers. The deceleration zone becomes parti-

  when it covers a region between the position where the moisture content of the leaf is

  30% and a certain downstream position. Reductions

  Individual speed controllers can be ordered at a variable rate of speed reduction, to take into account various moisture contents and varying degrees of contraction.

  veneer sheets. The compression can be performed

  in the state of a leaf treated by a

  softening to optimize compression. To simplify the system, it is possible to vary the diameters of the rollers for

14 2463668

  constitute a mechanism for substantially reducing speed.

  Not only does this system make it possible to

  inherent in the process of the invention, but it also functions

  with excellent efficiency-because a veneer is in direct contact with the heated surfaces of the rolls for

  to be dried, its opposite face being continually turned over.

  As a result, the drying operation consumes little

* time and its cost is low. Moreover, because of the trans-

  With the regular filling of the sheet, the desired length of hotplates can be produced by the simple installation of several additional rollers of small diameter. The transfer of

  sheet from one roll to another is done regularly.

  It can be seen from Fig. 9 that the elongated members 24 and 25 are installed in a number corresponding to the width of the veneer sheet 23. Coil springs are preferably used as elongate members because they transfer the sheet. desirably, even in the deceleration zone, without slipping or above, or in the annular channels on the rollers. When the elongated elements are constituted by coil springs, the two vertical series of rollers of FIG. 8 can be slightly spaced apart to make

  more regular transfer of the sheet from one roll to the other.

  The softening systems of Figures 2 and 3 are

described below in detail.

  In FIGS. 11 to 13, a softening device comprises, according to the invention, several parallel extensible elements 4 or flexible bellows, such as springs

  coil. These extensible elements, coil springs 4, are

  extend perpendicular to the axis of a roll 8, so that a conveying path for a veneer sheet 3 is

  defined between the coil springs 4 and the roller 8. The

  The outer periphery of the roll 8 is covered with an elastic layer of rubber, for example, and the roll is rotated, to transfer the sheet 3. A roll 6, or other cylindrical pressing element, is located on the back of the coil springs 4 it presses towards the roller 8, so that the coil springs 4 which move with the sheet 3 are pressed against the surface

of the leaf.

2463668

  In this device, the pressure roller 6 arches the coil springs 4 vei-s the roller 8, together with the sheet

  3, thus enlarging the spacing between adjacent turns

  of each coil spring. More particularly, the portions of the springs 4 engaged with the sheet 3 lengthen in the length direction. This has the effect of locally subjecting the sheet 3 to a tensile force which results in successive formations of small cracks 2 in the sheet, in relation to the rotation of the roller 8. It should be noted that since the intensity of the tension force which is exercised on the

  veneer depends on the opening rate of the adjacent turns

  of the springs in the arched position, the cracks 2 may

  can be formed almost independently of

  such as thickness, resistance and speed of transmission.

  leaf, as well as the presence or absence of

  cracks on the back of the leaf and the orientation of these cra-

  whatever may be present. The elastic layer on the

  roller 8 facilitates the formation and enlargement of the cracks

  lures 2 in the face of the sheet 3 opposite the springs 4, in

  because of the local variation in speed resulting from his

  training. However, this does not favor the enlargement of the cracks beyond the necessary degree, because the extension of the cracks 2 is controlled by the springs 4. For this reason and because the cracking due to the tension is not accompanied

  no cut across the grain of the leaf, the

  shown has an effective and adequate softening effect as well as an extension, without

the veneer.

  The coil springs are an example of

  extensible 4, preferable to form fine cracks that expand the application area of the system and facilitate easy maintenance. FIG. 17 represents an example of a variant of the extensible elements, comprising a large number of blocks 4b arranged in the longitudinal direction of the elements.

  extensible, intimate contact or slightly spaced between them.

  Blocks 4b are interconnected on one side by a belt 4a of a relatively hard material. Each block may have a section like that shown in FIGS. 18a or 10b; the blocks

16 2463668

  4b and the belt 4a may also consist entirely of a hard resin or a hard rubber, for example, as shown in Figure 18c, the blocks being arranged in a comb-shaped configuration. Any other device for the expandable members 4 may be used, in so far as their portions engaged under pressure with the veneer sheet are aligned lengthwise, and the spacing between said adjacent portions being engaged may be increased. by

  camber extensible elements, as previously described.

  As already mentioned, the intensity of the tension or the dimension

  small cracks, depend on the degree of opening of the por-

  adjacent to the extensible elements in the arched position. he

  It is therefore preferable to choose the spacing of

  the engagement lengths, the length (thickness) of each engagement portion, etc. depending on a specific application and the degree of curvature attributed to the pressure roller. The extensible members are preferably suitably spaced, as shown in FIG. 11, to avoid any interference between

  adjacent extensible elements, as well as between cracks

  sines. If the extensible elements are endless elements,

  the whole system is small, which favors

  saddle. The coil springs are usually made of iron, or an iron alloy, but such a metal reacts with the sap of the veneer leaves, changing their color to brown. Therefore, when using the system to soften fresh veneer, it is preferable to use coil springs whose outer surfaces are coated with rubber or plated layers, provided that these layers do not impede Resilient actions of coil springs. If desired, the springs may be entirely made of stainless steel which is inactive with respect to the sap. In any case, a better effect is obtained by choosing the coil springs taking into account the conditions of the veneer to be treated, its applications, etc.

  With regard to the pressing element, it is preferable

  the curvature radius must be properly determined because it affects the degree of opening of the engagement portions of

17 2463668

  extensible elements. This curvature is however not limited to a constant value, such as that of a pressure roller. Yes

  a freely rotating, multi-cut, pressure roller is used

  gonale or elliptic for example, we can condition the craters

  in the sheet in a desirable way, adjusting the inten-

  sity and the point of impact of the tension. Moreover, we can replace

  the pressure roller freely rotating by means of

  non-rotating. In general, sheet 3 is conveyed by the

  rotation of the roll 8. If another means is

  Positive to advance Sheet 3, Roll 8 does not require

  you more control mechanism and can be freely rotatable.

  The meandering and similar actions of

  4 may interfere with the extensively

  between them, which then exert excessive pressure on the veneer. To avoid this effect, the pressing element 6

  may be provided with cheeks 6 ', on its outer periphery, with a di-

  radial dimension less than the thickness of

  and guiding and stopping the elements 4, as

  14. In a variant, annular recesses (not shown) can be formed on the pressing element 6 serving the same purpose. If necessary, a means of

  support (not shown) on the back of the pressing means 6, in order to

  bending, resulting from its pressure action.

  It can happen that when the extensible elements

  4 are released from the camber force, and o their portions ad-

  The engagement plies are closed, these pinch fine fibers of the plywood between their adjacent turns and then drive the sheet in their direction of travel. This disadvantage can be avoided if, as shown in FIG.

  13, the pressing element 6 and the extensible elements 4 are dis-

  laid in such a way that the adjacent turns of each element

  extendable to a position downstream of the pres-

  6, with respect to the conveying direction of the sheet, where the sheet is completely free of extensible elements. This problem can also be solved by placing a separator element 13 downstream of the pressing element 6, as

  shown in Figure 14. In addition, it is possible to construct a

  presser 6 and a roller 8 which can move away from each other,

18 2463668

  under pressure of a predetermined level, in order to cope with unusual pressure forces that could result

  a covering, or other accident, of the veneer.

  FIGS. 15 and 16 show a second and a third embodiment, according to the invention, each of which

  includes, in addition to the various components of the first embodiment,

  The roller 14 has a large number of short, piercing elements 12 on its outer periphery and it is possible to use a piercing roller 14 in the transfer path of a veneer sheet upstream of the pressure element 6. opposed to the roller 8 in such a way

  that he cuts the sheet 3 while pressing it.

  According to this variant, the piercing elements 12 on the roll 14 form a large number of notches (not shown)

  in sheet 3, with the rotation of the roll 8.

  the pressure water 6 presses the extensible elements 4, together with the sheet 3, to the roller 8, the turns of the elements 4 then opening in contact with the sheet, as previously described, to exert a local tension on the sheet. Since nicks made by the roller 14 are now present in the sheet 3, the tension focuses on the relatively small notches to form successive cracks from these nicks,

  In this way, cracks in the sheet of pla-

  cage, starting from the individual notches made by the roller 14, can be formed easily and surely. The cuts in the sheet are only for the purpose of

  the camber of elements 4, focuses on each portion

  hold while cracks or slits are formed only by tension. For this reason and because the elements 4

  regulate the extension of cracks, we can prevent the enlargement

  cracks beyond a given limit. If the

  in the leaf have irregular distributions of

  However, it is understood that an ordinary softening system simply added to the bead roll of the invention

  these irregular distributions and thus poses various

  such as a decrease in sheet strength and breakage. The device of the invention makes it possible to avoid these drawbacks and to obtain an improved effect of relaxation

19 2463668

and extension.

  By a suitable location of the piercing elements 12 on the roller 14, for example in a zigzag configuration, it is more surely avoided that neighboring cracks along the grain, do not communicate with each other. This shows that it is possible to achieve a higher rate of softening and expanding the sheet without decreasing the strength or failure. Planned only to cut the sheet, the short piercing elements on the roller 14 can be arranged in a sufficient density to effectively form cracks

  adequate even in very thin veneer sheets (thick

  sweat generally varies from 0.5 mm to imm), which the systems

  usual easing do not allow.

  Each piercing element 12 can be of any desirable shape, such as that of a needle, a cone, a pyramid or a wedge as long as it surely forms notches in the leaf without unnecessarily cutting the grain. It can also adjust its height, and other parameters, on the roller 14, depending on a specific application. It is preferable, in order to prevent the sheet from being driven around the roll 14 which has cut it, to place the elements 4 so as to guide the sheet towards the roll 8, in the transfer path, downstream of the roll 14 , or as shown in Figure 15, / as shown in Figure 16, to place a guide in the transfer path, downstream of the roller

  14. At the same time, elements 4 may extend over a

  a little larger on the periphery of the roll 8, as shown in Figure 15, upstream of the roll 6, or rollers 6 and 14, .the resulting transfer path then promotes a very precise transfer of the sheet and constitutes a precautionary measure against leaf meanders that may occur, in

  because of the formation of cracks or nicks.

  Figure 19 shows a further variant of the softening device according to the invention, which comprises a combined pressure roller and piercer, for simultaneously pressing the expandable member 4 and notching the veneer sheet. For this, the roller is placed on the face of the element 4 opposite the roller 8 so that it forces the expandable element towards the roller 8 and that it presses and cuts the veneer sheet

  through the interstices between the extendable elements

  llèles. We can form piercing elements, short 12 on the

  periphery of each of the multiple cheeks, disposed in localisa-

  axially equally spaced-on the roller 14 (see Figure 19). Alternatively, these piercing elements 12 can be directly doweled on the roller 14 (see Figure 20). The roller 14 which rotates freely, allows the elements 12 to engage

  sheet 3 before the elements 4 are arched to

  to eat the leaf. As a result, many cracks or cracks are formed successively from the notches provided

  by the elements 12. Although the effect obtained is the same as

  the device of FIGS. 15 and 16, the device of this

  variant simplifies the mechanism and, as a result, presents the

  to allow only one roll to make cuts and cracks. The piercing elements 12 press

  and notch the sheet through and between the elements exten-

  4. Because of this arrangement, and if the elements 12 are rigid, as is the case in Figures 19 and 20, the roller 14 allows the cheeks 6 'to serve as guides to avoid

meandering elements 4.

  The softening system of the invention effectively

  many small, adequate cracks, regardless of the physical properties of a veneer, such as its thickness or cracks on the back, the orientation of these cracks, the transfer speed of the sheet, and other conditions that have 'now opposed to diversity

  application of previous systems. The device of the invention

  This marks a clear progress in the counterfeiting industry.

  plated, by the improved effect obtained in the relaxation and

  the extension of the veneer sheets.

  Naturally, the invention is in no way limited to the embodiments of the example described and shown, it is capable of numerous variants accessible to those skilled in the art, depending on the applications envisaged and without departing for that purpose.

of the scope of the invention.

21 2463668

Claims (21)

claims   1. A process for drying a veneer sheet,   characterized in that it comprises the operations of softening a veneer sheet, by forming numerous small cracks in the sheet, to increase the range of elas-. in a direction substantially perpendicular to the grain and compression of said sheet in said direction, compression being effected during drying to prevent   cracking of the veneer sheet during drying.   2. Method according to claim 1, characterized in that   compression is performed after the softening operation.   3. Method according to claim 2, characterized in that   the softening is carried out before the drying operation.   4. Method according to claim 2, characterized in that   the softening is carried out during the drying operation.   5. Method according to claim 1, characterized in that   the softening is carried out after the drying operation.   6. Method according to one of claims 1 to 5, characterized   in that the easing operation includes a processing   primary element to form cracks in the foil   cage according to a given distribution and a secondary treatment   to form small slits along the fibers from said cracks.   7. Method according to claim 6, characterized in that the primary treatment confers a zigzag configuration   cracks in the veneer.   8. Method according to one of claims 2, 3, 4, 6 or   7, characterized in that the compression ratio obtained in the operation   compression ratio, has a substantially corresponding value   at the rate of extension of the veneer sheet obtained in the easing ration.   9. Apparatus for drying a veneer sheet   in that it comprises a transfer deceleration zone containing velocity reducing mechanisms and extending from a point of the transfer path for conveying the   plating to another point downstream of the first; a provision   tif of softening to form many small slits on the veneer sheet, located in a suitable position 22 2463668   on the upstream portion which also covers the decelerating zone   in relation to the transfer direction; and heating means in front of at least the portion of the transfer path   which covers the deceleration zone.   Apparatus for drying a veneer sheet, characterized in that it comprises a plurality of rolls; elongated elements passing over the rolls, holding a veneer sheet between them, to define a transfer path   in zigzag, said rollers having on their perimeter surfaces   of the annular recesses adapted to contain complete   those of the elongated elements located closer to the rollers than the veneer sheet, said rollers being heated,   speed reducing mechanisms defining a decelerating zone   transferring device in which a suitable number of rollers are driven at successively decreasing speeds; and a softening device for forming a plurality of small slits in the veneer sheet and located in a convenient position on the upstream portion, which also covers the area   deceleration, with respect to the transfer direction.   11. Apparatus according to claim 10, characterized in that the elongated elements comprise elongated elements   resilient, like coil springs.   12. Apparatus according to one of claims 10 and 11   characterized in that the speed reducing mechanisms can   wind operate at a variable rate of speed reduction.   13. Device for relaxing a sheet of pla-   cage, characterized in that it comprises: a plurality of parallel extensible elements extending in the direction of transfer of said sheet and moving in agreement with said transfer, said extensible elements having portions that can engage   under pressure with the sheet in transfer, forming continual-   lengthwise, and becoming convex by   xion, by stimulating the enlargement of spaces between spiers ad-   underlying said portions; a freely rotating roll arranged   on the face of engagement of the extensible elements and whose   outer layer is covered with an elastic layer,   extensible elements and the roller defining between them a   transfer jet of the veneer sheet; and a pressing element 23 2463668   disposed on the face of the extensible elements opposite their engagement face, and adapted to squeeze the extensible elements towards the roller.   14. Device according to claim 13, characterized in that the extensible elements comprise coil springs. 15. Device according to claim 13, characterized in that the extensible elements comprise a number of blocks arranged in the longitudinal direction in intimate or slightly spaced contact, and a belt connecting the blocks between them, on one of their sides.   16. Device for softening a sheet of pla-   cage characterized in that it comprises in addition to the components of the   device according to one of claims 13 to 15, a second   roller disposed in the transfer path upstream of the pressing element and provided with many small piercing parts on its   external periphery, to press and cut the sheet of cage.   17. A device for relaxing a sheet of pla-   cage, characterized in that it comprises, in addition to the components of the   device according to one of claims 13 to 15, a second   roll, arranged on the face of the extensible elements opposite to   their engagement face, and adapted to force the ex-   to the first roll and press and score the veneer sheet through and between the parallel expandable members.   18. Apparatus for drying a veneer sheet,   characterized in that it comprises a plurality of rotary heating elements, juxtaposed, adapted to convey the sheet in a predetermined direction; two groups of resilient elements   lying on top of the rollers to hold the sheet   the between the two groups, each rotary heating element having recesses on their periphery to receive the elongated resilient elements, the sheet, held between the two groups, being brought into contact with the rotary heating element; and speed reducing means for effecting a deceleration of the rotary heating elements, to a progressively increasing extent downstream from the movement of the leaf.   Apparatus according to claim 18, characterized in that each elongate resilient member comprises a coil spring.   20. Apparatus according to one of claims 18 and 19,   characterized in that the deceleration corresponds to the contrac- the veneer sheet.   21. Apparatus according to one of claims 18 to 20,   characterized in that both elements are elongated   adjacent in each group are spaced apart from one another   150 times the thickness of the veneer.