Dewatering method for correcting water content of green veneer for plywood and apparatus for dewatering the green veneer

A large number of green veneers for plywood respectively having high water contents and formed in a rectangular shape are vertically laminated to obtain a veneer laminate having a quadrangular prismatic shape. The veneer laminate is located between upper and lower platen members so that two opposite side faces of the veneer laminate vertically form cut face gathering planes. The upper and lower platen members are moved toward each other to apply a pressing force to the veneer laminate. The pressing force applied to the veneer laminate is released or weakened while the water drawn through the cut face gathering planes by the pressing force is dripping downward along the cut face gathering planes of the veneer laminate vertically formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a dewatering method for correcting water contents of green veneers for plywood. In the dewatering method, a pressure is vertically applied to a large number of vertically laminated green veneers for plywood so that the green veneers are compressed and dewatered for reduction of water contents of the green veneers. The invention also relates to an apparatus for dewatering the green veneers.

2. Description of the Related Art

Describing a plywood production process often employed, a log being rotated is peeled into thin band plates by the use of a lathe (plane), green veneers are obtained by cutting the peeled band plates in predefined dimensions and then dried, and a plurality of the green veneers is bonded to produce the plywood. In the process, the green veneers are compressed and dewatered by applying a pressure to the green veneers before the drying step because it is time-consuming to immediately dry the obtained green veneers.

The water contents of the respective green veneers thus dewatered are desirably as equal as possible not only among the laminated green veneers but also in different parts of each green veneer. A large difference between the water contents leads to a lengthy drying step and makes it difficult for the green veneers to be equally dried, in which case the water contents are still different from one green veneer to another and in different parts of one green veneer after the drying step. When the green veneers thus having different water contents are laminated to produce the plywood, warp and/or distortion is likely to occur.

Comparing sapwood and core pieces respectively obtained from outer layers and a core part of the log, the water contents of each green veneer before compressing step are largely different. For example, the water content of the sapwood is twice to three times as large as a relatively low water content of the wood core. When the sapwood and core pieces, each one of which is inadequate and unusable as a veneer, are joined and used as a patched veneer, the veneer may have water contents two-fold to three-fold different from one another in different parts of the patched veneer. In some of such green veneers, there may be differences by several-ten percentages or more among the water contents in different parts of one green veneer. The Applicant was granted two patents in Japan last year, U.S. Pat. No. 4,783,862 and U.S. Pat. No. 4,783,863 (both registered on Jul. 15, 2011). This invention is an independent invention distinctly different from these two patented inventions.

The Patent Document 1 discloses a roller dewatering apparatus. In the apparatus, green veneers are each transported through between squeeze rollers to be thereby pressed and dewatered. This apparatus which dewaters the green veneers one by one needs an extensive time for its whole operation. Further, the apparatus, wherein all of the green veneers are uniformly pressed by the rollers, is unable to correct a variability of water contents among the different green veneers.

The Patent Document 2 discloses a dewatering apparatus configured for laminate collective compression. In the apparatus, laminated green veneers are pressed collectively from an upper direction to be dewatered. The apparatus thus dewatering all of the green veneers at once achieves a better dewatering efficiency. However, the apparatus is similarly unable to correct a variability of water contents, whether they are different water contents among the green veneers and/or different water contents in different parts of one green veneer.

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

The invention provides a method and an apparatus for dewatering a plurality of green veneers while reducing a variability of water contents during the dewatering treatment.

Means for Solving Problems and Operational Effect

The invention provides a dewatering method as described below. A large number of green veneers for plywood respectively having high water contents and formed in a rectangular shape are vertically laminated. Cut faces of the green veneers for plywood, which are end faces of the green veneers for plywood intersecting with a direction of fibers, are vertically aligned. The veneer laminate is located between upper and lower platen members so that two opposite side faces of the veneer laminate vertically form cut face gathering planes. The upper and lower platen members are moved toward each other to apply a pressing force in the range of 15 to 50 kg/cm2(or more preferably in the range of 20 to 40 kg/cm2) to the large number of laminated green veneers for plywood constituting the veneer laminate. Accordingly, water contained in the green veneers for plywood is drawn through the cut faces of the green veneers and drips downward along the cut face gathering planes vertically formed where the cut faces of the green veneers for plywood are gathered. The pressing force applied to the veneer laminate is released or weakened in the range of 0 to 10 kg/cm2(or more preferably in the range of 0 to 5 kg/cm2) while the water is dripping downward so that the cut faces and fibers inside of the green veneers for plywood spread in a direction of original shape of the green veneers, generating a negative pressure. The water dripping downward along the cut face gathering planes is suctioned into fibers of the green veneer having a relatively low water content by a suctioning action generated from the cut faces toward the inside by the negative pressure. Then, the pressing force in the range of 15 to 50 kg/cm2is applied again to the large number of green veneers for plywood. As a result of at least one cycle of these steps that ends with the application of pressing force, a variability of the water contents in the veneer laminate is lessened among the green veneers for plywood and in different parts of each of the green veneers for plywood while an overall water content of the veneer laminate is reduced.

The veneer laminate is thus pressed by the upper and lower platen members to be dewatered and the pressing force applied to the veneer laminate is released or weakened while the water is dripping along the cut faces (perpendicular walls) of the veneer laminate. Therefore, the compressed veneer laminate swells under its own elasticity, generating the negative pressure in the fibers of the green veneers, and the dripping water is suctioned into the fibers by the negative pressure. Then, the water drawn from the green veneer or parts of the green veneer having the water content relatively high is transferred to the green veneer or parts of the green veneer having the water content relatively low. Thus, the green veneers are dewatered such that the water contents have a less variability from one green veneer to another and in different parts of one green veneer. Therefore, the green veneers can be thereafter dried efficiently with less time. When a plurality of green veneers is bonded to obtain a sheet of plywood, the plywood obtained as a product is unlikely to warp or distort because the water contents of the green veneers used in the plywood are not as different from one green veneer to another and/or in different parts of one green veneer.

According to an aspect of the invention, a plurality of cycles of the pressing force application—releasing steps or the pressing force application—weakening steps by the upper and lower platen members to the veneer laminate are repeatedly performed and end with the application of pressing force while the water drawn by the pressing force is dripping downward along the cut face gathering planes vertically formed.

According to the method, the water is transferred from the green veneer or parts of the green veneer having the water content relatively high to the green veneer or parts thereof having the water content relatively low. Then, the green veneers are compressed again so that the water is discharged from the fibers of the green veneers. When the water discharge, the water suction, and the water discharge again are performed repeatedly, the green veneers can be dewatered such that the variability of water contents is more effectively lessened from one green veneer to another and/or in different parts of one green veneer.

The invention provides a green veneer dewatering apparatus as described below. A large number of green veneers for plywood are vertically laminated to obtain a veneer laminate, and the veneer laminate is subject to a pressing force vertically applied to the veneer laminate to be compressed and dewatered to reduce a water content of the veneer laminate. The apparatus includes:

a support platen supporting the veneer laminate;

a pressing member provided in an upper part of the support platen and movable toward and away from the support platen;

a pressing cylinder adapted to drive and push the pressing member against the veneer laminate;

a regulating member provided so as to vertically move relative to the support platen, the regulating member being adapted to stand upright from the support platen to be in contact with or closely adjacent to perpendicular walls on at least two opposite sides of the veneer laminate and thereby regulate movement or extension of the veneer laminate while the veneer laminate is being pressed by the pressing member, the regulating member further being adapted to abut the pressing member moving downward to thereafter move downward integral with the pressing member;

a lifting and lowering device adapted to lift and lower the regulating member to and from an upright standing position; and

a control device adapted to control the pressing cylinder which drives the pressing member, the control device including:

a dewatering pressing stopper which controls the pressing cylinder so that the pressing force applied by the pressing member to the veneer laminate for dewatering is released or weakened in the range of 0 to 10 kg/cm2(or more preferably in the range of 0 to 5 kg/cm2) and the application of pressing force for dewatering stops while the veneer laminate is being pressed and dewatered by the pressing member under the pressing force in the range of 15 to 50 kg/cm2(or more preferably in the range of 20 to 40 kg/cm2); and

a dewatering pressing restarter which controls the pressing cylinder so that the pressing force applied by the pressing member to the veneer laminate for dewatering is increased in the range of 15 to 50 kg/cm2(or more preferably in the range of 20 to 40 kg/cm2) to restart the application of pressing force for dewatering, wherein

at least one cycle of the application of pressing force for dewatering and the stop of pressing force for dewatering is performed and ends with the application of pressing force for dewatering.

According to the apparatus, the regulating member reduces a likelihood of fracture in end portions of the green veneers that may be caused by the pressing force applied to the veneer laminate, making it difficult for the green veneers to be damaged by the dewatering treatment.

According to an aspect of the invention, the control device controlling the pressing cylinder includes: a first pressing stopper adapted to, in a step for subjecting the veneer laminate to a first pressing performed by the pressing member, release or weaken the pressing force applied by the pressing member while the water contained in the veneer laminate is being discharged from the veneer laminate by controlling the pressing cylinder so that the first pressing stops; and a second pressing starter adapted to restart the application of the pressing force to the veneer laminate by controlling the pressing cylinder so that a second pressing is performed by the pressing member.

Because the pressing force applied by the pressing member is released or weakened while the water is dripping along the perpendicular walls of the veneer laminate during the first pressing, the compressed veneer laminate starts to swell under its own elasticity, generating a negative pressure in the fibers of the green veneers. Then, the water dripping downward is suctioned by the negative pressure into the fibers of the green veneers, and the water discharged from the green veneer or any parts of the green veneer having the water content relatively high is transferred to the green veneer or parts of the green veneer having the water content relatively low. When the veneer laminate is compressed to be pressed and dewatered again in the second pressing for further water discharge, difference in the water contents are further reduced among the green veneers and/or in different parts of one green veneer during the dewatering treatment.

According to another aspect of the invention, the regulating member is positioned along the perpendicular walls on two opposite sides of the veneer laminate in a direction intersecting with the direction of fibers so that a stretch of the veneer laminate in the direction intersecting with the direction of fibers is regulated during the application of the pressing force.

This prevents or reduces a likelihood of any stretch of the end portions of the green veneers in the direction intersecting with the direction of fibers, making it difficult for the end portions to fracture.

According to still another aspect of the invention, the apparatus includes a pair of the regulating members facing each other along the perpendicular walls on opposite two sides of the veneer laminate, and a lateral movement device adapted to move one of the pair of the regulating members toward the other regulating member. The lifting and lowering device locates one of the pair of the regulating members at a standby position below a veneer supporting surface of the support platen when ready to place the veneer laminate on the support platen, and then lifts the one of the pair of the regulating members so as to stand upright on the support platen after the veneer laminate is placed on the support platen. The lateral movement device moves the one of the pair of the regulating members toward the other regulating member so that the veneer laminate is thereby sandwiched from two sides intersecting with the direction of fibers.

According to the apparatus, neither of the regulating members interferes with the veneer laminate when placed on the support platen, and the veneer laminate is sandwiched by the regulating members from two sides because one of the regulating members is moved toward the other regulating member after the veneer laminate is placed on the support platen. As a result, any stretch and fracture of the end portions of the green veneers are more effectively prevented or less likely while the pressing force is being applied to the green veneers.

In the apparatus according to still another aspect of the invention, a plurality of the pressing cylinders is coupled at different positions with the pressing member of pressing cylinders to drive the pressing member, and a plurality of lifting cylinders is coupled at different positions with the pressing member. The lifting cylinders are driven when the pressing member is lifted to return to a lift-up position after the pressing of the veneer laminate by the pressing member is over. The apparatus further includes: a stroke distance measuring device adapted to measure a stroke distance of each of the lifting cylinders that follow the plurality of the pressing cylinders while the plurality of the pressing cylinders is pressing the veneer laminate by the use of the pressing member; and a per-cylinder control device adapted to individually control the plurality of the pressing cylinders so as to lessen a deviation between the stroke distances of the lifting cylinders measured by the measuring device or a tilt of the pressing member calculated from the deviation.

According to the apparatus, the lifting cylinders having outputs relatively small but large enough to lift the pressing member are used to return the pressing member to the lift-up position, making it unnecessary to drive the pressing cylinders with very large outputs. This leads to energy saving. Further, in the apparatus, the stroke distances of the plurality of lifting cylinders is measured and the plurality of pressing cylinders is individually controlled so that the tilt of the pressing member is corrected based on the measured values. The apparatus can horizontally retain the veneer laminate as equally in height as possible during the pressing, thereby evenly dewatering the veneer laminate.

EXEMPLARY EMBODIMENT FOR CARRYING OUT THE INVENTION

An exemplary embodiment of the invention is described referring to examples illustrated in the accompanied drawings. First, a dewatering apparatus for correcting water contents suitably used in a method according to the invention is described. Then, examples of the method according to the invention are described in a manner that corresponds to the description of operations of the apparatuses.FIG. 1illustrates a green veneer dewatering apparatus1adapted to vertically apply a pressing force and thereby compress a veneer laminate (green veneer laminate) composed of a large number of vertically laminated green veneers for plywood to dewater the veneer laminate for reduction of a water content of the veneer laminate. The green veneer dewatering apparatus1has a support platen2supporting the veneer laminate, a press platen3provided in an upper section of the support platen2and serving as a pressing member movable toward and away from the support platen2, a pressing cylinder4adapted to drive the press platen3and push the press platen3against the veneer laminate, a pair of regulating members5provided so as to vertically move relative to the support platen2, the regulating members5being adapted to stand upright from the support platen2to be in contact with or closely adjacent to perpendicular walls on at least two opposite sides of the veneer laminate to thereby regulate movement or stretch of the veneer laminate while the veneer laminate is being pressed by the press platen3, the regulating members5further being adapted to abut the press platen3moving downward to thereafter move downward integral with the press platen3, a lifting and lowering cylinder6, which is an example of the lifting and lowering device, adapted to lift and lower the regulating members5to and from the upright standing position, and a pressing controller7, which is an example of the control device, adapted to control the pressing cylinder4which drives the press platen3. The support platen2and the press platen3are examples of the upper and lower platen members.

The support platen2, the pressing cylinder4, and the lifting and lowering cylinder6are secured to a frame8. The frame8is formed in a box shape, and the support platen2is located so as to horizontally traverse the frame8. A transport-in conveyer11which transports a veneer laminate B1to the support platen2is connected to one side of the support platen2, and a transport-out conveyer12which transports a veneer laminate B2already compressed and dewatered from the support platen2is connected to the other side of the support platen2.

The pair of regulating members5each has a planar (plate-like) shape facing perpendicular walls on opposite two sides of the veneer laminate B1and stand upright in parallel with each other. The green veneers have a square-like shape (conventionally, rectangular shape). When a direction of fibers and a direction intersecting with the direction of fibers are identified in the green veneer, the two perpendicular walls on two sides are in parallel with the direction of fibers. Therefore, a pair of the regulating members5is facing each other in the direction intersecting with the direction of fibers of the green veneers, and end faces of the fibers of the green veneers are exposed in a direction orthogonal to a plane of paper in the illustration ofFIG. 1. These end faces constitute cut face gathering planes where cut faces of the green veneers are gathered.

As an example of the lateral movement device, lateral movement cylinders13and13are provided to move one of the pair of regulating members5toward the other regulating member5. The lateral movement cylinders13and13are respectively connected to the regulating members5. The lateral movement cylinders13and13are secured to lifting and lowering bases14, and piston rods15of lateral movement cylinders13are coupled with the regulating members5. The pair of regulating members5each stands upright to extend upward through moving spaces16formed in the support platen2. The regulating members5are horizontally movable relative to the lifting and lowering bases14while retaining their upright positions within the moving spaces16. When at least one of the lateral movement cylinders15is driven to laterally move one of the regulating members5toward the other regulating member5, the veneer laminate B1is thereby sandwiched from two sides in the direction intersecting with the direction of fibers.

The lifting and lowering bases14are coupled with piston rods17of lifting and lowering cylinders6and6vertically installed. The regulating members5are coupled with the lifting and lowering cylinders6via the lifting and lowering bases14which respectively support the lateral movement cylinders13. The lifting and lowering cylinders6each has a stroke which lifts and lowers each of the regulating members5between an upright standing position where an upper end of each of the regulating members5protrudes upward through the support platen2beyond a height dimension of the veneer laminate B1and a standby position below an upper surface of the support platen2. The lifting and lowering cylinders6each has a vertical guide member vertically formed, not illustrated in the drawings, which directly guides each of the regulating members5upward and downward or indirectly guides each of the regulating members5by the use of a fitment formed integral with each of the regulating members5. When the regulating member5on the side of the transport-in conveyer11alone is at the standby position below the upper surface of the support platen2in the apparatus illustrated inFIG. 1, the veneer laminate B1is transported onto the support platen2. When at least the regulating member5on the side of the transport-out conveyer12is at the standby position below the upper surface of the support platen2in the apparatus, the dewatered veneer laminate B2is transported from the support platen2.

The support platen2has therein a built-in conveyer20adapted to lift itself slightly above the upper surface of the support platen2. The built-in conveyer20is, for example, a chain conveyer driven being supported by sprockets21and22provided on both end sides of the support platen2. The conveyer20is moved by a lifting and lowering device23(for example, lifting and lowering cylinder) to and from a transport position slightly above the upper surface of the support platen2and a standby position below the upper surface. The built-in conveyer20, when driven at the transport position slightly above the upper surface, guides the veneer laminate B1transported by the transport-in conveyer11to the support platen2. When the conveyer20is retreated to the standby position, the veneer laminate B1is placed on the upper surface of the support platen2. The dewatered veneer laminate B2is slightly lifted when the built-in conveyer20is lifted by the lifting and lowering device23and transported by the built-in conveyer20from the support platen2toward the transport-out conveyer12and thereby received by the transport-out conveyer12.

The pressing controller7which controls the pressing cylinder4has a first pressing stopper adapted to, in a step for subjecting the veneer laminate B1to a first pressing performed by the press platen3, release or weaken a pressing force applied by the press platen3while the water contained in the veneer laminate B1is being discharged from the veneer laminate B1by controlling the pressing cylinder4so that the first pressing stops; and a second pressing starter adapted to restart the application of the pressing force to the veneer laminate B1by controlling the pressing cylinder4so that a second pressing is performed by the press platen3. More specifically, the pressing controller7includes: at least a sequence program25run by a CPU to control a pressing pattern of the pressing cylinder; and a timer26measuring pressing times and pressing-release times. The controller7is connected to a pressure sensor28which detects a pressure level of the pressing cylinder4, an electromagnetic valve29which controls a fluid pressure (normally, oil pressure) to the pressing cylinder29, and, if necessary, a pressing force source such as an oil pressure pump30. The first pressing stopper and the second pressing starter include the sequence program25and the timer26.

Next, operation steps of the green veneer dewatering apparatus1as described above are hereinafter described. The description given below includes details of the sequence program25of the pressing controller7and an example of the dewatering method for correcting water contents according to the invention.

When the veneer laminate B1is transported by the transport-in conveyer11as illustrated inFIG. 1, the regulating member5on the side of the transport-in conveyer11is moved downward by the lifting and lowering cylinder6to the standby position below the upper surface of the support platen2as illustrated inFIG. 2, whereas the other regulating member5on the side of the transport-out conveyer12stays upright beyond the height dimension of the veneer laminate B1.

Next, the built-in conveyer20illustrated inFIG. 1is driven, and the veneer laminate B1on the transport-in conveyer11is received by the built-in conveyer20and then placed on the support platen2as illustrated inFIG. 3. At the time, the built-in conveyer20is slightly above the upper surface of the support platen2, and the veneer laminate B1on the built-in conveyer20is afloat. Then, the regulating member5below the support platen2is lifted from the support platen2by the lifting and lowering cylinder6to a position equal to the veneer laminate B1in height or is lifted a little beyond the position so as to protrude as illustrated inFIG. 4.

Then, the regulating member5on the side of the transport-in conveyer11is laterally moved in a small distance by the lateral movement cylinder13toward the regulating member5on the opposite side as illustrated inFIG. 5. As a result, the veneer laminate B1is sandwiched by the pair of regulating members5from two sides. The perpendicular wall on one side of the veneer laminate B1in the direction of fibers is butted to or located in close proximity of an inner surface of the regulating member5on the opposite side, while the perpendicular wall on the other side in the direction parallel to fibers is butted to an inner surface of the regulating member5laterally moved. After that, the built-in conveyer20illustrated inFIG. 1is moved downward by the lifting and lowering device23to a position lower than the support platen2. Then, the veneer laminate B1is seated on the upper surface of the support platen2.

Then, the pressing cylinder4is driven, and the press platen3thereby moves downward as illustrated inFIG. 6. During the downward movement, the press platen3abuts upper ends of the pair of regulating members5protruding upward from the upper face of the veneer laminate B1. A drive pressure of the pressing cylinder4is larger than pressures (holding pressures) of the lifting and lowering cylinders6of the regulating members5. After the press platen3abuts the upper ends, therefore, the pressing cylinder4pushes the pair of regulating members5downward while pushing the pistons of the lifting and lowering cylinders6downward.

As illustrated inFIG. 7, as soon as the press platen3is butted to the upper face of the veneer laminate B1(green veneer at the top) during the process, the veneer laminate B1starts to be compressed by the pressing force applied to the veneer laminate B1. Then, the press platen3driven by the pressing cylinder4continues to apply the pressing force to the veneer laminate B1over a predetermined period of time by moving the pair of regulating members5downward.

The veneer laminate B1is vertically compressed by the pressing force thus applied to the veneer laminate B1and thereby relatively reduced in height, and the water contained in the respective green veneers is squeezed out through the end faces of the green veneers in the direction of fibers (for example, perpendicular wall on the front illustrated inFIG. 7) and drips downward. During the dewatering treatment, the drive of the pressing cylinder4is suspended to release the pressing force (make the pressing force zero) to the veneer laminate B1from the press platen3or weaken the pressing force to a lower level as illustrated inFIG. 8. This is the stop of the first pressing while the water is dripping.

In a short period of time after the pressing stopped, the pressing cylinder4is driven again to proceed to a second pressing where the veneer laminate B1starts to be pressed again by the press platen3as illustrated inFIG. 9.

After the second pressing performed for a predetermined short period of time, it is suitably selected whether the dewatering treatment to the veneer laminate B1is ended or a third pressing starts after the second pressing stopped, while the water squeezed out of the fibers of the green veneers during the second pressing was dripping. As illustrated inFIG. 10, the pressing cylinder4is driven to the backward direction after an Nth pressing (N is an integer equal to or larger than 2) is over, and the press platen3starts to move upward and moves away from the upper face of the dewatered veneer laminate B2and the upper ends of the pair of regulating members5.

Then, the regulating member5at least on the side of the transport-out conveyer12is moved downward by the lifting and lowering cylinder6until the upper end of the regulating member5arrives at the standby position below the upper surface of the support platen2. The built-in conveyer20illustrated inFIG. 1is moved upward by the lifting and lowering device23so that the dewatered veneer laminate B2is thereby lifted from the support platen2and ready to be transported by the built-in conveyer20. When the conveyer20is driven, the veneer laminate B2moves away from the support platen2and continues to be transported by the transport-out conveyer12to a predefined site.

The operation of the pressing cylinder in the N-times pressing so far described is controlled by the sequence program25run by the pressing controller7illustrated inFIG. 1. The timer26is a structural element which decides duration time of the respective pressing and the respective pressing-release timing. When the times measured by the timer26are equal to duration time of the respective pressing times and pressing-release timing preset in the sequence program, the pressing controller7transmits a signal to the electromagnetic valve29and, if necessary, the pressing force source30to suspend or restart the operation of the pressing cylinder4. When the pressure of the pressing cylinder4obtained from the pressure sensor28and the times measured by the timer6are used as parameters for deciding timings of continuing and releasing the pressing force, the application of the pressing force is continued or released depending on several conditions described by logical operation such as AND or OR, etc. when the measured pressing force and times are equal to preset values or included in preset numeral ranges.

As a result of the lateral movement of one of the regulating members5illustrated inFIGS. 4 and 5, the veneer laminate B1is sandwiched by the regulating members5from two sides as illustrated in plan views ofFIG. 11. This not only lessens or prevents any tilt or misshaping of the veneer laminate B1while the pressing force is applied to the veneer laminate B1but also lessens or prevents any stretch of the end portions of the green veneers in the direction intersecting with the direction of fibers of the green veneers due to the pressing when the veneer laminate B1is sandwiched from two sides in the fiber-intersecting direction as illustrated inFIG. 12.

An unlimited stretch of the end portions is likely to cause fractures in the end portions of the green veneers (veneer laminate B1) in the direction of fibers as illustrated inFIG. 13. However, the pair of regulating members5can prevent the occurrence of such a stretch and resulting fractures in the end portions, as illustrated inFIG. 14.

FIGS. 15 to 18and21are conceptual views (images) of situations of the veneer laminate B1after the first pressing starts and stops as illustrated inFIGS. 7 to 8and the second pressing thereafter starts as illustrated inFIG. 9. When the veneer laminate B1is compressed by the pressing force in the first pressing as illustrated inFIGS. 15 and 16, the water is squeezed from the fibers of the green veneers and drips downward along the perpendicular walls of the veneer laminate B1.FIG. 21Aconceptually illustrates the veneer laminate before the pressing starts, andFIG. 21Bconceptually illustrates the veneer laminate currently being pressed. As illustrated inFIGS. 21A to 21C, when the pressing force is released (or weakened) while the water is dripping, the compressed fibers of the green veneers start to swell trying to regain the original shape, and a negative pressure is thereby generated in the fibers of the green veneers. Under the influence of the negative pressure thus generated, the water dripping along or staying on the wall surfaces of the veneer laminate B1is suctioned into the fibers of the green veneers. This suctioning under the negative pressure more markedly occurs in the green veneer or any parts of the green veneer relatively containing less water than the green veneer or any parts thereof relatively containing more water.

Accordingly, between the fibers of laminated green veneers b1and the fibers in different parts of each of the green veneers b1, the water transfer occurs from the green veneer having a high water content to the green veneer having a low water content or from any parts of one green veneer having a high water content to the other parts of the green veneer having a low water content. In other words, a negative pressure pumping action exerted by the green veneers per se when the pressing force is released during the dewatering of the green veneers serves to equalize the water contents in the whole structure of the veneer laminate B1.

Generally, there may be a relatively small variability of the water contents in one green veneer. To make use of a plurality of different pieces of wood, each one of which is inadequate and unusable as a veneer (inferior pieces of a log with holes or ruptures, or fragments of the pieces generated when the log with cavities, knots, or uneven periphery is cut), they may be joined by means of, for example, a tape, so that a patched veneer is formed and used as a material of plywood similarly to one-piece green veneers normally obtained. In a patched veneer b11illustrated inFIG. 19, for example, a sapwood piece A (from outer layer) of a cedar tree, a heartwood piece B (from mid layer), a sapwood piece C, and a core piece D (from center) are patched together. There are differences in the water contents of these pieces; twice to three times as different between the sapwood pieces A and C having high water contents and the core piece D having a low water content, and the water content of the heartwood piece B is somewhere between the water contents of these pieces. The negative pressure pumping action, which repeatedly applies the pressing force, release the pressing force, and applies the pressing force again, can more effectively transfer the water particularly between parts of the patched veneer b11having more different water contents, thereby equalizing the water contents in the patched veneer b11, as illustrated inFIGS. 20A and 20B. This is not a technical advantage limited to the patched veneer. In different parts of a green veneer obtained from a cedar tree, for example, the water content of a part may be larger or smaller by 20% to 150% than the other. Such a large variability is successfully lessened.

The water content equalizing effect thus far described is more enhanced as the release of the pressing force is repeated more often while the green veneers are being pressed and dewatered. Therefore, the pumping action (negative pressure suctioning) is desirably performed a plurality of times such that first pressing, release of first pressing while the water is dripping, second pressing, release of second pressing while the water is dripping, third pressing, release of third pressing while the water is dripping . . . .

To improve a dewatering efficiency by reducing a length of time of the dewatering treatment, it is necessary to coordinate how many times the pressing and pressing release should be repeated and a length of time of the dewatering necessary for one veneer laminate B1. A suggestion for reducing the dewatering time to the minimum is to complete the dewatering treatment for one veneer laminate B1in three steps; first pressing, release of first pressing, and second pressing.

FIG. 22Ais a graph illustrating an effect of the dewatering treatment in the veneer laminate B1described so far (particularly, effect of equalizing post-dewatering water contents). In a dewatering test performed according to the method described so far, water contents of the sapwood pieces were about 100% to 300% at most with such a large difference of 203% in an initial stage (before the dewatering treatment). However, the variability of the water contents was reduced to 95% after the dewatering treatment according to the invention. The variability was further reduced to 5% after the drying treatment subsequent to the dewatering treatment.

The cedar core showed the water contents of about 50% to 150% at most with the water content difference of 99% in the initial stage (before the dewatering treatment). The water content difference was reduced to 70% after the dewatering treatment and further reduced to 7% after the drying treatment.

As illustrated in an upper part ofFIG. 22B, 1) illustrates the water content uniformity when a cycle of pressing→release→pressing was repeated three to five times. The water content uniformity was checked in combinations of the dewatering pressures of 10, 15, 20, 30, 40, 50, and 60 kg/cm2and the release pressures of 0, 5 and 10 kg/cm2. A result thereby obtained was; the water content uniformity was not very good at the dewatering pressure of 10 kg/cm2(for example, water content variability of around 20% after drying), the water content uniformity was good at the dewatering pressure of 15 kg/cm2(for example, water content variability of at most 15%), the water content uniformity was good or very good at the dewatering pressure of 20 to 50 kg/cm2(for example, water content variability of less than 10%), and the water content uniformity was better at the release pressure of 0 or 5 kg/cm2than 10 kg/cm2. At the dewatering pressure of 60 kg/cm2, the water content uniformity was good after drying, however, fractures were generated in a part of the green veneers.

As illustrated in a lower part ofFIG. 22B, 2) illustrates the water content uniformity when a cycle of pressing→release→pressing was performed once or repeated twice. The water content uniformity was good after drying except for the dewatering pressure of 10 kg/cm2, however, the water content variability was smaller when the cycle was repeated at least three times.

Next, another example of the invention is described referring to an apparatus illustrated inFIGS. 23 to 29.

As is clear from an oil pressure system illustrated inFIG. 23, the apparatus used in the example includes a plurality of (four in this example) pressing cylinders50which pressurize the veneer laminate B1from an upper direction. The pressing cylinders50are coupled with a press platen51which is an example of the pressing member, and the pressing cylinders50are connected to an oil pressure source53(compressor or oil pressure pump) through electromagnetic valves52of the pressing cylinders50. A plurality of (for example, two each on two sides of the press platen51, four in total) lifting cylinders54is coupled with the press platen51in parallel with the pressing cylinders50to be located on outer sides of the pressing cylinders50. The lifting cylinders54are all connected to the oil pressure source53through a common electromagnetic valve55. As illustrated inFIG. 24, each of the electromagnetic valves55of the plurality of pressing cylinders50is connected to a controller (oil pressure controller)57, and the electromagnetic valve55of the plurality of lifting cylinders54is also connected to the controller57.

As illustrated inFIG. 25, the lifting cylinders54each has a linear encoder58incorporated in the lifting cylinders54or attached to the lifting cylinders54as a measuring device which measures a stroke (operation) distance (stretch distance of piston rods54a). The encoders58are connected to the controller57. When the pressing cylinders50are stretched to press the veneer laminate B1by the use of the press platen51, the piston rods54aof the four lifting cylinders54are stretched as the press platen51is moving downward. During the stretch, the linear encoders58measure stroke distances (stretch distances of the piston rods54a) L1, L2, L3, and L4of the lifting cylinders54and outputs measured values of the distances to the controller57.

Depending on a difference between the output values of the encoders58(deviation ΔL) or a three-dimensional tilt Δθ of the press platen51calculated from the output value deviation ΔL, the controller57controls the electromagnetic valves52of the pressing cylinders50(FIGS. 23 and 24) so that the deviation ΔL or the tilt Δθ are reduced to the minimum. Further, the controller57separately controls working pressures P1to P4of the pressing cylinders. As a result, the tilt of the press platen51relative to the veneer laminate B1is corrected. The piston rods54aof the lifting cylinders54illustrated inFIG. 25, therefore, are coupled rotatably (through a small degree) relative to the press platen51. The piston rods50aof the pressing cylinders50may be configured to abut the press platen51by means of, for example, hooks not illustrated in the drawings.

When the press platen51is lifted to a lift-up position after the veneer laminate B1is pressed and dewatered by the pressing cylinders50, the pressing cylinders50are not driven but the lifting cylinders54alone are driven (a fluid pressure is supplied from the pressure source53through the electromagnetic valve55) to elevate the press platen51to the lift-up position (original position). At the time, the piston rods50aof the plurality of pressing cylinders50shrink following the actions of the lifting cylinders54. A force for simply lifting the press platen51is obtained from the application of a cylinder pressure large enough to overcome the weight of the press platen51. If such a cylinder pressure is applied by the pressing cylinders50with large outputs, a very large pressure is needed to drive the heavy pistons. However, as far as the small-sized lifting cylinders54with low outputs are used to apply such a cylinder pressure, the press platen51can be lifted and returned to the original position by a small cylinder pressure and a low energy.

The lifting cylinders54are stretched in response to the actions of the pressing cylinders50(downward movement of the press platen51), and the strokes are plotted by the encoders58. Then, the pressing cylinders50are separately controlled based on the deviation ΔL or the tilt Δθ used as a parameter. Accordingly, the lifting cylinders54may be used without additionally providing a specific mechanism to correct the tilt of the press platen51during the application of the pressing force. Further, the veneer laminate B1can be equalized in height and thereby evenly dewatered.

FIGS. 26 and 27specifically illustrate a positional relationship between the pressing cylinders50and the lifting cylinders54. The pressing cylinders50are secured to inside of a frame60which is a securing member of the apparatus, and the lifting cylinders54is secured to an outer side of the frame60. Referring toFIG. 27, the piston rods54aof the lifting cylinders54are coupled with the press platen51by pins54b(for example, rotatable two-dimensionally or three-dimensionally on at least one of shafts X and Y).

As illustrated inFIG. 26, an upper surface of a support platen61is used as a support surface61asupporting the veneer laminate B1placed on the upper surface of a support platen61. A chain conveyer (built-in conveyer)62is provided in parallel with the support surface61a. The conveyer62has endless raceways63in two rows provided such that they are hidden immediately below the support surface61a(for example, chains), cyclic sprockets64and65which support the chains63so that these chains cyclically go around, a plurality of support sprockets66subject to loads acting on the chains63, a conveyer frame67which supports the sprockets64to66, a motor68supported by the frame67which drives the chains63, and a conveyer lifting and lowering cylinder69which lifts and lowers the whole structural elements by the use of the frame67.

As illustrated inFIG. 28, the upper surface of the support platen61(support surface61a) has chain grooves (slits)70for the chains63to travel through. The chains63in two rows are lifted and lowered in the chain grooves70by the conveyer lifting and lowering cylinder69to and from a transport position slightly higher than the upper surface of the support platen61and a standby position lower than the upper surface. While the veneer laminate B1is being pressurized, the chains63are at the standby position. When the veneer laminate B1is transported to and from the support platen61, the chains63are lifted by the conveyer lifting and lowering cylinder69to the transport position. A drive shaft (sprocket)71illustrated inFIG. 26is provided to make the chains63in two rows go around in synchronization with each other. The rotation of the motor68is transmitted to the sprockets65and71through a driving mechanism such as a chain, and the chains63are thereby synchronously driven.

In the illustration ofFIG. 26, regulating members72which regulate positions of two opposite sides (two faces) of the veneer laminate B1are supported relative to lateral movement members73standing upright so that the regulating members72can be vertically lifted and lowered by the use of lifting and lowering guides74as schematically illustrated inFIG. 29. Lifting and lowering cylinders75which lift the regulating members72are secured to the lateral movement members73, and piston rods75aof the lifting and lowering cylinders75are coupled with the regulating members72. The lateral movement members73are supported in the frame60of the apparatus by the lateral movement cylinders (lateral movement devices)76. When the lateral movement cylinders76are put in action, the regulating members72, the lateral movement devices73, and the lifting and lowering cylinders75are all laterally (horizontally) move at once in a given range of distances.

When the lifting and lowering cylinders75are operating (stretching), the regulating members72move upward under the guidance by the lifting and lowering guides74of the lateral movement members73. As illustrated inFIG. 26, the two regulating members72facing each other regulate the positions of opposite two end faces of the veneer laminate B1. As illustrated inFIG. 29, the regulating members72are moved horizontally by the lateral movement cylinders76by the use of lateral movement members73, and the veneer laminate B1staying afloat which is supported by the chain conveyer62is sandwiched by the regulating members72.

FIG. 28is a plan view specifically illustrating the structure schematically illustrated inFIG. 29. On right and left sides of the drawing are illustrated the structural elements at vertically different positions, however, the apparatus in practical use is basically laterally symmetrical. The chains63of the chain conveyer62are located in the tracks of the regulating members72moving upward and downward. Therefore, the regulating members72are respectively provided with relief grooves (slits)77to avoid any interference with the chains63. The relief grooves77are vertically formed in an enough length to meet the strokes of the regulating members72moving upward and downward. The lateral movement cylinders76are secured to the frame60at positions in front and back of a depth direction of the support plate61so as to extrude the lateral movement cylinders76from the frame60of the apparatus to the outside at the side of the apparatus, and the lateral movement members73standing upright are coupled with the cylinders76.

The regulating members72are located on inner sides of the lateral movement members73, in other words, respectively between the lateral movement members73and the frame60. The regulating members72are supported by the lateral movement members73by the use of the lifting and lowering guides74so as to move upward and downward and moved to right and left in the illustration ofFIG. 28by the lateral movement cylinders76. Though not illustrated inFIG. 28, the lateral movement cylinder76is provided on the left of the drawing similarly to the lateral movement cylinder76on the right, and functions similarly thereto. On the left of the drawing is illustrated a lateral movement guide78, which functions as a linear guide which couples the lateral movement member73with the frame60at a position different in height to the lateral movement cylinder76at positions in front and back of a depth direction of the support plate61to guide the lateral movement member73to right and left in the drawing. Though not illustrated inFIG. 28, a lateral movement linear guide is similarly provided on the right of the drawing to guide the lateral movement member73on the right to horizontally move.

As illustrated inFIG. 27, the regulating members72have longitudinal frame portions79and80which are rectangular pipe materials each formed in a frame shape, lateral frame portions81and82which vertically connect the longitudinal frame portions, inner spaces of the frame portions79to82, and plate members83which seal the spaces. The relief grooves (slits)77in the up-down direction are respectively formed in the longitudinal frame portions79and80so as to fit the chains63in two rows. The piston rods75aof the lifting and lowering cylinders75secured to the lateral movement members73are coupled with a lower surface of the lateral frame portion81on the upper side.

As illustrated inFIG. 27, the up and down movement of the press platen51is guided by the lifting and lowering guide74formed in the frame60. A pair of upper stoppers51a(stopper portions) are formed on a lower surface of the press platen51with an interval therebetween equal to the outer-side intervals of the pair of regulating members72(for example, long enough to meet a width dimension of the regulating member72as illustrated inFIG. 27). When the press platen51moving downward make contact with the upper ends of the pair of regulating members72, the pair of upper stoppers51aare in close proximity of the outer surfaces of the regulating members72, thereby preventing the pair of regulating members72from opening outward during the application of the pressing force.

Describing the basic operation in the example described so far, similarly to the example illustrated referring toFIGS. 1 to 21, after the veneer laminate B1is transported onto the support platen61by the chain conveyer62driven by the motor68while the regulating member72on the left inFIG. 26protrudes from the support platen61and the regulating member72on the right is receded from the support platen61, the regulating member72on the right inFIG. 26then protrudes from the support platen61. When the regulating member72thus protruding is laterally moved by the lateral movement cylinder76toward the regulating member72on the left, the veneer laminate B1is sandwiched by these regulating members72, and the conveyer lifting and lowering cylinder69moves the chain conveyer62downward. Then, the veneer laminate B1is placed on the upper surface (support surface)61aof the support platen61.

Then, the pressing cylinders50are driven, and the press platen51accordingly moves downward and abuts the upper ends of the pair of regulating members72. Then, the press platen51driven by the pressing cylinders50compresses the veneer laminate B1by pushing the regulating members72downward to squeeze the water contained in the veneer laminate B1. During the process, the stroke distances L1to L4of the plurality of lifting cylinders54that follow the pressing cylinders are plotted, and the plurality of pressing cylinders50is separately controlled so that the press platen51is not tilted, in other word, the veneer laminate B1is horizontally retained equally in height.

When the pressing force applied by the pressing cylinders50is released or weakened, the compressed fibers of the green veneers start to swell, and a negative pressure is thereby generated in the fibers of the green veneers. Under the influence of the negative pressure thus generated, the water dripping along the perpendicular walls of the veneer laminate B1is suctioned into the green veneer or any parts of the green veneer relatively containing less water. As a result, the water contents are more efficiently equalized in the green veneers and the whole structure of the veneer laminate B1. Further, the regulating members72regulate any stretch of the end portions of the green veneers in the direction intersecting with the direction of fibers, thereby reducing a likelihood of any fractures in the end portions.

When the dewatering treatment for equalizing the water contents is completed after the pressing and the pressing release (or the pressing force is reduced) are performed by the pressing cylinder50a suitable number of times (for example, once to three times), the regulating members72illustrated inFIG. 26are both moved downward to a lift-down position by the lifting and lowing cylinders75. Then, the chain conveyer62is elevated by the conveyer lifting and lowering cylinder69to lift the dewatered veneer laminate B2from the support surface61aof the support platen61. The chain conveyer62driven by the motor68transports the veneer laminate B2from the support platen61. Then, the same steps are performed for the next veneer laminate B1.

The example described so far succeeded in reducing the variability of the water contents as illustrated inFIG. 22.

The apparatuses illustrated inFIGS. 1,25, and26respectively have the regulating members5and72, the lifting and lowering cylinders6and75which move the regulating members5and72upward and downward, the lateral movement cylinders13and76which laterally move the regulating members5and72, and the lifting cylinders54. According to the dewatering method in which the apparatuses are used, the veneer laminate B1sandwiched by the regulating members5and72is pressed from upward. As illustrated inFIG. 30, the method according to the invention may be performed by a dewatering apparatus1′ having such a simple structure that the support platen2and the press platen3are principal structural elements. The dewatering apparatus1′ does not include the regulating members5and72, the lifting and lowering cylinders6and75which move the regulating members5and72upward and downward, the lateral movement cylinders13and76which laterally move the regulating members5and72, and the lifting cylinders54(other structural characteristics are similar to the illustrations ofFIGS. 1,25, and26).

When the apparatus1′ is used, the veneer laminate B1placed on the support platen2is pressed by the press platen3moved downward by the pressing cylinder4. The pressing force applied by the pressing cylinder4is released or weakened while the water contained in the veneer laminate B1thus pressed is squeezed through the cut faces of the veneer laminate B1and dripping downward. A negative pressure is accordingly generated in the cut faces of the veneer laminate B1, and the water dripping downward is suctioned into the fibers. Then, the pressing force is preferably applied again (second pressing) as illustrated inFIG. 32, and the veneer laminate B1is dewatered so that the water contents in the veneer laminate B1are less variable. After the dewatering treatment is over, the press platen3returns to the lift-up position, and the dewatered veneer laminate B2is discharged. Then, the same steps are performed for the next veneer laminate B1.

In the example described thus far, the veneer laminate B1is pressed to be dewatered, and the pressing force applied by the press platen3is released or weakened while the water is dripping downward. The timer26illustrated inFIGS. 1 and 30may be used to determine based on test values previously obtained that the water is still dripping within a time t1after the pressing started, and the drive pressure of the pressing cylinder4may be released or weakened in response to a time-up signal of the time t1as a trigger. However, a different member may be used in place of the timer26as described below.

As illustrated inFIG. 33, image pickup cameras80, for example, may be installed in place of the timer near the cut face gathering planes (perpendicular walls) of the veneer laminate B1. Image data of the cameras80is transmitted to the controller7(pressing controller), and the pressing controller7determines that the water pressed out of the veneer laminate is dripping downward when data indicating the dripping water, in other words, image (moving image) data including downward displacement is extracted from the image data, and the pressing controller7outputs a signal for releasing or weakening the drive pressure of the pressing cylinder4to the pressing cylinder4(to be precise, electromagnetic valve) while the water is still dripping. The water dripping on the side faces of the veneer laminate B1travels through a water passage91formed in the support platen2to be collected by a tub92and then discharged from the tub92.

As illustrated inFIG. 34, reflection sensors83, such as optical sensors, may be provided so as to face the cut face gathering planes of the veneer laminate B1. Reflection signals, which are output from the reflection sensors83in response to water screens, water drops, or water stream while the water is dripping and reflected by the water screens on the cut face gathering planes and returned, are transmitted to the pressing controller7, and the pressing controller7determines that the water is dripping on the cut face gathering planes of the veneer laminate B1as far as levels of the reflection signals are equal to or larger than a predetermined threshold value and outputs a signal for releasing or weakening the drive pressure of the pressing cylinder4to the electromagnetic valve of the pressing cylinder4.

As illustrated inFIG. 35, at least sound sensors84and/or temperature sensors85may be provided near the cut face gathering planes (perpendicular walls) of the veneer laminate B1. During the water is dropping, output levels of the sound sensors84which picked up the sound of the dripping water are equal to a certain value or higher, the temperature sensors85output values within a temperature variation or a predetermined temperature range because of the water dripping, and the pressing controller7checks at least one of the output signals of the sound sensors84and/or the temperature sensors85to release or weaken the drive pressure of the pressing cylinder4.

As illustrated inFIG. 36, a container86may be provided to receive the water dripping along the cut face gathering planes of the veneer laminate B1through the water passage91of the support platen2. A weight sensor87measures a weight increase of the container86where the dripping water is stored. As long as the water is dripping, the weight of the container86where the water is stored keeps increasing. Therefore, the pressing controller7, to which a signal from the weight sensor87is transmitted, determines whether an amount of the water stored in the container86increases based on the signal output from the weight sensor87. The pressing controller7, which detected any increase, outputs a signal for releasing or weakening the drive pressure of the pressing cylinder4during the increase to induce the compressed veneer laminate B1to regain the original shape (swell), so that the water is suctioned into the fibers of the green veneers by a negative pressure suctioning action caused by the swell.

In the illustrations ofFIGS. 33 to 36, detecting devices (80to87) which detect the water dripping are provided respectively on the cut face gathering planes of the veneer laminate B1opposite to each other in parallel. However, these detecting devices (80to87) may be provided on one of the cut face gathering planes alone.