Series Type Continuous Automatic ENF-Grade Plywood Production Line And Production Method

Abstract

A series type continuous automatic ENF-grade plywood production line and a production method is set forth. The production line is at least composed of three serially connected independent process units with the same processing flow, which are core initialization, thickening circulation and product setting. Each process unit at least includes the following procedures: surface sanding, gluing, automatic lay-up, constant-thickness hot pressing, board overturning and cooling, defect scanning and repairing. The thickening circulation process unit can form a ring-shaped production line through a loop formed by the above procedures, or can form a linear production line by repeatedly extending above procedures. The present disclosure has the beneficial effects that the procedures of aging and prepressing of veneers, which lead to the stagnation of production process, are omitted, and the main obstacles in the continuous and automatic production of plywood are overcome.

Claims

1. A series type continuous automatic ENF-grade plywood production line, wherein production line is at least composed of three serially connected independent process units with the same processing flow, which are core initialization, thickening circulation and product setting, each process unit comprises the following equipment in sequence: a sanding machine (1), a glue spreader (2), an automatic lay-up robot (3), a hot press (4), a board overturning and cooling device (5), a defect scanning and repairing device (6), a thickness detection device (7), and a conveying device (8).

2. The production line according to claim 1, wherein the thickening circulation process unit is able to form a ring-shaped production A through a loop formed by the sanding machine (1), the glue spreader (2), the automatic lay-up robot (3), a hot press (4), the board overturning and cooling device (5) and the defect scanning and repairing device (6), or is able to form a linear production line B by repeatedly extending the sanding machine (1), the glue spreader (2), the automatic lay-up robot (3), the hot press (4), the board overturning and cooling device (5) and the defect scanning and repairing device (6).

3. The production line according to claim 1, wherein the used glue spreader (2) includes a roller glue spreader, a glue dispensing machine, and a glue sprayer.

4. The production line according to claim 1, wherein the hot press used by the core layer initialization process unit and the thickening circulation process unit is a single-opening hot press and/or a continuous flat hot press, wherein the single-opening hot press is controlled by a thickness gage, and the continuous flat hot press is controlled by a position.

5. A series type continuous automatic ENF-grade plywood production method, at least comprising the following steps: (1) core layer initialization: S10: surface sanding, wherein the number of meshes of a used abrasive belt is 60-120; S20: gluing, wherein a thin board with a thickness of 2-6 mm is used as an initial core layer, a core layer glued for the second time and later is a semi-finished product obtained after previous hot pressing, a curing temperature of an adhesive is 60-80? C., and glue spread amount on both sides is 100-300 g/m.sup.2; S30: automatic lay-up, wherein sheeted veneers are selected for automatic lay-up by a robot, wherein the veneer timbers on an upper surface and a lower surface have the same grain direction; S40: constant-thickness hot pressing, wherein hot pressing is conducted at a temperature of 80-100? C., and a curing degree of the adhesive is controlled to be 80-90%, so as to obtain a pre-cured semi-finished product; S50: board overturning and cooling, after board overturning and cooling, a conversion of an upper surface and a lower surface of a preformed semi-finished product is completed, and a surface temperature after cooling is 50-70? C.; and S60: defect scanning and repairing, wherein an automatic scanning device is used to distinguish defects and repair open jointing and other defects on the surface; (2) thickening circulation: S70: repeating S10 to S60, enabling a semi-finished product which does not reach a thickness to enter a thickening circulation procedure and a semi-finished product which meets a thickness requirement to enter a product setting process unit after a thickness inspection and shunting procedure, and following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers in the process of lay-up, wherein a curing temperature of an adhesive is 80-90? C., the glue spread amount on both sides is 200-500 g/m.sup.2, the hot pressing is conducted at a temperature of 100-120? C., and the curing degree of the adhesive is controlled to be 60-80%, so as to obtain a pre-cured semi-finished product; and (3) product setting: S80: repeating S10 to S50, following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers in the process of lay-up, wherein the curing temperature of an adhesive is 90-100? C., the glue spread amount on both side is 200-500 g/m.sup.2, the hot pressing is conducted at a temperature of 120-180? C.

6. The production method according to claim 5, wherein the hot pressing in the constant-thickness hot pressing step lasts for 120-240 seconds.

7. The production method according to claim 5, wherein the adhesive used in the core layer initialization step is a commercially available isocyanate adhesive, the adhesive used in the thickening circulation step is hyperbranched melamine-urea-formaldehyde copolycondensation resin modified by polymethylol compound, and the adhesive used in the product setting step is melamine-urea-formaldehyde copolycondensation resin.

8. The production method according to claim 7, wherein the hyperbranched melamine-urea-formaldehyde copolycondensation resin modified by polymethylol compound is prepared from melamine, urea, formaldehyde and polymethylol compound in a weight ratio of 1:16-18:8-10:0.1-0.5, with synthesis steps as follows: adding metered formaldehyde aqueous solution into a reaction kettle, adjusting pH to 7.5-9.5 with ethylenediamine, and sequentially adding urea and melamine while stirring; after controlling a temperature between 80-95? C. and holding the temperature and reacting for 30 min, adjusting the pH to 5.0-6.5 with an acidic mixture, adding metered polymethylol compound, controlling the temperature between 60-80? C., reacting for 30-60 min, adjusting the pH to 7.0-8.0 with sodium hydroxide solution, adding urea, and holding the temperature and reacting for 30 min, thus obtaining the resin.

9. The production method according to claim 7, wherein the melamine-urea-formaldehyde copolycondensation resin is prepared from melamine, urea and formaldehyde in a weight ratio of 1:15-16:11-15, with synthesis steps as follows: adding metered formaldehyde aqueous solution into a reaction kettle, adjusting pH to 5.5-6.5 with sodium hydroxide aqueous solution, and adding urea and melamine while stirring; after controlling the temperature between 80-90? C. and holding the temperature and reacting for 30 min, adjusting the pH to 5.0-5.5 with formic acid solution; after controlling the temperature between 85-95? C. and keeping temperature and reacting for 30-60 min, adjusting the pH to 7.0-8.5 with sodium hydroxide aqueous solution; and controlling the temperature between 60-80? C. and reacting for 30-60 min, adding urea, and holding the temperature and reacting for 30 min, thus obtaining the resin.

10. The production method according to claim 7, wherein the commercially available isocyanate adhesive is polymerized diphenylmethane diisocyanate (PMDI), or polymerized hexamethylene diisocyanate (PHDI).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 is a series type continuous automatic ENF grade plywood ring-shaped production line A;

[0025] FIG. 2 is a series type continuous automatic ENF grade plywood linear production line B.

[0026] In the drawings: 1sanding machine, 2glue spreader, 3automatic lay-up robot; 4hot press, 5board overturning and cooling device, 6defect scanning and repairing device, 7thickness detection device, 8conveying device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] In order to better understand the technical solution of the present disclosure, exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be embodied in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided for a clearer and more thorough understanding of the present disclosure, and will fully convey the scope of the present disclosure to those skilled in the art.

[0028] Embodiment 1 Series type continuous automatic production method of plywood with a thickness of 18 mm

[0029] 1. Sand treatment. A wood veneer with a thickness of 2.2 mm is sanded, and a grain direction of the veneer is a parallel-to-grain direction.

[0030] 2. Gluing. An adhesive is polymerized diphenylmethane diisocyanate, and glue spread amount on both sides is 100 g/m.sup.2.

[0031] 3. Lay-up. Sheeted veneers with a thickness of 2.0 mm are selected for lay-up by a robot by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers, and the grain direction of the upper surface and lower surface is a cross-grain direction.

[0032] 4. Constant-thickness hot pressing. A single-opening hot press is used for hot pressing for 90 seconds at a temperature of 100? C., and a curing degree of the adhesive is controlled to be 90%, so as to obtain a semi-finished product with a thickness of 6.0 mm.

[0033] 5. Board overturning and cooling. After board overturning and cooling, a conversion of an upper surface and a lower surface of the preformed semi-finished product is completed, and the surface temperature is 70? C.

[0034] 6. Defect scanning and repairing. An automatic scanning device is used to distinguish defects and repair the defects such as open jointing on the surface, thus obtaining an initialized core layer.

[0035] 7. Surface treatment. The initialized core layer of 6.0 mm is sanded.

[0036] 8. Gluing. An adhesive is hyperbranched melamine-urea-formaldehyde copolycondensation resin modified by polymethylol compound, and the glue spread amount on both sides is 500 g/m.sup.2.

[0037] 9. Lay-up. Sheeted veneers with a thickness of 2.0 mm are selected for lay-up by a robot by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers, and the grain direction of the upper surface and lower surface is a parallel-to-grain direction.

[0038] 10. Constant-thickness hot pressing. A single-opening hot press is used for hot pressing for 120 seconds at a temperature of 100? C., and a curing degree of the adhesive is controlled to be 80%, so as to obtain a semi-finished product with a thickness of 10.0 mm.

[0039] 11. Board overturning and cooling. After board overturning and cooling, a conversion of an upper surface and a lower surface of the preformed semi-finished product is completed, and the surface temperature is 70? C.

[0040] 12. Defect scanning and repairing. An automatic scanning device is used to distinguish defects and repair the defects such as open jointing on the surface.

[0041] 13. A semi-finished product with a thickness of 10.0 mm is returned to the operation 7 by a conveyor belt, and then the operations 7-12 are repeated to obtain a semi-finished product with a thickness of 14.0 mm.

[0042] 14. Surface treatment. A semi-finished product with a thickness of 14.0 mm is sanded.

[0043] 15. Setting and gluing. An adhesive is melamine-urea-formaldehyde copolycondensation resin, and the glue spread amount on both sides is 300 g/m.sup.2.

[0044] 16. Setting and lay-up. Sheeted veneers with a thickness of 2.0 mm are selected for automatic lay-up by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers.

[0045] 17. Setting and hot pressing. The hot pressing is conducted at a temperature of 120? C. for 300 seconds.

[0046] 18. Finished product cooling. A final product with a thickness of 18 mm is obtained.

[0047] The melamine-urea-formaldehyde copolycondensation resin is prepared from melamine, urea and formaldehyde in a weight ratio of 1:15:11, with synthesis steps as follows: adding metered formaldehyde aqueous solution into a reaction kettle, adjusting pH to 5.5 with sodium hydroxide aqueous solution, and adding urea and melamine while stirring; after controlling the temperature at 80? C. and holding the temperature and reacting for 30 min, adjusting the pH to 5.0 with formic acid solution; after controlling the temperature at 85? C. and keeping temperature and reacting for 60 min, adjusting the pH to 7.0 with sodium hydroxide aqueous solution; and controlling the temperature at 60? C. and reacting for 30 min, adding urea, and holding the temperature and reacting for 30 min, thus obtaining the resin.

[0048] The hyperbranched melamine-urea-formaldehyde copolycondensation resin modified by polymethylol compound is prepared from melamine, urea, formaldehyde and polymethylol compound in a weight ratio of 1:16:8:0.1, with synthesis steps as follows: adding metered formaldehyde aqueous solution into a reaction kettle, adjusting pH to 7.5 with ethylenediamine, and sequentially adding urea and melamine while stirring; after controlling a temperature at 80? C. and holding the temperature and reacting for 30 min, adjusting the pH to 5.0 with an acidic mixture, adding metered polymethylol compound, controlling the temperature at 60? C., reacting for 30 min, adjusting the pH to 7.0 with sodium hydroxide solution, adding urea, and holding the temperature and reacting for 30 min, thus obtaining the resin.

[0049] The plywood production cycle is 5 min, and the formaldehyde emission of the obtained plywood is 0.019 mg/m.sup.3.

[0050] Embodiment 2 Series type continuous automatic production method of plywood with a thickness of 18 mm

[0051] 1. Sand treatment. A thin medium-density fiber board with a thickness of 2.2 mm is sanded.

[0052] 2. Gluing. An adhesive is polymerized hexamethylene diisocyanate, and glue spread amount on both sides is 300 g/m.sup.2. 3. Lay-up. Sheeted veneers with a thickness of 2.0 mm are selected for lay-up by a robot by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers, and the grain direction of the upper surface and lower surface is a cross-grain direction.

[0053] 4. Constant-thickness hot pressing. A single-opening hot press is used for hot pressing for 90 seconds at a temperature of 100? C., and a curing degree of the adhesive is controlled to be 90%, so as to obtain a semi-finished product with a thickness of 6.0 mm.

[0054] 5. Board overturning and cooling. After board overturning and cooling, a conversion of an upper surface and a lower surface of the preformed semi-finished product is completed, and the surface temperature is 70? C.

[0055] 6. Defect scanning and repairing. An automatic scanning device is used to distinguish defects and repair the defects such as open jointing on the surface, thus obtaining an initialized core layer.

[0056] 7. Surface treatment. The initialized core layer with a thickness of 6.0 mm is sanded.

[0057] 8. Gluing. An adhesive is hyperbranched melamine-urea-formaldehyde copolycondensation resin modified by polymethylol compound, and the glue spread amount on both sides is 300 g/m.sup.2.

[0058] 9. Lay-up. Sheeted veneers with a thickness of 2.0 mm are selected for lay-up by a robot by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers, and the grain direction of the upper surface and lower surface is a parallel-to-grain direction.

[0059] 10. Constant-thickness hot pressing. A single-opening hot press is used for hot pressing for 90 seconds at a temperature of 120? C., and a curing degree of the adhesive is controlled to be 60%, so as to obtain a semi-finished product with a thickness of 10.0 mm.

[0060] 11. Board overturning and cooling. After board overturning and cooling, a conversion of an upper surface and a lower surface of the preformed semi-finished product is completed, and the surface temperature is 70? C.

[0061] 12. Defect scanning and repairing. An automatic scanning device is used to distinguish defects and repair the defects such as open jointing on the surface.

[0062] 13. Surface treatment. The semi-finished product with a thickness of 10.0 mm is sanded.

[0063] 14. Gluing. An adhesive is hyperbranched melamine-urea-formaldehyde copolycondensation resin modified by polymethylol compound, and the glue spread amount on both sides is 300 g/m.sup.2.

[0064] 15. Lay-up. Sheeted veneers with a thickness of 2.0 mm are selected for lay-up by a robot by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers, and the grain direction of the upper surface and lower surface is a parallel-to-grain direction.

[0065] 16. Constant-thickness hot pressing. A single-opening hot press is used for hot pressing for 180 seconds at a temperature of 100? C., and a curing degree of the adhesive is controlled to be 80%, so as to obtain a semi-finished product with a thickness of 14.0 mm.

[0066] 17. Board overturning and cooling. After board overturning and cooling, a conversion of an upper surface and a lower surface of the preformed semi-finished product is completed, and the surface temperature is 50? C.

[0067] 18. Defect scanning and repairing. An automatic scanning device is used to distinguish defects and repair the defects such as open jointing on the surface.

[0068] 19. Surface treatment. A semi-finished product with a thickness of 14.0 mm is sanded.

[0069] 20. Setting and gluing. An adhesive is melamine-urea-formaldehyde copolycondensation resin, and the glue spread amount on both sides is 300 g/m.sup.2.

[0070] 21. Setting and lay-up. Sheeted veneers with a thickness of 2.0 mm are selected for automatic lay-up by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers.

[0071] 22. Setting and hot pressing. The hot pressing is conducted at a temperature of 180? C. for 180 seconds.

[0072] 23. Finished product cooling. A final product with a thickness of 18 mm is obtained.

[0073] The melamine-urea-formaldehyde copolycondensation resin is prepared from melamine, urea and formaldehyde in a weight ratio of 1:16:15, with synthesis steps as follows: adding metered formaldehyde aqueous solution into a reaction kettle, adjusting pH to 6.5 with sodium hydroxide aqueous solution, and adding urea and melamine while stirring; after controlling the temperature at 90? C. and holding the temperature and reacting for 30 min, adjusting the pH to 5.5 with formic acid solution; after controlling the temperature at 85? C. and keeping temperature and reacting for 60 min, adjusting the pH to 8.5 with sodium hydroxide aqueous solution; and controlling the temperature at 80? C. and reacting for 60 min, adding urea, and holding the temperature and reacting for 30 min, thus obtaining the resin.

[0074] The hyperbranched melamine-urea-formaldehyde copolycondensation resin modified by polymethylol compound is prepared from melamine, urea, formaldehyde and polymethylol compound in a weight ratio of 1:18:10:0.5, with synthesis steps as follows: adding metered formaldehyde aqueous solution into a reaction kettle, adjusting pH to 9.5 with ethylenediamine, and sequentially adding urea and melamine while stirring; after controlling a temperature at 95? C. and holding the temperature and reacting for 30 min, adjusting the pH to 6.5 with an acidic mixture, adding metered polymethylol compound, controlling the temperature at 80? C., reacting for 60 min, adjusting the pH to 8.0 with sodium hydroxide solution, adding urea, and holding the temperature and reacting for 30 min, thus obtaining the resin.

[0075] The plywood production cycle is 3 min, and the formaldehyde emission of the obtained plywood is 0.016 mg/m.sup.3.

[0076] Embodiment 3 Series type continuous automatic production method of plywood with a thickness of 18 mm

[0077] 1. Surface treatment. Commercially available sheet plastic with a thickness of 6.5 mm is sanded.

[0078] 2. Gluing. An adhesive is polymerized diphenylmethane diisocyanate, and glue spread amount on both sides is 100 g/m.sup.2. 3. Lay-up. Sheeted veneers with a thickness of 2.0 mm are selected for lay-up by a robot by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers, and the grain direction of the upper surface and lower surface is a cross-grain direction.

[0079] 4. Constant-thickness hot pressing. A single-opening hot press is used for hot pressing for 120 seconds at a temperature of 90? C., and a curing degree of the adhesive is controlled to be 80%, so as to obtain a semi-finished product with a thickness of 10.0 mm.

[0080] 5. Board overturning and cooling. After board overturning and cooling, a conversion of an upper surface and a lower surface of the preformed semi-finished product is completed, and the surface temperature is 60? C.

[0081] 6. Defect scanning and repairing. An automatic scanning device is used to distinguish defects and repair the defects such as open jointing on the surface, thus obtaining an initialized core layer.

[0082] 7. Surface treatment. The initialized core layer with a thickness of 10.0 mm is sanded.

[0083] 8. Gluing. An adhesive is hyperbranched melamine-urea-formaldehyde copolycondensation resin modified by polymethylol compound, and the glue spread amount on both sides is 350 g/m.sup.2.

[0084] 9. Lay-up. Sheeted veneers with a thickness of 2.0 mm are selected for lay-up by a robot by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers, and the grain direction of the upper surface and lower surface is a parallel-to-grain direction.

[0085] 10. Constant-thickness hot pressing. A single-opening hot press is used for hot pressing for 150 seconds at a temperature of 90? C., and a curing degree of the adhesive is controlled to be 70%, so as to obtain a semi-finished product with a thickness of 14.0 mm.

[0086] 11. Board overturning and cooling. After board overturning and cooling, a conversion of an upper surface and a lower surface of the preformed semi-finished product is completed, and the surface temperature is 60? C.

[0087] 12. Defect scanning and repairing. An automatic scanning device is used to distinguish defects and repair the defects such as open jointing on the surface.

[0088] 13. Surface treatment. A semi-finished product with a thickness of 14.0 mm is sanded.

[0089] 14. Setting and gluing. An adhesive is melamine-urea-formaldehyde copolycondensation resin, and the glue spread amount on both sides is 290 g/m.sup.2.

[0090] 15. Setting and lay-up. Sheeted veneers with a thickness of 2.0 mm are selected for lay-up by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers.

[0091] 16. Setting and hot pressing. The hot pressing is conducted at a temperature of 150? C. for 240 seconds.

[0092] 17. Finished product cooling. A final product with a thickness of 18 mm is obtained.

[0093] The melamine-urea-formaldehyde copolycondensation resin is prepared from melamine, urea and formaldehyde in a weight ratio of 1:15:11, with synthesis steps as follows: adding metered formaldehyde aqueous solution into a reaction kettle, adjusting pH to 5.5 with sodium hydroxide aqueous solution, and adding urea and melamine while stirring; after controlling the temperature at 80? C. and holding the temperature and reacting for 30 min, adjusting the pH to 5.0 with formic acid solution; after controlling the temperature at 85? C. and keeping temperature and reacting for 60 min, adjusting the pH to 7.0 with sodium hydroxide aqueous solution; and controlling the temperature at 60? C. and reacting for 30 min, adding urea, and holding the temperature and reacting for 30 min, thus obtaining the resin.

[0094] The hyperbranched melamine-urea-formaldehyde copolycondensation resin modified by polymethylol compound is prepared from melamine, urea, formaldehyde and polymethylol compound in a weight ratio of 1:16:8:0.1, with synthesis steps as follows: adding metered formaldehyde aqueous solution into a reaction kettle, adjusting pH to 7.5 with ethylenediamine, and sequentially adding urea and melamine while stirring; after controlling a temperature at 80? C. and holding the temperature and reacting for 30 min, adjusting the pH to 5.0 with an acidic mixture, adding metered polymethylol compound, controlling the temperature at 60? C., reacting for 30 min, adjusting the pH to 7.0 with sodium hydroxide solution, adding urea, and holding the temperature and reacting for 30 min, thus obtaining the resin.

[0095] The plywood production cycle is 4 min, and the formaldehyde emission of the obtained plywood is 0.009 mg/m.sup.3.

[0096] Embodiment 4 Series type continuous automatic production method of ultrathick plywood with a thickness of 25 mm

[0097] 1. Grading treatment. A wooded veneer with a thickness of 2.4 mm and with inner layer quality (classified by IX/T 1599-2011 rotary veneer) is used as a core veneer, and the grain direction of the veneer is a parallel-to-grain direction.

[0098] 2. Gluing. An adhesive is polymerized diphenylmethane diisocyanate, and glue spread amount on both sides is 100 g/m.sup.2.

[0099] 3. Initial lay-up. Five sheeted veneers with a thickness of 2.4 mm are used for lay-up by a robot by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers, and the grain direction of the upper surface and lower surface is a parallel-to-grain direction.

[0100] 4. Constant-thickness hot pressing. A single-opening hot press is used for hot pressing for 240 seconds at a temperature of 100? C., and a curing degree of the adhesive is controlled to be 90%, so as to obtain a semi-finished product with a thickness of 10.8 mm.

[0101] 5. Board overturning and cooling. After board overturning and cooling, a conversion of an upper surface and a lower surface of the preformed semi-finished product is completed, and the surface temperature is 70? C.

[0102] 6. Defect scanning and repairing. An automatic scanning device is used to distinguish defects and repair the defects such as open jointing on the surface, thus obtaining an initialized core layer.

[0103] 7. Surface treatment. The initialized core layer with a thickness of 10.8 mm is sanded, and the thickness of the initialized core layer is about 10 mm after sanding treatment.

[0104] 8. Gluing. An adhesive is hyperbranched melamine-urea-formaldehyde copolycondensation resin modified by polymethylol compound, and the glue spread amount on both sides is 200 g/m.sup.2.

[0105] 9. First thickening lay-up treatment. Two sheeted cross-band veneers with a thickness of 2.4 mm and two surface veneers with a thickness of 2.4 mm are selected, and by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers, one layer of cross-band veneer and one layer of surface veneer are successively laid on each of the upper surface and lower surface of the core layer, and after lay-up, the grain direction of each of the upper surface veneer and lower surface veneer of the slab is a parallel-to-grain direction, and the lay-up is completed by a robot.

[0106] 10. Constant-thickness hot pressing. A single-opening hot press is used for hot pressing for 200 seconds at a temperature of 100? C., and a curing degree of the adhesive is controlled to be 80%, so as to obtain a semi-finished product with a thickness of 18.5 mm.

[0107] 11. Board overturning and cooling. After board overturning and cooling, a conversion of an upper surface and a lower surface of the preformed semi-finished product is completed, and the surface temperature is 60? C.

[0108] 12. Defect scanning and repairing. An automatic scanning device is used to distinguish defects and repair the defects such as open jointing on the surface.

[0109] 13. Surface treatment. The semi-finished product with a thickness of 18.5 mm is sanded, and the thickness of the initialized core layer is about 17.7 mm after sanding treatment.

[0110] 14. Setting and gluing. An adhesive is melamine-urea-formaldehyde copolycondensation resin, and the glue spread amount on both sides is 200 g/m.sup.2.

[0111] 15. Second thickening lay-up treatment. A semi-finished product with a thickness of 17.7 mm is returned to the operation 1 by a conveyor belt, and then the operations 7-12 are repeated to obtain a semi-finished product with a thickness of 14.0 mm. Two sheeted cross-band veneers with a thickness of 2.4 mm and two surface veneers with a thickness of 2.4 mm are selected, and by following the principle of perpendicular cross of grains of adjacent veneers and the principle of vertical symmetry of core layers, one layer of cross-band veneer and one layer of surface veneer are successively laid on each of the upper surface and lower surface of the core layer, and after lay-up, the grain direction of each of the upper surface veneer and lower surface veneer of the slab is a parallel-to-grain direction, and the lay-up is completed by a robot.

[0112] 16. Setting and hot pressing. The hot pressing is conducted at a temperature of 120? C. for 400 seconds, so as to obtain a finished plywood with a thickness of 26.2 mm.

[0113] 17. Finished product cooling. A final product of the ultrathick plywood with a thickness of about 25 mm is obtained after sanding.

[0114] The melamine-urea-formaldehyde copolycondensation resin is prepared from melamine, urea and formaldehyde in a weight ratio of 1:15:11, with synthesis steps as follows: adding metered formaldehyde aqueous solution into a reaction kettle, adjusting pH to 5.5 with sodium hydroxide aqueous solution, and adding urea and melamine while stirring; after controlling the temperature at 80? C. and holding the temperature and reacting for 30 min, adjusting the pH to 5.0 with formic acid solution; after controlling the temperature at 85? C. and keeping temperature and reacting for 60 min, adjusting the pH to 7.0 with sodium hydroxide aqueous solution; and controlling the temperature at 60? C. and reacting for 30 min, adding urea, and holding the temperature and reacting for 30 min, thus obtaining the resin.

[0115] The hyperbranched melamine-urea-formaldehyde copolycondensation resin modified by polymethylol compound is prepared from melamine, urea, formaldehyde and polymethylol compound in a weight ratio of 1:16:8:0.1, with synthesis steps as follows: adding metered formaldehyde aqueous solution into a reaction kettle, adjusting pH to 7.5 with ethylenediamine, and sequentially adding urea and melamine while stirring; after controlling a temperature at 80? C. and holding the temperature and reacting for 30 min, adjusting the pH to 5.0 with an acidic mixture, adding metered polymethylol compound, controlling the temperature at 60? C., reacting for 30 min, adjusting the pH to 7.0 with sodium hydroxide solution, adding urea, and holding the temperature and reacting for 30 min, thus obtaining the resin.

[0116] The plywood production cycle is 14 min, and the formaldehyde emission of the obtained plywood is 0.022 mg/m.sup.3.

[0117] Although the embodiments of the present disclosure have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be construed as limitations of the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.