Method and system for repairing surface defects of a plywood blank

Abstract

The application discloses a kind of plywood blank surface defect repair method and system.Method includes:S1, preparation blank defect repair putty, the putty component includes stone powder, water and urea-formaldehyde glue;S2, to the blank with surface defect, using coating device is coated on both sides, the vertical pressure applied by the coating device, so that putty is forced to be extruded into the defect of the blank surface;S3, after coating, the blank is turned to vertical state and is sequentially dried and cooled;S4, sanding is carried out to the blank after cooling.The system includes coating device, vertical circulating drying and cooling system and sanding machine group.The application realizes the forced accurate filling of putty to defect, and avoids wet putty layer being contaminated and scratched by vertical conveying, significantly improves repair quality, yield and drying efficiency.

Description

Technical Field

[0001] This invention relates to the field of plywood processing technology, and specifically to a method and system for repairing surface defects in plywood blanks. Background Technology

[0002] During plywood production, defects such as holes and cracks often appear on the surface of the plywood blanks, requiring repair to ensure the quality of the finished product. In existing technologies, defects are typically filled with putty manually or using simple tools. For example, patent document CN106182220A discloses a plywood production process that involves filling holes, cracks, and gaps on the plywood with putty after hot pressing.

[0003] However, the aforementioned existing technologies have many inherent defects in practical applications. Specifically, firstly, existing technologies typically use general-purpose putty or simply formulated putty for surface application or smoothing, which is essentially a passive covering. Because the putty components lack optimized design for deep penetration and bonding with wood fibers, it is difficult to form effective mechanical interlocking and chemical bonding with the porous, loose wood substrate, resulting in weak adhesion between the repair layer and the substrate. This makes it prone to detachment due to stress during subsequent processing or use. Secondly, conventional "filling" or "scraping" operations only apply putty to the defect surface, failing to force and fully penetrate the repair material into the depths of the defects (especially internal cracks and deep pores). This leads to incomplete repairs with internal gaps, affecting not only the smoothness of the appearance but also severely weakening the overall mechanical strength of the area, becoming a hidden weak point in the board. Furthermore, existing technologies lack a systematic and controlled post-processing procedure for the repaired board. The repair area differs from the original substrate in moisture content, internal stress distribution, and adhesive curing state. If these differences are not minimized through precise heat treatment and curing processes, thermal stress can easily accumulate within the slab, leading to deformation, warping, or problems such as repair material adhesion and surface contamination during stacking and storage. This severely impacts production yield and finished product stability. Furthermore, sanding to achieve a smooth surface requires precise gradient control of the sanding amount and grit sequence. Without this control, it is difficult to efficiently remove excess repair material while accurately ensuring the finished product thickness and avoiding excessive damage to the substrate.

[0004] Therefore, there is an urgent need in this field for a method to repair surface defects of plywood blanks that can achieve a deep and firm bond between the repair material and the wood substrate, ensure that the defects are fully and densely filled, and make the physical and chemical properties of the repair area consistent with those of the substrate through an efficient and stable post-processing process. Summary of the Invention

[0005] In view of the problems existing in the prior art, such as the difficulty of repair materials penetrating deep into the wood fibers, insufficient bonding force leading to easy detachment, and the large difference in physical and chemical properties between the repair area and the substrate affecting the overall stability, the purpose of this invention is to provide a method and system for repairing surface defects of plywood blanks that can achieve deep and firm bonding between the repair material and the wood substrate, and ensure the stability of the physical and chemical properties of the repair area.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for repairing surface defects in plywood blanks, comprising the following steps: S1. Prepare putty for repairing defects in slabs, wherein the putty components include stone powder, water and urea-formaldehyde resin; S2. For slabs with surface defects, a coating device is used to coat both the top and bottom surfaces. The vertical pressure applied by the coating device forces the putty into the defects on the surface of the slab. S3. Turn the coated slab into a vertical position and perform drying and cooling treatments in sequence. S4. Sand the cooled slab.

[0007] Furthermore, the putty preparation steps include: S101. Mix a portion of the stone powder with the special putty powder evenly; S102. Add the first portion of water to the premixed material and stir to form a paste; S103. Add the remaining stone powder to the paste and stir thoroughly; S104. Add the second part of water and urea-formaldehyde resin to the solidified material.

[0008] Preferably, the stone powder has a mesh size of 280-320; the first portion of water is 50-60 kg, the second portion of water is 10-15 kg, the urea-formaldehyde adhesive is 10-15 kg, the total amount of stone powder is 200 kg, and the special putty powder is 7 kg.

[0009] Furthermore, in step S2, the vertical pressure applied by the coating device is adjusted according to the physical properties of the slab material.

[0010] Furthermore, in step S3, the vertically positioned slabs are supported by a vertically arranged circulating drying and cooling system, so that a uniform airflow gap is formed between adjacent slabs.

[0011] Furthermore, the drying temperature is The duration is 30 minutes.

[0012] Preferably, the cooling process lasts for 30 minutes.

[0013] Furthermore, step S4 further includes: after the cooling treatment, the slab is left to stand and cure at room temperature for 4 days.

[0014] The present invention also provides a repair system for surface defects in plywood blanks, comprising: A coating apparatus includes a frame and an upper coating module and a lower coating module arranged opposite each other. Each upper and lower coating module includes a pressure injection chamber and a scraper blade disposed at the outlet of the pressure injection chamber. A pressure loading mechanism is provided between the scraper blade and the pressure injection chamber, and a mechanical pressurization mechanism is provided inside the pressure injection chamber. A vertical circulating drying and cooling system includes a chain conveyor, several equally spaced tilting supports fixed on the chain conveyor, and a drying zone and a cooling zone through which the tilting supports pass in sequence. The sanding unit is located downstream of the vertical circulating drying and cooling system. The sanding unit is arranged in a gradient, specifically with 60-mesh sanding belt, 80-mesh sanding belt and 120-mesh sanding belt arranged in sequence.

[0015] Furthermore, the spacing between the comb-shaped flip-up brackets is 8cm.

[0016] Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses a putty formula composed of stone powder, special putty powder, water and urea-formaldehyde glue in a specific ratio and follows a specific preparation process, so that the putty has both high solid content and suitable rheological properties, thereby achieving deep penetration and firm bonding between the repair material and wood fiber, fundamentally overcoming the problem of easy peeling of traditional repair layers.

[0017] (2) The present invention uses an upper and lower opposing scraping module to form an instantaneous sealed space between the slab surface and the injection slit through vertical pressure, and uses local mechanical pressure to force the putty into the defect, so that the putty can fill the holes and cracks by injection rather than surface covering, thereby achieving dense and gapless filling of the defect and significantly improving the density of the repair area.

[0018] (3) The present invention flips the coated slab to a vertical position and limits it with a comb-shaped flipping bracket with an 8cm interval, so that the surface of the slab has the maximum contact area and heat exchange efficiency with the air during the drying and cooling process, thereby realizing the rapid and uniform release of thermal stress, effectively preventing the slab from stacking and sticking, and promoting the deep cross-linking and curing of the adhesive inside the putty.

[0019] (4) This invention adopts a gradient sanding process of “coarse sand smoothing (60 mesh sanding belt) - fine sand thickness setting (80 mesh and 120 mesh sanding belt group)” and precisely controls the amount of sanding each time (0.5 mm). This allows the repair area to achieve a high surface finish while its thickness is precisely unified with the surrounding substrate. This ensures that the repair area is physically consistent with the slab substrate and guarantees the overall quality uniformity of the finished product. Attached Figure Description

[0020] Figure 1 This is a flowchart of the method for repairing surface defects in plywood blanks according to the present invention; Figure 2 This is a schematic diagram of the repair system of the present invention. Figure 1 ; Figure 3 This is a schematic diagram of the vertical circulating drying and cooling system of the repair system of the present invention; Figure 4 This is a schematic diagram of the repair system of the present invention. Figure 2 ; Figure 5 This is a detailed structural diagram of the comb-shaped flip-up bracket of the repair system of the present invention; Reference numerals: 1-Coating device; 2-Putty preparation and feeding system; 3-Vertical circulating drying and cooling system; 4-Slab; 5-Chain conveyor; 6-Comb-shaped turning support; 7-Drying zone; 8-Cooling zone. Detailed Implementation

[0021] To facilitate understanding of the present invention, a more complete description of this application will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the invention. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to enable a more thorough and complete understanding of the disclosure of the present invention.

[0022] It should be noted that the terms "vertical," "horizontal," "up," "down," "left," "right," and similar expressions used in this article are for illustrative purposes only and do not represent the only possible implementation.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] Example 1. This example provides a method for repairing surface defects in plywood blanks and a system for implementing the method.

[0025] The steps are as follows: First, the plywood blanks with surface defects (such as holes and cracks) are pre-treated. The pre-treatment includes ensuring that the center line of the blank is aligned with the travel axis of the subsequent coating device by using a mechanical centering device. Then, the blanks are sawn on all four sides to make their geometric dimensions uniform and to provide regular edge conditions for subsequent coating.

[0026] Subsequently, a putty for repairing defects in the slab is prepared. The putty components include stone powder, water, and urea-formaldehyde resin. The prepared putty is then conveyed to a coating device 1, into which the pretreated slab 4 is fed. The coating device 1 includes a frame and an upper and lower scraping module arranged vertically opposite each other. Both the upper and lower scraping modules include a pressure injection chamber and a scraper blade located at the outlet of the pressure injection chamber. A pressure loading mechanism is provided between the scraper blade and the pressure injection chamber to form a momentarily sealed injection chamber between the surface of the slab 4 and the scraper blade. The pressure injection chamber is equipped with a mechanical pressurizing mechanism for squeezing the putty into the injection chamber. When the slab 4 passes through the coating device 1, the upper and lower scraping modules apply vertical pressure to the slab, creating a momentarily sealed space between the slab surface and the scraper blade. Under this pressure, the putty is forced into the defects on the surface of the slab 4, achieving injection-type filling rather than simple surface application.

[0027] Next, the coated slab 4 is fed into the vertical circulating drying and cooling system 3. The vertical circulating drying and cooling system 3 includes a chain conveyor 5 and multiple comb-shaped turning supports 6 fixed at equal intervals on the chain conveyor 5. The path of the chain conveyor 5 passes through the drying zone 7 and the cooling zone 8. The chain conveyor 5 and the comb-shaped turning supports 6 work together to turn the coated slab 4 into a vertical position, and then pass through the drying zone 7 and the cooling zone 8 in sequence for drying and cooling. The slab 4 enters the drying zone 7 in a vertical position and is dried at a suitable drying temperature to allow the putty to initially solidify. After drying, the slab 4 remains in a vertical position and enters the cooling zone 8, where it is cooled by forced airflow (e.g., airflow generated by a fan) for a sufficient cooling time to release thermal stress.

[0028] Finally, after the cooling process is completed, the slab is removed from its vertical position and stacked horizontally. The surface of the slab is then subjected to gradient sanding to fix the thickness and achieve a smooth finish. First, a lower mesh sanding belt (60 mesh) is used for coarse sanding to remove obvious surface unevenness. Then, a higher mesh sanding belt set (80 mesh and 120 mesh) is used in sequence for fine sanding to fix the thickness and control the final product thickness and smoothness. The amount removed by each sanding is 50 mils, or 0.5 mm.

[0029] Technical Effects: This embodiment utilizes vertical pressure to force the putty deep into the defect, achieving dense filling. Subsequently, drying and cooling are performed vertically, and the resulting airflow channels greatly improve heat exchange efficiency, allowing for rapid and uniform release of thermal stress. This effectively prevents the board from plywood from stacking and sticking together, and promotes putty curing. The entire process provides a good foundation for subsequent conventional sanding and thickness setting, ultimately resulting in a plywood product with a strong bond between the repaired area and the substrate, and stable physical and chemical properties.

[0030] Example 2. This example provides a preferred method for repairing surface defects in plywood blanks. Based on Example 1, it further specifies the putty formula and preparation process for extrusion filling to better achieve deep penetration and strong bonding between the putty and wood fibers.

[0031] The repair method of this embodiment further includes a putty preparation step before the extrusion and filling step. The putty comprises stone powder, special putty adhesive powder, water, and urea-formaldehyde resin, and its preparation process is strictly carried out in the following order: Step S101: Add a portion of stone powder (150kg) and special putty powder (7kg) into a mixer and mix them evenly at low speed to form a premixed dry material.

[0032] Step S102, Initial Emulsification: Add the first portion of water (50-60 kg) to the premixed dry material, increase the mixer speed to medium and continue stirring until the material forms a uniform paste. This step aims to fully hydrate the adhesive powder and form a preliminary bonding network.

[0033] Step S103: Add the remaining stone powder (50 kg) to the paste and continue stirring at medium speed to evenly disperse the stone powder and embed it into the paste, significantly increasing the solid content and consistency of the putty and forming a reinforced paste with sufficient cohesion.

[0034] Step S104: Add the second portion of water (10-15 kg) and urea-formaldehyde resin (10-15 kg) to the strengthening paste, adjust the stirring speed to low, and mix evenly. Adding urea-formaldehyde resin for modification can further improve the final bonding strength and water resistance of the putty after curing.

[0035] Technical effects: Through the above-mentioned specific formula and preparation process, the resulting putty has a high solids content and optimized rheological properties. Its viscosity and cohesion are balanced, which allows the putty to flow effectively under vertical pressure and penetrate deeply into the tiny defects between wood fibers during the subsequent coating steps. It can also maintain its shape after the pressure is removed and is not easy to bounce back or collapse. This provides a key material guarantee for the entire repair method and is the material basis for achieving deep penetration into defects and forming a dense and firm repair layer.

[0036] Example 3. Based on the system framework described in Example 1, this example provides a more preferred repair system for surface defects in plywood blanks, the specific structure and workflow of which are as follows.

[0037] The spacing between the comb-shaped flipping supports 6 of the vertical circulating drying and cooling system 3 is 8cm. This design allows for the formation of uniform and continuous airflow channels between the vertically placed slabs 4. Compared to the wider support strips in Embodiment 1, the comb-shaped flipping supports 6 greatly reduce the contact area between the slabs 4 and the supports, effectively reducing the risk of putty or wood sticking to the supports due to excessively high contact surface temperature during subsequent heat treatment. Furthermore, hemispherical protrusions are provided on the contact surface between the comb-shaped flipping supports 6 and the slabs 4. These hemispherical protrusions are evenly spaced along the length of the comb-shaped flipping supports 6. By setting these hemispherical protrusions, the comb-shaped flipping supports 6 maintain a minimum contact area with the slabs during transport, further reducing the contact area with the slabs 4 and preventing damage to the putty layer on the slab surface during transport.

[0038] The comb-shaped flipping support 6 carrying the vertical slab 4 is moved into the drying zone 7 by the chain conveyor 5. The temperature in the drying zone 7 is maintained at a stable 50℃. The slab 4 is dried in this constant temperature environment for a duration strictly controlled to 30 minutes. During this process, because the slab 4 is in a vertical state and there is a uniform gap of 8cm between the slabs, the hot air can fully and evenly sweep over the front and back of the slab 4, achieving efficient and uniform heat exchange. This ensures that the putty (especially the urea-formaldehyde resin component) can fully complete the cross-linking and curing reaction, and avoids local thermal stress caused by uneven heating.

[0039] After drying, the comb-shaped tilting support 6 moves into the cooling zone 8 along with the chain conveyor 5. The blower in the cooling zone 8 is started to generate forced convection airflow. The slab 4 is cooled while maintaining a vertical position. The cooling treatment duration is also set to 30 minutes. This specific cooling time ensures that the slab 4 can be cooled uniformly and steadily from 50°C to near room temperature, thereby completely releasing the residual thermal stress that may have accumulated during the drying process and preventing the slab 4 from warping or micro-cracks from forming at the repair interface due to excessively rapid cooling.

[0040] Technical Effects: By implementing the optimized scheme of this embodiment, the "comb-shaped support structure," "8cm interval distance," "50℃ constant temperature drying for 30 minutes," and "30 minutes of forced convection cooling" together constitute a synergistically optimized heat treatment process window. Actual measurements show that this parameter combination makes the heating and cooling curves of the slab during heat treatment smoother and more uniform. Its direct effects are: First, the slab deformation rate is significantly reduced; the warpage of the slab treated in this embodiment can be controlled within 5mm / m in subsequent measurements. Second, it completely eliminates adhesion between slabs and between the slab and the support frame, improving production continuity and equipment cleanliness. Third, the curing of the repair putty is more thorough and uniform, reliably ensuring the final bonding strength and water resistance of the repaired area, achieving high efficiency, stability, and high quality in the post-treatment process.

[0041] Example 4. This example provides a preferred method for repairing surface defects in plywood blanks. Based on Example 1, it further specifies that after the vertical heat treatment step, a static curing step is included to achieve final stabilization of the repaired area.

[0042] After cooling, the slabs are transported to a temperature and humidity controlled warehouse (e.g., temperature (22±2)℃, relative humidity (55±5)%) via a conveyor line. Inside the warehouse, the slabs 4 are stacked horizontally, with wooden blocks separating each stack to maintain ventilation. The slabs 4 are then left to cure in this environment for a period of 4 days.

[0043] Technical Effects: By implementing the static curing step in this embodiment, sufficient time is provided for the repair area (the interface between the putty and the wood) to allow residual stress to be released slowly and thoroughly. Simultaneously, the moisture in the putty and the surrounding wood substrate gradually reach equilibrium in a constant temperature and humidity environment. Actual measurements show that after 4 days of curing, the dimensional stability of the repair area is significantly improved, with its linear expansion rate differing from the surrounding substrate by an average of less than 0.5%. This ensures that the final physical and mechanical properties of the repair area (such as strength, hardness, and water resistance) are highly consistent with the original wood substrate, fundamentally solving the long-term reliability problem caused by the mismatch between the physicochemical properties of the repair material and the substrate, and achieving long-term stability of the repair effect.

[0044] Comparative Example 1. This comparative example describes a traditional method for repairing surface defects in plywood blanks, including the following steps: Step S1, Manual Scraping: Take a plywood blank with surface holes and defects, and use ordinary gypsum putty or commercially available wood putty (e.g., whose main components are gypsum powder and glue). The operator holds a scraper and manually applies and smooths the putty to the defects on the surface of the blank. The main purpose of this operation is to "fill" or "cover" the defect surface with putty. The filling is achieved by the weight of the putty itself and the smoothing action of the scraper. It is not possible to apply vertical pressure to the putty to force it into the interior of the defect.

[0045] Step S2, Horizontal Stacking and Drying: The hand-coated slabs are stacked horizontally on wooden pallets. The stacked slabs are then pushed into a traditional drying chamber. The drying chamber uses hot air circulation heating, with the temperature set at 50-60℃ and the drying time set at 2-4 hours. Due to the close horizontal stacking of the slabs, hot air cannot circulate effectively between them. Heat is mainly transferred through the perimeter and top of the stack, resulting in uneven heating of the slabs inside the stack. After drying, the slab stacks are allowed to cool naturally inside the drying chamber or after being removed, and then subsequent processes such as sanding are performed.

[0046] Comparative effect analysis: Comparing the conventional method of this comparative example with the method of Embodiment 1 of the present invention highlights the non-obviousness and technical effects of the present invention: (1) Comparison of repair bond strength and durability Traditional manual application methods can only cover the surface or shallow layer of the defect with putty, failing to penetrate into the microscopic pores of the wood fibers. The bond between the cured repair layer and the substrate is primarily physical, resulting in weak adhesion. During subsequent handling or post-processing (such as sanding and trimming), the repair layer is easily detached due to vibration. In actual use, the interface is prone to stress cracking due to changes in ambient temperature and humidity. This invention, however, uses a "vertical extrusion filling" step, forcibly injecting and penetrating the putty into the roots of pores and cracks and the surrounding gaps in the wood fibers under pressure. After curing, it forms a "root-like" anchoring structure, achieving deep mechanical interlocking. The urea-formaldehyde resin in the synergistically optimized putty formula can also chemically cross-link with lignin, further enhancing the interfacial adhesion. Under the same testing conditions, the adhesive strength of the repaired area using this invention can be consistently above 1.2 MPa, and the repair layer did not peel off in the immersion peel test, indicating a fundamental improvement in its bonding reliability and durability.

[0047] (2) Comparison of flatness of slabs after treatment Traditional horizontal stacking drying methods result in extremely uneven heating due to the lack of effective airflow channels between slabs. This leads to large moisture content gradients and inconsistent shrinkage across different parts of the slab. Furthermore, the curing shrinkage stress of the repair putty cannot be evenly released, easily causing warping and deformation of the slab. This invention's unique "vertical circulating drying and cooling" step places each slab independently and vertically, forming an 8cm uniform hot air channel, ensuring uniform and efficient heat exchange. Precise control of 30 minutes of gentle drying and 30 minutes of forced cooling ensures that the moisture content gradient and residual stress across the entire slab are uniform, and minor shrinkage stress is slowly released in a free state. Actual measurements show that slabs treated with this invention have a warpage that can be stably controlled within 0.3% before sanding, providing a good planar reference for subsequent precision thickness sanding and significantly improving the yield.

[0048] (3) Comparison of production efficiency and energy consumption Traditional drying methods have a drying cycle of 2-4 hours and are intermittent, resulting in huge energy consumption and becoming a bottleneck for production capacity. The vertical circulation system of this invention enables continuous assembly line operation, precisely compressing the total drying and cooling time to about 1 hour. It matches the processing rhythm with the preceding and following processes, eliminates the need for work-in-process inventory, and reduces the heat energy consumption per unit product by more than 50%, significantly improving production efficiency and economy.

[0049] Obviously, the above description is only a part of the embodiments of the present invention, and not all of the embodiments. The above embodiments are not intended to limit the present invention, and various modifications and variations can be made to the present invention by those skilled in the art. Any combination, modification, equivalent substitution, improvement, and all other embodiments that can be made by those skilled in the art within the spirit and principles of the present invention should be within the protection scope of the present invention.

Claims

1. A method for repairing surface defects in plywood blanks, characterized in that, Includes the following steps: S1. Prepare putty for repairing defects in slabs, wherein the putty components include stone powder, water and urea-formaldehyde resin; S2. For slabs with surface defects, a coating device is used to coat both the top and bottom surfaces. The vertical pressure applied by the coating device forces the putty into the defects on the surface of the slab. S3. Flip the coated slab to a vertical position and perform drying and cooling treatments in sequence. S4. Sand the cooled slab.

2. The method for repairing surface defects of plywood blanks according to claim 1, characterized in that, The putty preparation steps include: S101. Mix a portion of the stone powder with the special putty powder evenly; S102. Add the first portion of water to the premixed material and stir to form a paste; S103. Add the remaining stone powder to the paste and stir thoroughly; S104. Add the second part of water and urea-formaldehyde resin to the solidified material.

3. The method for repairing surface defects of plywood blanks according to claim 2, characterized in that, The stone powder has a mesh size of 280-320; the first portion of water is 50-60 kg, the second portion of water is 10-15 kg, the urea-formaldehyde adhesive is 10-15 kg, the total amount of stone powder is 200 kg, and the special putty powder is 7 kg.

4. The method for repairing surface defects in plywood blanks according to claim 1, characterized in that, In step S2, the vertical pressure applied by the coating device is adjusted according to the physical properties of the slab material.

5. The method for repairing surface defects of plywood blanks according to claim 1, characterized in that, In step S3, a vertical circulating drying and cooling system supports the vertically positioned slabs, creating uniform airflow gaps between adjacent slabs.

6. The method for repairing surface defects in plywood blanks according to claim 1 or 5, characterized in that, The temperature of the drying process is: The duration is 30 minutes.

7. The method for repairing surface defects in plywood blanks according to claim 6, characterized in that, The cooling process lasts for 30 minutes.

8. The method for repairing surface defects in plywood blanks according to claim 1, characterized in that, Step S4 further includes: after the cooling treatment, the slab is left to stand and cure at room temperature for 4 days.

9. A repair system for surface defects in plywood blanks, characterized in that, include: A coating apparatus includes a frame and an upper coating module and a lower coating module arranged opposite each other. Each upper and lower coating module includes a pressure injection chamber and a scraper blade disposed at the outlet of the pressure injection chamber. A pressure loading mechanism is provided between the scraper blade and the pressure injection chamber, and a mechanical pressurization mechanism is provided inside the pressure injection chamber. A vertical circulating drying and cooling system includes a chain conveyor, several equally spaced tilting supports fixed on the chain conveyor, and a drying zone and a cooling zone through which the tilting supports pass in sequence. The sanding unit is located downstream of the vertical circulating drying and cooling system. The sanding unit is arranged in a gradient, specifically with 60-mesh sanding belt, 80-mesh sanding belt and 120-mesh sanding belt arranged in sequence.

10. The repair system for surface defects in plywood blanks according to claim 9, characterized in that, The spacing between the comb-shaped flip-up brackets is 8cm.

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