A drying method for suppressing large face checking of wood

Abstract

The present application relates to the technical field of wood processing, in particular to a drying method for inhibiting large-section wood cracking. The present application adopts heating softening treatment, modification treatment, modification recovery treatment and drying treatment on sawn timber in sequence to obtain dried wood. If cracks are found during the drying treatment, the modification recovery treatment is continued and the drying treatment is performed again. The drying method of the present application can inhibit both surface cracking and internal cracking of wood, has fewer treatment procedures, low treatment cost, and maintains the mechanical strength of large-section wood containing pith. In the present application, residual stress elimination treatment can be performed on the dried wood to release the residual stress, thereby providing a theoretical basis for obtaining high-quality wood.

Description

Technical Field

[0001] This invention relates to the field of wood processing technology, specifically a drying method for inhibiting large-section cracking of wood. Background Technology

[0002] With the development of my country's national economy and the improvement of people's living standards, timber-framed buildings, with their numerous advantages such as naturalness, environmental friendliness, energy saving and insulation, structural safety, and material recyclability, are increasingly favored, and demand is increasing year by year. As the demand for large-section structural timber used in timber buildings increases accordingly, achieving efficient and high-quality drying of these timbers has become a critical issue that urgently needs to be addressed. In particular, large-section pith-containing square timbers suitable for timber-framed building columns, due to their anisotropic drying shrinkage, will inevitably generate stress due to asynchronous tangential and radial shrinkage even without a moisture content gradient during the drying process and below the fiber saturation point. Therefore, they are highly susceptible to drying cracking, and research on inhibiting drying cracking has become a difficult problem that relevant scholars are continuously striving to solve.

[0003] Timber drying is a crucial step in timber processing, and its quality directly affects the subsequent processing and service life of the boards. Currently, one of the biggest problems facing the application of large-section timber with pith is severe drying cracking. Due to the large thickness of large-section timber with pith and the inclusion of pith in the cross-section, the significant differences in the properties of heartwood and sapwood, as well as the differences in tangential and radial shrinkage, along with difficulties in heat and mass transfer, inevitably lead to uncontrollable drying cracking and a slow drying rate.

[0004] There are two main types of methods for solving the drying cracking problem in large-section timber containing pith. One type involves drying without any moist heat treatment, using only conventional drying, high-temperature drying, or high-frequency drying methods. However, existing literature shows that this method results in severe cracking of the sawn timber, a long drying cycle, and is not an effective solution to the cracking problem. The other type uses high-temperature settling technology to suppress drying cracking. This technology originated in Japan. The process involves softening the wood with saturated moist air or atmospheric pressure saturated steam at 85℃–98℃ before drying, then rapidly raising the temperature to a range of 105℃–140℃ and reducing the humidity to 30%–40%, allowing for rapid dehydration over several hours. The rapidly dehydrated surface layer undergoes creep settling in the softened state, thus inhibiting surface cracking. The results show that this technology dries quickly and can achieve good surface quality. However, because the drying of the wood surface moisture is very intense in the early stage of drying, the rapid evaporation of moisture causes the wood surface to shrink and fix itself. However, in the later stage of drying, the internal shrinkage leads to severe internal cracking and a decrease in mechanical strength.

[0005] Considering the shortcomings of high-temperature deformation technology, Japanese scholars have also developed a pre-drying technology for large-section square timber with pith, which involves laser micro-perforation, grooving along the fiber direction on the unseen side, and drilling along the longitudinal direction of the core. This technology has a significant effect on improving drying speed and suppressing visible cracking. However, due to the increased processing steps and costs, as well as the reduced mechanical strength, it has not yet been applied in actual production.

[0006] Therefore, there is a need for a drying treatment method that has fewer processing steps, lower cost, maintains the mechanical strength of large-section square timber with pith, and can suppress both surface cracking and internal cracking of the square timber. Summary of the Invention

[0007] To address the shortcomings of the existing technology, this invention provides a drying method for suppressing large-section cracking of wood, thereby solving the problem that existing high-temperature stabilization techniques easily lead to internal cracking of wood during the drying process. Furthermore, the method of this invention can suppress both surface and internal cracking of wood, requires fewer processing steps, has lower processing costs, and maintains the mechanical strength of large-section pith-containing square timber. This invention also performs residual stress relief treatment on the dried wood to release residual stress.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A drying method for inhibiting large-section cracking of wood includes the following steps:

[0010] S1. The sawn timber is heated and softened in saturated humid air at 90℃~95℃. At this time, the dry bulb temperature is 90℃~95℃ and the wet bulb temperature is 90℃~95℃, resulting in wood I. Softening serves the subsequent shaping treatment. Wood is a natural viscoelastic material. After high-temperature and humid heat treatment, it will exhibit a certain degree of viscoelasticity, that is, it will become soft. At this time, it will be transferred to the shaping treatment. During the treatment, the surface layer loses a large amount of moisture rapidly, causing the surface layer to shrink, which will result in surface hardening. In this way, the surface layer of the wood is not easy to crack. At the same time, heating and softening can also regulate the uniformity of the internal moisture content of the wood, which is a commonly used method for wood drying.

[0011] S2. Under the conditions of dry bulb temperature of 115℃~125℃, wet bulb temperature of 90℃~95℃, and relative humidity of 30%~40%, wood I is subjected to a change-fixing treatment to obtain wood II. The change-fixing treatment is performed under the condition of rapid temperature rise and rapid humidity drop, which causes the surface of the wood to lose water rapidly, resulting in surface shrinkage and fixation. The surface moisture content drops to about 20%, while the core layer remains basically consistent with the initial moisture content. At this time, the surface moisture of the wood evaporates rapidly, and the surface layer that dehydrates quickly produces creep fixation in a softened state, thereby inhibiting surface cracking. The change-fixing treatment is a technique to fix the surface layer and inhibit surface cracking.

[0012] S3. Wood II is subjected to a resizing treatment in saturated humid air at 90℃~95℃, with both dry-bulb and wet-bulb temperatures at 90℃~95℃, resulting in wood III. After the resizing treatment, a large amount of moisture remains in the core layer. The moisture in the core layer begins to migrate to the surface layer. At this point, the surface layer loses its shrinkage ability due to the previous surface hardening, while the core layer begins to shrink due to water loss. This results in the core layer shrinking, but the surface layer does not allow it to, leading to internal cracking later on. Therefore, the surface layer is subjected to another resizing treatment, namely, a high-temperature and high-humidity softening treatment. The purpose is to allow the surface layer to reabsorb moisture, so that the surface layer will dry and shrink along with the core layer as it loses water. This synchronous shrinkage reduces the stress gradient between the core layer and the surface layer, thereby alleviating the occurrence of internal cracking.

[0013] Therefore, although surface cracking was suppressed after the fixation treatment, the surface layer was still very brittle. In order to improve the surface performance, this invention carried out a fixation recovery treatment, that is, after the fixation treatment, the wood continued to absorb water in saturated humid air. After the fixation recovery treatment, the surface moisture content reached about 40%, while the core layer moisture content decreased by about 20% compared with the initial stage. The reason for the decrease in core layer moisture is that there is a moisture content gradient between the surface layer and the core layer throughout the drying process. Where there is a gradient, there is moisture migration. During the fixation recovery treatment, although the surface layer of the wood increased its moisture, it still had less moisture than the core layer. Therefore, during this process, some moisture from the core layer migrated to the surface layer. Without the fixation recovery treatment, the wood surface would experience severe surface plastic hardening because the surface layer would be almost completely dry after being in the fixation process for a long time, while the core layer would still have a lot of moisture. Therefore, the fixation recovery treatment was carried out to moderate the surface moisture of the wood, reduce the degree of surface hardening, and facilitate subsequent drying.

[0014] In steps S1-S3, the function of dry bulb is to raise the ambient temperature, thereby heating the wood; the function of wet bulb is to maintain the relative humidity of the environment, thus slowing down the evaporation of moisture from the wood during heating.

[0015] Wood III is subjected to conventional drying treatment to remove moisture from it, resulting in dried wood.

[0016] Preferably, in steps S1 and S3, the water vapor pressure in the saturated humid air is 0.1 MPa to 0.3 MPa, and the saturated humid air in steps S1 and S3 provides humidity to the wood, causing the wood to soften.

[0017] Preferably, in the heat softening treatment, the relative humidity of the environment is 100%, and the treatment time is recorded when the core temperature of the wood reaches the ambient temperature, and the treatment lasts for 10 to 12 hours. This application also explored heat softening treatments of 8 hours and 14 hours, but the results were not ideal. After 8 hours of treatment, the core temperature just reached the target temperature, and the wood softening effect was insufficient. After 14 hours of treatment, the surface moisture of the wood lost a lot, which was not conducive to the change treatment in step S2.

[0018] Preferably, in the conditioning process, the ambient humidity is reduced and the temperature is increased. The relative humidity of the environment is 30% to 40%. When the core temperature of wood I reaches 110℃ to 115℃, the treatment time is recorded and the treatment lasts for 10 to 12 hours. Increasing the temperature during the conditioning process causes the moisture inside the wood to vaporize and be discharged to the outside. At this time, the humidity of the environment is reduced to accept the moisture evaporated from the wood. If the humidity is not reduced, the moisture will remain on the surface of the wood. Increasing the temperature and reducing the humidity is a method to achieve rapid drainage.

[0019] Preferably, in the deformation and restoration treatment, the relative humidity of the environment is 100%. When the core temperature of wood II reaches the ambient temperature, the treatment time is recorded, and the deformation and restoration treatment lasts for 8 to 10 hours with an ambient cooling rate of 10℃ / h. Here, we explored the deformation and restoration treatment for 6 hours and 12 hours. The effect of 6-hour treatment was not obvious, and the wood absorbed too much moisture in 12-hour treatment, which was also not ideal. The deformation and restoration treatment uses ambient heating of the wood to bring the core temperature of the wood close to the ambient temperature and increase the humidity again. The purpose is to allow the surface of the wood to absorb water and alleviate the problems caused by the deformation process.

[0020] Preferably, during the drying process, the dry bulb temperature is 70℃~80℃ and the relative humidity is 40%~50%, which are the conventional drying conditions.

[0021] Preferably, if cracks are found during the drying process, the wood is further treated in saturated humid air at 90℃~95℃ for 2~4 hours; after treatment, drying continues. If cracks are found in the later stages of drying, the humidity is increased again to allow the wood to absorb water, while relieving drying stress. This can reduce the formation of cracks because wood has the characteristics of hygroscopic release and shrinkage and expansion when drying; after absorbing water and expanding, it can relieve stress and prevent cracking.

[0022] Preferably, after drying, the dried wood undergoes a residual stress relief treatment. This treatment involves high-frequency heating of the dried wood at 27.12 MHz and 800W–1000W for 0.5–1 hour. Residual stress relief is essential to ensure high drying quality. High-frequency heating targets only the areas with moisture, thus mitigating uneven moisture distribution within the wood and improving moisture uniformity. With more uniform moisture, stress is eliminated, as the internal stress of the wood is caused by uneven moisture content leading to shrinkage differences.

[0023] This invention also protects the dried wood obtained by the above-mentioned drying method, the moisture content of which is 8% to 12%. Under normal circumstances, the equilibrium moisture content of the environment is around 12%, so the wood will not absorb or release moisture due to the environment, thus improving its stability.

[0024] Preferably, the raw material for drying wood is large-section wood containing pith.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. This invention takes pine logs with a cross-section of 120mm-150mm containing pith as the research object, uses humid air as the heat source, and studies the effects of softening, stabilization treatment, and stabilization recovery treatment conditions on subsequent conventional drying performance and wood products. The influence mechanism is analyzed, and suitable softening, stabilization treatment, and stabilization recovery treatment processes are explored, providing a theoretical basis, operating steps, and process parameters for obtaining high-quality wood.

[0027] 2. This invention provides a drying method to suppress large-section cracking in wood. This method can suppress both surface and internal cracking, primarily due to the use of a stress-restoration treatment. This treatment allows the wood surface to absorb moisture, alleviating stress and moisture content differences between the surface and core layers, creating stress and moisture content gradients. This reduces the stress difference caused by the subsequent decrease in core moisture content. Therefore, this process requires strict control of temperature, humidity, and treatment time, with the stress-restoration treatment cyclically repeated, followed by drying to gradually remove moisture from the core material without causing internal or external cracking. Through continuous adjustment and verification, this invention has proven that the stress-restoration treatment at 90℃~95℃ and 100% relative humidity for 8h~10h is the suitable condition.

[0028] 3. Compared with the existing high-temperature variable-setting technology drying treatment method, the existing technology is characterized by suppressing the surface cracking of wood; while the present invention is characterized by suppressing not only surface cracking, but also internal cracking. After the variable-setting treatment, the present invention is supplemented with variable-setting recovery treatment to form a relieved stress gradient and moisture content gradient to reduce the generation of internal cracks. At the same time, a high-frequency treatment process is added to reduce the final residual stress index.

[0029] 4. Compared with the existing technology, this invention proposes a new drying concept for the first time: "drying under the conditions of softening, stabilization, stabilization recovery, creep and stress relaxation". After the wood is fully softened, its surface layer is quickly dehydrated, resulting in surface plasticization and stabilization, which inhibits the generation of surface cracks. At the same time, after a long period of stabilization recovery treatment, the wood will inevitably undergo a certain degree of creep and stress relaxation. That is, the surface stabilization recovers its elasticity after the stress shifts. The creep recovery effect is obvious in the later stage of drying, thereby inhibiting the generation of internal cracks in the wood. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 The graphs show the changes in moisture content of dried wood over time in Examples 1, 4, and Comparative Example 1 of this invention.

[0032] Figure 2 This is a moisture content distribution diagram of sawn timber after different treatments in Example 4 of the present invention;

[0033] Figure 3 A schematic diagram of sawing for measuring moisture content distribution. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] To address the problem that existing wood drying processes easily lead to severe internal cracking in wood, this invention provides a drying method to suppress large-section cracking in wood. This method employs heat softening and tempering treatments to address surface cracks, and tempering recovery treatments to address internal cracks. After tempering recovery treatments, both surface and core layers are dried simultaneously, resulting in a drying method that suppresses both surface and internal cracking. Because no cracks are generated after drying, the mechanical strength of large-section pith-containing square timber is maintained.

[0036] In addition, after obtaining dried wood, residual stress relief treatment can be carried out on the dried wood, and high-frequency heating can be used to achieve uniform distribution of moisture in the dried wood, thereby improving the drying quality.

[0037] The technical solution of the present invention will be further described below with reference to embodiments and comparative examples, as detailed below:

[0038] The test materials used in the embodiments and comparative examples of this invention are all plantation-grown Scots pine timber with pith and core, with a cross-sectional size of 120mm to 150mm and a length of 1m, and a density of 0.376g / cm³. 3 With a moisture content of 80% to 120%, it comes from Dongxing Town, Mulan County, Heilongjiang Province.

[0039] Example 1

[0040] A drying method for inhibiting large-section cracking of wood includes the following steps:

[0041] S1. Heat softening treatment: Set the dry bulb temperature of the drying kiln to 95℃ and the wet bulb temperature to 95℃. Place the sawn timber into the drying kiln and heat soften it in saturated humid air with an ambient relative humidity of 100% for 12 hours to obtain wood I.

[0042] S2. Stabilization treatment: Set the dry bulb temperature of the drying kiln to 120℃ and the wet bulb temperature to 90℃. Place wood I into the drying kiln and stabilize it under the condition of relative humidity of 35% for 10 hours to obtain wood II.

[0043] S3. Stabilization and Restoration Treatment: Set the dry bulb temperature of the drying kiln to 95℃ and the wet bulb temperature to 95℃. Place wood II into the drying kiln and perform stabilization and restoration treatment in saturated humid air with an ambient relative humidity of 100% for 8 hours to obtain wood III.

[0044] S4. Conventional drying treatment: Set the dry ball temperature of the drying kiln to 75℃ and the relative humidity to 45%, and dry the wood III until the target moisture content reaches 11%, thus obtaining dried wood.

[0045] Example 2

[0046] A drying method for inhibiting large-section cracking of wood includes the following steps:

[0047] S1. Heating and softening treatment: Set the dry bulb temperature of the drying kiln to 90℃ and the wet bulb temperature to 90℃. Place the sawn timber into the drying kiln and heat it in saturated humid air with an ambient relative humidity of 100% for 11 hours to obtain wood I.

[0048] S2. Stabilization treatment: Set the dry bulb temperature of the drying kiln to 125℃ and the wet bulb temperature to 95℃. Place wood I into the drying kiln and stabilize it under the condition of relative humidity of 30% for 11 hours to obtain wood II.

[0049] S3. Stabilization and Restoration Treatment: Set the dry bulb temperature of the drying kiln to 90℃ and the wet bulb temperature to 90℃. Place wood II into the drying kiln and perform stabilization and restoration treatment in saturated humid air with an ambient relative humidity of 100% for 9 hours to obtain wood III.

[0050] S4. Conventional drying treatment: Set the dry ball temperature of the drying kiln to 70℃ and the relative humidity to 50%. Dry the wood III until the target moisture content reaches 12% to obtain dried wood. The number of surface cracks and the number of internal cracks in the obtained dried wood are 1.

[0051] Example 3

[0052] A drying method for inhibiting large-section cracking of wood includes the following steps:

[0053] S1. Heat softening treatment: Set the dry bulb temperature of the drying kiln to 95℃ and the wet bulb temperature to 90℃. Place the sawn timber into the drying kiln and heat soften it in saturated humid air with an ambient relative humidity of 100% for 10 hours to obtain wood I.

[0054] S2. Stabilization treatment: Set the dry bulb temperature of the drying kiln to 110℃ and the wet bulb temperature to 90℃. Place wood I into the drying kiln and stabilize it under the condition of 40% relative humidity for 12 hours to obtain wood II.

[0055] S3. Stabilization and Restoration Treatment: Set the dry bulb temperature of the drying kiln to 90℃ and the wet bulb temperature to 95℃. Place wood II into the drying kiln and perform stabilization and restoration treatment in saturated humid air with an ambient relative humidity of 100% for 10 hours to obtain wood III.

[0056] S4. Conventional drying treatment: Set the dry ball temperature of the drying kiln to 80℃ and the relative humidity to 40%. Dry the wood III until the target moisture content reaches 8% to obtain dried wood. The number of surface cracks and internal cracks of the obtained dried wood is 1.

[0057] Example 4

[0058] A drying method for inhibiting large-section cracking of wood is the same as the preparation steps in Example 1, except that a residual stress relief treatment is performed after the drying process, including the following steps:

[0059] S1. Heat softening treatment: Set the dry bulb temperature of the drying kiln to 95℃ and the wet bulb temperature to 95℃. Place the sawn timber into the drying kiln and heat soften it in saturated humid air with an ambient relative humidity of 100% for 12 hours to obtain wood I.

[0060] S2. Stabilization treatment: Set the dry bulb temperature of the drying kiln to 120℃ and the wet bulb temperature to 90℃. Place wood I into the drying kiln and stabilize it under the condition of relative humidity of 35% for 10 hours to obtain wood II.

[0061] S3. Stabilization and Restoration Treatment: Set the dry bulb temperature of the drying kiln to 95℃ and the wet bulb temperature to 95℃. Place wood II into the drying kiln and perform stabilization and restoration treatment in saturated humid air with an ambient relative humidity of 100% for 8 hours to obtain wood III.

[0062] S4. Conventional drying treatment: Set the dry bulb temperature of the drying kiln to 75℃ and the wet bulb temperature to 60℃, and dry wood III until the target moisture content reaches 11%, to obtain wood IV;

[0063] S5. Residual stress relief treatment: Wood IV is subjected to high-frequency heating treatment at a frequency of 27.12MHz and a power of 1000W for 0.5h to obtain dried wood.

[0064] Example 5

[0065] A drying method for inhibiting large-section cracking of wood includes the following steps:

[0066] S1. Heat softening treatment: Set the dry bulb temperature of the drying kiln to 90℃ and the wet bulb temperature to 90℃. Place the sawn timber into the drying kiln and heat soften it in saturated humid air with an ambient relative humidity of 100% for 12 hours to obtain wood I.

[0067] S2. Stabilization treatment: Set the dry bulb temperature of the drying kiln to 125℃ and the wet bulb temperature to 95℃. Place wood I into the drying kiln and stabilize it under the condition of relative humidity of 30% for 10 hours to obtain wood II.

[0068] S3. Stabilization and Restoration Treatment: Set the dry bulb temperature of the drying kiln to 90℃ and the wet bulb temperature to 95℃. Place wood II into the drying kiln and perform stabilization and restoration treatment in saturated humid air with an ambient relative humidity of 100% for 8 hours to obtain wood III.

[0069] S4. Conventional drying treatment: The dry bulb temperature of the drying kiln is set to 75℃ and the relative humidity to 45%. Wood III is dried. During the drying process, cracks are found. The change-fixation recovery treatment is repeated. Wood III is changed-fixed and recovered in saturated humid air with a dry bulb temperature of 90℃ and a wet bulb temperature of 95℃ for 3 hours. Then it is dried until the target moisture content reaches 12%. The dried wood has 0 surface cracks and 1 internal crack.

[0070] Comparative Example 1

[0071] A drying method for inhibiting large-section cracking of wood, which has the same preparation steps as in Example 1, except that there is no change-restoration treatment, includes the following steps:

[0072] S1. Heat softening treatment: Set the dry bulb temperature of the drying kiln to 95℃ and the wet bulb temperature to 95℃. Place the sawn timber into the drying kiln and heat soften it in saturated humid air with an ambient relative humidity of 100% for 12 hours to obtain wood I.

[0073] S2. Stabilization treatment: Set the dry bulb temperature of the drying kiln to 120℃ and the wet bulb temperature to 90℃. Place wood I into the drying kiln and stabilize it under the condition of relative humidity of 35% for 10 hours to obtain wood II.

[0074] S3. Conventional drying treatment: Set the dry bulb temperature of the drying kiln to 75℃ and the wet bulb temperature to 60℃, and dry the wood II until the target moisture content reaches 11%, thus obtaining dried wood.

[0075] Examples 1-5 of this invention all yielded dried wood that suppressed both surface and internal cracking. The dried wood from Examples 1 and 4 are used as examples for comparison with the dried wood from Comparative Example 1. Specific research methods and results are shown below:

[0076] Moisture content test method:

[0077] pass Figure 3 The moisture content distribution map is obtained by sawing. This involves measuring the moisture content at each location and summarizing it in a matrix table, using different colors to represent different values, thus visually showing the moisture content distribution of the square timber. Specifically, moisture content test pieces with dimensions of 120mm × 120mm × 10mm are cut... Figure 3Draw lines as shown to divide the specimen into 25 identical specimens, each measuring 24mm × 24mm × 10mm. Label, split, and measure the mass at different times in sequence, then calculate using the following formula:

[0078]

[0079] Where: MC i —Moisture content of sample i, m i — Actual weight of sample i, m i0 —The oven-dry weight of sample i;

[0080] like Figure 2 As shown, Figure 2 The distribution of moisture content of the test material at different stages during the wood drying process provided in Example 4 is illustrated by way of example.

[0081] After heat softening treatment, the uniformity of moisture content distribution was improved based on the sawn moisture content test material. It showed a trend of gradually decreasing moisture content from the surface layer to the core layer. The average moisture content of the core layer of the test material was about 10% lower than that of the surface layer. At the same time, the temperature of both the core layer and the surface layer of the test material rose to around 95℃.

[0082] After the change treatment, based on the moisture content of the sawn test material, it can be seen that the average moisture content of the test material decreased significantly, and the internal moisture content distribution still showed a trend of gradually decreasing from the surface layer to the core layer. The surface temperature reached 110℃, while the core layer and intermediate layer temperatures were around 100℃.

[0083] After the change-fixed recovery treatment, based on the moisture content of the sawn test material, it can be seen that the uniformity of the moisture content distribution of the test material is further improved. At this time, the moisture content of the core layer is high, the moisture content of the surface layer is low, and the temperature gradient between the core and the surface layer is reduced.

[0084] The quality assessment of sawn timber after different treatment groups is shown in Table 1.

[0085] via Figure 1 The quality assessment data obtained in Table 1 are shown below:

[0086] Table 1. Sawn Timber Quality Assessment under Different Treatments

[0087]

[0088] As shown in Table 1, the treatment group with the variable-stress recovery treatment significantly suppressed internal cracks; meanwhile, the treatment group with the residual stress relief treatment had low residual stress. Table 1 also clearly shows that the single variable-stress group exhibited significant internal cracking; while the addition of variable-stress recovery treatment significantly suppressed both surface and internal cracks, but had little effect on residual stress; finally, the addition of residual stress relief treatment effectively suppressed residual stress. Therefore, the process employed in this invention can greatly improve the quality of wood drying.

[0089] The residual stress was relieved by using high frequency. Because the residual stress of thick boards is very large, stress relief is necessary to ensure drying quality. Thin boards do not require residual stress relief.

[0090] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0091] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims and their equivalents, this invention also intends to include these modifications and variations. The above-described embodiments are merely preferred embodiments for fully illustrating the invention, and their scope of protection is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on this invention are all within the scope of protection of this invention, which is defined by the claims.

Claims

1. A drying method for suppressing large-section cracking of wood, characterized in that, Includes the following steps: The sawn timber was heated and softened in saturated humid air at 90℃~95℃ to obtain wood I. During the heating and softening treatment, the relative humidity of the environment was 100%. When the center temperature of the sawn timber reached the ambient temperature, the treatment time was recorded and the heating and softening treatment lasted for 10h~12h. Under the conditions of dry bulb temperature of 115℃~125℃, wet bulb temperature of 90℃~95℃, and relative humidity of 30%~40%, wood I was subjected to a change fixation treatment, which caused wood I to lose moisture rapidly, resulting in wood II. During the change fixation treatment, when the center temperature of wood I reached 110℃~115℃, the treatment time was recorded and the change fixation treatment lasted for 10h~12h. Wood II was subjected to a stress recovery treatment in saturated humid air at 90℃~95℃ to alleviate the stress and moisture content between the surface and core layers of wood II, thereby reducing the stress gradient and moisture content gradient, and thus obtaining wood III. During the change-fixation recovery treatment, the relative humidity of the environment is 100%. When the center temperature of wood II reaches the ambient temperature, the treatment time is recorded and the change-fixation recovery treatment lasts for 8 to 10 hours. Wood III is dried to obtain dried wood.

2. The drying method for suppressing large-section cracking of wood according to claim 1, characterized in that, During the drying process, the dry bulb temperature is 70℃~80℃ and the relative humidity is 40%~50%.

3. The drying method for suppressing large-section cracking of wood according to claim 1, characterized in that, If cracks are found during the drying process, continue the conditioning and recovery treatment in saturated humid air at 90℃~95℃ for 2h~4h, and then continue drying.

4. The drying method for suppressing large-section cracking of wood according to claim 1, characterized in that, After drying, the dried wood was also subjected to residual stress relief treatment to release residual stress.

5. The drying method for suppressing large-section cracking of wood according to claim 4, characterized in that, The residual stress relief treatment is performed by heating the dried wood at a frequency of 27.12MHz and a power of 800W~1000W for 0.5h~1h.

6. A dried wood prepared by the drying method for inhibiting large-section cracking of wood according to any one of claims 1 to 5, characterized in that, The moisture content of dried wood is 8% to 12%.

7. The dried wood according to claim 6, characterized in that, The raw material for dried timber is large-section timber containing pith.

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