A method of drying a tree disc

Abstract

The application discloses a kind of drying methods of tree tray, including pre-drying treatment to tree tray, so that the moisture content of tree tray reaches pre-drying moisture content M 预 , obtain pre-drying tree tray;Then the average moisture content of pre-drying tree tray is monitored, according to the general drying standard procedure, drying is carried out until the average moisture content of tree tray pile is less than 15%, stop drying, obtain dry tree tray.The drying defect of tree tray is reduced by using the method of the application, the radial shrinkage of tree tray is less than the critical value of the radial shrinkage of tree tray by measuring the radial shrinkage of tree tray during drying, controlling the moisture content of each tree tray at different radial level position in real time, so as to reduce the cracking of tree tray and improve the utilization efficiency of tree tray.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wood drying and modification, and particularly relates to a method for reducing drying defects of tree disks. BACKGROUND

[0002] The tree disk is obtained by cross-cutting the log, and the processing method of the tree disk is simple, i.e., only sawing from the log alone, without a large amount of splicing treatment and complex processing, and the yield is higher than that of other wood raw materials. After drying, the tree disk can be processed into a menu, a fine handicraft, a standing wood floor block, a watch disk, a heat insulation pad, etc., and embodies the value concept of green environmental protection. Not only can the added value be increased, but also the utilization rate is high, which is of great significance for alleviating the above-mentioned contradiction.

[0003] High-quality drying is the key to determining the high yield of the above-mentioned products, but drying defects will occur in the wood drying process, which are mainly caused by drying stress. Without considering the influence of the growth stress of the wood itself, the drying stress is mainly caused by the anisotropy of drying shrinkage and the moisture content gradient. Due to the anisotropy of wood drying shrinkage, even if there is no moisture content gradient in the drying process, stress will inevitably occur below the fiber saturation point, so that the wood is extremely prone to cracking during and after drying, thereby causing waste and damage of the raw material, and seriously affecting its application and value.

[0004] In order to avoid wood drying defects, people have done a lot of research on reducing stress and overcoming stress during wood drying process. For example, the patent application No. 201610127930.2 discloses a cross-laminated timber structure and a manufacturing method. The cross-laminated timber is composed of at least three layers of material, which are the first surface layer in the upper layer, the core layer in the middle layer, and the second surface layer in the lower layer. The first surface layer, the core layer and the second surface layer are fixed by glue. The manufacturing method includes the following steps: material selection, rounding, stress release slot opening, drying, cutting, combing, embryo assembly, and plate pressing. This method effectively releases drying stress, reduces drying defects, and reduces drying energy consumption. Because the stress release slots are retained in the two surface layer finger joint plates of the cross-laminated timber, the cross-laminated timber has high dimensional stability after forming in humid and dry environments. In addition, the stress release slots are relatively dispersed in the cross-laminated timber, so they do not affect the mechanical strength, and the technical problems of low strength and poor stability in the existing cross-laminated timber technology are well solved. For another example, the utility model patent No. 201721699890.5 discloses a device for uniformizing and stress relieving of veneer permeability. It is composed of a frame type mechanism box, a feeding port, an inlet and outlet pressure roller pair, a permeability uniformization and stress relieving roller, a permeability uniformization and stress relieving roller lifting adjustment mechanism, a supporting roller, a supporting roller lifting adjustment mechanism, a driving system, and a discharge port. The permeability uniformization and stress relieving roller and the supporting roller must exist in pairs. The distance between the two rollers can be adjusted according to needs. Under the joint action of the permeability uniformization and stress relieving roller and the supporting roller, the sharp disc-shaped knife blade cuts uniform knife marks on the veneer, thereby converting large internal stress and drying stress into multiple small internal stress and drying stress, greatly reducing the internal stress non-uniformity of the veneer, and increasing the permeability of the veneer. The permeability is more uniform, effectively solving the problems of veneer deformation and cracking, and helping to improve production efficiency and reduce energy consumption. The invention patent No. 201910432465.7 discloses a method for inhibiting wood cracking during drying process, which includes the following steps: step one, installing a drying stress detection device in the wood drying kiln; step two, installing a compression prestress generator in the wood drying kiln; step three, drying the wood and starting the compression prestress generator within the set drying stress range; step four, when the drying stress is lower than the predetermined value, the compression prestress generator is turned off. This method can effectively inhibit the occurrence of cracking during the drying process, and the treated wood has high drying quality and few defects. The invention patent No. 201610648344.2 discloses a sawn timber drying stress evaluation method for wood quality control. This method solves the problems of low precision in detecting and analyzing drying stress and residual stress in the wood drying process, and cannot achieve the goal of controlling drying quality and shortening drying cycle.The method measures the viscoelastic creep of the plate in the width direction under dry conditions and the free dry shrinkage strain of small-size test pieces of the same tree species, and calculates the mechanical adsorption creep strain of the plate in the width direction based on the principle of wood drying rheology. In the method, the wood drying mechanical adsorption creep gradient is defined, the influence mechanism of the wood mechanical adsorption creep gradient, the wood moisture content gradient and other parameters on the stress release process of the plate during drying is determined, the technical ambiguity generated by the traditional "fork tooth section method" in describing the wood drying stress is overcome, the method can be used for quantitative description of the needle wood drying stress, and scientific evaluation of the wood drying quality is realized.

[0005] Although there are many studies on wood drying stress at present, there are few studies on tree disc drying stress, and these studies have limitations in suitable size range and small drying batch,

[0006] For example, the invention patent 201610128125.1 discloses a drying method of round timber, which comprises the following steps: selecting appropriate log size and tree species and performing round processing to obtain round timber; according to the size of the round timber, stress release grooves are made at both ends; the round timber is naturally dried; the naturally dried round timber is placed in a drying kiln for drying; and the moisture content of the round timber is controlled according to the purpose. The method releases the growth stress and drying stress of the round timber by making stress release grooves, thereby reducing the cracking of the wood during drying; and the deformation defect of the wood during drying is avoided. However, the method damages the wood by making stress release grooves at both ends of the round timber, and is only suitable for drying of round timber with long axial length. For example, the invention patent 202110391761.4 discloses a wood tree disc high-frequency drying device, which can effectively inhibit the cracking of the tree disc during the drying process, has fast drying efficiency and is convenient to control and adjust. However, the amount of tree disc dried by the device is small, the drying process cannot be accurately controlled, a large amount of tree disc cannot be dried, the drying efficiency is low, special drying equipment is needed, the cost of tree disc drying is high, and the drying moisture loss of different parts of the tree disc cannot be accurately controlled during the drying process, and the tree disc drying defect is large.

[0007] The current technical invention is still lacking in tree disc drying. Regardless of the drying method used, the technical problem of easy cracking during the tree disc drying process has not been well solved. The method of the present invention can batch dry tree discs with relatively short thickness (i.e., tree discs with small thickness), effectively control the drying process, solve the cracking problem during the tree disc drying process, have high drying efficiency, and reduce the drying cost.

[0008] The present application provides a method for reducing defects of tree disc drying, which is caused by the anisotropy of shrinkage of the treated tree disc and the moisture content gradient from the pith to the bark of the tree disc during the tree disc drying process. The moisture content of each tree disc at different diameter levels is detected in real time, the radial shrinkage amount of the position below the fiber saturation point is calculated, and the radial shrinkage amount is controlled to be less than the allowable theoretical critical value of the to-be-dried tree disc, so as to ensure the processing quality of the tree disc during the drying process, reduce the cracking of the tree disc, and improve the utilization efficiency of the tree disc. SUMMARY

[0009] The present application provides a method for reducing defects of tree disc drying, which is caused by the anisotropy of shrinkage of the treated tree disc and the moisture content gradient from the pith to the bark of the tree disc during the tree disc drying process. The moisture content of each tree disc at different diameter levels is detected in real time, the radial shrinkage amount of the position below the fiber saturation point is calculated, and the radial shrinkage amount is controlled to be less than the allowable theoretical critical value of the to-be-dried tree disc, so as to ensure the processing quality of the tree disc during the drying process, reduce the cracking of the tree disc, and improve the utilization efficiency of the tree disc.

[0010] To achieve the object of the present application, the present application provides a method for drying tree disc, which comprises the following steps in sequence:

[0011] 1) Pre-drying treatment is performed on the tree disc, so that the moisture content of the tree disc reaches a pre-drying moisture content M 预 , and a pre-dried tree disc is obtained, wherein the pre-drying moisture content M 预 is 55-65%;

[0012] 2) The average moisture content of the pre-dried tree disc is monitored, and drying is performed according to the general drying procedure until the average moisture content of the tree disc pile is less than 15%, and the drying is stopped to obtain a dried tree disc.

[0013] In step 1), the pre-drying treatment is performed according to the following steps:

[0014] 1-1) The initial total mass G1 of the to-be-dried tree disc is weighed;

[0015] 1-2) The initial moisture content M 初 of the tree disc is measured;

[0016] 1-3) The pre-drying total mass G2 of the tree disc when the tree disc is dried to the pre-drying moisture content is calculated according to formula (7);

[0017]

[0018] In formula (7), G2 is the pre-drying target mass of the tree disc after pre-drying treatment in the tree disc pile, g; G1 is the initial total mass of the tree disc in the tree disc pile before pre-drying treatment, g; M 初The initial moisture content of the tree basin to be dried, in %; M 预 The target moisture content after pre-drying treatment of the tree basin, in %;

[0019] 1-4) Dry the tree trays until the total mass of the trees in the drying kiln reaches G2, then stop heating and drying to obtain pre-dried tree trays. The moisture content of the pre-dried tree trays reaches M. 预 .

[0020] In particular, M described in steps 1-3) 预 It is 55-65%.

[0021] In particular, the initial moisture content M of the tree basin mentioned in steps 1-2) 初 The following method was used for determination:

[0022] First: Randomly select several representative tree trays from the tree trays to be dried according to the sampling inspection standards, and weigh them (m). 初 ;

[0023] Next: Place the tree in an oven at 103±2℃ and dry it. Weigh it every 6 hours. When the difference between two consecutive weighings is less than 0.02g, it is considered to be dried to an absolutely dry state. The absolutely dry mass of the tree basin is the absolutely dry mass, denoted as m. 干 ;

[0024] Then: Calculate the initial moisture content M of the tree basin to be dried according to formula (6). 初 ,

[0025]

[0026] In equation (6), M 初 The initial moisture content of the tree basin to be dried, in %; m 初 The initial mass of the tree tray to be dried is g; m 干 Let g be the absolute dry mass of the tree basin.

[0027] In particular, it also includes the pre-drying treatment after stacking the tree trays to be dried, wherein the stacking of the tree trays to be dried is carried out in the following manner: all tree trays to be dried are weighed to obtain the initial total mass G1 of the tree trays to be dried; then the tree trays are stacked, wherein the tree trays are placed horizontally and stacked horizontally in a manner of one layer of tree tray and one layer of spacer strip, and stacked into a cuboid-shaped stack of tree trays to be dried.

[0028] In particular, it also includes the number of spacers used (y) during the palletizing process, and the mass of a single spacer (G3).

[0029] In particular, it also includes installing moisture content sensors on the stacked tree trays to determine the moisture content of the tree trays, wherein the moisture content sensors are installed on the tree trays in the following manner:

[0030] A) After removing the pith from the tree tray where the moisture content sensor is to be installed, divide it into p tree tray rings along the radial direction of the tree tray from the inside to the outside. Each tree tray ring is defined as a diameter-class tree tray ring, where the width of each diameter-class tree tray ring is 2 cm, that is, the inner diameter r 内 and the outer diameter r 外 differ by 2 cm; and the diameter-class tree trays are sequentially defined as the 1st to the pth diameter-class tree tray rings from the inside to the outside (i.e., from the pith to the bark). The inner diameter of the 1st diameter-class tree tray ring is the radius r0 of the pith circle of the tree tray, and the outer diameter of the 1st diameter-class tree tray ring is (r0 + 2) cm; and the inner diameter of the subsequent diameter-class tree tray ring is the outer diameter of the previous diameter-class tree tray ring; where p ≈ [(D / 2) - r0] / 2, and the value of p is rounded to an integer, r0 is the pith radius, in cm; D is the diameter of the tree tray, in cm;

[0031] B) The ring with the average value of the sum of the inner diameter and the outer diameter of each diameter-class tree tray ring as the radius and the center point of the pith of the tree tray as the origin is defined as the middle line of the corresponding diameter-class tree tray ring, that is, the radius r 中环 of the middle line of each diameter-class tree tray ring 内 =(r 外 + r

[0032] C) Install moisture content sensors on the middle lines of each diameter-class tree tray ring of the tree tray. The moisture content sensors are evenly distributed along the middle line of each diameter-class tree tray ring, and the number of moisture content sensors on each diameter-class tree tray ring is 4i, where i is an integer, i = 1, 2, 3,..., p, where p ≈ [(D / 2) - r0] / 2, and the value of p is rounded to an integer.

[0033] In particular, install the moisture content sensors on the two ends of the tree tray stack where the drying medium flows in and out according to the direction of the flow of the drying medium.

[0034] In particular, 9 groups are respectively arranged at the inlet end and the outlet end of the tree tray stack where the moisture content sensors are installed, and are arranged in a "field" shape.

[0035] In particular, during the pre-drying process, control the drying temperature to be 70 - 90 °C; the relative humidity Φ is maintained at greater than 85%.

[0036] Especially, when Φ ≤ 85%, start the steam generator in the drying chamber and spray steam into the drying kiln to increase the relative humidity in the drying kiln; when Φ ≥ 98%, turn off the steam generator and stop spraying steam to keep the relative humidity in the drying kiln always higher than 85%, and defects are not likely to occur in the tree tray.

[0037] In particular, during the pre-drying process, use a temperature and humidity sensor to measure the temperature and relative humidity of the drying medium in the drying kiln.

[0038] In particular, after the tree disks are stacked, a temperature and humidity sensor group is installed on the outside of the dry medium inflow end and outflow end of the tree disk stack in the flow direction of the dry medium, for measuring the temperature and humidity of the dry medium in the drying kiln.

[0039] In particular, a moisture content sensor is installed on the tree disks near the position where the temperature and humidity sensor group is arranged on the inflow / outflow end of the tree disk stack, for monitoring the moisture content of the tree disks in the tree disk stack.

[0040] In particular, the moisture content sensors are evenly arranged on the middle ring line of each radial disk ring of the tree disk, wherein the radius of the middle ring line of each radial disk ring is half the sum of the inner diameter and the outer diameter of the corresponding radial disk ring.

[0041] In particular, the diameter of the tree disk to be dried is 8-30 cm, preferably 10-25 cm; the thickness is less than 5 cm, preferably 2-3 cm.

[0042] In particular, the tree disk to be dried is a fast-growing small-diameter tree disk.

[0043] In particular, the fast-growing small-diameter tree is selected from eucalyptus, poplar, pine, willow, cedar, cryptomeria, etc.

[0044] In particular, the average moisture content of the pre-dried tree disk stack is monitored in step 2) according to the following method:

[0045] 2-1) Calculate the average moisture content of each tree disk in the tree disk stack that is installed with a moisture content sensor according to formula (8)

[0046]

[0047] In formula (8), is the average moisture content of any one tree disk in the tree disk stack that is installed with a moisture content sensor, %; M i is the moisture content of the different radial disk rings of the tree disk installed with a moisture content sensor, i.e. the moisture content of the i-th radial disk ring on the tree disk, wherein i is an integer, i=1, 2, 3, …, p, wherein p≈[(D / 2)-r0] / 2, the value of p is rounded to an integer; D is the diameter of the tree disk, mm; r0 is the radius of the pith of the tree disk, mm; r i外 is the outer diameter of the i-th radial disk ring on the tree disk, i.e. the distance from the outer ring of the i-th radial disk ring to the center point of the pith of the tree disk, mm; r i内 is the inner diameter of the i-th radial disk ring on the tree disk, i.e. the distance from the inner ring of the i-th radial disk ring to the center point of the pith of the tree disk, mm;

[0048] 2-2) Calculate the average moisture content of each tree disk in the tree disk stack that is installed with a moisture content sensor The average moisture content of the pre-drying log pile is obtained by averaging.

[0049] In particular, according to the measured average moisture content of the log pile, the drying medium dry bulb temperature, the dry-bulb wet-bulb temperature difference, the drying medium relative humidity, the drying medium equilibrium moisture content during the drying process are adjusted in stages according to the general reference procedure to dry the logs.

[0050] In particular, in step 2) during drying according to the general reference procedure, the moisture content of each diameter class log ring on the log pile is monitored in real time by the moisture content sensor, wherein:

[0051] I) In each drying stage of the drying, if the moisture content M i of the i-th diameter class log ring of a certain log is monitored to be lower than the fiber saturation point M FSP , then the radial shrinkage amount X i of the i-th diameter class log ring with moisture content lower than the fiber saturation point is calculated in real time according to formula (9)

[0052] X i = K Ti ×(M FSP -M i )×(r i外 +r i内 ) / 2-K Ri ×(M FSP -M i )×s (9)

[0053] In formula (9), X i is the radial shrinkage amount of the i-th diameter class log ring with moisture content lower than the fiber saturation point, mm; K Ti is the chordwise shrinkage coefficient of the i-th diameter class log ring with moisture content lower than the fiber saturation point; K Ri is the radial shrinkage coefficient of the i-th diameter class log ring with moisture content lower than the fiber saturation point; M FSP is the fiber saturation point moisture content, %; M i is the moisture content of the i-th diameter class log ring measured by the moisture content sensor when the moisture content is lower than the fiber saturation point, %; r i外 is the outer diameter of the i-th diameter class log ring corresponding to the moisture content sensor group when the moisture content is lower than the fiber saturation point, mm; r i内 is the inner diameter of the i-th diameter class log ring corresponding to the moisture content sensor when the moisture content is lower than the fiber saturation point, mm; s is the difference between the inner diameter and the outer diameter of the corresponding diameter class log ring, mm, s is 20 mm; wherein i is an integer, i = 1, 2, 3, …, p, p ≈ [(D / 2)-r0] / 2, p is rounded to the nearest integer;

[0054] When the radial shrinkage X of the i-th diameter-order tree ring is calculated according to formula (9) i When the theoretical allowable radial shrinkage of the eucalyptus tree in the drying basin reaches ≥ the theoretical allowable radial shrinkage measured in the specific method described in this invention (2 mm), the steam generator in the drying kiln is turned on to inject steam into the drying kiln, increasing the relative humidity inside the drying kiln, until the moisture content sensor on the tree basin measures a moisture content M. i Above the fiber saturation point, i.e., M i ≥M FSP Turn off the steam generator and stop steam injection; circulate steam injection and stop steam injection to control the radial shrinkage of the radial tree ring to always be less than the theoretically allowable radial shrinkage of the tree ring to be dried.

[0055] II) During each drying stage, if the moisture content M of two adjacent diameter-class tree rings (i′ and (i′+1) diameter-class tree rings) is monitored... i ′ and M (i′+1) All below the fiber saturation point M FSP Then, according to formula (10) or (11), the total radial shrinkage X′ of the i′ and (i′+1) diameter-class tree rings with moisture content below the fiber saturation point is calculated in real time; where,

[0056] II-A) If M i ′ <M FSP M (i′+1) <M FSP And M (i′+1) >M i Then, according to equation (10), the total radial shrinkage X′ of the tree ring at two adjacent diameter levels is calculated.

[0057] X′=[K Ti ′×(M FSP -M i ′)×(r i′外 +r i′内 ) / 2-K Ri ′×(M FSP -M i ′)×s]-[K T(i′+1) ×(M FSP -M (i′+1) )×(r (i′+1)外 +r (i′+1)内 ) / 2-K R(i′+1) ×(M FSP -M (i′+1) )×s] (10)

[0058] II-B) If M i ′ <M FSP M (i′+1) <M FSP And M(i′+1) ≤M i ′; then the total radial shrinkage X' of the adjacent two radial class ring is calculated according to formula (11),

[0059] X' = [K Ti ′ × (M FSP -M i ′) × (r i′外 +r i′内 ) / 2 - K Ri ′ × (M FSP -M i ′) × s] + [K T(i′+1) × (M FSP -M (i′+1) ) × (r (i′+1)外 +r (i′+1)内 ) / 2 - K R(i′+1) × (M FSP -M (i′+1) ) × s] (11) In formula (10), (11), X' is the total radial shrinkage of the adjacent two radial class ring, mm; M (i′+1) is the moisture content of the i'+1 radial class ring close to the bark side in the adjacent radial class, %; M i ′ is the moisture content of the i' radial class ring close to the pith side in the adjacent radial class, %; K Ti ′ is the chord shrinkage coefficient of the i' radial class ring close to the pith side in the adjacent radial class; K T(i′+1) is the chord shrinkage coefficient of the i'+1 radial class ring close to the bark side in the adjacent radial class; K Ri ′ is the radial shrinkage coefficient of the i' radial class ring close to the pith side in the adjacent radial class; K R(i′+1) is the radial shrinkage coefficient of the i'+1 radial class ring close to the bark side in the adjacent radial class; M FSP is the fiber saturation point moisture content of the ring, %; r i′外 is the outer diameter of the i' radial class ring close to the pith side in the adjacent radial class, i.e. the distance from the outer ring of the i' radial class ring to the center point of the pith of the ring, mm; r (i′+1)外 is the outer diameter of the i'+1 radial class ring close to the bark side in the adjacent radial class, i.e. the distance from the outer ring of the i'+1 radial class ring to the center point of the pith of the ring, mm; r i′内 is the inner diameter of the i' radial class ring close to the pith side in the adjacent radial class, i.e. the distance from the inner ring of the i' radial class ring to the center point of the pith of the ring, mm; r (i′+1)内is the inner diameter of the i'+1th radial ring of the tree disc adjacent to the bark side in the adjacent radial level, i.e. the distance from the inner ring of the i'+1th radial ring of the tree disc to the center point of the pith of the tree disc, mm; s is the difference between the inner diameter and the outer diameter of the corresponding radial ring of the tree disc, mm, s is 20 mm; wherein i' is an integer, i' = 1, 2, 3,..., p-1, wherein p ≈ [(D / 2)-r0] / 2, the value of p is rounded, and an integer; D is the diameter of the tree disc, mm; r0 is the radius of the pith, mm;

[0060] When the total radial shrinkage X' of the two adjacent radial rings of the tree disc calculated according to formula (10) or (11) is greater than or equal to the theoretical allowable radial shrinkage of the tree disc to be dried (the theoretical allowable radial shrinkage of the eucalyptus tree measured in the specific manner described in the present application is 2 mm), the steam generator in the drying kiln is started to spray steam into the drying kiln to increase the relative humidity in the drying kiln; when the total radial shrinkage X' of the two adjacent radial rings of the tree disc calculated according to formula (10) or (11) is less than half of the theoretical allowable radial shrinkage of the tree disc to be dried, the steam generator is stopped to stop spraying steam; continue drying until the moisture content of the two adjacent radial rings of the tree disc measured by the moisture content sensor group on the tree disc is lower than the fiber saturation point, and then calculate the total radial shrinkage X' of the two adjacent radial rings of the tree disc according to formula (10) or (11); cycle the spraying and stopping of steam to control the total radial shrinkage X' of the two adjacent radial rings of the tree disc to be always less than the theoretical allowable radial shrinkage of the tree disc to be dried;

[0061] III) During each drying stage according to the general reference procedure, the moisture content of each radial ring of the tree disc is monitored in real time by the moisture content sensor, and the average moisture content of the tree disc pile is calculated, and the dry bulb temperature, the dry-wet bulb temperature difference, the relative humidity of the drying medium, and the equilibrium moisture content of the drying medium during the drying process are adjusted according to the average moisture content of the tree disc pile, and the tree disc drying process is carried out in stages according to the general reference procedure until the average moisture content of the tree disc is less than 15%, and a dried tree disc is obtained.

[0062] In particular, if both conditions exist during the drying process, the radial shrinkage X of the radial ring of the tree disc with a moisture content lower than the fiber saturation point is calculated according to formula (9), and the total radial shrinkage X' of the two adjacent radial rings of the tree disc is calculated according to formula (10) or (11), and X and X' are controlled to be always less than 2 mm.

[0063] In particular, the theoretical allowable radial shrinkage of the tree disc to be dried is measured by the following method:

[0064] a) randomly select at least 5 tree disks to be dried, and draw concentric circles on the surface of each tree disk with the center of the heartwood of the tree disk as the origin, wherein: the radius of the heartwood circle is r0; the radius of other concentric circles, i.e. the original radius, is r n , where n is an integer, n = 1, 2, 3, …; the difference between the radii of two adjacent concentric circles, except the heartwood circle, is Δr, where Δr = 0.2-1 cm;

[0065] b) place the tree disks after drawing concentric circles in an oven for drying treatment, measure the radius of each concentric circle drawn on the tree disk after drying treatment, i.e. the drying radius, r′ n , every δt during the drying process, and record the drying radius value of each measurement, while observing the cracking of the tree disk during the drying process;

[0066] c) when the first cracking of the tree disk is observed, the difference between the drying radius (r′ n ) of the concentric circle corresponding to the cracking measured at the last time and the original radius r n of the concentric circle is defined as the theoretical allowable radial shrinkage z of the tree disk, i.e. the original radius of the concentric circle corresponding to the cracking of the tree disk minus the drying radius of the concentric circle corresponding to the cracking of the tree disk measured at the last time when the cracking is first observed, and the theoretical allowable radial shrinkage z of the tree disk is calculated according to formula (1),

[0067] z = r n -r′ n (1)

[0068] In formula (1), z is the theoretical allowable radial shrinkage of the tree disk, cm; r′ n is the drying radius of the concentric circle corresponding to the cracking of the tree disk measured at the last time when the cracking is first observed, cm; and r n is the original radius of the concentric circle corresponding to the cracking of the tree disk, cm.

[0069] In particular, the drying temperature in step b) is 40-103℃, preferably 50℃; the shorter the interval time δt is, the more accurate it is, and generally δt is less than 0.5h, preferably 10-15min.

[0070] In particular, if multiple cracks at different positions of the same tree disk are observed during the drying process, the minimum difference z calculated is selected as the theoretical allowable radial shrinkage of the tree disk.

[0071] In particular, the theoretical allowable radial shrinkages of each tree disk are averaged to obtain the theoretical allowable radial shrinkage of the tree disk to be dried.

[0072] In particular, the chord shrinkage coefficient K of the tree disk ring of the diameter class isT , the radial shrinkage coefficient K R , is determined by the following method:

[0073] 1') respectively measure the tangential size L and the radial size L 1R试 of the small test pieces of the green wood of the tree disc rings of different diameter classes;

[0074] 2') respectively place the small test pieces of the tree disc rings of different diameter classes in the drying oven for drying treatment, wherein the drying temperature is 40-103°C, and during the drying process, the mass of the small test pieces of the tree disc rings of different diameter classes is measured every δt' time interval, wherein the shorter the interval of δt', the more accurate the measurement, and generally t' is less than 30 min (preferably 10-30 min);

[0075] 3') when the mass of the small test pieces of the tree disc rings of different diameter classes reaches the respective air-dry mass m 2试 , again respectively measure the air-dry tangential size L 0T试 and the air-dry radial size L 0R试 of the small test pieces of the tree disc rings of different diameter classes in the air-dry state;

[0076] 4') respectively substitute the tangential sizes of the green wood and the air-dry wood of the small test pieces of the tree disc rings of different diameter classes into formula (4-1) to calculate the tangential shrinkage rate β T试 of the small test pieces of the tree disc rings of different diameter classes:

[0077]

[0078] In formula (4-1), β T试 is the tangential shrinkage rate of the small test pieces of the tree disc rings of different diameter classes, %; L 1T试 is the tangential size of the small test pieces of the tree disc rings of different diameter classes in the green state, mm; L 0T试 is the tangential size of the small test pieces of the tree disc rings of different diameter classes in the air-dry state, mm;

[0079] 5') respectively substitute the radial sizes of the green wood and the air-dry wood of the small test pieces of the tree disc rings of different diameter classes into formula (4-2) to calculate the radial shrinkage rate β R试 of the small test pieces of the tree disc rings of different diameter classes:

[0080]

[0081] In formula (4-2), β R试 is the radial shrinkage rate of the small test pieces of the tree disc rings of different diameter classes, %; L 1R试 is the radial size of the small test pieces of the tree disc rings of different diameter classes in the green state, mm; L 0R试 is the radial size of the small test pieces of the tree disc rings of different diameter classes in the air-dry state, mm;

[0082] 6′) Calculate the tangential shrinkage coefficient K of small specimens of tree rings of different diameter classes according to formula (5-1). T试 ,

[0083]

[0084] In equation (5-1), K T试 The tangential shrinkage coefficient of small specimens from tree disc rings of different diameter classes; β T试 The tangential shrinkage rate of small specimens of tree disc rings of different diameter classes is %, %; EMC is the equilibrium moisture content under air-drying conditions, %;

[0085] 7′), Calculate the radial shrinkage coefficient K of small specimens of different diameter class tree rings according to formula (5-2). R试 ,

[0086]

[0087] In equation (5-2), K R试 β represents the radial shrinkage coefficient of small specimens from different diameter-class tree rings; R试 Radial shrinkage rate of small specimens of tree disc rings of different diameter classes, %; EMC is the equilibrium moisture content under air-dried conditions, %;

[0088] The tangential / radial shrinkage rates of small specimens of tree rings of different diameters are used to represent the tangential / radial shrinkage rates of tree rings of different diameters, respectively; the tangential / radial shrinkage coefficients of small specimens of tree rings of different diameters are used to represent the tangential shrinkage coefficients K of tree rings of different diameters, respectively. T Radial shrinkage coefficient K R .

[0089] In particular, the air-dry mass m of the small specimens of different diameter-class tree disc rings described in step 3') 2试 The following method was used for determination:

[0090] 3′-A) After removing the pith from the tree basin, divide it into p rings from the inside out along the radius of the tree basin. Each ring is defined as a diameter-class tree basin ring, and the width of each diameter-class tree basin ring is 2cm, that is, the inner diameter r of each diameter-class tree basin. 内 With outer diameter r 外 The difference is 2cm; and the diameter class tree discs are defined sequentially from the inside out as the 1st to the pth diameter class tree discs, where the inner diameter of the 1st diameter class tree disc is the radius r0 of the pith circle, and the outer diameter of the 1st diameter class tree disc is (r0+2)cm; the inner diameter of the subsequent diameter class tree disc ring is the outer diameter of the previous diameter class tree disc ring; where p≈[(D / 2)-r0] / 2, the value of p is rounded to the nearest integer, r0 is the pith radius, cm; D is the diameter of the tree disc, cm;

[0091] 3'-B) According to the national standard "GB / T 1932-2009 Wood Shrinkage Determination Method", each diameter grade tree disc ring is sawn into small test pieces with a size of 2cm*2cm*(2-3)cm, and the sawn small test pieces of different diameter grade tree disc rings are obtained;

[0092] 3'-C) A number of representative small test pieces are randomly selected from the sawn small test pieces of each diameter grade tree disc ring, the radial size of each diameter grade tree disc ring is measured, and the average value is taken as the radial size L of the small test pieces of the corresponding diameter grade tree disc ring 1R试 ; The tangential size of each diameter grade small test piece is measured, and the average value is taken as the tangential size L of the small test pieces of the corresponding diameter grade tree disc ring 1T试 ;

[0093] 3'-D) The initial bulk volume of the small test pieces selected from each diameter grade tree disc ring, i.e. the green volume of the test pieces, V 0试 , is calculated, and weighed m 0试 ; Then the weighed test pieces of different diameter grade tree disc rings are placed in an oven with a temperature of (103±2)℃, and weighed every 6h, when the difference between the weights of two consecutive weighings is less than 0.02g, it is considered to be dried to an absolute dry state, and the absolute dry mass (m 1试 ) of the small test pieces selected from different diameter grade tree disc rings is obtained by weighing;

[0094] 3'-E) The density (ρ 试 ) of the small test pieces of different diameter grade tree disc rings is calculated according to formula (2),

[0095]

[0096] In formula (2), ρ 试 is the density of the small test pieces of different diameter grade tree disc rings, g / cm 3 ; m 1试 is the absolute dry mass of the small test pieces of different diameter grade tree disc rings, g; V 0试 is the green volume of the small test pieces of different diameter grade tree disc rings, cm 3 ;

[0097] 3'-F) The air-dry mass m 2试 of the small test pieces corresponding to different diameter grade tree disc rings is calculated according to formula (3);

[0098] m 2试 = ρ 试 V 0试 ×(1+EMC) (3)

[0099] In formula (3), m 2试 is the air-dry mass of the small test pieces of different diameter grade tree disc rings, g; ρ 试is the basic density corresponding to each small specimen of the tree disc rings with different diameters, g / cm 3 ; V 0试 is the green volume corresponding to each small specimen of the tree disc rings with different diameters, cm 3 ; EMC is the equilibrium moisture content in the air-dried state, %.

[0100] In particular, during the drying process according to the general reference procedure, when the average moisture content of the tree disc stack is higher than the fiber saturation point, there is a moisture content of a certain diameter tree disc ring on the tree disc lower than the fiber saturation point M FSP , or / and the moisture contents of two adjacent diameter tree disc rings on the tree disc are both lower than the fiber saturation point M FSP ; when the average moisture content of the tree disc stack is higher than the fiber saturation point, there are moisture contents of two adjacent diameter tree disc rings on the tree disc both lower than the fiber saturation point M FSP .

[0101] In particular, during the drying process, the moisture content sensor measures the moisture content values at various positions on the tree disc every △τ, where △τ is 10 - 20 s, and the shorter the △τ interval time, the more accurate it is.

[0102] In particular, the general reference drying procedure described in step 2) is as follows:

[0103]

[0104] On the other hand, the present invention provides a dried tree disc dried according to the above drying method.

[0105] Among them, before the pre-treatment and drying treatment are carried out, it also includes sawing the fast-growing small-diameter timber into tree discs with appropriate thickness along the direction perpendicular to the fiber.

[0106] Among them, it also includes the installation of a temperature and humidity sensor group, and the temperature and humidity sensor group is uniformly arranged on the left and right sides of the wood stack;

[0107] In particular, there are 9 temperature and humidity sensor groups.

[0108] In particular, the temperature and humidity sensor groups are uniformly distributed on the left and right sides of the wood stack that are opposite to each other.

[0109] In particular, when there are 9 temperature sensor groups on the left and right sides of the wood stack that are opposite to each other, the temperature sensor groups are uniformly distributed at the left end, middle, right end of the inflow end of the wood stack or the left end, middle, right end of the outflow end, and are uniformly arranged in a "field" shape.

[0110] Among them, in order to ensure that there are no drying defects during the drying process of the tree disc, the pre-drying moisture content M at the end of the pre-drying treatment of the tree disc 预is 55-65%, preferably 60%. The target mass G2 of the log at the end of the pre-drying is calculated according to formula (7).

[0111]

[0112] In formula (7), G2 is the pre-drying target mass of the log after pre-drying in the material pile, g; G1 is the initial total mass of the log in the material pile before pre-drying, g; M 初 is the initial moisture content of the log to be dried, %; M 预 is the pre-drying target moisture content of the log after pre-drying, %.

[0113] In addition, the moisture content sensors are installed on the logs near the temperature and humidity sensor group, i.e. 9 moisture content sensors are respectively arranged on the logs at the inlet and outlet of the drying medium flowing into and out of the material pile (i.e. 9 moisture content sensors are respectively arranged on the logs at the inflow end of the material pile along the direction of the flow of the drying medium; 9 moisture content sensors are respectively arranged on the logs at the outflow end of the material pile).

[0114] In particular, the moisture content measurement points of the moisture content sensor group are uniformly arranged on the middle ring line of each diameter class log ring of the log, and the radius of the middle ring line of different diameter class log rings is half of the sum of the inner diameter and the outer diameter of the corresponding diameter class log ring, i.e. on the circumference with a radius of (r i外 +r i内 ) / 2, i is an integer, i = 1, 2, 3, …, p, where p ≈ [(D / 2)-r0] / 2, the value of p is rounded to an integer; and from inside to outside (i.e. from the pith to the bark direction), the radius of the middle ring line increases by 2 cm and the moisture content measurement points increase by 4 for each outward extension.

[0115] In particular, during the drying process, the moisture content sensor measures the moisture content value of each position of the log every △τ (usually 10-20 seconds).

[0116] Compared with the prior art, the present application has the following advantages and benefits:

[0117] 1. The application range of the present application is wide, and it can be used for drying fast-growing wood and small-diameter logs;

[0118] 2. The present application controls the radial shrinkage amount of the moisture content below the fiber saturation point to be less than the theoretical allowable radial shrinkage amount of the log, reduces the drying defects of the log, and solves the problem of easy occurrence of drying defects in the drying process of the log;

[0119] 3. The moisture content sensor is used to detect the moisture content of each log at different diameter class positions in real time, which is accurate in control, simple in operation, and low in equipment investment cost;

[0120] 4. The fast-growing small-diameter timber tree trays dried using the method of this invention overcome the problems of drying defects such as cracking, warping and deformation that are prone to occur during the drying process of fast-growing small-diameter timber tree trays, greatly improving the drying quality of fast-growing small-diameter timber tree trays and increasing the qualified rate and yield of tree trays. Attached Figure Description

[0121] Figure 1a This is a schematic diagram showing the concentric circles of the tree basin to be dried;

[0122] Figure 1b A schematic diagram of a small specimen with a tree basin intercept;

[0123] Figure 2a A front view of the log stack along the longitudinal direction of the drying kiln;

[0124] Figure 2b for Figure 2a A cross-sectional view along BB;

[0125] Figure 2c for Figure 2a A cross-sectional view along CC;

[0126] Figure 2d A schematic diagram showing the setup of the temperature and humidity sensor group on the inflow / outflow end face of the tree basin drying medium;

[0127] Figure 3 A schematic diagram showing the installation location of a moisture content sensor in a single tree basin;

[0128] Explanation of reference numerals in the attached figures:

[0129] 1. Drying kiln; 2. Circulating fan; 3. Heater; 4. Partition plate; 5. Temperature and humidity sensor group; 6. Tree tray to be dried; 7. Spacer bar; 8. Steam generator; 9. Moisture content sensor location; 10. Tree tray; 11. Temperature and humidity sensor group bracket. Detailed Implementation

[0130] This invention uses the drying process of eucalyptus tree receptacles as an example for illustration, but receptacles for other tree species are also applicable to this invention. Taking a eucalyptus tree receptacle with a diameter of 20-24 cm (the pith diameter is 2 cm, though the pith size varies among different tree species; in this embodiment, a pith diameter of 2 cm is used as an example) and a thickness of 2-3 cm as an example, other sizes, such as receptacles with a diameter greater than 8 cm (preferably 10-30 cm) and a thickness less than 5 cm (preferably 2-3 cm), are also applicable to this invention.

[0131] Example 1: Determination of the theoretically permissible radial shrinkage Z and shrinkage coefficient K of the tree basin

[0132] 1. The tree-circle theory allows for the determination of radial shrinkage (z).

[0133] 1a, randomly select 10 eucalyptus tree disks with a diameter of 20-24 cm. As Figure 1a , take the center of the tree disk pith as the origin, draw concentric circles on the surface of each tree disk along the diameter direction, wherein

[0134] The radius of the pith circle is r0; the radius of the other concentric circles from the pith outward (the original radius, that is, the radius of the concentric circle without any other treatment) is denoted as r n , where n is an integer, n = 1, 2, 3,...; the difference between the radii of the other two adjacent concentric circles (Δr = r n+1 -r n ) is 0.5 cm (usually the smaller the better, Δr = 0.2-1 cm), and the radius r n of the pith circle and the radius r n+1 of each concentric circle drawn is recorded, where n is an integer, n = 1, 2, 3,....

[0135] In this embodiment, Δr = 0.5 cm is taken as an example (i.e. r n+1 -r n = 0.5 cm).

[0136] The radius of the pith circle is determined according to the size of the pith of the tree disk, and in the specific embodiment of the present application, the pith circle radius r0 is 1 cm. The radius of the pith circle of other tree disks is determined according to the size of the pith of the tree disk of each tree species.

[0137] 1b, place the tree disk test piece after marking the concentric circles in the oven for drying treatment, wherein the drying temperature is 50°C (usually 40-103°C), and the radius of each concentric circle drawn on the tree disk after drying treatment (i.e. the drying radius, denoted as r′ n , that is, the distance r′ n of the concentric circle after drying treatment to the center point of the tree disk pith circle) is measured every δt (δt = 15 min) during the drying process, and the drying radius value of each measurement is recorded, while the cracking of the tree disk during the drying process is observed.

[0138] The shorter the interval time of δt, the more accurate it is, usually δt is less than 0.5h, preferably 10-15 min.

[0139] The drying radius r′ n of the concentric circle drawn on the tree disk is determined every δt during the drying process, and the drying radius is the distance of each concentric circle drawn on the tree disk to the center of the tree disk pith during the drying process of the tree disk.

[0140] 1c. If a crack is observed in the tree basin for the first time, the drying radius (r′) of the concentric circle corresponding to the crack, as previously measured, shall be used. n The difference between the original radius rn of the concentric circle and the original radius rn is defined as the allowable radial shrinkage z of the tree basin theory. That is, the original radius of the concentric circle corresponding to the crack in the tree basin minus the drying radius of the concentric circle corresponding to the crack in the tree basin when the crack was first observed. The allowable radial shrinkage z of the tree basin theory is calculated according to formula (1).

[0141] z = r n -r′ n (1)

[0142] In formula (1): z is the allowable radial shrinkage of the tree basin, in cm; r′ n The radius of the concentric circles corresponding to the crack in the tree basin, measured in cm, is the radius of the dry area measured before the crack was first observed. n Let n be the original radius of the concentric circles corresponding to the crack in the tree basin, in cm; where n is an integer, n = 1, 2, 3, ...

[0143] If multiple cracks are observed at different locations within the same tree basin during the drying process, the smallest calculated difference z is selected as the theoretical allowable radial shrinkage of that tree basin.

[0144] The theoretical allowable radial shrinkage of each tree basin was averaged to obtain the theoretical allowable radial shrinkage of the tree basin to be dried. In this embodiment, the theoretical allowable radial shrinkage of the eucalyptus tree basin to be dried was measured to be 2 mm.

[0145] 2. Determine the shrinkage coefficient of the tree ring around the tree of different diameters.

[0146] 2-1. Grouping by tree diameter

[0147] After removing the pith, the tree disc is divided into p rings along the radial direction. Each ring is defined as a diameter-order tree disc ring, where the inner diameter (r) of each diameter-order tree disc ring is... 内 ) and outer diameter (r) 外 The difference is 2cm, where the inner diameter (r) of the first-diameter tree ring is 2cm. 内 ) represents the radius r0 of the pith center circle of the tree disc, and the outer diameter (r) 外 The inner diameter of the tree disc ring of the next diameter class is r0+2cm; the outer diameter of the tree disc ring of the previous diameter class is the inner diameter of the (i+1)th diameter class tree disc ring (r (i+1)内 ) is the outer diameter (r) of the i-th diameter-level tree disk ring. i外 ), that is (r (i+1)内 ) = r i外wherein i is an integer, i = 1, 2, 3, …, p, wherein p ≈ [(D / 2)-r0] / 2, p is rounded, and r0 is the pith radius, cm; and D is the tree disk diameter, cm.

[0148] For example, the outer diameter of the first radial tree disk ring is the inner diameter of the second radial tree disk ring, the inner diameter of the third radial tree disk ring is the outer diameter of the second radial tree disk ring, and so on.

[0149] The first radial tree disk ring has a pith circle radius r0 as the inner diameter (r 1内 ) and r0+2 cm as the outer diameter (r 1外 ).

[0150] After removing the pith from the tree disk, the tree disk is divided into p tree disk annuli from the inside to the outside, which are simply referred to as p radial tree disk annuli. Each radial tree disk annulus is defined as a radial tree disk ring. The difference between the inner diameter (r 内 ) and the outer diameter (r 外 ) of each radial tree disk annulus is 2 cm, and the width of each radial tree disk annulus is 2 cm. The difference between the outer diameters of two adjacent radial tree disk annuli is 2 cm. The inner diameter (r 内 ) of the first radial tree disk annulus is the pith circle radius r0, and the outer diameter (r 外 ) is r0+2 cm. The inner diameter of the next radial tree disk annulus is the outer diameter of the previous radial tree disk annulus, i.e., the inner diameter of the (i+1)th radial tree disk annulus is the outer diameter of the ith radial tree disk annulus, wherein i is an integer, i = 1, 2, 3, …, p, wherein p ≈ [(D / 2)-r0] / 2, p is rounded, and r0 is the pith radius, cm; and D is the tree disk diameter, cm.

[0151] The width of each radial tree disk annulus is 2 cm, i.e., the difference between the inner diameter and the outer diameter of each radial tree disk annulus is 2 cm. When the width of the outermost tree disk ring near the bark is >1 cm, it is the pth radial tree disk ring; if it is <1 cm, it is discarded and not counted as the corresponding radial tree disk.

[0152] 2-2, the middle ring line of the radial tree disk

[0153] The average of the sum of the inner diameter and the outer diameter of each radial tree disk annulus is taken as the radius, and the annulus with the pith center point of the tree disk as the origin is defined as the middle ring line of the corresponding radial tree disk annulus, i.e., the middle ring line radius r 中环 of each radial tree disk annulus is (r 内 +r 外 ) / 2.

[0154] The middle ring line of each radial stage tree disc ring is a circular ring with an average value of the inner diameter and the outer diameter of the corresponding radial stage tree disc circular ring as the radius; or the radius (r 中环 ) of the middle ring line of each radial stage tree disc circular ring is the inner diameter of the corresponding radial stage tree disc ring + 1 cm, that is, r i中环 =(r i内 +1) cm, where r i内 =r0+[2×(i-1)], i is an integer, i=1, 2, 3, …, p, where p≈[(D / 2)-r0] / 2, the value of p is rounded to an integer

[0155] In the specific embodiment of the present application, the pith radius r0 is taken as an example of 1 cm. The tree disc is divided into 5-6 radial stage tree disc circular rings. For ease of understanding, the present application is described in the specific manner with the tree disc diameter of 22 cm as an example, and the tree disc is divided into 5 radial stages, that is, p=5, and there are 1-5 radial stage tree disc rings.

[0156] 2-3, preparation of tree disc sawn small test pieces

[0157] As Figure 1b , according to the national standard “GB / T 1932-2009 Wood Shrinkage Determination Method”, each radial stage tree disc ring is sawn into small test pieces with a size of 2 cm*2 cm*(2-3) cm, and sawn small test pieces of different radial stage tree discs are obtained, wherein 4 small test pieces are obtained by sawing the first radial stage tree disc ring of each tree disc, 8 small test pieces are obtained by sawing the second radial stage tree disc ring, 16 small test pieces are obtained by sawing the third radial stage tree disc ring; 16 small test pieces are obtained by sawing the fourth radial stage tree disc ring; and 16 small test pieces are obtained by sawing the pth radial stage tree disc ring. The greater the circumferential radius of the radial stage tree disc ring, the more small test pieces are obtained. In order to facilitate sawing, part of the small test pieces are selected for sawing.

[0158] 2-4, determination of the density p of the small test pieces of different radial stage tree disc rings 试

[0159] 2-4a: 5 representative small test pieces are randomly selected from each radial stage tree disc ring sawn small test piece, the radial size of each radial stage tree disc ring small test piece is first measured using a vernier caliper, and the average value is taken as the radial size L 1R试 of the corresponding radial stage tree disc ring small test piece; the chord size of each radial stage small test piece is measured, and the average value is taken as the chord size L 1T试 of the corresponding radial stage tree disc ring small test piece;

[0160] 2-4b: the initial total volume (i.e. the green volume of the test piece, V 0试 ) of the 5 small test pieces of each radial stage tree disc ring is calculated, and weighed (m 0试) ; then the weighed test pieces of different diameter levels of tree disc rings are placed in an oven with a temperature of (103±2) °C for drying, and weighed every 6 h, and when the difference between the weights of two consecutive weighings is less than 0.02 g, it is considered that the drying is to the absolute dry state, and the absolute dry mass (m 1试 ) of the test piece of the tree disc ring of the corresponding diameter level is obtained by weighing.

[0161] 2-4c: the density (p 试 ) of the test piece of different diameter levels is calculated according to formula (2).

[0162]

[0163] In formula (2), p 试 is the density of the test piece of different diameter levels of tree disc rings, g / cm 3 ; m 1试 is the absolute dry mass of the test piece of different diameter levels of tree disc rings, g; V 0试 is the green volume of the test piece of different diameter levels of tree disc rings, cm 3 .

[0164] The density measurement results of the test pieces of different diameter levels of tree disc rings in this embodiment are shown in Table 1.

[0165] Table 1: Theoretical allowable radial shrinkage of tree disc and characteristics of test pieces of different diameter levels of tree disc rings

[0166]

[0167] 2-5, the air-dry mass m 2试

[0168] Green wood refers to freshly cut wood that has not been dried and has a moisture content above the fiber saturation point. Air-dry wood is wood that has been stored in the atmosphere for a long time and has reached equilibrium with the relative humidity of the atmosphere. The mass of the test pieces of different diameter levels of tree disc rings in the air-dry state is measured. The moisture content in the air-dry state is adjusted using a constant temperature and humidity chamber (in this embodiment, the equilibrium moisture content is taken as 12%, i.e. EMC = 12%), and the air-dry mass m 2试 of the test piece of different diameter levels of tree disc rings is calculated according to formula (3) according to the basic density formula of wood.

[0169] m 2试 = p 试 V 0试 × (1 + EMC) (3)

[0170] In formula (3), m 2试 is the air-dry mass of the test piece of different diameter levels of tree disc rings, g; p 试 is the basic density of the test piece of different diameter levels of tree disc rings, g / cm 3 ; V0试 The green volume of small specimens with different diameter rings is given in cm. 3 EMC is the equilibrium moisture content under air-dry conditions, expressed as a percentage. In this example, the EMC is 12%.

[0171] 2-6. Measure the tangential shrinkage β of small specimens from tree disc rings of different diameter classes. T试 Radial shrinkage β R试

[0172] 2-6a. Use vernier calipers to measure the tangential dimensions of small green timber specimens from tree rings of different diameter classes. ) and radial dimension (L 1R试 );

[0173] 2-6b. Place the small test pieces in an oven for drying at a temperature of 50℃ (usually 40-103℃). During the drying process, weigh the corresponding diameter-class tree disc ring at intervals of δt' using an electronic balance. The shorter the interval of δt', the more accurate the result. Typically, δt is less than 0.5h, preferably 10-30min. In this embodiment of the invention, δt' = 0.5h.

[0174] 2-6c. Weigh the small specimens during the drying process using a balance. When the mass of the small specimens of different diameter resin rings reaches their respective corresponding air-dried mass m... 2试 Then, the chordal dimension (L) of the small specimens of different diameter rings under air-dried conditions was measured again using vernier calipers. 0T试 ) and radial dimension (L 0R试 );

[0175] 2-6d. Substitute the tangential dimensions of the small specimens in the tree rings of different diameter classes under both green and air-dried conditions into formula (4-1) to calculate the tangential shrinkage rate β of the tree ring specimens of different diameter classes. T试 :

[0176]

[0177] In formula (4-1), β T试 The tangential shrinkage (%) of small specimens from tree disc rings of different diameter classes; L 1T试 The tangential dimension (mm) of small specimens of different diameter tree rings when the moisture content is higher than the fiber saturation point (i.e., wet material); L 0T试 The tangential dimensions (mm) of small specimens of tree disc rings of different diameters during air drying are shown in Table 1. The results of the tangential shrinkage rate determination of small specimens of tree disc rings of different diameters are also shown in Table 1.

[0178] 2-6e. Substitute the radial dimensions of the small specimens of different diameters under both green and air-dried conditions into formula (4-2) to calculate the radial shrinkage rate β of the tree ring specimens of different diameters. R试 :

[0179]

[0180] In formula (4-2), β R试 is the radial shrinkage rate (%) of the tree disc ring small test piece of different diameter grades; L 1R试 is the radial size (mm) of the tree disc ring small test piece of different diameter grades when the moisture content is higher than the fiber saturation point (i.e. wet wood); L 0R试 is the radial size (mm) of the tree disc ring small test piece of different diameter grades when air-dried.

[0181] 2-7, calculating the tangential and radial shrinkage coefficients KTtestand KRtestof different diameter grade small test pieces

[0182] 2-7a, calculating the tangential shrinkage coefficients K T试 of the tree disc ring small test pieces of different diameter grades according to formula (5-1) respectively.

[0183]

[0184] In formula (5-1), K T试 is the tangential shrinkage coefficient of the tree disc ring small test piece of different diameter grades; β T试 is the tangential shrinkage rate (%) of the tree disc ring small test piece of different diameter grades; EMC is the equilibrium moisture content (%) in the air-dried state, and in this embodiment, EMC = 12%.

[0185] 2-7b, calculating the radial shrinkage coefficients K R试 of the tree disc ring small test pieces of different diameter grades according to formula (5-2) respectively.

[0186]

[0187] In formula (5-2), K R试 is the radial shrinkage coefficient of the tree disc ring small test piece of different diameter grades; β R试 is the radial shrinkage rate (%) of the tree disc ring small test piece of different diameter grades; EMC is the equilibrium moisture content (%) in the air-dried state, and in this embodiment, EMC = 12%.

[0188] The tangential and radial shrinkage rate measurement results of the tree disc ring small test pieces of different diameter grades are shown in Table 1. The tangential and radial shrinkage rates of the tree disc rings of different diameter grades are represented by the tangential and radial shrinkage rates of the tree disc ring small test pieces of different diameter grades respectively. The tangential and radial shrinkage coefficients of the tree disc rings of different diameter grades are represented by the tangential and radial shrinkage coefficients of the tree disc ring small test pieces of different diameter grades respectively.

[0189] Example 2:

[0190] 1. Determining the initial moisture content of the tree disc

[0191] Randomly select 5 representative tree discs from the tree discs to be dried, weigh (m 初) and dried in an oven with temperature of (103±2)℃, and weighed every 6h, when the difference of the mass of two times of weighing is less than 0.02g, it is considered that the drying is finished, and the mass of the tree disc at this time is the absolute dry mass (m 干 ) and the initial moisture content of the tree disc to be dried (M 初 ) is calculated according to formula (6).

[0192]

[0193] In formula (6), M 初 is the initial moisture content of the tree disc (%); m 初 is the initial mass of the tree disc (g); and m 干 is the absolute dry mass of the tree disc (g).

[0194] In the embodiment of the present application, the initial moisture content M 初 of the tree disc to be dried is 130% (usually 120-150%).

[0195] In the embodiment, the size of the tree disc to be dried is exemplified by the eucalyptus tree disc with diameter of 22cm and thickness of 2cm, and other sizes such as diameter of 8-30cm and thickness of less than 5cm, preferably 2-3cm, are also applicable to the present application.

[0196] 2. Piling

[0197] The total mass of the tree disc to be dried 10 is weighed to obtain the initial total mass G1 (g) of the tree disc to be dried, and then the tree disc is piled, wherein the tree disc is placed horizontally, and the tree disc and the spacer 7 are stacked in one layer, and the tree disc to be dried is piled into a cuboid, as shown in Figure 2a 、 2b , 2c.

[0198] As shown in Figure 2a 、 2b , 2c, in the piling process, the distance between the adjacent two tree discs in the same layer of tree disc is x (wherein x=1-2cm, and in the embodiment, x=1.5cm); in the same layer of spacer, a column of tree discs is placed along the length direction of the spacer, and two spacers are placed under the same column of tree discs, and the distance between the two spacers is 1 / 2 of the diameter of the tree disc (in the embodiment, it is 11cm); the tree disc layer on the height of the timber pile has c layers (usually c≥5, and preferably c is 8-15); and the same layer of tree disc in each tree disc pile has k tree discs (usually k≥10, and preferably k=18-25).

[0199] Under each tree tray, 2 spacers are used, and the distance between the 2 spacers is 1 / 2 of the diameter of the tree tray; in this embodiment, the number of tree tray layers c in the height direction of the stacked tree tray wood stack is 11; the number of tree trays k in the same tree tray layer is 25. The thickness of the spacer is 20 - 30 mm, and the spacer can be made of wood or metal. The stacked tree tray wood stack is placed in the drying kiln 1, and the circulating fan 2 and the heater 3 are fixedly installed on the upper part of the partition board 4 located above the tree tray wood stack to be dried.

[0200] In the specific embodiment of the present invention, the schematic diagram of the tree tray stacking method is as Figure 2a , 2b , 2c shows that the tree trays are placed flat in the drying kiln, the length direction of the spacer is consistent with the transverse direction of the drying kiln, and the height of the wood stack is consistent with the vertical direction of the drying kiln. In the specific embodiment of the present invention, the two sides along the transverse direction of the drying chamber (i.e., the left and right sides of the wood stack) are the two sides for the drying medium to enter and exit the wood stack.

[0201] 3. Install the temperature and humidity sensor group

[0202] As Figure 2a , 2c , 2d shows that, according to the flowing direction of the drying medium, 9 groups of temperature and humidity sensor groups 5 are respectively arranged on the outer sides of the two ends where the drying medium flows into / flows out of the tree tray wood stack, and are respectively located at the upper, middle, and lower parts of the outer sides of the inflow / outflow ends of the wood stack. The connecting lines of the setting positions of the 9 groups of temperature and humidity sensor groups at the inflow / outflow ends are in the shape of a "field", and are evenly distributed. The temperature and humidity sensors are used to measure the temperature and humidity of the drying medium in the drying kiln.

[0203] 4. Install the moisture content sensor group

[0204] On the inflow / outflow ends of the tree tray wood stack, and on the tree trays near the setting positions of the temperature and humidity sensor groups, the moisture content sensor group 9 is installed. The tree trays with the moisture content sensor group are arranged in a "field" shape on the tree tray wood stack, with the same setting method as the temperature and humidity sensor group; among them, within the same layer of tree trays, 3 moisture content sensor groups are respectively arranged at the inflow end and the outflow end of the tree tray wood stack, as Figure 2c , 2d . The tree trays with the moisture content sensor group at the inflow and outflow ends of the tree tray wood stack are respectively located at the upper, middle, and lower parts of the inflow and outflow ends of the wood stack, as Figure 2d ; and within the same tree tray layer, 3 moisture content sensor groups are respectively arranged at the inflow and outflow ends, as Figure 2c .

[0205] On the tree trays with the moisture content sensor group, the moisture content sensor group is evenly arranged on the middle ring line of each diameter-level tree tray ring of the tree tray, that is, the setting sites 12 of the moisture content sensor group are evenly distributed on the middle ring line of each diameter-level tree tray ring of the tree tray, as Figure 3The radius of the middle ring line of the tree disc ring of different diameters is half of the sum of the inner diameter and the outer diameter of the corresponding tree disc ring, that is, on the circumference with a radius of (r i外 +r i内 ) / 2, i is an integer, i = 1, 2, 3, …, p, wherein p ≈ [(D / 2)-r0] / 2, and p is rounded to an integer.

[0206] In the embodiment, the setting measurement points of the water content sensor groups arranged on the tree disc rings of different diameters are located at the middle ring lines of the corresponding tree disc rings with a radius of 2 cm, 4 cm, 6 cm, 8 cm and 10 cm, and the water content measurement points increase by 4 every time the radius of the middle ring line extends outward by 2 cm (i.e. from the pith to the bark direction), such as Figure 3 .

[0207] The water content sensor groups are arranged on each tree disc ring of different diameters, and the water content sensor groups are uniformly distributed on the middle ring lines of each tree disc ring, that is, the water content sensor groups are uniformly distributed along the middle ring lines of each tree disc ring, and the difference between the number of water content sensor groups arranged on the tree disc rings of adjacent diameters is 4, that is, the number of water content sensor groups arranged on the middle ring line of the (i+1)th tree disc ring is the number of water content sensor groups arranged on the middle ring line of the ith tree disc ring + 4. The number of water content sensor groups on each tree disc ring is 4i, wherein i is an integer, i = 1, 2, 3, …, p, wherein p ≈ [(D / 2)-r0] / 2, and p is rounded to an integer.

[0208] Four water content sensor groups are uniformly arranged on the first tree disc ring, and the water content sensor groups are installed on the middle ring line of the first tree disc ring, the radius of the middle ring line of the first tree disc ring is (r 内 )+1 cm.

[0209] In the embodiment, the radius of the middle ring line of the first tree disc ring is 2 cm, the radius of the middle ring line of the second tree disc ring is 4 cm, the radius of the middle ring line of the third tree disc ring is 6 cm, and so on, the radius of the middle ring line of the third tree disc ring is 8 cm, and the radius of the middle ring line of the fifth tree disc ring is 10 cm.

[0210] As shown in Figure 3In the embodiment of the present application, the radius of the middle ring line of the first radial level tree disc ring is 2 cm, and 4 moisture content sensor groups are evenly arranged on the middle ring line of the first radial level tree disc ring; the radius of the middle ring line of the second radial level tree disc ring is 4 cm, and 8 moisture content sensor groups are evenly arranged on the middle ring line of the second radial level tree disc ring; the radius of the middle ring line of the third radial level tree disc ring is 6 cm, and 12 moisture content sensor groups are evenly arranged on the middle ring line of the third radial level tree disc ring; and so on, and the moisture content sensor groups are evenly arranged on the middle ring line of each radial level tree disc ring, and the number of the moisture content sensor groups evenly arranged on the middle ring line of the i+1 radial level tree disc ring is 4 more than the number of the moisture content sensor groups evenly arranged on the middle ring line of the i radial level tree disc ring.

[0211] The number of the moisture content sensor groups arranged on the different radial level tree disc rings is h=4i, wherein i is an integer, i=1, 2, 3, …, p, wherein p≈[(D / 2)-r0] / 2, and p is rounded to an integer.

[0212] During the drying process, the moisture content sensor groups measure the moisture content values of each position on the tree disc every △τ (usually 10-20 s).

[0213] Example 3: Tree disc pre-drying treatment

[0214] 1. Calculate the target mass G2 of the tree disc pile after pre-drying treatment

[0215] In order to ensure that no drying defects occur in the later drying process of the tree disc, the pre-drying target moisture content M 预 of the tree disc at the end of the pre-drying treatment is usually 55-65% (in the embodiment of the present application, the pre-drying target moisture content M 预 of the tree disc at the end of the pre-drying treatment is taken as 60% for illustration); and the pre-drying target mass G2 of the tree disc pile at the end of the pre-drying treatment is calculated according to formula (7).

[0216]

[0217] In formula (7), G2 is the pre-drying target mass of the tree disc after pre-drying treatment, g; G1 is the initial total mass of the tree disc in the pile before pre-drying treatment, g; M 初 is the initial moisture content of the tree disc to be dried, %; M 预 is the pre-drying target moisture content of the tree disc after pre-drying treatment, %.

[0218] 2. Turn on the heater 3 and the circulating fan 2 arranged at the top of the drying kiln to pre-dry the tree disc, wherein the heating rate is 7.5°C / h (usually 5-10°C / h), and the dried medium flows into the material pile from one side and flows out from the other side under the action of the circulating fan. In the embodiment of the present application, the dried medium flows into the material pile from the left side and flows out from the right side. The temperature and relative humidity Φ of the dried medium in the drying kiln are measured by the temperature and humidity sensor group during the pre-drying process, and the temperature of the dried medium is kept at 80°C (usually 70-90°C), and the relative humidity Φ is kept greater than 85%;

[0219] When Φ≤85%, turn on the steam generator 8 of the drying chamber to spray steam into the drying kiln to increase the relative humidity in the drying kiln; when Φ≥98%, turn off the steam generator to stop spraying steam, so that the relative humidity in the drying kiln is always higher than 85%, and the tree disc is not prone to defects.

[0220] During the pre-drying process of the tree disc, the mass of the tree disc in the material pile is weighed, and the pre-drying process is ended after the target mass is reached. The moisture content of the tree disc after the pre-drying process is 60% (usually 55-65%), the heater is turned off, and the exhaust port is kept closed to obtain the pre-dried tree disc.

[0221] Embodiment 4: Drying treatment of tree disc

[0222] After the pre-drying process, the pre-dried tree disc is subjected to a drying treatment.

[0223] 1. Turn on the heater and the circulating fan arranged in the drying kiln to dry the pre-treated pre-dried tree disc. Due to the different drying rates of the tree disc rings of different diameters, the moisture content changes. The average moisture content of a certain tree disc (pith) during the drying process is calculated according to formula (8)

[0224]

[0225] In formula (8), is the average moisture content (%) of a certain tree disc in the material pile; M i is the moisture content of the tree disc ring of different diameters, i.e. the moisture content of the i-th tree disc ring, wherein i is an integer, i=1, 2, 3, …, p, wherein p≈[(D / 2)-r0] / 2, the value of p is rounded off to an integer; D is the diameter of the tree disc, mm; r0 is the pith radius, mm; r i外 is the outer diameter of the i-th tree disc ring, i.e. the distance from the outer ring of the i-th tree disc ring to the center point of the pith of the tree disc (mm); r i内 is the inner diameter of the i-th tree disc ring, i.e. the distance from the inner ring of the i-th tree disc ring to the center point of the pith of the tree disc (mm).

[0226] The average moisture content of the tree tray in the tree tray stack is measured by the moisture content sensor group set in each tree tray The average moisture content of the tree tray in the tree tray stack is measured by the moisture content sensor group set in each tree tray

[0227] In this embodiment, the tree tray is divided into p tree ring levels, where p = 5; 18 tree trays in the tree tray stack are provided with moisture content sensor groups, and the average moisture content of the 18 tree trays provided with moisture content sensor groups is measured during the drying process, and then the average value is taken, which is the average moisture content of the tree tray stack.

[0228] 2. According to the average moisture content of the tree tray stack, the corresponding general drying reference program is found, and the tree tray is dried according to the general drying reference program, and the drying program of the tree tray is adjusted in real time according to the average moisture content of the tree tray stack at different times during the drying process, wherein the reference program is shown in Table 2.

[0229] Table 2 Tree Tray Drying Reference Program Table

[0230]

[0231] The drying process is carried out according to the tree tray drying reference program in Table 2 as follows:

[0232] 2-1, first stage of drying

[0233] When the measured average moisture content of the tree tray stack is ≥ 50%, the drying temperature used during the drying process is 40°C, the dry-wet bulb temperature difference is 5°C, and the relative humidity is 71%;

[0234] In the first stage of drying, the moisture content of each tree ring level on the tree tray is monitored in real time by the moisture content sensor group, and if the moisture content of a certain tree ring level (the i-th tree ring level) of a certain tree tray is monitored during the drying process to be lower than the fiber saturation point (i.e. M i ) < M i <M FSP ), then the i-th tree ring level begins to shrink, and the radial shrinkage X i of the i-th tree ring level with moisture content lower than the fiber saturation point is calculated in real time according to formula (9);

[0235] X i = K Ti ×(M FSP -M i )×(r i外 +r i内 ) / 2-K Ri ×(M FSP -M i )×s (9)

[0236] In formula (9), X iK represents the radial shrinkage (mm) of the i-th diameter dendritic ring with a moisture content below the fiber saturation point; Ti K is the chordal shrinkage coefficient of the i-th diameter class tree ring with a moisture content below the fiber saturation point; Ri M is the radial shrinkage coefficient of the i-th diameter class tree ring with a moisture content below the fiber saturation point; FSP The fiber saturation point moisture content (%) is used in this invention, where M is the value of the fiber. FSP =30% (explained); M i The moisture content (%) of the i-th diameter class tree ring when the moisture content is below the fiber saturation point, as measured by a moisture content sensor; r i外 The outer diameter (mm) of the i-th diameter class tree disc ring when the moisture content, as measured by the moisture content sensor group, is below the fiber saturation point; r i内 s is the inner diameter (mm) of the i-th diameter class tree ring when the moisture content measured by the moisture content sensor is lower than the fiber saturation point; s is the difference between the inner diameter and outer diameter of the corresponding diameter class tree ring (mm, s is 20mm), where i = 1, 2, 3, ..., p, p≈[(D / 2)-r0] / 2, and the value of p is rounded to the nearest integer.

[0237] For example: in this embodiment, p = 5; M FSP =30%; if the moisture content measured by the moisture content sensor group of the second diameter class tree ring is less than 30% during the drying process, then K T2 K is the tangential shrinkage coefficient of the second-diameter tree ring with a moisture content below the fiber saturation point. R2 The radial shrinkage coefficient of the second-diameter tree ring with a moisture content below the fiber saturation point; r 2外 r is the outer diameter of the second-order tree ring when the moisture content, as measured by the moisture content sensor group, is below the fiber saturation point. 2外 =r 2内 +20; r 2内 s represents the outer diameter of the tree basin in the first diameter class, and s represents the difference between the outer and inner diameters of the tree basin in the second diameter class, which is 20 mm.

[0238] When the radial shrinkage amount X of the i-th diameter class tree ring is calculated according to formula (9) i <2mm (i.e., the radial shrinkage of the tree ring in the i-th diameter class X) i If the radial shrinkage is less than the theoretically permissible radial shrinkage of the tree basin to be dried, continue drying until the radial shrinkage of the i-th diameter class tree basin ring X, calculated according to formula (9), is reached. i ≥2mm (i.e., the radial shrinkage of the i-th diameter class tree disc ring X) i When the moisture content (greater than the theoretical allowable radial shrinkage of the tree basin to be dried) is reached, the steam generator in the drying chamber is turned on to inject steam into the drying kiln, increasing the relative humidity inside the kiln and thus increasing the moisture content. The moisture content M is measured by the moisture content sensor group on the tree basin. i Above the fiber saturation point (i.e., M)i ≥M FSP Turn off the steam generator and stop steam injection;

[0239] Continue drying until the moisture content M of the tree ring at a certain diameter class (i-th diameter class) is measured by the moisture content sensor group on the tree ring. i Below the fiber saturation point (i.e., M) i <M FSP When the moisture content is below the fiber saturation point, the radial shrinkage X of the i-th diameter class tree ring is calculated in real time according to formula (9). i X calculated according to formula (9) i Value, if X i For a moisture content ≥2mm, steam is injected into the drying kiln to increase the relative humidity inside, until the moisture content sensor group on the tree tray measures the moisture content M. i Stop steaming above the fiber saturation point; then calculate X according to formula (9) when the measured moisture content is below the fiber saturation point. i The value is maintained by repeatedly injecting and stopping steam into the drying kiln, ensuring that the radial shrinkage of the tree ring X is always maintained. i Always less than 2mm; by increasing the moisture content, the radial shrinkage at each diameter grade is controlled to reduce drying defects.

[0240] The drying process continues until the average moisture content of the log stacks is below 50%, at which point the drying of the log stacks enters the second stage of the drying baseline procedure.

[0241] 2-2. Second stage of drying

[0242] When the average moisture content of the log stack is less than 50% and greater than or equal to 35%, the drying process is adjusted to stage 2. This involves adjusting the dry-bulb temperature, wet-bulb temperature difference, relative humidity, and equilibrium moisture content of the drying medium based on the calculated average moisture content. Specifically, the drying temperature used during this stage is 45℃, the wet-bulb temperature difference is 7℃, and the relative humidity is 63%. In this second drying stage, two scenarios exist:

[0243] Case 1: During this drying stage, if the moisture content (M) of a certain diameter class (i-th diameter class) ring still exists... i Below the fiber saturation point (i.e., M) i <M FSP Then, according to formula (9), the radial shrinkage X of the i-th diameter tree ring with a moisture content lower than the fiber saturation point is calculated in real time; when the radial shrinkage X of the tree ring is ≥ 2 mm, the steam generator of the drying chamber is turned on to spray steam into the drying kiln to increase the relative humidity in the drying kiln, thereby increasing the moisture content of the drying kiln; the moisture content M is measured by the moisture content sensor on the tree ring after the steam is sprayed. i Above the fiber saturation point (i.e., M) i ≥MFSP ), the steam generator is turned off and the steam injection is stopped.

[0244] The second case: in this drying stage, the moisture content of the two adjacent diameter classes (i.e. the i'+1 and i' (i'=1, 2, 3, 4…), p-1, p≈[(D / 2)-r0] / 2, the value of p is rounded, and the integer) of the tree disc rings are lower than the fiber saturation point. As the moisture content difference between the two diameter classes increases, the radial shrinkage of the two diameter classes of the tree disc rings is mutually restrained or interacts. The diameter class of the tree disc ring close to the bark is the i'+1 diameter class, and the moisture content measured by the moisture content sensor group in real time is M (i′+1) ; the diameter class of the tree disc ring close to the pith is the i' diameter class, and the moisture content measured by the moisture content sensor group in real time is M i ′:

[0245] 1) If the moisture content M (i′+1) of the i'+1 diameter class of the adjacent diameter class is greater than the moisture content M i ′ of the i' diameter class, i.e. M i ′<M FSP , M i′+1 <M FSP ; M i′+1 >M i ′; then the total radial shrinkage X' of the adjacent two diameter classes is calculated according to formula (10); X'=[K Ti ′×(M FSP -M i ′)×(r i ′外 +r i′内 ) / 2-K Ri ′×(M FSP -M i ′)×s]-[K T(i′+1) ×(M FSP -M (i′+1) )×(r (i′+1)外 +r (i′+1)内 ) / 2-K R(i′+1) ×(M FSP -M (i′+1) )×s] (10)

[0246] 2) If M (i′+1) of the two adjacent diameter classes of the tree disc rings is less than or equal to M i ′, i.e. M i ′<M FSP , M i′+1 <M FSP ; M i′+1 ≤M i ′; then the total radial shrinkage X' of the adjacent two diameter classes is calculated according to formula (11);

[0247] X' = [K Ti ' x (M FSP -M i ') x (r i′外 +r i′内 ) / 2 - K Ri ' x (M FSP -M i ') x s] + [K T(i′+1) x (M FSP -M (i′+1) ) x (r (i′+1)外 +r (i′+1)内 ) / 2 - K R(i′+1) x (M FSP -M (i′+1) ) x s] (11) In formula (10), (11), X' is the total radial shrinkage (mm) of the adjacent two tree disc rings of the radial class; M (i′+1) is the moisture content (%) of the i'+1 tree disc ring of the adjacent radial class close to the bark; M i ' is the moisture content (%) of the i'tree disc ring of the adjacent radial class close to the pith; K Ti ' is the tangential shrinkage coefficient of the i'tree disc ring of the adjacent radial class close to the pith; K T(i′+1) is the tangential shrinkage coefficient of the i+1 tree disc ring of the adjacent radial class close to the bark; K Ri ' is the radial shrinkage coefficient of the i'tree disc ring of the adjacent radial class close to the pith; K R(i′+1) is the radial shrinkage coefficient of the i'+1 tree disc ring of the adjacent radial class close to the bark; M FSP is the fiber saturation point moisture content (%) of the tree disc; r i′外 is the outer diameter of the i'tree disc ring of the adjacent radial class close to the pith, i.e. the distance (mm) from the outer ring of the i'tree disc ring to the center point of the pith of the tree disc; r (i′+1)外 is the outer diameter of the i'+1 tree disc ring of the adjacent radial class close to the bark, i.e. the distance (mm) from the outer ring of the i'+1 tree disc ring to the center point of the pith of the tree disc; r i′内 is the inner diameter of the i'tree disc ring of the adjacent radial class close to the pith, i.e. the distance (mm) from the inner ring of the i'tree disc to the center point of the pith of the tree disc; r (i′+1)内 is the inner diameter of the i'+1 tree disc ring of the adjacent radial class close to the bark, i.e. the distance (mm) from the inner ring of the i'+1 tree disc ring to the center point of the pith of the tree disc; s is the difference (mm, usually 20 mm) between the inner diameter and the outer diameter of the corresponding tree disc ring.

[0248] For example, in this embodiment, p = 5; MFSP = 30%; if the moisture content (M2, M3) of the second and third diameter grade tree disc rings is monitored during the drying process and is lower than the fiber saturation point, then s is the difference between the inner and outer diameters of the second and third diameter grade tree disc rings, respectively, and the difference between the inner and outer diameters of each diameter grade tree disc ring in the present application is 20 mm.

[0249] When the total radial shrinkage X' of the two adjacent diameter grade tree discs calculated according to formula (10) or (11) is < 2 mm (i.e., the total radial shrinkage X' of the two adjacent diameter grade tree disc rings is less than the theoretical allowable radial shrinkage of the tree disc to be dried, which is measured to be 2 mm in the specific embodiments of the present application), the drying continues; until the total radial shrinkage X' of the two adjacent diameter grade tree disc rings calculated according to formula (10) or (11) is ≥ 2 mm (i.e., the total radial shrinkage X' of the two adjacent diameter grade tree disc rings is greater than the theoretical allowable radial shrinkage of the tree disc to be dried), the steam generator of the drying chamber is turned on to spray steam into the drying kiln to increase the relative humidity in the drying kiln and slow down the drying rate; when the total radial shrinkage X' of the two adjacent diameter grade tree discs calculated according to formula (10) or (11) is < 1 mm (i.e., the total radial shrinkage X' of the two adjacent diameter grade tree disc rings is less than half of the theoretical allowable radial shrinkage of the tree disc to be dried), the steam generator is turned off and the steam spraying is stopped; the drying continues until the moisture content sensors on the tree disc measure that the moisture content of the two adjacent diameter grade tree disc rings of the tree disc is lower than the fiber saturation point, and then the total radial shrinkage X' of the two adjacent diameter grade tree disc rings is calculated according to formula (10) or (11); the steps of spraying steam and stopping steam spraying are repeated to always control the total radial shrinkage X' of the two adjacent diameter grade tree disc rings to be always less than 2 mm;

[0250] If both conditions exist at the same time, the radial shrinkage X of the diameter grade tree disc ring with a moisture content lower than the fiber saturation point is calculated according to formula (9), and the total radial shrinkage X' of the two adjacent diameter grade tree disc rings is calculated according to formula (10) or (11), and X and X' are always controlled to be less than 2 mm (i.e., the theoretical allowable radial shrinkage of the tree disc to be dried).

[0251] Until the average moisture content of the tree disc stack is lower than 35%, the tree disc stack drying enters the third stage of the drying reference program;

[0252] 2-3, third stage of drying

[0253] When the average moisture content of the tree disc stack is less than 35% and greater than or equal to 25%, the drying process program is adjusted to the third stage, i.e., the drying medium dry bulb temperature, the dry-wet bulb temperature difference, the drying medium relative humidity, and the drying medium equilibrium moisture content are adjusted according to the calculated average moisture content of the tree disc stack, i.e., the drying temperature used during the drying process is 50°C, the dry-wet bulb temperature difference is 10°C, and the relative humidity is 54%; in the third drying stage, there are two conditions:

[0254] The first case: in this drying stage, if the moisture content (M i ) of a certain diameter class (the i diameter class) ring is still lower than the fiber saturation point (i.e. M i <M FSP ), the radial shrinkage X of the i diameter class ring with moisture content lower than the fiber saturation point is calculated in real time according to formula (9); when the radial shrinkage X of the ring is greater than or equal to 2mm, the steam generator of the drying chamber is started to spray steam into the drying kiln to increase the relative humidity in the drying kiln, thereby increasing the moisture content of the drying kiln; the steam is sprayed until the moisture content M i is measured by the moisture content sensor group on the ring, which is higher than the fiber saturation point (i.e. M i ≥ M FSP ), and the steam generator is stopped.

[0255] The second case: in this drying stage, the moisture content of the adjacent two diameter classes (i.e. the i'+1 and i' (i'=1, 2, 3, 4…, p-1, p≈[(D / 2)-r0] / 2, p is rounded to an integer) rings in the ring may start to be lower than the fiber saturation point, and the same method as in 2-2) Drying Stage 2, Case 2 is used for processing, wherein: if M i′+1 >M i ', the total radial shrinkage X' of the adjacent two diameter classes is calculated according to formula (10); if M i′+1 <M i ', the total radial shrinkage X' of the adjacent two diameter classes is calculated according to formula (11); the steps of spraying steam and stopping spraying steam are repeated to always control the total radial shrinkage X' of the adjacent two diameter classes to be less than 2mm;

[0256] If both cases exist, the radial shrinkage X of the diameter class ring with moisture content lower than the fiber saturation point is calculated according to formula (9), and the total radial shrinkage X' of the adjacent two diameter class rings is calculated according to formulas (10) and (11), and X and X' are always controlled to be less than 2mm.

[0257] Until the average moisture content of the ring stack is less than 25%, the ring stack enters the fourth stage of the drying reference program.

[0258] 2-4, Drying Stage 4

[0259] When the average moisture content of the tree disc pile is less than 25% and greater than or equal to 15%, the drying process procedure is adjusted to the fourth stage, that is, the drying medium dry bulb temperature, the dry-wet bulb temperature difference, the drying medium relative humidity, and the drying medium equilibrium moisture content are adjusted according to the calculated average moisture content of the tree disc pile, that is, the drying temperature used in the drying process is 55℃, the dry-wet bulb temperature difference is 15℃, and the relative humidity is 40%. In the fourth drying stage, the following situations exist:

[0260] In this drying stage, the moisture content of the adjacent two diameter levels (i.e., the moisture content of the i'+1 and i'(i'=1, 2, 3, 4..., p-1, p≈[(D / 2)-r0] / 2, the value of p is rounded to an integer) tree disc rings) in the tree disc may be lower than the fiber saturation point, and then the same method as in the second case of the second drying stage in 2-2) is used for processing, wherein: if M i ′ +1 >M i ′, the total radial shrinkage X' of the adjacent two diameter levels is calculated according to formula (10); if M i ′ +1 <M i ′, the total radial shrinkage X' of the adjacent two diameter levels is calculated according to formula (11); the steam spraying and stopping steps are repeated, and the total radial shrinkage X' of the adjacent two diameter levels is always controlled to be less than 2mm;

[0261] The drying continues until the average moisture content of the tree disc pile is less than 15% (usually 10%-15%), and the drying process is stopped.

[0262] After the dried tree disc is cooled to room temperature, no drying cracks, warping, cracking, or deformation are found in the tree disc, indicating that the eucalyptus tree disc dried by the method has high drying quality, and the qualified rate and yield of the tree disc drying are improved.

[0263] It should be noted that the adjustment of the drying medium state during the drying process of the tree disc is based on the drying reference. The drying reference refers to a parameter table for adjusting the drying medium temperature, the dry bulb and wet bulb temperature difference, etc. in the drying chamber according to different drying stages during the drying process. The usual drying stages are divided according to the change stages of the overall average moisture content of the tree disc to be dried. For different moisture content stages, there are corresponding drying medium temperature and dry-wet bulb temperature difference and moisture content. By controlling the temperature of the drying medium flowing into the drying chamber and the dry-wet bulb temperature difference of the drying medium during the drying process, the moisture content in the drying chamber is always less than the moisture content of the tree disc at that time, so that the moisture in the tree disc is always in an evaporation state until the required moisture content is reached.

Claims

1. A method of drying a tree disc, characterized in that, The method comprises the following steps in sequence: 1) subjecting the tree disc to a pre-drying treatment so as to bring the water content of the tree disc to a pre-drying water content M 预 , obtaining a pre-dried tree disc, wherein said pre-drying water content M 预 is comprised between 55 and 65%; 2) The average moisture content of the pre-dried tree disc is monitored according to the following method: 2-1) Calculate the average moisture content of each tree disk in the tree disk pile equipped with a moisture content sensor according to formula (8) In formula (8), M is the average moisture content of any tree disk in the tree disk pile equipped with a moisture content sensor, %; i M is the moisture content of different diameter grade tree disk rings of the tree disk equipped with a moisture content sensor, i.e. the moisture content of the i-th diameter grade tree disk ring on the tree disk, where i is an integer, i = 1, 2, 3, …, p, where p ≈ [(D / 2)-r0] / 2, the value of p is rounded to an integer; D is the diameter of the tree disk, mm; r0is the pith radius of the tree disk, mm; riis the outer diameter of the i-th diameter grade tree disk ring on the tree disk, mm; and riis the inner diameter of the i-th diameter grade tree disk ring on the tree disk, mm. i外 M is the moisture content of different diameter grade tree disk rings of the tree disk equipped with a moisture content sensor, i.e. the moisture content of the i-th diameter grade tree disk ring on the tree disk, where i is an integer, i = 1, 2, 3, …, p, where p ≈ [(D / 2)-r0] / 2, the value of p is rounded to an integer; D is the diameter of the tree disk, mm; r0is the pith radius of the tree disk, mm; riis the outer diameter of the i-th diameter grade tree disk ring on the tree disk, mm; and riis the inner diameter of the i-th diameter grade tree disk ring on the tree disk, mm. i内 M is the moisture content of different diameter grade tree disk rings of the tree disk equipped with a moisture content sensor, i.e. the moisture content of the i-th diameter grade tree disk ring on the tree disk, where i is an integer, i = 1, 2, 3, …, p, where p ≈ [(D / 2)-r0] / 2, the value of p is rounded to an integer; D is the diameter of the tree disk, mm; r0is the pith radius of the tree disk, mm; riis the outer diameter of the i-th diameter grade 2-2) Average moisture content of each tree tray in the tree tray stack equipped with a moisture content sensor Taking the average, the average moisture content of the pre-dried tree tray stack is obtained; 3) Drying is carried out according to the general standard drying procedure until the average moisture content of the tree disc pile is less than 15%, and the drying is stopped to obtain dried tree discs, wherein: During the drying according to the general standard procedure, the moisture content of each diameter class tree disc ring on the tree disc is monitored in real time by the moisture content sensor, wherein, during each drying stage according to the general standard procedure, 3Ⅰ) in each drying phase, if the moisture content M of the i-th girth of the tree disk is monitored i below the fiber saturation point M FSP then the radial shrinkage X of the i-th girth of the tree disk below the fiber saturation point is calculated in real time according to equation (9) i , X i = K Ti × (M FSP - M i ) × (r i外 + r i内 ) / 2 - K Ri × (M FSP - M i ) × s (9) In formula (9), X i is the radial shrinkage of the i-th diameter level ring of the tree disc, mm; K Ti is the chord shrinkage coefficient of the i-th diameter level ring of the tree disc when the moisture content is below the fiber saturation point; K Ri is the radial shrinkage coefficient of the i-th diameter level ring of the tree disc when the moisture content is below the fiber saturation point; M FSP is the fiber saturation point moisture content, %; M i is the moisture content of the i-th diameter level ring of the tree disc when the moisture content is below the fiber saturation point, %; r i外 is the outer diameter of the i-th diameter level ring of the tree disc when the moisture content is below the fiber saturation point, mm; r i内 is the inner diameter of the i-th diameter level ring of the tree disc when the moisture content is below the fiber saturation point, mm; s is the difference between the inner diameter and the outer diameter of the corresponding diameter level ring of the tree disc, mm, s is 20 mm; wherein i is an integer, i = 1, 2, 3, …, p, p ≈ [(D / 2)-r0] / 2, the value of p is rounded off to the nearest integer; When the radial shrinkage X of the i-th radial stage ring of the tree disk calculated according to formula (9) i ≥ the theoretical allowable radial shrinkage of the tree disk to be dried, the steam generator in the drying kiln is started to spray steam into the drying kiln to increase the relative humidity in the drying kiln until the moisture content sensor on the tree disk measures the moisture content M i Above the fiber saturation point, i.e. M i ≥ M FSP , the steam generator is turned off and the spraying of steam is stopped; the cycle of spraying steam and stopping the spraying of steam controls the radial shrinkage of the radial tree disk ring to be always less than the theoretical allowable radial shrinkage of the tree disk to be dried; 3Ⅱ), if the moisture content M of the two adjacent tree disk rings, i.e. the i', (i'+1)th diameter class tree disk rings, on the tree disk is monitored in each drying stage i′ and M (i′+1) are lower than the fiber saturation point M FSP , the total radial shrinkage X' of the i' and (i'+1)th diameter class tree disk rings with moisture content lower than the fiber saturation point is calculated in real time according to formula (10) or (11); wherein, 3 If M i′ M FSP , M (i′+1) M FSP , and M (i′+1) M i′ , then the total radial contraction X' of the two adjacent radial class tree disk rings is calculated according to formula (10) X' = [K Ti′ x (M FSP - M i′ ) x (r i′外 + r i′内 ) / 2 - K Ri′ x (M FSP - M i′ ) x s] - [K T(i′+1) x (M FSP - M (i′+1) ) x (r (i′+1)外 + r (i′+1)内 ) / 2 - K R(i′+1) x (M FSP - M (i′+1) ) x s] (10) 3 If M i′ <M FSP , M (i′+1) <M FSP , and M (i′+1) ≤ M i′ ; then the total radial contraction X' of the two adjacent radial class tree disk rings is calculated according to formula (11) X' = [K Ti′ × (M FSP -M i′ ) x (r i′外 +r i′内 ) / 2 - K Ri′ × (M FSP -M i′ ) x s] + [K T(i′+1) × (M FSP -M (i′+1) ) x (r (i′+1)外 +r (i′+1)内 ) / 2 - K R(i′+1) × (M FSP -M (i′+1) ) x s] (11) In formula (10) and (11), X' is the total radial shrinkage of the two adjacent radial level tree disc rings, mm; M (i′+1) is the moisture content of the i'+1 radial level tree disc ring close to the bark side in the adjacent radial level, %; M i′ is the moisture content of the i'th radial level tree disc ring close to the pith side in the adjacent radial level, %; K Ti′ is the tangential shrinkage coefficient of the i'th radial level tree disc ring close to the pith side in the adjacent radial level; K T(i′+1) is the tangential shrinkage coefficient of the i'+1 radial level tree disc ring close to the bark side in the adjacent radial level; K Ri′ is the radial shrinkage coefficient of the i'th radial level tree disc ring close to the pith side in the adjacent radial level; K R(i′+1) is the radial shrinkage coefficient of the i'+1 radial level tree disc ring close to the bark side in the adjacent radial level; M FSP is the fiber saturation point moisture content of the tree disc, %; r i′外 is the outer diameter of the i'th radial level tree disc ring close to the pith side in the adjacent radial level, i.e. the distance from the outer ring of the i'th radial level tree disc ring to the center point of the pith of the tree disc, mm; r (i′+1)外 is the outer diameter of the i'+1 radial level tree disc ring close to the bark side in the adjacent radial level, i.e. the distance from the outer ring of the i'+1 radial level tree disc ring to the center point of the pith of the tree disc, mm; r i′内 is the inner diameter of the i'th radial level tree disc ring close to the pith side in the adjacent radial level, i.e. the distance from the inner ring of the i'th radial level tree disc to the center point of the pith of the tree disc, mm; r (i′+1)内 is the inner diameter of the i'+1 radial level tree disc ring close to the bark side in the adjacent radial level, i.e. the distance from the inner ring of the i'+1 radial level tree disc ring to the center point of the pith of the tree disc, mm; s is the difference between the inner diameter and the outer diameter of the corresponding radial level tree disc ring, mm, s is 20 mm; wherein i' is an integer, i'=1, 2, 3,..., p-1, wherein p≈[(D / 2)-r0] / 2, the value of p is rounded off to an integer; D is the diameter of the tree disc, mm; r0 is the radius of the pith, mm; When the total radial shrinkage X' of the adjacent two diameter class tree discs calculated according to formula (10) or (11) is greater than or equal to the theoretical allowable radial shrinkage of the tree disc to be dried, the steam generator in the drying kiln is started to spray steam into the drying kiln to increase the relative humidity in the drying kiln; when the total radial shrinkage X' of the adjacent two diameter class tree discs calculated according to formula (10) or (11) is less than half of the theoretical allowable radial shrinkage of the tree disc to be dried, the steam generator is stopped to stop spraying steam; continue drying until the moisture content of the adjacent two diameter class tree disc rings on the tree disc measured by the moisture content sensor group is less than the fiber saturation point, and then calculate the total radial shrinkage X' of the adjacent two diameter class tree disc rings according to formula (10) or (11); cycle the spraying and stopping of steam to control the total radial shrinkage X' of the adjacent two diameter class tree disc rings to be always less than the theoretical allowable radial shrinkage of the tree disc to be dried; 3III), during each drying stage according to the general standard procedure, the moisture content of each diameter class tree disc ring on the tree disc is monitored in real time by the moisture content sensor, and the average moisture content of the tree disc pile is calculated, and the dry bulb temperature, the dry-wet bulb temperature difference, the relative humidity of the drying medium, and the equilibrium moisture content of the drying medium during the drying process are adjusted according to the average moisture content of the tree disc pile, and the tree disc drying process is carried out in stages according to the general standard procedure until the tree disc is dried to an average moisture content of less than 15% to obtain dried tree discs.

2. The drying method according to claim 1, wherein The pre-drying treatment in step 1) is carried out according to the following steps: 1-1), weighing the initial total mass G1 of the tree disc to be dried; 1-2) Determining the initial moisture content M of the tree disk 初 ; 1-3) calculating the pre-drying total mass G2 of the tree disc according to formula (7) when the tree disc is dried to the pre-drying moisture content; In formula (7), G2 is a pre-drying target mass of the tree disks in the tree disk stack after pre-drying treatment, g; G1 is an initial total mass of the tree disks in the tree disk stack before pre-drying treatment, g; M 初 is an initial moisture content of the tree disks to be dried, %; M 预 is a pre-drying target moisture content of the tree disks after pre-drying treatment, %. 1-4) drying the tree tray until the total mass of the tree tray in the drying kiln reaches G2, stopping heating and drying, obtaining a pre-dry tree tray, and the moisture content of the pre-dry tree tray reaches M 预 .

3. The drying method according to claim 1 or 2, characterized in that, It also includes that after the tree disc to be dried is stacked, the pre-drying treatment is carried out, wherein the stacking of the tree disc to be dried is carried out according to the following method: all the tree discs to be dried are weighed to obtain the initial total mass G1 of the tree disc to be dried; then the tree discs are stacked, wherein the tree discs are placed horizontally and stacked in the form of one layer of tree discs and one layer of spacing strips to form a cuboid-shaped tree disc pile to be dried.

4. The drying method according to claim 1 or 2, characterized by, During the pre-drying process, the drying temperature is controlled to be 70-90℃, and the relative humidity Φ is maintained to be greater than 85%.

5. The drying method according to claim 1, wherein The tangential contraction coefficient K of the radial tree disc ring T , the radial contraction coefficient K R , is determined as follows: 1') measuring the tangential dimension L of the small test pieces of the living wood of the different diameter classes of the tree disk rings 1T试 and the radial dimension L 1R试 ; 2'), the small test pieces corresponding to different diameter class tree disc rings are placed in the oven for drying treatment, wherein the drying temperature is 40-103℃, and the mass of the small test piece corresponding to the diameter class tree disc ring in the drying process is weighed every δt' time interval, wherein the shorter the interval time δt', the more accurate, and usually δt is less than 30min; 3′), when the mass of the small test pieces of the different diameter class tree disc rings reaches the respective corresponding air-dry mass m 2试 , the air-dry tangential size L 0T试 and the air-dry radial size L 0R试 of the small test pieces of the different diameter class tree disc rings in the air-dry state are again respectively measured; 4', the tangential shrinkage rate β of the test piece of different diameter grade tree disc ring was calculated by substituting the tangential size of the green wood and air-dried wood of the small test piece of different diameter grade tree disc ring into formula (4-1) T试 : In formula (4-1), β T试 is the tangential shrinkage of the small test piece of the tree disk ring of different diameter grades, %; L 1T试 is the tangential size of the green wood of the small test piece of the tree disk ring of different diameter grades, mm; L 0T试 is the tangential size of the air-dried small test piece of the tree disk ring of different diameter grades, mm; 5′), the radial dimension of the green wood and air-dried wood of the small test piece of different diameter grade tree disc ring is respectively substituted into formula (4-2), and the radial shrinkage rate β of the test piece of different diameter grade tree disc ring is calculated R试 : In formula (4-2), β R试 is the radial shrinkage rate (%) of the small test piece of the tree disc ring of different diameter grades; L 1R试 is the radial size of the small test piece of the tree disc ring of different diameter grades when the wood is green, mm; L 0R试 is the radial size of the small test piece of the tree disc ring of different diameter grades when the wood is air-dried, mm; 6', the tangential shrinkage coefficients K of the small test pieces of different diameter classes of tree disc rings are calculated according to formula (5-1) respectively T试 , In formula (5-1), K T试 is the tangential shrinkage coefficient of small test pieces of different diameter class tree disk rings; β T试 Tangential shrinkage, % for small test pieces of different diameter classes of tree disks; EMC is the equilibrium moisture content, % in air-dry state. 7', the radial shrinkage coefficient K of the small test piece of different diameter grade tree disc ring is calculated according to formula (5-2) respectively R试 , In formula (5-2), K R试 is the radial shrinkage coefficient of the small test piece of the tree disc ring of different diameter grades; β R试 is the radial shrinkage rate of the small test piece of the tree disc ring of different diameter grades, %; EMC is the equilibrium moisture content in air-dried state, %. The tangential / radial shrinkage of the small test pieces of the different diameter class tree disk rings respectively represents the tangential / radial shrinkage of the different diameter class tree disk rings; The tangential / radial shrinkage coefficient of the small test piece with different diameter class tree disc ring respectively represents the tangential shrinkage coefficient K of different diameter class tree disc ring T / radial shrinkage coefficient K R .

6. The drying method according to claim 5, wherein the respective corresponding air-dry mass m of the small test pieces of the different diameter classes of tree disks in step 3') 2试 is determined as follows: 3′-A) After removing the pith from the tree basin, divide it into p rings from the inside out along the radius of the tree basin. Each ring is defined as a diameter-class tree basin ring, and the width of each diameter-class tree basin ring is 2cm, that is, the inner diameter r of each diameter-class tree basin. 内 With outer diameter r 外 The difference is 2cm; and the diameter class tree discs are defined sequentially from the inside out as the 1st to the pth diameter class tree discs, where the inner diameter of the 1st diameter class tree disc is the radius r0 of the pith circle, and the outer diameter of the 1st diameter class tree disc is (r0+2)cm; the inner diameter of the subsequent diameter class tree disc ring is the outer diameter of the previous diameter class tree disc ring; where p≈[(D / 2)-r0] / 2, the value of p is rounded to the nearest integer, r0 is the pith radius, cm; D is the diameter of the tree disc, cm; 3'-B) According to the national standard "GB / T 1932-2009 Wood Shrinkage Determination Method", each diameter class tree disk ring is sawn into small test pieces with a size of 2cm*2cm*(2-3)cm, and small test pieces of different diameter class tree disk rings are obtained respectively; 3'-C) randomly select several small test pieces from each diameter class tree disc ring respectively, first measure the radial size of each diameter class tree disc ring small test piece respectively, and take the average value, recorded as the radial size L of the corresponding diameter class tree disc ring small test piece 1R试 ; measure the chordal size of each diameter class small test piece respectively, and take the average value, recorded as the chordal size L of the corresponding diameter class tree disc ring small test piece 1T试 ; 3'-D) Calculate the initial total volume of each small test piece selected from the corresponding DBH class tree disc ring, i.e. the green volume of the test piece, V 0试 , and weigh m 0试 ; then place the weighed test pieces of different DBH class tree disc rings in an oven with a temperature of (103±2) °C for drying, weigh every 6 h, and when the weight difference between two consecutive weighings is less than 0.02 g, it is considered to be dried to an absolute dry state, and the absolute dry mass (m 1试 ) of the corresponding small test piece selected from the different DBH class tree disc rings is obtained by weighing. 3'-E) The density (p) of the small test pieces of the different diameter classes of tree disks rings was calculated according to formula (2) respectively 试 ), In formula (2), p 试 is the density of the small test piece of the tree disk ring of different diameter grades, g / cm 3 ; m 1试 is the absolute dry mass of the small test piece of the tree disk ring of different diameter grades, g; V 0试 is the green volume of the small test piece of the tree disk ring of different diameter grades, cm 3 ; 3'-F) The air-dry mass m of the small test piece corresponding to the tree disc ring of different diameter class is calculated according to formula (3) 2试 ; m 2试 = p 试 V 0试 x (1 + EMC) (3) In formula (3), m 2试 is the air-dry mass of the small test piece of the tree disk ring of different diameter grades, g; p 试 is the basic density corresponding to each of the small test pieces of the tree disk ring of different diameter grades, g / cm 3 ; V 0试 is the green volume corresponding to each of the small test pieces of the tree disk ring of different diameter grades, cm 3 ; EMC is the equilibrium moisture content in the air-dry state, %.

7. The drying method according to claim 1, wherein In the process of drying according to the general reference procedure, when the average moisture content of the tree disk stack is higher than the fiber saturation point, the moisture content of a certain diameter class tree disk ring on the tree disk is lower than the fiber saturation point M FSP , and / or the moisture content of two adjacent diameter class tree disk rings on the tree disk is lower than the fiber saturation point M FSP ; when the average moisture content of the tree disk stack is higher than the fiber saturation point, the moisture content of two adjacent diameter class tree disk rings on the tree disk is lower than the fiber saturation point M FSP .

8. A drying tree tray characterized by, Prepared according to the drying method as claimed in any one of claims 1-7.

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