JP4064222B2 - How to dry wood - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for drying wood, and more specifically, it is possible to obtain data that accurately reflects the state of drying stress inside the wood during drying, and efficient wood that achieves both suppression of internal cracking and shortening of drying time. An object of the present invention is to provide a method for drying wood that can be dried.
[0002]
[Prior art and problems to be solved by the invention]
Artificially dried wood is widely used as building materials and furniture materials such as columns, beams, and construction materials in order to prevent deformation and cracking due to shrinkage.
In conventional artificial drying of wood, it is common to measure the moisture content, weight, strain, etc. of the sample material in the dryer, assemble a drying schedule from the measured data, and proceed with drying, but these measurements are It does not directly measure the dry stress state of wood, which affects cracks, bends, warpage, etc. that occur during drying.
[0003]
As a method of observing the stress during drying, there are methods of taking a sample set in the dryer from time to time to create a comb-shaped test piece to judge the stress, and taking the strain to obtain a measured value of the stress. Since the work is complicated and only discontinuous information can be obtained, it is difficult to assemble an appropriate drying schedule according to the drying state. In particular, in high-temperature drying, it is difficult to take out a sample from the dryer itself.
[0004]
Japanese Laid-Open Patent Publication No. 50-122971 discloses a method for measuring the drying stress using the warping stress of wood, and Japanese Laid-Open Patent Publication No. 51-84451 is obtained by such a method. A method for automatically controlling the humidity of the drying chamber and automating the drying schedule by using the output to be disclosed is disclosed.
However, in these methods, since the stress is determined from the degree of deformation (warping or warping force) of the wood, the state of the drying stress inside the wood cannot be accurately determined. In addition, since the test piece is obtained by dividing the plate material into two in the plate thickness direction and coating the surfaces other than the original front and back surfaces, data reflecting the state of the original drying stress of wood cannot be obtained.
In short, there has not yet been provided a method for drying wood that obtains data that accurately reflects the state of the drying stress inside the wood during drying, and that efficiently uses the data to dry the wood.
[0005]
[Patent Document 1]
JP-A-50-122971 [Patent Document 2]
JP-A-51-84451 [0006]
Therefore, the object of the present invention is to obtain data that accurately reflects the state of the drying stress inside the wood during drying, and to achieve efficient wood drying that achieves both suppression of internal cracking and shortening of the drying time. It is to provide a method for drying wood.
[0007]
[Means for Solving the Problems]
The present invention is a distortion detecting means, is fixed to the inside of the wood, while controlling the drying conditions on the basis of the data obtained from the strain sensing means, a drying method of drying a row Cormorants timber of the wood, the The wood is a cored square, a centered square, a cored flat or a centered flat, and on the cross section perpendicular to the longitudinal direction of the wood, the widthwise central portion of one side of the wood and the one side The strain detection means is fixed near the center point of the line segment when assuming a line segment connecting between the other side surfaces and forming an angle of 45 with respect to the one side surface. The above-mentioned object is achieved by providing a method for drying wood, which is characterized by being fixed in an integrated state with surrounding wood through an adhesive .
In addition, when the wood has a flat core or a flat core, other than the long side of the rectangle from one side which forms the short side of the rectangle of the cross section perpendicular to the longitudinal direction of the wood, as the line segment Assume a line segment going to the side.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on preferred embodiments thereof.
As the strain detection means used in the present invention, various known devices can be used, but a strain gauge is preferably used.
The strain gauge is formed by fixing a sensing element (grid) made of a thin metal wire or foil of copper / nickel alloy or the like to a gauge base (hereinafter referred to as a base) made of an insulating material made of resin or the like. A change in electrical resistance is caused by expansion or contraction of a thin metal wire or foil. The change in electrical resistance is usually replaced with a change in voltage by a bridge circuit or the like, and the voltage is further amplified so that it can be read by various meters and digital values.
[0009]
As the strain detection means, one that shows high sensitivity to expansion and contraction in a specific direction is preferably used, and particularly has a cylindrical base and has high sensitivity to expansion and contraction in the axial direction of the cylindrical base. A strain gauge is preferred.
As such a strain gauge, a strain gauge for bolt axial force measurement manufactured by Kyowa Denki Co., Ltd., in particular, the model name “KFG-3-120-C20-11” is preferably used. This strain gauge undergoes a greater resistance change when the cylindrical base expands and contracts in the axial length direction than when the axial length of the cylindrical base deforms.
[0010]
The fixing position of the strain detecting means with respect to the wood is not particularly limited as long as it is inside the wood, but it is preferably a position that is separated from both ends of the wood by 10 cm or more, particularly 25 cm or more in the longitudinal direction of the wood, It is preferable that the distance from each side surface (referring to four surfaces along the longitudinal direction of the wood) of the wood is 2 cm or 1/4 of the thickness, whichever is smaller.
[0011]
The strain detection means is preferably fixed in the following modes (1) and / or (2) from the viewpoint of efficiently detecting an important strain change that leads to the occurrence of internal cracks.
[0012]
(1) When using a strain detection means that shows high sensitivity to expansion and contraction in a specific direction, the strain detection means is such that the specific direction is parallel to a plane perpendicular to the longitudinal direction of the wood and the specific direction is It is preferable to fix the lumber in the vicinity of one annual ring so as to be parallel to the tangential direction of the annual ring.
[0013]
In FIG. 1, a strain gauge 1 having a cylindrical base and having high sensitivity to expansion and contraction in the axial length direction of the cylindrical base is disposed inside a core support square 2 (regular angle, without splitting back). A fixed state is shown. In the figure, the four strain gauges 1A to 1D are all arranged on one surface (cross section) orthogonal to the longitudinal direction of the cored square member 2, and each strain gauge 1 is formed of a cylindrical base. The axial length direction is parallel to the cross section. Further, the axial length direction of the cylindrical base in the strain gauges 1A, 1C, and 1D is substantially parallel to the tangential direction of the annual ring 3 in the vicinity of the annual ring 3 of the core support square member 2, and the strain gauge 1B. The axial length direction of the cylindrical base is substantially parallel to the tangential direction of the annual ring 3 ′ in the vicinity of the annual ring 3 ′.
Note that the strain gauge 1 in which a sensitive element made of a thin metal wire or foil is fixed to a cylindrical base has a high sensitivity to expansion and contraction in a specific direction. It is preferable to fix in an aspect.
[0014]
(2) When the wood to which the strain detecting means is fixed is a square member, particularly a cored square, a centered square, a cored flat or a centered flat, on a plane (cross section) orthogonal to the longitudinal direction of the wood And the center of the line segment when assuming a line segment connecting the central part in the width direction of one side surface of the wood and the other side surface adjacent to the one side surface and forming an angle of 45 with respect to the one side surface. It is preferable to fix the strain detecting means near the point.
[0015]
In the example shown in FIG. 1, the four strain gauges 1 are fixed corresponding to the four corners of the core holding positive angle 2, but the description will be given focusing on one of the strain gauges 1 </ b> A. As shown in FIG. 2 schematically showing the cross section corresponding to FIG. 1, the strain gauge 1 </ b> A has a width of one side surface 21 of the core support square 2 on the transverse cross section shown in FIG. Near the center point 4a of the line segment 4A when assuming a line segment 4A connecting the direction center portion 21a and the other side surface 22 adjacent to the one side surface 21 and forming an angle of 45 with respect to the one side surface 21 It is fixed to. The other strain gauges 1B to 1D are also fixed in this mode, and are fixed near the center points 4b to 4d of the respective line segments 4B to 4D shown in FIG. The vicinity of the center point of the line segment means not only on the center point that bisects the line segment but also the vicinity of the center point, and the center that accurately bisects the line segment. It suffices if it is within a circle P with the point being the center of the circle and the half length of the line segment being the diameter, and in particular, the center point that accurately bisects the line segment is the center of the circle and the line segment It is preferable to be within a circle having a diameter of 1/3.
[0016]
FIG. 3 shows the location where the internal crack 5 is likely to occur and the direction in which the internal crack 5 is likely to occur when the cored square is dried by the conventional method. By disposing the strain detection means in the above-mentioned aspects (1) and / or (2), particularly in the four aspects corresponding to each corner of the square bar in the above-mentioned aspects (1) and / or (2), The danger of such internal cracks occurring at the holding angle can be detected more accurately. In addition, the embedded part of the strain gauge (strain detecting means) shown in FIG. 1 is a position corresponding to the quadrant of the diagonal line of the cross section of the wood, and the part where the internal stress during drying is the largest and the internal crack is likely to occur. is there.
[0017]
FIG. 4 is a diagram showing a state in which the strain detection means is fixed to the centering positive angle, the centering flatness, and the centering flatness in the mode (1) and / or (2). FIG. 4 also shows the locations where internal cracks 5 are likely to occur and the direction in which internal cracks 5 are likely to occur when they are dried by a conventional method.
In FIG. 4A, two strain gauges 1A and 1B are fixed on the same cross section of the centering positive angle 2 in the manner of (1) and (2).
In FIG. 4B, six strain gauges are fixed on the same cross section of the core-supporting flat angle 2, and four strain gauges 1A among them are the modes (1) and (2). The other two strain gauges 1B are fixed in the mode (1).
In FIG. 4 (c), four strain gauges are fixed on the same cross section of the centering flat angle 2, and each of the strain gauges 1A and 1B is in the form of (1) and (2). It is fixed.
[0018]
A preferred method of fixing the strain detection means inside the wood will be described with reference to FIG. 5 by taking as an example a case where the strain gauge is fixed inside the core holding positive angle.
First, a hole or the like is drilled with a drill or the like from the central portion in the width direction of each side surface of the cored square member 2 until it penetrates the central portion in the width direction of the adjacent side surface at an angle of 45 ° to each side surface [FIG. (See (a)). The inner diameter of the through hole is just enough for the strain gauge to enter or slightly larger.
Next, the strain gauge 1 is inserted into the through hole 23 (see FIG. 5B), and the strain gauge 1 is positioned at the center between both ends of the through hole 23. Then, the gauge lead 6 extending from the strain gauge 1 is temporarily fixed outside the through hole 23.
In this state, an adhesive is injected into the through hole 23 [see FIG. 5 (c)]. The adhesive is injected from one end opening until it flows out from the other end opening, and it is confirmed that the entire inside of the through hole is filled with the adhesive.
Then, the gauge lead 6 protruding out of the through hole is connected to the heat-resistant lead wire 8 through the gauge terminal 7 (see FIG. 1) for protecting the gauge lead, and the periphery of the connection portion of the through hole 23 is connected. Cover with the heat-resistant coating 9 including the entrance [see FIG. 5 (d)].
In this way, the strain gauge 1 can be fixed in the state shown in FIG.
[0019]
The drying of the wood in the present invention is performed under the control of temperature and humidity.
This drying is usually performed by accommodating several to several hundreds of wood in a dryer whose temperature and humidity can be controlled, and the wood to which the strain detection means is attached may be one of them (FIG. 6). reference). However, it can also be attached to a plurality.
[0020]
As a method for controlling the temperature and humidity during the drying of the wood, for example, the resistance change generated in the strain detection means is converted into data that can be read by a predetermined device, and the data obtained from the strain detection means is monitored. When drying and the data show that the internal stress (strain) of the wood has increased to such an extent that internal cracking occurs, the temperature and / or humidity can be reduced in a direction that reduces the drying stress (lowering the drying rate). When the data confirms that the risk of internal cracking has been sufficiently reduced, change the temperature and / or humidity in the direction opposite to the direction to relieve the drying stress (in the direction of increasing the drying speed). change. For example, by drying the wood while repeating such control, the drying time can be shortened while suppressing internal cracking of the wood.
[0021]
As an example of a preferable control method in the wood drying method of the present invention, the drying conditions are controlled based on data obtained from the strain detection means so that the amount of strain deformation per fixed time does not exceed a predetermined value. For example, if the amount of strain change per hour exceeds a predetermined value, the risk of internal cracking is increased, so the drying conditions are changed in the direction of slowing the drying speed, and the amount of strain change is less than the predetermined value. When the process returns to step S1, it is considered that the drying conditions are changed in the direction of increasing the drying speed, assuming that the risk of internal cracking has decreased. By controlling in this way, drying time can be shortened while preventing internal cracks.
[0022]
【Example】
Hereinafter, the method for drying wood according to the present invention will be described in more detail with reference to examples.
(Preliminary test)
70 core-supported squares (132 mm × 132 mm × 3000 mm) with no back split made from one cedar log into one grinding angle were used as materials to be dried.
A strain measurement specimen having a 132 mm square and a total length L = 1200 mm is cut out from one of the materials to be dried, and the distance from one end (the end face of the specimen) of the specimen is 1/4 of the total length L. And each four strain gauges were embedded and fixed on each cross section at a position of 1/2 of the total length L. The embedding position and the arrangement direction of each gauge were as shown in FIG. 1, and the fixing method was the method described above (see FIG. 5). In addition, the following strain gauges manufactured by Kyowa Denki Co., Ltd. were used as strain gauges.
"KFG-3-120-C20-11 (with gauge lead)", adhesive for fixing the gauge; "EP-34B", gauge terminal; "TF-28", heat-resistant lead wire; "L-" 12 ", heat-resistant coating;" SKF-3059 "
[0023]
The strain measurement specimen is housed in a high-temperature specification IF-type steam dryer “SK-IF10LHP” manufactured by Shinshiba Equipment together with other materials to be dried, and the heat-resistant lead wire extended outside the dryer It was connected to a data logger (“THS-1100” manufactured by Tokyo Sokki Co., Ltd.) by a 1-gauge 3-wire method so that strain during drying could be measured. In addition, the amount of change in strain per hour was output during analysis.
In addition, an electrical resistance type moisture content meter and a thermocouple for temperature measurement inside the wood (K thermocouple, temperature range 0 to 150 ° C.) are used for the strain measurement specimen, and the intermediate layer corresponding to the position where the strain gauge is embedded. (About 28 mm depth) and a central layer (about 66 mm depth) at the center of the cross section of the material so that the moisture content and temperature inside the wood during drying can be measured.
[0024]
After completion of such preparation, as a preliminary test, drying was performed according to the drying schedule shown in FIG. 7, and the relationship between strain change and internal cracking was examined. In this preliminary test, the drying conditions were not controlled based on the data obtained from the strain gauge.
After drying, the cross section of the strain gauge embedded part of the measurement specimen was inspected, and no internal cracks were observed in the three gauge embedded parts of the four strain gauges, and the remaining one gauge embedded part Was found to have internal cracks. Looking at the transition of strain change per hour based on the data obtained from each strain gauge, the change amount at the point of maximum strain change is- Whereas it was within 300 μm, the strain variation per hour reached a maximum of nearly −500 μm at the embedded portion of one gauge where internal cracks occurred. From these results, it was determined that there was a risk of internal cracking when the amount of change in the measured internal strain exceeded −300 μm per hour. Note that the strain change amount data shown in FIG. 7 is data on an embedded portion of one gauge in which an internal crack has occurred.
[0025]
(Example)
The dimension of the core holding square that is the material to be dried is 115 mm × 115 mm × 3000 mm, and from one of them, a 115 mm square, L = 1200 mm strain measurement specimen is cut out, and the strain measurement specimen is Prepare for drying in the same manner as in the preliminary test except that the strain gauge, the electric resistance type moisture content meter and the thermocouple (K thermocouple, temperature range 0 to 150 ° C.) etc. were similarly attached. went.
[0026]
And it dried with the drying schedule shown in FIG. The details will be described below with reference to FIG.
First, steam was sprayed into the dryer, and initial steaming was performed at 96 ° C. and a relative humidity of 100%. This initial steaming was carried out for 8 hours, and the temperature of the wood in the dryer was raised to a predetermined temperature, and then switched to the drying process at time point (1) in the figure. In the first drying step, drying was performed at a dry bulb temperature of 110 ° C. or higher. In the first drying step, drying was continued while monitoring the moisture content of the intermediate layer corresponding to the gauge embedding part, and the moisture content became a fiber saturation point (30%) at which internal cracks easily occur. At the time of (2) in the figure, the dry bulb temperature was switched from 112 ° C. to 108 ° C. to switch to the second drying step.
[0027]
In this example, the drying conditions were controlled based on the data obtained from the strain detection means in the second drying step following the first drying step in which the dry bulb temperature was 110 ° C. or higher. That is, if the drying at the dry bulb temperature of 108 ° C. is continued, the strain change amount per hour (hereinafter simply referred to as strain change amount) decreases. Then, at the point of (3) in the figure where the recovery was made to −100 μm, the wet bulb temperature was lowered from 86 ° C. to 83 ° C. in order to increase the drying rate.
As a result, the strain change amount increased from a decrease to an increase. Furthermore, by continuing the same conditions, the amount of strain change became -250μ, which is close to the danger zone (-300μ) where internal cracks occur, so at that time (point of (4) in the figure) Therefore, the dry-bulb temperature was lowered from 108 ° C. to 105 ° C. (the drying speed was reduced).
[0028]
As a result, the amount of change in distortion turned from increasing to decreasing. Then, at the time point when it recovered to −250 μ after 4 hours (time point (5) in the figure), in order to increase the drying rate, the dry bulb temperature was raised from 105 ° C. to 108 ° C. and the wet bulb temperature was changed from 83 ° C. to 81 ° C. Lowered.
As a result, the amount of change in strain again began to increase from a decrease, and by continuing the same conditions, the amount of change in strain became -250μ again. At that time (point 6 in the figure), the wet bulb The dry bulb temperature was lowered from 108 ° C. to 105 ° C. with the temperature kept unchanged, and the drying rate was slowed down.
[0029]
As a result, the amount of change in distortion turned from increasing to decreasing. Then, at the time point when it recovered to −250 μ after 4 hours (point of (7) in the figure), in order to increase the drying speed, the dry bulb temperature was increased from 105 ° C. to 108 ° C. and the wet bulb temperature was changed from 81 ° C. to 79 ° C. Lowered.
When drying was continued under these conditions, the moisture content of the intermediate layer corresponding to the gauge embedding site became 15% and the strain change amount was within −200 μm, and the risk of occurrence of internal cracks was reduced. Then, when the moisture content at the center of the wood becomes 35% and the material temperature reaches 102 ° C. (point of (8) in the figure), the dry bulb temperature is lowered to 105 ° C., and the drying conditions based on the strain change amount Control of was terminated.
[0030]
Subsequent drying at a dry bulb temperature of 105 ° C. for a relatively long period of time is intended to prevent various deformations due to shrinkage of the central part, and to control the humidity in order to finish a uniform drying material without unevenness in drying. In this example, after the temperature of the dry bulb was further lowered at 132 hours from the start of the initial cooking, the drying was finished in about 12 hours.
[0031]
When the cross section of the strain gauge embedded portion of the strain measurement specimen dried according to the example was visually inspected, no internal crack was observed in any of the gauge embedded portions. Further, each material to be dried at the same time was cut at a position of 30 cm and a central position in the longitudinal direction from the both mouth ends, and the presence or absence of internal cracks was visually observed for each cross section. No internal cracks were observed for 64 of the desiccants, and the degree of the remaining 5 cracks for which internal cracks were observed was extremely small.
Note that the strain change data shown in FIG. 8 is the gauge of the fastest drying speed among the eight strain gauges (the gauge embedded in the position of 1/4 of the total length L, the gauge indicated by 1C in FIG. 1). ).
[0032]
From the results of the examples, it can be seen that internal cracking can be prevented without unnecessarily extending the drying time by controlling the drying conditions so as to suppress the amount of strain change per predetermined time to a predetermined value or less. . The method for drying wood according to the present invention is not limited to the case where the timber produced from the coniferous tree is provided with a drying step of drying at a dry bulb temperature of 100 ° C., particularly 110 ° C. or more, as in the above example. The present invention can also be applied to the case where the sawn square is dried at a temperature of 100 ° C. or lower.
[0033]
【The invention's effect】
According to the present invention, it is possible to obtain data that accurately reflects the state of the drying stress inside the wood during drying, and wood that can efficiently dry the wood while suppressing internal cracking and shortening the drying time. The drying method can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a timber showing a state in which a strain detecting means is fixed inside the timber.
FIG. 2 is a diagram schematically showing a cross section corresponding to FIG. 1;
FIG. 3 is a cross-sectional view of wood schematically showing a portion where an internal crack is likely to occur and a direction in which the internal crack is likely to occur when the wood has a positive angle with a center.
FIG. 4 is a cross-sectional view of wood schematically showing a state in which strain detection means is fixed to the wood, along with a portion where the internal crack of the wood is likely to occur and a direction in which the internal crack is likely to occur, (a) is a centering square, (b) is a centering flat, and (c) is a diagram showing a centering flat.
FIGS. 5A and 5B are diagrams showing a procedure for fixing the strain detection means to the wood, in which FIG. 5A shows a state in which a through hole for inserting the strain detection means is formed in the wood, and FIG. 5B shows a through hole; (C) is a state in which an adhesive is injected into the through hole after the strain detection unit is inserted, and (d) is a state in which a gauge terminal and the like are covered with a heat-resistant coating together with the opening of the through hole. FIG.
FIG. 6 is a perspective view schematically showing a state in which the wood to which the strain detecting means is attached is arranged in the dryer together with other wood.
FIG. 7 is a diagram showing a drying schedule in a preliminary test.
FIG. 8 is a drying history graph showing a transition of a control history of a drying condition and a strain change amount in an example.
[Explanation of symbols]
1,1A-1D strain gauge (strain detection means)
2 Wood 3 Annual ring 5 Internal crack

Claims (4)

Distortion detecting means, is fixed to the inside of the wood, while controlling the drying conditions on the basis of the data obtained from the strain sensing means, a drying method of drying a row Cormorants timber of the wood,
The wood is a cored square, a centered square, a cored flat, or a cored flat, and on a cross section perpendicular to the longitudinal direction of the wood, the widthwise central portion of the one side and the one side The strain detection means is fixed near the center point of the line segment when assuming a line segment connecting the other side surface adjacent to the side surface and forming an angle of 45 with respect to the one side surface. Is a method for drying wood, which is fixed in an integrated state with surrounding wood through an adhesive . The strain detection means is highly sensitive to expansion and contraction in a specific direction. The strain detection means is configured so that the specific direction is parallel to a plane perpendicular to the longitudinal direction of the wood and the specific direction is the wood. The method for drying wood according to claim 1 , wherein the lumber is fixed so as to be parallel to a tangential direction of the annual ring in the vicinity of one annual ring. A through hole extending from the one side surface to the other side surface adjacent to the one side surface is formed in at least one side surface of the wood, and the strain detecting means is inserted into the through hole, and an adhesive is filled in the through hole and cured. The method for drying wood according to claim 1 or 2, wherein the strain detecting means is fixed inside the wood. The method for drying wood according to any one of claims 1 to 3 , wherein drying conditions are controlled based on data obtained from the strain detection means so that the amount of strain deformation per fixed time does not exceed a predetermined value.

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