JP2004190957A - Timber drying method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently dry timber while compatibly suppressing internal cracking and shortening a drying time by acquiring data accurately reflecting the conditions of drying stress in the timber being dried. <P>SOLUTION: The timber drying method comprises fixing a distortion detecting means 1 into the timber 2 and drying the timber 2 while controlling the drying conditions in accordance with data obtained from the distortion detecting means 1. The drying conditions are controlled in such a manner that, for example, when a distortion variation per one hour exceeds a preset value, there is a higher degree of potential for internal cracking and so the drying conditions are changed into a lower drying speed, and when the distortion variation is turned down to a preset value or less, there is a lower degree of potential for internal cracking and so the drying conditions are changed into a higher drying speed. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for drying wood, in particular, it is possible to obtain data accurately reflecting the state of drying stress inside the wood during drying, and to efficiently suppress the occurrence of internal cracks and shorten the drying time. An object of the present invention is to provide a method for drying wood that can be dried.
[0002]
Problems to be solved by the prior art and the invention
As building materials and furniture materials such as columns, beams, construction materials, etc., artificially dried wood is generally used in order to prevent the occurrence of deformation, cracks, and the like due to shrinkage.
In the conventional artificial drying of wood, it is common to measure the moisture content, weight, strain, etc. of the sample material in the dryer, and assemble a drying schedule from the measured data to proceed with drying. It does not directly measure the dry stress state of wood, which affects cracking, bending, warping, etc., occurring during drying.
[0003]
As a method of observing the stress during drying, a sample set in a dryer is occasionally taken out, a comb-shaped test piece is created to determine the stress, or a method of measuring the stress by removing the strain is used. Since the operation 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 the sample from the inside of the dryer.
[0004]
Also, Japanese Patent Application Laid-Open No. Sho 50-122971 discloses a method for measuring the drying stress by using the warpage stress of wood, and Japanese Patent Application Laid-Open No. 51-84451 discloses such a method. A method for automatically controlling the humidity of a drying chamber and automating a drying schedule using the output of the drying chamber 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. Moreover, since the plate material is divided into two in the plate thickness direction and a test piece coated on a surface other than the original front and back surfaces is used, data reflecting the original dry stress state of wood cannot be obtained.
In short, there has not yet been provided a method of drying wood that acquires data accurately reflecting the state of drying stress inside the wood during drying and utilizes the data to efficiently dry the wood.
[0005]
[Patent Document 1]
JP-A-50-122971 [Patent Document 2]
JP-A-51-84451
Therefore, an object of the present invention is to obtain data accurately reflecting the state of drying stress inside wood during drying, and to perform efficient wood drying while suppressing internal cracks and shortening the drying time. It is an object of the present invention to provide a method for drying wood.
[0007]
[Means for Solving the Problems]
The present invention is characterized in that the strain detecting means is inserted and fixed inside the wood, and the wood is dried while controlling drying conditions based on data obtained from the strain detecting means. The object has been achieved by providing a method.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail based on preferred embodiments.
As the strain detecting means used in the present invention, various known means can be used, but it is preferable to use a strain gauge.
The strain gauge is formed by fixing a sensing element (grid) made of a thin wire or foil of a metal such as a copper / nickel alloy to a gauge base (hereinafter, referred to as a base) made of an insulating material made of a resin or the like. The expansion or contraction of a thin metal wire or foil causes a change in electrical resistance. The change in electric resistance is usually replaced by 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 or digital values.
[0009]
As the strain detecting means, those having high sensitivity to expansion and contraction in a specific direction are preferably used, and particularly have a cylindrical base and have high sensitivity to expansion and contraction in the axial direction of the cylindrical base. Strain gauges are preferred.
As such a strain gauge, a strain gauge for measuring a bolt axial force manufactured by Kyowa Dengyo Co., Ltd., particularly, a model name “KFG-3-120-C20-11” is preferably used. In this strain gauge, a larger resistance change occurs when the cylindrical base expands and contracts in the axial direction than when the cylindrical base deforms so as to bend in the axial direction.
[0010]
The position at which the strain detection means is fixed to the wood is not particularly limited as long as it is inside the wood, but it is preferably a position separated from the mouths 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 (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]
It is preferable that the strain detecting means is fixed in the following modes (1) and / or (2) from the viewpoint of efficiently detecting an important strain change leading to the occurrence of an internal crack.
[0012]
(1) In the case where a strain detector having high sensitivity to expansion and contraction in a specific direction is used as the strain detection unit, the distortion detection unit is configured such that the specific direction is parallel to a plane orthogonal to the longitudinal direction of the wood and the specific direction is It is preferable that the timber is fixed near one annual ring so as to be parallel to a 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 direction of the cylindrical base is provided inside a cored square member 2 (regular angle, no split). The fixed state is shown. In the figure, all four strain gauges 1A to 1D are arranged on one surface (cross section) orthogonal to the longitudinal direction of the cored square bar 2, and each strain gauge 1 has a cylindrical base. The axial direction is parallel to the cross section. The axial length direction of the cylindrical base in each of the strain gauges 1A, 1C, 1D is substantially parallel to the tangential direction of the annual ring 3 near one annual ring 3 of the centered square bar 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 one annual ring 3 ′ of the cored square bar 2.
Incidentally, the strain gauge 1 in which the sensing element made of a thin metal wire or foil is fixed to the cylindrical base can be separated from the problem of whether or not it shows high sensitivity to expansion and contraction in a specific direction. It is preferable to fix in an aspect.
[0014]
(2) When the timber for fixing the strain detecting means is a square lumber, particularly a squared square, a squared square, a squared squared or squared square, on a plane (transverse cross section) orthogonal to the longitudinal direction of the wood. The center of the line segment assuming a line segment connecting the widthwise central portion of one side surface of the wood and the other side surface adjacent to the one side surface and making an angle of 45 with respect to the one side surface It is preferable to fix the distortion detecting means near the point.
[0015]
In the example shown in FIG. 1, four strain gauges 1 are fixed corresponding to the four corners of the centered square 2, but when focusing on one strain gauge 1A, the following description will be given. As shown in FIG. 2, which schematically shows a cross section corresponding to FIG. 1, the strain gauge 1A has a width of one side surface 21 of the cored square 2 on a cross section of the cored square 2 shown in FIG. Near the center 4a of the line segment 4A assuming a line segment 4A connecting the central portion 21a in the direction and the other side surface 22 adjacent to the one side surface 21 and making an angle of 45 with the one side surface 21 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 at which the line segment is bisected, but also at the vicinity of the center point. It is preferably within a circle P whose center is the center of the circle and whose diameter is half the length of the line segment. In particular, the center point which exactly bisects the line segment is the center of the circle and the line segment is Is preferably within a circle whose diameter is equal to 1/3 of the length.
[0016]
FIG. 3 shows locations where internal cracks 5 are likely to occur and directions in which internal cracks 5 are likely to occur when the centering square is dried by a conventional method. By disposing the strain detecting means in the aspect of (1) and / or (2), particularly in the four places corresponding to the respective corners of the timber in the aspect of (1) and / or (2), It is possible to more accurately detect the risk of occurrence of such internal cracks at a right angle. The embedding site of the strain gauge (strain detecting means) shown in FIG. 1 is a position corresponding to a quadrant of a diagonal line of the wood cross section, and is a site where internal stress during drying is the largest and internal cracks are easily generated. is there.
[0017]
FIG. 4 is a view showing a state in which the distortion detecting means is fixed to the squared square, the squared square, and the squared squared in the modes (1) and / or (2). FIG. 4 also shows locations where internal cracks 5 are likely to occur and directions 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 cored square 2 in the modes (1) and (2).
In FIG. 4 (b), six strain gauges are fixed on the same cross section of the centering flat angle 2, and four strain gauges 1A are the same as those of the above (1) and (2). , And the other two strain gauges 1B are fixed in the above-described mode (1).
In FIG. 4 (c), four strain gauges are fixed on the same cross section of the cored flat square 2, and any of the strain gauges 1A and 1B is in the form of (1) and (2). Fixed.
[0018]
A preferred method of fixing the strain detecting 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 centered square.
First, a hole or the like is drilled from the center in the width direction of each side surface of the cored square bar 2 at an angle of 45 ° to each side surface until it penetrates the center in the width direction of the adjacent side surface (FIG. 5). (A)]. The inside diameter of the through-hole is just enough to accommodate the strain gauge 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 to the outside of the through hole 23.
Then, in this state, an adhesive is injected into the through hole 23 (see FIG. 5C). The injection of the adhesive is performed until the adhesive is injected from one end opening and 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 from the through hole is connected to the heat-resistant lead wire 8 through a gauge terminal 7 for protecting the gauge lead (see FIG. 1). The area including the entrance is covered with a heat-resistant coat 9 (see FIG. 5D).
Thus, the strain gauge 1 can be fixed in a state as shown in FIG.
[0019]
Drying of wood in the present invention is performed under control of temperature and humidity.
This drying is usually performed by storing several to several hundreds of wood in a dryer capable of controlling the temperature and humidity, and one of the woods to which the strain detecting means is attached may be used (FIG. 6). reference). However, it can be attached to a plurality.
[0020]
As a method of controlling the temperature and humidity during drying of the wood, for example, a resistance change generated in the strain detecting means is converted into data readable by a predetermined device, and the data of the wood is monitored while monitoring the data obtained from the strain detecting means. When the drying is performed and the data indicates that the internal stress (strain) of the wood has increased to such an extent that internal cracks occur, the temperature and / or humidity may be adjusted in a direction to relieve the drying stress (slowing the drying speed). Direction), and when the data confirms that the risk of internal cracking has been sufficiently reduced, the temperature and / or humidity are changed in the direction opposite to the direction in which the drying stress is relieved (the direction in which the drying speed is increased). change. For example, by drying wood while repeating such control, it is possible to reduce the drying time while suppressing internal cracks in the wood.
[0021]
As an example of a preferable control method in the method for drying wood according to the present invention, the drying conditions are controlled based on data obtained from the strain detecting 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 and time exceeds a predetermined value, it is determined that the risk of internal cracks has increased, and the drying conditions are changed in a direction to reduce the drying speed, and the amount of strain change is equal to or less than a predetermined value. When returning to the above, it is conceivable that the danger of internal cracking is reduced and the drying conditions are changed in a direction to increase the drying speed. By performing such control, the drying time can be shortened while preventing internal cracks.
[0022]
【Example】
Hereinafter, the method for drying wood of the present invention will be described in more detail with reference to examples.
(Preliminary test)
Seventy squares (132 mm x 132 mm x 3000 mm) with no back split and sawn from one cedar log to one grind angle were used as the material to be dried.
From one of the materials to be dried, a 132 mm square, total length L = 1200 mm sample for strain measurement is cut out, and the distance from one end of the sample (cutting surface) is 1/4 of the total length L. Four strain gauges were embedded and fixed on each cross section at the 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 above-described method (see FIG. 5). Further, the following strain gauges and the like manufactured by Kyowa Dengyo Co., Ltd. were used.
Strain gauge; "KFG-3-120-C20-11 (with gauge lead)", adhesive for fixing gauge: "EP-34B", gauge terminal: "TF-28", heat-resistant lead wire: "L- 12 ", heat-resistant coat;" SKF-3059 "
[0023]
Then, the sample for strain measurement was housed in a high-temperature specification IF type steam dryer “SK-IF10LHP” made by Shinshiba Equipment together with other materials to be dried, and a heat-resistant lead wire extended outside the dryer was used. It was connected to a data logger ("THS-1100" manufactured by Tokyo Sokki Co., Ltd.) by a 1-gauge three-wire method so that distortion during drying could be measured. At the time of analysis, the amount of change in distortion per hour was output.
In addition, an electric resistance type moisture content meter and a thermocouple (K thermocouple, temperature range 0 to 150 ° C.) for measuring the temperature inside the wood are provided on the strain measurement specimen, respectively, in the middle layer corresponding to the embedding position of the strain gauge. (At a depth of about 28 mm) and a central layer (at a depth of about 66 mm) at the center of the cross section of the timber so that the moisture content and temperature inside the wood during drying can be measured.
[0024]
After such preparation was completed, as a preliminary test, drying was performed according to the drying schedule shown in FIG. 7, and the relationship between the change in strain and internal cracks was examined. In this preliminary test, control of the drying conditions based on the data obtained from the strain gauge was not performed.
After the drying was completed, the cross section of the strain gauge embedded portion of the test specimen was inspected. As a result, no internal crack was found in the embedded portion of three of the four strain gauges, and the embedded portion of the remaining one gauge was embedded. Had internal cracks. Looking at the transition of the amount of strain change per hour based on the data obtained from each strain gauge, it can be seen that, at the embedded portion of the three gauges where there is no internal crack, the amount of change is-even at the time when the maximum amount of strain change is shown. In contrast to 300 μm or less, at the embedded portion of one gauge where internal cracks occurred, the maximum amount of strain change per hour reached near −500 μm. From these results, it was determined that there was a risk that internal cracks would occur if the measured amount of change in internal strain exceeded -300 μm per hour. The data on the amount of strain change shown in FIG. 7 is data on the embedded portion of one gauge in which an internal crack has occurred.
[0025]
(Example)
The dimensions of the cored square, which is the material to be dried, are 115 mm x 115 mm x 3000 mm, and a 115 mm square, total length L = 1200 mm strain measurement specimen is cut out from one of them, and the strain measurement specimen is Preparation for drying was carried out in the same manner as in the above preliminary test, except that the above-described strain gauge, electric resistance moisture content meter, thermocouple (K thermocouple, temperature range 0 to 150 ° C.), and the like were similarly attached. went.
[0026]
Then, drying was performed according to the drying schedule shown in FIG. Hereinafter, the details will be described with reference to FIG.
First, steam was injected into the dryer to perform initial cooking at 96 ° C. and a relative humidity of 100%. This initial steaming was performed for 8 hours, the temperature of the wood in the dryer was raised to a predetermined temperature, and then the drying process was switched at the 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, the drying was continued while monitoring the moisture content of the intermediate layer corresponding to the embedded portion of the gauge, and the moisture content reached a fiber saturation point (30%) at which internal cracks are likely to occur rapidly. At the time point {circle around (2)} in the figure, the dry bulb temperature was switched from 112 ° C. to 108 ° C., and switched to the second drying step.
[0027]
In the present embodiment, in the second drying step following the first drying step in which the dry-bulb temperature is set at 110 ° C. or higher, the drying conditions are controlled based on the data obtained from the strain detecting means. That is, when drying at a dry-bulb temperature of 108 ° C. is continued, the amount of change in strain per hour (hereinafter, simply referred to as the amount of change in strain) decreases. Then, at the point of (3) in the figure, which recovered to −100 μ, the wet bulb temperature was lowered from 86 ° C. to 83 ° C. in order to increase the drying speed.
As a result, the amount of strain change turned from decreasing to increasing. By continuing the same conditions, the amount of strain change became -250μ, which is close to the danger zone (-300μ) where the occurrence of internal cracks occurred. The dry-bulb temperature was reduced from 108 ° C. to 105 ° C. (the drying speed was reduced).
[0028]
As a result, the amount of strain change turned from increasing to decreasing. After 4 hours, when the temperature recovered to −250 μm (at the time point (5) in the figure), the dry bulb temperature was raised from 105 ° C. to 108 ° C. and the wet bulb temperature was raised from 83 ° C. to 81 ° C. in order to increase the drying speed. Lowered to
As a result, the amount of change in strain changes from a decrease to an increase again, and by continuing the same conditions, the amount of change in strain again becomes -250 μm. While maintaining the temperature, the dry bulb temperature was reduced from 108 ° C. to 105 ° C., and the drying speed was reduced.
[0029]
As a result, the amount of change in strain changed from increasing to decreasing. After 4 hours, when the temperature has recovered to −250 μm (at the time point {circle around (7)} in the figure), in order to increase the drying speed, the dry bulb temperature is increased from 105 ° C. to 108 ° C. and the wet bulb temperature is increased from 81 ° C. to 79 ° C. Lowered to
Then, when drying was continued under these conditions, the moisture content of the intermediate layer corresponding to the embedded portion of the gauge became 15%, the amount of change in strain was within -200 μm, and the risk of occurrence of internal cracks was reduced. Then, when the water content in the center of the wood becomes 35% and the material temperature reaches 102 ° C. (at the time of (8) in the figure), the dry bulb temperature is lowered to 105 ° C. Was terminated.
[0030]
The subsequent drying at a dry-bulb temperature of 105 ° C for a relatively long time is intended to prevent various deformations due to shrinkage of the central part and to adjust the humidity in order to finish the drying material uniformly without drying unevenness. In the present example, the dry-bulb temperature was further reduced at 132 hours from the start of the initial steaming, and then the drying was completed in about 12 hours.
[0031]
When a 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 found in any of the embedded portions of the gauge. In addition, each material to be dried simultaneously was cut at a position of 30 cm from each of the two cut surfaces and at a central position in the longitudinal direction, and each cross section was visually observed for internal cracks. No internal cracks were observed at all for 64 of the dried materials, and the degree of the internal cracks was extremely small for the remaining five tubes.
It should be noted that the strain change data shown in FIG. 8 is a gauge having the fastest drying speed among the eight strain gauges (a gauge embedded at a position of 1/4 of the entire length L, and a gauge indicated by 1C in FIG. 1). ).
[0032]
From the results of the examples, it can be seen that by controlling the drying conditions so as to suppress the amount of strain change per fixed time to a predetermined value or less, it is possible to prevent internal cracks without wasting the drying time. . Incidentally, the method for drying wood of the present invention is not limited to the case of having a drying step of drying a lumber sawn from softwood at a dry bulb temperature of 100 ° C., particularly 110 ° C. or more, as in the above-described embodiment. The present invention is also applicable to a case where a sawn timber is dried at a temperature of 100 ° C. or less.
[0033]
【The invention's effect】
According to the present invention, it is possible to obtain data that accurately reflects the state of drying stress inside wood during drying, and to perform efficient wood drying while suppressing internal cracks and shortening the drying time. Can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a piece of wood showing a state in which strain detection means is fixed inside the wood.
FIG. 2 is a diagram schematically showing a cross section corresponding to FIG. 1;
FIG. 3 is a cross-sectional view of the lumber schematically showing a portion where the internal crack is likely to occur and a direction in which the internal crack is likely to occur when the wood has a centered square angle.
FIG. 4 is a cross-sectional view of the wood schematically showing a state in which the strain detection means is fixed to the wood, together with a portion where the internal crack is likely to occur in the wood and a direction in which the internal crack is likely to occur; FIG. 7A is a diagram illustrating a case where the center angle is square, FIG. 7B is a diagram illustrating the case where the center angle is flat, and FIG.
5A and 5B are diagrams showing a procedure for fixing the strain detecting means to the wood, wherein FIG. 5A shows a state in which a through hole for inserting the strain detecting means is formed in the wood, and FIG. (C) Injecting an adhesive into the through hole after insertion of the strain detecting means, and (d) Covering the gauge terminals and the like together with the opening of the through hole with a heat-resistant coat. 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 a 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 control history of drying conditions and a change in distortion change amount in the embodiment.
[Explanation of symbols]
1,1A-1D strain gauge (strain detecting means)
2 Wood 3 Ring 5 Internal crack

Claims (5)

A method for drying wood, wherein the strain detecting means is fixed inside the wood, and the wood is dried while controlling drying conditions based on data obtained from the strain detecting means. The strain detecting means has high sensitivity to expansion and contraction in a specific direction, and the strain detecting means is configured such that the specific direction is parallel to a plane orthogonal to a longitudinal direction of the wood and the specific direction is the wood. 2. The method for drying wood according to claim 1, wherein the fixing is performed in the vicinity of the one annual ring so as to be parallel to a tangential direction of the annual ring. A through hole is formed in at least one side surface of the wood from the one side surface to the adjacent other side surface, 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 wood is a square cored, squared squared, squared squared or squared squared, and on a plane perpendicular to the longitudinal direction of the wood, a widthwise central part of one side of the wood and the one side The strain detecting means is fixed to a vicinity of a center point of a line segment connecting the other side surface adjacent to the one and forming an angle of 45 with respect to the one side surface. The method for drying wood according to any one of the above. The method for drying wood according to any one of claims 1 to 4, wherein drying conditions are controlled based on data obtained from the strain detecting means so that the amount of strain deformation per predetermined time does not exceed a predetermined value.

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