CN112394101A - Online detection method and device for wood surface drying shrinkage strain - Google Patents
Online detection method and device for wood surface drying shrinkage strain Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
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- G01N27/48—Systems using polarography, i.e. measuring changes in current under a slowly-varying voltage
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/16—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge
- G01B7/18—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge using change in resistance
Abstract
The invention provides an online detection method and device for wood surface drying shrinkage strain. The detection method comprises the steps that a layer of conductive belt is arranged on the surface of a sample to be detected, and two ends of the conductive belt are connected to probes of an electrochemical workstation to form a closed loop; under a specified voltage, measuring the current of the closed loop by using the electrochemical workstation, and obtaining the resistance of the sample to be measured, so as to obtain the resistance change rate of the sample to be measured; and obtaining the dry shrinkage strain of the sample to be detected according to a standard curve of the dry shrinkage strain along with the change rate of the resistance of the wood sample based on the change rate of the resistance of the sample to be detected. Compared with the existing dry shrinkage strain detection method, the method has the advantages that the online detection of the surface dry shrinkage strain in the wood drying process can be realized, and the method has higher detection precision. The online detection method for the wood surface drying shrinkage strain is simple in connection operation, convenient to use and high in detection precision.
Description
Technical Field
The invention belongs to the technical field of wood processing, relates to an online detection method and device for surface drying shrinkage strain of wood, and particularly relates to an online detection method and device for surface drying shrinkage strain in a wood drying process.
Background
As a moisture-absorbing porous material, wood is dried and shrunk as one of the main characteristics in the wood drying process, and is also an important factor influencing wood processing. The phenomenon of dry shrinkage mainly occurs when the moisture content of the wood is reduced below a fiber saturation point, so that the size and the volume of the wood are changed, and the existence of the dry shrinkage difference of different texture directions and wood parts can cause larger drying stress, so that the drying defects of deformation, cracking and the like are generated, and the efficient processing and utilization of the wood are seriously restricted. Therefore, the online accurate detection of the drying shrinkage strain in the wood drying process is particularly important.
The dry shrinkage strain can be used as an index to evaluate dimensional stability during wood drying. Which can be determined by conventional slicing and strain gauge methods. In the slicing method, since contact measurement is performed by a vernier caliper or a micrometer, a manual measurement error is inevitably generated, and there is a certain requirement for the size of a specimen. In the strain gauge method, perfect bonding between the strain gauge and the sample is critical. In addition, the use temperature and relative humidity also have a great influence on the test results. In addition, in order to improve the measurement accuracy and visualize the drying shrinkage process of wood, some non-contact optical measurement methods (e.g., digital image correlation and near infrared spectroscopy) have been used to determine the drying shrinkage strain. However, the optical method requires real-time image acquisition for the wood drying process, which results in limitation of further popularization thereof.
The existing online detection method for wood drying shrinkage strain is mainly a sensor method, but the sensor belongs to a sensitive element, the sensor needs to be pasted on the surface of wood during testing, the testing result is greatly influenced by factors such as temperature and humidity conditions of a using environment, roughness of the pasted surface of the wood, curing degree of used adhesive and the like, and the use of the sensor in special drying modes such as high temperature and high pressure, high frequency vacuum and the like is limited.
Cited documents:
cited document 1: CN101149370A
Cited document 2: CN102621189A
Cited document 3: CN106225969A
Disclosure of Invention
Problems to be solved by the invention
The invention aims to overcome the defects of the prior art, provides an online detection method for the dry shrinkage strain on the surface of wood, and can effectively solve the problems of complex operation, unstable detection precision and the like of the online detection of the dry shrinkage strain in the drying process of the wood.
Furthermore, the invention also provides an online detection device for the wood surface dry shrinkage strain, the online detection device can realize the online detection of the wood surface dry shrinkage strain, and the detection precision is high.
Means for solving the problems
The invention provides an on-line detection method of wood surface drying shrinkage strain, wherein,
arranging a layer of conductive belt on the surface of a sample to be detected, and connecting two ends of the conductive belt to probes of an electrochemical workstation to form a closed loop;
under a specified voltage, measuring the current of the closed loop by using the electrochemical workstation, and obtaining the resistance of the sample to be measured, so as to obtain the resistance change rate of the sample to be measured;
and obtaining the dry shrinkage strain of the sample to be detected according to a standard curve of the dry shrinkage strain along with the change rate of the resistance of the wood sample based on the change rate of the resistance of the sample to be detected.
According to the online detection method for the drying shrinkage strain on the surface of the wood, the material of the conductive belt comprises one or a combination of more than two of conductive metal paint, graphite conductive adhesive and carbon material conductive adhesive.
The online detection method for the drying shrinkage strain on the surface of the wood is characterized in that the coating thickness of the conductive belt is 0.1-0.5 mm.
4. The method for detecting the drying shrinkage strain on the surface of the wood according to any one of claims 1 to 3, wherein the width of the conductive band is less than or equal to the width of the sample to be detected.
The online detection method for the wood surface drying shrinkage strain is characterized in that the potential setting range of the electrochemical workstation is-10V; the current setting range of the electrochemical workstation is-250 mA; the lower limit of the battery measurement of the electrochemical workstation is below 50 pA.
The online detection method for the drying shrinkage strain on the surface of the wood is characterized in that the current of the closed loop is measured by utilizing a linear sweep voltammetry method.
According to the online detection method for the wood surface drying shrinkage strain, the electrochemical workstation adopts a current-time curve for testing, and the parameters are set as follows: the potential is-1 to 1V, the sampling interval is 0.001 to 0.05s, and the scanning rate is 0.01 to 0.5V/s.
The invention relates to an online detection method of wood surface drying shrinkage strain, wherein the manufacturing method of the standard curve comprises the following steps:
forming a layer of conductive tape on the surface of the wood sample;
drying the wood sample at the same temperature, measuring the lengths of the conductive strips corresponding to different drying times, and acquiring corresponding drying shrinkage strain according to the lengths of the conductive strips;
measuring the current of the wood sample corresponding to different drying times by adopting the electrochemical workstation, and obtaining the resistance of the wood sample corresponding to different drying times so as to obtain the resistance change rate of the wood sample;
and obtaining the standard curve according to the drying shrinkage strain and the resistance change rate of the wood sample corresponding to the different drying times.
The online detection method for the drying shrinkage strain on the surface of the wood is characterized in that the drying temperature is 10-120 ℃.
The invention also provides an online detection device for implementing the online detection method for the wood surface dry shrinkage strain, which comprises an electrochemical workstation and a data acquisition device which are connected; wherein, the electrochemical workstation is connected with a probe by a lead.
ADVANTAGEOUS EFFECTS OF INVENTION
Compared with the existing dry shrinkage strain detection method, the method has the advantages that the online detection of the surface dry shrinkage strain in the wood drying process can be realized, and the method has higher detection precision.
The online detection method for the wood surface drying shrinkage strain is simple in connection operation, convenient to use and high in detection precision.
Drawings
FIG. 1 shows a schematic diagram of the online detection method of the drying shrinkage strain on the surface of wood according to the present invention;
FIG. 2 shows the current change with time when the dry shrinkage strain is measured at a constant voltage of 1V for a wood sample of example 1 of the present invention;
FIG. 3 shows the resistance over time when the dry shrinkage strain is measured at a constant voltage of 1V for a wood sample of example 1 of the present invention;
figure 4 shows a fitted curve of the dry shrinkage strain versus the rate of change of resistance for a wood sample of example 1 of the invention.
Detailed Description
The present invention will be described in detail below. The technical features described below are explained based on typical embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:
in the present specification, the numerical range represented by "numerical value a to numerical value B" means a range including the end point numerical value A, B.
In the present specification, "plural" in "plural", and the like means a numerical value of 2 or more unless otherwise specified.
In this specification, the terms "substantially", "substantially" or "substantially" mean an error of 5% or less, or 3% or less or 1% or less, compared to the relevant perfect or theoretical standard.
In the present specification, "%" denotes mass% unless otherwise specified.
In the present specification, the meaning of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.
In the present specification, when "normal temperature" or "room temperature" is used, the temperature may be 10 to 40 ℃.
In the present specification, the "water" used may be tap water, distilled water, deionized water, ion-exchanged water, high purity water, purified water, or the like, which is available in the art, unless otherwise specified.
In this specification, "optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.
In the present specification, reference to "some particular/preferred embodiments," "other particular/preferred embodiments," "embodiments," and the like, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.
First aspect
The invention provides an online detection method of wood surface drying shrinkage strain, which comprises the following steps:
arranging a layer of conductive belt on the surface of a sample to be detected, and connecting two ends of the conductive belt to probes of an electrochemical workstation to form a closed loop;
under a specified voltage, measuring the current of the closed loop by using the electrochemical workstation, and obtaining the resistance of the sample to be measured, so as to obtain the resistance change rate of the sample to be measured;
obtaining the dry shrinkage strain of the sample to be detected based on the resistance change rate of the sample to be detected and according to a standard curve of the dry shrinkage strain along with the resistance change rate of the wood sample;
the invention establishes the relation between the dry shrinkage strain and the wood resistance change rate according to the fact that the dry shrinkage strain continuously changes along with the difference of the wood resistance change rate, thereby obtaining the dry shrinkage strain in the wood drying process according to the wood resistance change rate. The online detection method for the drying shrinkage strain on the surface of the wood can realize online detection of the drying shrinkage strain in the drying process, and has high detection precision.
Sample to be tested
The sample to be tested according to the present invention may be any available wood. Generally, in the test, wood needs to be subjected to pretreatment such as cutting. Specifically, wood is cut to a feasible size for testing as a sample to be tested. The size of the sample to be measured is not particularly limited in the present invention, and may be, for example, a chordal cutting plate of 100 to 150 mm (chordal direction) × 20 to 30 mm (radial direction) × 800 to 1000 mm (longitudinal direction), and the cut chordal cutting plate has no visible defects as much as possible. In addition, in a specific embodiment, the cut sample to be tested is wrapped with a preservative film and stored in a refrigerator to maintain its moisture content.
Specifically, during testing, a layer of conductive tape may be disposed on the surface of the sample to be tested, and the two ends of the conductive tape are connected to the probes of the electrochemical workstation to form a closed loop.
As for the material of the conductive tape, the material of the conductive tape is not particularly limited in the present invention, and may be some conductive materials commonly used in the art that can be coated, for example: the conductive belt is made of one or a combination of more than two of conductive metallic paint, graphite conductive adhesive and carbon material conductive adhesive. For electrically conductive metallic lacquers, for example: can be conductive silver paint, conductive copper paint, etc.
The present invention is not particularly limited as to the thickness of the coating, as long as the application is uniform. Specifically, in the present invention, the conductive tape is coated to a thickness of 0.1mm to 0.5 mm.
Further, as for the width of the conductive strip, in general, the width of the conductive strip is less than or equal to the width of the sample to be measured. Preferably, the width of the conductive strip is smaller than the width of the sample to be measured. Specifically, the width of the conductive belt can be 1/6-1/4 of the width of the sample to be detected.
Electrochemical workstation
The electrochemical method is a simple, convenient, rapid, accurate and sensitive characterization method, and plays an important role in scientific research and production all the time. The method is mainly characterized in that the relation between the electric parameters and the measured substances is established according to the electrochemical properties and the change rule of the substances in the solution, and then the qualitative and quantitative analysis is carried out on the components. The invention utilizes the electrochemical workstation to establish the relationship between the electrical parameters and the measured substances, and further measure the dry shrinkage strain of the wood surface of the sample to be measured.
Specifically, the electrochemical workstation of the invention comprises a rapid digital signal generator, a direct digital signal synthesizer for high-frequency alternating-current impedance measurement, a dual-channel high-speed data acquisition system, a potential current signal filter, a multi-stage signal gain, an iR drop compensation circuit, a double potentiostat and a galvanostat. Specifically, the potential ranges are all-10V to 10V. The current range is-250 mA, the potential resolution is 0.1mV, the lower limit of current measurement is lower than 50pA, and the sensitivity is more than 1 e-6A/V.
The external part of the electrochemical workstation is connected with a lead, and the end part of the lead is provided with a probe. And connecting the two ends of the conductive belt of the sample to be measured to probes of an electrochemical workstation to form a closed loop, and then measuring. Specifically, the current of the closed loop is measured by using the electrochemical workstation, so that the resistance of the sample to be measured can be obtained, and the resistance change rate of the sample to be measured can be further obtained.
In the present invention, the current of the closed loop is measured by linear sweep voltammetry at a predetermined voltage. Linear sweep voltammetry is a method in which a linearly varying voltage is applied to an electrode, i.e., the electrode potential is a method in which the electrolytic current on the working electrode is recorded as the voltage applied changes. The invention can accurately measure the current of the closed loop by utilizing the linear sweep voltammetry, and obtains the resistance of the sample to be measured, thereby obtaining the resistance change rate of the sample to be measured.
The present invention is not particularly limited as long as an accurate test result can be obtained, with respect to specific test conditions. Specifically, in the present invention, when measuring the current of the closed loop, the electrochemical workstation performs a test using a current-time curve, and specific parameters are set as follows: the potential is-1 to 1V, the sampling interval is 0.001 to 0.05s, and the scanning rate is 0.01 to 0.5V/s.
Standard of meritCurve line
The method is based on the resistance change rate of the sample to be detected, and obtains the dry shrinkage strain of the sample to be detected according to a standard curve of the dry shrinkage strain along with the resistance change rate of the wood sample.
In some embodiments, a calibration curve may be generated using the relationship of the dry-shrink strain to the rate of change of resistance.
Specifically, the method for manufacturing the standard curve comprises the following steps:
arranging a layer of conductive belt on the surface of the wood sample;
drying the wood sample at the same temperature, measuring the lengths of the conductive strips corresponding to different drying times, and acquiring corresponding drying shrinkage strain according to the lengths of the conductive strips;
measuring the current of the wood sample corresponding to different drying times by adopting the electrochemical workstation, and obtaining the resistance of the wood sample corresponding to different drying times so as to obtain the resistance change rate of the wood sample;
and obtaining the standard curve according to the drying shrinkage strain and the resistance change rate of the wood sample corresponding to the different drying times.
For drying, the wood sample can be placed in a drying oven for drying, and then the lengths of the conductive strips on the surface of the wood sample corresponding to different drying times are obtained, so that the drying shrinkage strains of the wood sample corresponding to different drying times are calculated. In the present invention, the same temperature means that the drying temperature is almost constant throughout the drying process.
Further, the dry shrinkage strain is calculated according to the following formula (1):
wherein S is the dry shrinkage strain of the wood sample;
L0the initial length of the conductive band on the surface of the wood sample;
Lithe lengths of the surface conductive strips corresponding to different drying times (i.e. different moisture contents) of the wood sample are obtained.
Fiber Saturation Point (FSP) is the percentage of water in the wood that is saturated only by adsorbed water in the cell walls, but not by free water in the cell cavities and interstitial spaces. When the water content of the wood is larger than the fiber saturation point, the moisture content of the wood is not only saturated by absorbed water, but also has a certain amount of free water. In this case, the wood is only changed by free water if it is dried or moistened, so that it does not cause wet swelling and dry shrinkage. When the moisture content of the wood is less than the fiber saturation point, the adsorbed water of the wood is unsaturated, and no free water exists. In this case, the wood is dried or moistened, and the swelling and drying shrinkage of the wood are caused, which has an influence on the strength and volume of the wood. Therefore, the initial length of the sample surface conductive tape may be a length of the sample surface conductive tape corresponding to a moisture content of the wood at or above a fiber saturation point (moisture content of about 30%).
The resistance change rate was calculated by the following formula (2):
wherein Δ R is the rate of change of resistance of the wood sample;
Riis the initial resistance of the wood sample;
and R is the resistance of the wood sample corresponding to different drying time (namely different water content).
And then obtaining the standard curve according to the drying shrinkage strain and the resistance change rate of the wood sample corresponding to different drying times.
Further, as for the temperature of drying, the present invention is not particularly limited, and may be a temperature conventional in the art, for example: 10 to 120 ℃. The drying time can be set according to needs, and the interval between two times of drying can be 10-360 min.
Second aspect of the invention
The second aspect of the invention provides a device for realizing the online detection method of the wood surface drying shrinkage strain of the first aspect of the invention, which comprises an electrochemical workstation and a data acquisition device which are connected with each other; wherein, the electrochemical workstation is connected with a probe by a lead.
The electrochemical workstation of the present invention is the main body site for signal acquisition and processing analysis. The data acquisition device can display the data and the image measured by the electrochemical workstation, further obtain the resistance value, and then obtain the dry shrinkage strain of the sample to be measured according to the standard curve. In the invention, the probe can be an alligator clip, and the connection of the circuit is realized by using the probe and a lead.
Examples
Embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
Examples dry shrinkage strains of wood surfaces were measured using a CHI760E electrochemical workstation test system (chenhua instruments ltd, shanghai, china). Wherein the potential range is-10 to 10V, the potential resolution is 0.1mV, the current range is-250 to 250mA, and the lower limit of the current measurement is lower than 50 pA. The computer is used for data acquisition, storage and processing. The test equipment is shown in fig. 1.
Example 1
Preparation of Standard Curve
Eucalyptus (Eucalyptus exserta) obtained from high-state city, Guangdong, China. A slit plate having a size of 120 mm (chord direction) × 25 mm (radial direction) × 900 mm (longitudinal direction) and no visible defects was cut from a eucalyptus log, wrapped with a wrap film and stored in a refrigerator to maintain its moisture content, and the initial moisture content of the slit plate was 45%.
Wood samples having dimensions of 120 mm (chord wise) × 25 mm (radial) × 10 mm (longitudinal) were cut from the above chord cut out boards for making a calibration curve.
Firstly, the test surface of a wood sample is planed, then the conductive silver paint is sprayed on the middle position of the wood sample to be used as a conductive band, the length of the conductive silver paint is approximately the same as the length of the wood sample, the width of the conductive silver paint is 3mm, and the thickness of the conductive band is 0.3 mm.
The initial length of the conductive tape of the wood sample was measured before drying and the wood sample was subjected to electrochemical testing to obtain an initial current value. Thereafter, the wood sample was placed in a DKN611 type drying box (Japan David and science Co., Ltd.) and dried at a constant temperature of 60 ℃ and the wood sample was taken out at drying times of 30min, 60min, 90min, 120min, 180min and 240 min. And (2) respectively carrying out electrochemical test on each wood sample to obtain the current of each test, measuring the length of the conductive band of the wood sample, and measuring the length of the conductive band by using a vernier caliper, wherein the specific test result is shown in the following table 1.
Wherein the current is measured by an electrochemical workstation. The parameters of the electrochemical workstation were set as follows: initial potential-1V, end potential 1V, scanning speed 0.1V/s, sampling interval 0.01V, standing time 2s, sensitivity 1e-6A/V。
And the resistance of the wood sample corresponding to different drying times was obtained according to the following calculation formula, and the results are shown in table 1:
R＝U/I
wherein R is the resistance of the wood sample corresponding to different drying times;
u is a constant voltage;
i is the current for the wood samples at different drying times.
TABLE 1
And then calculating the drying shrinkage strains of the wood samples corresponding to different drying times according to the following formula:
wherein S is the dry shrinkage strain of the wood sample;
L0the initial length of the conductive band on the surface of the wood sample;
Lithe lengths of the surface conductive strips corresponding to different drying times (i.e. different moisture contents) of the wood sample are obtained.
And (3) calculating according to the following formula to obtain the resistance change rates of the wood samples corresponding to different drying times:
wherein Δ R is the rate of change of resistance of the wood sample;
Riis the initial resistance of the wood sample;
and R is the resistance of the wood sample corresponding to different drying time (namely different water content).
TABLE 2
Then, a standard curve between the dry shrinkage strain and the resistance change rate is obtained according to the dry shrinkage strain and the resistance change rate in table 2, and specifically, as shown in fig. 3, the formula of the standard curve is shown in the following formula (a).
S＝0.852+0.021e0.113ΔR (A)
In the formula (A): s is the drying shrinkage strain of the wood sample;
Δ R is the rate of change of resistance of the wood sample.
Detection of sample to be tested
The sample to be tested was Eucalyptus (Eucalyptus exserta) collected from Gaozhou, Guangdong province in China, and the sample used in the standard curve was taken from a different tree strain. A slit board without visible defects having dimensions of 120 mm (chord wise) x 25 mm (radial) x 900 mm (longitudinal) was sawn from eucalyptus logs with an initial moisture content of 45%.
From the above chord cut plate, a sample to be measured having a size of 120 mm (tangential) × 25 mm (radial) × 10 mm (longitudinal) was sawed. Firstly, the test surface of a sample to be tested is planed, and then the conductive silver paint is sprayed on the middle position of the sample to be tested to be used as a conductive band, wherein the length of the conductive silver paint is approximately the same as the length to be tested, the width of the conductive silver paint is 3mm, and the thickness of the conductive band is 0.3 mm.
And measuring the initial length of the conductive band of the sample to be tested before drying, and carrying out electrochemical test on the sample to be tested to obtain an initial current value. Thereafter, the sample to be tested was placed in a DKN611 type drying oven (Japan Dai & science Co., Ltd.) and dried at a constant temperature of 60 ℃ and the sample to be tested was taken out at drying times of 60min, 120min, 180min and 240 min. Conducting strip length measurement is carried out on each sample to be tested, electrochemical test is carried out, current and resistance of each test are obtained, resistance change rate is calculated, and specific results are shown in table 3.
Measuring the current and the resistance by using an electrochemical workstation, wherein the parameters of the electrochemical workstation are set as follows: initial potential-1V, end potential 1V, scanning speed 0.1V/s, sampling interval 0.01V, standing time 2s, sensitivity 1e-6A/V。
TABLE 3
And calculating by using the resistance value to obtain the resistance change rate, and substituting the resistance change rate into the standard curve to obtain the dry shrinkage strain of the sample to be detected. In addition, the dry shrinkage strain obtained by the length calculation method is the change rate of the length of the conductive strip, and the specific test result is shown in table 4.
TABLE 4
As can be seen from Table 4, the dry shrinkage strain of the sample to be measured in the drying process measured by the method of the present invention is substantially consistent with the dry shrinkage strain measured by the length meter algorithm. Therefore, the online detection method for the moisture content of the wood can realize online detection of each drying shrinkage strain stage of the wood in the drying process, and has high detection precision.
Example 2
The test sample in example 1 was replaced with Eucalyptus (Eucalyptus exserta) of high city, Guangdong, China, but the test samples used for the standard curve were taken from different tree strains and were also different from those of the Eucalyptus in example 1. A slit board without visible defects having dimensions of 120 mm (chord wise) x 25 mm (radial) x 900 mm (longitudinal) was sawn from eucalyptus logs with an initial moisture content of 45%.
Samples to be measured having dimensions of 120 mm (chord direction) × 25 mm (radial direction) × 10 mm (longitudinal direction) were sawn from the above chord-cut plate for resistance measurement.
Firstly, the test surface of a sample to be tested is planed, and then the conductive silver paint is sprayed on the middle position of the sample to be tested to be used as a conductive band, wherein the length of the conductive silver paint is approximately the same as the length to be tested, the width of the conductive silver paint is 3mm, and the thickness of the conductive band is 0.3 mm.
And measuring the initial length of the conductive band of the sample to be tested before drying, and carrying out electrochemical test on the sample to be tested to obtain an initial current value. Thereafter, the sample to be tested was placed in a DKN611 type drying oven (Japan Dai & science Co., Ltd.) and dried at a constant temperature of 60 ℃ and the sample to be tested was taken out at drying times of 60min, 120min, 180min and 240 min. Conducting strip length measurement is carried out on each sample to be tested, electrochemical test is carried out, current and resistance of each test are obtained, resistance change rate is calculated, and specific results are shown in table 5.
Measuring the current and the resistance by using an electrochemical workstation, wherein the parameters of the electrochemical workstation are set as follows: initial potential-1V, end potential 1V, scanning speed 0.1V/s, sampling interval 0.01V, standing time 2s, sensitivity 1e-6A/V。
TABLE 5
And calculating by using the resistance value to obtain the resistance change rate, and substituting the resistance change rate into the standard curve to obtain the dry shrinkage strain of the sample to be detected. In addition, the dry shrinkage strain obtained by the length calculation method is the change rate of the length of the conductive strip, and the specific test result is shown in table 6.
TABLE 6
As can be seen from Table 6, the dry shrinkage strain of the sample to be measured in the drying process measured by the method of the present invention is substantially consistent with the dry shrinkage strain measured by the length meter algorithm. Therefore, the online detection method for the moisture content of the wood can realize online detection of each drying shrinkage strain stage of the wood in the drying process, and has high detection precision.
Example 3
Preparation of Standard Curve
The cork oak wood is collected from the ecological protection center of Tan Jiahe in the Nanwan forest farm of Xinyang city in Henan province, the altitude of the sampling place is 200m, the east longitude is 113 degrees and 55 degrees, and the north latitude is 31 degrees and 52 degrees. The tree ages are all 60 years, and the average breast diameter of the cork oak is 38 cm. The sample was sawed into several pieces of 900 mm (length) x 120 mm (width) x 25 mm (thickness), and the initial water content of the sample was 50%.
Wood samples having dimensions of 120 mm (chord wise) × 25 mm (radial) × 10 mm (longitudinal) were cut from the above chord cut out boards for making a calibration curve. Firstly, the test surface of a wood sample is planed, then the conductive silver paint is sprayed on the middle position of the wood sample to be used as a conductive band, the length of the conductive silver paint is approximately the same as the length of the wood sample, the width of the conductive silver paint is 3mm, and the thickness of the conductive band is 0.3 mm.
The initial length of the conductive tape of the wood sample was measured before drying and the wood sample was subjected to electrochemical testing to obtain an initial current value. Thereafter, the wood sample was placed in a DKN611 type drying box (Japan David and science Co., Ltd.) and dried at a constant temperature of 60 ℃ and the wood sample was taken out at drying times of 30min, 60min, 90min, 120min, 180min and 240 min. And respectively carrying out electrochemical test on each wood sample to obtain the current of each test, and measuring the length of the conductive band of the wood sample, wherein the length of the conductive band is measured by adopting a vernier caliper. The specific test results are shown in table 7 below.
Wherein the current is measured by an electrochemical workstation whose parameters are set as follows: initial potential-1V, end potential 1V, scanning speed 0.1V/s, sampling interval 0.01V, standing time 2s, sensitivity 1e-6A/V。
And the resistance of the wood samples corresponding to different drying times was obtained according to the following calculation formula, and the results are shown in table 7:
R＝U/I
wherein R is the resistance of the wood sample corresponding to different drying times;
u is a constant voltage;
i is the current for the wood samples at different drying times.
TABLE 7
And then calculating the drying shrinkage strains of the wood samples corresponding to different drying times according to the following formula:
wherein S is the dry shrinkage strain of the wood sample;
L0the initial length of the conductive band on the surface of the wood sample;
Lithe lengths of the surface conductive strips corresponding to different drying times (i.e. different moisture contents) of the wood sample are obtained.
And (3) calculating according to the following formula to obtain the resistance change rates of the wood samples corresponding to different drying times:
wherein Δ R is the rate of change of resistance of the wood sample;
Riis the initial resistance of the wood sample;
and R is the resistance of the wood sample corresponding to different drying time (namely different water content).
TABLE 8
Then, a standard curve between the dry shrinkage strain and the resistance change rate is obtained according to the dry shrinkage strain and the resistance change rate in table 8, and specifically, as shown in fig. 3, the formula of the standard curve is shown in the following formula (a 1).
S＝0.625+0.025e0.094ΔR (A1)
In the formula (A): s is the drying shrinkage strain of the wood sample;
Δ R is the rate of change of resistance of the wood sample.
Detection of sample to be tested
The cork oak wood is collected from the ecological protection center of Tan Jiahe in the Nanwan forest farm of Xinyang city in Henan province, the altitude of the sampling place is 200m, the east longitude is 113 degrees and 55 degrees, and the north latitude is 31 degrees and 52 degrees. The tree ages are all 60 years, and the average breast diameter of the cork oak is 38 cm. The sample was sawed into several pieces of 900 mm (length) x 120 mm (width) x 25 mm (thickness), and the initial water content of the sample was 50%.
From the above chord cut plate, a sample to be measured having a size of 120 mm (tangential) × 25 mm (radial) × 10 mm (longitudinal) was sawed. Firstly, the test surface of a sample to be tested is planed, and then the conductive silver paint is sprayed on the middle position of the sample to be tested to be used as a conductive band, wherein the length of the conductive silver paint is approximately the same as the length to be tested, the width of the conductive silver paint is 3mm, and the thickness of the conductive band is 0.3 mm.
And measuring the initial length of the conductive band of the sample to be tested before drying, and carrying out electrochemical test on the sample to be tested to obtain an initial current value. Thereafter, the sample to be tested was placed in a DKN611 type drying oven (Japan Dai & science Co., Ltd.) and dried at a constant temperature of 60 ℃ and the sample to be tested was taken out at drying times of 60min, 120min, 180min and 240 min. Conducting strip length measurement is conducted on each sample to be tested, electrochemical testing is conducted on the samples to be tested, current and resistance of each test are obtained, resistance change rate is calculated, and specific results are shown in table 9.
Measuring the current and the resistance by using an electrochemical workstation, wherein the parameters of the electrochemical workstation are set as follows: initial potential-1V, end potential 1V, scanning speed 0.1V/s, sampling interval 0.01V, standing time 2s, sensitivity 1e-6A/V。
TABLE 9
And calculating by using the resistance value to obtain the resistance change rate, and substituting the resistance change rate into the standard curve to obtain the dry shrinkage strain of the sample to be detected. The dry shrinkage strain obtained by the length calculation method is the change rate of the length of the conductive tape, and the specific test results are shown in table 10.
Watch 10
As can be seen from Table 10, the dry shrinkage strain of the sample to be measured in the drying process measured by the method of the present invention is substantially the same as the dry shrinkage strain measured by the length meter algorithm. Therefore, the online detection method for the moisture content of the wood can realize online detection of each drying shrinkage strain stage of the wood in the drying process, and has high detection precision.
Example 4
Preparation of Standard Curve
New Zealand imported radiata pine (Pinus radiata) grows for 15-20 years, and the diameter at breast height is more than 50 cm. The sample was sawed into several pieces of 900 mm (length) x 120 mm (width) x 25 mm (thickness), and the initial water content of the sample was 30%.
Wood samples having dimensions of 120 mm (chord wise) × 25 mm (radial) × 10 mm (longitudinal) were cut from the above chord cut out boards for making a calibration curve. Firstly, the test surface of a wood sample is planed, then the conductive silver paint is sprayed on the middle position of the wood sample to be used as a conductive band, the length of the conductive silver paint is approximately the same as the length of the wood sample, the width of the conductive silver paint is 3mm, and the thickness of the conductive band is 0.3 mm.
The initial length of the conductive tape of the wood sample was measured before drying and the wood sample was subjected to electrochemical testing to obtain an initial current value. Thereafter, the wood sample was dried in a DKN611 type drying box (japan major and scientific corporation) at a constant temperature of 60 ℃, and the wood sample was taken out at drying times of 30min, 60min, 90min, 120min, 150min, and 180 min. And respectively carrying out electrochemical test on each wood sample to obtain the current of each test, and measuring the length of the conductive band of the wood sample, wherein the length of the conductive band is measured by adopting a vernier caliper. The specific test results are shown in table 11 below.
Wherein the current is measured by an electrochemical workstation whose parameters are set as follows: initial potential-1V, end potential 1V, scanning speed 0.1V/s, sampling interval 0.01V, standing time 2s, sensitivity 1e-6A/V。
And the resistance of the wood samples corresponding to different drying times was obtained according to the following calculation formula, and the results are shown in table 11:
R＝U/I
wherein R is the resistance of the wood sample corresponding to different drying times;
u is a constant voltage;
i is the current for the wood samples at different drying times.
TABLE 11
And then calculating the drying shrinkage strains of the wood samples corresponding to different drying times according to the following formula:
wherein S is the dry shrinkage strain of the wood sample;
L0the initial length of the conductive band on the surface of the wood sample;
Lithe lengths of the surface conductive strips corresponding to different drying times (i.e. different moisture contents) of the wood sample are obtained.
And (3) calculating according to the following formula to obtain the resistance change rates of the wood samples corresponding to different drying times:
wherein Δ R is the rate of change of resistance of the wood sample;
Riis the initial resistance of the wood sample;
and R is the resistance of the wood sample corresponding to different drying time (namely different water content).
TABLE 12
Then, a standard curve between the dry shrinkage strain and the resistance change rate is obtained according to the dry shrinkage strain and the resistance change rate in table 12, and specifically, as shown in fig. 3, the formula of the standard curve is shown in the following formula (a 2).
S＝0.582+0.366e0.059ΔR (A2)
In the formula (A): s is the drying shrinkage strain of the wood sample;
Δ R is the rate of change of resistance of the wood sample.
Detection of sample to be tested
New Zealand imported radiata pine (Pinus radiata) grows for 15-20 years, and the diameter at breast height is more than 50 cm. The sample was sawed into several pieces of 900 mm (length) x 120 mm (width) x 25 mm (thickness), and the initial water content of the sample was 30%.
From the above chord cut plate, a sample to be measured having a size of 120 mm (tangential) × 25 mm (radial) × 10 mm (longitudinal) was sawed. Firstly, the test surface of a sample to be tested is planed, and then the conductive silver paint is sprayed on the middle position of the sample to be tested to be used as a conductive band, wherein the length of the conductive silver paint is approximately the same as the length to be tested, the width of the conductive silver paint is 3mm, and the thickness of the conductive band is 0.3 mm.
And measuring the initial length of the conductive band of the sample to be tested before drying, and carrying out electrochemical test on the sample to be tested to obtain an initial current value. Thereafter, the sample to be tested was placed in a DKN611 type drying oven (Japan Daitan and science Co., Ltd.) and dried at a constant temperature of 60 ℃ and the sample to be tested was taken out at drying times of 60min, 120min and 180 min. Conducting strip length measurement is conducted on each sample to be tested, electrochemical testing is conducted on the samples to be tested, current and resistance of each test are obtained, resistance change rate is calculated, and specific results are shown in table 13.
Measuring the current and the resistance by using an electrochemical workstation, wherein the parameters of the electrochemical workstation are set as follows: initial potential-1V, end potential 1V, scanning speed 0.1V/s, sampling interval 0.01V, standing time 2s, sensitivity 1e-6A/V。
Watch 13
And calculating by using the resistance value to obtain the resistance change rate, and substituting the resistance change rate into the standard curve to obtain the dry shrinkage strain of the sample to be detected. The dry shrinkage strain obtained by the length calculation method is the change rate of the length of the conductive tape, and the specific test results are shown in table 14.
TABLE 14
As can be seen from Table 14, the dry shrinkage strain of the sample to be measured in the drying process measured by the method of the present invention is substantially the same as the dry shrinkage strain measured by the length meter algorithm. Therefore, the online detection method for the moisture content of the wood can realize online detection of each drying shrinkage strain stage of the wood in the drying process, and has high detection precision.
It should be noted that, although the technical solutions of the present invention are described by specific examples, those skilled in the art can understand that the present invention should not be limited thereto.
Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen in order to best explain the principles of the embodiments, the practical application, or improvements made to the technology in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
Claims (10)
1. An on-line detection method for wood surface drying shrinkage strain is characterized in that,
arranging a layer of conductive belt on the surface of a sample to be detected, and connecting two ends of the conductive belt to probes of an electrochemical workstation to form a closed loop;
under a specified voltage, measuring the current of the closed loop by using the electrochemical workstation, and obtaining the resistance of the sample to be measured, so as to obtain the resistance change rate of the sample to be measured;
and obtaining the dry shrinkage strain of the sample to be detected according to a standard curve of the dry shrinkage strain along with the change rate of the resistance of the wood sample based on the change rate of the resistance of the sample to be detected.
2. The online detection method for the drying shrinkage strain on the surface of the wood according to claim 1, wherein the material of the conductive band comprises one or a combination of more than two of conductive metallic paint, graphite conductive adhesive and carbon material conductive adhesive.
3. The online detection method of the drying shrinkage strain on the surface of the wood according to claim 1 or 2, wherein the conductive tape is coated to a thickness of 0.1mm to 0.5 mm.
4. The method for detecting the drying shrinkage strain on the surface of the wood according to any one of claims 1 to 3, wherein the width of the conductive band is less than or equal to the width of the sample to be detected.
5. The online detection method for the drying shrinkage strain on the surface of the wood according to any one of claims 1 to 4, wherein the potential setting range of the electrochemical workstation is-10V to 10V; the current setting range of the electrochemical workstation is-250 mA; the lower limit of the battery measurement of the electrochemical workstation is below 50 pA.
6. A method for the on-line detection of the drying shrinkage strain on the surface of wood according to any one of claims 1 to 5, wherein the closed loop current is measured by linear sweep voltammetry.
7. The method for on-line detection of wood surface drying shrinkage strain according to claim 6, wherein the electrochemical workstation is tested by using a current-time curve, and the parameters are set as follows: the potential is-1 to 1V, the sampling interval is 0.001 to 0.05s, and the scanning rate is 0.01 to 0.5V/s.
8. The method for on-line detection of wood surface drying shrinkage strain according to any one of claims 1 to 7, wherein the method for making the standard curve comprises the following steps:
forming a layer of conductive tape on the surface of the wood sample;
drying the wood sample at the same temperature, measuring the lengths of the conductive strips corresponding to different drying times, and acquiring corresponding drying shrinkage strain according to the lengths of the conductive strips;
measuring the current of the wood sample corresponding to different drying times by adopting the electrochemical workstation, and obtaining the resistance of the wood sample corresponding to different drying times so as to obtain the resistance change rate of the wood sample;
and obtaining the standard curve according to the drying shrinkage strain and the resistance change rate of the wood sample corresponding to the different drying times.
9. The online detection method for the drying shrinkage strain on the surface of the wood according to claim 8, wherein the drying temperature is 10-120 ℃.
10. An on-line detection device for implementing the on-line detection method of the wood surface dry shrinkage strain according to any one of claims 1 to 9, which is characterized by comprising an electrochemical workstation and a data acquisition device which are connected; wherein, the electrochemical workstation is connected with a probe by a lead.
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