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GB/T 35807-2018: Rubber, vulcanized -- Determination of thermal diffusivity -- Flash method
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Rubber, vulcanized -- Determination of thermal diffusivity -- Flash method
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GB/T 35807-2018
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Basic data | Standard ID | GB/T 35807-2018 (GB/T35807-2018) | | Description (Translated English) | Rubber, vulcanized -- Determination of thermal diffusivity -- Flash method | | Sector / Industry | National Standard (Recommended) | | Classification of Chinese Standard | G40 | | Classification of International Standard | 83.060 | | Word Count Estimation | 18,178 | | Date of Issue | 2018-02-06 | | Date of Implementation | 2018-09-01 | | Issuing agency(ies) | State Administration for Market Regulation, China National Standardization Administration | GB/T 35807-2018: Rubber, vulcanized -- Determination of thermal diffusivity -- Flash method---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
Rubber, vulcanized--Determination of thermal diffusivity--Flash method
ICS 83.060
G40
National Standards of People's Republic of China
Determination of thermal diffusivity of vulcanized rubber
Published on.2018-02-06
2018-09-01 implementation
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
China National Standardization Administration issued
Foreword
This standard was drafted in accordance with the rules given in GB/T 1.1-2009.
This standard was proposed by the China Petroleum and Chemical Industry Federation.
This standard is under the jurisdiction of the National Rubber and Rubber Products Standardization Technical Committee (SAC/TC35).
This standard was drafted. Shuangqian Tire Co., Ltd., Beijing Physical and Chemical Analysis and Testing Center, Yiweiyi Rubber Research Institute Co., Ltd., Fengshen
Tire Co., Ltd., Nichi Scientific Instrument Trading (Shanghai) Co., Ltd., Beijing Rubber Industry Research and Design Institute.
The main drafters of this standard. Dong Wenwu, Huang Zhongyu, Zou Tao, Zhao Wei, Zhu Yi, Liu Aiqin, Ren Shaowen, Liu Qingqing, Wang Rong, Xie Junfang, Li Jing.
Introduction
The test method for measuring the thermal diffusivity by the flash method has a wide measurement range, high temperature, high speed, and the measurement process can be in the oxidizing gas.
Features such as atmosphere, inert gas or vacuum environment, but also have the advantages of simple geometric structure, small size and fast test.
widely used. Especially in the rubber field, the thermal diffusivity is measured by analyzing the thermodynamic properties of the tire, especially for the tire temperature field.
An important prerequisite for research. By monitoring the thermal diffusivity of the materials in various parts of the tire, it can effectively avoid or reduce the heat of certain parts of the tire during driving.
Heavy causes potential risk factors such as punctures. Studying and determining the thermal diffusivity of tire rubber materials can provide important protection for the safe use of tires.
Barriers, especially for the improvement of green tire performance, provide important technical basis and design reference.
Determination of thermal diffusivity of vulcanized rubber
Caution - Personnel using this standard should have practical experience in formal laboratory work. This standard does not indicate all possible security questions.
The user is responsible for taking appropriate safety and health measures and ensuring compliance with the relevant national regulations.
1 Scope
This standard specifies that a flash source is applied to the front side of the sample to calculate the material heat by detecting the temperature rise time of the back side of the sample.
The method of diffusion coefficient.
This standard is applicable to the measurement of temperature in the range of 20 ° C ~ 250 ° C, the thermal diffusivity of the body above 0.01mm2/s evenly
Isotropic vulcanized rubber.
Note 1. If the sample is accompanied by decomposition or morphological changes within the measured temperature range, the test temperature range is adjusted accordingly.
Note 2. Since the flash method is a non-contact measurement method, it may be different from the results measured by other physical quantity principles (eg, heat flow meter method, protective hot plate method).
Wait).
2 Normative references
The following documents are indispensable for the application of this document. For dated references, only dated versions apply to this article.
Pieces. For undated references, the latest edition (including all amendments) applies to this document.
GB/T 2941 Rubber Physical Testing Methods General Procedures for Sample Preparation and Regulation
GB/T 14838 Determination of the standard precision of rubber and rubber products
3 Terms and definitions
The following terms and definitions apply to this document.
3.1
Thermal diffusion coefficient thermaldiffusivity
A measure of the rate at which a disturbance in temperature at one point in an object is transmitted to another point.
Note. The thermal diffusivity is usually expressed in α and is expressed in square millimeters per second (mm2/s).
4 symbols and footers
4.1 Relevant symbols and their units used in this standard
D --- diameter in millimeters (mm);
k --- a constant based on a percentage in the thermal diffusion equation;
L --- sample thickness in millimeters (mm);
t --- response time, in seconds (s);
T1/2 --- half temperature rise time, that is, the time when the back surface temperature rises to half of the maximum value, in seconds (s);
T --- temperature in Kelvin (K);
β --- the pulse duration score required to reach the highest intensity;
K1, K2---based on the constant of β;
ρ --- density in megagrams per cubic meter (Mg/m3);
Δt5 ---T(5t1/2)/T (t1/2);
Δt10 ---T(10t1/2)/T (t1/2);
ΔTmax --- the difference between the highest temperature and the baseline in Kelvin (K);
τ --- pulse duration (see Figure 1).
Figure 1 Laser pulse shape
4.2 Specific footing instructions in this standard
x --- percentage increase;
R --- ratio;
Max---maximum;
p --- constant pressure.
5 Method Overview
A small, thin disk-shaped sample is irradiated with a high-intensity energy pulse for a short period of time. The schematic diagram is shown in Fig. 2. Positive sample
The surface absorbs the pulse energy and records the change in the back surface temperature (temperature self-recording curve) caused by it. Thermal diffusion coefficient through the thickness and back of the sample
The time required for a certain ratio of temperature rise to the maximum value (see Figure 3) is calculated. When it is necessary to determine the heat of the sample in a temperature range
When the diffusion coefficient is required, it needs to be tested separately at each required temperature.
Note. This test method is described in detail in a large number of published books and review articles, and the principles are outlined in Appendix A.
Figure 2 Flash mechanism
Description.
ΔT/ΔTmax--the ratio of the temperature rise value to the maximum temperature rise value at a certain time t;
t/t1/2 --- The ratio of a certain time t to the half temperature rise time.
Figure 3 Sample temperature rise record on the back of the sample
6 equipment
6.1 The basic structure of the device is shown in Figure 4. It mainly includes flash source, sample cell, detector, signal processing device, etc.
Figure 4 Flash system module design
6.2 Flash source. It can be a laser pulse, a flash lamp or other device capable of forming short-cycle high-energy pulses. The circumference of the energy pulse
The period should be less than 2% of t1/2. The intensity of the pulse irradiated on the surface of the sample should be uniform. The pulse duration used should be 0.5% to 2% of t1/2
In order to further reduce the influence of the pulse width on the temperature rise curve, pulse width correction is required.
6.3 Environmental control equipment. For testing under non-room temperature conditions, it is necessary to configure environmental control equipment to achieve the required temperature of the sample.
degree. The temperature control accuracy is 0.1 °C.
6.4 Detector. The detector that measures the temperature rise of the sample can be a thermocouple, an infrared detector, an optical pyrometer or other small temperature changes.
A device capable of providing a linear electrical signal output and should be capable of detecting a change of 0.05K above the initial temperature of the sample. Detector and its
The response time of the matching amplifier should be less than 2% of t1/2. In order to be as close as possible to the sample, the temperature measuring element should be in close contact with or fixed to the sample holder.
On the sample holder. The temperature measuring element should not be in contact with the sample, and it is not allowed to be embedded in the sample.
6.5 Signal processing device. including electronic circuit, pulse peak filter, amplifier and analog-number reading the difference between sample temperature and ambient temperature
Word converter.
6.6 Data Acquisition and Recording System. The data acquisition system should have a sufficiently fast speed, and the sampling frequency should be less than 1% of t1/2.
7 sample
7.1 Size and shape
Specimens should be representative and should have no visible or visible defects. The sample usually used is a thin disc, the diameter of which depends on
The instrument used has a smaller frontal area than the energy beam spot. The typical sample diameter is 10.0mm~12.5mm, and the sample thickness is 1mm~
3mm. If other sample sizes are used, the ratio of diameter to thickness should be greater than 3.
7.2 Number of samples
Parallel tests should be no less than two.
7.3 Thickness measurement
The thickness gauge used for thickness testing shall comply with the requirements of Method A of GB/T 2941. The prepared sample should have a smooth surface and parallelism.
Within 0.5% of the thickness, the surface should not be defective (such as pits, scratches or marks).
Note. Samples whose surfaces are not completely parallel can also be tested, but large errors will occur. The average thickness of the test surface should be taken during the test.
7.4 Surface treatment
Prior to testing, the upper and lower surfaces of the sample were treated with very thin, uniform graphite or other high emissivity coatings. Can be used
Spray, smear, and spray to treat the surface of the sample to increase the sample's ability to absorb energy, especially for high reflectance samples.
7.5 Adjustment and parking
The adjustment and parking of the sample shall comply with the provisions of GB/T 2941.
8 Calibration and calibration
8.1 Periodically verify equipment performance and evaluation errors by measuring one or several materials with known thermal diffusivity. Appendix B gives
The verification procedure for the thermal diffusivity.
8.2 Temperature Calibration of the Flash Tester There are currently two main methods.
a) Curie point standard calibration method. find a series of standard samples whose Curie point transition temperature is within the measured temperature range of the instrument, and measure
The deviation of the phase transition temperature from the theoretical value to correct the temperature inside the instrument;
b) External standard thermocouple method. The internal temperature of the instrument is corrected by a calibrated thermocouple.
The above two methods are user selectable. The user can perform a self-check or commission a qualified metrology agency to calibrate.
8.3 Use standard materials to verify the data of unknown materials, pay attention to the performance of the standard materials (including half-temperature rise time and thermal diffusivity) and
Unknown similarity, and the same way of measuring the temperature rise curve is effective.
8.4 When making corrections, an important test for data validity is to change the thickness of the specimen. Because the half-temperature rise time varies with L2, that is, the sample thickness
The degree is reduced by half and the half-heating time is correspondingly reduced to a quarter of its original value. Therefore, if the same material is representative of different thicknesses
When the measured thermal diffusivity is the same (applying a suitable heat loss correction), the measured data can be considered to be true and effective.
9 test steps
9.1 Determine and record the thickness of the sample.
9.2 Surface the sample (see 7.4) according to the sample and place it in the sample holder.
9.3 Determine the sample temperature.
9.4 Selection of energy pulses. Under the premise of ensuring measurable temperature rise, the lowest possible energy pulse should be used to ensure that the detector is in its line.
Working within the sex range (especially during low temperature testing), while preventing large pulse energy from causing a significant increase in the temperature of the absorber layer on the surface of the sample
(In extreme cases, the surface of the sample may be decomposed).
9.5 After the pulse is emitted, the initial or processed temperature profile is monitored to determine the appropriate energy range.
9.6 Before or during the test, the stability of the temperature rise signal baseline should be verified manually or automatically to ensure that it is 4% of the maximum temperature rise.
Within.
9.7 Determine the ambient temperature of the sample at baseline stability, test with the energy selected in 9.4, and collect baseline and instantaneous
The temperature is raised and the cooling data is analyzed according to the provisions of Chapter 10. In the case of multiple sample tests, the samples are placed in sequence at the same temperature.
The rows are measured sequentially (saving time) and then warmed to the next temperature to be measured.
9.8 Change or set the ambient temperature of the sample according to the requirements, and repeat the data acquisition process, and test at different temperatures.
9.9 If necessary, cycle test the sample cooling or repeated heating process at each test temperature.
10 calculation
10.1 Calculation of thermal diffusivity
10.1.1 First determine the baseline and the highest temperature rise, get the temperature change ΔTmax, and then determine the temperature of the back of the sample from the pulse emission to the rise
The time required to reach half of ΔTmax, that is, the half temperature rise time t1/2. According to the thickness L and t1/2 of the sample, the thermal expansion is calculated by the formula (1)
The coefficient of dispersion α.
α=0.13879L2/t1/2 (1)
The validity of the measurement can be calculated from the thermal diffusion coefficient α calculated by the equation (2) by at least two points other than the half temperature rise time on the temperature rise curve.
verification.
α=kxL2/tx (2)
In the formula.
Kx---constant, the value of which is shown in Table 1;
Tx - the time required for the temperature to rise to x (%) of ΔTmax.
Table 1 The value of the constant kx for each percentage temperature rise
x/% kx
10 0.066108
20 0.084251
25 0.092725
30 0.101213
33.33 0.106976
40 0.118960
50 0.138790
x/% kx
60 0.162236
66.67 0.181067
70 0.191874
75 0.210493
80 0.233200
90 0.303520
10.1.2 Ideally, the alpha values calculated for different x(%) values should be the same. If the x (%) value is 25%, 50%,
When the calculated alpha value error at 75% is controlled within ±2%, the overall error of the test at half temperature rise time will be within ±5%. in case
If the alpha value is outside this range, the response curve should be further analyzed to determine if there is radiant heat loss, limited pulse time, or
Non-uniform heating effect.
10.1.3 The radiant heat loss effect can be easily identified from the response characteristics of the sample temperature and the back surface temperature after 4 t 1/2. Recommender
The method is. plot a curve of ΔT/ΔTmax with respect to t/t1/2, and add a mathematical model theoretical curve to the figure (see Table 2 for some data).
Table 2 Theoretical model plotting temperature time values
ΔT/ΔTmax t/t1/2
0 0
0.0117 0.2920
0.1248 0.5110
0.1814 0.5840
0.2409 0.6570
0.3006 0.7300
0.3587 0.8030
0.4140 0.8760
0.4660 0.9490
0.5000 1.0000
0.5587 1.0951
0.5995 1.1681
0.6369 1.2411
0.6709 1.3141
0.7019 1.3871
0.7300 1.4601
ΔT/ΔTmax t/t1/2
0.7555 1.5331
0.7787 1.6061
0.7997 1.6791
0.8187 1.7521
0.8359 1.8251
0.8515 1.8981
0.8656 1.9711
0.8900 2.1171
0.9099 2.2631
0.9262 2.4091
0.9454 2.6281
0.9669 2.9931
0.9865 3.6502
0.9950 4.3802
0.9982 5.1102
10.1.4 The theoretical model curve can be drawn according to the ΔT/ΔTmax and t/t1/2 values in the table, and the test data is normalized, all normalized.
The test curve should pass through points ΔT/ΔTmax=0.5 and t/t1/2=1.0. The calculation needs to include 25%~35% and 65%~80%
Point to compare the experimental data with the theoretical curve.
10.1.5 As shown in Fig. 5, Fig. 6, and Fig. 7, in the example of the normalized test curve drawn near the ideal case, there is radiant heat loss and
Finite pulse time effect. Methods for correcting these effects can be found in the literature, and a description of the modified exceptions is given in 10.2 and 10.3.
Figure 5 Comparison of the dimensionless temperature curve with the mathematical model
Figure 6 Normalized back temperature rise curve. mathematical model (without finite pulse time effect)
Comparison with test results (with finite pulse time effect)
Figure 7 Normalized back temperature rise curve. comparison of mathematical model (no radiant heat loss) and test results (radiation heat loss)
10.1.6 The finite pulse time effect decreases as the thickness increases, and the heat loss decreases as the thickness decreases. Select the appropriate sample.
The thickness minimizes the correction.
10.1.7 Due to the existence of two-dimensional heat flow, the non-uniform heating effect also causes the deviation of the test curve from the downward movement of the model curve. non-
Uniform heating may be caused by the nature of the energy pulse, such as the thermal center (high sample center temperature) is similar to the example of radiant heat loss, also
May be caused by non-uniform absorption of the front side of the sample, such as the cold center (low temperature of the sample center), the back surface temperature continues to be significant after 4t1/2
Rising, the former case should be eliminated by replacing the energy source, which can be eliminated by adding an absorption layer such as graphite spray.
10.2 Limited pulse time correction
It can generally be corrected using equation (3).
α=K1L2/(K2tx-τ) (3)
As shown in Fig. 1, in order to make it effective, the pulse intensity changes with a duration τ and a triangle of time βτ reaching the maximum intensity.
Said. The shape of the laser energy pulse can be determined using an optical detector. From the shape of the pulse, β and τ can be obtained. Corresponding to the beta value
The values of the constants K1 and K2 for correcting αx are listed in Table 3.
Table 3 Finite pulse time factor
β K1 K2
0.15 0.34844 2.5106
0.28 0.31550 2.2730
Table 3 (continued)
β K1 K2
0.29 0.31110 2.2454
0.30 0.30648 2.2375
0.50 0.27057 1.9496
10.3 Heat Loss Correction
10.3.1 Cowan method
The ratio of the net temperature rise at 5 times t1/2 and 10 times t1/2 to the net temperature rise at t1/2 is Δt5 and Δt10, respectively. if there is not
For heat loss, Δt5=Δt10=2.0. The correction factor (Kc) of 5t1/2 and 10t1/2 is calculated according to formula (4).
Kc=AB(Δt) C(Δt)2 D(Δt)3 E(Δt)4 F(Δt)5 G(Δt)6 H(Δt)7 (4)
The values of the coefficients A to H in the formula are listed in Table 4. The corrected diffusion coefficient is calculated according to equation (5).
Correctcorrected=α0.5Kc/0.13885 (5)
In the formula, α0.5 = uncorrected thermal diffusivity calculated by t1/2.
Table 4 Cowan corrected coefficient values
Coefficient Δt5 Δt10
A -0.1037162 0.054825246
B 1.239040 0.16697761
C -3.974433 -0.28603437
D 6.888738 0.28356337
E -6.804883 -0.13403286
F 3.856663 0.024077586
G -1.167799 0.0
H 0.1465332 0.0
10.3.2 Clark and Taylor [1], [2] methods
According to the time when the temperature rises to 75% ΔTmax divided by the time to increase to 25% ΔTmax, that is, the ratio of t0.75/t0.25, the theoretical value is
2.272. From the test data, t0.75/t0.25 is obtained, and then the correction coefficient KR is calculated according to the formula (6).
KR=-0.3461467 0.361578(t0.75/t0.25)-0.06520543(t0.75/t0.25)2 (6)
The corrected thermal diffusivity is αcorrected=α0.5KR/0.13885. Other different ratios can also be used for correction.
11 report
The test report should contain the following.
a) the name and number of this standard;
b) the thickness of the sample;
c) test temperature;
d) calculating the thermal diffusivity at x=50% at the test temperature;
e) repeat the results of the test at each temperature point;
f) a description of the correction process for heat loss and finite pulse time effects;
g) Manufacturer and model of the instrument used.
12 precision
12.1 Overview
The precision calculations regarding repeatability and reproducibility are performed in accordance with GB/T 14838 and follow the concepts and terminology expressed in the standard. Attached
Record C gives an application guide for repeatability and reproducibility.
12.2 Precision results
The precision results of the thermal diffusivity measurement are shown in Table 5.
Table 5 Precision of thermal diffusivity measurement
Temperature range/°C Relative (r)/% Relative (R)/%
30~100 ≤3.0 ≤5.0
100~150 ≤5.0 ≤8.0
150~250 ≤7.0 ≤15.0
Note. r = repeatability, unit of thermal diffusivity;
(r) = repeatability, percentage (relative);
R = reproducibility, unit of thermal diffusivity;
(R) = reproducibility, percentage (relative).
Appendix A
(informative appendix)
principle
A.1 Ideal situation - the physical model of the pulse method is based on the thermal properties of the adiabatic (isolated heat exchange) sheet material at a constant temperature
Next, its front is subjected to an instantaneous energy pulse, and the model assumes the following.
a) one-dimensional heat flow;
b) there is no heat loss on the surface of the board;
c) uniformly absorbing the pulse on the front side;
d) the pulse duration is extremely short;
e) only a very thin layer of absorbed energy pulses;
f) the plate material is uniform and isotropic;
g) The properties of the material do not change with temperature under the test conditions.
Parker derives the number of thermal diffusivity calculations based on the temperature distribution equation in a solid thermal insulation material with a uniform thickness (thickness L).
For the expression, see the formula (A.1) given by Carslaw and Jaeger.
T(x,t)=
L∫
T(x,0)dx
L∑
n=1
Exp
-n2π2αt
L2
÷·cosnπxL∫
T(x,0)cosnπxL dx
(A.1)
In the formula.
α---The thermal diffusivity of the material.
When an energy radiation pulse Q instantaneously illuminates the front side of the sample (x = 0) and is uniformly absorbed, the depth of the absorption layer is g, and the temperature is divided at this time.
The cloth is.
When 0 \u003cx\u003cg时,见式(A.2).
T(x,0)=
ρ·C·g
(A.2)
When g \u003cx\u003cL 时,见式(A.3).
T(x,0)=0 (A.3)
Under this initial condition, equation (A.1) can be written as equation (A.4).
T(x,0)=
ρCL
1 2∑
n=1
cosnπxL
sinnπgL
Nπg
·exp
-n2π2
L2
Ttæ
(A.4)
In the formula.
ρ---material density;
C---material specific heat.
For opaque materials, g is very small, so there is a formula (A.5)
sinnπgL ≈
Nπg
(A.5)
On the back side, ie x=L, the temperature change over time can be expressed by equation (A.6).
T(L,t)=
ρCL
1 2∑
n=1
(-1)n·exp
-n2π2
L2
Ttæ
Êê
Úú (A.6)
Two dimensionless parameters, V and ω are defined by equations (A.7) and (A.8).
V(L,t)=
T(L,t)
TM
(A.7)
ω=
Π2αt
L2
(A.8)
TM represents the highest temperature on the back, and the simultaneous (A.6)~ (A.8) formula (A.9).
V=1 2∑
n=1
(-1)n·exp(-n2ω) (A.9)
When V = 0.5, ω = 1.38, see equation (A.10).
α=
1.38·L2
Π2t1/2
(A.10)
Or formula (A.11).
α=0.1388
L2
T1/2
(A.11)
Where t1/2 is the time required for the backside temperature to reach half of its maximum temperature. The principle of the flash method can be illustrated in Figure 2.
A.2 Non-ideal situation---The actual test will violate the above assumption to some extent, so the above Parker method is introduced, it does not
The foot is very obvious. Since then, researchers have used various theories to describe the actual process and to correct the boundary conditions that violate the hypothesis. ideal
The correction should include all the factors, but so far there is no such correction. And someone uses a single or paired correction method to calculate the bias
difference. The result is a revised series of data that is different from each other. From a historical point of view, this is understandable, each research
Researchers focus on correcting one or two deviations in the ideal model, assuming that the other factors are ideal and constant. But this itself
The principle is violated, because in reality the test will always be interfered to by certain test conditions to a certain extent, and all parameters are changing at the same time. some
The situation may increase the influence of a certain condition, such as the pulse is too long, and some may cause other deviations, such as the front due to excessive pulse energy
Excessive heat loss, etc. Therefore, it is important for researchers t...
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