JP2898333B2 - Method and apparatus for measuring thermal expansion coefficient of long sample - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for measuring the coefficient of thermal expansion of a long sample such as carbon fiber.

[Prior Art] The following differential measurement method is known as one of the general methods for measuring the coefficient of thermal expansion. In this measurement method, a measurement sample and a reference sample such as quartz glass whose thermal expansion coefficient is known in advance are set in a heating furnace, and each of these samples is brought into contact with a push rod made of quartz, The displacement of the tip of the push rod is detected by a differential transformer, and the thermal expansion coefficient of the measurement sample is measured from the difference in thermal expansion between the two samples.

[Problems to be Solved by the Invention] However, the above-described conventional method has the following problems.

(1) The conventional measuring method is relatively short (for example, 10 cm
), The absolute value of the dimensional change becomes smaller if the coefficient of thermal expansion of the sample is small.
There is a problem that the measurement accuracy is reduced.

(2) On the other hand, when the measurement sample is lengthened, the influence of the variation in the temperature distribution of the heating furnace becomes large, and the measurement accuracy is reduced. Therefore, the measurement sample is not suitable for measurement of a long sample.

(3) Since it is difficult to attach a temperature detector such as a thermocouple to the measurement sample, the ambient temperature in the heating furnace is measured, and the temperature is regarded as the temperature of the measurement sample. May cause a temperature difference, which also contributes to a decrease in measurement speed.

(4) Further, in a measurement method in which one end of a measurement sample is gripped outside the heating furnace, a temperature gradient occurs in a sample portion near the heating furnace, and the measurement accuracy is reduced due to a dimensional change due to the temperature gradient.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a measuring method and an apparatus for accurately measuring a thermal expansion coefficient of a long sample.

[Means for Solving the Problems] As a result of studying to solve the problems of the above-described conventional method, the present inventors focused on a change in electric resistance due to a temperature change of a long sample. That is, as shown in FIG. 2, in the case of a long sample such as carbon fiber, there is a temperature range in which the relationship between electric resistance and temperature can be approximated by a linear equation, and
As shown in FIG. 3, attention was paid to the fact that the coefficient of thermal expansion of the sample shows a constant value in this temperature range (the temperature change and the length change show a proportional relationship).

The present inventors measure the change in length of a long sample having a temperature change in an intermediate portion based on such knowledge, and at both end portions of the long sample, and the temperature change. Measure the electrical resistance between two points that are not substantially affected,
This electrical resistance is converted into the average temperature change between the two points, and the thermal expansion coefficient of the long sample is calculated using the average temperature change, thereby causing the variation in the temperature change of the heating means and the temperature in the sample. It has been conceived that high-precision measurement in which the influence of the gradient is corrected can be performed.

Hereinafter, it will be described that even if the long sample has a temperature gradient, the thermal expansion coefficient of the sample can be measured by knowing the average temperature change.

FIG. 4 is a diagram schematically showing a temperature distribution (temperature gradient) generated at the end of the heating furnace when a temperature change is applied to the middle portion of the sample.

In the figure, T ₀ is the uniform initial temperature before heating, T ₁ is the temperature in the heating furnace, and T (x) is the temperature at an arbitrary point x in the sample area (non-uniform temperature distribution area) at the end of the heating furnace. . The temperature change ΔT (x) at the point x is expressed by the following equation (1).

ΔT (x) = T (x) −T ₀ (1) On the other hand, the average temperature of the sample in the non-uniform temperature distribution region (0 <x <L in the figure) is represented by the following equation (2).

In addition, the length change ΔL of the sample in the non-uniform temperature distribution region
Is represented by the following equation (3).

Here, assuming that the thermal expansion coefficient α is constant irrespective of the temperature, the above equation (3) is expressed as follows.

From the equations (1), (2), and (4), ΔL is expressed as follows.

According to the equation (5), even if the sample has a non-uniform temperature distribution, if the coefficient of thermal expansion α is constant regardless of the temperature, the change in the length of the sample is proportional to the change in the average temperature of the sample. I understand.

In short, even if there is a temperature gradient in the sample, knowing the length L of the sample, the length ΔL due to the temperature change, and the average temperature change ΔT (= −T ₀ ) of the sample, the thermal expansion coefficient α of the sample Can be requested. Then, the average temperature change ΔT of the sample can be easily known by measuring the temperature by the electric resistance of the sample as described above.

The method for measuring the coefficient of thermal expansion of a long sample according to the present invention based on the above-mentioned findings is to fix the one end of the long sample and apply tension to the other end of the long sample in the longitudinal direction of the sample. A temperature change is applied to an intermediate portion, an electric resistance between two points near both ends of the sample which is not substantially affected by the temperature change is measured, and the electric resistance is converted into an average temperature change (ΔT) of the sample. The average thermal change (ΔT), the sample length (L) between the two points before the temperature change is given, and the sample length change (ΔL) caused by the temperature change, the thermal expansion coefficient (α) ) Is what you want.

A long sample suitable for the method of the present invention has a temperature range in which the relationship between electric resistance and temperature can be approximated by a linear equation, such as carbon fiber, and has a coefficient of thermal expansion of the sample in this temperature range. Is a sample having characteristics that can be considered to be constant. However, looking at the wide temperature range,
Even if the relationship between the electrical resistance and the temperature cannot be approximated by a linear equation, or if the sample does not have a constant coefficient of thermal expansion, the sample of the present invention can be used as long as the sample has the above characteristics in a narrow temperature range. Can be applied.

Further, the measuring device for performing the method of the present invention is a fixing means for fixing one end of the long sample, a tension applying means for applying a tension to the other end of the sample, and surrounding the intermediate portion of the sample, Heating means for applying a temperature change to the intermediate portion;
A detecting means for detecting a change in the longitudinal direction of the end of the elongated sample in the length direction, and a current is supplied between two points near both ends of the sample which are substantially unaffected by the temperature change by the heating means. And a voltage measuring means for measuring a voltage between the two points.

[Operation] According to the method for measuring the coefficient of thermal expansion of a long sample according to the present invention, the electric resistance between two points at both ends of the sample, which is substantially unaffected by a temperature change, is measured, and the electric resistance is calculated as the average temperature. Since the change is converted into a change, the coefficient of thermal expansion can be accurately measured even if the sample is affected by temperature variations in the heating means and temperature gradients at both ends of the heating means.

Further, according to the measuring device of the present invention, a change in the length of the sample before and after heating is measured by detecting a change in the length direction of the end of the long sample on the tension applying side end. In addition, a predetermined current is applied between the two points at both ends of the sample by the energizing means,
The electric resistance between the two points is determined by measuring the potential difference between the two points at that time by a voltage measuring means.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory diagram showing a schematic configuration of a measuring apparatus using the method of the present invention.

In the figure, the symbol S is a long sample to be measured.
The upper end of the sample S is gripped by a clamp mechanism 2 as a fixing means supported by the column 1. The column 1 is preferably formed of a material having a small coefficient of thermal expansion, for example, quartz or invar. Further, it is preferable to attach a suitable length detector to the support 1 in order to confirm a change in the length of the support 1 due to a change in the temperature of the atmosphere during measurement.
If the temperature of the atmosphere is stable, it is not necessary to attach such a length detector.

At the lower end of the sample S, a weight 3 as tension applying means and a marker 4 which is a part of a means for detecting a change in the position of the lower end of the sample S are attached. Note that, depending on the position change detection method, the displacement of the weight 3 can be detected without using the marker 4. If the marker 4 has an appropriate weight, it is not necessary to attach the weights 3 individually. Reference numeral 5 denotes a laser scan micrometer which constitutes a means for detecting a change in the position of the lower end of the sample S together with the marker 4, and detects a transmitted light amount of the laser which changes in accordance with the displacement of the marker 4, thereby detecting A change in the length of S is detected in a non-contact manner, and the change value is output to the display 6. As a means for detecting the displacement of the lower end of the sample S, a differential transformer or the like can be used.

Reference numeral 7 denotes a heating furnace as a heating means for giving a temperature change to an intermediate portion of the sample S. Inside the changing furnace 7, there is a furnace core tube 8 capable of replacing the atmosphere with an inert gas such as nitrogen gas. The sample S is suspended so as to penetrate the furnace core tube 8.

At both ends of the sample S, current terminals a ₁ and a ₂ for supplying a current to the sample S and voltage terminals b for detecting a potential difference between both ends are provided.
₁ and b ₂ are provided. The positions of both ends of the sample S where the terminals are provided are set so as not to be substantially affected by the temperature change given by the heating furnace 7. To each terminal, a gold wire is electrically connected to each terminal at a silver pace or the like so as not to hinder detection of a change in the length of the sample S, and the gold wire is used as a conductive wire. A constant current power supply 9 as a current supply means is connected to the current terminals a ₁ and a ₂ through such conductors, and a voltage measurement device 10 as a voltage measurement means is connected to the voltage terminals b ₁ and b _2. I have.

As described above, the measurement of the electrical resistance in the length direction of the sample S is preferably performed by so-called four-terminal measurement, but may be performed by two-terminal measurement. As an example of the measurement method, JIS
There is C2525.

Hereinafter, a measurement example of the thermal expansion coefficient of the long sample S performed by the above-described example apparatus will be described.

Here, as sample S, a carbon fiber “Torayca T800H” manufactured by Toray Industries, Inc. was used. FIG. 2 shows the temperature characteristics of the electrical resistance of the sample S measured in advance in order to convert the electrical resistance measured by the above-described apparatus into an average temperature. In order to obtain this temperature characteristic in advance, the sample S was set in the atmosphere of a hot-air circulating thermostat, and the electric resistance was measured by the four-terminal method in the same manner as in the above-described embodiment. Was measured by

As is clear from FIG. 2, it is understood that the sample S has a temperature range in which the relationship between the electric resistance and the temperature can be approximated by a linear equation. Here, since the sample provided for preparing the calibration diagram of FIG. 2 and the sample provided for actually measuring the coefficient of thermal expansion have the same cross-sectional area, the unit of electrical resistance is Ω / cm However, when the lengths of both samples are equal, the unit of the electric resistance may be represented by Ω. When the cross-sectional area of the sample can be easily measured, it may be represented by volume resistivity.

FIG. 3 shows the sample S (carbon fiber: trading card T800) described above.
FIG. 2H is a characteristic diagram showing the relationship between the obtained length change and the average temperature measured by the apparatus of the embodiment shown in FIG. In the figure, the circles indicate measured values obtained during the temperature rising process, and the triangles indicate measured values obtained during the cooling process. The vertical axis represents the change value ΔL of the length of the sample S measured by the laser scan micrometer 5 and the change rate (ΔL / L × 10 ³ ) obtained by dividing the change in length by the sample length before the temperature change. is there. The horizontal axis is a constant current I that does not self-heat the sample itself during the heating or cooling process, and the voltage value V at that time is measured.
A resistance value R is obtained from a relationship of resistance R = V / I, and the resistance value is divided by a sample length L between the voltage terminals b ₁ and b ₂ to obtain a resistance value per unit length [Ω / cm]. The resistance value is converted into a temperature using the calibration diagram of FIG.

As is clear from FIG. 3, the coefficient of thermal expansion of the sample S is constant within the measurement temperature range, and the relationship between the length of the sample S and the temperature does not change at the time of temperature rise and temperature decrease.

From the measurement data thus obtained, an appropriate average temperature change (ΔT) of the sample S and a change in the sample length (ΔL) at that time are obtained, and the voltage terminals b ₁ and b ₂ before the temperature change are obtained. When the coefficient of thermal expansion (α) is obtained from the sample length (L) between
The thermal expansion coefficient of the sample S was -0.55 * 10 < ^-6 >. Incidentally, when a voltage terminal is set near the end of the heating furnace 7 affected by the temperature change and the coefficient of thermal expansion of the sample S is measured, the influence of the length change due to the temperature gradient near both ends of the heating furnace 7 indicates that The value became −0.58 × 10 ⁻⁶ .

In the measuring apparatus shown in FIG. ₁ , the voltage value between two points (between the voltage terminals b ₁ and b _{2 in} FIG. ₁ ) at both ends of the sample S, which is not affected by the temperature change, The average temperature of the sample S between the points is obtained by detecting a voltage value in each of a plurality of sections obtained by further dividing the two points and calculating a resistance value of each section. Average temperature change ΔT ₁ , ΔT
₂ , TT ₃ , ...
The thermal expansion coefficient α may be obtained.

ΔL = α ₁ · L ₁ · ΔT ₁ + α ₂ · L ₂ · ΔT ₂ + α ₃ · L ₃ · ΔT ₃ + ... = α (L ₁ · ΔT ₁ + L ₂ · ΔT ₂ + L ₃ · ΔT ₃ + ...) ... (7) Here, α ₁ = α ₂ = α ₃ (= α), and L ₁ , L ₂ , L ₃ ,... Are the sample lengths before the temperature change in each section.

[Effects of the Invention] As is clear from the above description, according to the method and the apparatus for measuring the thermal expansion coefficient of a long sample according to the present invention, the effects of temperature changes at both ends of the long sample are substantially reduced. The resistance value between the two points which are not subjected to the measurement is measured, the resistance value is converted into the average temperature change of the sample S between the two points, and the thermal expansion coefficient is obtained based on the average temperature change. The coefficient of thermal expansion of the long sample can be accurately measured without being affected by the variation in the temperature distribution of the means or the influence of the temperature gradient at the end of the heating means.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a schematic configuration of a device for measuring the thermal expansion coefficient of a long sample according to one embodiment of the present invention, FIG. 2 is a temperature characteristic diagram of the electrical resistance of the sample, and FIG. FIG. 4 is a characteristic diagram showing a relationship between a change in length and a change in average temperature, and FIG. 4 is a schematic diagram showing a temperature distribution in a non-uniform temperature distribution region in a sample. S ... Long sample, 1 ... Post 2 ... Clamp mechanism 3 ... Weight 4 ... Marker 5 ... Laser scan micrometer 6 ... Display 7 ... Heating furnace, 8 ... Core tube 9 ...... constant current source, 10 ...... voltmeter a _1, a ₂ ...... current terminal b _1, b ₂ ...... voltage terminal

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) G01N 25/00-25/72 JICST file (JOIS)

Claims (3)

(57) [Claims] In a state where one end of a long sample is fixed and tension is applied to the other end, a temperature change is applied to an intermediate portion in the longitudinal direction of the sample, and the temperature change is substantially affected. The electrical resistance between two points near both ends of the sample is measured, and the electrical resistance is converted into an average temperature change (ΔT) of the sample. The coefficient of thermal expansion (α) is determined by the sample length (L) between points and the change in sample length (ΔL) caused by a temperature change. A method for measuring the coefficient of thermal expansion of a long sample, characterized in that: 2. The method according to claim 1, wherein the elongated sample is a carbon fiber.
4. The method for measuring the coefficient of thermal expansion of a long sample according to item 1. 3. A fixing means for fixing one end of a long sample,
Tension applying means for applying a tension to the other end of the sample, heating means for surrounding an intermediate portion of the sample and changing the temperature of the intermediate portion, and a length of a tension applying side end of the elongated sample. Detecting means for detecting a change in position in the direction; energizing means for energizing between two points near both ends of the sample which are substantially unaffected by the temperature change by the heating means; and a voltage for measuring a voltage between the two points An apparatus for measuring the thermal expansion coefficient of a long sample, comprising a measuring means.