JPH03269352A - Method and instrument for measuring thermal expansion coefficient of long sized sample - Google Patents

Abstract

PURPOSE:To accurately measure the thermal expansion coefficient of a long pized sample by measuring electric resistance between two end points of a sample which does not practically receive the influence of a temperature change and converting the electric resistance into an average temperature change. CONSTITUTION:A laser scanning micrometer 5 contactlessly detects a change in the length of a sample S by detecting the quantity of transmitted light of laser beams which is varied according to the displacement a marker 4. Current terminals a1, a2 for supplying current to the sample S and voltage terminals b1, b2 for detecting the potential difference between both the end parts of the sample S are connected to both the end parts. Both the end parts of the sample S to which respective terminals are connected are set up on positions which are not practically influenced by a temperature change applied by a heating furnace 7. The proper average temperature change of the sample S and the change in the length of the sample are found out from the obtained measurement data and the thermal expansion coefficient is found out from the sample length between both the voltage terminals b1, b2 obtained before the temperature change.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for measuring the coefficient of thermal expansion of a long sample such as carbon fiber.

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

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

(1) Conventional measurement methods use relatively short lengths (for example, 10cm
Since the measurement sample is of the order of m), there is a problem that if the coefficient of thermal expansion of the measurement sample is small, the absolute value of the dimensional change will be small and the measurement accuracy will be reduced.

(2) On the other hand, if the measurement sample is made long, the influence of variations in the temperature distribution of the heating furnace increases, which reduces measurement accuracy, and therefore is not suitable for measurement of long samples.

(3) Also, since it is difficult to attach a temperature detector such as a thermocouple to the measurement sample, the atmospheric temperature inside the heating furnace is measured and that temperature is assumed to be the temperature of the measurement sample, but there is a difference between the two. There may also be a temperature difference between the two, which is also a factor in reducing measurement accuracy.

(4) Furthermore, in a measurement method in which one end of the measurement sample is held outside the heating furnace, a temperature gradient occurs in the part of the sample near the heating furnace, and measurement accuracy decreases due to dimensional changes caused by this.

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

[Means for Solving the Problems] As a result of studies to solve the problems of the above-mentioned conventional methods, the present inventors focused on changes in electrical resistance caused by temperature changes in a long sample. That is, as shown in Figure 2,
In the case of long samples such as carbon fibers, the relationship between electrical resistance and temperature has a temperature range that can be approximated by a linear equation, and
As shown in the figure, we focused on the fact that the thermal expansion coefficient of the sample shows a constant value in this temperature range (temperature change and length change show a proportional relationship).

Based on these findings, the present inventors measured the length change of a long sample with a temperature change applied to the middle part, and also measured the length change of the long sample at both ends of the long sample due to the temperature change. Measure the electrical resistance between two points that are virtually unaffected, convert this electrical resistance to the average temperature change between the two points, and use this average temperature change to calculate the coefficient of thermal expansion of the long sample. By doing so, we have come up with the idea that it is possible to perform highly accurate measurements that correct for variations in temperature changes in the heating means and the effects of temperature gradients in the sample.

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

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

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

ΔT (x) −T (x) To
--(1) On the other hand, non-uniform temperature distribution region (0〈X〈
The average temperature T of the sample L) is expressed by the following equation (2).

I+ Also, the sample length change ΔL in the non-uniform temperature distribution region is
It is expressed by the following equation (3).

ΔL-1 α・ΔT(x)dx ・・・・・・
(3) Here, assuming that the coefficient of thermal expansion α is constant regardless of temperature, equation (3) can be expressed as follows.

Δ■, -αS: ΔT(x)dx ・・・・・・
・(4)(1), (2) From equation (4), Δ1. is expressed as follows.

ΔL−aS′; (T (x)−T.) dx−α(T−
To) L ...... (5) From equation (5), even if the sample has an uneven temperature distribution, the thermal expansion coefficient α
If is constant regardless of temperature, the change in length of the sample is
It can be seen that it is proportional to the average temperature change of the sample.

In short, even if there is a temperature gradient in the sample, the sample length I
-, the length ΔL due to temperature change, and the average temperature change Δ of the sample
By knowing T (=T To ), the thermal expansion coefficient α of the sample can be determined. The average temperature change Δc of the sample can be easily determined by temperature measurement based on the electrical 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 knowledge is to fix one end of the long sample and apply tension to the other end, and to measure the coefficient of thermal expansion of the sample in the longitudinal direction. Apply a temperature change to the middle part, measure the electrical resistance between two points near both ends of the sample that are not substantially affected by this temperature change, and convert this electrical resistance to the average temperature change (ΔT) of the sample. ,
The thermal expansion coefficient (α) is determined by this average temperature change (ΔT), the sample length (L) between the two points before applying the temperature change, and the sample length change (ΔL) caused by the temperature change. This is what we seek.

A long sample suitable for the method of the present invention, such as carbon fiber, has a temperature range in which the relationship between electrical resistance and temperature can be approximated by a linear equation, and the thermal expansion coefficient of the sample in this temperature range. This is a sample with characteristics that can be considered constant. However, in a wide temperature range, the relationship between electrical resistance and temperature cannot be approximated by a linear equation,
Even if the coefficient of thermal expansion is not constant, the method of the present invention can be applied to the sample as long as it is recognized to have the above characteristics in a narrow temperature range.

Further, the measuring device for carrying out the method of the present invention includes a fixing means for fixing one end of the elongated sample, a tension applying means for applying tension to the other end of the sample, and a tension applying means that surrounds the middle part of the sample. a heating means for applying a temperature change to the intermediate portion; a detection means for detecting a change in the position of the tension-applying side end of the elongated sample in the longitudinal direction; and substantially unaffected by the temperature change caused by the heating means. It is equipped with a current supply means for supplying current between two points near both ends of the sample, and a voltage measurement means for measuring the voltage between the two points.

[Function] According to the method for measuring the coefficient of thermal expansion of a long sample according to the present invention, the electrical resistance between two points at both ends of the sample, which is not substantially affected by temperature changes, is measured, and this electrical resistance is calculated as the average temperature. Since it is converted into a change, it is possible to account for variations in temperature in the heating means,
Even if the sample is affected by the temperature gradient at both ends of the heating means, the coefficient of thermal expansion can be accurately measured.

Further, according to the measuring device according to the present invention, by detecting a change in the position of the tension-applying side end of the elongated sample in the longitudinal direction,
Measure the change in length of the sample before and after heating. Furthermore, the electrical resistance between the two points is determined by passing a predetermined current between two points on both ends of the sample using the current supply means and measuring the potential difference between the two points using the voltage measuring means.

[Example] Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is an explanatory diagram showing a schematic configuration of a measuring device 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 that is supported by a support 1 and serves as a fixing means. The support column 1 is preferably made of a material with a small coefficient of thermal expansion, such as quartz or invar.

In addition, it is preferable to attach an appropriate length detector to the pillar 1 in order to check the change in the length of the pillar 1 due to changes in the temperature of the atmosphere during measurement, but if the temperature of the atmosphere is stable, There is no need to install such a length detector.

A weight 3 as a tension applying means and a marker 4 as a part of means for detecting a change in the position of the lower end of the sample S are attached to the lower end of the sample S.

Note that depending on the position change detection method, it is also possible to detect the displacement of the weight 3 without using the marker 4. Further, if the marker 4 has an appropriate weight, there is no need to attach the weight 3 separately. 5 is sample S with marker 4.
This laser scanning micromake device constitutes a means for detecting changes in the position of the lower end of the sample S, and detects changes in the length of the sample S by detecting the amount of transmitted laser light that changes in accordance with the displacement of the marker 4. is detected without contact, 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, it is also possible to use a differential transformer or the like.

Reference numeral 7 denotes a heating furnace as a heating means for applying a temperature change to the middle portion of the sample S. Inside the heating furnace 7, there is a furnace core tube 8 that can replace the atmosphere with an inert gas such as nitrogen gas.
The sample S is suspended so as to pass through the furnace core tube 8.

At both ends of the sample S, a current terminal al+82 for supplying current to the sample S and voltage terminals S, B2 for detecting a potential difference between both ends are provided.

The positions of both ends of the sample S where each terminal is provided are located at the heating furnace 7.
The temperature is set so that it is virtually unaffected by temperature changes caused by. A gold wire is electrically connected to each terminal with silver paste or the like so as not to interfere with the detection of a change in the length of the sample S, and the gold wire is used as a conducting wire. A constant current power source 9 as a current supply means is connected to the current terminal alt82 through such a conductive wire, and a voltage measuring device 1 as a voltage measuring means is connected to the voltage terminals b+ and bz.
0 is connected.

As described above, it is preferable to measure the electrical resistance in the longitudinal direction of the sample S by a so-called four-terminal measurement, but it may also be carried out by a two-terminal measurement. An example of a measurement method is JIS
There is C2525.

Hereinafter, an example of measuring the coefficient of thermal expansion of the elongated sample S using the above-mentioned embodiment apparatus will be described.

Here, as sample S, carbon fiber manufactured by Toshi Co., Ltd.
Trading card T800 HJ was used. FIG. 2 shows the temperature characteristics of the electrical resistance of the sample S, which was measured in advance in order to convert the electrical resistance measured by the above-described embodiment apparatus into an average temperature. In order to obtain this temperature characteristic in advance, the sample S was placed in the atmosphere of a hot air circulation type constant temperature bath. Measured by reference thermometer.

As is clear from FIG. 2, this sample S has a temperature range in which the relationship between its electrical resistance and temperature can be approximated by a linear equation. Here, since the sample used to create the calibration diagram in Figure 12 and the sample used to actually measure the thermal expansion coefficient have the same cross-sectional area, the unit of electrical resistance is Ω. / cm was used, but if both samples have the same length, the unit of electrical resistance may be expressed in Ω. Alternatively, if the cross-sectional area of the sample can be easily measured, it may be expressed in terms of volume resistivity.

Figure 3 shows the above-mentioned sample S (carbon fiber: Trading card T800
FIG. 2 is a characteristic diagram showing the relationship between the obtained length change and the average temperature when H) was measured using the embodiment apparatus shown in FIG. 1. In the figure, the ○ mark indicates the measured value obtained during the temperature rising process, and the Δ mark indicates the measured value obtained during the temperature decreasing process. The vertical axis represents the change value ΔL in the length of the sample S measured by the laser scanning micrometer 5 and the rate of change (ΔL/L×103) obtained by dividing this length change by the sample length before the temperature change. The horizontal axis is
A constant current I is applied to the sample S during the temperature raising or cooling process to the extent that the sample itself does not heat up, and the voltage value (■) at that time is measured.The resistance value R is determined from the relationship R=V/I. The resistance value was divided by the sample length L between voltage terminals b2 1 and b2 to obtain the resistance value per unit length [07 cm], and the resistance value was converted to temperature using the calibration diagram in Figure 2. It is something.

As is clear from FIG. 3, the coefficient of thermal expansion of this sample S is constant within the measurement temperature range, and it can be seen that the relationship between the length of the sample S and the temperature does not change when the temperature is increased or decreased.

From the measurement data obtained in this way, find the appropriate average temperature change (ΔT) of the sample S and the change in sample length (ΔL) at that time, and calculate the difference between the voltage terminals S, B2 before the temperature change. When the thermal expansion coefficient (α) was determined from the sample length (L), the thermal expansion coefficient of the sample S was −0.55×10 −6 . Incidentally, if the thermal expansion coefficient of the sample S is measured by setting a voltage terminal near the ends of the heating furnace 7 that are affected by temperature changes, the thermal expansion coefficient of the sample S will be The value became -0,58X10-'.

In addition, in the measuring device shown in FIG. 1, from the voltage value between two points (between voltage terminals b+ and bz in FIG. 1) that are not affected by temperature changes at both ends of the sample S, The average temperature of the sample S is determined by dividing the two points into smaller sections, detecting the voltage value in each section, determining the resistance value in each section, and calculating the average temperature in each section. Change ΔT1
．． ΔT2 ΔT3. The coefficient of thermal expansion α may be determined by converting them into the following equation and substituting them into the following equation.

ΔL-α1 ・Ll ・ΔT, 4-α2 ・L2 ・
ΔT2+α3 ・1,3 ・ΔT3+...=α(L
+ ・ΔT1+L2 ・ΔT2+L, ・ΔT3+
・・・） ・・・・・・(7) Here, α1−α
2-α3 (-α), L+, L2+'-'1+...
is the sample length before temperature change in each section.

[Effects of the Invention] As is clear from the above explanation, according to the method and apparatus for measuring the thermal expansion coefficient of a long sample according to the present invention, the influence of temperature changes at both ends of the long sample can be substantially suppressed. The resistance value between two points that are not affected by the temperature is measured, the resistance value is converted to the average temperature change of the sample S between the two points, and the coefficient of thermal expansion is calculated based on this average temperature change. It is possible to accurately measure the coefficient of thermal expansion of a long sample without being influenced by variations in the temperature distribution of the means or the temperature gradient at the end of the heating means.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the schematic configuration of a thermal expansion coefficient measuring device for a long sample according to an embodiment of the present invention, Fig. 2 is a temperature characteristic diagram of electrical resistance of the sample, and Fig. 3 is a diagram of the temperature characteristics of the sample A characteristic diagram showing the relationship between length change and average temperature change, and FIG. 4 is a schematic diagram showing the temperature distribution in the non-uniform temperature distribution region in the sample. S... Long sample 1... Support 2... Clamp mechanism 3... Weight 4... Marker 5... Laser scan micrometer 6... Display 7... Heating furnace 8 ...Furnace core tube 9...Constant current source 10...Voltage measuring device al+ a2...
・Current terminal 5 b+, bz...Voltage terminal 6

Claims (3)

[Claims] (1) With one end of a long sample fixed and tension applied to the other end, a temperature change is applied to the middle part of the sample in the longitudinal direction, and a sample is not substantially affected by this temperature change. Measure the electrical resistance between two points near both ends, convert this electrical resistance into the average temperature change (ΔT) of the sample, and calculate the difference between this average temperature change (ΔT) and the two points before applying the temperature change. The coefficient of thermal expansion (α) α=1/L・ΔL/ΔT is determined from the sample length (L) and the change in sample length (ΔL) caused by temperature change. Method for measuring thermal expansion coefficient of sample. (2) The method for measuring the coefficient of thermal expansion of an elongated sample according to claim (1), wherein the elongated sample is carbon fiber. (3) A fixing means for fixing one end of a long sample, a tension applying means for applying tension to the other end of the sample, and a heating means for surrounding an intermediate portion of the sample and applying a temperature change to the intermediate portion. , a detection means for detecting a change in position in the length direction of the tension-applying side end of the elongated sample, and a detection means for detecting a change in position in the length direction of the tension-applying side end of the elongated sample; An apparatus for measuring a coefficient of thermal expansion of a long sample, comprising: a current supply means for supplying current; and a voltage measurement means for measuring the voltage between the two points.