JPH0627288B2 - Strain gauge alloy and method for manufacturing strain gauge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to iron (Fe), chromium (Cr), cobalt (Co), tungsten (W), molybdenum (Mo), niobium (Nb) and tantalum.
The present invention relates to a method for producing a strain gauge alloy containing (Ta) element and a small amount of impurities, and a strain sensor using this alloy, the purpose of which is to heat at a temperature of 550 ° C or higher and 1000 ° C or lower after processing. It is to provide a manufacturing method for obtaining the maximum value 12 of the gauge factor by processing.

(Prior Art) Strain gauges (hereinafter simply referred to as gauges) are strain sensors for measuring strain and stress in civil engineering, machinery, various structures, etc. It has come to be used even in the fields of various measuring instruments and electronic scales for management.

The gauge is a thin metal wire (13 to 25 μmφ) or foil (thickness 3 to 5 μmt) formed in the shape of a grid or rosette, and the strain generated in the strainable body is attached to the strainable body with an adhesive. It is measured indirectly from the change in resistance of the gauge. The sensitivity of the gauge to strain is determined by the gauge factor K and is expressed by the following equation.

Here, R is the total resistance, σ is the Poisson's ratio, ρ is the specific electric resistance, and l is the total length.

By the way, in recent years, the demand for gauges has greatly increased with the progress of automation technology, but on the other hand, there is considerable room for improvement in the performance, stability or reliability of gauges. In particular, since the accuracy can be further improved by increasing the measurement resolution, it is strongly desired to develop a material having a large gauge factor.

Table 1 shows the gage characteristics (gauge ratio K, copper thermoelectromotive force Emf, specific electric resistance ρ, and temperature coefficient TCR of specific electric resistance) of major gauge materials that are currently known. In Table 1, there are Pt-Ir alloys, Pt-Rh-Pd alloys, pure platinum, pure nickel, semiconductors, etc. as the materials showing the above-mentioned purpose, that is, high gauge ratio, but the former three are very expensive, Pure nickel has not only poor linearity in the resistance-strain curve, but also has a very large TCR, and semiconductors have various drawbacks such as a large variation in gauge factor. The reality is that they have not been found.

(Problems to be Solved by the Invention) Previously, the inventors of the present invention proposed a Fe-Cr-Co alloy (Japanese Patent Publication No.
No. 29) and Fe-Cr-Co-W-Mo-Nb-Ta-based alloys (Japanese Patent Laid-open No. Sho 5)
No. 8-171557) was proposed as a material having a high gauge factor, but the maximum value of the gauge factor is about 6, and it is impossible to obtain a larger value by the above-mentioned method for producing the prior alloy. . Therefore, in order to find a material with a large gauge ratio, the inventors have conducted earnest research for the purpose of manufacturing a strain sensor having high sensitivity by improving the manufacturing method of the above-mentioned alloy of the prior application, and as a result, the gauge ratio is a prior application. We have succeeded in obtaining a value that is about twice as high as that obtained by the manufacturing method of the alloy.

That is, according to the conventional manufacturing method of the above-mentioned prior alloy, the area reduction rate is 1
%, The gauge characteristics are stabilized by heating the alloy cold-worked at a temperature of 400% or less at a temperature of 400 ° C. or less for 1 minute or more and 100 hours or less, and a relatively large gauge ratio of 2 to 5.7 is obtained. However, it has been known that heating at a high temperature of 400 ° C. or higher not only lowers the gauge factor of the prior alloy, but also deteriorates the oxidation resistance.
The reason for the decrease in gauge factor is that the alloy structure is α single phase over a wide composition range and does not change structurally even if it is heated above 400 ° C, but the internal strain due to processing gradually decreases. It is conceivable that this will reduce the gauge factor. However, if this internal strain can be increased by some method, the gauge factor may increase, so
First, the present inventors show Fe-Cr- at 20 ° C. shown in FIG.
As a result of studying the phase diagram of Co-based alloys, α-phase alloys in contact with ε-phase and γ-phase have the possibility of precipitation of ε-phase and μ-phase. Expected to increase the rate. It is considered that this effect is enhanced by adding other elements such as Mo, W, Nb or Ta.

As a result of various researches conducted by the present inventors based on the above concept, after cold working, heating is performed at 550 ° C. or higher, preferably 600 ° C. or higher and 1000 ° C. or lower for 1 minute or longer and 100 hours or shorter, and then cooled by an appropriate method. It has become clear that a maximum gauge factor of 12 is obtained.

(Means for Solving Problems) In the method for manufacturing the alloy for strain gauges of the present invention, the weight ratio of chromium is 3 to 35%, cobalt is 40% or less, and tungsten is 9% or less, molybdenum is 10 or less, niobium is 7% or less, An alloy containing a small amount of impurities of 0.01 to 15% in total of one or more selected from 10% or less of tantalum, the balance being substantially iron, and a reduction rate of 1% or more.
Cold-worked at 99.9% or less and further 550 ° C or more 10
It is characterized in that an alloy having a gauge factor of 3 or more is obtained by heating at a temperature of 00 ° C. or less for 1 minute or more and 100 hours or less.

The strain gauge manufacturing method of the present invention is selected from chromium 3 to 35% by weight, cobalt 40% or less, and tungsten 9% or less, molybdenum 10% or less, niobium 7% or less, tantalum 10% or less. One or two or more of these alloys containing 0.01 to 15% in total and a small amount of impurities, and the balance consisting essentially of iron.
Wire diameter obtained by cold working below 99.9% 0.05 to 0.02
After heat-treating the ultrafine wire of mm at a temperature of 550 ° C or more and 1000 ° C or less for 1 minute or more and 100 hours or less, and then arranging it in a desired shape of a grid or rosette on an electrically insulating thin film substrate, fixing and adhering it. Further, the curing is performed at a temperature of 400 ° C. or lower.

(Operation) The present invention will be described in detail below.

To produce the alloy of the present invention, Cr3 to 35% by weight,
Co0-40% and W9% or less, Mo10% or less, Nb7%
Below, alloys of one or more of Ta 10% or less 0.
An alloy consisting of 01 to 15% and the balance Fe is melted in air, preferably in a non-oxidizing atmosphere or in a vacuum using a suitable melting furnace, and a small amount (1% or less) of a deoxidizing agent and a desulfurizing agent is added. Then, impurities are removed as much as possible, and the mixture is sufficiently stirred to make the composition uniform.

This is then poured into a mold of suitable shape and size to obtain a sound ingot. Further, this ingot is subjected to cold working at a high temperature or a normal temperature by a method such as forging, rolling, or drawing to reduce the surface area by 1% or more and 99.9% or less, and a target shape, for example, an ultrafine wire with a diameter of 0.02 mmφ. Or thickness 0.02mm
The above foil material is prepared, and heat treatment is performed by heating the foil material in a vacuum, a reducing gas, or an inert gas at a temperature of 550 ° C. or more and 1000 ° C. or less for 1 minute or more and 100 hours or less to obtain a target sample. At this time, in the case of a heating furnace having a relatively low degree of vacuum, placing a gas absorbent having a strong activation force in the vicinity of the material will have a remarkable effect of preventing oxidation. Incidentally, the ultrafine wire or foil material obtained by the continuous casting method or liquid quenching method in the above-mentioned manufacturing method can obtain a high gauge ratio like the manufacturing method of the present invention by subjecting it to the heat treatment according to the present invention. Is possible.

Further, even when the ultrafine wire or foil material obtained by the above-mentioned manufacturing method is formed into a gauge shape and is attached to an object to be measured with an adhesive, the gauge characteristics are not different from those of the alloy material.

That is, an ultrafine wire having a wire diameter of 0.05 to 0.02 mm obtained by the above-mentioned processing method is heat-treated at a temperature of 550 ° C. or higher, preferably 600 ° C. or higher and 1000 ° C. or lower for 1 minute or longer and 100 hours or shorter, and then placed on an electrically insulating thin film substrate. After arranging in grid or rosette, fixing and adhering, add 40 more if necessary.
The gauge characteristics of the strain gauge cured at a temperature of 0 ° C. or lower exhibited the alloy characteristics sufficiently.

In addition, a foil material having a thickness of 25 to 1 μm obtained by the above processing method is
After heat treatment at a temperature of 50 ° C. or higher, preferably 600 ° C. or higher and 1000 ° C. or lower for 1 minute or longer and 100 hours or shorter, it is shaped into a grid or rosette by a photoresist method, laser trimming method or the like, and has electrical insulation properties. After placing, fixing and adhering on the thin film substrate, further 4 if necessary
The gauge characteristics of the strain gauge cured at a temperature of 00 ° C. or lower exhibited the alloy characteristics sufficiently.

Further, the strain gauge manufactured from the above ultrafine wire or foil material is also useful as a strain sensor for various measuring instruments, and is also applicable to load cells, electronic scales, pressure gauges, power factor meters, tensile testers, etc. to which this is applied. It is industrially advantageous to provide a manufacturing method capable of sufficiently exhibiting the characteristics of the alloy and capable of sufficiently satisfying the strict requirements of various industries.

Then, when the gauge characteristics of the alloy sample obtained by the above-mentioned manufacturing method were measured, K: 4-12, Em
f: ± 3 μV / ° C, ρ: 50 μΩ-cm or more and TCR: 1
A characteristic of 5 × 10 ⁻⁴ / ° C. or less is obtained.

Figures 1, 2, 3, and 4 show Fe-15% Cr-0.
70% Co alloy with W7%, Mo4%, Nb3% and Ta respectively
The change of the gauge rate with respect to the amount of Co when 5% is added is shown. The temperature in the figure indicates the optimum heat treatment temperature. FIG. 5 shows the composition dependency of the added amount of W, Mo, Nb, or Ta on the gauge factor.

(Example) Next, the Example of this invention is described.

Example 1 Alloy No. 121 (composition Fe = 56.1%, Cr = 14.0%, Co = 23.4
%, W = 6.5%) As a raw material, 99.97% pure electrolytic iron, 99.44% pure metallic chromium, 99.59% pure electrolytic cobalt and 99.9% pure metallic tungsten were used. In order to prepare a sample, the raw material was put into an alumina crucible in a total weight of 100 g and melted in a high frequency induction electric furnace in air while blowing argon gas on the surface to prevent oxidation. Then, the mixture was well stirred to form a homogeneous molten alloy. Next, this is 10 mm in inside diameter and 120 in height.
The ingot was cast into an iron mold of mm. The ingot was forged at 1000 ° C. to form a round bar having an outer diameter of 5 mm, further annealed at 1000 ° C., and then swaged and cold drawn to a diameter of 0.
The thickness was 5 mm, intermediate annealing was performed again at 1000 ° C., and cold drawing was performed to obtain an ultrafine wire having a diameter of 0.02 mm. Next, it was wound around a quartz bobbin with an outer diameter of 20 mm, and this was 400 to 120 in vacuum.
After holding at various temperatures of 0 ° C. for 1 hour, the sample was cooled in the furnace to room temperature. The gauge factors corresponding to the heat treatment temperature and the holding time of this sample are as shown in FIGS. 6 and 7, respectively. It can be seen from the curve (B) in FIG. 6 that the maximum value of the gauge factor of 11.5 is obtained at the heat treatment temperature of 850 ° C.

Example 2 Alloy No. 200 (Composition Fe = 53.0%, Cr = 14.4%, Co = 28.8
%, Mo = 3.8%) of the alloy is manufactured. The raw materials are iron, chromium and cobalt of the same purity as in Example 1 and 9
Molybdenum with 9.9% purity was used. The method for manufacturing the sample is the same as that in the first embodiment. The sample was subjected to the same heat treatment as in Example 1 to obtain the characteristics shown in FIGS. 8 and 9.
It can be seen from the curve (B) in FIG. 8 that the maximum value of the gauge factor of 9.5 is obtained at the heat treatment temperature of 700 ° C.

Example 3 Alloy No. 333 (Composition Fe = 53.4%, Cr = 14.6%, Co = 29.1
%, Nb = 2.9%) of the alloy is manufactured. The raw materials are iron, chromium and cobalt of the same purity as in Example 1 and 9
Niobium metal with a purity of 9.95% was used. The method for manufacturing the sample is the same as that in the first embodiment. The sample was subjected to the same heat treatment as in Example 1 to obtain the characteristics shown in FIG. 10 and FIG. It can be seen from the curve (B) in FIG. 10 that the maximum value of the gauge factor of 9.9 is obtained at the heat treatment temperature of 800 ° C.

Example 4 Alloy No. 402 (Composition Fe = 52.3%, Cr = 14.3%, Co = 28.6
%, Ta = 4.8%) of the alloy, and the raw materials were iron, chromium, and cobalt of the same purity as in Example 1 and 9
9.9% pure metal tantalum was used. The method for manufacturing the sample is the same as that in the first embodiment. The sample was subjected to the same heat treatment as in Example 1 to obtain the characteristics shown in FIGS. 12 and 13. It can be seen from the curve (B) in FIG. 12 that the maximum value of the gauge factor is 10.3 at the heat treatment temperature of 850 ° C.

Example 5 Alloy No. 555 (Composition Fe = 46.9%, Cr = 18.9%, Co = 26.7
%, W = 6.5%, Nb = 1.0%) of the alloy production raw material iron, chromium, cobalt of the same purity as in Example 1, 8
Ferrotungsten with 0.0% purity and ferroniobium with 64.1% purity were used. The method for manufacturing the sample is the same as that in the first embodiment. The sample was held in a hydrogen atmosphere at various temperatures of 400 to 1000 ° C. for 1 hour and then cooled in the furnace to room temperature. The characteristic curves of this sample are shown in FIGS. 14 and 15. It can be seen from the curve (B) in FIG. 14 that the maximum value of the gauge factor of 12.0 is obtained at the heat treatment temperature of 800 ° C.

The gauge characteristics of typical alloys belonging to the alloy region of the present invention are shown in Table 2.

As can be seen from FIGS. 1 to 15, Examples 1 to 5 and Table 2, the present invention has Cr3 to 35% and Co0.
-40% and W9% or less, Mo10% or less, Nb7% or less, Ta10% or less, one or more alloys 0.01
Area reduction of 1% or more to 99.9% for alloy consisting of ~ 15% and balance Fe
After being subjected to the following cold working, 550 ° C., preferably 600
According to the manufacturing method in which the heat treatment is performed for 1 minute or more and 100 hours or less at a temperature of up to 1000 ° C.
A value 2 to 3 times larger than that of heat treatment at 0 ° C or less 4
It is possible to obtain ~ 12, and the stability of the gauge characteristics becomes good. Furthermore, according to the above manufacturing method, the hardness is 500 in the processed state.
To 350 or less, but since it has an appropriate elasticity, it is convenient when used as a gauge.

Next, the reasons for limiting the numerical values such as the composition, working rate and heat treatment conditions of the alloy of the present invention will be described.

First, the composition of the alloy is Cr3 to 35%, Co is 40% or less, and W
9% or less, Mo 10% or less, Nb 7% or less, Ta 10% or less, a total of 0.01 to 15% of 1 or 2 or more and the balance.
As is clear from FIGS. 1 to 15, each of the examples and Table 2, the reason for limiting to Fe is such that the gauge ratio becomes 4 or less when the composition range deviates from the range, and the workability deteriorates, which is expected. This is because the requirements cannot be satisfied and it is unsuitable as a strain gauge alloy or strain sensor. Table 3 shows the relationship between the composition and various properties.

Further, in the method for producing the alloy of the present invention, the reduction rate of cold working is 1% or more and 99.9% or less, and the heating temperature is 550 ° C. or more and 1000
The reason why the heating temperature is limited to 1 ° C. or less and the heating time is 1 minute or more and 100 hours or less is as follows:
In addition, workability, manufacturing cost, and stability of gauge characteristics are seriously problematic, which makes it unsuitable as a method for manufacturing a strain gauge alloy. Table 4 shows the relationship between the manufacturing conditions and the gauge ratio, workability, manufacturing cost, and stability of gauge characteristics.

The reason for limiting the heat treatment temperature of the alloy of the present invention to 550 ° C to 1000 ° C is as follows. That is, the crystal structure was a body-centered cubic structure (BCC) when heat-treated at 400 ° C or lower, but a face-centered cubic structure (FCC) when the temperature exceeded 400 to 500 ° C.
Partly, the face-centered cubic structure increases as the heat treatment temperature increases, the degree of electron scattering increases, the resistance value increases, and the gauge factor K increases to K = 4 to 12 depending on the composition. is there.

However, if the heat treatment temperature exceeds 1000 ° C, the crystal structure becomes too many face-centered cubic structures, the crystal structure becomes homogeneous, the degree of electron scattering decreases, the resistance value decreases, and the gauge factor K decreases. It seems to do.

Such knowledge was first discovered by experiments, and is the opposite of what was imagined in the conventional technical common sense. I could not foresee it. This is shown in Figures 6, 8, 10, and 12 of the attached drawings.
This is shown in Figure 14 and Figure 14. In the present invention, the heat treatment temperature is limited to 550 ° C. or higher and 1000 ° C. or lower based on the above findings.

(Effects of the Invention) As described above, according to the present invention, a known Fe-Cr-Co alloy or Fe-Cr-Co-W is used.
-It is possible to provide a strain gauge alloy manufacturing method and a strain sensor having a gage factor more than twice as high and stability as compared with only the cold working method of Mo-Nb-Ta alloy. The strain sensor, the load cell, various scales and pressure gauges using the load cell, which are required to have high sensitivity and high stability, can sufficiently exhibit the characteristics of the alloy of the present invention.

[Brief description of drawings]

1 to 4 are characteristic charts showing the change of the gauge ratio with respect to the Co amount for alloys containing Fe-15% Cr-Co system with W, Mo, Nb or Ta, and Fig. 5 is Fe-15%. Cr-30% Co + [W, Mo, Nb or Ta]
Regarding the gauge factor of the alloy, the characteristic diagram showing the composition dependence of W, Mo, Nb or Ta addition, FIG. 6, FIG. 8, FIG. 10, FIG. 12 and FIG. 111, alloy number 5, 2
No. 00 and 212, alloy Nos. 5,333 and 301, alloy Nos. 5,402 and 444, and alloy Nos. 5 and 555, characteristic curve diagrams showing the relationship between the gauge rate and the heating temperature, FIG. 7, FIG. 9, FIG. Figures 13, 13 and 15 are characteristic diagrams showing the relationship between the gage factor of alloy Nos. 121, 200, 333, 402 and 555 and the holding time of heating, respectively, and Fig. 16 is Fe-Cr-Co at 20 ° C. It is a phase diagram of a system alloy.

Claims (3)

[Claims] 1. By weight ratio, chromium is 3 to 35% and cobalt is 40%.
The following are contained, and a small amount of impurities such as a total of 0.01 to 15% of one or two or more selected from the following: tungsten 9% or less, molybdenum 10% or less, niobium 7% or less, tantalum 10% or less, and the balance. An alloy consisting essentially of iron is cold-worked with a surface reduction rate of 1% or more and 99.9% or less, and further 550 ℃
A method for producing an alloy for strain gauges, which comprises heating at a temperature of 1000 ° C or lower for 1 minute or longer and 100 hours or shorter to obtain an alloy having a gauge ratio of 4 or higher. 2. Chromium 3 to 35% and cobalt 40% by weight
The following are contained, and a small amount of impurities such as a total of 0.01 to 15% of one or two or more selected from the following: tungsten 9% or less, molybdenum 10% or less, niobium 7% or less, tantalum 10% or less, and the balance. Wire diameter obtained by subjecting an alloy consisting essentially of iron to cold working with a surface reduction rate of 1% or more and 99.9% or less
Heat treatment of 0.05 to 0.02 mm ultrafine wire at a temperature of 550 ℃ or more and 1000 ℃ or less for 1 minute or more and 100 hours or less, and then place and fix it in a desired grid or rosette shape on the electrically insulating thin film substrate. A method for manufacturing a strain gauge having a high gauge ratio, which comprises curing at a temperature of 400 ° C. or lower after bonding. 3. Chromium 3 to 35% and cobalt 40% by weight
The following are contained, and a small amount of impurities such as a total of 0.01 to 15% of one kind or two or more kinds selected from the following, tungsten 9% or less, molybdenum 10% or less, niobium 7% or less, tantalum 10% or less, and the balance. Thickness obtained by cold working an alloy consisting essentially of iron with a surface reduction rate of 1% or more and 99.9% or less
After heat-treating a foil material of 25 to 1 μm at a temperature of 550 ° C. or more and 1000 ° C. or less for 1 minute or more and 100 hours or less, a grid-like or rosette-like desired processing method selected from the photoresist method or the laser trimming method is used. Processed into a shape,
This is placed and fixed on a thin film substrate having electrical insulation,
A method for manufacturing a strain gauge having a high gauge ratio, which comprises curing at a temperature of 400 ° C. or lower after bonding.