JP2002188965A - Thermocouple - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermocouple having excellent durability and excellent responsiveness in temperature measurement. SOLUTION: This thermocouple 1 dipped in molten metal 15 having a melting point <=120 deg.C for measuring temperature of the molten metal 15. The temperature sensing point of a thermocouple wire is faced and arranged inside the closed end of a heat resistant alloy sheath 2 having one closed end, and the heat resistant alloy sheath 2 is stored in a protective sheath 3, and the clearance S between the heat resistant alloy sheath 2 on the closed end side of the protective sheath 3 and the protective sheath 3 is filled and fixed with filler 4 comprising an inorganic compound or ceramic powder, and the heat resistant alloy sheath 2 on the open end side of the protective sheath 3 is supported and fixed with a support ring 6 having a bellows-shaped ring hole 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermocouple, and more particularly to a thermocouple used for measuring a temperature of a molten metal such as an Al molten metal.

[0002]

2. Description of the Related Art When a molten metal is discharged, the temperature of the molten metal is measured in order to determine whether or not the molten metal is completely melted, and the temperature of the molten metal is higher than a predetermined temperature. Is reached, the dissolution is considered complete. A thermocouple is generally used for this temperature measurement.

Here, in order to measure the temperature of a molten metal having a melting point of 1200 ° C. or less, such as Al, an Al alloy, and an Sn alloy, a thermocouple element made of chromel alumel, iron constantan, or the like is made of a stainless steel prepared by a squeeze method or the like. In addition, a housing type thermocouple which is housed and arranged in a heat-resistant alloy sheath containing the same, and in which magnesia powder is filled in the sheath, and a bare type thermocouple using a bare chromel alumel wire are mainly used. In addition, a housing type thermocouple using a ceramic sheath instead of a heat-resistant alloy sheath is also used.

[0004]

Incidentally, in a storage type thermocouple (or a bare thermocouple) using a heat-resistant alloy sheath, a heat-resistant alloy sheath (or a bare thermocouple element wire) is immersed in a molten metal. This causes a corrosion reaction. This corrosion gradually progresses with repeated immersion, and eventually leads to a decrease in the replacement life (durability) of the sheath (or thermocouple wire). There was a problem that would not be.

Therefore, as a method for suppressing the corrosion reaction, there is a method in which ceramic powder is applied to the surface of a heat-resistant alloy sheath or the surface of a thermocouple wire.
Scattering of the ceramic powder causes deterioration of the work site environment.

[0006] Further, in the storage type thermocouple using the ceramic sheath, there is a problem that the response at the time of temperature measurement is not so good because there is heat insulation between the ceramic sheath and the thermocouple wire.

Further, in the housed thermocouple, cracks or the like are generated in the heat-resistant alloy sheath or the ceramic sheath as the temperature of the molten metal is repeatedly measured. The wire causes a corrosion reaction with the molten metal. As a result, accurate temperature measurement cannot be performed, and the replacement life of the thermocouple wire is shortened.

An object of the present invention, which has been made in view of the above circumstances, is to provide a thermocouple having good durability and responsiveness at the time of temperature measurement.

[0009]

In order to achieve the above object, a thermocouple according to the present invention is a thermocouple used for measuring the temperature of a molten metal, wherein a thermocouple wire is provided inside a closed end of a heat-resistant alloy sheath having one end closed. The heat-resistant alloy sheath is placed inside the protective sheath, and the gap between the heat-resistant alloy sheath and the protective sheath at the closed end of the protective sheath is filled with a filler made of an inorganic compound or ceramic powder. The heat-resistant alloy sheath on the open end side of the protective sheath is fixed and supported and fixed by a support ring having a bellows-like ring hole.

A thermocouple according to another embodiment is a thermocouple used for measuring the temperature of a molten metal, in which a temperature measuring point of a thermocouple wire faces a closed end of a heat-resistant alloy sheath having one end closed. The heat-resistant alloy sheath is housed in the protective sheath, and the gap between the heat-resistant alloy sheath and the protective sheath on the closed end side of the protective sheath is filled and fixed with a filler made of an inorganic compound or ceramic powder, and protected. Fix the heat-resistant alloy sheath on the open end side with a support ring having a bellows-shaped ring hole, connect one conductor to the heat-resistant alloy sheath, immerse and connect the other conductor to the molten metal, and measure the resistance of each conductor. Connected to the container.

According to the above construction, the heat-resistant alloy sheath is housed in the protective sheath to improve durability, and the gap between the heat-resistant alloy sheath and the protective sheath at the closed end of the protective sheath is filled with the filler. Thereby, the responsiveness at the time of temperature measurement is improved. Further, by connecting and dipping each lead wire of the resistance measuring device in the heat-resistant alloy sheath and the molten metal, it is possible to detect the presence or absence of abnormality in the protective sheath.

The protective sheath and the support ring on the open end side of the protective sheath are fixed with an adhesive made of an inorganic compound.

Preferably, the inorganic compound is made of a dehydration-condensation type glass and contains O, Mg, Al, and P.

Further, the ceramic powder preferably contains at least O and Mg.

The protective sheath is made of Si_Three N_Four The main component
And Al_Two O_Three , Y_Two O_Three , Ta _Two O_Five Of TiN
Formed of a ceramic material containing at least one of
Things.

The protective sheath is made of Si_Three N_Four The main component
And Al_Two O_Three , Y_Two O_Three , Ta _Two O_Five Of TiN
Containing at least one of the following, and having conductivity
It is formed of a mic material.

Further, the thermocouple wire is chromel alumel,
It is formed of chromel constantan, iron constantan, or copper constantan.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic sectional view of a thermocouple according to the first embodiment.

As shown in FIG. 1, a thermocouple 1 according to the first embodiment includes a thermocouple wire (see FIG. 1) inside a closed end (lower end in FIG. 1) of a heat-resistant alloy sheath 2 having one end closed. (Not shown), the heat-resistant alloy sheath 2 is accommodated in the protective sheath 3, and the heat-resistant alloy sheath 2 on the closed end (lower end in FIG. 1) side of the protective sheath 3 is protected. The gap S of the sheath 3 is filled and fixed with a filler 4 made of an inorganic compound (or ceramic powder), and the heat-resistant alloy sheath 2 on the open end (upper end in FIG. 1) of the protective sheath 3 is provided with a bellows-shaped ring hole. It is supported and fixed by a support ring 6 having a support ring 5. A temperature indicator 13 is connected to the thermocouple wire on the open end (the upper end in FIG. 1) of the heat-resistant alloy sheath 2.

The protective sheath 3 and the support ring 6 on the open end side of the protective sheath 3 are made of an adhesive (not shown) made of an inorganic compound.
It is fixed at. Since the heat-resistant alloy sheath 2 is formed sufficiently longer than the protective sheath 3, the heat-resistant alloy sheath 2 protrudes from the support ring 6, and the protruding portion 2a
Is covered with a protective tube 11. Further, the open end side of the heat-resistant alloy sheath 2 is supported and fixed by an upper support ring 12 having a ring hole (not shown).

The constituent material of the heat-resistant alloy sheath 2 is a material having heat resistance to the melting temperature of the molten metal to be measured, more specifically, a material having heat resistance to a temperature of 1200 ° C. or less. There is no particular limitation, and examples include stainless steel.

The protective sheath 3 is mainly composed of Si ₃ N ₄ (silicon nitride), and is made of Al ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O.
_5. It is formed of a ceramic material containing at least one of TiN.

Examples of the inorganic compound constituting the filler 4 and the adhesive include a dehydration-condensation type glass containing O, Mg, Al and P. In addition, examples of the ceramic powder constituting the filler 4 include ceramics containing at least O and Mg.

The support ring 6 has a ring hole 5 formed in a bellows shape in order to absorb the thermal expansion of the heat-resistant alloy sheath 2, and at least the ring hole 5 has good heat resistance and flexibility. It is formed of a material, for example, stainless steel.

The thermocouple wires include chromel alumel wire, chromel constantan wire, iron constantan wire,
Or a copper constantan wire is mentioned.

As a constituent material of the protective tube 11, a material having heat resistance equal to or substantially equal to the constituent material of the heat-resistant alloy sheath 2 is preferable, for example, stainless steel.

Next, the operation of the present invention will be described.

The tip of the thermocouple 1 according to the present invention is connected to the melting furnace 1
The temperature of the molten metal 15 is measured by immersing it in the molten metal 15 in 4 and measuring the thermoelectromotive force value, and converting the temperature of the thermoelectromotive force value. At this time, in the thermocouple 1, the protective sheath 3 actually comes into contact with the molten metal 15.

In the thermocouple 1 according to the present invention, the protective sheath 3 is formed of a ceramic material containing silicon nitride as a main component. Since silicon nitride has poor wettability to the molten metal 15, the molten metal 15 hardly adheres to the protective sheath 3. Therefore, the thermocouple 1 is connected to the molten metal 15.
Even if the protective sheath 3 is repeatedly immersed, the corrosion of the protective sheath 3 hardly progresses, and the replacement life of the thermocouple 1 can be extended, that is, the durability can be improved.

In addition, the conventional thermocouple using a ceramic sheath has a problem that the temperature measurement response is not good. Therefore, in the thermocouple 1 according to the present invention, the thermocouple wire is housed in the heat-resistant alloy sheath 2, and the heat-resistant alloy sheath 2 has a double sheath structure housed in the protective sheath 3. The gap S between the heat-resistant alloy sheath 2 and the protective sheath 3 on the closed end side is filled with a filler 4 made of an inorganic compound (or ceramic powder). The protective sheath 3 and the heat-resistant alloy sheath 2 are integrated by the filler 4, and the heat of the molten metal 15 is not insulated, but is directly transmitted from the protective sheath 3 → the filler 4 → the heat-resistant alloy sheath 2 to the thermocouple element. Conducted to the wire. Therefore, the thermocouple 1 according to the present invention has a temperature measurement response substantially equal to or higher than that of the housed thermocouple using the conventional heat-resistant alloy sheath.

Next, a thermocouple according to a second embodiment will be described with reference to FIG.

The thermocouple 21 according to the second embodiment differs from the thermocouple 1 according to the previous embodiment shown in FIG.
3a, which is connected to a resistance measuring device 23 having a comparison inspection function.
“a” faces the heat-resistant alloy sheath 2 and the other conductive wire 24 b faces the metal melt 15, that is, is connected to a terminal 25 provided by immersion.

Next, the operation of the present embodiment will be described with reference to FIGS.

After the thermocouple 21 according to the present embodiment is immersed in the molten metal 15, prior to the temperature measurement, the resistance measuring device 2 is used.
3 to start measuring the loop resistance (Step 4)
1). At this time, the loop resistance value Rs when the thermocouple 21 is normal is measured in advance (step 42).

Next, the loop resistance value R1 is measured (step 43), and the loop resistance value R1 is compared with the previously measured loop resistance value Rs (step 44).
The presence or absence of an abnormality such as a crack in the protective sheath 3 of the thermocouple 21 can be detected. At this time, both resistance values Rs, R1
Are substantially equal, it means that the protective sheath 3 is normal and normal. Conversely, if there is a difference between the two resistance values Rs, R1, that is, if the measured loop resistance value R1 is smaller, it means that there is an abnormality in the protective sheath 3.
The difference between the two resistance values Rs and R1 is caused by the fact that the temperature is repeatedly measured to cause a crack or the like in the protective sheath 3. This is because conduction occurs between 24a and 24b.

After comparing the two resistance values Rs and R1 (step 44), if the two resistance values Rs and R1 are substantially equal (step 44a), it is determined that the state is normal (step 45), and the temperature measurement of the molten metal 15 is continued. Continue (step 46).

Conversely, after comparing the two resistance values Rs and R1 (step 44), if the loop resistance value R1 is smaller (step 44b), the alarm 7 such as a lamp or a buzzer is activated.
, An abnormality is detected (step 47), and the measurement is temporarily stopped (step 48). Thereafter, the thermocouple 21 (or only the protective sheath 3) is replaced with a new one (step 4).
9) The new thermocouple 21 (or the thermocouple 21 in which only the protective sheath 3 has been replaced with a new one) is immersed in the molten metal 15 and the process returns to step 41 again to detect the abnormality of the thermocouple 21 again.

Next, a thermocouple according to a third embodiment will be described with reference to FIG.

As shown in FIG. 3, a thermocouple 31 according to the third embodiment has the same configuration as the thermocouple 21 according to the second embodiment shown in FIG. The protective sheath 33 is formed of a ceramic material having the following.

More specifically, the protective sheath 33 is made of Si
₃ N ₄ as a main component, Al ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O
_5. It is formed of a conductive ceramic material containing at least one of TiN.

Next, the operation of the present embodiment will be described with reference to FIGS.

After the thermocouple 31 according to the present embodiment is immersed in the molten metal 15, prior to the temperature measurement,
3 to start measuring the loop resistance (step 5).
1). At this time, the loop resistance Ra when the thermocouple 31 is normal is measured in advance (step 52). Here, since the protective sheath 33 has conductivity, the thermocouple 3
The loop resistance value Ra of 1 is smaller than the loop resistance value Rs of the thermocouple 21 of the previous embodiment. Further, since the protective sheath 33 has conductivity, conduction is detected by immersing the thermocouple 31 in the molten metal 15, and the loop resistance Ra at the time of detecting the conduction indicates that the surface of the molten metal 15 is molten. You can know the position.

Next, the loop resistance R2 is measured (step 53), and the loop resistance R2 is compared with the previously measured loop resistance Ra (step 54).
The presence or absence of an abnormality such as a crack in the protective sheath 33 of the thermocouple 31 can be detected. At this time, both resistance values Ra and R
When 2 is substantially equal, there is no abnormality in the protective sheath 33 and it is normal. Conversely, if there is a difference between the two resistance values Ra and R2, that is, if the measured loop resistance value R2 is smaller, it means that there is an abnormality in the protective sheath 33. The difference between the two resistance values Ra and R2 is similar to the difference between the two resistance values Rs and R1 described above, and the resistance between the conductors 24a and 24b slightly changes (decreases). It is.

After comparing the two resistance values Ra and R2 (step 54), if the two resistance values Ra and R2 are substantially equal (step 54a), it is determined that the state is normal (step 55), and the temperature of the molten metal 15 is directly measured. Continue (step 56).

Conversely, after comparing the two resistance values Ra and R2 (step 54), if there is a difference between the two resistance values Ra and R2 (step 54b), the magnitudes of the two resistance values Ra and R2 are compared (step 54b). Step 57) If the loop resistance value R2 is smaller than Ra (Step 57b), an abnormality is detected by the alarm 7 such as a lamp or a buzzer (Step 59), and the measurement is suspended (Step 60). After that, thermocouple 3
1 (or only the protective sheath 33) is replaced with a new one (step 61), and a new thermocouple 31 (or the thermocouple 31 with only the protective sheath 33 replaced with a new one) is immersed in the molten metal 15 and step 51 is performed again. Then, the presence or absence of abnormality of the thermocouple 31 is detected again.

On the other hand, when the molten metal 15 is discharged from the tapping port 16 of the melting furnace 14, the molten metal surface 15a falls. However, as the molten metal surface 15a decreases, the measured loop resistance value R2 decreases. It is getting bigger and bigger. Therefore, even if there is no abnormality in the protection tube 33, if the loop resistance value R2 increases due to the decrease of the molten metal surface 15a, the step 5
With only the determination of 4, it is determined that the protection tube 33 has an abnormality.

Therefore, when the molten metal 15 is sufficiently filled in the melting furnace 14, the loop resistance value Rm in that state is measured in advance (not shown). After the tapping is repeated and the level 15a is lowered, the two resistance values Ra and R2 are compared (step 54). If there is a difference between the two resistance values Ra and R2 (step 54b), the two resistance values Ra and R2 are obtained. Are compared (step 57). At this time, the loop resistance R
If 2 is equal to or greater than Ra (step 57a), both resistance values R
A comparison is made between 2 and Rm (step 58). If the loop resistance value R2 is equal to or less than Rm (step 58a), it is determined to be normal (step 55), and the temperature measurement of the molten metal 15 is continued (step 56). Conversely, if the loop resistance value R2 is larger than Rm (step 58b), an abnormality is detected by the alarm 7 such as a lamp or a buzzer (step 59), and the measurement is suspended (step 6).
0). Thereafter, as described above, the appropriate members are replaced, and the process returns to step 51 again to detect whether or not the thermocouple 31 is abnormal.

By using the flow described above,
Even if the amount of the molten metal 15 in the melting furnace 14 changes over time and the loop resistance value R2 changes, it is possible to reliably detect the presence or absence of an abnormality in the thermocouple 31 of the present embodiment.

[0050]

(Example 1) The temperature of a molten aluminum at 700 ° C. was measured using the thermocouple according to the present invention described above. Here, a stainless steel sheath made of SUS310S is used as a constituent material of the heat-resistant alloy sheath, and Si ₃ N ₄ is used as a main component as a constituent material of the protective sheath, and Al ₂ O ₃ and Y ₂ O _{3 are used.}
, Ta ₂ O ₅ , a dehydration-condensed glass as a filler, and a chromel alumel wire as a thermocouple wire. (Comparative Example 1) The temperature of an Al molten metal at 700 ° C was measured using a storage type thermocouple using a conventional heat-resistant alloy sheath. Here, the material of the heat-resistant alloy sheath is SUS310S
A magnesia powder was used as a filler, and a chromel alumel wire was used as a thermocouple wire.

The responsiveness and durability of each thermocouple of Example 1 and Comparative Example 1 were evaluated. Here, the response at the time of temperature measurement was evaluated based on the time until the thermoelectromotive force value was stabilized, that is, the time until the display temperature of the temperature indicator was stabilized. The durability was evaluated based on the number of times the thermocouple was used when the temperature measurement was repeatedly performed.

FIG. 5 shows the relationship between the immersion time of each thermocouple of Example 1 and Comparative Example 1 and the display temperature.
FIG. 6 shows the number of times the respective thermocouples can be used. Here, the horizontal axis in FIG. 5 indicates the elapsed time (sec) from the start of immersion, the vertical axis indicates the display temperature (° C.) of the temperature indicator, and the square mark in FIG. The mark indicates Comparative Example 1.

As shown in FIG. 5, when the temperature was measured using the thermocouple of Example 1, the displayed temperature was about 3 from the start of immersion.
The temperature rises rapidly in seconds, and 700 seconds after the start of immersion.
It was almost stable at ° C. In contrast, when the temperature was measured using the thermocouple of Comparative Example 1, the displayed temperature was about 8
Gradually rises for about 10 seconds, and reaches 70
It was almost stable at 0 ° C. That is, when the temperature was measured using the thermocouple of Example 1, the response time until the display temperature was stabilized was less than half that of the case where the temperature was measured using the thermocouple of Comparative Example 1. It was confirmed that the device had excellent responsiveness.

As shown in FIG. 6, when temperature measurement is performed using the thermocouple of the first embodiment, accurate temperature measurement is still possible even if the cumulative number of temperature measurements reaches 4000. At the same time, adhesion of the molten aluminum to the protective sheath was not observed. In contrast, when temperature measurement was performed using the thermocouple of Comparative Example 1, when the cumulative number of temperature measurements reached 400, corrosion of the heat-resistant alloy sheath prevented further temperature measurement. It has become possible. That is, the service life of the thermocouple of Example 1 was at least 10 times the service life of the thermocouple of Comparative Example 1, and it was confirmed that the thermocouple had excellent durability.

As described above, the embodiments of the present invention are not limited to the above-described embodiments, and it is needless to say that various other embodiments are also conceivable.

[0056]

In summary, according to the present invention, the following excellent effects are exhibited. (1) By storing the heat-resistant alloy sheath in which the thermocouple wires are stored in the protective sheath, the heat-resistant alloy sheath does not come into direct contact with the molten metal, and the durability is improved. (2) By filling the gap between the heat-resistant alloy sheath and the protective sheath on the closed end side of the protective sheath with a filler, the heat-resistant alloy sheath and the protective sheath are integrated, and the response at the time of temperature measurement is improved.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a thermocouple according to first and second embodiments.

FIG. 2 is a flowchart of a loop resistance measuring method using a thermocouple according to a second embodiment.

FIG. 3 is a schematic sectional view of a thermocouple according to a third embodiment.

FIG. 4 is a flowchart of a loop resistance measuring method using a thermocouple according to a third embodiment.

FIG. 5 is a diagram showing the relationship between the immersion time of each thermocouple and the display temperature in Example 1 and Comparative Example 1.

FIG. 6 is a diagram showing the number of service times of each thermocouple of Example 1 and Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermocouple 2 Heat-resistant alloy sheath 3 Protective sheath 4 Filler 5 Ring hole 6 Support ring 15 Metal melt 23 Resistance measuring device 24a, 24b Conducting wire S Gap

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuo Osumi, 8 clay bowls at Fujisawa City, Kanagawa Prefecture Inside Isuzu Ceramics Research Institute Co., Ltd. (72) Inventor Hideki Kita 8 clay bowls at Fujisawa City, Kanagawa Prefecture Isuzu Ceramics Co., Ltd. F term in the laboratory (reference) 2F056 BP01 BP03 BP06 BP07 KC02 KC06 KC08 KC11 KC18

Claims (8)

[Claims] 1. A thermocouple used for measuring a temperature of a molten metal, wherein a thermocouple wire is disposed inside a closed end of a heat-resistant alloy sheath having one end closed so as to face a temperature measuring point of a thermocouple wire, and the heat-resistant alloy sheath is protected by a protective sheath. The gap between the heat-resistant alloy sheath and the protective sheath at the closed end of the protective sheath is filled and fixed with a filler made of an inorganic compound or a ceramic powder, and the heat-resistant alloy sheath at the open end of the protective sheath is bellows-shaped. A thermocouple characterized by being supported and fixed by a support ring having a ring hole. 2. A thermocouple used for measuring the temperature of a molten metal, wherein a thermocouple wire is arranged inside a closed end of a heat-resistant alloy sheath having one end facing the temperature measuring point of the thermocouple wire, and the heat-resistant alloy sheath is protected by a protective sheath. The gap between the heat-resistant alloy sheath on the protective sheath closed end side and the protective sheath is filled and fixed with a filler made of an inorganic compound or ceramic powder, and the heat-resistant alloy sheath on the protective sheath open end side is bellows-shaped. A thermocouple characterized by being fixed with a support ring having a ring hole, connecting one conductor to a heat-resistant alloy sheath, immersing and connecting the other conductor to a molten metal, and connecting each conductor to a resistance measuring instrument. . 3. The protective sheath and the support ring on the open end side of the protective sheath are fixed with an adhesive made of an inorganic compound.
Or the thermocouple according to 2. 4. The thermocouple according to claim 1, wherein the inorganic compound is a dehydration-condensation type glass and contains O, Mg, Al, and P. 5. The thermocouple according to claim 1, wherein the ceramic powder contains at least O and Mg. 6. The protective sheath is formed of a ceramic material mainly composed of Si ₃ N ₄ and containing at least one of Al ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ and TiN. The thermocouple according to any one of 1 to 5. 7. The protective sheath is mainly composed of Si ₃ N ₄ , contains at least one of Al ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , and TiN, and has conductivity. The thermocouple according to any one of claims 1 to 5, wherein the thermocouple is formed of a ceramic material. 8. The thermocouple according to claim 1, wherein the thermocouple element wire is formed of chloromer alumel, chromel constantan, iron constantan, or copper constantan.