JPH0658816A - Consuming type optical fiber temperature measuring apparatus - Google Patents

Abstract

PURPOSE:To measure temperature at a high accuracy by enabling stable insertion into molten metal to lower consumption of an optical fiber. CONSTITUTION:A tip part of a double-sheathed optical fiber 1 covered with a protective tube 12 and a heat insulating material 13 is made to act as temperature measuring section. When the tip part of the double-sheathed optical fiber 1 is inserted into a molten metal or in measurement, the optical fiber 11 is protected with the protective tube 12 and the heat insulating material 13 to reduce consumption of the optical fiber. When the measurement is repeated, light energy obtained at the final end of the optical fiber 11 is corrected from an initial length of the optical fiber, a loss per unit length and a change in the feeding of the optical fiber for each measurement thereby removing changes in transmission loss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a consumable optical fiber temperature measuring device for measuring the temperature of high temperature liquid metal such as molten steel.

[0002]

2. Description of the Related Art In a continuous casting process, for example, it is necessary to accurately know the temperature of molten steel and the level of molten steel during casting in order to improve quality and yield of production. Conventionally,
As a method for measuring the temperature of molten steel in a tundish or mold, a solidification chamber into which molten steel flows is provided inside the carbon sleeve, and a consumable immersion thermocouple with a thermocouple attached to this solidification chamber, Contact thermometers using thermocouples covered with ceramic protective tubes are used.

The consumable immersion thermocouple is deteriorated by one measurement because the thermocouple directly contacts the molten steel. For this reason, the temperature measuring probe at the tip is detachable, and this temperature measuring probe is exchanged for each measurement. As described above, since the expensive temperature measuring probe is disposable after each measurement, it is difficult to increase the number of times of measurement.

Further, when the thermocouple is covered with a ceramic protective tube, the thermocouple does not directly contact the molten steel, so that the measurement can be continuously performed. However, even in this case, there is a limit to the durability of the ceramic protection tube due to heat shock, melting damage due to slag, etc.
It lasted only about 100 hours and could not be used repeatedly for a long time.

In order to solve such a problem, for example, a molten metal immersion thermometer in which the tip of an optical fiber is continuously inserted into a molten metal and an infrared ray sensor detects an infrared ray passing through the optical fiber is known. It is disclosed in Kaisho 62-19727.

[0006]

In the above molten metal immersion thermometer, the optical fiber is continuously inserted into the molten steel while gradually descending at a speed of 300 mm / hour. When the ordinary vinyl-coated optical fiber is brought close to the molten steel surface, the coating starts to burn and only the core wire of the optical fiber is left, resulting in a marked decrease in strength.
On the other hand, there are layers of slag and powder on the surface of molten steel. If this layer is torn and inserted with an optical fiber having a reduced strength, the optical fiber is easily broken and it is difficult to immerse the optical fiber in the molten steel.

Further, when the energy of light sent from the start end to the end of the optical fiber is measured by a general monochromatic radiation thermometer,
When the length of the optical fiber becomes shorter, the transmission loss of the optical fiber becomes smaller, and the temperature indicated by the thermometer rises from the initial value, causing an error. For example, a Si optical detector is used, and a GI fiber (50/125 μm) made of quartz for communication is used for 1500
When the temperature of ° C is measured, the error becomes 10 to 15 ° C when the length of the optical fiber differs by 100 m. Therefore, when the temperature of the molten steel is measured while gradually feeding the amount of heat consumed by the optical fiber, the temperature error gradually increases, and it is difficult to obtain a predetermined temperature accuracy.

The present invention has been made in order to solve the above disadvantages, and it is possible to stably insert the molten metal into the molten metal, and to prevent the occurrence of temperature error due to the consumption of the optical fiber and to perform the measurement with high accuracy. The purpose of the present invention is to obtain a consumable optical fiber temperature measuring device.

[0009]

SUMMARY OF THE INVENTION A consumable optical fiber temperature measuring device according to the present invention comprises a temperature measuring section at the tip of a double coated optical fiber in which an outer surface of a protective tube coated with the optical fiber is coated with a heat insulating material. The optical fiber has a melting temperature higher than the temperature of the molten metal to be measured, and the protective tube and the heat insulating material have a heat resistant temperature lower than the temperature of the molten metal to be measured.

The protective tube is preferably a metal tube having a higher heat resistance temperature than the heat insulating material.

Further, an optical fiber conveying means for intermittently sending and rewinding the double-coated optical fiber to the surface of the molten metal, and optical energy obtained at the end of the optical fiber with a predetermined initial length of the optical fiber. It is characterized by comprising a correction means for correcting the loss per unit length and the change in the feed amount of the optical fiber for each measurement detected by the optical fiber conveying means.

[0012]

In this invention, the tip end of the double coated optical fiber coated with the protective tube and the heat insulating material is inserted into the molten metal as a temperature measuring portion. When the tip of the double coated optical fiber is inserted into the molten metal, the optical fiber is covered with the protective tube, so that the optical fiber itself can be inserted without damage.

Further, since the optical fiber has a melting temperature higher than the temperature of the molten metal to be measured, and the protective tube and the heat insulating material have a heat resistance temperature lower than the temperature of the molten metal to be measured, the double coating is applied. When the optical fiber is inserted into the molten metal,
At the tip of the double-coated optical fiber, the heat insulating material on the outer side is first burned to expose the protective tube, and then the protective tube is burned to expose the optical fiber. The temperature of the molten metal is detected from the energy of light incident from the exposed optical fiber.

The protective tube is formed of a metal tube having a heat resistance higher than that of the heat insulating material, and a delay time is provided from the burning of the heat insulating material at the tip to the melting of the protective tube to protect the tip of the optical fiber. A uniform temperature is applied to the entire tip of the optical fiber.

When the double-coated optical fiber is inserted into the molten metal in this way, the tip of the optical fiber is melted and consumed.
Therefore, if the double coated optical fiber is continuously inserted into the molten metal, the amount of consumption of the optical fiber increases. Therefore, the double coated optical fiber is intermittently inserted into the molten metal while being sent out and rewound by the optical fiber conveying means.

When the tip portion of this double-coated optical fiber is worn out sequentially, the total length of the optical fiber becomes shorter, the transmission loss of the optical fiber becomes smaller, and the energy of the light emitted from the terminal end of the optical fiber becomes larger, resulting in a measured value. It rises and causes an error. Therefore, the optical energy obtained at the end of the optical fiber is determined from the initial length of the optical fiber determined by the correction means and the loss per unit length, and the change in the feed amount of the optical fiber for each measurement detected by the optical fiber conveying means. Correct to eliminate the change in transmission loss.

[0017]

1 is a block diagram showing an embodiment of the present invention. As shown in the figure, for example, a temperature measuring device for measuring the temperature of molten steel includes a double coated optical fiber 1 wound around a supply drum 2, an optical fiber conveying means 3, a feeding control means 4 and a signal processing section 5. Have.

The double coated optical fiber 1 is used as a temperature measuring section as well as a light transmission path, and the optical fiber 11 of the core wire is made of silica glass GI fiber, and as shown in FIG. Formed by coating the outer surface of an optical fiber 11 coated with cross-linked plastic with a protective tube 12 made of a stainless tube, and coating the outer surface of the protective tube 12 with a heat insulating material 13 made of a synthetic resin such as polyethylene or glass fiber. Has been done.

The optical fiber conveying means 3 feeds the double-coated optical fiber 1 wound around the supply drum 2 continuously or intermittently at a constant speed while feeding the tip of the double-coated optical fiber 1 from the upper part of the powder 6. After being inserted into the molten steel 7, the double-coated optical fiber 1 is rewound and a tip portion is pulled out from the molten steel 7 after a lapse of a certain time. The feeding control means 4 drives intermittently while controlling the feeding amount of the optical fiber feeding means 3.

The signal processing section 5 includes an optical detector 51 and a correction means 5.
2. It has a storage means 53, a peak-hold circuit 54, a recording means 55 and a display means 56. The optical detector 51 outputs an electric signal proportional to the power of the incident light, and its input section is connected to the terminal section of the double-coated optical fiber 1. The storage means 53 stores the initial length L ₀ of the double-coated optical fiber 1 and the loss α per unit length. The correction means 52 influences the electric loss of the electric signal sent from the optical detector 51 for each measurement due to the change of the transmission loss of the optical fiber 11, and the initial length L ₀ of the double coated optical fiber 1 stored in the storage means 53.
And loss per unit length α and change ΔL in the feed amount of the double coated optical fiber 1 sent from the feed control means 4 for each measurement.
n, that is, the amount of wear of the tip portion of the double-coated optical fiber 1 is used for correction. The peak hold circuit 54 detects the peak value of the signal sent from the correction means 52 and holds it for a certain period of time.

In measuring the temperature of the molten steel 7 with the temperature measuring device constructed as described above, the initial length L ₀ and the loss per unit length of the double coated optical fiber 1 wound around the supply drum 2 in advance. α is measured and stored in the storage means 53. After that, while feeding the double-coated optical fiber 1 by the optical fiber conveying means 3, the tip end portion of the double-coated optical fiber 1 is inserted into the molten steel 7 from the upper part of the powder 6. When an ordinary optical fiber is inserted into the molten steel 7, the coating layer of the optical fiber burns out even if the tip is brought close to the molten steel 7, and the optical fiber itself breaks when passing through the powder 6. Since the coated optical fiber 1 covers the optical fiber 11 with the protective tube 12 made of a stainless tube and the heat insulating material 13, the heat insulating material 13 is thermally decomposed when the tip of the double coated optical fiber 1 passes through the powder 6. It takes a certain amount of time for the heat insulating material 13 to disappear,
The protective tube 12 can be stably inserted into the molten steel 7 without damaging it.

When the tip of the double coated optical fiber 1 is inserted into the molten steel 7 having a temperature of 1500 ° C. or higher in this way, the temperature of the tip of the double coated optical fiber 1 rises sharply and The strength of the heat insulating material 13 suddenly decreases and begins to burn out, and the protective tube 12 is gradually exposed from the tip. Since the protective tube 12 is formed of a stainless tube having a melting point of approximately 1400 to 1430 ° C., it begins to melt when exposed in the molten steel 7 having a temperature of 1500 ° C. or higher, and as shown in the cross-sectional view of FIG. Is gradually exposed from the tip.

Light depending on the temperature of the molten steel 7 is immediately incident from the exposed tip of the optical fiber 11. This light is sent to the signal processing unit 5 through the double coated optical fiber 1,
It is converted into an electric signal and converted into temperature.

When the tip of the double coated optical fiber 1 is inserted into the molten steel 7 in this way, the optical fiber 11 is exposed from the tip after a time lag between the heat insulating material 13 and the protective tube 12 melting. The tip of the optical fiber 11 can be held at a position where the molten steel 7 has a constant depth. Moreover, the optical fiber 11 has a temperature higher than the temperature of the molten steel 7 of 1600 ° C.
Since it is made of quartz glass having a softening point of some extent, even if it is exposed, it does not melt for a certain period of time and retains its shape. Therefore, the internal temperature of the molten steel 7 can be obtained quickly and accurately.

The exposed end of the optical fiber 11 is attached to the molten steel 7
When it is inserted into the optical fiber for a long time, the coating layer of the optical fiber 11 is gasified due to the high temperature, and the optical fiber 11 is gradually melted from the tip and consumed. So after measuring the temperature of molten steel 7,
Immediately, the optical fiber conveying means 3 is reversed to pull up the tip of the double coated optical fiber 1 from the molten steel 7,
The consumption of 1 is reduced. As shown in FIG. 4, the heat-insulating material 13 burns from the tip of the double-coated optical fiber 1 that has been pulled up, and the outer diameter of the heat-insulating material 13 increases substantially uniformly. It covers the tip of the fiber 11.
In this way, the protective tube 12 is attached to the tip of the double-coated optical fiber 1.
And the heat insulating material 13 remain, and the protective tube 12 serves as the optical fiber 1.
Since the tip of No. 1 is covered, the powder 6 can be easily pierced at the time of the next measurement and can be stably inserted into the molten steel 7. Further, the portion of the protective tube 12 that covers the tip of the optical fiber 11 begins to melt immediately when it is inserted into the molten steel 7, exposing the optical fiber 11 and bringing it into a temperature measuring state. Therefore, the temperature of the molten steel can be measured by repeatedly using the tip of the double coated optical fiber 1 without processing each time measurement is performed.

Next, the state of the tip of the double coated optical fiber 1 when the temperature of the molten steel 7 is actually measured will be described with reference to a specific example.

The double coated optical fiber 1 is made of silica glass GI fiber, and the outer surface of a 50/125/250 optical fiber 11 coated with UV cross-linking plastic is coated with a protective tube 12 made of stainless steel. Outer diameter is 1.2 mm
A metal tube-coated optical fiber having a diameter of 4 mm was used, the surface of which was coated with a heat insulating material 13 made of polyethylene resin and coated with a heat insulating material 13 made of glass fiber or the like.

The temperature of the double coated optical fiber 1 was measured by intermittently repeating insertion of about 200 mm into the molten steel 7 and holding for 2 seconds. As a result of investigating the shape of the tip of the double coated optical fiber 1 for each measurement,
When the tip portion inserted 200 mm is pulled up from the molten steel 7, as shown in FIG.
mm remains and double coated optical fiber 1 for 2 seconds
It was confirmed that the tip portion of No. 1 melted about 100 mm, but the tip was held in the molten steel 7, and the internal temperature was measured instead of the temperature of the powder 7 on the surface of the molten steel 7.

As shown in FIG. 5, the measured temperature has a peak value difference of about 1 ° C. between the first measurement and the nth measurement, and a plurality of measurement values are measured by a continuous thermometer. The actual temperature of the molten steel 7 was followed by about ± 1 ° C. In FIG. 5, the measured value sharply drops from the peak value, which is considered to indicate the temperature change when the exposed tip of the optical fiber 11 is melted and a new portion is exposed.

FIG. 6 shows the result of temperature measurement by intermittently repeating inserting the tip of the double coated optical fiber 1 into the molten steel 7 for about 200 mm and holding it for 1 second. When the tip end of the double coated optical fiber 1 is repeatedly immersed in the molten steel 7 for 1 second, it accurately follows the actual temperature change of the molten steel 7 measured by the continuous thermometer, and The length of the tip of the double coated optical fiber 1 which is consumed by one measurement is 10
It was about 20 mm. Therefore, the temperature can be accurately measured in a short time, and the double coated optical fiber 1
It was possible to reduce the amount of erosion loss.

As described above, when the double coated optical fiber 1 is repeatedly inserted into the molten steel 7 to measure the temperature, the tip portion of the double coated optical fiber 1 is melted and damaged at every measurement. The total length of the heavy-coated optical fiber 1 becomes short. 2 like this
When the total length of the heavy-coated optical fiber 1 becomes short, the optical fiber 11
Transmission loss decreases, the energy of light emitted from the terminal end of the optical fiber 11 increases, and an error occurs in the measured value. Then, the light energy from the end of the optical fiber 11 is sent to the photodetector 51 of the optical energy signal processing unit 5, and the light energy incident on the photodetector 51 is converted into a current signal In proportional to the power and sent to the correction means 52. The correction means 52 sends the sent current signal I
n is corrected from the initial length L ₀ of the optical fiber 11 stored in the storage means 53, the loss α per unit length, and the change ΔLn in the feed amount of the optical fiber for each measurement sent from the feed control means 4. The correction value Inc from which the change in the transmission loss has been removed is sent to the peak-hold circuit 54. Peak-hold circuit 54
Holds the peak value of the sent correction value Inc for a predetermined period of time, displays the sending temperature on the display means 56 and records it on the recording means 55.

In this way, the optical fiber 11 is corrected by the correction means 52.
Since the change in the transmission loss is corrected, it is possible to prevent an error in the measurement temperature even if the tip of the double-coated optical fiber 1 is consumed, and to stabilize the temperature of the molten steel 7 for a long time. Can be measured. Further, as shown in FIG. 7, the peak value of the corrected measured value Inc is held for a certain period of time, for example, about 1 second, so that the measured temperature is surely displayed and recorded on the display means 56 and the recording means 55. be able to. Further, by detecting and holding the peak value of the measured value Inc, the tip end of the double-coated optical fiber 1 is melted into the molten steel 7
The immersion time can be shortened, the consumption of the double coated optical fiber 1 can be reduced, and long time measurement can be performed using one double coated optical fiber 1. it can.

In the above embodiment, the optical fiber 11 made of quartz glass and the protective tube 12 made of stainless steel are used to measure the temperature of the molten steel 7 which is as high as 1500 ° C. or more. A multi-component glass optical fiber 11 having a softening point of about 1000 ° C. is covered with a protective tube 12 such as carbon, and a heat insulating material 13 of synthetic resin is coated on the outer surface thereof to measure a temperature of about 1000 ° C. be able to.

[0034]

As described above, according to the present invention, since the optical fiber is covered with the protective tube when the tip of the optical fiber is inserted into the molten metal as a temperature measuring portion, the optical fiber itself is damaged. It can be inserted stably without giving.

Further, the optical fiber has a melting temperature higher than the temperature of the molten metal to be measured, and the protective tube and the heat insulating material have a heat resistance temperature lower than the temperature of the molten metal to be measured,
Since there is a time lag from when the double-coated optical fiber is inserted into the molten metal to when the tip of the optical fiber is exposed, the tip of the optical fiber can be reliably held in the molten metal for a certain period of time. The internal temperature of the metal can be obtained quickly and accurately.

Further, by forming the protective tube from a metal tube having a higher heat resistance temperature than the heat insulating material, a delay time is given from the burnout of the heat insulating material at the tip end to the burnout of the protective tube, and the tip portion of the optical fiber is provided. Can be protected and the entire tip of the optical fiber can be kept at a uniform temperature.

Further, when the double coated optical fiber is inserted into the molten metal, the optical fiber is protected by the protective tube and the heat insulating material. Even if it is inserted into the molten metal intermittently, the amount of wear of the tip of the double coated optical fiber can be reduced, and long time measurement can be performed using one double coated optical fiber. You can

Further, by correcting the change in the transmission loss due to the amount of wear of the tip of the double-coated optical fiber, it is possible to prevent an error in the measurement temperature even if the tip of the double-coated optical fiber is worn. The temperature of the molten metal can be measured stably over a long period of time.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view showing a double-coated optical fiber.

FIG. 3 is a cross-sectional view showing a double-coated optical fiber in a measurement state.

FIG. 4 is a cross-sectional view showing a burned state of a double-coated optical fiber.

FIG. 5 is a waveform diagram showing measured temperatures.

FIG. 6 is a waveform diagram showing measured temperatures.

FIG. 7 is a waveform diagram showing a measured temperature with a peak hold.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Double-coated optical fiber 2 Supply drum 3 Optical fiber conveyance means 4 Feed control means 5 Signal processing part 11 Optical fiber 12 Protective tube 13 Thermal insulation material 51 Optical detector 52 Correction means 53 Storage means 54 Peak-hold circuit 55 Recording Means 56 Display means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasushi Kaneda 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Masayuki Nakata 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Main Steel Pipe Co., Ltd.

Claims (3)

[Claims] 1. A consumable optical fiber temperature measuring device, wherein a tip of a double coated optical fiber having an outer surface of a protective tube coated with the optical fiber coated with a heat insulating material is used as a temperature measuring unit, wherein the optical fiber is measured. An expendable optical fiber temperature measuring device, characterized in that it has a melting temperature higher than the temperature of the molten metal to be measured, and that the protective tube and the heat insulating material have a heat resistant temperature lower than the temperature of the molten metal to be measured. 2. The consumable optical fiber temperature measuring device according to claim 1, wherein the protective tube is a metal tube having a higher heat resistance temperature than the heat insulating material. 3. An optical fiber conveying means for intermittently sending and rewinding the double coated optical fiber to the surface of the molten metal, and optical energy obtained at the end of the optical fiber with a predetermined initial length of the optical fiber. The consumable optical fiber temperature measuring device according to claim 1 or 2, further comprising: a correction unit that corrects the loss per unit length and the change in the feed amount of the optical fiber for each measurement detected by the optical fiber conveying unit.