JP5299032B2 - Continuous temperature measurement method for molten steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for continuous measurement of temperature which makes accurate measurement of temperature compatible with suppression of shortening of the lifetime of a temperature sensing element owing to erosion, breakage, etc. of the element, in regard to a method for continuously measuring the temperature of molten steel in a treatment container. <P>SOLUTION: In the method, continuous measurement of the temperature of the molten steel 6 is performed by the temperature sensing element 11 having a thermocouple 12 covered with a protective tube 13. The material of the protective tube 13 is cermet, and the continuous measurement of the temperature is performed by inserting the temperature sensing element 11 into the molten steel 6 through the side wall 5 of a refining container 2 holding the molten steel 6. The outer diameter &phiv; of the temperature sensing element 11 is made 10-50 mm and the projection length L of the element 11 from the inner surface 2a of the refining container 2 is made 50-300 mm. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for continuously measuring the temperature of molten steel in a refining vessel in which molten steel is accommodated and processing such as refining is performed.

  If the temperature control of the molten steel in the refining process is insufficient, the casting speed during continuous casting may decrease. It is important to improve the accuracy of temperature control of molten steel in the refining process in order to avoid this and improve productivity and avoid excessive heating in the refining process and reduce unnecessary costs. .

  Conventionally, in secondary refining, which is the final step of refining, a probe equipped with a thermocouple is immersed in the molten steel pan during refining processing to measure temperature. However, erosion of the probe immersed in high-temperature molten steel is severe, and conventionally, temperature measurement is intermittently performed, and temperature transition is predicted from the temperature measurement result to adjust the temperature. For this reason, the data is discontinuous, and it is difficult to accurately grasp temperature changes due to, for example, alloy addition or heat loss during actual processing, which causes variations in temperature after secondary refining processing. It was. For this reason, there has been a waste of excessive heating so as not to cause operational troubles due to the temperature falling below the management reference lower limit.

  Therefore, in recent years, continuous temperature measurement of molten steel has been performed by immersing a temperature measuring body covering a thermocouple with a protective tube having excellent heat resistance and thermal conductivity in the molten steel. For example, as disclosed in Patent Document 1, a method of immersing a temperature measuring body from above the molten steel is generally known. In Patent Document 1, a measurement hole is provided in a refining furnace, and the measurement hole is measured. A method for measuring the temperature of molten steel in a refining furnace by inserting a warm body is described.

  Patent Document 2 discloses that a temperature measuring body whose tip is covered with a ceramic cap is embedded in a furnace wall, and a weir is provided to protect the temperature measuring body from a sudden molten metal flow. ing.

JP-A-5-39516 Japanese Laid-Open Patent Publication No. 1-167592

  However, in Patent Document 1, since the measurement hole is installed above the surface of the molten metal, when the temperature measuring body is immersed in the molten metal from above, the temperature is measured by the filler or slag present on the surface of the molten metal. The body surface is covered, and the temperature measurement accuracy decreases.

  Moreover, since the said patent document 2 measures the temperature enclosed in the weir, there is a problem that a highly accurate temperature measurement result cannot be obtained.

  An object of the present invention is a continuous temperature measurement in which a method for continuously measuring the temperature of molten steel in a processing vessel achieves both highly accurate temperature measurement and suppression of a decrease in the life of the temperature measuring element due to erosion or breakage of the temperature measuring element. It is to provide a method.

In order to solve the above-mentioned problem, the present invention is a method for continuously measuring the temperature of molten steel in a refining vessel which is an RH vacuum degassing tank by a temperature measuring body in which a thermocouple is covered with a protection tube, material is cermet, said temperature sensing element, wherein through the side wall of the smelting vessel is inserted into the molten steel, have rows continuous temperature measurement, the temperature sensing element, the protruding length from the inner surface of the refining vessel The temperature measuring body tip is located outside the upper opening of a dip tube provided at the lower part of the smelting vessel, and the temperature measuring body tip is located outside the upper opening of the smelting vessel. . By using a cermet with a high thermal conductivity and a high heat shock resistance as the material of the protective tube, it is possible to continuously measure the temperature continuously inserted in the molten steel. Furthermore, by inserting a temperature measuring element into the molten steel from the side wall of the refining vessel, high-precision measurement can be performed without being affected by the filler and slag existing on the surface of the molten metal. In addition, it has a structure that can be easily replaced as necessary when the temperature measuring body inserted into the refining vessel becomes impossible to measure temperature due to melting or breakage.

The outer diameter of the temperature measuring element is preferably 10 mm to 50 mm . The protective tube may have a tapered shape with an outer diameter that decreases toward the tip.

  ADVANTAGE OF THE INVENTION According to this invention, the molten steel in the refining process can be continuously measured with high accuracy. Thereby, temperature control accuracy in the refining process is improved, and productivity can be improved. Moreover, since excessive heating is not required, the refining time is shortened, and the cost can be reduced.

It is sectional drawing which shows embodiment which applied this invention to RH vacuum degassing apparatus, (a) is a refining container, (b) is an enlarged view of the A section of (a). It is a graph which shows the relationship between the outer diameter of a temperature sensing element, the error of a temperature measurement value, and the lifetime of a temperature sensing element. It is a graph which shows the relationship between the protrusion length of a temperature sensing element, the error of a temperature measurement value, and the lifetime of a temperature sensing element. It is a graph which shows the measured value by batch temperature measurement and continuous temperature measurement of this invention for every processing time. It is a graph which shows distribution of the temperature error rate of the batch temperature measurement of FIG. 4, and continuous temperature measurement.

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

  FIG. 1 is an example of a refining vessel that continuously measures the temperature of molten steel according to the present invention, and shows a state during temperature measurement in an RH vacuum degassing tank. The outer wall of the refining vessel 2 composed of a degassing tank containing the molten steel 6 is formed by an outer iron skin 3 and a refractory layer 4 provided on the inner side. The molten steel 6 accommodated in the ladle 7 is degassed by the vacuum refining vessel 2.

A temperature sensing element 11 is inserted from the outside of the refining vessel 2 through the lower side wall 5 of the refining vessel 2. As shown in FIG. 1B, the temperature measuring body 11 is a thermocouple 12 covered with a protective tube 13. The thermocouple 12 is a platinum-platinum rhodium alloy or the like that has little variation and deterioration even when used at a high temperature. The material of the protective tube 13 is a cermet having excellent heat resistance, and for example, a molybdenum zirconia (80% Mo-20% ZrO ₂ ) tube having high thermal conductivity and excellent heat shock resistance is preferable.

  The outer diameter φ of the protective tube 13 is 10 to 50 mm, preferably 30 to 40 mm. When the outer diameter φ is smaller than 10 mm, the thermocouple 11 is easily affected even if the protective tube 13 is slightly eroded, and the life of the temperature measuring element 11 is shortened. When the outer diameter φ is larger than 50 mm, the thermocouple 12 is less likely to be eroded, and the life of the temperature measuring element 11 is prolonged, but the distance between the molten steel 6 and the thermocouple 11 is increased and the temperature measuring accuracy is lowered. . The protruding length L of the temperature measuring element 11 from the inner surface 2a of the refining vessel 2 is 50 to 300 mm, preferably 100 to 150 mm. The protruding length L of the temperature measuring element 11 is an insertion dimension into the molten steel 6, and if it is shorter than 50 mm, the protective tube 13 is less eroded and the life is increased, but the temperature measuring accuracy is lowered. When the protrusion length L is longer than 300 mm, the temperature measurement accuracy is improved, but erosion is severe and the life is shortened.

  Moreover, in order to improve the workability at the time of attaching and replacing the temperature measuring body 11 to the container 2, the protective tube 13 preferably has a tapered shape in which the tip end side is narrowed.

  As shown in FIG. 1, by directly inserting the tip of the temperature measuring body 11 into the molten steel 6 in the refining vessel 2 and connecting it to a measuring instrument (not shown) from the connector 14 arranged outside the refining vessel 2, The temperature of the molten steel 6 during the degassing process can be continuously measured in real time. Moreover, as shown in the figure, the temperature measuring element 11 is inserted into the molten steel 6 so that it can be measured accurately without being affected by the filler and slag present on the molten metal surface. And by making the material of a protective tube, the outer diameter of a temperature measuring body, and the insertion dimension into molten steel into the said conditions, it is possible to make measurement accuracy and life compatible.

  As described above, even when the protective tube 13 made of molybdenum / zirconia, for example, is used, the surface layer may be peeled off intensely in about 8 hours in the atmosphere exceeding 1500 ° C. In the refining vessel 2, since the heat retaining gas is used to keep the heat in the refining vessel 2 not only during the treatment but also in the high-temperature molten steel 6 being treated, the temperature sensing element 11 is always at a high temperature. Exposed to. Therefore, in order to prevent oxidation of the temperature measuring element 11, mortar may be applied to the surface of the temperature measuring element 11, or magnesium oxide (MgO) may be sprayed.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to this example. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

  The present invention was applied to the RH vacuum degassing treatment, and the temperature of the molten steel during the refining reaction was measured in real time by changing the outer diameter of the temperature measuring body, and the temperature measuring accuracy and the life of the temperature measuring body were investigated. The outer diameter of the temperature measuring element was 8 types of 5 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, and 70 mm. The results are shown in FIG. In addition, the lifetime of the temperature sensing element preferable for practical use was set to 20 charges or more. The preferred temperature measurement accuracy was set such that the error from the measurement result by batch temperature measurement was 5 ° C. or less.

  As shown in FIG. 2, when the outer diameter of the temperature measuring element was 5 mm, the life was significantly reduced. When the outer diameter was 60 mm or 70 mm, the life of the temperature measuring element was improved, but the temperature measuring error was extremely large. The temperature measuring object has an error of 5 ° C. or less and the temperature measuring element has a life of 20 charges or more, as in the present invention, when the outer diameter of the temperature measuring element is in the range of 10 mm to 50 mm.

  The present invention is applied to the RH vacuum degassing process, and the length of the temperature measuring body protruding from the inner surface of the container, that is, the insertion dimension into the molten steel is changed, and the temperature of the molten steel during the refining reaction is measured in real time. And the lifetime of the temperature sensor was investigated. The protruding lengths of the temperature measuring elements were nine types of 30 mm, 50 mm, 100 mm, 120 mm, 150 mm, 200 mm, 250 mm, 300 mm, and 400 mm. The results are shown in FIG.

  As shown in FIG. 3, the life of the temperature measuring element decreases as the protrusion length increases. In the case of 400 mm, the life significantly decreases. Further, when the protrusion length is short, the life of the temperature measuring element is improved, but when it is 30 mm, the temperature measuring error becomes extremely large. As in Example 1, when the temperature measurement error preferred for practical use is set to 5 ° C. or less and the lifetime of the temperature measuring device is set to 20 charges or more, both conditions are satisfied according to the present invention. The protruding length was in the range of 50 mm to 300 mm.

  Using a molybdenum / zirconia (80% Mo-20% Zr) tube as a temperature measuring tube, and from the results of Examples 1 and 2, etc., in the RH vacuum degassing tank, the outer diameter φ of the temperature measuring device = 32 mm and the length L = 120 mm of the temperature measuring element protruding into the container was found to be suitable, and under these conditions, continuous temperature measurement of the molten steel was performed. Furthermore, mortar application and MgO spraying were performed on the temperature sensing element to improve the oxidation resistance of the temperature sensing element.

  Batch temperature measurement is performed as a comparison value, and the temperature error rate ((T−Tb) / Tb × 100) expressed by the difference between the continuous temperature measurement value T according to the present invention and the batch temperature measurement value Tb with respect to the batch temperature measurement value Tb. Was calculated. When the target value of the temperature error is 5 ° C. or less and this is expressed as a temperature error rate at 1600 ° C., it becomes 0.31%. FIG. 4 shows measured values of continuous temperature measurement and batch temperature measurement for each processing time, and FIG. 5 shows a distribution of temperature error rates.

  As shown in FIG. 4, the batch temperature measurement and the continuous temperature measurement are very similar, and the temperature measurement can be accurately performed in real time by the continuous temperature measurement. The average temperature error rate was 0.18%, which was 0.31% or less of the target value. The standard deviation at 40 batch temperature measurements was 0.11%. Thus, according to the present invention, the temperature of the molten steel during the refining reaction can be measured continuously and accurately in real time.

  The present invention can be applied not only to continuous temperature measurement of molten steel in a refining vessel, but also to a refining vessel for molten metal other than molten steel.

2 Refining vessel 3 Iron skin 4 Refractory layer 5 Side wall 6 Molten steel 11 Temperature sensor 12 Thermocouple 13 Protective tube 14 Connector L Projection length φ Outer diameter

Claims (3)

A method for continuously measuring the temperature of molten steel in a refining vessel, which is an RH vacuum degassing tank, with a temperature measuring body covering a thermocouple with a protective tube,
The material of the protective tube is cermet, said temperature sensing element, wherein through the side wall of the smelting vessel is inserted into the molten steel, have rows continuous temperature measurement,
The temperature measuring body has a protruding length from the inner surface of the refining vessel of 50 to 300 mm, and the temperature measuring body tip is located outside the upper opening of a dip tube provided at the lower portion of the refining vessel. characterized in that the continuous temperature measuring method of the molten steel. 2. The continuous temperature measuring method for molten steel according to claim 1, wherein an outer diameter of the temperature measuring element is 10 mm to 50 mm. The molten steel continuous temperature measuring method according to claim 1, wherein the protective tube has a tapered shape whose outer diameter decreases toward the tip.

Images