JPH05264366A - Temperature sensor for metal melting furnace and temperature measurement controlling method - Google Patents

Abstract

PURPOSE:To obtain a temperature sensor which is not heavily eroded by a high- temperature molten metal, etc., and does not cause any spalling by which the sensor is cracked by thermal shocks even when the sensor is dipped in the molten metal, etc., in a melting furnace and a temperature measurement controlling method using the temperature sensor. CONSTITUTION:A thermocouple temperature sensor 10 is constituted by housing thermocouple element wires 16 and 18 made of platinum-rhodium and platinum in a nonmetallic protective tube 20 of alumina, etc., and concentrically inserting the tube 20 into a cylindrical protective tube 22 made of a heat resistant material, such as zirconia, etc., having an excellent erosion resistance against a molten metal in a melting furnace and a high-melting point metal, such as molybdenum, etc., having a spalling resistance when the metal is brought into contact with the molten metal. The sensor 10 is protruded into the furnace and the temperature of the molten metal is controlled by continuously measuring the actual temperature of the molten metal and comparing the measured temperature with a set temperature which is a target value for control, and then, feeding back a correction commanding value corresponding to the difference between the measured temperature and target value to an electrical control system which is the heating source of the furnace.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature sensor exterior structure which does not cause melting loss or spalling even when used in a metal melting furnace such as an induction furnace, and a furnace using the sensor. The present invention relates to a temperature measurement control method capable of continuously measuring the temperature of molten metal therein.

[0002]

2. Description of the Related Art For example, in an induction furnace in which a metal in a furnace is melted by induction heating, a thermocouple type temperature sensor is used for measuring the temperature of the molten metal. In this thermocouple temperature sensor, two types of metal element wires are connected to form a closed circuit, and the magnitude of thermoelectromotive force generated when heat is applied to the sensor is the same as those of the two types of metal. The Seebeck effect, which is determined by the temperature of both contacts, is the principle of temperature detection. Since the molten metal in the induction furnace has an extremely high temperature (for example, 1600 ° C.), platinum metal and rhodium wire, which can be used at the highest temperature among industrial thermocouples, are widely used as the metal wires constituting the sensor. Has been adopted. This platinum rhodium-platinum thermocouple (hereinafter referred to as "PR thermocouple") is housed in a sheath-shaped protective tube in order to protect the detection element and the lead wire connected thereto from high heat. However, since the material of the protective tube does not withstand high temperatures with ordinary metals, and both platinum rhodium wire and platinum wire are deteriorated by metal vapor or reducing gas, pure sintered alumina (aluminum oxide Al ₂ O ₃ ) Or silicon nitride
A non-metal material such as (Si ₃ N ₄ ) is used.

[0003]

As described above, the PR thermocouple is housed in a protective tube made of a heat-resistant material such as alumina, but it can be used for a long time while being immersed in the molten metal in the furnace. It wasn't something. That is, the PR thermocouple
It can be used only as a consumable thermocouple because the molten metal and the slag floating in it melts gradually at high temperatures, so it is often used as a P
There was the inconvenience of replacing the R thermocouple and it was extremely uneconomical.
For this reason, in so-called metal melting furnaces such as induction furnaces, arc furnaces and other gas furnaces, it has been impossible to continuously measure the present temperature of the molten metal in the furnace during the operating period of the furnace. This means that it is not possible to carry out fine control to maintain the temperature inside the furnace at a preset target temperature value, which also adversely affects the quality of the product obtained from the molten metal.

[0004]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the problems inherent in the above-mentioned prior art, and has been proposed to suitably solve the problems. Even when immersed, the temperature of the molten metal does not easily melt due to the high temperature of the metal or the floating slag, and the temperature of the molten metal can be maintained for a long time by using the temperature sensor, which does not cause spalling due to thermal shock. An object of the present invention is to provide a temperature measurement control method capable of continuously measuring the temperature.

[0005]

In order to overcome the above problems and achieve the intended object, the present invention uses a platinum rhodium wire and a platinum wire as a thermocouple wire, and protects this wire with a non-metallic material such as alumina. In a thermocouple temperature sensor housed in a tube, a heat-resistant substance such as zirconia that has excellent erosion resistance against molten metal or slag in a metal melting furnace such as an induction furnace, when contacting the molten metal or the like And a refractory metal such as molybdenum having spalling resistance, which constitutes a cylindrical protective tube, and the non-metallic protective tube is concentrically inserted into the cylindrical protective tube.

Further, a temperature measuring control method of a metal melting furnace according to another invention of the present application relates to the invention using the above temperature sensor, wherein a thermocouple wire of platinum rhodium and platinum is protected by a non-metal protective tube such as alumina. A heat-resistant substance such as zirconia that is excellent in melting resistance against molten metal or slag in a metal melting furnace such as an induction furnace, and molybdenum having spalling resistance when contacted with the molten metal or the like. A non-metal protective tube is concentrically inserted into a cylindrical protective tube made of a high melting point metal such as to form a thermocouple temperature sensor, and the thermocouple temperature sensor is exposed to the inside of the metal melting furnace. The actual temperature of the molten metal in the melting furnace is continuously measured by the sensor, the measured temperature value is compared with a temperature set value which is a control target value, and a correction command value corresponding to the difference from the target value is set. Electricity of heating source in the melting furnace And performing control for feeding back to the control system.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a temperature sensor and a temperature measurement control method for a metal melting furnace according to the present invention will be described with reference to the accompanying drawings with reference to preferred embodiments. FIG. 2 shows a state in which the temperature sensor 10 according to the embodiment is inserted into the metal melting furnace 12, and FIG. 1 is a vertical cross-sectional view showing the internal structure of the temperature sensor 10. Here, the temperature sensor 10 is basically composed of the above-mentioned PR thermocouple, and the metal melting furnace 12 is structured as an induction furnace in which the induction coil 14 is embedded in the furnace body.

In the PR thermocouple 10 shown in FIG. 1, platinum rhodium wire 16 and platinum wire 18 are used as thermocouple wires, and between the wires 16, 18, for example, a mullite-like electrically insulating tube is used. Is installed. Both thermocouple wires 16 and 18 are hermetically housed inside a long protective tube 20 made of a non-metal sintered body such as alumina (Al ₂ O ₃ ) and the non-metal protection is performed. The tube 20 is concentrically inserted into a cylindrical protective tube 22 made of, for example, molybdenum-zirconia (Mo-ZrO ₂ ). That is, the cylindrical protection tube 22 is made of a sintered body in which a refractory material such as zirconia (ZrO ₂ ) is used as a material and a refractory metal such as molybdenum (Mo) is dispersed in the material at a required ratio. There is. Here, zirconia is a heat-resistant substance that is less likely to be melted down even by the high temperature of the molten metal 24 in the induction furnace 12 and the slag 26 floating in the molten metal 24, and has excellent so-called melting resistance. Further, molybdenum is a high melting point metal having extremely good thermal conductivity, and even if the cylindrical protective tube 22 comes into contact with the molten metal 24 and the slag 26, the thermal shock is eliminated by suppressing the temperature difference to be small, This causes cracks and cracks,
It contributes to reduce spalling such as peeling.

As described above, the protective tube 22 is composed of a heat-resistant material such as zirconia having an excellent corrosion resistance and a refractory metal such as molybdenum having a spalling resistance. The mixing ratio of the two is determined so as to obtain a good balance with the poling property. In the examples, suitable results were obtained by setting zirconia as the heat resistant material to 60 to 80% and molybdenum as the high melting point metal to 40 to 20%. Further, it was suitable to use molybdenum having a particle diameter in the range of several microns to several hundreds of microns. In addition to zirconia, magnesia (magnesium oxide MgO), zircon (Zr
SiO ₄ ), silica (SiO ₂ ), etc. are selectively used.
In addition to molybdenum, tungsten (W) and niobium (Nb) can be used as refractory metals having excellent spalling resistance.
Other tantalum (Ta) is preferably used.

As shown in FIG. 2, the PR thermocouple 10 having the above-mentioned structure is immersed in the molten metal 24 in the induction furnace 12 and used for measuring the temperature of the metal. In this case P
Since the R thermocouple 10 is equipped with a cylindrical protective tube 22 having an excellent corrosion resistance and spalling resistance as an exterior (sheath), it does not melt due to the high temperature of the molten metal 24. It is possible to continuously measure temperature for a long period of time while immersed in it. Further, even if the protective tube 22 is brought into contact with the molten metal 24 and the slag 26, the heat transfer efficiency is high, so that spalling does not occur and the protective tube 22 can be used stably.

In FIG. 2, the PR thermocouple 10 in which the detecting portion is immersed in the molten metal 24 is the platinum rhodium wire 16 thereof.
A thermoelectromotive force is generated between the platinum wire 18 and the platinum wire 18, and the temperature measurement value based on the thermoelectromotive force is input to the comparator 28. In addition, the comparator 28
A temperature set value, which is a control target value, is input in advance for the temperature of the metal in the furnace to be kept in a molten state. Therefore, in the comparator 28, the actual temperature measurement value obtained from the PR thermocouple 10 is compared with the temperature set value which is the control target value, and the correction command value corresponding to the difference between the target value and the induction set value is obtained. It is fed back to the power supply device (inverter) 30 that supplies high-frequency power to the coil 14. That is, if the comparison result in the comparator 28 is less than the temperature set value as the control target, the excitation voltage applied from the power supply device 30 to the induction coil 14 is increased by the difference to raise the melting temperature. .. Further, when the comparison result in the comparator 28 is positive than the control target value, the melting temperature is lowered by lowering the excitation voltage by the difference, whereby the molten metal 2 in the induction furnace 12 is reduced.
The temperature of 4 can be always maintained at an appropriate set value.

Although the induction furnace 12 is used as the metal melting furnace in the illustrated example, the present invention can be applied to any type of furnace as long as the heating source in the melting furnace can be temperature-controlled by an electric control system. can do. For example, an arc furnace that inserts an arc electrode into the furnace and a gas furnace that melts aluminum alloy with a flame of a gas burner electrically control the voltage applied to the electrode and the opening / closing of the burner valve body. Therefore, it can be suitably applied to these.

[0013]

As described above, according to the temperature sensor of the metal melting furnace according to the present invention, even if the metal or the floating slag is immersed in the molten metal in the metal melting furnace such as the induction furnace for a long time. It is less likely to melt due to high temperature, and spalling due to thermal shock does not occur, so that it can be used stably. Further, according to the temperature measurement control method according to another invention of the present application using this temperature sensor, the temperature measurement in the molten metal in the metal melting furnace, which has been impossible in the past, is continuously measured for a long time. As a result of fine temperature control, it is possible to produce a product of stable quality.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an internal structure of a PR thermocouple according to an embodiment.

FIG. 2 is a schematic explanatory diagram showing a state in which the temperature sensor according to the embodiment is inserted into a metal melting furnace.

[Explanation of symbols]

 10 Thermocouple Temperature Sensor (PR Thermocouple) 12 Metal Melting Furnace 14 Heating Source (Induction Coil) 16 Platinum Rhodium Wire 18 Platinum Wire 20 Non-metal Protective Tube 22 Protective Tube 24 Molten Metal 26 Slag 30 Electric Control System

Claims (2)

[Claims] 1. A thermocouple comprising a platinum rhodium wire (16) and a platinum wire (18) as thermocouple wires, the wires (16, 18) being housed in a non-metal protection tube (20) such as alumina. In the temperature sensor (10), the molten metal (24) and slag (2) in the metal melting furnace (12) such as induction furnace
6) Cylindrical protective tube made of a heat-resistant substance such as zirconia having excellent melting resistance and a refractory metal such as molybdenum having spalling resistance when brought into contact with the molten metal or the like (2
2), and the non-metal protective tube (20) is concentrically inserted into the cylindrical protective tube (22), particularly a thermocouple used in a metal melting furnace. Temperature sensor. 2. A thermocouple wire of platinum rhodium and platinum (16,
18) is housed in a non-metal protection tube (20) such as alumina, and zirconia, etc., which has excellent corrosion resistance to molten metal (24) and slag (26) in a metal melting furnace (12) such as an induction furnace. Cylindrical protection tube made of a heat-resistant substance and a refractory metal such as molybdenum having spalling resistance when contacted with the molten metal or the like (22)
A thermocouple temperature sensor (10) is concentrically inserted through the non-metal protective tube (20) to, and this thermocouple temperature sensor (10) is exposed to the inside of the metal melting furnace (12), The actual temperature of the molten metal (24) in the melting furnace (12) is continuously measured by the sensor (10), the measured temperature value is compared with a temperature set value which is a control target value, and the target value A method for controlling temperature measurement in a metal melting furnace, characterized in that a correction command value corresponding to the difference is returned to the electric control system (30) of the heating source (14) in the melting furnace (12).