JP3022764B2 - Induction furnace sensors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor for an induction furnace capable of detecting a molten metal leak in a crucible-type induction furnace and continuously measuring a molten metal temperature.

[0002]

2. Description of the Related Art FIG. 3 is a schematic diagram of a conventional induction furnace provided with a molten metal leak detection sensor for detecting a molten metal leak of a crucible type induction furnace and a temperature sensor for continuously measuring a molten metal temperature. FIG. In FIG. 3, 1 is a molten metal, 2 is a refractory formed in a crucible shape, 3 is an induction heating coil,
4 denotes a first antenna, 4a denotes a tip of the first antenna 4, 5 denotes a second antenna, 6 denotes a power source, 7 denotes an ammeter, and 8 denotes an immersion type temperature sensor. In FIG. 3, the refractory 2 and the second
The antenna 5 and the induction heating coil 3 are spaced apart for easy understanding. The second antenna 5
The mica sheet 10 is described with its thickness enlarged.

In FIG. 3, a molten metal 1 is melted from a solid metal in a refractory 2 formed into a crucible shape by an electromagnetic induction action of an induction heating coil 3 and is added to a target component by an additive or the like. It is adjusted and heated to the target temperature before tapping.

A second antenna 5 is mounted between substantially the entire outer peripheral portion of the refractory 2 and the induction heating coil 3.
A first antenna 4 is embedded in the furnace bottom of the crucible formed of the refractory 2 so that the tip 4 a of the first antenna 4 contacts the molten metal 1.

The second antenna 5 is composed of a strip-shaped aluminum foil or a stainless steel foil which is long in the crucible height direction and is arranged at intervals of 5 to 100 mm with the adjacent foils, and the same foil is used at one place in the circumferential direction. An electrically short-circuited sheet is sandwiched between insulating sheets such as mica and Teflon sheets, and a sheet having a structure sandwiched between the induction heating coils 4 is formed.

In this state, when the molten metal 1 leaks through a crack formed in the refractory 2 and contacts the second antenna 5, the first antenna 4 and the second antenna 5 are electrically connected through the molten metal 1, and the first antenna 4 The current flows through the power supply 6 and the ammeter 7 connected between the first antenna 5 and the second antenna 5, and the pointer of the ammeter 7 swings, so that it is detected that the molten metal 1 has leaked to the second antenna 5.

In a few hours to two or three days after the leak is detected, the melt leaks and the molten metal 1 reaches the induction heating coil 3.
When the water-cooled induction heating coil 3 is melted and the molten metal 1 comes into contact with the water, the water is instantaneously vaporized, causing a steam explosion and possibly destroying the furnace. Stop and discharge the molten metal 1 to empty the furnace, and then replace the refractory 2.

On the other hand, the temperature measurement of the molten metal 1 is performed by immersing a disposable immersion type temperature sensor 8 in the molten metal 1 immediately before tapping.

Instead of the immersion type temperature sensor 8, the refractory 2
Japanese Patent Application Laid-Open Nos. 3-207988 and 1-167592, and Japanese Utility Model Laid-Open No. 4-64739 disclose examples in which a temperature sensor with a protective tube is embedded in the inside.

[0010]

The disposable immersion type temperature sensor shown in FIG. 3 has a immersion time of 5 minutes.
It is 30 seconds at most from the second, and the temperature sensor is immersed in the molten metal after making a visual judgment just before the molten metal reaches the target temperature.
In order to raise the temperature of the molten metal to an accurate temperature, it is necessary to measure the temperature at least once, and furthermore, since the temperature is discarded, there is a problem that a large number of disposable immersion type temperature sensors must be used. .

Further, the material of the protection tube of the temperature sensor with a built-in protection tube disclosed in the above publication is alumina (Al _2).
O ₃ ) -based materials, which have an order of magnitude lower thermal conductivity than metals, have poor responsiveness to changes in the temperature of the object to be measured, and therefore have a problem that they are difficult to use in a furnace having a high temperature raising capability.

Further, when the temperature sensor is embedded in the refractory, the temperature sensor is embedded in addition to the embedding of the first antenna as a leak detection sensor. Therefore, an increase in the number of embedded sensors is caused by a smooth expansion of the refractory. In addition, there is a problem in that shrinkage is hindered, the life of the refractory is shortened, and the danger of hot water leaking from the sensor wall in the furnace wall is increased.

An object of the present invention is to provide an induction furnace sensor which has a small influence on the life of a refractory and is capable of detecting molten metal leakage from a crucible-type induction furnace and continuously measuring a molten metal temperature.

[0014]

According to the present invention, there is provided an induction furnace in which a coil is wound around a crucible made of a refractory, and a conductive bottomed cylindrical tube is melted in a refractory of the induction furnace. In order to detect that the molten metal in the induction furnace has leaked through the refractory by burying the conductive bottomed cylindrical tube as the first antenna and arranging the second antenna on the outer periphery of the crucible, A temperature sensor for measuring the temperature of molten metal that is insulated from the conductive bottomed cylindrical tube by an insulating material in the conductive bottomed cylindrical tube. The conductive bottomed cylindrical tube is also used as a first antenna of the hot water leak detection sensor and a protection tube of the temperature sensor.

According to a second aspect of the present invention, in the sensor for an induction furnace according to the first aspect, the conductive bottomed cylindrical tube is made of any one of a metal, a metal-ceramic composite material, and a conductive ceramic.

According to a third aspect of the present invention, in the sensor for an induction furnace according to the first aspect, the conductive bottomed cylindrical tube is made of molybdenum-zirconia (Mo-ZrO ₂ ).

According to a fourth aspect of the present invention, in the sensor for an induction furnace according to any one of the first to third aspects, the conductive bottomed cylindrical tube is in contact with the molten metal at the tip of the furnace bottom of the crucible type induction furnace. Shall be embedded.

[0018]

In the present invention, the conductive bottomed cylindrical tube forming the leak detection sensor constitutes a protective tube of the temperature sensor for measuring the temperature of the molten metal. Therefore, in the present invention, the hot water leak detection sensor and the temperature sensor are integrated.

At this time, the material (molybdenum-zirconia (Mo-ZrO ₂ )) of the conductive bottomed cylindrical tube of the leak detection sensor constituting the protection tube of the temperature sensor has a maximum operating temperature of 1700 ° C. Excellent erosion resistance to copper and aluminum. Further, the thermal conductivity is 0.23 at 1400 ° C.
cal / cm.sec..degree. C., having substantially the same thermal conductivity as aluminum, and having a volume resistivity of 10 to 100.times.10.sup.- ^6.
Ω-cm and has a volume resistivity substantially equal to that of iron. The high thermal conductivity, when used as a protective tube for a temperature sensor, reduces errors in transmitting a temperature change of an object to be measured to the temperature sensor and improves responsiveness. In addition, since the volume resistivity is small, it is possible to make resistance values other than the adjustment resistance of the molten metal leak detection sensor, the ammeter, and the power supply other than the adjustment resistance almost zero, so that the presence or absence of the molten metal leaks. Make the detected current difference remarkable.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a main part of an embodiment of the present invention, and FIG. 2 is a schematic diagram showing a state of use thereof. In FIGS. 1 and 2, the members denoted by the same reference numerals as those of the conventional example have almost the same functions, and therefore the description thereof will be omitted.

First, in FIG. 2, 1 is a molten metal, 2 is a refractory formed in a crucible shape, 3 is an induction heating coil arranged on the outer peripheral side of the refractory 2, and 5 is almost all of the outer peripheral portion of the refractory 2. A second antenna mounted between the and the induction heating coil 3,
Reference numeral 6 denotes a power source, 7 denotes an ammeter, and 9 denotes a sensor for an induction furnace according to the present invention.

As shown in FIG. 1, the induction furnace sensor 9 includes a hot water leak detection sensor 9a composed of a conductive bottomed cylindrical tube (for example, a test tube type made of molybdenum-zirconia), A thermocouple-type temperature sensor (e.g., platinum-platinum rhodum) mounted in a conductive bottomed cylindrical tube forming the hot water leak detection sensor 9a and insulated from the conductive bottomed cylindrical tube by an insulating material 9c to measure the temperature of molten metal. Thermocouple) 9b. At this time, the conductive bottomed cylindrical tube forming the leak detection sensor 9a constitutes a protection tube of the thermocouple type temperature sensor 9b for measuring the temperature of the molten metal.

The second antenna 5, the ammeter 7, and the power source 6
Is electrically connected to a conductive bottomed cylindrical tube forming the leak detection sensor 9a of the induction furnace sensor 9. The conductive bottomed cylindrical tube constituting the hot water leak detection sensor 9a is shown in FIG.
In order to fulfill the function of the first antenna described in (1), the tip is buried in the crucible bottom formed of the refractory 2 so as to contact the molten metal 1.

The induction heating coil 3 of most induction furnaces is of a water-cooled type, and the induction heating coil 3 is grounded with a high resistance through a water circuit (not shown). If the resistance other than the adjustment resistance of the leak detection circuit is close to or greater than the ground resistance of the water circuit, the reading of the ammeter 7 by detecting the leak and the reading of the ammeter 7 by grounding the water circuit The difference disappears and the leak of hot water cannot be detected. For this reason, it is desired that the material of the hot water leak detection sensor has a low volume resistivity. In addition, in a crucible-type induction furnace, it is common to ground the molten metal through a first antenna in order to lower the floating potential of the molten metal to ground.

In the crucible type induction furnace equipped with the induction furnace sensor 9 according to the present invention, the molten metal 1 is melted from solid metal in the refractory 2 formed into a crucible shape by the electromagnetic induction of the induction heating coil 3. Then, the components are adjusted by additives and the like so as to become the target components, and heated to the target temperature before tapping.

The second antenna 5 is composed of a strip-shaped aluminum foil or a stainless steel foil which is long in the crucible height direction and is arranged at intervals of several tens of millimeters from adjacent foils. An electrically shorted sheet is sandwiched by an insulating sheet such as a mica sheet or a Teflon sheet and a sheet having a structure sandwiched between the induction heating coils 4 is formed.

In this state, when the molten metal 1 penetrates through cracks generated in the refractory 2 and comes into contact with the second antenna 5, the molten metal 1
The leak sensor (first antenna) 9a of the sensor 9 for the induction furnace and the second antenna 5 are electrically connected to each other, and the power source 6 and the ammeter 7 connected between the leak sensor 9a and the second antenna 5 are electrically connected. And the pointer of the ammeter 7 swings, it is detected that the molten metal 1 has leaked to the second antenna 5.

In a few hours to two or three days after the leak is detected, the leak proceeds and the molten metal 1 reaches the induction heating coil 3.
When the water-cooled induction heating coil 3 is melted and the molten metal 1 comes into contact with the water, the water is instantaneously vaporized, causing a steam explosion and possibly destroying the furnace. Stop and discharge the molten metal 1 to empty the furnace, and then replace the refractory 2.

The temperature of the molten metal 1 is measured by a molten metal leak detection sensor 9a.
Is continuously performed by a thermocouple-type temperature sensor 9b mounted in a bottomed cylindrical tube forming the following.

The conductive bottomed cylindrical tube forming the leak detecting sensor 9a can be made of any one of metal, metal-ceramic composite material, and conductive ceramic.

[0032]

According to the present invention, a temperature sensor for measuring the temperature of a molten metal is inserted inside a conductive bottomed cylindrical tube constituting a sensor for detecting a molten metal, and the sensor for detecting the molten metal and the temperature sensor for the molten metal are connected. Because they are integrated, the number of places where the crucible made of refractory is embedded in the furnace wall can be reduced. At this time, according to the present invention, molybdenum-zirconia (Mo-Zr) is added to the conductive bottomed cylindrical tube constituting the hot water leak detection sensor.
When O ₂ ) is used, the resistance value other than the adjustment resistance of the molten metal leak detection circuit can be made almost zero, so that there is an effect that the conductive bottomed cylindrical tube can be used also as the ground electrode (first antenna) of the molten metal, and the life is shortened. Molybdenum-zirconia (Mo-Zr
300 when the thickness of the conductive bottomed cylindrical tube of O ₂ ) is 3 mm
Use for more than an hour has become possible.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram showing a crucible-type induction furnace in which the induction furnace sensor of the present invention is installed.

FIG. 3 is a schematic configuration diagram showing a conventional crucible-type induction furnace.

[Explanation of symbols]

1 ... Molten metal, 2 ... Refractory, 3 ... Induction heating coil, 5 ... Second
Antenna, 6 power supply, 7 ammeter, 9 sensor for induction furnace, 9a hot water leak detection sensor, 9b thermocouple type temperature sensor, 9c insulating material.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shizuo Hayashi 1-1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Examiner, Fuji Electric Co., Ltd. Kazumasa Yamamoto (56) References JP-A-53-8883 (JP JP-A-1-196493 (JP, A) JP-A-6-82171 (JP, A) JP-A-63-101792 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB Name) F27B 14/20 F27D 21/00

Claims (4)

(57) [Claims] 1. An induction furnace having a coil wound around a crucible made of a refractory, wherein a conductive bottomed cylindrical tube is buried in a refractory of the induction furnace so as to be in contact with a molten metal; A cylindrical tube is used as a first antenna, and a second antenna is arranged on the outer periphery of the crucible to form a molten metal leak detection sensor for detecting that molten metal in the induction furnace has leaked through a refractory; A temperature sensor for measuring the temperature of the molten metal insulated from the conductive bottomed cylindrical tube by an insulating material in a conductive bottomed cylindrical tube to form a molten metal leak detection sensor; A sensor for an induction furnace, wherein the sensor also serves as a first antenna of a hot water leak detection sensor and a protective tube of a temperature sensor. 2. The induction furnace sensor according to claim 1, wherein
The sensor for an induction furnace, wherein the conductive bottomed cylindrical tube is made of any one of a metal, a metal-ceramic composite material, and a conductive ceramic. 3. The sensor for an induction furnace according to claim 1, wherein
The conductive bottomed cylindrical tube is made of molybdenum-zirconia (Mo).
-ZrO ₂ ). A sensor for an induction furnace, comprising: 4. A sensor for an induction furnace according to claim 1, wherein said conductive bottomed cylindrical tube is embedded in a furnace bottom of a crucible-type induction furnace so that a tip thereof contacts a molten metal. A sensor for an induction furnace characterized by the above-mentioned.