JPH0682171A - Crucible induction furnace - Google Patents

Abstract

PURPOSE:To avoid bridging in the supply of cold stock that may cause an accident of serious proportions and secure the safety of operation without depending on operators' observation which requires skill and keen attentiveness. CONSTITUTION:A coil 4 is wound around a crucible made of a refractory material 1. A thermocouple 5a, 5b is buried in the lower part, including the bottom, of the refractory material 1 up to a height lower than one third of the refractory in height. One thermocouple constituent 5a is connected to a circuit breaker 11 through output contacts of a temperature recorder 6. The other thermocouple constituent 5b is designed to serve concurrently as a second antenna so as to function also in an ordinary device for detecting run-out. The thermocouple 5a, 5b is connected together with a first antenna 7 which is electrically conductive and exposed at the bottom, a run-out detective circuit 8, and an ordinary second antenna 9 and through the output contacts of the temperature recorder to the circuit breaker 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for preventing hanging of cold material in a crucible induction furnace.

[0002]

2. Description of the Related Art In order to operate a crucible induction furnace, a cold material is put into the furnace and then electricity is supplied. The material melts by induction heating and becomes a molten metal one after another and enters the furnace. When there is a space at the top of the furnace that can be charged with the cold material again, new cold material is sequentially added to fill the molten metal. At this time, if the material has a skeleton shape such as a cast return material, the materials are entangled with each other and fall into the molten metal so that it does not go and a so-called hanging is formed, and only the molten metal in the lower portion is excessively heated. Overheating causes an accident, and if it is too large, there is a risk that the refractory will be rapidly melted and the bottom of the furnace will be pulled out, or the water cooling coil will be melted and a steam explosion will occur. Further, in the case of a vacuum induction furnace, when the hanging material falls into the molten metal in a vacuum, gas may be generated rapidly, and the volume in the vacuum furnace may be expanded rapidly to cause an explosion.

In the groove-type holding furnace, there is a type in which a thermocouple using a ceramic protective tube is immersed in the molten metal. However, when the groove-type holding furnace pours the molten metal and the molten metal decreases, the molten metal is supplied one after another. Is always kept at a constant high temperature and there is no heat shock. However, if it is used in a crucible induction furnace that melts only from cold material and repeats normal temperature and high temperature every few hours, the thermocouple rapidly breaks due to heat shock. When high-heat-resistant molybdenum is used, damage due to heat shock is eliminated, but molybdenum dissolves in molten metal such as steel and is worn away.

For this reason, the conventional method of avoiding such hanging of a rack which triggers such a serious accident relies on the operator monitoring the top of the furnace. It monitors the temperature of the molten metal and the melted state of the material by observing the molten metal being entrained by the method of charging the material so that the molten metal surface in the furnace can be seen through.

[0005]

In the conventional method for operating a crucible induction furnace, the above-mentioned conventional method requires a great deal of operator's skill and attention in order to avoid the hanging of the rack which triggers a large accident, and the safety is not high. Not sure. Further, in the case of a vacuum induction furnace, a material close to the total amount is often put into the furnace from the beginning, and the monitoring after sealing the furnace lid is insufficient, so the safety is not certain.

The object of the present invention is to measure the temperature of a high-temperature molten metal and to avoid the hanging of a rack which triggers a major accident without depending on the monitoring of an operator who requires a great deal of skill and attention. It is to provide a crucible-type induction furnace capable of ensuring safety.

[0007]

The crucible-type induction furnace of Invention 1 is a crucible-type induction furnace in which a coil is wound around a crucible made of refractory through a heat insulating material and an insulating material.
A thermocouple is embedded in a lower portion including a bottom portion having a height not more than one third of the height of the refractory material. At this time, the second aspect of the present invention is that the thermocouple also serves as the second antenna, and forms a hot water leak detection device together with the conductive first antenna exposed at the bottom and the hot water leak detection circuit.

A crucible-type induction furnace according to a third aspect of the present invention is a crucible-type induction furnace in which a coil is wound around a crucible made of a refractory with a heat insulating material and an insulating material interposed therebetween. The tip of the thermocouple tube is exposed and fixed in the crucible at the lower part including the bottom part having a height of 1 or less, and the thermocouple tube has a bottomed cylindrical zirconia outer periphery of the thermocouple connected to the lead wire. It is surrounded by a protective tube made of an alloy with molybdenum, the zirconia content is 30 to 70% by weight, and the balance is molybdenum. At this time, Invention 4 forms a ceramic or graphite film on the outer periphery of the protective tube exposed in the crucible.

[0009]

In the invention 1 or 2, reference is made to FIG. The thermocouple 5 embedded in the lower part including the bottom part of the refractory 1 measures the temperature of the molten metal in the lower part of the crucible in the state of being hung on a shelf,
If the temperature of the molten metal rises excessively, the circuit breaker 11 will operate and the furnace will be stopped, so hanging from a shelf can be avoided. Once again, thermocouple 5
Before b measures the upper limit temperature of the molten metal, the overheated molten metal locally wears the refractory 1 and if the thermocouple 5b is so-called blazed, the thermocouple 5b burns out and contacts the molten metal at the same time. The molten metal leak detection device operates, and the circuit breaker 11 also operates at this time to stop the furnace. This structure in which the thermocouple 5 is embedded in the refractory 1 is a normal thermocouple, and can withstand heat even if the molten metal is steel-based and the temperature is high.

In the invention 3 or 4, reference is made to FIG.
The protective tube 22 made of an alloy of zirconia and molybdenum has a toughness of molybdenum and a low thermal expansion coefficient and is resistant to heat shock. Although zirconia is a ceramic type and has a slightly high thermal expansion coefficient, it prevents melting loss of molybdenum into a molten metal. At this time,
The ceramic or graphite film 23 itself is slightly vulnerable to heat shock and causes minute cracks, but further prevents melting damage of the protective tube 22.

[0011]

FIG. 1 is a sectional view including a circuit diagram of the first embodiment, and FIG.
6 is a sectional view of a thermometer used in the crucible induction furnace of Example 2. FIG. In FIG. 1, the crucible-type induction furnace is formed by winding a coil 4 around a crucible made of refractory 1 with a heat insulating material 2 and an insulating material 3 in between. Then, the thermocouple 5 (5a, 5b) is embedded in the refractory 1. This thermocouple 5 may be equipped with an ordinary protection tube. It is advisable to embed the thermocouple 5 in the lower part including the bottom having a height not more than one third of the height of the refractory material 1. One thermocouple 5a is connected to the circuit breaker 11 via the output contact of the temperature recorder 6. The other thermocouple 5b also serves as a second antenna so as to form a normal hot water leak detection device, and has a conductive first antenna 7 exposed at the bottom, a hot water leak detection circuit 8, and a normal second antenna 9. Connected with.
Then, it is connected to the circuit breaker 11 via the output contact of the temperature recorder. Electric power is supplied to the coil 4 via the circuit breaker 11, the transformer 12, the rectifier 13, the reactor 14, the inverter 15, and the like. A matching device 16 is connected between the inverter 15 and the coil 4.

According to such a structure, the thermocouple 5 embedded in the lower part of the refractory 1 including the bottom part measures the temperature of the molten metal in the lower part of the crucible in the state of being suspended, and if the molten metal rises excessively. When the temperature rises, the circuit breaker 11 operates to shut down the furnace,
Ensure safety by avoiding the hangings that will trigger a major accident. Also, if the overheated molten metal locally wears the refractory 1 before the thermocouple 5b measures the upper limit temperature of the molten metal and the thermocouple 5b is so-called blazed, the thermocouple 5b burns out. At the same time, the molten metal leak detection device operates in contact with the molten metal, and the circuit breaker 11 also operates at this time to shut down the furnace. In this structure where the thermocouple 5 is embedded in the refractory 1,
It is a normal thermocouple, and it withstands heat even if the melt is steel-based and the temperature is high.

The thermometer used in the crucible induction furnace of the second embodiment shown in FIG. 2 has no melting loss due to the molten metal even if the thermocouple tube is directly exposed to the molten metal at high temperature, and is resistant to heat shock. . As shown in FIG. 1, in a crucible-type induction furnace in which a coil is wound around a crucible made of refractory through an insulating material and an insulating material, as shown in FIG. The tip of the thermocouple tube 20 is exposed and fixed in the crucible at the lower part including the bottom of the height. The thermocouple tube 20
The outer circumference of the thermocouple 21 connected to the lead wire is surrounded by a protective tube 22 made of an alloy of zirconia and molybdenum having a bottom, and the zirconia is 30 to 70% by weight and the balance is molybdenum. A ceramic or graphite coating 23 may be formed on the outer periphery of the protective tube 22 exposed in the crucible.
The conductor is protected by an insulator tube 24 and an alumina protective tube 25 as usual.

According to such a structure, the protective tube 22 made of an alloy of zirconia and molybdenum is resistant to heat shock due to the toughness of molybdenum and a low coefficient of thermal expansion, and the coefficient of thermal expansion is somewhat high because zirconia is a ceramic type. Prevents the melting of molybdenum into the melt. At this time, the ceramic or graphite film 23 itself is slightly vulnerable to heat shock and causes minute cracks, but it further prevents melting damage of the protective tube 22.

[0015]

According to the crucible-type induction furnace of Invention 1, the thermocouple having relatively low heat resistance, but having the heat resistance secured by being embedded in the refractory, measures the temperature of the molten metal in the lower part of the crucible. Since the temperature is raised, there is an effect that safety can be ensured by avoiding the hanging of a rack that triggers a large accident without depending on the monitoring of an operator who requires a great deal of skill and attention. At this time, according to the second aspect of the invention, the thermocouple also serves as a hot water leak detection device, and there is an effect that it is possible to urgently respond to an excessive temperature rise of the molten metal and avoid hanging from a shelf to further ensure safety. .

According to the crucible-type induction furnace of Invention 3, the toughness of zirconia and molybdenum and the coefficient of thermal expansion are harmonized to withstand heat shock, prevent melting loss to the molten metal, and directly measure the temperature of the molten metal. There is an effect that safety can be ensured by avoiding the hanging of a rack which triggers a large accident, without depending on the monitoring of an operator who requires a great deal of skill and attention. At this time, the ceramic or graphite film has an effect of further preventing melting damage of the protective tube.

[Brief description of drawings]

FIG. 1 is a sectional view including a circuit diagram of a first embodiment.

FIG. 2 is a sectional view of a thermometer used in the crucible-type induction furnace of Example 2.

[Explanation of symbols]

 1 Refractory 2 Thermal Insulation 3 Insulation 4 Coil 5a Thermocouple 5b Thermocouple 6 Temperature Recorder 7 First Antenna 8 Hot Water Leak Detection Circuit 9 Second Antenna 11 Circuit Breaker 20 Thermocouple Tube 21 Thermocouple 22 Protective Tube 23 Film

Claims (4)

[Claims] 1. A crucible-type induction furnace comprising a crucible made of refractory and a coil wound around the crucible with a heat insulating material and an insulating material interposed between the crucible and the crucible. A crucible induction furnace characterized in that a thermocouple is embedded in a lower portion including a bottom portion. 2. The crucible induction furnace according to claim 1, wherein
The crucible-type induction furnace, wherein the thermocouple also serves as a second antenna, and forms a hot water leak detection device together with a conductive first antenna exposed at the bottom and a hot water leak detection circuit. 3. A crucible-type induction furnace comprising a crucible made of refractory and a coil wound around the crucible via an insulating material and an insulating material, wherein the height of the refractory is 1/3 or less. The tip of the thermocouple tube is exposed and fixed in the crucible at the lower part including the bottom, and the thermocouple tube is protected by an outer circumference of the thermocouple connected to the conductor made of an alloy of zirconia and molybdenum having a bottomed cylindrical shape. A crucible induction furnace, characterized in that it is surrounded by a tube and contains 30 to 70% by weight of the zirconia and the balance is the molybdenum. 4. The crucible-type induction furnace according to claim 3,
A crucible-type induction furnace, wherein a ceramic or graphite film is formed on the outer periphery of the protective tube exposed in the crucible.