JPH0494090A - Magnetic field controlling method in induction heating electric furnace - Google Patents

Abstract

PURPOSE:To locally control the temperature and stirring of an object to be heated by inserting a magnetic field controlling coil locally between an induction coil of an induction heating electric furnace and the object to be heated and controlling the intensity of the induction current induced by the controlling coil. CONSTITUTION:A magnetic field controlling coil 6 is put between an induction coil 3 and a molten iron 5 and its height is short as compared with the induction coil 3 and it has a sufficient length to cover the molten iron locally and is put at a proper position, for example near the surface of the molten iron 5, and both ends of it are taken outside and connected with an inductance variable outside coil 7. Consequently, the inductance of the outside coil 7 is changed and the induction current running in the magnetic field controlling coil 6 is changed, so that the distribution of the magnetic field in a furnace becomes possible to be controlled.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magnetic field control method for locally controlling continuous heating and stirring in an induction electric furnace widely used in the steel and non-ferrous metal manufacturing fields. [Conventional technology] The induction electric furnace that is currently in widespread use is characterized by rapid heating and melting by inputting large amounts of electric power into the heated object, and intense induction stirring that occurs inside the molten metal. Molten X It is widely used for the purpose of uniformly mixing alloy components and refining molten metal by adding slag. [Problem to be solved by the invention] Induction electric furnaces have excellent heating and stirring functions, but on the other hand, they are prone to melting of furnace materials due to localized overheating and flow, contamination of molten metal due to entrainment of slabs, etc. This includes serious problems such as deterioration in the flotation and separation properties of non-metallic inclusions.

In order to meet the severe demands for high cleanliness imposed on steel and non-ferrous metal materials in recent years, there is an urgent need to solve the above-mentioned problems as soon as possible. To solve this problem, it is necessary to perform local humidity control or stirring control within the furnace. However, heating and stirring in an induction electric furnace are both performed by an alternating magnetic field generated within the furnace, but the distribution of the magnetic field is fixed depending on the design conditions of the induction electric furnace. Therefore, local temperature control and stirring control within the furnace is not possible with conventional techniques.

In view of this point, the present invention aims to perform local temperature control and stirring control without making major changes to existing induction electric furnaces.

[Means to solve the problem]

A magnetic field control method in an induction electric furnace according to the present invention to achieve the above object includes inserting a magnetic field control coil locally into the gap between the induction coil and the object to be heated in the induction electric furnace, and generating a magnetic field in the magnetic field control coil. The strength of the induced current is adjusted, thereby locally controlling the magnetic field within the induction electric furnace, thereby locally controlling the temperature and stirring of the object to be heated.

Note that as a means for adjusting the strength of the induced current generated in the above-mentioned magnetic field control coil, it is possible to regulate it by an external coil connected to this coil and having a variable inductance.

Alternatively, regulation may be performed using a variable resistor instead of this external coil.

In another invention, an electrically conductive cylinder is locally inserted into the gap between an induction coil and an object to be heated in an induction electric furnace, and the strength of the induced current generated in this cylinder is adjusted. The magnetic field inside the furnace is locally controlled, and the temperature and stirring of the heated object are locally controlled.

In order to adjust the strength of the induced current generated in the cylinder, a part of the cylinder may be cut out, both ends of which may be connected to a variable resistor, and the current may be regulated by the variable resistor.

Alternatively, instead of this variable resistor, an external coil with variable inductance may be used.

[For production]

The induced current generated in the magnetic field control coil or conductive cylinder reduces the alternating magnetic field applied to the object to be heated. Therefore, the temperature and stirring of the object to be heated facing the magnetic field control coil or conductive cylinder are locally controlled. Ru.

〔Example〕

1 to 4 show a first embodiment of the present invention. The induction electric furnace 1 is equipped with an induction coil 3 around the outer periphery of a reaction vessel 2 for adjusting the atmosphere, and a crucible 4 in the center. 5 is molten iron stored in a crucible, and a normal induction electric furnace is constructed as described above.

Reference numeral 6 denotes a magnetic field control coil, which is disposed between the induction coil 3 and the molten iron 5, has a shorter height than the induction coil 3, has a length that locally covers the molten iron 5, and has a length that covers the molten iron 5 locally. It is installed at a suitable location, for example, near the surface, and its both ends are taken out to the outside and connected to an external coil 7 with variable inductance.

This changes the inductance of the external coil 7,
By changing the induced current flowing through the magnetic field control coil 6, it is possible to control the magnetic field distribution within the furnace.

FIG. 2 shows an example of the state of the magnetic field controlled using the above-mentioned device, in which the axial magnetic flux density distribution on the central axis of the induction coil is shown using the inductance of the external coil as a parameter. The conditions in the figure are that the furnace frequency is 30 KHz, the number of turns of the induction coil is 129 turns, the inner diameter is 11 cm, the number of turns of the magnetic field control coil is 4 turns, the outer diameter is 8C, the magnetic field control coil 6 is placed in the center of the induction coil 3, and the object to be heated is placed in the center of the induction coil 3. Measured without. According to the figure, the magnetic flux density is the highest when the circuit of the magnetic field control coil 6 is opened.In other words, when the magnetic field control coil is not installed (white circle in the figure), the magnetic flux density is maximum at the center, but by closing the circuit of the magnetic field control coil, it is The degree of decrease varies depending on the inductance I of the external coil 7.

In this way, use the magnetic field control coil 6 and connect the external coil 7 to m.
By controlling the small inductance, the magnetic flux density within the furnace can be controlled, and thereby the temperature or agitation of the heated object can be locally controlled.

Next, FIG. 3 shows an example in which this magnetic field control is applied to local stirring control of molten iron. Note that it is difficult to quantitatively measure the stirring intensity inside molten iron. Therefore, a graphite round rod was immersed in molten iron, and the distribution of the dissolved amount was determined from the change in diameter.
Let us make an analogy to the flow state in the height direction in molten iron.

In Figure 3, the vertical axis shows the local mass transfer coefficient, which is an index representing the amount of dissolved graphite, and the horizontal axis shows the height from the bottom of the crucible, and the effect of the magnetic field control coil is calculated at a molten iron temperature of 1400°C1.
The figure shows the case of 500g of molten iron*f. However, the magnetic field control coil was installed opposite the top of the molten iron in the experiment. According to this, the stirring in the upper part of the molten iron is at its maximum when the circuit of the magnetic field control coil is opened, that is, when the inductance is set to infinite.In other words, when the magnetic field control coil is not inserted, the stirring at the top of the molten iron is at its maximum. Strength is weakened.

This is because the stirring intensity was reduced by controlling the magnetic field in the furnace using the magnetic field *J ij coil as described above.

Next, FIG. 4 shows a second embodiment. In this embodiment, a variable resistor I18 is attached in place of the external coil 7 of the previous example. The rest of the structure is the same as that of the previous example, and the same parts are given the same reference numerals and explanations will be omitted.

In the embodiment described above, the inductance of the magnetic field control coil 6 is regulated by the inductance of the external coil 7,
In this embodiment, the Ii flow is regulated by the variable resistor 8, and the experimental results showed that control equivalent to that shown in FIGS. 2 and 3 above was possible. Therefore, the experimental results are the same as those of the first embodiment, so the explanation will be omitted.

Next, FIGS. 5 and 6 show a third embodiment.

In this embodiment, a conductive cylinder io is inserted between the induction coil 3 and the object to be heated 5 instead of the magnetic field control coil 6 of each of the above embodiments, and the induced current generated in the cylinder 1o is regulated. The configuration of the induction electric furnace 1 is the same as in each of the embodiments described above, and the same parts are denoted by the same reference numerals and the explanation thereof will be omitted.

In the experiment, the cylinder 10 was made of molybdenum, and in order to control the induced current, a notch II was formed at one location t in the cylinder 10, and both ends of the cylinder 1o were connected to an external variable resistor 12.

In the case of this embodiment as well, the control of the magnetic field distribution by the cylinder 10 is
This is the same as in each of the above embodiments, and FIG. 6 shows the experimental results of termination of local stirring control using the cylinder 1o.

Also in this NJ example, in the upper part of the molten iron where the conductive cylinder 18 was installed, a remarkable change in the amount of melting due to the change in resistance t was observed.

Next, FIG. 7 shows a fourth embodiment. In this embodiment, an external coil with variable inductance is attached in place of the variable resistor 12 of the third embodiment. The rust induction II flow generated in the cylinder 10 by the external coil 13 and the accompanying f#lJ control of the magnetic field distribution are the same as those in the first embodiment, and the explanation thereof will be omitted.

In each of the above examples, the change in the amount of dissolved graphite has been explained, but this change in the amount of dissolved graphite corresponds to a change in the local stirring intensity of molten iron, and does not indicate the local stirring control according to the present invention. be.

It is clear that local temperature control can also be performed by in-furnace magnetic field control as shown in FIG. 2, similar to stirring control.

Furthermore, although the above embodiments show the results of experiments using a small induction electric furnace with a frequency of 30 KHz, the principle of magnetic field control according to the present invention is not necessarily limited to this, and can be applied regardless of the frequency of the furnace and the size of the furnace. [Effects of the Invention] According to the present invention, a magnetic field control coil or a conductive cylinder is locally inserted between the induction coil of the induction electric furnace and the object to be heated, and By adjusting the strength of the induced current, the part of the magnetic field in the electric furnace that faces these magnetic field control coils or cylinders is controlled, so the temperature and stirring of the heated object can be locally controlled. can.

In addition, the strength of the induced current can be adjusted by cutting out these control coils or cylinders and connecting them to external coils or variable resistors, respectively! By using Section II, it is possible to control heating and stirring to the required degree at the required time without stopping the operation of the furnace.

Moreover, the attachment of the magnetic field control coil or the conductive cylinder can be easily modified without making any major changes to the existing induction electric furnace.

[Brief explanation of drawings]

Figures 1 to 3 relate to the first embodiment, Figure 1 is a longitudinal section of the induction furnace, Figure 2 is a graph showing how to control the magnetic field by the magnetic field control coil, and Figure 3 is the graph showing the magnetic field control coil. A graph showing the control procedure for stirring molten iron. Fig. 4 relates to the second embodiment, a longitudinal cross-sectional view of the induction electric furnace, Figs. 5 and 6 relate to the third embodiment, and Fig. 5 shows a longitudinal cross-section of the induction electric furnace. Explanation: FIG. 6 is a graph showing a stirring control procedure using a conductive cylinder, and FIG. 7 is a longitudinal cross-sectional view of an induction electric furnace according to the fourth embodiment. 1 is an induction electric furnace, 3 is an induction coil, 5 is molten iron, 6 is a magnetic field control coil, 7 and 13 are external coils, 8° 12 is a variable resistor, and 10 is a conductive cylinder. Figure 3 Figure 2 RO 913: Height of the island (Cm) Distance from Furuya and Jikara (cm) Figure 6 Ru 1γ Yuri Struggle (cm)

Claims (6)

[Claims] (1) A magnetic field control coil is inserted locally into the gap between the induction coil and the object to be heated in the induction electric furnace, and the strength of the induced current generated in this magnetic field control coil is adjusted, thereby controlling the inside of the induction electric furnace. A method for controlling a magnetic field in an induction electric furnace, the method comprising locally controlling the magnetic field in the induction furnace, and locally controlling the temperature and stirring of a heated object. (2) The induction electric furnace according to claim 1, wherein an external coil with variable inductance is connected to the magnetic field control coil, and the induced current generated in the magnetic field control coil is continuously regulated by the external coil. magnetic field control method. (3) A variable resistor is connected to the magnetic field control coil, and the induced current generated in the magnetic field control coil is continuously regulated by the variable resistor. Magnetic field control method. (4) A conductive cylinder is locally inserted into the gap between the induction coil and the object to be heated in the induction electric furnace, and the strength of the induced current generated in the cylinder is adjusted, thereby controlling the temperature inside the induction electric furnace. A method for controlling a magnetic field in an induction electric furnace, characterized by locally controlling a magnetic field, and locally controlling the temperature and stirring of an object to be heated. (5) A part of the conductive cylinder is cut out and both ends thereof are connected to a variable resistor, and the induced current generated in the cylinder is continuously regulated by the variable resistor. A magnetic field control method in an induction electric furnace described in . (6) A part of the conductive cylinder is cut out, both ends of which are connected to an external coil with variable inductance, and the induced current generated within the conductive cylinder is continuously regulated by this external coil. The magnetic field control method in an induction electric furnace according to claim 4.