JPH0235004B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic desulfurization apparatus for removing sulfur from a molten metal by electromagnetically stirring the molten metal and a desulfurization agent.

Cupora is widely used as a means of obtaining molten metal in iron foundries, etc., but since cupola uses coke as a fuel, the molten metal melted using cupola contains high-density sulfur. On the other hand, demand and production of spheroidal graphite cast iron as a high-quality cast iron are increasing, but when using Kyupora molten metal, graphite spheroidization by adding a spheroidizing agent is not successful due to the sulfur content. Therefore, in the production of spheroidal graphite cast iron using Kyupora molten metal, a desulfurization step is generally provided before adding the spheroidizing agent. This deflowing step is a step in which a powdery desulfurizing agent is added to the molten metal and desulfurization is carried out through a chemical reaction, and calcium carbide, calcium oxide, etc. are used as the degranulating agent. Here, the desulfurization process when calcium carbide is used is as follows: CaC ₂ +S→CaS+2C (1). CaS in equation (1) floats to the top of the molten metal as a so-called slag, and when the molten metal temperature is high, it vaporizes and disperses into the atmosphere. In the above-mentioned desulfurization process, since the specific gravity of the desulfurization agent is small, it is necessary to stir the molten metal to promote the reaction, and the porous plug method, gas injection method, etc. have conventionally been used as the stirring method. However, with these stirring methods, the temperature of the molten metal decreases significantly due to stirring, so it is necessary to raise the temperature of the molten metal after desulfurization, and a heating furnace (for example, a groove-type induction furnace) must be separately installed to raise the temperature. This has always been a problem, especially in small-scale production plants, where the expense ratio for heating equipment becomes large.

Therefore, in order to solve the above-mentioned problem, the present applicant first developed an electromagnetic desulfurization device that can raise the temperature and stir at the same time. Figure 1A is a cross-sectional view showing the configuration of this electromagnetic desulfurization equipment, and Figure 1B is A-A shown in Figure A.
It is a line arrow view. In this figure, 1 is a crucible whose horizontal cross section is of the type shown in B of the figure.
Reference numeral 2 denotes a cylindrical communication passage communicating with the bottom of the crucible 1 and extending vertically upward. The crucible 1 and the communication path 2 are each formed using a refractory material 3 inside a cylindrical coil path material 11 around which a coil 5 is wound. The yoke 6 is arranged radially around the outer circumference of the coil 5 as shown in FIG. This prevents heat generation due to eddy current in the steel materials (not shown) that make up the structure. The height of the above-mentioned upper end of the coil 5 is equal to the level of the molten metal in the crucible 1 except for the molten metal discharge port 15, and the height of the upper end of the coil 5 is equal to the level of the molten metal in the crucible 1 at the portion where the molten metal is discharged. positioned. The reason why the upper end position of the coil 5 is made equal to the level of the molten metal except at the discharge port 15 is to improve the induction efficiency and obtain a large stirring flow. For example, if the upper end of the coil 5 is lower than the molten metal level, the induction efficiency will improve, but the molten metal near the molten metal surface will not be electromagnetically induced, and the stirring flow will become weak near the molten metal surface due to the static pressure of the molten metal in this area. Moreover, if the upper end of the coil 5 is higher than the molten metal level, the induction efficiency itself will deteriorate. Also,
This coil 5 is formed of a hollow copper tube, and during operation, forced water cooling is performed by flowing water through the hollow part. 7 is Kyupora molten metal continuously supplied from Kyupora,
8 is a desulfurizing agent whose main ingredients are calcium carbide and calcium oxide.

When an alternating current is supplied to the coil 5 in the above-described configuration, a flow of molten metal is generated in the crucible 1 as shown by the arrow in the figure, similar to an induction furnace, etc., and at the same time, heat is generated in the molten metal in the crucible due to eddy current. happens. In this way, the molten metal in the crucible is stirred, drained, and heated, and the drained molten metal 10 is discharged to the outside through the communication path 2.

As described above, the electromagnetic desulfurization apparatus previously developed by the present applicant had an extremely large economic effect because stirring and temperature raising could be performed simultaneously.

By the way, if the device has the same effect,
A smaller size is extremely advantageous in terms of production costs, maintenance costs, maintenance work, installation space, etc.

In view of the above circumstances, the present invention takes the previously developed electromagnetic desulfurization device one step further, and provides an electromagnetic desulfurization device that can efficiently desulfurize, stir, and raise the temperature of molten metal while having the minimum necessary size. The crucible capacity is set so that the average residence time of the molten metal is 5 to 10 minutes, which is determined by the ratio of the inlet flow rate to the crucible capacity, and the temperature rise of the molten metal during the average residence time is 50 to 10 minutes. It is characterized in that the diameter/depth ratio of the crucible is set so that when electric power at 100° C. is supplied to the induction coil, the surface height of the molten metal in the crucible is 8 to 16 cm.

Embodiments of the present invention will be described below with reference to the drawings.

The mechanical configuration in one embodiment of the present invention is similar to that of the electromagnetic desulfurization apparatus previously developed by the applicant, that is, the same as that shown in FIGS. 1A and 1B. However, in this embodiment, the size relationships of the various parts of the device are as described below, and the size is the minimum while achieving the maximum efficiency.

Next, how to derive the dimensions of each part of the device in this embodiment will be explained.

Due to the characteristics of the cupola, the flow rate of the cupola molten metal 7 shown in FIG. Then, the time T [min] during which the Kyupora molten metal 7 stays in the crucible 1
is the inflow amount Q [Kg/min] of the Kyupora molten metal 7 and the amount of molten metal that the crucible 1 can accommodate (hereinafter referred to as crucible capacity)
It is determined by W [Kg], and T=W/Q...(2). This residence time T [min] is the time during which the desulfurization reaction shown by equation (1) is carried out, and is an extremely important element in the desulfurization process. As a result of experiments conducted by the inventor, it was found that the desulfurization reaction is efficiently completed when the residence time T is 5 to 10 minutes. )
It can be seen that the crucible capacity W may be set so that T in the equation is 5 to 10.

Next, how much the temperature of the molten metal in the crucible 1 should be raised will be explained.

In the production process of ductile cast iron in a typical cupola operation, cupola taps at 1530℃ → conventional desulfurization equipment (1500℃) ――――――→ 1450℃ spheroidization treatment (1480℃) ――――――→ 1400℃ casting …
...Final mold casting (1420℃) 1350℃ process. In this diagram, the temperatures shown in parentheses are the required temperatures for each process calculated backward from the appropriate casting temperature in the final mold. Temperatures without parentheses are the actual temperatures, and the actual temperatures are clearly too low. I understand. For this,
Conventionally, a heating furnace has been installed after the desulfurization equipment, which has already been described as an economic problem in ductile production using cupola operation. Therefore, in the desulfurization equipment, the temperature must be raised by at least 50°C as shown in the diagram above. In addition, depending on the circumstances of the factory, even larger temperature increases may be necessary, but generally 50
It can be said that a temperature increase in the range of ~100°C is sufficient.

By the way, the specific heat of cast iron is generally expressed as P ₁₀₀ = 21 [kwh/ton] ...(3), which indicates that the energy required to raise the temperature of 1 ton of molten metal by 100℃ is 21 kwh. . Therefore, the retained molten metal is △Te (50≦
The power P required to raise the temperature by △Te≦100)
[kw] is if the inflow is Q′ [ton/min].

P=21×△Te／100×T／60×60×Q′ =0.21△Te・T・Q′ ……(4), and Q′ [ton/min] in this equation (4) is
Converting to [Kg/min] and setting the constant part as K ₁ , we get P=K ₁・△Te・T・Q ……(5). Therefore, since it is sufficient that the electric power calculated by this equation (5) is induced into the molten metal in the crucible, the electric power to be supplied to the coil 5 is determined in accordance with P shown in the equation (5). It is well known that in this type of apparatus, all of the electric power induced into the molten metal in the crucible becomes heat, and less than 0.1% of the total becomes stirring energy.

Next, FIG. 2 shows a model system in which the crucible 1 is viewed as a cylinder, where d is the inner diameter and l is the depth. This depth l is determined by the height of the opening of the communication path 2 (FIG. 1A). As already mentioned, when power is supplied to the coil 5, a stirring flow is generated in the molten metal in the crucible as shown by the arrow in the figure.At this time, the top surface of the molten metal in the crucible is open upward, so It becomes exciting as shown in .
It is known that if this raised height is h [cm], h is expressed by the following formula.

In addition, ρ [Ω-cm]: Electric specific resistance of the molten metal P [kw]: Power induced in the molten metal s [g/cm ³ ]: Specific gravity of the molten metal [Hz]: At the frequency of the power supply supplied to the coil 5. be.

It is easy to understand that this height h corresponds to the strength of the stirring flow, but according to the inventor's experiments, when the height h is 8 to 16 cm, it is necessary and sufficient to promote the desulfurization reaction. It was found that a stirred flow was obtained.
Also, from equation (6), the stirring power is proportional to the input power,
It can be seen that it is inversely proportional to the diameter and depth of the crucible. Then, the constant part (ρ, ,
If we set π, s, 3.16, 10 ³ ) as K ₂ and dl=η, we get h=K ₂ P/η ...(7), and substitute 8 to 16 for h in equation (7), By substituting the power value determined by the heating temperature into P, it is possible to obtain η (that is, d·l) that provides a necessary and sufficient stirring flow. On the other hand, the crucible volume V can be expressed as V=πd ² /4・l...(8) from Figure 2, so the crucible volume W mentioned above is W=πd ² /4・l・S×10 ^-3 ... It can be expressed as (9), and if the constant part of this equation is set as K ₃ , it can be expressed as W=K ₃・η・d (10).

Now, as mentioned above, the residence time T is 5 to 10 minutes,
The heating temperature △Te is 50 to 100℃, and the height of the rise h is 8 to 100℃.
When each is set to 16 cm, the inner diameter d and depth l that maximize the efficiency of desulfurization, stirring, and temperature increase while being the minimum necessary for the crucible 1 can be determined by the procedure shown below.

: The electric power P to be induced into the molten metal in the crucible can be uniquely determined from the above-mentioned equation (5).

: Using P obtained in equation (7), η that provides a necessary and sufficient stirring flow is determined.

: From equation (2), the minimum required crucible capacity W corresponding to the capacity of the cupola to be used can be uniquely determined.

: The inner diameter d of the crucible 1 is determined from equation (10) using η determined by and W determined by .

: The crucible depth l can be uniquely determined from equation (9) using d determined by and W determined by.

As described above, the volume, inner diameter, and depth of crucible 1 are calculated in order to obtain an appropriate stirring power with the electric power required for temperature rise, and to obtain a residence time that allows sufficient desulfurization reaction. be able to.

As explained above, according to the present invention, the crucible capacity is set so that the average residence time of the molten metal is 5 to 10 minutes, which is determined by the ratio of the inlet flow rate to the crucible capacity, and The diameter/depth ratio of the crucible is set so that when power is supplied to the induction coil so that the temperature of the molten metal rises from 50 to 100°C, the surface height of the molten metal in the crucible is 8 to 16 cm. As a result, it is possible to efficiently desulfurize, stir, and raise the temperature of the molten metal while maintaining the minimum necessary size.

[Brief explanation of drawings]

Figure 1A is a cross-sectional view showing the configuration of an electromagnetic desulfurization device previously developed by the applicant, Figure 1B is a view taken along the line A-A shown in Figure A, and Figure 2 shows the crucible 1 in a cylindrical shape. FIG. 2 is a schematic configuration diagram showing a model system when viewed from above. 1... Crucible, d... Diameter, l... Depth, h...
climax height.

Claims (1)

[Scope of Claims] 1. A crucible to which molten metal is continuously supplied, and a communication path that communicates with the bottom of the crucible and has an opening above the bottom to discharge the molten metal after desulfurization to the outside. In an electromagnetic desulfurization device that is installed inside an induction coil wound in a cylindrical shape and simultaneously raises the temperature and stirs the molten metal in the crucible by electromagnetic induction, (a) the crucible has the following characteristics: When the induction coil has a capacity such that the average residence time of the molten metal determined by the ratio is 5 to 10 minutes, and power is supplied to the induction coil such that the temperature rise of the molten metal during the average residence time is 50 to 100 ° C. (b) The induction coil has a diameter/depth ratio such that the surface height of the molten metal in the crucible is 8 to 16 cm; An electromagnetic desulfurization device characterized by the following: