JP2014037568A - Hot pig iron preliminary processing method and agitation body for hot pig iron preliminary processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce oscillation of an agitation apparatus even when the number of revolutions of an impeller is made high in order to improve reaction efficiency in hot pig iron preliminary processing that is performed while agitating hot pig iron by using an agitation body including a rotation axis and an impeller and rotating the impeller immersed in the hot pig iron.SOLUTION: In the hot pig iron preliminary processing method, an impeller 3 attached to a tip of a rotation axis 2 having such a shape that the width is made a tapered from a top edge toward a bottom edge is immersed in a hot pig iron 5 in a refining vessel 4, and the immersed impeller is rotated, thereby the hot pig iron and an additive 6 are agitated to perform the hot pig iron preliminary processing method, and a resonance frequency of primary flexure of the rotation axis is made larger than the number of revolutions of the impeller that agitates the hot pig iron to perform the agitation.

Description

  The present invention stirs hot metal and an additive having a lower specific gravity than the hot metal by immersing an impeller attached to the tip of the rotary shaft in the hot metal and rotating the impeller through the rotary shaft. And a stirring body used in hot metal pretreatment such as desulfurization and dephosphorization.

  Conventionally, in refining to remove impurities in hot metal (hereinafter also referred to as “hot metal pretreatment” as appropriate), an additive (refining agent) for reacting with impurities to remove the impurities is added to the hot metal, Is stirred and mixed to promote the reaction between the additive and the impurities. This agitation / mixing is performed to increase the reaction interface area between the hot metal and the additive because the refining reaction takes place at the interface between the hot metal and the additive. In addition, the additive generally has a specific gravity smaller than that of the hot metal, so that the hot metal floats on the surface of the hot metal. Therefore, the hot metal must be stirred even when the hot metal and the additive are reacted.

  As a method of stirring the hot metal, a gas blowing stirring method in which gas is blown into the hot metal and a mechanical stirring method in which a rotating stirring body such as an impeller is immersed in the hot metal to mechanically stir the hot metal are performed. . Comparing the gas blowing agitation method with the mechanical agitation method, the mechanical agitation method is more efficient in refining reaction because it is easy to repeat the additive that floated on the hot metal surface after being entrained in the hot metal surface. As a result, the mechanical stirring method is currently the mainstream.

  For example, in the hot metal desulfurization process, which is one of the hot metal pretreatments, the impeller is immersed in the hot metal contained in the refining vessel, and the desulfurizing agent is added to the hot metal in the refining vessel while rotating the impeller to stir the hot metal. A mechanical stirring type desulfurization method for adding and desulfurizing hot metal is widely performed.

  In the mechanical stirring desulfurization method of hot metal using an impeller, various proposals have been made to achieve efficient desulfurization treatment for the purpose of shortening the processing time and reducing the basic unit of desulfurization agent. As described in Non-Patent Document 1, by increasing the rotational speed of the impeller and increasing the speed, the reaction interface area between the hot metal and the additive is increased and the reaction efficiency is improved. It is effective to rotate it.

  However, when the rotation of the impeller is increased, vibration is increased and damage to the stirring device is caused. Therefore, conventionally, as disclosed in Patent Document 1, for example, when the impeller is rotated at a high speed, the upper limit of the stirring power is increased. It has been done to limit the value so that excessive force due to vibration does not act on the stirrer. However, in this method, since the upper limit value of the stirring power is limited, the stirring ability cannot be said to be sufficient, and the reaction efficiency cannot be sufficiently improved.

  On the other hand, in order to suppress the vibration caused by the rotation of the impeller, Patent Document 2 discloses a stirring device that supports the lifting mechanism of the impeller using a spring. In this stirrer, it is possible to suppress a certain amount of vibration with a spring, but if the rotation speed increases, centrifugal force due to mass imbalance and stirring reaction force from hot metal increase. While the vibration suddenly increases, the force that can be supported by the spring is limited, and therefore it is difficult to suppress vibration during high-speed rotation even with this stirring device.

  Thus, in hot metal pretreatment using an impeller, it is known that increasing the rotation speed of the impeller is effective from the viewpoint of improving the reaction efficiency, but from the viewpoint of preventing damage to the equipment, There was a situation that the rotation speed of the impeller could not be increased beyond a certain level.

JP 2005-290434 A JP 2005-48226 A

Iron and steel, vol. 90 (2004) No. 6. p. 322-328

  The present invention has been made in view of the above circumstances, and an object thereof is to use a stirrer provided with a rotating shaft and an impeller while rotating the impeller immersed in the hot metal while stirring the hot metal. In hot metal pretreatment, it is to provide a hot metal pretreatment method capable of reducing the vibration of the stirring device even if the impeller is rotated at a high speed in order to improve the reaction efficiency. It is an agitator provided with an impeller attached thereto, and is to provide an agitator for hot metal pretreatment that can reduce vibration of an agitator even when rotated at a high speed.

  The present inventors have intensively studied to solve the above problems. As a result, in the stirrer including the rotating shaft and the impeller, the shape of the rotating shaft is controlled so that the resonance frequency of the primary bending of the rotating shaft is higher than the rotational speed of the impeller that stirs the molten iron. It has been found that even when the number of rotations is increased, the vibration of the stirring device does not increase and the molten iron can be stirred more strongly.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] A hot metal preliminary treatment method in which an impeller attached to a tip portion on the lower end side of a rotating shaft is immersed in hot metal in a refining vessel, and the hot metal and the additive are agitated by rotating the immersed impeller. The rotating shaft has a shape with a diameter tapered from the upper end to the lower end, and the resonance frequency of the primary bending of the rotating shaft is higher than the rotational speed of the impeller that stirs the hot metal and the additive. A hot metal pretreatment method characterized by enlarging and stirring.
[2] The hot metal preliminary treatment method according to [1], wherein the resonance frequency of the primary bending is 1.2 times or more the rotation speed of the impeller.
[3] The hot metal preliminary treatment method according to [1] or [2] above, wherein the rotating shaft has a hollow structure.
[4] The hot metal preliminary treatment method according to any one of [1] to [3] above, wherein the rotation speed of the impeller is 140 rpm to 200 rpm.
[5] A rotary shaft having a shape whose diameter tapers from the upper end toward the lower end, and an impeller attached to a tip portion on the lower end side of the rotary shaft, and the diameter d _{1 of the} rotary shaft on the upper end side. The hot metal pretreatment stirrer characterized in that the ratio (d ₂ / d ₁ ) of the diameter d ₂ of the rotating shaft on the lower end side to the lower end is 0.34 or more and 0.55 or less.
[6] The hot metal pretreatment stirrer according to [5] above, wherein the resonance frequency of the primary bending of the rotating shaft is 2.8 to 4.0 Hz.
[7] The stirrer for hot metal pretreatment according to [5] or [6] above, wherein the rotating shaft has a hollow structure.

  According to the present invention, the hot metal is stirred using the hot metal pretreatment stirrer including the rotating shaft and the impeller having a diameter tapered from the upper end to the lower end, thereby resonating the primary bending of the rotating shaft. The frequency can be increased, and as a result, the resonance frequency of the primary bending of the rotating shaft can be made larger than the rotational speed of the impeller that stirs the molten iron. For this reason, an increase in vibration due to resonance of the stirrer can be avoided, so that the stirrer can be rotated at high speed. Thereby, it is realized that the additive supplied to the hot metal is efficiently dispersed in the hot metal, and the hot metal is stirred with a higher reaction efficiency than in the past. As a result, for example, in the case of desulfurization treatment of hot metal, reduction of the desulfurizing agent basic unit and reduction of the amount of generated slag associated therewith are achieved, and an industrially beneficial effect is brought about.

It is the schematic which carries out the desulfurization process of hot metal, stirring hot metal using the stirring body which concerns on this invention. It is a schematic sectional drawing when the stirring body shown in FIG. 1 is cut | disconnected in the surface which passes along the centerline of a rotating shaft. It is a schematic sectional drawing by the arrow view from the III-III line | wire shown in FIG. It is a graph showing the relationship between the upper side of the rotary shaft lower side rotary shaft ratio of diameter d ₂ of the relative diameter d ₁ of the (d ₂ / d ₁₎ and the axis of rotation of the relative resonant frequency _(f tapered / f _linear). It is a schematic sectional drawing of an example different from the example of FIG. 2 when the stirring body shown in FIG. 1 is cut | disconnected in the surface which passes along the centerline of a rotating shaft. The relationship between the ratio (d _i1 / d _o1 ) of the inner diameter d _i1 of the rotating shaft to the outer diameter d _o1 of the rotating shaft of the hollow structure and the relative resonance frequency (f _hollow / f _solid ) of the rotating shaft is shown, and (d _i1 / d _o1) is a graph showing the relationship between the ratio of the outer diameter d _o1 of rotation axis of the hollow structure (d _o1 / d) of a solid structure and to the diameter d of the rotating shaft. It is a graph which shows a frequency response function of a rotating shaft which is a solid structure and has a constant diameter from the upper end toward the lower end.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing an example in which hot metal preliminary treatment is performed while stirring hot metal by applying the present invention, and is a schematic diagram of desulfurizing hot metal while stirring hot metal using the stirrer according to the present invention. is there.

  A hot metal preliminary treatment stirrer 1 according to the present invention includes a metal rotating shaft 2 and an impeller 3 that is attached to the tip of the rotating shaft 2 and projects in the radial direction of the rotating shaft 2. . A flange 2a is installed at the upper end of the rotating shaft 2. The flange 2a is connected to a rotating device (not shown) including an electric motor, a speed reducer, a turning shaft, and the like, and drives the rotating device. Thus, the rotating shaft 2 and the impeller 3 are configured to rotate at an arbitrary number of rotations.

When desulfurizing the hot metal 5 as the hot metal pretreatment, the rotating shaft 2 and the impeller 3 are lowered together with the rotating device, and the impeller 3 is immersed in the hot metal 5 accommodated in the refining vessel 4 from above, The impeller 3 is rotated via the rotation shaft 2. As the impeller 3 rotates, the hot metal 5 is stirred, and the additive 6 (in this case, a desulfurizing agent) supplied on the bath surface of the hot metal 5 and the hot metal 5 are stirred and mixed by this stirring, and the sulfur in the hot metal And the additive 6 proceed, sulfur in the hot metal is absorbed by the additive 6 and the hot metal 5 is subjected to desulfurization treatment. In the desulfurization treatment of the hot metal 5, quick lime (CaO) alone, CaO—CaF ₂ desulfurization agent, CaO—Al ₂ O ₃ desulfurization agent, or the like is used as the additive 6, that is, as the desulfurization agent.

  The detailed structure of the stirring body 1 for hot metal pretreatment used in this way will be described. 2 is a schematic cross-sectional view when the stirring body shown in FIG. 1 is cut along a plane passing through the center line of the rotation axis, and FIG. 3 is a schematic cross-sectional view taken along the line III-III shown in FIG. is there. The rotating shaft 2 shown in FIG. 2 has a solid cylindrical structure.

As shown in FIG. 2, the rotating shaft 2 has a shape whose diameter tapers from the upper end toward the lower end. As shown in FIGS. 2 and 3, a plurality of metal plates 3a serving as a core metal of a stirring blade of the impeller 3 are connected to the tip portion on the lower end side of the rotating shaft 2 by welding or the like. The impeller 3 is formed by covering the surroundings with a refractory 7. The rotating shaft 2 is also covered with a refractory 7 in the vicinity of the impeller 3. The hot metal 5 is at a high temperature, and the refractory 7 ensures the durability of the impeller 3 when immersed in the hot metal 5. The reason for covering the lower part of the rotating shaft 2 with the refractory 7 is to protect the rotating shaft 2 from the heat of the hot metal 5. As the refractory 7, for example, Al ₂ O ₃ , MgO, SiO ₂ and compounds or mixtures thereof are used, and the rotating shaft 2 and the metal plate 3 a may be made of steel. In FIG. 3, the impeller 3 has four stirring blades, but any number of stirring blades may be used as long as there are two or more stirring blades.

  When the impeller 3 immersed in the hot metal 5 is rotated, a radial force, that is, a force in the direction of bending the rotary shaft 2 acts on the stirring blade portion of the impeller 3 due to the centrifugal force and the stirring reaction force. Since force is periodically generated according to the rotation speed of the impeller 3 during stirring, if the rotation frequency of the impeller 3 and the resonance frequency of the primary bending of the rotating shaft 2 coincide, a resonance phenomenon occurs and a large vibration is generated. To do. Therefore, by designing the rotating shaft 2 so that the resonance frequency of the primary bending of the rotating shaft 2 is higher than the target rotating frequency of the impeller 3, it is possible to achieve high speed at the target rotating frequency without generating large vibrations. Rotation is possible, and an effective stirring effect can be obtained. Further, as the impeller width D (see FIG. 3) from one end of the stirring blade to the other end increases and the diameter of the rotary shaft 2 on the lower end side decreases, the stirring blade moves to the hot metal 5. Since the effective area of the stirring blade portion to which force is applied can be increased, the stirring effect can be improved.

  Specifically, the shape of the rotating shaft 2 is controlled using the following method so that the resonance frequency of the primary bending of the rotating shaft 2 is higher than the rotating shaft of the impeller 3.

  Since the bending of the rotating shaft 2 can be modeled as a bending vibration of a beam having a concentrated mass, the resonance frequency f of the primary bending of the rotating shaft 2 can be expressed by the following equation (1).

In the equation (1), C ₁ represents a constant, E is the Young's modulus (Pa) of the rotating shaft 2, L is the length (m) of the rotating shaft 2, and I is the secondary moment of inertia (m ⁴ ) of the rotating shaft 2. ), M is the mass (kg) of the rotating shaft 2, and M is the concentrated mass (kg) acting on the tip of the rotating shaft 2, which is the total mass of the refractory and the metal or slag that adheres during stirring.

  The Young's modulus E of the rotating shaft 2 is a constant determined by the material. The length L of the rotating shaft 2 is a constant determined by the mechanical stirring environment because the maximum length is restricted by the volume (depth) of the refining vessel 4. The concentrated mass M is also a constant determined by the amount of the hot metal 5 in the refining vessel 4 and is a constant determined by the environment of mechanical stirring. Here, it is assumed that the mass m of the rotating shaft 2 is constant.

As shown in FIG. 2, the rotary shaft 2 has a shape in which the shaft diameter (width) decreases from the upper end to the lower end and the rate of change of the shaft diameter is constant, that is, the rotary shaft 2 is tapered. And the density ρ (kg / m ³ ) of the rotating shaft 2 is constant, the mass m _tapered of the rotating shaft 2 is expressed by the following equation (2).

In the equation (2), the diameter of the rotary shaft 2 on the upper end side is d ₁ (m), and the diameter of the rotary shaft 2 on the lower end side is d ₂ (m).

Further, the sectional secondary moment I _tapered of the _tapered rotating shaft 2 is expressed by the following equation (3).

  Substituting equation (3) into equation (1) leads to equation (4) below.

Divide both sides of equation (4) by the mass m _tapered (equation (2)) of the rotating shaft 2, that is, divide the left side of equation (4) by the left side of equation (2) and replace the right side of equation (4) with ( When dividing by the right side of the equation (2), the resonance frequency f _tapered per unit mass m _tapered can be expressed by the following equation (5).

Meanwhile, in the rotation shaft 2 shown in FIG. 2, if the same diameter d ₂ of the rotary shaft 2 of the lower end and the diameter d ₁ of the rotary shaft 2 of the upper side, the rotary shaft 2, the diameter from top to bottom It has a certain shape, that is, it is linear. Therefore, when obtaining the resonant frequency f _linear per unit mass m _linear is a linear diameter d of the rotary shaft at which the mass m _linear axis of rotation (5) of the same and the mass m _Tapered, equation d ₁ And d ₂ can be substituted to express f _linear / m _linear by the following equation (6).

Divide both sides of equation (5) by equation (6), that is, divide the left side of equation (5) by the left side of equation (6), divide the right side of equation (5) by the right side of equation (6), Furthermore, when dividing the molecular and denominator of the right side in d ₁ ^2, by the following equation (7), it is possible to represent the relative resonant frequency _f tapered / f _linear.

The horizontal axis is the ratio d ₂ / d ₁ of the diameter d ₂ of the rotating shaft on the lower end side to the diameter d ₁ of the rotating shaft on the upper end side, and the vertical axis is the relative resonance frequency f _tapered / f _linear , A graph showing the relationship between (d ₂ / d ₁ ) and the relative resonance frequency (f _tapered / f _linear ) is shown in FIG. As shown in FIG. 4, when the ratio of d ₂ / d ₁ is in the range of 0.34 to 0.55, the relative resonance frequency (f _tapered / f _linear ) can be 1.2 or more. For this reason, while maintaining the mass m _linear of the rotating shaft 2, the rotating shaft 2 has a shape in which the diameter _tapers from the upper end to the lower end, thereby _reducing the resonance frequency f _tapered of the rotating shaft 2 from the upper end to the lower end. The resonance frequency f _linear of the rotary shaft having a constant diameter can be increased to 1.2 times or more, and the rotational speed of the rotary shaft 2 can be increased without being affected by resonance.

The inventors further examined what difference occurs in the vibration of the stirrer 1 between the case where the rotating shaft 2 has a solid structure and the case where the rotating shaft 2 has a hollow structure. FIG. 5 shows a stirring body having a rotating shaft 2 having a hollow structure with a constant diameter from the upper end toward the lower end. As shown in FIG. 5, when the rotating shaft 2 is a hollow circular tube having an outer diameter d _o1 and an inner diameter d _i1 , and is configured in a straight line from the upper end to the lower end, the sectional secondary moment I _{hollow of the} rotating shaft 2. Is represented by the following equation (8).

The mass m _hollow of the rotating shaft 2 of the hollow circular tube can be expressed by the following equation (9).

By substituting the equation (8) into the moment of inertia I of the section of the rotating shaft 2 in the equation (1) and dividing both sides by the equation (9) (mass m _hollow of the rotating shaft 2), the rotation per unit mass m _hollow The following equation (10) representing the resonance frequency f _hollow of the primary bending of the shaft 2 is derived.

When the diameter of the rotating shaft having the mass m _solid of the _solid structure that is the same as the mass m _hollow of the rotating shaft 2 of the hollow circular tube is d, per unit mass m _solid of the rotating shaft of the solid structure The resonance frequency f _solid of the rotating shaft 2 can be expressed by the following equation (11) by substituting d _o1 = d and d _i1 = 0 in the equation (10).

When the equation (10) is divided by the equation (11), the relative resonance frequency f _hollow / f _solid can be expressed by the following equation (12).

The left vertical axis is the relative resonance frequency f _hollow / f _solid , the horizontal axis is d _i1 / d _o1 , and (d _i1 / d _o1 ) represented by the equation (12) and the relative resonance frequency of the rotation axis (f _hollow / A graph showing the relationship of f _solid ) is shown in FIG. 6 as a solid curve. According to FIG. 6, the rotary shaft 2 having a hollow structure with d _i1 / d _o1 = 0.42 or more has the same mass as the rotary shaft 2 and has a solid structure (d _i1 / d _o1 = 0). Compared with the shaft 2, the resonance frequency f _hollow can be 1.2 times or more. For this reason, the number of rotations can be increased more than the rotation shaft of the solid structure without being affected by resonance.

The mass m _solid of the rotating shaft when the diameter of the rotating shaft of the solid structure is d is expressed by the following equation (13) obtained by substituting d _o1 = d and d _i1 = 0 into equation (9). Is done.

Since the mass m _hollow of the rotating shaft 2 of the hollow circular tube is the same as the mass m _solid of the rotating shaft of the _solid structure, the diameter of the rotating shaft 2 of the solid structure is calculated from the equations (9) and (13). The relationship expressed by the following equation (14) is established between the ratio (d _o1 / d) of d _o1 of the rotary shaft 2 having a hollow structure to d and d _i1 and d _o1 .

Under the condition that the mass m _hollow of the rotating shaft 2 of the hollow structure having d _i1 and d _o1 is the same as the mass m _solid of the rotating shaft 2 when the diameter of the rotating shaft 2 of the solid structure is d. the ratio of the rotational shaft 2 of d _o1 hollow structure (d _o1 / d) and the right vertical axis with respect to the diameter d of the rotary shaft 2 of the actual structure, the horizontal axis (d _i1 / d _o1), in (14) A graph representing the relationship between (d _i1 / d _o1 ) and (d _o1 / d) is shown in FIG. 6 as a broken line curve. In the case of d _i1 / d _o1 = 0.42, the outer diameter d _{o1 of the} hollow structure rotating shaft 2 is about 1.1 times the diameter d of the solid structure rotating shaft. When the impeller width D (see FIG. 3) and mass are the same for the solid structure rotation shaft and the hollow structure rotation shaft, the diameter of the hollow structure rotation shaft is equal to that of the solid structure rotation shaft. Since it becomes larger than a diameter, there exists a tendency for the effective area of the impeller for stirring to become small.

  However, as described above, the diameter of the lower end side of the rotating shaft 2 can be reduced by making the rotating shaft 2 have a shape in which the diameter is tapered from the upper end toward the lower end while the rotating shaft 2 has a hollow structure. It is possible to design the rotating shaft 2 so that the resonance frequency f of the primary bending obtained by the equation (1) is higher than the rotational frequency of the impeller 3 without reducing the effective area of the impeller. .

  In addition, when the stirring body 1 cannot be newly designed, the impeller 3 is set so that the rotational speed of the impeller 3 becomes smaller than the resonance frequency f of the primary bending of the rotating shaft 2 obtained by the equation (1). The vibration can also be suppressed by adjusting the number of rotations.

  By adjusting the resonance frequency f of the primary bending of the rotating shaft 2 to be 1.2 times or more the rotation speed of the impeller 3, it is possible to reliably suppress the vibration of the stirring body 1 during the hot metal pretreatment. It becomes. The rotational speed of the impeller 3 is preferably in a range of 140 rpm (2.33 Hz) or more and 200 rpm (3.33 Hz) or less from the viewpoint of enhancing the stirring and enhancing the reaction efficiency. When the rotation speed of the impeller 3 is less than 140 rpm, the stirring intensity is weak and the desired reaction efficiency cannot be obtained. On the other hand, when the rotation speed of the impeller 3 exceeds 200 rpm, the reaction efficiency is saturated and the reaction efficiency is increased. This is because not only the number is reduced, but the disadvantages due to the increase in load power increase. Further, the resonance frequency f of the primary bending of the rotating shaft 2 is in the range of 2.8 Hz (= 140 rpm × 1.2 / 60 sec) or more and 4.0 Hz (= 200 rpm × 1.2 / 60 sec) according to the rotation speed of the impeller 3. It is preferable to control. When the resonance frequency f of the primary bending of the rotating shaft 2 exceeds 4.0 Hz, the stirring body 1 becomes large in terms of equipment, so 4.0 Hz is a preferable upper limit. The frequency f may exceed 4.0 Hz.

The hot metal preliminary treatment targeted in the present invention is desiliconization treatment, desulfurization treatment, and dephosphorization treatment. Here, the desiliconization process means that iron oxide is added to the hot metal 5 in the smelting vessel, or oxygen gas is blown, or both are used together, and the hot metal is made of oxygen in the iron oxide or oxygen in the oxygen gas. It is a refining process that removes oxidized silicon. If silicon is present in the hot metal, the dephosphorization reaction of the hot metal is impaired. Therefore, in order to efficiently perform the dephosphorization process, the desiliconization process is performed at a stage prior to the dephosphorization process. The desiliconization treatment may be performed by adding a CaO-based solvent to the hot metal container in order to dilute the generated silicon oxide (SiO ₂ ).

In addition, the dephosphorization treatment means that iron oxide is added to the hot metal 5 in the smelting vessel, or oxygen gas is blown, or both are used in combination with oxygen in the iron oxide or oxygen in the oxygen gas. In this refining process, the phosphorous oxide (P ₂ O ₅ ) produced by oxidizing the phosphorus is fixed with a CaO-based medium solvent added to the refining vessel to remove phosphorus in the hot metal.

  In any of the pre-treatments of desiliconization and dephosphorization, the impeller 3 immersed in the hot metal 5 is rotated to stir the hot metal 5 to promote the reaction between the added iron oxide or oxygen gas and the hot metal.

  As described above, according to the present invention, when the hot metal 5 is stirred using the hot metal pretreatment stirrer 1 including the rotary shaft 2 and the impeller 3, the resonance frequency f of the primary bending of the rotary shaft 2 is obtained. However, since the stirring body 1 larger than the rotational speed of the impeller 3 that stirs the molten iron 5 is used, an increase in vibration due to resonance of the stirring body 1 can be avoided, so that the stirring body 1 can be rotated at high speed. As a result, it is possible to efficiently disperse the additive 6 added to the hot metal 5 in the hot metal, and to achieve a stirring treatment of the hot metal with higher reaction efficiency than in the past.

<Comparative example>
The hot metal desulfurization treatment shown in FIG. 1 was performed using a stirring body having a constant diameter from the upper end to the lower end and having a solid rotating shaft. The rotating shaft of this stirring body was made of carbon steel. For this rotating shaft, Young's modulus E was 2.1 × 10 ¹¹ Pa, density ρ was 7800 kg / m ³ , length L was 4.5 m, the cross-sectional shape was a circle, and the diameter was 0.3 m. An impeller having a mass of 7650 kg was attached to the rotating shaft, and a hammering vibration test was performed to obtain a frequency response function of the rotating shaft. The frequency response function is shown in FIG.

  In the hammering vibration test, an impact hammer having a hammer weight of 5.5 kg is used, and the impeller 3 is vibrated with a force of about 1.5 kN with the stirrer 1 connected to the rotating device. Was measured using a servo accelerometer. Hammering was performed 5 times, and the frequency response function was obtained from the average of the results.

  As shown in FIG. 7, the frequency response function of the rotating shaft has a peak (= resonance frequency) at 2.9 Hz, and the resonance frequency of the primary bending of the rotating shaft is 2.9 Hz. The critical speed is 174 rpm corresponding to the resonance frequency of 2.9 Hz. In the operation using this stirring body, the hot metal in the hot metal ladle is desulfurized with 145 rpm which is 1 / 1.2 of the critical speed as the upper limit of the rotation speed.

<Invention Example 1>
Next, a stirrer 1 having a shape with a diameter tapered from the upper end toward the lower end and having a solid structure rotating shaft 2 shown in FIG. 2 was prepared. This rotating shaft 2 was made to have the same Young's modulus E, density ρ, length L, and mass m of the rotating shaft as the rotating shaft of the stirring body in the comparative example. The rotating shaft 2 is tapered so that the rate of change in width from the upper end to the lower end is constant, and d ₁ = 0.385 m and d ₂ = 0.207 m (d ₂ / d ₁ = 0.54). . An impeller having the same mass as that of Comparative Example 1 was attached to the rotating shaft 2, a hammering vibration test was performed, and the frequency response of the rotating shaft was measured.

The resonance frequency of the primary bending of the rotating shaft in Example 1 of the present invention was 3.49 Hz. By applying a taper of d ₂ / d ₁ = 0.54, the resonance frequency can be increased to 1.2 times while maintaining the same mass as the rotation shaft of the comparative example. 209 rpm corresponding to 3.49 Hz becomes a critical speed. In the operation using the stirring body having the rotating shaft, the hot metal in the hot metal ladle was desulfurized with 174 rpm which is 1 / 1.2 of the critical speed as the upper limit of the number of rotations. Double-speed rotation is possible, an effective stirring effect can be obtained, and the desulfurization speed and desulfurization rate are improved.

<Invention Example 2>
Furthermore, a stirrer having a shape with a tapered diameter from the upper end toward the lower end and having a hollow rotating shaft was prepared. This rotating shaft also had the same Young's modulus E, density ρ, length L, and mass m of the rotating shaft as the rotating shaft of the stirring body in the comparative example.

The rotating shaft 2 is tapered with a constant rate of change in width from the upper end to the lower end, and the outer diameter _do2 ( _do2 / _do1 ) of the lower end relative to the outer diameter _do1 of the upper end is 0.54, The inner diameter d _i1 (d _i1 / d _o1 ) at the upper end relative to the outer diameter d _{o1 at} the upper end and the inner diameter d _i2 (d _i2 / d _o2 ) at the lower end relative to the outer diameter d _{o2 at} the lower end were set to 0.425, respectively. Moreover, this rotation axis | shaft was made the same with the rotation axis | shaft of the stirring body of a comparative example. An impeller having the same mass as that of Comparative Example 1 was attached to the rotating shaft, a hammering vibration test was performed, and the frequency response of the rotating shaft was measured (Example 2 of the present invention).

The resonance frequency of the rotating shaft in Example 2 of the present invention was 4.19 Hz, and the resonance frequency was 1.44 times the resonance frequency of the rotating shaft in the comparative example (1. 2 times). 4. 252 rpm corresponding to 19 Hz becomes a critical speed. In the operation using the stirring body having this rotating shaft, the hot metal in the hot metal ladle was desulfurized with 209 rpm, which is 1 / 1.2 of the critical speed, as the upper limit of the number of revolutions, and as a result, 1.44 times that of the impeller of the comparative example. High-speed rotation (1.2 times that of Example 1) became possible. Furthermore, while the diameter d on the side where the impeller is attached was 0.300 m (comparative example), in Example 2, the diameter became thinner as d _o2 = 0.181 m, and the effective area of the impeller was increased. Thus, a higher stirring effect could be obtained, and the desulfurization speed and desulfurization rate were improved.

DESCRIPTION OF SYMBOLS 1 Stirring body 2 Rotating shaft 2a Flange 3 Impeller 3a Metal plate 4 Smelting vessel 5 Hot metal 6 Additive 7 Refractory

Claims (7)

A hot metal preliminary treatment method in which the impeller attached to the tip portion on the lower end side of the rotating shaft is immersed in the hot metal in the refining vessel, and the hot metal and the additive are stirred by rotating the impeller,
The rotating shaft has a shape with a tapered diameter from the upper end toward the lower end,
A hot metal preliminary treatment method characterized in that stirring is performed with a resonance frequency of primary bending of the rotating shaft larger than the rotational speed of an impeller that stirs the hot metal and the additive.   The hot metal preliminary treatment method according to claim 1, wherein a resonance frequency of the primary bending is 1.2 times or more of an impeller rotation speed.   The hot metal preliminary treatment method according to claim 1, wherein the rotating shaft has a hollow structure.   The hot metal preliminary treatment method according to any one of claims 1 to 3, wherein a rotation speed of the impeller is 140 rpm or more and 200 rpm or less. A rotating shaft having a tapered shape from the upper end to the lower end;
An impeller attached to a tip portion on the lower end side of the rotating shaft,
The ratio of the diameter d ₂ of the rotating shaft on the lower end side to the diameter d _{1 of the} rotating shaft on the upper end side (d ₂ / d ₁ ) is 0.34 or more and 0.55 or less. Stirring body.   The stirring body for hot metal pretreatment according to claim 5, wherein a resonance frequency of primary bending of the rotating shaft is 2.8 to 4.0 Hz.   The hot metal pretreatment stirrer according to claim 5 or 6, wherein the rotating shaft has a hollow structure.

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