JP3282543B2 - Apparatus and method for preheating and preserving cylindrical immersion pipe for ladle refining of molten steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for preheating and preserving a cylindrical immersion pipe (snorkel) used for ladle refining of molten steel.

[0002]

2. Description of the Related Art Conventionally, for example, the following method has been known as a method for refining or raising the temperature of molten steel in a ladle using a cylindrical immersion tube.

(A) An inert gas is blown from the bottom of a ladle, an immersion tube is inserted into the ladle while stirring molten steel, and an oxidizing agent such as Al (aluminum) or an Al alloy is added into the immersion tube. Thereafter, a method of heating the molten steel in the ladle in which an oxidizing gas is blown to the surface of the molten steel in the immersion tube through an upper blowing lance (Japanese Patent Laid-Open No. 61-235506).

(B) After injecting an inert gas with a bubbling lance deeply immersed in molten steel in a ladle, the molten steel is stirred, and a snorkel (immersion tube) is immersed in the exposed molten steel surface to cut slag. A method of raising the temperature of molten steel in a ladle, in which a heating agent is added to the snorkel and oxygen is blown with an upper blowing lance (Japanese Patent Application Laid-Open No. 64-56816).

(C) A cylindrical immersion pipe is immersed in molten steel in a ladle to secure a bare surface of the molten steel, and the immersion pipe is evacuated and evacuated to remove inert gas from a lance or a bottom tuyere. Ladle scouring method of blowing (Japanese Patent Laid-Open No. 1-92314).

[0006] As described above, when refining or raising the temperature of molten steel using a ladle, a cylindrical immersion pipe is widely used.
At that time, before use of the cylindrical immersion tube, usually, pre-heat treatment is performed to prevent wear of the refractory due to thermal shock,
This preheating is performed by a method of heating with a gas burner from below the immersion tube in the same manner as in the case of preheating the immersion tube of the RH furnace. For example, a device such as a heat shield device is not used. Also, when refining or raising heat treatment of one charge is completed, when performing the next charge processing, no heat retention during non-operation of the dip tube between charges is performed, and until the next charge processing It is left in the air-cooled state.

However, since the cylindrical immersion pipe has a larger surface area of the refractory than the immersion pipe of the RH furnace, the heating method using a gas burner from below which is performed during the preheating of the immersion pipe of the RH furnace does not provide the refractory. The material cannot be sufficiently preheated, and when the immersion tube is immersed in molten steel, the surface of the refractory of the immersion tube peels or cracks due to thermal shock, and the life of the refractory is significantly impaired.

[0008] Further, when the cycle time between the converter and the continuous casting machine is deviated, or when trouble occurs, there is a case where there is an interval until the next charge processing. At this time, if the tubular immersion tube is not kept warm and is left as it is after use, cooling is promoted by heat radiation from the surface of the refractory, so that it is immersed for the next charge processing. When the pipe is immersed in the molten steel, as in the case of using the immersion pipe with insufficient preheating as described above, the surface of the refractory also peels or cracks due to thermal shock, and the life of the refractory decreases. The problem arises.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the wear of refractories caused by thermal shock when a cylindrical immersion pipe is immersed in molten steel, which is a problem in ladle refining described above. In order to preheat the refractory of the immersion tube uniformly before using the cylindrical immersion tube, and to perform the next charge treatment after refining or heating treatment of one charge is completed, The purpose of the present invention is to establish an apparatus and a method capable of suppressing heat radiation from a refractory surface and keeping heat.

That is, an object of the present invention is to suppress rapid temperature fluctuation of a refractory of a submerged pipe when a cylindrical submerged pipe used for ladle refining is immersed in molten steel, and to cause peeling and cracking by thermal shock. It is an object of the present invention to provide a device for preheating and keeping heat of a cylindrical immersion tube, which can reduce the temperature and improve the life of a refractory, and a method for preheating and maintaining a heat of a cylindrical immersion tube using the device.

[0011]

SUMMARY OF THE INVENTION The gist of the present invention is as follows: (1) a device for preheating and keeping heat of a cylindrical immersion pipe;
And (3) a method for preheating a cylindrical immersion pipe using this apparatus.

(1) A method for removing molten steel, comprising: a heat shield device surrounding an outer peripheral portion of a cylindrical immersion tube used for ladle refining; and a gas burner for heating the inside of the immersion tube from above. Preheating and heat retention equipment for cylindrical immersion tubes for pot refining.

(2) Ladle refining cylindrical dipping of molten steel characterized by the following steps, which are performed by using a preheating and heat retaining device for the tubular dipping tube for ladle refining of molten steel according to (1). Tube preheating method.

A step of inserting a cylindrical immersion pipe used for ladle refining into a heat shield device; and a step of lowering a gas burner from above the cylindrical immersion pipe to heat the inside of the cylindrical immersion pipe.

(3) Ladle refining cylindrical immersion of molten steel characterized by the following steps performed using a preheating and heat retaining device for the cylindrical immersion pipe for ladle refining of molten steel according to (1) above. Tube heat retention method.

A step of inserting the tubular immersion pipe used in the ladle refining into a heat shield device, lowering a gas burner from above the tubular immersion pipe, heating the inside of the tubular immersion pipe, For maintaining the heat of the immersion tube.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention (the above (1) to (1))
The invention (3) will be described in detail with reference to the drawings.

FIG. 1 is a partial longitudinal sectional view showing a schematic configuration of an example of a preheating / heating device (hereinafter, also referred to as "the device of the present invention") of the cylindrical immersion tube for ladle refining of the above (1). It is.

In FIG. 1, a cylindrical heat shield device 1 having a bottom portion filled with sand 12 is placed on a holding table 13 attached to a truck 3. The holding table 13 is configured to be able to move up and down by the hydraulic cylinder 2. The lower part of the cylindrical immersion pipe 4 that is detachable from the upper tank 6 by the flange 5 is inserted into the heat shield device 1, and is surrounded by the side wall of the heat shield device 1. A thermocouple 10 for temperature monitoring and a immersion tuyere 11 are provided on the side surface of the tubular immersion tube 4.

The upper tank 6 is provided with a heating gas burner 9 that can move up and down from the upper part into the cylindrical immersion pipe 4 through the refractory wall. This gas burner 9 is detachable. Further, the upper part of the exhaust port 7 of the upper tank 6 can be closed by the suction damper 8, so that heat radiation to the upper part can be suppressed.

FIG. 2 is a perspective view of the above heat shield device.
As shown in the figure, the heat shield device 1 has a cylindrical shape and has a bottom, and a filling sand 12 is spread on the bottom to reduce a gap between the lower end of the immersion pipe 4 and increase heating efficiency. Have been.

The heat shield device 1 is preferably made of inexpensive general structural steel, has a wall thickness of 20 to 80 mm, and is entirely made of a refractory material. For example, an empty pot may be used,
In that case, a pot after completion of casting is desirable. This is because a further heat retention effect can be expected because the heat is stored.

The height HS of the heat shield device 1 is higher than the height HL of the cylindrical immersion tube 4 (the length from the tip of the immersion tube to the flange 5... See FIG. 1). It is desirable to satisfy the condition of 2/3. When the cylindrical immersion pipe 4 is immersed in the molten steel in the ladle to perform the vacuum refining process, the height of the molten steel sucked into the immersion pipe 4 (the molten steel level) is immersed from the tip of the immersion pipe 4. Since HS / HL <2/3, the cylindrical immersion tube 4
Cannot be completely surrounded by the side wall of the heat shield device 1, heat radiation occurs from the outer surface of the cylindrical immersion pipe 4 during heating by the gas burner 9, and sufficient local heating can be performed. This is because an unoccupied area is likely to occur. It is desirable that HS / HL be 1.0 or less. It is necessary to enclose the side wall of the heat shield device 1 in the portion of the tubular immersion pipe 4, and the manufacturing cost increases even if the height of the heat shield device 1 is unnecessarily increased.

FIG. 3 is a diagram showing the effect of HS / HL on the heat radiation at the molten steel level of the cylindrical immersion tube. This is obtained by the heat shield device and the cylindrical immersion tube used in the examples described later. After immersing the cylindrical immersion tube 4 in molten steel and performing a vacuum refining process, the cylindrical immersion tube 4 is inserted into the heat shield device 1, and the thermocouple 10 embedded in the back of the refractory (brick) at a portion corresponding to the molten steel level inside the immersion pipe 4, that is, the thermocouple 10 embedded in the outside of the immersion pipe 4, is used to remove the refractory. It is the result of measuring the change with time of the back surface temperature. At this time, heating by the gas burner 9 from above was not performed.

As shown in the figure, when HS / HL> 2/3, the back surface temperature of the refractory declined slowly and the heat retention was good. However, when HS / HL <2/3, the refractory was rejected. The back surface temperature decreased significantly. This is because the heat radiation to the outside from the refractory at the molten steel level became large,
It is desirable that HS / HL≥2 / 3.

It is desirable that the heat shield device 1 satisfies the following relationship with the cylindrical immersion pipe 4.

100 ≦ DS−DL ≦ 600, where DS is the inner diameter (mm) of the heat shield device, and DL is the outer shape (mm) of the cylindrical immersion tube. The distance between the immersion pipe 4 and the heat shield device 1 is important, and if DS-DL is greater than 600 mm, the heat shield device 1
Reduces the heat insulating effect. On the other hand, DS-DL is 100
If it is less than mm, when slag or the like adheres to the outer surface of the cylindrical immersion tube 4, there is a possibility that the insertion into the heat shield device 1 may be difficult.

FIG. 4 shows that a cylindrical immersion tube (DL = 3500 mm) used in an embodiment to be described later is immersed in molten steel and subjected to a vacuum refining process. FIG. 2 is a diagram showing the effect of DS-DL (i.e., the distance between the cylindrical immersion tube and the heat shield) on thermal radiation at the molten steel level, inserted into the apparatus 1; As shown, DS -D
When L was larger than 600 mm, the back surface temperature of the refractory decreased significantly. Therefore, DS -DL is 600m
m or less.

As the filling sand 12 to be spread on the bottom of the heat shield device 1, refractory particles or powders are desirable, and refractory sands such as silica sand and zircon sand generally used in tapping holes of a ladle are particularly desirable. If it is easy to sinter, the filled sand sinters and adheres to the leading end of the immersion tube 4 when the tip of the treated immersion tube 4 comes into contact with the filling sand 12, and at the time of the next processing, This is because there is a high risk of being brought into the molten steel.

The height of the filling sand 12 is desirably 30 mm or more. If it is less than 30 mm, if the holding table 13 attached to the carriage 3 is raised too much, the tip of the immersion tube 4 may contact the bottom of the heat shield device 1 and damage the tip.

The gas burner 9 for heating the cylindrical immersion tube 4 is
There is no particular limitation as long as it can be attached to the refractory wall of the upper tank 6 as required and can be moved up and down from the upper part into the cylindrical immersion pipe 4. For example, a gas burner using LPG, coke oven generated gas, or the like as a fuel can be used.

The use of the above-described apparatus of the present invention makes it possible to suppress thermal shock destruction of a refractory caused by a rapid temperature change when a cylindrical immersion pipe is immersed in molten steel, as described below. It is possible to improve the refractory life of the tubular immersion tube.

The invention of the above (2) is a method of preheating a ladle refining cylindrical immersion pipe for molten steel performed by using the apparatus of the present invention.

When preheating the cylindrical immersion tube by applying the method of the invention (2), for example, the apparatus having the configuration shown in FIG. 1 is used and the following steps are performed. The term "preheating of the cylindrical immersion pipe" used herein refers to preheating when a new cylindrical immersion pipe is used for the first time and preheating when using a cylindrical immersion pipe that has not been used for a long time. Less than,
This preheating is referred to as "preheating before the first use of the cylindrical immersion tube".

A step of inserting a cylindrical immersion pipe used for ladle refining into a heat shield device; a step of lowering a gas burner from above the cylindrical immersion pipe to heat the inside of the cylindrical immersion pipe.

A case where the preheating of the cylindrical immersion tube before the first use is performed by using the apparatus shown in FIG. 1 will be specifically described.

The above-mentioned step is a “step of inserting a cylindrical immersion pipe used for ladle refining into a heat shield device”. It is a cylindrical immersion tube to be used. First, the carriage 3 on which the heat shield device 1 is mounted on the holding table 13 in FIG. 1 is moved to below the cylindrical immersion pipe 4, and then the holding table 13 is moved by the hydraulic cylinder 2.
And insert the cylindrical immersion pipe 4 into the heat shield device 1. At this time, the tube is fixed at a position where the tip of the tubular immersion pipe 4 contacts the filling sand 12 (FIG. 2) spread on the bottom of the heat shield device 1 or a position immediately before the contact. It may be fixed at a position immediately before contact with the filling sand 12, but it is desirable to fix at a position where the contact is made in order to suppress heat radiation downward.

The step is a step of heating the inside of the tubular immersion pipe by lowering the gas burner from above the tubular immersion pipe. Gas burner 9 attached to upper tank 6 connected to upper part of cylindrical immersion pipe via flange 5
Is lowered from above the cylindrical immersion pipe 4 and the inside of the immersion pipe 4 is heated. During this heating, the refractory from the tip of the immersion pipe 4 to a portion corresponding to the molten steel level is efficiently removed. For heating, it is desirable to install a thermocouple on the back side (that is, outside) of the refractory of the tubular immersion pipe.

The purpose is the following two points.

1) Temperature monitoring at the time of preheating Heating at the time of preheating is performed by setting the thickness of the refractory of the cylindrical immersion pipe to 150 to
Assuming 300 mm, the back of the refractory is 200-500 ° C
It is desirable to carry out until the temperature rises to the temperature range. this is,
This is because if the back surface temperature of the refractory is within the above range, the operating surface (the inner surface of the immersion tube) is preheated to 1200 ° C. or more. That is, when the back surface temperature of the refractory is less than 200 ° C., the inner surface of the refractory is not sufficiently heated, and the amount of wear of the refractory after immersion in the dipping tube and molten steel increases. on the other hand,
When the back surface temperature of the refractory exceeds 500 ° C., the core of the immersion tube may be deformed, and the refractory may fall off.

FIG. 5 is a diagram showing the influence of the preheating temperature on the wear of the refractory after the first use of the cylindrical immersion pipe. This is a result obtained by the heat shield device and the cylindrical immersion tube used in the examples described later. The estimated refractory wear amount was determined from the following equation from the increase in the Cr concentration in the molten steel.

[0042]

(Equation 1)

As shown in FIG. 5, the preheating temperature is 200 ° C.
If it is less than this, the amount of wear of the refractory is large, and the life of the refractory decreases.

2) Detection of insertion of molten steel When molten steel is inserted (phenomenon of molten steel entering joints of a damaged brick), the indicated value of the thermocouple in the immediate vicinity is based on the indicated values of thermocouples in other parts. Also, if the treatment is continued as it is, the indicated value of the thermocouple is further increased, eventually melting the steel shell and causing steel leakage. Therefore, operation troubles can be prevented to a minimum for abnormality detection.

In order to sufficiently fulfill the objects 1) and 2), the cylindrical immersion tube (3000 m in height) used in the examples was used.
m, outer diameter of 3500 mm), the thermocouple is installed at 4 to 5 locations every 400 to 500 mm from the tip of the dip tube in the vertical direction of the tubular dip tube, and 90 to 1 in the circumferential direction.
It is desirable that the number is 3 to 4 at intervals of 20 degrees, and the total number is 12 to 20. Thereby, it is possible to substantially uniformly heat each part of the immersion tube.

The invention of the above (3) is a method for keeping heat in a cylindrical immersion pipe for ladle refining of molten steel, which is performed by using the apparatus of the present invention.

In the case of applying the method of the invention (3) to heat the cylindrical immersion tube, for example, the apparatus having the configuration shown in FIG. 1 is used and the following steps are performed. The term “heat retention of the cylindrical immersion tube” as used herein refers to the heat retention of the cylindrical immersion tube during non-operation between the end of one charge process and the start of the next charge process. Say. Hereinafter, this heat retention is referred to as “heat retention of the tubular immersion tube when the process is not performed”.

A step of inserting the tubular immersion pipe used in the ladle refining into the heat shield device; lowering the gas burner from above the tubular immersion pipe to heat the inside of the tubular immersion pipe; A step of keeping the heat of the cylindrical immersion tube.

In the above-mentioned process, first, the cart 3 on which the heat shield device 1 is mounted on the holding table 13 shown in FIG. 1 is moved to a position below the cylindrical immersion pipe 4 used for ladle refining. Stand 13
And insert the cylindrical immersion pipe 4 into the heat shield device 1. Next, the holding table 13 is raised by the hydraulic cylinder 2, and the cylindrical immersion pipe 4 is inserted into the heat shield device 1. At this time, it is desirable to fix the holding table 13 at a position where the tip of the cylindrical immersion pipe 4 contacts the filling sand 12, as in the method of the invention (2).

In the step (3), the gas burner 9 attached to the upper tank 6 connected to the upper part of the cylindrical immersion pipe is lowered from above the cylindrical immersion pipe 4, and the inside of the immersion pipe 4 is heated. Until the start of the processing of the next charge, the tubular immersion tube 4 is kept warm.

In order to effectively keep the refractory from the tip of the cylindrical immersion pipe 4 to the portion corresponding to the molten steel level,
The operating position of the gas burner 9 is important.

FIG. 6 shows the position of the tip of the gas burner at the time of heat retention, which affects the wear of the refractory of the cylindrical immersion pipe after being used for ladle refining (here, this position is referred to as the “position of the gas burner”). FIG. This is a result obtained by the heat shield device and the cylindrical immersion tube used in the examples described later, and the position of the gas burner is measured from the distal end of the cylindrical immersion tube 4 to a portion corresponding to the molten steel level ( 200
0 mm) within the range of 20 mm from the tip of the dip tube.
The wear rate of the refractory at each position of 0 mm, 1000 mm and 1800 mm was measured. The position of the gas burner is a distance from the portion corresponding to the molten steel level (that is, a portion 2000 mm from the tip of the dip tube) toward the tip of the dip tube.

As shown in FIG. 6, when the position of the gas burner 9 is less than 500 mm, 1800 m from the tip of the dip tube.
The wear rate of the upper refractory (indicated by a circle in the figure) at the position m is increased. On the other hand, when the position of the gas burner is 150
If the thickness exceeds 0 mm, the wear rate of the lower refractory (indicated by a mark in the figure) increases. Therefore, when performing heat retention of the cylindrical immersion tube during non-operation during processing, it is desirable to install the gas burner so that the position of the gas burner is within a range of 500 to 1500 mm from the tip of the cylindrical immersion tube 4.

It is preferable that the inner refractory of the cylindrical immersion pipe for heating or keeping heat by the apparatus of the present invention is made of magnesia chrome. This is because they have excellent thermal shock resistance and erosion resistance during scouring.

By performing the method of the invention of (2) above, the refractory of the immersion pipe when immersing the cylindrical immersion pipe used for ladle refining in molten steel at the first use of the cylindrical immersion pipe. Sharp fluctuations in temperature can be suppressed, peeling and cracking due to thermal shock can be reduced, and the life of the refractory can be improved.
Further, according to the method of the present invention of (3), when the processing of the next charge is started after the processing of one charge is completed,
It is possible to reduce peeling and cracking of the refractory of the immersion tube due to thermal shock when immersing the cylindrical immersion tube in molten steel.

[0056]

Example: Molten steel (carbon concentration: 0.05) roughly decarburized in a converter
０．１0.13% by weight, end point temperature 1630-1660 ° C.) in a 250-ton ladle. The temperature in steel is 1610-1
660 ° C. During tapping, metal Al is used for deoxidation.
Was added at a rate of 1-4 kg / t of molten steel.

A cylindrical immersion tube was immersed in molten steel in a ladle to a distance of 2 m from the tip, and the interior of the immersion tube was evacuated to vacuum. Ladle refining was performed in which Ar gas was blown in from an inner diameter of 3 mm x 12 pieces and installed at an interval of 15 degrees on a half circumference to agitate the molten steel.

At this time, processing was carried out by the method of the present invention (the method (2) or (3)) using the apparatus of the present invention having the configuration shown in FIG. For comparison, a treatment was also performed by a method that deviated from the conditions defined by the method of the present invention. Table 1 shows an outline of the heat shield device and the cylindrical immersion pipe used.

[0059]

[Table 1]

(Example 1): Preheating of the cylindrical immersion tube before the first use was carried out, and the heat of the cylindrical immersion tube was not kept during non-operation during the treatment. Insert into the LPG
The position of the gas burner using as fuel was 1000 mm from the tip of the cylindrical immersion tube, and the flow rate of LPG was 80 Nm.
Preheating was started at ³ / h. Preheating is performed for 60 hours. During this time, the position of the gas burner is set at 500 to 1500 mm from the tip of the immersion tube so that all of the 16 thermocouples installed on the back of the refractory of the cylindrical immersion tube are at about 350 ° C. , And the flow rate of LPG was adjusted in the range of 50 to 100 Nm ³ / h. After the processing was completed, when the apparatus was not operated while waiting for the next charge, the apparatus was not inserted into the heat shield device and was left in an air-cooled state.

(Example 2): Preheating before first use was not performed, and heat was kept during non-operation between treatments. A cylindrical immersion pipe was immersed in molten steel without preheating for the first time, and used. When not in operation while waiting for charging, after inserting into the heat shield device, the position of the gas burner using LPG as fuel was set to a position 1000 mm from the tip of the cylindrical immersion pipe,
The heat retention was performed while the flow rate of G was kept constant at 80 Nm ³ / h.

(Example 3): Both preheating before first use and heat retention during non-operation between treatments were performed. A cylindrical immersion tube was inserted into a heat shield before the first use, and LPG was initially used. The position of the gas burner using as a fuel was set to a position 1000 mm from the tip of the cylindrical immersion pipe, and the preheating was started with the flow rate of LPG at 80 Nm ³ / h. Preheating is performed for 60 hours. During this time, the position of the gas burner is set at 500 to 1500 from the tip of the immersion tube so that all of the 16 thermocouples installed on the back of the refractory of the cylindrical immersion tube are at about 350 ° C.
mm, and adjust the LPG flow rate to 50-100 Nm.
^It was adjusted within the range of ³ / h.

In the non-operation time while waiting for the next charge, after inserting the cylindrical immersion pipe into the heat shield device, the position of the gas burner using LPG as fuel is set at 100 degrees from the tip of the cylindrical immersion pipe.
The heat was kept at a position of 0 mm and the flow rate of LPG was kept constant at 80 Nm ³ / h.

(Comparative Example 1): Neither preheating before first use nor heat preservation during non-operation between treatments was performed, and the cylindrical immersion tube was immersed in molten steel without preheating and used, and non-operation was performed. At that time, it was left in an air-cooled state.

(Comparative Example 2): Preheating before first use was not performed, and only heat shielding by an empty pan was performed during non-operation between treatments. A cylindrical immersion pipe was immersed in molten steel without preheating and used, and non-operation was performed. At that time, heating by gas burner cooking was not performed, and only heat shielding was performed using an empty pot.

FIG. 7 shows the results of an investigation on the life of the refractory of the cylindrical immersion pipe in each of the above-mentioned Examples 1 to Comparative Example 2. As shown in this figure, it was found that the life of the refractory was improved by preheating or keeping the heat of the immersion tube, and the life of the refractory was further extended significantly by carrying out both the preheating and the heat retention.

[0067]

According to the method of the present invention, when the cylindrical immersion pipe is immersed in the molten steel when the cylindrical immersion pipe is used for the first time, or when it is used again after being used for ladle refining, Abrupt temperature fluctuations of the refractory can be suppressed, peeling and cracking due to thermal shock can be reduced, and the life of the refractory can be improved. This method can be easily performed using the apparatus of the present invention.

[Brief description of the drawings]

FIG. 1 is a partial longitudinal sectional view showing a schematic configuration of an example of the apparatus of the present invention.

FIG. 2 is a perspective view of a heat shield device in the device of the present invention.

FIG. 3 is a diagram showing the effect of HS / HL on heat radiation at the molten steel level of a cylindrical immersion tube.

FIG. 4 is a diagram showing the effect of DS-DL on thermal radiation at the molten steel level of a cylindrical immersion tube.

FIG. 5 is a diagram showing the effect of preheating temperature on the wear of refractories after the first use of a cylindrical immersion tube.

FIG. 6 is a view showing the effect of the position of a gas burner during heat retention on the wear of refractories of a cylindrical immersion pipe after being used for ladle refining.

FIG. 7 is a diagram showing the effect of preheating and / or heat retention on the life of a refractory in a cylindrical immersion tube.

[Explanation of symbols]

 1: Heat shield device 2: Hydraulic cylinder 3: Dolly 4: Cylindrical immersion pipe 5: Flange 6: Upper tank 7: Exhaust port 8: Suction damper 9: Gas burner 10: Thermocouple 11: Immersion tuyere 12: Filling Sand 13: Holder

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-93219 (JP, A) JP-A-1-159312 (JP, A) JP-A-5-339621 (JP, A) 38282 (JP, B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) C21C 7/10

Claims (3)

(57) [Claims] 1. A ladle for molten steel, comprising: a heat shield device surrounding an outer peripheral portion of a cylindrical immersion tube used for ladle refining; and a gas burner for heating the inside of the immersion tube from above. Preheating and heat retention equipment for cylindrical immersion pipes for refining. 2. A ladle refining cylindrical immersion pipe for molten steel characterized by the following steps which are carried out using the apparatus for preheating and keeping heat of the cylindrical immersion pipe for ladle refining of molten steel according to claim 1. Preheating method. A step of inserting a cylindrical immersion pipe used for ladle refining into a heat shield device; a step of lowering a gas burner from above the cylindrical immersion pipe to heat the inside of the cylindrical immersion pipe. 3. A cylindrical immersion pipe for ladle refining of molten steel, characterized by the following steps carried out by using the apparatus for preheating and keeping heat of the cylindrical immersion pipe for ladle refining of molten steel according to claim 1. Heat retention method. Inserting the cylindrical immersion pipe after use in the ladle refining into the heat shield device, lowering the gas burner from the upper part of the cylindrical immersion pipe, heating the inside of the cylindrical immersion pipe to heat the cylindrical immersion pipe The step of keeping heat.