JPH10287914A - Method for preventing deformation of steel shell in rh vacuum degassing furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preventing method of the deformation of an steel shell in an RH vacuum degassing furnace which restrains the deformation of circulating tubes formed as downward widening shape, prevents the interference between the immersion tubes and a ladle and can effectively repair and secure the stable service life. SOLUTION: Ununiformity of temp. of the steel shell caused by the heat transfer from molten steel 10 in the ladle 9 is mitigated, by blowing gas to the iron shell at the bottom part of a lower vessel 2. The blowing quantity and the blowing position of the gas are beforehand decided to be the quantity and the position thereof, by which the temp. of the iron shell does not become ununiform, or the relation between the iron shell temp. and expanding quantity or deforming quantity, is beforehand grasped and the iron shell temp. is always measured and the flow rate of the gas is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an RH (Ruhrstahl-Hera) used for processing molten steel in a ladle.
us) The present invention relates to a method of preventing deformation of a steel shell of a degassing furnace.

[0002]

2. Description of the Related Art In a lower tank in which molten steel stays in an RH vacuum degassing furnace, a reflux pipe in which a dip pipe immersed in molten steel in a ladle is attached via a flange is formed integrally with a steel shell of the lower tank. ing. In such a lower tank of the RH vacuum degassing furnace, a portion where the temperature rises due to the heat transfer from the molten steel in the ladle during the molten steel processing, and whether the influence is small,
Alternatively, since there is a part that is not affected by the influence, the thermal expansion of the steel shell in the lower part of the lower tank becomes non-uniform for each part, and there is a problem that the reflux pipe is deformed in a C shape.

[0003] Such a deformation of the reflux pipe leads to a dip pipe attached via a flange being mounted in a state of opening in a C shape, and when the degree of the deformation increases, the dip pipe and the ladle side wall are connected. Molten steel treatment cannot be performed due to the interference of the steel. In addition, if there is such a deformation, there will be problems with the installation of the immersion pipe, the repair of the refractory lining of the immersion pipe and the reflux pipe, and the repair of the lower tank floor, etc., resulting in unstable furnace life and the operation of molten steel processing. affect. Therefore, there has been a long-felt need for a method for preventing the deformation of the steel skin.

As a technique for responding to such a request, Japanese Utility Model Laid-Open Publication No. 2-087056 discloses a technique for preventing deformation of a steel shell of a lower tank and a bottom plate of a lower tank of an RH vacuum degassing furnace and a flange portion of a reflux pipe. A lower tank of an RH vacuum degassing furnace in which a heat insulating plate is disposed between the two is disclosed.

[0005]

However, in the above method, the heat shield plate itself is deformed by the heat from the molten steel in the ladle, and the heat shield plate needs to be repaired or replaced, and the heat shield plate support jig needs to be repaired.
In addition to the cost and labor involved, there is a problem in that it hinders the operation of molten steel processing. In addition, a gap is created between the heat-insulating plate and the reflux tube when attaching the heat-insulating plate, but the effect of heat through this gap is not negligible, and in fact, the U-shaped deformation of the reflux tube is inevitable. .

[0006] Therefore, the present invention does not hinder the operation of the RH vacuum degassing furnace, eliminates the need for repair and replacement, and alleviates the non-uniform expansion of the steel shell due to the heat transfer from the molten steel in the ladle, so that the reflux tube It is an object of the present invention to provide a method for preventing the deformation of the steel shell of the RH vacuum degassing furnace, which can suppress the C-shaped deformation.

[0007]

SUMMARY OF THE INVENTION The present invention has been provided to solve the above problems, and the gist of the invention is as follows.
It is as follows. (1) A gas body is sprayed on the steel shell at the bottom of the lower tank of the RH vacuum degassing furnace to reduce the uneven temperature of the steel shell due to the heat transfer from the molten steel in the ladle. A method for preventing deformation of a steel shell of an RH vacuum degassing furnace, characterized by suppressing a U-shaped deformation of a reflux tube formed integrally with the furnace.

(2) The temperature of the steel shell at the bottom of the lower tank is measured, and the flow rate of the gas body blown to the steel shell at the bottom of the lower tank is controlled based on the measurement result. 3. The method for preventing deformation of a steel shell of an RH vacuum degassing furnace according to item 1.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The method for preventing the deformation of a steel shell of an RH vacuum degassing furnace according to the present invention is to blow a gas body onto a steel shell at the bottom of a lower tank whose temperature rises due to heat transfer from molten steel in a ladle.
By reducing the temperature difference from the temperature of the steel shell, which has little or no thermal influence, the thermal expansion of the steel shell is prevented from becoming uneven. Since it is a method of spraying a gas body, there is no particular need for repair during use, and there is no cost, labor, or hindrance to operation.

[0010] In advance, the temperature difference of the steel shell between the portion affected by heat transfer from the molten steel in the ladle and the portion not affected by heat transfer, and the flow rate of the gas body in which the recirculation tube does not cause a U-shaped deformation. By grasping in relation to the amount of heat transfer from the molten steel in the ladle, and continuously measuring the temperature of the steel at the parts affected by heat transfer and those not affected by the heat transfer during operation, Since the flow rate of the gas body can be controlled according to the change in the amount of heat transfer due to the temperature, the level of the molten metal, the immersion depth, etc., it is possible to prevent the deformation of the steel shell without being affected by the operating conditions.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. One embodiment of the present invention is shown in FIG. In FIG. 1, the RH vacuum degassing furnace includes a dip tube 1, a lower tank 2, an upper tank 3, and a canopy 4. In the lower tank 2, a reflux tube 5 is formed integrally with a steel shell of the lower tank 2. The lower tank 2 and the upper tank 3, and the upper tank 3 and the canopy 4 are attached via flanges 11, 11 '. Further, the immersion pipe 1 and the reflux pipe 5 are also attached via the flange 6. The immersion tube 1
During the molten steel treatment, it is immersed in the molten steel 10 in the ladle 9
Is sucked up from one side of the dip tube 1 and discharged from the other side.

A compressed air header pipe 7a is provided on both sides of the steel shell on the side wall of the lower tank 2 between the two reflux pipes 5, and the header pipe 7a is provided.
A branch pipe 7b is arranged so that compressed air blows out from a toward the steel shell of the lower tank 2 between both reflux pipes 5. An on-off valve (not shown) for adjusting the flow rate of the compressed air is installed in an air pipe (not shown) for supplying the compressed air to the header pipe 7a.

FIG. 2 is an enlarged view of a lower portion of the lower tank 2, and FIG. 3 is an AA view of the lower tank viewed from below. A thermocouple 8 is provided between the two reflux pipes 5 and outside the both reflux pipes 5 on the steel shell of the lower tank 2.
a and 8b are installed. Signals from the thermocouples 8a and 8b are transmitted to a control panel (not shown) via wires. The control panel (not shown) is provided with an on-off valve (not shown) for adjusting the flow rate of the compressed air so that opening and closing can be controlled.

The rise in the temperature of the steel shell at the bottom of the lower tank 2 is caused by the ladle 9
This is generated by heat transfer from the molten steel 10 in the inside, and the form of the heat transfer includes convection heat transfer and radiant heat transfer. The following measures are conceivable to reduce the rise in steel shell temperature. In the case of convection heat transfer, the iron shell of the lower tank 2 is prevented from coming into contact with the high temperature atmosphere. In the case of radiant heat transfer, the steel shell of the lower tank 2 and the molten steel 10 are made invisible from each other. In any case, it seems effective to install a shielding plate between the steel at the bottom of the lower tank 2 and the molten steel 10. However, it is difficult to install a shielding plate that satisfies the above measures. That is, the C-shaped deformation is recognized even in the method of installing the heat insulating plate of the related art. This is because the heat shield and the reflux pipe 5
This is because a gap is generated between the gaps and heat transfer occurs through the gap.

As described above, it is practically difficult to cut off the heat transfer from the molten steel 10 in the ladle 9, and in order to fundamentally suppress the U-shaped deformation of the reflux tube 5, the lower tank is required. It has been noted that it is important to prevent the temperature of the steel shell at the bottom of the two from becoming uneven. Compressed air is blown between the two recirculation tubes 5 where the temperature rise of the shell due to heat transfer is remarkable, thereby avoiding contact between the high-temperature atmosphere due to convection heat transfer and the shell at the bottom of the lower tank 2, that is, the shell. And the high temperature atmosphere are shut off with an air curtain. Further, the heat stored in the steel shell by the radiant heat transfer is removed by the compressed air, that is, the steel shell is gas-cooled.

The temperature of the shell at the bottom of the lower tank 2 between the two convection tubes 5 due to convective heat transfer and radiant heat transfer from the molten steel 10 in the ladle 9 rises. Since the influence of the convective heat transfer and the radiant heat transfer on the temperature of the lower tank 2 is small, the temperature of the steel shell is lower than the temperature of the shell between the two reflux tubes 5. For this reason, in the steel shell of the lower tank 2, both reflux pipes 5 spread outward due to a difference in thermal expansion. That is, it is transformed into a C-shape.

Therefore, the thermocouple 8b installed between the two reflux pipes 5 having a large influence of heat transfer and the thermocouple 8a installed outside the two reflux pipes 5 having little influence of the heat transfer are obtained by setting the temperature of the steel shell of the lower tank 2 to a large value. The compressed air is blown from the branch pipe 7b so as to reduce the temperature of the shell between the two reflux pipes 5 so as to reduce the temperature difference between the two. At this time, the flow rate of the compressed air is adjusted by an on-off valve (not shown). The control panel (not shown) to which signals from the thermocouples 8a and 8b are transmitted calculates the temperature difference. By controlling the opening and closing of an on-off valve (not shown) of the compressed air so that the temperature difference becomes small,
Corresponding to the change in the amount of heat transfer, the C-shaped deformation of the reflux tube 5 can be efficiently reduced.

The temperature and capacity of the molten steel 10 in the ladle 9
The relationship between the heat amount such as the processing time of the molten steel 10 and the difference between the temperature of the iron shell at which the recirculation tube 5 does not deform in a U-shape and the flow rate of the compressed air to be blown is grasped, and a fixed amount of compressed air is flown before the processing. You may do it.

As shown in Table 1, in the method according to the present invention, the time required to replace the heat shield plate can be reduced as compared with the conventional method in which heat transfer from molten steel is prevented by attaching the heat shield plate. As for the running cost, the production, repair, replacement and the like of the heat insulating plate are not required, so that the cost was reduced by 1 / 2.5 to 1/3. In addition, since the steel shell deformation is small regardless of the passage of time, effective repair can be performed and a stable life can be obtained. The service life can be extended up to 30% in the lower tank with the reflux tube and up to 20% in the immersion tube. It was planned.

[0020]

[Table 1]

The number, the diameter, the cross-sectional shape, and the blowing direction of the branch pipe 7b for blowing the compressed air are not particularly limited, as long as the shell temperature can suppress the C-shaped deformation of the reflux pipe. Further, the adjustment of the flow rate of the compressed air is not limited to being performed at the entrance side of the header pipe, but may be performed for each branch pipe after the header pipe, and the installation of the header pipe is not essential.

The gas is not limited to air, but may be any gas which can be used safely at high temperatures and which does not affect the operator even if it is released into the atmosphere. Furthermore, the immersion tube is not limited to the one attached to the reflux tube via the flange, and may be integrated with the reflux tube. In addition to the method of spraying a gas body, the same effect as the present invention can be obtained by adopting a method of attaching a cooling box into which a gas body flows into a steel shell of a portion affected by heat transfer from molten steel in a ladle. .

[0023]

As described above in detail, according to the present invention, R
H-shaped deformation of the lower tank reflux tube of the H vacuum degassing furnace can be prevented,
Because the immersion pipe can be installed vertically, interference between the immersion pipe and the ladle can be prevented, and effective repair can be performed, so a stable life can be ensured. Further, repair and replacement are not required. The present invention is an industrially valuable invention because it has effects such as no cost and labor and no hindrance to the operation of molten steel processing.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a method of preventing deformation of a steel shell of an RH vacuum degassing furnace according to one embodiment of the present invention.

FIG. 2 is an enlarged view of the vicinity of a lower tank of the RH vacuum degassing furnace of FIG.

FIG. 3 is a schematic explanatory view of the lower tank viewed from below.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Immersion pipe 2 Lower tank 3 Upper tank 4 Canopy 5 Recirculation pipe 6 Flange 7a Header pipe 7b Branch pipe 8a Thermocouple 8b Thermocouple 9 Ladle 10 Molten steel 11 Flange 11 'Flange

Claims (2)

[Claims] 1. A gas body is sprayed on a steel shell at the bottom of a lower tank of an RH vacuum degassing furnace to mitigate uneven temperature of the steel shell due to heat transfer from molten steel in a ladle. A method for preventing the deformation of a steel shell of an RH vacuum degassing furnace, comprising suppressing a U-shaped deformation of a reflux tube formed integrally with a steel shell. 2. A steel shell temperature at the bottom of the lower tank is measured,
2. The method according to claim 1, wherein the flow rate of the gas body sprayed on the steel shell at the bottom of the lower tank is controlled based on the measurement result.