JPS59159923A - Operating method of rh vacuum degassing device - Google Patents

Abstract

PURPOSE:To permit easy exchanging of an immersion pipe and to extend considerably the life of a lower tank by using more than once the immersion pipe of an RH vacuum degassing device preliminarily to use for rising a molten steel thereby removing the solidified layer in the pipe. CONSTITUTION:The same immersion pipe 14 is first used as a riser up to about half its life and gaseous Ar is blown through a gas blowing pipe 16 to obtain stable reflux of molten steel. Said pipe is used as a downcomer for the remaining half of the life and during this time the gaseous Ar is not blown into the pipe and therefore the molten steel intrudes and solidifies in the pipe 16 thereby cloggint the pipe. The pipe 14 as a downcomer is used temporarily as a riser by blowing the gaseous Ar from an Ar brick 30 in the stage of RH treatment of a non-high grade steel just prior to exchanging of the pipe 14 when the pipe 14 is used to the limit and the other immersion pipe for the riser attains about half of its limit. The base metal slag, etc. sticking the inside surface of a reflux pipe 12 and the pipe 14 are therefore removed, by which the removal of the pipe 14 is made easy and the damage in the brick of the pipe 12 is thoroughly eliminated. The life of a lower tank 6 is thus considerably extended.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating an RH vacuum degassing apparatus, and more particularly to a method of operating an RH vacuum degassing apparatus, which facilitates the replacement of the immersion tube and extends the life of the lower tank.

In recent years, as steel usage technology on the customer side has progressed, there has been a growing demand for reduction of gases, nonmetallic inclusions, etc. in steel9, and the importance of the RH vacuum degassing method has increased.

The RH degassing device will be explained with reference to FIG. The R and H degassing tank is composed of an upper lid 2, a middle tank 4, and a lower tank 6, and the upper part is provided with a vacuum exhaust hole 8, an alloy inlet 10, and the lower tank 6.
A reflux pipe 12 is provided at the bottom of the reflux pipe 12, and a dipping pipe 14 is further attached to the lower part of the reflux pipe 12. Porous bricks (hereinafter referred to as Ar bricks) have been conventionally used in which Ar gas is blown into the joint between the reflux pipe 12 and the immersion pipe 14 as a rising gas. However, Ar gas tends to leak easily and it is difficult to obtain a stable molten steel circulation, and if it blows through to the bottom of the lower tank 6, there are many disadvantages such as significant wear and tear on the bottom brick and also large melting damage to the Ar brick itself. In order to solve this problem, a method of embedding a pipe inside the immersion pipe 14 and providing a gas blowing pipe 16 has been considered, and considering the recent trend of increasing the flow rate of molten steel, the method using the gas blowing pipe 16 is likely to be adopted. It has become.

The RH vacuum degassing method uses the above-mentioned apparatus, and immerses the immersion tube 14 in the molten steel 20 in the nodule 18, and the inside of the tank is 0.1-5.
A vacuum of 0 torr is applied, and the pressure difference between the atmospheric pressure and the
Inert gas is blown at a rate of about 500 to 2000 l/min from the gas blowing pipe 16 of the immersion pipe 14 for lifting, and the molten steel 20 is raised and lowered from the other immersion pipe 14 for descending.
It performs deoxidation, dehydrogenation membrane nitrogen and decarburization. Although FIG. 1 shows one immersion tube 14 for raising and one for lowering, the number of immersion tubes 14 may be further increased in order to increase the recirculation amount.

In this RH vacuum degassing device, a lower tank 6, a reflux pipe 12
In addition, improving the life of the immersion tube 14 is extremely important in terms of unit management of refractories. In general, the life of the lower tank 6 is limited by the reflux pipe 12 and immersion pipe 14, which are washed violently by molten steel and subjected to frequent heating and cooling cycles, but the rate of erosion is high in the ascending and descending pipes. The difference is very different, for rising,
0.1-0.3 mm/heat for reflux tube, 0 for dip tube
．． 5 to 0.8 rrtm/he). On the other hand, there is almost no melting loss on the descending side. Therefore, in order to improve the life of the lower tank 6 and the reflux, an operating method has been adopted in which the immersion pipe is used for the first half of its life for upward movement and for the second half of its life, as shown in FIG. 2. In FIG. 2, the solid line is for ascending, the dotted line is for descending, the mark A indicates replacement of the lower tank, and the mark Δ indicates replacement of the dipping tube. That is, at first, the A series reflux tube and immersion tube were used for ascending, the B series reflux tube and immersion tube were used for descending, and then the human series was used after about 60 heats, which is about 1/2 the life of the A series immersion tube. are used for descending, and the immersion tubes of the B series that have reached the end of their service life are replaced with new ones to be used for ascending. Thereafter, as shown in FIG. 2, rising and falling are repeated alternately. FIG. 3 shows a comparison of the life of the immersion tube when the immersion tube is used only for ascending purposes and when the immersion tube is used for changing from ascending to descending as described above. As is clear from FIG. 3, when the dipping tube is used for changing from ascending to descending, the service life is twice as long as when it is used only for ascending.

However, if we adopt the operation method of changing the same immersion pipe from ascending to descending as described above, the second half of the immersion pipe used for descending will be replaced, but both the reflux pipe and the immersing pipe for ascending will have internal surfaces. The joints of the bricks are exposed and there is almost no deposit, but since the temperature of the molten steel is low in the descending process and there is no vigorous stirring of the molten steel in the ascending process, a mixed solidified layer of slag and steel forms on the inner surface of the immersion pipe brick. There is. This layer is very strong and cannot be easily removed. Therefore, when replacing the immersion tube, the immersion tube must be forcibly removed from the reflux tube, which is not easy to do, and the reflux tube bricks are frequently damaged.As a result, only some bricks of the reflux tube are damaged, and the lower Situations often occur that require the entire tank to be replaced and repaired.
This has traditionally been a big problem.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above and to provide a method for operating an RH vacuum degassing apparatus in which the immersion tube can be easily replaced.

The gist of the present invention is as follows.

In other words, after the immersion tube is newly attached to the reflux tube, the RH vacuum degassing is performed to replace the hind immersion tube, which was used for ascending the molten steel with a lot of melting loss during the first half of its life heat count, and for descending the molten steel with a small amount of melting loss during the second half of its life. A method of operating a vacuum degassing apparatus is characterized in that, prior to replacing the immersion tube, the immersion tube is used one or more times for lifting molten steel to remove a solidified layer inside the tube.

The details of the present invention will be explained with reference to an embodiment and the drawings. Fourth
The figure shows the details of the immersion tube used in the example.The immersion tube brick 22 is lined with a monolithic reinforced material 28 reinforced with iron plates 24 and anchor coils 26, and is made of Ar bricks (porous bricks) for inert gas injection. ) 30 and gas blowing pipe 16
A flange 32 for connection to the circulation pipe is attached to the upper part.

Next, the method of the present invention using the dip tube shown in FIG. 4 will be explained. As explained in Fig. 2, the same immersion tube is used for ascending and descending, but first, about half of its life is used for ascending, and during this time Ar gas is blown into it using the gas blowing pipe 16 to stabilize it. After that, half of the life is used for descending, and during this period, Ar gas is not injected, so A
Molten steel enters and solidifies into the gas blowing pipe 16 for the r-gaz, causing it to become clogged. Next, when the descending immersion tube reaches the end of its life and the other ascending immersion tube reaches about half its life, and just before replacing the descending immersion tube, Ar gas is applied from Ar brick 30 during the H treatment of non-high grade steel. By blowing in and temporarily using the descending dipping tube for ascending, the base metal slag adhering to the inner surface of the reflux tube and dipping tube can be removed, and then by replacing the dipping tube, p removal is extremely easy. There was no damage to the bricks in the N9 reflux pipe, and the life of the lower tank was greatly improved. FIG. 5 shows a comparison of the lifespan of the lower tank of the present invention example and the conventional example.

However, the display in Figure 5 is as follows.

・Example marked 2 (dipping tube used half for ascending and half for descending, then temporarily used for ascending and then replaced) ○ mark: Conventional example (dipping tube used half for ascending and half descending, then replaced) From FIG. 5, it can be seen that in the method of the present invention, the variation in the life of the lower tank is reduced and the life is improved.

Note that by temporarily using the descending dipping tube for ascending, the other ascending dipping tubes are used for descending and the gas blowing tube is blocked, but there is no problem since it is used as is for descending.

Furthermore, when temporarily switching to ascending mode after being used for descending, it is difficult to inject Ar gas from the Ar brick through the coagulated layer, but a small amount of gas may be generated due to small cracks or leakage in the coagulated layer. Once started, the solidified layer is melted by the upward flow of molten steel and the reflux becomes active, causing no problems in the process.

The number of heats used for raising the temperature by temporarily blowing Ar gas through the Ar bricks was usually 1 to 3 heats, and the coagulated layer could be almost completely dissolved.

As is clear from the above embodiments, the present invention uses the immersion tube for ascending during the first half of its lifespan, uses it for descending during the latter half, and temporarily uses it for ascending before replacement. B. The coagulated layer inside the immersion pipe is removed, the replacement work is facilitated, the life of the lower tank is greatly extended, and the unit consumption of refractories and labor costs are reduced.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the RH vacuum degassing device, Figure 2 is a schematic diagram showing the use of a conventional reflux tube and immersion tube in ascending and descending directions, and Figure 3 is a diagram showing the use of a conventional reflux tube and immersion tube in ascending and descending directions. Figure 2 is a frequency graph showing the life of the immersion tube in the case of switching use, Figure 4 is a sectional view showing the immersion tube of the present invention, and Figure 5 is the erosion rate of the reflux tube of the embodiment and conventional rows. It is a figure which shows the relationship between and a lower tank lifetime. 6...Lower tank 12...Recirculation pipe 14...Immersion pipe 16...Gas blowing pipe 30...Porous brick (Ar brick) agent Patent attorney Takeo Nakaji 1st b Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] (1) After newly attaching the immersion tube to the circulation pipe, replace the hind-limb immersion tube that was used for the first half of the life heat cycle to ascend the molten steel, which has a lot of melting loss, and in the second half, to descend the molten steel, which has a small amount of melting loss.R
A method for operating an RH vacuum degassing device, characterized in that, prior to replacing the immersion tube, the immersion tube is used one or more times for raising molten steel to remove a solidified layer inside the tube.