JPS61149423A - Operating method of vacuum degassing device provided with heating electrode - Google Patents

Abstract

PURPOSE:To prevent the consumption of a heating electrode owing to oxidation and the sticking of a base metal to the inside wall of a vacuum degassing vessel by detecting the O2 and CO2 concn. in the waste gas from said vessel and adjusting the exothermic temp. of the heating electrode according to the concn. thereof. CONSTITUTION:The temp. on the surface of the heating electrode 1 is measured by a noncontacting type surface thermometer 3 and the signal corresponding thereto is outputted to a central control unit 7. On the other hand, the O2 and CO2 concn. in the waste gas in the vacuum degassing vessel 11 is analyzed and the value thereof is converted to a processable signal which is outputted to the central control unit 7. The central control unit 7 determines the surface temp. of the heating electrode 1 as the target value in accordance with the input value from an IR gas analyzing instrument 6, compares the same with the actually measured value from the noncontacting type surface thermometer 3 and controls the electric energy to be thrown by a heating control circuit 8 to an electric power source 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of operating a vacuum degassing facility equipped with a molten metal heating electrode.

[Conventional technology]

In a vacuum degassing device, when molten steel tapped from a refining furnace such as a converter or an electric furnace is refined, an electrode is used to prevent metal from adhering to the vacuum degassing tank inside the device. Installation of heating devices is being carried out. In addition, this electrode heating device generally uses a method in which a direct current is passed through an electrode rod (carbon rod) to generate heat, and the inside of the degassing tank is heated by the radiant heat. Therefore, when a current is passed through the electrode rod to generate heat, the gas composition in the vacuum degassing tank greatly influences the life of the electrode rod.

That is, since the electrode rod is made of carbon, it has a temperature of 02, C at high temperatures.
+11. to oxidizing gas such as O2. As shown in equation (2), it is oxidized and its consumption is accelerated.

C (electrode rod) +CO2 → 2CO (1) C (electrode rod) +02 → 2CO (2) Therefore, for the purpose of decarburization or heat raising during vacuum degassing treatment, When oxygen gas or a mixed gas containing oxygen gas is supplied to molten steel, the electrode rod is oxidized and consumed by unreacted gas or generated CO2 gas, and oxygen gas or a mixed gas containing oxygen gas cannot be supplied. The life of the electrode rod will be significantly shorter than that of the previous one.

(Table 1) General molten steel components during molten steel processing using vacuum degassing equipment,
Table 1 shows the oxygen supply conditions during oxygen supply, and FIG. 1 shows the change over time in the gas composition in the degassing tank when degassing was performed under these conditions.

Most of the oxygen supplied from the tuyeres immersed in the molten steel reacts with C in the molten steel to become CO or CO2. Also, some oxygen is absorbed by metal elements 2 in molten steel, such as Fe, St, Aj
! , Mn, Cr, etc., but some of it floats up in the molten steel as unreacted oxygen gas and is exhausted. For this reason, the oxygen concentration in the exhaust gas may be several percent depending on the processing conditions.
It may exist. Of course, this oxygen concentration is greatly influenced by the composition of the molten steel during treatment, the amount of oxygen supplied, and the depth of immersion of the tuyere into the molten steel.

As shown in FIG. 2, the rate of wear of the electrode rod depends largely on the surface temperature of the electrode rod during processing and the 02, COZ tM degree in the gas. That is, it can be seen that the higher the surface temperature and the higher the oxidizing gas concentration, the more the electrode rod wear rate increases significantly.

[Problem that the invention seeks to solve]

When the inside of the vacuum degassing tank is at high temperature and under reduced pressure, CO is chemically more stable than CO2 in the presence of carbon, so the reaction of formula (1) above is promoted, and o
In the presence of 2, the reaction of formula (2) is likely to be promoted due to the combustion reaction. In either of these conditions, there is a problem in that when the inside of the vacuum degassing tank is at a high temperature, the electrode rod, whose constituent material is carbon, is rapidly consumed due to oxidation.

[Means for solving problems]

This invention uses a vacuum degassing device equipped with a heating electrode,
In a method for operating a vacuum degassing apparatus for degassing molten steel while supplying oxygen gas or a mixed gas containing oxygen gas to the molten steel, 02. The CO2 concentration is detected and the heating temperature of the heating electrode is adjusted according to these concentrations, and when the concentration is high, the temperature in the vacuum degassing tank is lowered and the above (
By slowing down the progress of the 11,f21 reaction,
This method prevents consumption of electrodes whose constituent material is carbon due to oxidation, and when the concentration of carbon is low, maintains the temperature at a predetermined value to prevent metal from adhering to the inner wall of the vacuum degassing tank, thereby improving yield. We aim to improve

〔Example〕

Figure 3.4 shows an embodiment of the invention, Figure 3 shows the RH
The figure shows a type vacuum degassing device. In both figures, numeral 11 is a vacuum degassing tank, and l is a rod-shaped heating electrode containing carbon as a constituent component. The heating electrode 1 is installed in a vacuum degassing tank 11. The vacuum degassing tank 11 is provided with an exhaust duct 4, which is continuous with an exhaust device (path in the figure). One end of a gas sampling tube 5 is connected to the exhaust duct 4, and an infrared gas analyzer 6 is connected to the other end.

Further, the tip of the oxygen blowing tuyere 12 and the base end of the reflux gas supply pipe 13 face the vacuum degassing tank 11, respectively.

A 1° ladle of melted F414 is placed below the vacuum degassing tank 11. A non-contact surface thermometer 3 is placed on the top surface of the vacuum degassing tank 11 with a heat-resistant glass 2 interposed therebetween. In FIG. 4, 7 is a central control device, 8 is a heating control circuit, and 9 is a power source.

The non-contact surface thermometer 3 measures the temperature on the surface of the heating electrode 1 and outputs a signal corresponding to the temperature to the central controller 7, while the infrared gas analyzer 6 measures the temperature inside the vacuum degassing tank 11. 02. contained in the exhaust gas of The concentration of CO2 is analyzed, the value is converted into a signal that can be processed by the central control device 7, and the signal is output to the central control device 7.

The central controller 7 inputs signals from the non-contact surface thermometer 3 and the infrared gas analyzer 6 and controls the amount of power that the heating control circuit 8 should input to the power source 9 . This control is based on the input value from the infrared gas analyzer 6.
With reference to a two-dimensional memory table for calculating the surface temperature Tfj of the heating electrode 1 from the relationship between i and the C0zfi degree Yj,
A surface temperature Tij as a target value of the heating electrode 1 is determined, and this is compared with an actual value of the surface temperature of the heating electrode 1 based on a signal input from the non-contact surface thermometer 3. and,
When the measured value exceeds the target value, the power source 9 turns the heating electrode 1 on.
A signal for reducing the amount of power input to the heating control circuit 8 is output to the heating control circuit 8. It is assumed that this process is performed at regular intervals. The surface temperature Tij as the target value is approximately 60
It is set in a range of about 0 to 800°C. The reason for this is that the rate of wear of the heating electrode 1 increases rapidly when its surface temperature exceeds 1000°C.

Note that when the oxygen blowing process from the oxygen blowing tuyere 12 is completed, 02. Since the generation of CO2 is reduced, the power supplied to the heating electrode 1 is increased to prevent metal from adhering to the vacuum degassing tank 11 while the oxygen is not being blown into the vacuum degassing tank 11. Raise the temperature to a predetermined temperature and maintain it.

The inventor conducted the following experiment to confirm the effects of this invention.

That is, the C and Mn tapped from the converter are each 0.10
%, 0.30%, molten steel at 1635° C. was subjected to vacuum degassing treatment using an RH type vacuum degassing device. In order to decarburize in a short time, 0.035Nn per minute is applied to 1 ton of molten steel from the shoulder. of oxygen was blown through the oxygen blowing tuyere for 5 minutes.

During this period, the exhaust gas composition is 35 to 35% immediately after the start of treatment.
45% CO, 10~15% CO2 12~4%02, and then CO and CO2 gradually decrease to 74 degrees until 0
The temperature increased slightly by 24 degrees. This is thought to be because the decarburization reaction was completed to some extent, and the amounts of Co and CO2 were relatively reduced.

In this experiment, Oz? Since it was previously set to control the surface temperature of the heating electrode 1 using the table when the i degree is 1% or more and the CO2'1M degree is 3% or more, the central controller 7 can control the surface temperature of the heating electrode 1. A power value according to the table was applied to the central controller 7 for the heating control circuit 8 .

If the method according to this invention is not carried out, it is usually 60
Electric power of 0 to 750 kwH is applied to the vacuum degassing tank 11.
The wall temperature is set to 900-100 to prevent metal from adhering to the
Although the temperature was raised to 0°C, in this experiment, the power input was limited to 150 to 250kwt+ according to the values in the table above, and the surface temperature of the heating electrode 1 was maintained at 950°C or lower.

After that, after finishing oxygen injection, 02. Since the amount of CO2 generated was significantly reduced to less than 1% and less than 3%, respectively, the maximum power of 600 to 750 kiIH was applied until the end of the degassing treatment as described above, and vacuum degassing treatment was performed for 15 minutes. Metal adhesion inside the vacuum degassing tank 11 was prevented.

(Table 2) As a result of continuing this control for each oxygen blowing process, the wear rate of the heating electrode 1 is low: $i (improvement in the life of the heating electrode 1) and the wear rate due to metal adhesion inside the vacuum degassing tank 11 is reduced. The effect of preventing a decrease in yield could be confirmed.

Table 2 compares the rate of wear of the diameter of the carbon rod for heating electrode 1 between the method of this invention and the conventional method, and it can be seen that the rate of wear is extremely low in the case of the method of this invention.

Although a rod-shaped electrode was used as the heating electrode 1 in this experiment, the shape of the heating electrode 1 is not necessarily limited to the rod-shape.
Various shapes can be used.

〔Effect of the invention〕

As explained above, according to the present invention, 02.0% in the exhaust gas from the vacuum degassing tank. It detects the CO2 concentration and adjusts the heating temperature of the heating electrode according to these concentrations.When the concentration is high, the temperature inside the vacuum degassing tank is lowered, and when the concentration is low, the temperature inside the vacuum degassing tank is lowered. By maintaining the temperature at a predetermined value, it is possible to prevent the electrodes containing carbon from being consumed due to oxidation, and at the same time to prevent the metal from adhering to the inner wall of the vacuum degassing tank, thereby improving the yield. There is an effect that can be achieved.

[Brief explanation of the drawing]

Figure 1 shows the change over time in the gas composition in the degassing tank during degassing treatment, and Figure 2 shows the surface temperature of the electrode rod during treatment and the 02. FIG. 3 is an explanatory diagram showing one embodiment of the present invention, and FIG. 4 is a block diagram showing one embodiment of the present invention. 1... Heating electrode, 3... Non-contact surface thermometer, 4...
...Exhaust duct, 5...Gas sampling pipe, 6...
・Infrared gas analyzer, 7... Central control unit, 8...
・Heating control circuit, 9...Power supply, 10...Ladle, 11
...Vacuum degassing tank, 12...Oxygen blowing tuyere,

Claims (1)

[Claims] In a method for operating a vacuum degassing device that uses a vacuum degassing device equipped with a heating electrode to degas molten steel while supplying oxygen gas or a mixed gas containing oxygen gas to the molten steel,
A method for operating a vacuum degassing apparatus equipped with a heating electrode, characterized in that during vacuum degassing treatment, O_2 and CO_2 concentrations in exhaust gas are detected and the heating temperature of the heating electrode is adjusted according to these concentrations. .