JPH02111813A - Method for controlling circulating flow condition of molten metal - Google Patents

Abstract

PURPOSE:To eliminate mal-circulating flow condition of molten metal and to easily recover this to the normal condition by measuring vibration of a vacuum vessel in RH vacuum degassing apparatus, grasping the circulating flow condition of the molten metal and executing increase of circulating flow gas quantity and charge of flux. CONSTITUTION:Inert gas 6 is blown into an uptake tube 3a from gas blowing pipe 4, and the molten steel 1 is ascended through the uptake tube 3 and passed through the vacuum vessel 3 to execute the degassing treatment, etc., and returned to a molten steel ladle 2 through a downtake tube 3b to continuously circulate the molten steel 1. Then, the vibration of the vacuum vessel 3 is measured with a vibration sensor 7 arranged at the vacuum vessel 3 and the electric charge output is converted to the voltage with a converter 8 and the circulating flow quantity is calculated based on the pre-made vibration quantity with a computing element 9. By this method, at the time of judging to the mal-circulating flow, the increase of circulating flow gas from the gas pipe 4 for circulation and/or the charge of flux 10 into the vacuum vessel 3 are executed. By this method, the circulating flow of the molten steel 1 is easily recovered to the normal condition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for controlling the reflux state of molten metal in a reflux vacuum degassing facility.

[Conventional technology]

In general, 7 volumes of molten steel produced in coppermaking furnaces that melt and refine in the atmosphere, such as converters, electric furnaces, and open hearths, contain large amounts of gas components such as oxygen, hydrogen, and nitrogen. Components precipitate during or after solidification of molten steel, which can cause various defects in products. therefore,
Vacuum degassing equipment is used to reduce the gas components in the molten steel, eliminate these defects, reduce nonmetallic inclusions, equalize the concentration and components, and improve the internal quality and mechanical properties. It is being One type of vacuum degassing equipment is to install two pipes at the bottom of the vacuum chamber, one for suction (rising pipe) and one for exhaust (downcoming pipe), and inert gas such as argon is blown into the rising pipe. There is a recirculation vacuum degassing facility (so-called RH vacuum degassing facility) that continuously sucks up and degasses molten steel using the principle of a gas lift pump.

In order to efficiently process molten steel in this RH vacuum degassing equipment, it is necessary to feed the melt into the vacuum chamber in as short a time as possible, and it is important to process the molten steel at an optimal recirculation rate.

However, during degassing treatment, non-metallic inclusions such as β203 are often deposited in the ascending or descending pipe, reducing the inner diameter of the tube.In this case, the recirculation flow rate decreases and the degassing is no longer carried out efficiently.

Conventionally, such troubles occurred when measuring temperature after PH degassing treatment.
Alternatively, when the analysis value of the molten copper component at the end of the treatment is determined, it is determined based on temperature non-uniformity, component segregation, etc., and countermeasures are taken such as extending the treatment time of the RH treatment or bubbling treatment.

[Problem to be solved by the invention]

However, in the above method, the inclusions are removed after the RH treatment, which disrupts the time schedule of the entire factory.

Therefore, the main object of the present invention is to provide a method capable of detecting poor reflux in real time at the initial stage of RH degassing treatment and returning the reflux condition to normal.

[Means for Solving the Problems] The present invention for solving the above problems provides a vacuum tank above a molten metal container, introduces molten metal into the vacuum tank from a riser pipe and degasses it, In a recirculation type vacuum degassing device that circulates molten metal into a container via a downcomer, the vibration of the vacuum chamber is measured by a vibration sensor, and the recirculation state of the molten metal is determined based on the output from this sensor, and the recirculation state is determined. Based on this, at least one of increasing the amount of recirculating gas and introducing flux for melting oxides attached to the downcomer pipe is performed.

[For production]

The first feature of the present invention is to measure vibrations associated with circulation in an RH vacuum chamber. This vibration is caused by the reflux energy of the fusion metal and the energy of the rupture of the reflux gas in a vacuum atmosphere, and the amount of vibration and the amount of reflux uniquely correspond. Therefore, by measuring the amount of vibration,
The amount of recirculation, that is, the state of recirculation can be detected.

Next, the second feature of the present invention is that when the recirculation condition is poor, the amount of recirculation gas is increased and the flux is added. The reason why the reflux condition becomes poor is that oxides of specific substances (Al2O2, etc.) adhere to the bottom of the vacuum chamber or the downcomer pipe, and the pipe diameter decreases. According to the present invention, the poor recirculation condition can be eliminated by increasing the amount of recirculation gas or by introducing a flux with a dissolving power such as this oxide into the vacuum chamber.

Specific configuration of this invention] The present invention will be explained in more detail below.

FIG. 1 is a schematic explanatory diagram of an R H vacuum degassing apparatus to which the present invention is applied. A vacuum tank 3 is disposed on the -F side of a molten steel ladle 2 filled with molten steel 1 as an example of molten metal, and an upper tube 3a and a downcomer tube 3b provided at the bottom of the vacuum chamber 3 are immersed in the molten wAl. Thereafter, when the pressure in the vacuum chamber 3 is lowered using a vacuum pump (not shown) or the like, the molten steel 1 is sucked up into the vacuum chamber 3. The suction of the molten steel 1 stops at the liquid level where the pressure exerted by the steel 1 becomes equal to the atmospheric pressure.

Next, an inert gas 6 such as argon gas is supplied from the gas blowing pipe 4.
When molten steel 1 is blown into the rising pipe 3a, the molten steel 1 rises through the rising pipe 3a according to the principle of a gas lift pump, and after being degassed while passing through the vacuum chamber 3, it is transferred to the descending pipe 3b.
After that, the molten steel 1 is returned to the molten steel ladle 2, and thereafter the molten steel 1 is continuously circulated.

The vacuum chamber 3 vibrates with the reflux, and the amount of vibration increases as the reflux flow increases. Therefore, by continuously measuring the amount of vibration, it is possible to grasp the circulation state. Therefore, in the present invention, a vibration sensor 7 is installed in the vacuum chamber 3,
Through a converter 8 that converts the charge output of the vibration sensor 7 into a voltage, a calculation unit 9 calculates the amount of recirculation from a relational expression between the amount of vibration and the amount of recirculation created in advance.

On the other hand, in FIG. 1, a flux 10
A tank 11 containing the following is provided. If it is determined that the recirculation is insufficient by the method described above, the amount of recirculation gas from the recirculation gas pipe 4 is increased and/or the flux 10 is introduced into the vacuum chamber 3. This flux uses a substance that has the effect of dissolving deposits attached to the downcomer pipe 3b and the like.

FIG. 2 shows the results of an investigation into the relationship between the amount of vibration of the vacuum chamber and the amount of molten steel circulating in the present invention. Here, the reflux amount is C
This is an actual value obtained by adding u as a tracer and using the following equation from the homogeneous mixing time of Cu.

w = 3.33X D ” “W” 33.t −”
74W: Circulation amount (Ton/m1n) D: Down pipe diameter (cm) W: Processing amount (Ton) t: Uniform mixing time (sec) As is clear from Figure 2, the recirculation amount is 40Ton/min.
A recirculation failure occurred in the following cases, but the amount of vibration when the failure occurs varies depending on the amount of recirculation gas at that time. Therefore, poor recirculation is determined for each recirculated gas based on the criteria listed in Table 1.

Regarding the judgment of the reflux condition in the above table, when there is little difference in temperature and components between the upper and lower layers of the ladle, it is judged as normal (○), and when the difference is large, it is judged as bad (×).

If it is determined to be defective, the amount of reflux gas is increased and flux is added. This increases vibration and avoids non-uniformity of components and temperature. FIG. 3 shows an example of the change in vibration caused by this flux injection.

In this example, flux input is 400 kg, flux: Ca070%, CaFz: 30%, reflux gas amount:
6oo ~ 120'01/min, reflux N: 30Ton
/min~50Ton/min.

Next, FIG. 4 is a diagram showing the relationship between the amount of recirculated gas and the amount of vibration.

As shown in the example in Figure 3, when measures are taken to avoid poor circulation, the amount of vibration increases;
If the normal boundary reference line L (corresponding to the boundary between x and ○ in Table 1) is exceeded (A), it is assumed that the perfusion state has returned to normal and the process is continued. However, even if the amount of vibration increases, if it does not exceed the reference line (B), it has not recovered and should be dealt with by replacing the vacuum chamber. The increase in vibration in case (B) does not correspond to the amount of recirculation, but is considered to be the increase in vibration due to the dissipation of the recirculation gas into the vacuum atmosphere. Note that the reference line in Fig. 4 was determined based on actual results in past actual operations.

The following can be used as the flax and soybean paste used in the present invention. Note that CaFz has the effect of dissolving β203 and the like (lowering the melting point).

Moreover, the flux input amount is preferably 200 to 800 kg/charge (160 tons of molten steel). This is because if the weight is less than 200 kg, the effect of adding flux will be weak, and if it exceeds 800 kg, the refractory material will suffer significant melting loss.

Next, the mounting location of the vibration sensor in the present invention will be explained with reference to FIG.
The upper exhaust gas pipe 1 is fixed to a support frame 13 installed in the
It vibrates using the expansion 15 of No. 4 as a spring.

Therefore, it is preferable to install the vibration sensor at a position away from the supporting part at the center of the tank, since a large amount of vibration can be obtained. On the other hand, if it is too low in the vacuum chamber, it is not shown in the diagram. 8E
As it gets close to the liquid level, the radiant heat from the melting will cause trouble to the vibration sensor and cable. Therefore, for example, in the case of a vacuum chamber of the size specifically shown numerically in FIG. 5, the position is preferably about 1 m or more below the support frame, usually 2 m below.

The amount of vibration in the present invention can be detected in the form of vibration velocity, vibration acceleration, displacement, etc. However, high-frequency vibrations are generally detected by vibration acceleration, and low-frequency vibrations are detected by vibration velocity or displacement. In the case of the example shown in the third figure, since the vibration is in a low frequency range, it is detected by vibration velocity. is preferable. Note that an example of measurement conditions in this case will be added.

Vibration sensor type...Piezoelectric acceleration sensor Vibration sensor Charge sensitivity...15.1 pc/g Charge amplifier (converter) Voltage sensitivity -316mVS/cm The vibration sensor in the present invention is a piezoelectric acceleration sensor.
Any known vibration sensor such as a sensor, an electrodynamic vibration sensor, or a servo acceleration sensor can be used.

Next, we investigated frequencies suitable for understanding the circulation state. First, in FIG. 6, 3H2 and 5H2 also have peaks, but according to the knowledge of the present inventors, these are based on the natural vibration of the vacuum chamber and are not directly related to the reflux amount. By the way, as shown in Figure 7, even in a non-reflux state,
It has 3H1 and 5H2 peaks. Therefore, 1
It was found that only the 0H2 peak was related to the reflux amount.

In this way, depending on the model and size of the vacuum chamber,
Since it exhibits a unique vibration, it is desirable to measure the vibration state in a non-reflux state in advance and then pick up the frequency and peak that indicate the amount of reflux.

On the other hand, in the present invention, although it is desirable that the amount of vibration be detected continuously, it may be detected intermittently.

〔Effect of the invention〕

As described above, according to the present invention, poor recirculation can be detected in real time at the initial stage of RH degassing treatment, and the recirculation can be easily restored to a normal state.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the recirculation type (RH) vacuum degassing equipment according to the present invention, Fig. 2 is a correlation diagram between the molten steel recirculation flow rate, the vibration speed of the vacuum chamber, and the recirculation gas amount, and Fig. 3 is a flux injection Figure 4 is a graph showing the relationship between the amount of circulating gas and the amount of vibration, Figure 5 is an explanatory diagram of the installation location of the vibration sensor, and Figure 6 is a graph showing the vibration of the vacuum chamber when it vibrates. A diagram showing frequency bands, FIG. 7 is a frequency band diagram at the time of non-recirculation. 1... Molten steel (molten metal), 2... Molten steel pot (molten metal container), 3... Vacuum tank, 3a... Rising pipe, 3b...
- Descending pipe, 4... Circulation gas pipe, 6... Inert gas, 7... Vibration sensor, 8... Converter, 9... Arithmetic unit, 10... Flux. Fig. 3 Fig. 2'O Fig. 4 Flight 3t 1 person capacity t4 Fig. fig.

Claims (1)

[Claims] (1) In a recirculation type vacuum degassing device in which a vacuum chamber is provided above the molten metal container, the molten metal is introduced into the vacuum chamber from the riser pipe, degassed, and then refluxed to the molten metal container via the downcomer pipe. , the vibration of the vacuum chamber is measured by a vibration sensor, the reflux condition of the molten metal is determined based on the output from this sensor, and based on the reflux condition, an increase in the amount of reflux gas and oxides attached to the downcomer are detected. 1. A method for controlling a molten metal circulation state, comprising: performing at least one of introducing flux to melt the molten metal.