JPS58161730A - Method and device for vacuum degassing of molten metal - Google Patents

Abstract

PURPOSE:To subject the molten metal in a vacuum vessel to vacuum degassing with the prescribed required circulating flow by measuring the surface temp., etc. of the molten metal continuously, determining the flow rate thereof, and controlling the blowing rate of a gas so as to obtain the prescribed flow rate. CONSTITUTION:In a vacuum degassing device 1 which circulates molten metal by blowing an inert gas such as Ar through a riser 14 and a downcomer 13 between a ladle 2 and a vacuum vessel 11 and degasses the molten metal by the evacuation with a vacuum pump VP, the surface temp. of the molten metal 3 is measured continuously with a measuring means for surface temp. or the quantity of radiation heat utilizing a combination of phototransistors or the like, and the velocity at which the min. temp. point formed with the tracers 4 discharged between the points P1 and P2 of a prescribed intervals moves, is determined. From the flow rate thereof, the blowing rate of the gaseous Ar necessary for obtaining the circulation rate of the prescribed metal 3 is calculated with a calculating means Cal, and the blowing rate of the Ar is controlled manually or automatically in accordance with said rate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for vacuum degassing of molten metal and molten steel, and improvements to equipment used therein.

As one of the refining techniques for producing high-grade steel, vacuum degassing, especially RH vacuum degassing, is carried out. In this method, two pipes hanging from the bottom of a vacuum vessel are immersed in molten steel in a ladle, a vacuum pump is activated to suck up the molten steel into the vacuum vessel, and one pipe (rising pipe) is immersed in molten steel in a ladle. By blowing an inert gas such as argon into the area, the apparent specific gravity of the molten steel in that area is lowered and raised, and the molten steel is returned to the ladle through the other pipe (downcomer pipe) to circulate and return to the vacuum vessel. The gas is degassed inside the tank.

In this vacuum degassing, the success or failure of the process is determined by the smooth return flow of molten steel, so it is important to accurately grasp the flow rate of molten steel during operation.

Generally, if the amount of inert gas blown to raise the molten steel is increased, the recirculation amount will increase. Now, when gas is injected at Q (Q/min) into a riser pipe with inner diameter R (CI), it is known that the molten steel circulation flow rate V (t/sin) is as follows, where K is the constant of proportionality. .

However, this is a relationship that is established only if other conditions are kept constant; in actual operation, the inner diameter expands and deforms due to erosion of the refractory on the inner surface of the tube, and Complicated factors such as the pinching caused by clothing and changes in the shape of the circulation path inside the vacuum apparatus are involved, so the flow rate of molten steel cannot be controlled solely by the amount of inert gas blown into it.

Therefore, there is a need for a method to determine the amount of molten steel recirculated.
There have been several proposals so far, for example,
No. 5-141515 discloses that the amount of recirculation can be determined by measuring various elements of vibration of a vacuum container caused by recirculation.

The inventors of the present invention attempted to monitor the recirculation flow rate of molten steel more directly, and as a result of their research, they found that there is a certain proportional relationship between the flow velocity at the surface of the molten metal and the recirculation flow rate. By knowing, it is possible to judge whether or not the reflux is occurring normally as expected, and also to check for irregularities in the surface temperature or amount of radiant light, 1. In other words, slight differences in the temperature or amount of radiant light depending on the location. However, as the molten metal moves without much change over a limited distance as the molten metal flows, the present invention was based on the finding that by measuring the speed of movement, the flow velocity on the surface of the molten metal can be measured.

The vacuum degassing method of the present invention is a method in which molten metal is introduced into a vacuum vessel through a riser pipe by blowing inert gas, and returned through a downcomer pipe to reflux, and during this time, degassing is carried out under actual conditions. In this method, the surface temperature or radiation light at multiple points in the flow direction of the molten metal is measured over a certain period of time, and the time required for the molten steel to move is determined by the cross-correlation method or the spatial filter method, and the flow velocity at the surface is determined. However, the blowing of the inert gas for reflux is adjusted so that the surface flow velocity does not fall below a predetermined value.

To explain one embodiment with reference to the drawings, as shown in FIG. 1, the molten metal 3 in the ladle 2 is introduced into the vacuum vessel 11 through the riser pipe 12 by blowing an inert gas, for example, argon. After degassing there, it is returned through the downcomer pipe 13 and refluxed. In the vacuum vessel 11, the surface temperature (T and T) at two points (P and T) in the flow direction of the molten metal is measured at regular intervals, and the temperature peaks (T, p and T□p) or the bottom (from Tb and T), or both, know and express the wlIIIl it takes to move between P and P.
Shut out the flow velocity V, -4 on the h plane.

The appropriate measurement point for the surface concentration is somewhere within the line connecting the centers of the ascending pipe and the downcomer pipe, slightly closer to the downcomer pipe. Although it differs somewhat depending on the measuring means, both points have a certain area, and the temperature is given as the average value of the surface temperature of that area.

-For example, it has the size and distance as shown in Figure 2. (In the figure, the arrows indicate the temperature T at both flow points of mus, and the graph shown in Figure 3 is an example of recording the changes in T. It can be seen that T and b pass through point day and day 1 with a difference of about 0.1 seconds.

Since the distance between 1 and P4 is 180 mm as shown in Figure 2, the flow velocity on the surface is 180 gv 10.1 sec - 1300 va/sec, or 1/sec.
．． This means 8-.

This flow rate is often used when the molten metal is steel.
This is a standard value for a vacuum degassing device that is combined with a ladle that is about 0 tons thin.

The flow velocity is determined by the cross-correlation method, for example, as follows. T-line also measures atrophy at minute intervals at two measurement points P and P.
λ and record changes. FIG. 4 shows an example of the results, in which sampling was performed 230 times (therefore, over about 7.6 seconds) every 3318 (milliseconds). When the data obtained in this way is processed as shown in Figure 5, the highest correlation is observed when the sampling points are shifted by three points. 33111S X3 valve passed at 0.1S, so you can see that it should be considered. F? The interval between and is also 118-0s from No. 1-, and in this case, the flow velocity on the molten steel surface is 180m510.1s-1800ms/
seconds, or 1.8 seconds per second.

Even in cases other than the above examples, those skilled in the art can determine V, - It will be possible to determine the lower limit of the reference value.

Specifically, we first performed vacuum degassing on a specific molten metal using a newly manufactured vacuum degassing device.
The amount of inert gas blown and V.

Measure the relationship and show it in a graph. Next, the minimum required recirculation amount for vacuum degassing is determined based on the steel type, processing time, etc., and the amount of inert gas blown necessary to satisfy this is given by the above equation (1).
Then, ■1−λ corresponding to the inert gas injection theory
The value of is determined from the above graph.

In actual operation, the I
! Measure the temperature lvt-wise, continuously obtain 1-4, look at the change trend, and increase the inert gas weight if there is a possibility of it falling below the standard value. It is preferable to control the inert gas streamline adjusting means to automatically adjust the gas blowing wax so as to reduce the inert gas flow rate when the tit inert gas flow rate is greatly exceeded.

As shown in Figure 3, when the molten metal is steel, there is temperature unevenness on its surface of several tens of degrees Celsius (65 degrees Celsius in the range shown in the figure), and even in molten metals of other metals. , it is not particularly difficult to detect temperature peaks and bottoms, as we can usually expect the existence of temperature irregularities similar to this.

However, the more uneven the temperature is, the easier and more accurate the measurement will be. A larger wA degree unevenness can be formed by dropping a low-temperature object as a tracer onto the surface of the molten metal flow to temporarily create a clearly lower temperature area than the surrounding area.

This is an important aspect of the present invention and is a recommended embodiment.

Examples of low-temperature objects to be dropped as tracers include carbon particles, which float on top of the molten metal and are not immediately dissolved and lost.

When, as is often done, adding linear components for alloy production at the same time as vacuum degassing, some or all of the added elements can be used as tracers.

If it is desired to avoid further changes in the composition of the molten metal, solid particles of metal having the same composition as the molten metal may be dropped as tracers.

These tracers are dropped onto the flow of the molten metal by using the tracer dropping means 17, which is a combination of a tracer container and a valve shown in FIG.

Whether a tracer is required or not, and the excess tracer acid if necessary, can also be determined by the calculator and automatically adjusted according to the trend of lagoonal change.

The vacuum degassing method of the present invention not only has the effect of controlling inert gas blowing based on the surface flow velocity to ensure the correct reflux velocity, but also achieves a predetermined total reflux velocity by integrating the flow velocity. It can be determined that the flow rate has been achieved and therefore initial degassing has occurred.

In the past, there was a lack of appropriate means to know the total amount of recirculation, so operations had to be carried out in a vain manner for safety reasons. The losses during this period, including the temperature drop of the molten metal and the melting loss of the refractory, cannot be ignored, but can be avoided by the present invention.

Furthermore, it is possible to accurately determine when the vacuum vessel should be repaired based on the decrease in flow velocity.

As mentioned in the introduction, the invention also encompasses an apparatus for carrying out the vacuum degassing method described above. The device
As shown in the figure, a vacuum vessel 11 is equipped with a vacuum pump VP 1 and has a rising pipe 12 and a descending pipe 13 for molten metal at the bottom.
A vacuum degassing device 1 having an inert gas blowing nozzle 14 in the riser pipe includes a means 15 for measuring the surface humidity or the amount of radiant light at multiple points in the flow direction of the molten metal, and a change in the surface temperature or the amount of radiant light. Calculating means cat, J' for determining the flow velocity on the surface and using that value to calculate the recirculation amount or necessary inert gas blowing fog according to a predetermined formula; and means for displaying the results 1nd; It is characterized by the addition of.

Various means have been devised to non-contactly measure the surface temperature or the amount of emitted light of a highly humid object, but in order to detect momentarily changing temperature, for example, a combination of phototransistors is used to detect changes in surface brightness. Appropriate is a device that can be used for measurement.

In order to achieve the required inert gas injection amount, the result of the above calculation may be displayed and the pulp 16 may be manually operated accordingly to adjust the gas flow from the inert gas source Ar. Automatic adjustment can also be employed.

When using a tracer, a tracer dropping means 17 as described above is added to the vacuum vessel.

[Brief explanation of the drawing]

FIG. 1 is an explanatory longitudinal sectional view of an apparatus showing a situation in which vacuum degassing of molten steel is carried out according to the present invention. 2 and 3 are diagrams for explaining an example in which the present invention is applied to molten steel. The figure is a graph showing changes in surface temperature over time at each measurement point. 4 and 5 are diagrams illustrating the measurement of moving speed by the cross-correlation method in another example in which the present invention is applied to molten steel, and FIG. 4 shows measurement point P and town. Fig. 5 shows the results of correlation obtained from the data in Fig. 4. 1... Vacuum degassing device 11... Actual container 12... Rising pipe 13... Descending pipe 1
4... Inert gas blowing nozzle 15...
... Surface temperature measuring means 17 ... Tracer dropping means 2 ... Ladle 3 ... Molten metal 4 ...
...Tracer vp...Vacuum pump A"...Inert gas source Cal...Director means Ind...
...Display means patent applicant Daido Steel Co., Ltd. Agent Patent attorney Sou Suga Figure 1 143 - Figure 2 Figure 8

Claims (9)

[Claims] (1) In this method, molten metal is introduced into a vacuum vessel through a riser pipe by blowing inert gas and returned from a downcomer pipe to reflux, during which time the molten metal is exposed to vacuum conditions and degassed. Measure the surface temperature or radiance at multiple points in the flow direction over a certain period of time, calculate the surface flow velocity by knowing the time required for the molten steel to move using the cross-correlation method or spatial filter method, and calculate the surface flow velocity. 1. A vacuum degassing method for molten metal, characterized in that the amount of inert gas blown in for reflux is adjusted so that the amount of reflux does not fall below a predetermined value. (2) The temperature or radiation light on the surface of the molten metal is continuously measured, and the amount of gas blown is automatically adjusted by controlling the inert gas flow adjustment means according to the tendency of the surface flow velocity to change. The method according to claim 1. (3) A method according to claim 1 or 2, characterized in that the measurement is carried out by dropping a tracer onto the surface of the flow of molten metal to form a particularly low temperature or synchrotron radiation eel. (4) The method according to claim 3, wherein the tracer dropped onto the surface of the molten metal is made of a substance that floats on the molten metal and does not dissolve immediately. (5) The method according to claim 3, wherein the tracer dropped onto the surface of the molten metal is an element added for alloy production. (6) The method according to claim 3, wherein the tracer dropped onto the surface of the molten metal is a solid metal having the same composition as the molten metal. (7) The method according to any one of claims 1 to 6, wherein the molten metal is molten steel. (8) In a vacuum-equipped gas device, which is equipped with a vacuum pump and consists of a vacuum vessel with a rising pipe and a descending pipe for molten metal at the bottom, and an inert gas blowing nozzle in the rising pipe, multiple points in the flow direction of the molten metal are used. A means of measuring the surface temperature or radiated light at 1. A vacuum degassing apparatus for molten metal, characterized in that it is further equipped with a calculation means for calculating gas injection and a means for displaying the result. (9) Claim 8, which is configured to automatically adjust the inert gas blowing pulp based on the result of calculation.
Sectional equipment. <10) The apparatus according to claim 8, comprising means for dropping a tracer onto the surface of the flow of molten metal.