JPS625210B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a blown gas control device for a recirculation type vacuum degassing device, and in particular, to make the gas blown in from a plurality of inlets into an equal flow rate, and to prevent the inlets from clogging due to clogging. The present invention relates to a blown gas control device that keeps the total flow rate of blown gas constant even if a portion of the flow rate decreases.

A vacuum tank, a suction pipe and a discharge pipe that communicate with the vacuum tank and are immersed in molten steel, and a plurality of blowing pipes connected to a plurality of blowing ports provided in the suction pipe, In a circulation type vacuum degassing device that circulates molten steel in a vacuum chamber by blowing an inert gas into the suction pipe from the blowing pipe and degasses the molten steel, the reflux speed of the molten steel is determined by the degassing speed. In order to maintain efficiency and product quality, the amount of gas blown into the suction pipe is kept constant to maintain a predetermined constant speed, and the amount of gas blown into the suction tube is kept constant to maintain the rate of droplet splash. In order to prevent a decrease in the service life of the gas, it is desired that the amount of gas blown in from each inlet be as equal as possible.

To deal with this, each of the above-mentioned blowing pipes is provided with a flow rate control valve and a flow rate detector, and the target flow rate of each blowing pipe is set in advance by equally dividing the gas flow rate necessary for blowing into the suction pipe. BACKGROUND ART A blowing gas control device has been proposed that drives a flow rate control valve based on the actual gas flow rate detected by a flow rate detector, and controls the gas flow rate of each blowing pipe to match its target flow rate.

However, according to such a conventional blow gas control device, if one of the blow pipes becomes clogged, the amount of operation (opening degree) of the flow rate control valve of that blow pipe becomes clogged.
When it reaches 100% and exceeds the controllable range, other blowing pipes are controlled to a preset target flow rate, which causes the inconvenience that the total gas flow rate blown into the suction pipe becomes insufficient. . In other words, clogging tends to occur near the injection port due to the adhesion of foreign substances such as solidified steel and iron oxide, and if the total gas flow rate is insufficient due to such clogging, the circulation speed of molten steel decreases and a constant Since sufficient degassing is not achieved within the working time, product quality may deteriorate.

The present invention was made against the background of the above-mentioned circumstances, and its purpose is to maintain a constant total gas flow rate blown into the suction pipe even if the blowing pipe becomes clogged, and to prevent the blockage from occurring. It is an object of the present invention to provide a blowing gas control device for a recirculation type vacuum degassing device, in which the amount of gas blown through another blowing pipe line without a blowing pipe is evenly controlled.

In order to achieve such an object, the present invention provides a vacuum tank, a suction pipe that communicates with the vacuum tank and is immersed in molten steel, a discharge pipe that is connected to a plurality of inlets provided in the suction pipe, respectively. A blowing gas control device for a circulation type vacuum degassing apparatus, which is equipped with a plurality of blowing pipes, and circulates molten steel into the vacuum chamber by blowing inert gas from the blowing pipes into the suction pipe. Detecting the flow rate of each gas flowing through the blowing pipes and the total gas flow rate of the blowing pipes, and detecting a pipe flow rate signal representing the pipe flow rate and a total gas flow rate representing the total gas flow rate. a flow rate detection device that outputs a flow rate signal; a flow rate control valve provided in each of the blowing pipes to adjust the flow rate of gas flowing through the blowing pipe; and a flow rate control valve for each pipe flow represented by the pipe flow rate signal. and a common target value, and driving the flow rate control valve so that the difference between them becomes zero, and causing the gas flow rate of each of the blowing pipes to match the target value; The total gas flow rate represented by the total flow rate signal is compared with a predetermined constant value, and the target value is determined so that the difference between the two becomes zero, and the amount of gas blown into the suction pipe is determined. and a control device having a second control means for matching the value to a constant value.

In this way, the target value is determined so that the difference between the total gas flow rate and a predetermined constant value is zero, and the gas flow rate of each blowing pipe is controlled to match the common target value. Therefore, even if a blockage occurs in some of the plurality of blowing pipes, the target value of the other blowing pipes is raised so that the total gas flow rate matches a predetermined constant value, and the total gas flow rate is increased. is maintained constant, and the gas flow rates in the other blowing pipes are equally controlled.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below based on the drawings.

In FIG. 1, a suction pipe 16 and a discharge pipe 18 are formed in the vacuum tank 10 and are connected to the vacuum tank 10 and immersed in the molten steel 14 in the ladle 12. The inside of the vacuum chamber 10 is evacuated by an exhaust device that does not require a vacuum pump. In addition, 19 is a refractory material used as a lining. A plurality of blowing pipes 20a to 20e are connected to the suction pipe 16.
When inert gas is blown into the suction pipe 16 through a to 20e, the molten steel 14 rises with the gas inside the suction pipe 16, enters the vacuum chamber 10, and enters the ladle 12 through the discharge pipe 18. I'm getting used to being able to return and circulate. In such a reflux process, the molten steel 14 exposed in the vacuum chamber 10 is degassed, and the reflux speed is set at a desired constant value in order to maintain degassing efficiency, product quality, etc. . In other words, if the reflux rate is too high, it not only causes consumption of the refractories used for lining the vacuum chamber 10, etc., but also is unfavorable for degassing reactions, while if the reflux rate is too low, it takes time for the degassing process. This results in a decrease in degassing efficiency.

As shown in detail in FIG. 2, five inlets 22a to 22e are provided at equal angular intervals on the peripheral wall of the suction pipe 16, and inert gas is supplied to these inlets 22a to 22e. Blow conduits 20a to 20e are connected between the header 24 and the header 24. In these blowing pipes 20a to 20e, there are flow rate sensors 28 for detecting the flow rate of the inert gas.
a to 28e and a flow rate control valve 30a that adjusts the flow rate.
30e to 30e are inserted respectively.

The flow rate sensors 28a to 28e detect the gas flow rate using an orifice or the like, and output pipe flow rate signals SFa to SFe, which are analog electrical signals representing the gas flow rate, to the flow rate controllers 32a to 32e, respectively. The flow rate controllers 32a to 32e, which are the first control means, are so-called cascade type controllers, and are configured to control a target value represented by a target signal SC supplied from a main controller 34, which will be described later, and a pipe flow rate signal SFa.
Compare the actual gas flow rates represented by SFe to SFe, and adjust the flow rate control valve 3 so that the difference between them becomes zero.
Drive signals SDa to SDe for changing the opening degrees of the flow control valves 0a to 30e are output to the flow rate control valves 0a to 30e, respectively. The flow control valves 30a to 30e are equipped with actuators such as diaphragms and electric motors, and change the valve opening degree according to the supplied drive signals SDa to SDe.

The pipe flow signals SFa to SFe are also supplied to an adder 36, and the contents (current signal or voltage signal) of these signals SFa to SFe are added to produce a total flow signal ST representing the total gas flow rate. is supplied to the main controller 34 via a delay element 38.
Therefore, the flow rate sensors 28a to 28e and the adder 36 constitute a flow rate detection device that detects the flow rate of gas flowing into the blowing pipes 20a to 20e and the total gas flow rate.

In the main controller 34 which is the second control means,
A desirable constant value M of gas flow rate to be blown into the suction pipe 6 is set in advance, and the total flow rate signal ST
Compare the actual total gas flow rate X represented by the constant value M, and set the target signal so that the difference between them becomes zero
SC is determined. For example, assuming that the total gas flow rate is X, the target value A, which is the content of the target signal SC, is controlled by the following equation.

A=K(E+ ¹ _Ti ∫Edt) ...(1) Here, K is gain, E is deviation (M-X), Ti
is the integration time. In this way, the main controller 34 and the flow rate controllers 32a to 32e control the total gas flow rate sucked into the suction pipe 16 to a constant value, and also uniformly control the gas flow rate in each of the blowing pipes 20a to 20e. It constitutes the control device that controls it. Note that the delay element 38 has its transfer function G(s)
It is configured as a first-order lag element with 1/(1+TS), and its time constant T is appropriately determined based on the response characteristics of the control system in order to stabilize the control system.

The operation of this embodiment will be explained below.

When there is little foreign matter adhering to the suction ports 22a to 22e, etc., each flow control valve 30a to 30
e is the drive signal from the flow rate controllers 32a to 32e
The gas flow rate is adjusted according to SDa to SDe, and the gas flow rate of each of the blowing pipes 20a to 20e is made to match the target value A. This target value A is the main controller 34
is determined according to equation (1), but in the above case where the blowing pipes 20a to 20e are not clogged and their flow rates are controlled to the target values, the deviation E is usually almost the same. is zero. For example, if a predetermined constant value M is blown into the suction pipe 16,
If it is 1000N/min, the target value A will be 200N/min according to equation (1), and the target signal representing that value will be
Each flow rate controller 32a to 32e performs constant value control according to SC, and the total gas flow rate blown into the suction pipe 16 becomes 1000 N/min.

Next, as the adhesion of foreign substances such as iron oxide to the suction ports 22a to 22e progresses, even if the flow rate control valve 30a is fully opened due to, for example, a blockage in the blowing pipe 20a, the gas flow rate will not reach the target level. When the value becomes lower than the value A, the total gas flow rate X starts to decrease. However, since the target value A is automatically increased by the main controller 34, some of the blowing pipes 2
Regardless of the decrease in the flow rate of 0a, the total gas flow rate blown into the suction pipe 16 is maintained constant.

That is, for example, if the total gas flow rate X represented by the total flow rate signal ST is 900 N/min, the target value A is set in the main controller 34 according to equation (1).
It becomes 2225N/min. Therefore, the gas flow rate of each of the other blowing pipes 20b to 20e is 225N.
/min, the total gas flow rate blown into the suction pipe 16 is 1000N/min.

As described above, according to this embodiment, the target value A is determined so that the total gas flow rate blown into the suction pipe 16 becomes a predetermined desirable constant value M, and each of the blowing pipes 20a to 20e Since the flow rate is controlled so that it matches the common target value A, even if a part of the blowing line 20 becomes clogged, the amount of flow reduction due to the blockage and that of other normal blowing lines will be reduced. The target value A is determined so that the amount of increase in flow rate is equal to the amount of increase in flow rate, and the total gas flow rate is maintained constant. Therefore, a constant flow rate of molten steel can be obtained in the suction pipe 16 regardless of a part of the blowing pipes 20a to 20e being clogged, so a constant degassing effect can always be obtained and product quality can be maintained at a high level. At the same time, the air inlet 2
Therefore, the maintenance period for clogging of 2a to 22e can be extended. Moreover, the blowing pipes 20a to 2
Since the pipes where no clogging has occurred yet are controlled to have a uniform flow rate according to the common target value A, the height of the splashing of molten steel splashing into the vacuum chamber 10 due to the concentration of the blown gas in the specific pipes This prevents the refractory material 19 at the top of the vacuum chamber 10 from being melted and damaged.

Next, another embodiment of the present invention will be described. Incidentally, the same reference numerals are given to the parts common to those of the above-mentioned embodiment, and the explanation thereof will be omitted.

In the exemplary embodiment described above, the adjustment device enclosed by the dashed-double line in FIG. 2 is also constituted by a so-called digital computer. That is, in Figure 3,
The pipe flow signals SFa to SFe are supplied to the A/D converter 40.
The signal is supplied to the I/O port 42 via the I/O port 42.
The I/O port 42 sends these signals SFa to SFe to the CPU 44 and RAM 4 via the data bus line.
6. Supply to ROM48. CPU44 is RAM46
The signals SFa to SFe are processed according to the control program stored in advance in the ROM 48 while utilizing the storage function of the ROM 48, and the total gas flow rate and target value A are determined.
It is supplied to the flow control valves 30a to 30e through the port 42 and the A/D converter 40, respectively.

That is, as shown in the flowchart of FIG. 4, when the control program is started by a start signal (not shown), pipe flow signals SFa to SFe are read in step S1. Next, in step S2, the signals SFa to
SFe is added to calculate the total gas flow rate, and the pre-stored constant value M and the total gas flow rate X
Based on this, for example, a target value A such that the total gas flow rate X matches the constant value M is calculated from the above-mentioned equation (1). The above steps S1 and S2 are the second control means.

Next, steps S3 to S6 are executed, and the new target value A is updated after a certain period of time T in order to stabilize the control system, and the gas flow rate of the blowing pipes 20a to 20e is kept constant within that certain period of time. Control is performed to That is, in step S3, interrupts are enabled, and in step S4
In step S5, the control program is inactive for a certain period of time T, and after interrupts are disallowed after the certain period of time T in step S5, the target value is updated to the new target value A determined in step S2 in step S6. . Then, between steps S3 and S5, an interrupt routine, which is the first control means shown in FIG. 5, is repeatedly executed.
The gas flow rate of each blowing pipe 20a to 20e is controlled. The interrupt routine is composed of similar control subroutines for each of the blowing lines 20a to 20e connected to steps SS1 to SS5. For example, the control subroutine SS1 for the blowing line 20a is configured as shown in FIG. It is composed of

That is, first, step SB1 is executed to read the actual gas flow rate represented by the pipe flow rate signal SFa, and step SB2 is executed to compare the actual gas flow rate of the blowing pipe 20a with the target value A. It is determined whether the gas flow rate exceeds the target value A or not. If the actual gas flow rate does not exceed the target value A, step SB3 is executed and a drive signal SDa that opens the flow rate control valve 30a by a certain opening degree is output, and the actual gas flow rate is increased so that it approaches the target value A. , if the actual gas flow rate is greater than the target value A, step SB4 is executed and a drive signal SDa is output to close the flow rate control valve 30a by a certain opening degree, so that the actual gas flow rate is decreased so as to approach the target value A. Then, such a control subroutine is repeatedly executed, and the gas flow rate of the blowing pipe 20a is controlled to match the target value A.

Therefore, according to this embodiment, the gas flow rate of each blowing pipe 20a to 20e is controlled to be constant according to the common target value A, and the target value A is such that the total gas flow rate X is the constant value M. Therefore, the same effects as those of the previous embodiment can be obtained, and there is an advantage that the CPU 44, RAM 46, and ROM 48 can be shared with a control computer for other purposes.

Although the embodiment of the present invention has been described above based on the drawings, the present invention can also be applied to other aspects.

For example, the total gas flow rate blown into the suction pipe 16 may be detected by a flow sensor provided in the pipe supplying the inert gas to the header 24.
In this case, there is an advantage that there is no need for means for performing addition calculations on the pipe flow rate signals SFa to SFe.

In addition, the number of blowing pipes 20a to 20e, flow rate sensors 28a to 28e, and flow rate control valve 30a
Various types can be selected from 30e to 30e.

Further, flow rate controllers 30a to 30e, step
The operating amounts of the flow control valves 30a to 30e determined in SB3 and SB4 are proportional, integrated, or differentiated amounts as necessary with respect to the deviation between the target value A and the actual gas flow rate of each blowing pipe 20a to 20e. Of course, it can be used.

The above-mentioned embodiment is merely one embodiment of the present invention, and various modifications may be made to the present invention without departing from the spirit thereof.

As described in detail above, according to the blown gas control device of the present invention, the total gas flow rate blown into the suction pipe is determined to be a predetermined desirable constant value, and the gas flow rate of each blown pipe line is is controlled so that it matches the common target value, so even if a part of the suction pipe becomes clogged, the flow rate reduction due to the blockage will be compensated for by the amount of gas in other normal suction pipes. The flow rate is increased to control the total gas flow rate constant. Therefore, a constant flow rate of molten steel in the suction pipe can be obtained regardless of the clogging of a part of the blowing pipe, so that a constant degassing effect can always be obtained and the product quality can be maintained at a high level. At the same time, regardless of the clogging of a part of the blowing line, the gas flow rate of other normal lines is equally controlled according to the common target value, so that the concentration of the blowing gas in a specific line is reduced. An increase in the height of molten steel splash in the vacuum chamber is prevented, and in particular, melting and damage of the refractory material at the top of the vacuum chamber is prevented.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the configuration of a circulation type vacuum degassing apparatus to which the present invention is applied. FIG. 2 is an explanatory diagram showing the configuration of an embodiment of the present invention. FIG. 3 is a diagram corresponding to FIG. 2 showing another embodiment of the present invention. 4 to 6 are flowcharts showing the programs in the embodiment of FIG. 3, respectively. 10... Vacuum tank, 14... Molten steel, 16... Suction pipe, 1
8...Discharge pipe, 20a-20e...Blowing pipe, 22a
~22e...Inlet, {28...Flow rate sensor, 36...
Adder} (flow rate detection device), {32a to 32e...Flow rate controller, 34...Main controller, 44...CPU, 46
...RAM, 48...ROM} (control device).

Claims (1)

[Scope of Claims] 1. A vacuum tank, a suction pipe that communicates with the vacuum tank and is immersed in molten steel in a molten steel container, and a discharge pipe that is connected to a plurality of inlets provided in the suction pipe, respectively. A blowing gas control device for a circulation type vacuum degassing device, which is equipped with a plurality of blowing pipes, and circulates molten steel into the vacuum chamber by blowing inert gas from the blowing pipes into the suction pipe. The flow rate of each gas flowing through the blowing pipes and the total gas flow rate of the blowing pipes are detected, and a pipe flow rate signal representing the pipe flow rate and a total flow rate representing the total gas flow rate are detected. a flow rate detection device that outputs a signal; a flow rate control valve that is provided in each of the blowing pipes and adjusts the flow rate of the gas flowing through the blowing pipe; and the flow rate of each pipe represented by the pipe flow rate signal; a first control means for driving the flow rate control valve so that the difference between the two and a common target value becomes zero, and causing the gas flow rate of each of the blowing pipes to match the target value; and the total flow rate. The common target value is determined by comparing the total gas flow rate represented by the signal with a predetermined constant value so that the difference between them becomes zero, and the total gas amount sucked into the suction pipe is determined. 1. A blowing gas control device for a recirculation type vacuum degassing device, comprising: a control device having a second control means for making the gas match a constant value;