CA1073540A - Teeming rate control in metal ingot making - Google Patents
Teeming rate control in metal ingot makingInfo
- Publication number
- CA1073540A CA1073540A CA272,712A CA272712A CA1073540A CA 1073540 A CA1073540 A CA 1073540A CA 272712 A CA272712 A CA 272712A CA 1073540 A CA1073540 A CA 1073540A
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- control signal
- rate
- teeming
- signal
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Abstract
ABSTRACT OF THE DISCLOSURE
Steel ingot making apparatus including a ladle and a mould. The teeming rate is programmed and used to control the gate valve in the ladle so that the teeming rate is controlled as desired. The actual teeming rate is intermittently measured and used to modify the programmed control. Specific means is used in calculating the teeming rate from the change in weight of the ladle so that the effect of possible errors in the weight measuring scale can be eliminated or substantially decreased.
Steel ingot making apparatus including a ladle and a mould. The teeming rate is programmed and used to control the gate valve in the ladle so that the teeming rate is controlled as desired. The actual teeming rate is intermittently measured and used to modify the programmed control. Specific means is used in calculating the teeming rate from the change in weight of the ladle so that the effect of possible errors in the weight measuring scale can be eliminated or substantially decreased.
Description
107354~ ~
The present invention relates in general to ingot making processes in steel manufacturing. More particularly, the present invention pertains to a control of teeming rate in such ingot making processes.
In typical steel manufacturing processes, -the molten steel is first received in a ladle and then poured into moulds to form ingots. The ingots thus formed are subjected to further working operations such as rolling operations or forging opera-tions. It has widely been recognized that the quality of the final steel products is in large part dependent on the quality of the ingots and that the quality of the ingots are substantially affected by the process condition in pouring operation of the molten metal, particularly by the rate of pouring into the mould.
Conventionally, the teeming rate has been adjusted by the use of pouring nozzles in various diameters. However, it has been experienced that the conventional method has not been effective to provide stable and desired control of the teeming rate. For example, it has been difficult to maintain a constant rate of rise of the surface of the molten metal w'nich is believed to have influence on the skin thickness of the ingot particularly in the manufacture of rimmed steel. Further, it has also been difficult to prevent or at least decrease surface defects due to the splash of molten metal at the initial stage of the pouring process.
In order to eliminate the above problems, it has been proposed by Japanese patent application Sho 49-35799, filed on March 30, 1974 and laid open to public inspection on October 9, 1975 under the disclosure number Sho 50-128631, to detect or measure the teeming rate in terms of the change in weight of the pouring ladle and control the opening degree of the pouring nozzle in accordance with the results of the measurement.
-- 1 -- ~k .. . . .
The process as proposed in the above Japanese patent application is considered as being able to provide a programmed control of the teeming rate of the molten metal. However, the most serious problem in the above process is that it cannot provide the progra~med control with satisfactorily small errors.
For example, when the above-mentioned process is put into practice, a so-called "crane scale" is usually employed for measuring the change of the weight of the pouring ladle. The problem herein is that such a crane scale usually has measuring errors which amount to 10 percent of the maximum value of the scale. Therefore, in order to obtain the change in weight of the pouring ladle with an adequate accuracy, it becomes necessary to increase the time interval between two succeeding measuring points.
The present invention has therefore an object to provide an apparatus for controlling under program the rate of pouring or teeming molten metal in a steel manufacturing process.
Another object of the present invention is to provide an apparatus for making metal ingots, in which the rate of teem-
The present invention relates in general to ingot making processes in steel manufacturing. More particularly, the present invention pertains to a control of teeming rate in such ingot making processes.
In typical steel manufacturing processes, -the molten steel is first received in a ladle and then poured into moulds to form ingots. The ingots thus formed are subjected to further working operations such as rolling operations or forging opera-tions. It has widely been recognized that the quality of the final steel products is in large part dependent on the quality of the ingots and that the quality of the ingots are substantially affected by the process condition in pouring operation of the molten metal, particularly by the rate of pouring into the mould.
Conventionally, the teeming rate has been adjusted by the use of pouring nozzles in various diameters. However, it has been experienced that the conventional method has not been effective to provide stable and desired control of the teeming rate. For example, it has been difficult to maintain a constant rate of rise of the surface of the molten metal w'nich is believed to have influence on the skin thickness of the ingot particularly in the manufacture of rimmed steel. Further, it has also been difficult to prevent or at least decrease surface defects due to the splash of molten metal at the initial stage of the pouring process.
In order to eliminate the above problems, it has been proposed by Japanese patent application Sho 49-35799, filed on March 30, 1974 and laid open to public inspection on October 9, 1975 under the disclosure number Sho 50-128631, to detect or measure the teeming rate in terms of the change in weight of the pouring ladle and control the opening degree of the pouring nozzle in accordance with the results of the measurement.
-- 1 -- ~k .. . . .
The process as proposed in the above Japanese patent application is considered as being able to provide a programmed control of the teeming rate of the molten metal. However, the most serious problem in the above process is that it cannot provide the progra~med control with satisfactorily small errors.
For example, when the above-mentioned process is put into practice, a so-called "crane scale" is usually employed for measuring the change of the weight of the pouring ladle. The problem herein is that such a crane scale usually has measuring errors which amount to 10 percent of the maximum value of the scale. Therefore, in order to obtain the change in weight of the pouring ladle with an adequate accuracy, it becomes necessary to increase the time interval between two succeeding measuring points.
The present invention has therefore an object to provide an apparatus for controlling under program the rate of pouring or teeming molten metal in a steel manufacturing process.
Another object of the present invention is to provide an apparatus for making metal ingots, in which the rate of teem-
2~ ing can be accurately controlled under program.
A further object of the present invention is to providemeans for modifying the teeming rate during the teeming process.
According to the present invention, the above and other objects can be accomplished by an apparatus for making metal ingots, which comprises passage means with gate valve means for allowing molten metal to pass into a mould, teeming rate -programming means for providing a primary control signal, feed forward circuit means connected with said programming means to receive the primary rate control signal thererom and produce a secondary rate control signal, actuator means for controlling the gate valve means in accordance with the secondary rate control signal, means for measuring the teeming rate and producing a teeming rate signal, modifying signal circuit means for comparing the primary rate control signal and the teeming rate signal and producing a modifying signal when there is any difference between the two signals. According to the feature of the present invention, the programmed rate control signal is sent through the feed forward circuit means to the actuator means so that the teeming rate control can be effected with a satisfactory accuracy. Since the rate of flow of the molten metal is affected not only by the opening degree of the gate valve means but also by the wear and clogging of the passage means and head pressure of molten metal in the ladle, the relationship between the valve opening degree and the actual teeming rate must always be taken into account. Therefore, according to the present invention, the actual measurement of the teeming rate is compared with the programmed rate signal, that is, the primary rate control signal to modify the secondary rate control signal.
According to a further feature of the present invention, a particular method is employed in calculating the actual teeming rate. More specificallyl the teemed weight is measured at predetermined intervals, and the results of the measurements are all taken into account so that the average slope of the change in the teemed weight can be calculated. For the purpose, when the measurement is made by means of a crane scale which measures the weight of the ladle, the calculation is performed in accordance with the following formula:
~ (i 2 )W;
bn = ~ T n(n+l)(n+2) (1) where: bn is the calculated teeming rate;
Wj is an indication of the crane scale:
T is the interval of each two measurements;
n is the number of measurements substracted by one.
: According to a further feature of the present inven-tion, means are provided for calculating the relationship between the valve opening degree and the rate of teeming and modifying the second rate control signal before it is applied to the actuator means. For the purpose, an assumption may be made that there is a linear relationship between the valve opening degree and the teeming rate and the slope and con-stant in the linear equation is determined through calcula-tion.
In accordance with a further aspect of the present invention, there is provided apparatus for producing metal ingots including passage means with gate valve means for allowing molten metal to pa~s into a mould, teeming rate programming means for providing a primary control signal, feed forward circuit means connected with said programming means to receive the primary rate control signal thereform and produce a secondary rate control signal, actuator means operatively associated with said gate valve means for con-tr~lling the gate valve means in accordance with the second-ary rate control signal, means for measuring the teeming rate and producing a teeming rate signal, said teeming rate mea-~uring means including means for measuring moulded weight of metal and means for calculating the teeming rate in accordance with change~ in the moulded weight, modifying signal circuit mean for comparing the primary rate control ~ignal and the teeming rate signal and producing a modifying signal when there is any difference between the two signal~, said modify-ing ~ignal being used to modify the secondary rate control signal, characterized in that said weight measuring means is a 3Q crane scale for measuring weight of ladle means and that said teeming rate calculating means includes means for making calculations in accordance with an equation L~ .
I ~ ~ -4-~073540 12 ~ )Wj b = _ _ n(n+l)(n+2) where: bn is the calculated teeming rate, Wj is an indication o~ the crane scale:
T is the interval between each two measurements, n is one less than number of measurements.
In accordance with a further aspect of the present invention, there is provided apparatus for producing metal ingots including passage means with gate valve means for allowing molten metal to pass into a mould, teeming rate pro-gramming means for providing a primary control signal, feed forward circuit means connected with said programming means :
to receive the primary rate control signal therefrom and pro-duce a secondary rate control signal, actuator means operative- ~-ly associated with said gate valve means for controlling the gate valve means in accordance with the secondary rate control signal, means for mea~uring the teeming rate and producing a teeming rate signal, said teeming rate measuring means includ-ing means for measuring moulded weight of metal and means for calculating the teeming rate in accordance with changes in the moulded weight, modifying signal circuit means for comparing the primary rate control signal and the teeming rate signal and producing a modifying signal when there is any difference between the two signals, said modifying signal being used to modify the secondary rate control si~nal, characterized in that valve control signal generating means is provided between the feed forward circuit means and the actuator means so as to receive the secondary rate control signal and produce on the basis of the following equation a valve control signal which is applied to the actuator means to control the gate valve means:
.
! A ~ -4a-: ' .
~ `` 1073540 bn = PXn + q - wherein: bn represents the primary teeming rate control signal, Xn is the valve control signal:
p and q are constants.
In order that the present invention is more clearly understood, it will further be described by way of embodiments taking reference to the accompanying drawings, in which:
Figure 1 is a diagrammatical view of a ladle and a mould provided with teeming rate control means in accordance with one embodiment of the present invention:
Figure 2 is a block diagram showing one example of the control means in accordance with the present invention:
Figure 3 is a block diagram showing another example of the present invention:
Figure 4 is a diagram showing a typical example of the programmed pattern of the teeming rate control; and Figure 5 is a diagram showing the result of rate calculation in accordance with the present invention.
Referring now to the drawing~, particularly to Figure 1, there is 3hown an ingot making device comprising a pouring ladle 1 and a mould 2 located beneath the ladle 1.
As in conventional in the art, the ladle 1 is charged with molten metal which is teemed into the mould to make an ingot.
To control the rate of pouring or teeming, the ladle 1 is provided with a gate valve 7 : ' ', ~ 4b-' ' ~4 ' 1~73540 of which opening degree is controlled by means of a servo actuator 6.
The ladle 1 is suspended by means of suspending arms 3 of an overhead crane. In the embodiment, the suspending arms 3 are provided with weight measuring means, such as a crane scale 4, for measuring the weight of the ladle 1. The crane scale 4 is connected with teeming rate control means 5. The rate con-trol means 5 receives a weight signal from the crane scale 4 and produces an output which is utilized to control the servo actuator 6.
Referring to Figure 2, the control means 5 comprises a teeming rate programmer 10 in which a teeming rate pattern is programmed in terms of millimeter per second which represents the rising rate of the surface level of molten metal in the mould. The programmer 10 is connected with unit converting means 11 which receives a programmed signal from the programmer 10 and produces a first rate control signal in terms of kilograms per second. The unit converting means 11 is connected with a feed forward means 12 which receives the first rate control signal from the unit converting means 11 and produces a second rate control signal in accordance with the first rate control signal.
The second control signal is then applied to the servo actuator 6 which determines the opening degree of the gate valve 7 in accordance with the second control signal.
The control means 5 further includes a teeming rate signal generator 13 which is connected with the crane scale 4 to receive a weight signal therefrom and produces a teeming rate signal in accordance with a change in weight of the ladle 1. The teeming rate signal generator 13 is connected through a sampling device 14 with a hold circuit 15. The sampling device 1~ is in -~
the form of a switch which is closed at periodical intervals so that the teeming rate signal is allowed to pass therethrough -~
.:
1~73540 intermittently with predetermined intervals. The hold circuit 15 maintains a previously received teeming rate signal until a next signal is received. Further, the hold circuit 15 produces an output signal which is the same as that maintained therein and applied to modifying signal generator 18.
The modifying signal generator 18 also receives the first rate control signal from the unit converting means 11 and compares the first rate control signal with the teeming rate signal from the hold circuit 15 to produce a modifying signal which corresponds to the difference between the first rate con-trol signal and the teeming rate signal. The modifying signal is applied to the feed forward means 12 to modify the second rate control signal produced therein.
The output of the hold circuit 15 is also applied to unit converting means 16 which converts the signal in kilograms per second from the holding circuit 15 to a corresponding signal in terms of millimeters per second and the latter signal is utilized to effect a proper indication at an indicator 17.
There is also provided moulding weight setting means 19 which produces a signal corresponding to a desired ingot weight for each mould 2. The output of the setting means 19 is connected with a stop circuit 20 which also receives the teeming rate signal from the teeming rate signal generator 13. The circuit 20 integrates the teeming rate signal from the device 13 to obtain the weight of the moulded metal and, as soon as the weight becomes equal to the weight as determined by the device 19, it produces a stop signal which is applied to the servo actuator 6.
Referring to Figure 4, there is shown a typical pattern of the teeming rate program for rimmed steel. According to the pattern, the gate valve 7 is at first opened to the full open position for the first or leading mould 2 as shown by A so that 1~7354() an adequate passage is established for the molten metal. After a short period, the valve is closed to a restrlcted position as shown by B. Then, after a certain time interval, the gate valve is gradually opened along the line C to the position D and main-tained at the level for a certain period to the point E.
The period B and the gradual opening of the gate valve 7 are required for preventing turbulence at the bottom part of the mould 2 and avoid surface defects (so-called "scab") which may otherwise be produced near the bottom cide of the ingot.
During the period D, the teeming rate is maintained as high as possible within a limit in which surface defects such as "hair crack" can be avoided.
At the point E, the gate valve 7 is closed by a certain amount to decrease the rate of teeming as shown by F and after a certain period, it is further closed to decrease the rate as shown by G. As soon as the weight of the moulded metal reaches a desired value, the gate valve 7 is closed to the restricted position H to complete the teeming operation for the first mould 2. This stepped closing of the gate valve from the period E to H is required to prevent turbulence at the top portion of the poured metal and avoid surface defects which may otherwise be produced on the top surface of the weight.
Thereafter, a second mould 2 is placed beneath the pouring ladle and the gate valve 7 is gradually opened along the line I to a position J to conduct a second casting operation.
In operation, the programmer 10 produces a signal which varies as shown in Figure 4 and the signal is modified by the unit converting means 11 into the first teeming rate control signal. The first teeming rate control signal is received by the feed forward means 12 to be passed therethrough and applied a9 the second rate control signal to the servo actuator 6 to determine the opening degree of the valve in accordance with the ... . .. ...
programmed pattern.
The teeming rate signal generator 13 continuously calculates the rate of teeming and the output therefrom is inter-mittently passed through the sampling device 14 at predetermined intervals, for example, at every three seconds. T'nus, the teem-ing rate signal from the holding circuit 15 is renewed at the predetermined intervals and applied to the modifying signal generator 18.
The modifying signal generator 18 compares the rate signal from the holding circuit 15 with the first rate control signal from the device-ll and, if there is any difference there-between, it produces a modifying signal preferably in accordance with the following equation:
C = k (~b = 1 ~ t~b dt) (2) o wherein C : value of the modifying signal b : the difference between the rate signal from the the holding circuit 15 and the first rate control signal kp : proportional gain Tl : integral time.
The modifying signal thus produced is applied to the feed forward means 12 to modify the second rate control signal. When the cal-culated weight of the moulded metal reaches the programmed weight which is represented by the signal from the device 19, the stop circuit 20 produces a stop signal to close the gate valve to the restricted position to decrease the teeming rate to a minimum value as shown by H in Figure 4. As soon as a subsequent mould is located beneath the pouring ladle 1, the programmer 10 sends a further signal to repeat a subsequent moulding cycle~
One of the most important features of the present ~73540 invention is in the manner o~ calculating the rate of teeming.
More specifically, the circuit 13 intermittently conducts calcu-lations at time intervals of, for example, three seconds based on the equation (1) which has previously been referred to.
Through the calculations, it is possible to eliminate or at least decrease the effect of possible errors in the crane scale as shown in Figure 5.
Figure 3 shows another embodiment of the present inven-tion in which corresponding parts are designated by the same reference numerals as in Figure 2. In the embodiment, valve control signal generating means 21 is interposed between the feed forward means 12 and the servo actuator 6. The valve control signal means 21 functions to make calculations based on a pre-determined equation xn = f (bn) which represents the relation-ship between the teeming rate bn and the valve openlng xn.
Practically, the relationship may be assumed as being represented by a linear equation n PXn + q (3) wherein p and q are constants.
In the embodiment shown in Figure 3, calculating means 22 is ~rovided in order to obtain the constants p and q. The calculating means 22 receives signals from the valve control signal generating means 21 and the teeming rate signal generating means 13 and conducts a calculation based on the equation I = ~ n(bn - PXn q) wherein ~n = ~N n, ~ being constant smaller than one. For example, ~ ma~ be 0.99. The calculating means 22 intermittently makes calculations,~for example, at the time interval of three seconds to obtain the values p and q where the value I is the smallest.
The output of the means 22 is thus considered as _ g _ ' ' - j - . . .
: , 1~73540 representing the constants p and q and the output is then inter- ~
mittently applied to thinning-out means 23 which permits the ~-signal from the calculating means 22 to pass therethrough once per several times of signal inputs. The signal passed through the thinning-out means 23 is applied to the valve control signal generating means 21 to determine the relationship between the teeming rate control signal and the valve control signal. When the output of the calculating means 22 is directly applied to the valve control signal generating means 21, there may be a possibility of overshooting or hunting. Therefore, it is prefer-able to provide the thinning-out means 23 as shown, however, in some cases, it may be omitted.
Practically, the calculation of the teeming rate in accordance with the equation (1) does not always represent the actual rate Vj but there is a time lag which is estimated as being represented by the following equation n n(n+l)(n+2) (5) Therefore, it is necessary to have the valve control signal from the means 21 correspondingly modified before the calculation is performed by the calculating means 22. Such modification is recommendably made in accordance with the equation ~, j(n+l-j)xn Xn 6 n(n+l)(n+2) (6) Thus, the calculation should be made using the value ; Xn in the place of xn in the equations (3) and (4). According to the control of the present invention, the most desirable operating condition can be attained within a few minutes after starting of teeming operation and the adjustments or modifica-~ tions performed in previous teeming operation can all be :~ - 10 -.; .
~073540 utilized in the succeeding operation.
The invention has thus been shown and described with reference to specific embodiments which are shown in the accom-panying drawings, however, it should be noted that the invention is in no way limited to the details of the illustrated arrange-ment but changes and modifications may be made without departing from the scope of the appended claims. Although the present invention has been described with reference to an ingot making process in which the molten metal is poured from a ladle into the mould, it can also be applied to a process wherein molten metal is through an opening formed in the bottom of the mould.
A further object of the present invention is to providemeans for modifying the teeming rate during the teeming process.
According to the present invention, the above and other objects can be accomplished by an apparatus for making metal ingots, which comprises passage means with gate valve means for allowing molten metal to pass into a mould, teeming rate -programming means for providing a primary control signal, feed forward circuit means connected with said programming means to receive the primary rate control signal thererom and produce a secondary rate control signal, actuator means for controlling the gate valve means in accordance with the secondary rate control signal, means for measuring the teeming rate and producing a teeming rate signal, modifying signal circuit means for comparing the primary rate control signal and the teeming rate signal and producing a modifying signal when there is any difference between the two signals. According to the feature of the present invention, the programmed rate control signal is sent through the feed forward circuit means to the actuator means so that the teeming rate control can be effected with a satisfactory accuracy. Since the rate of flow of the molten metal is affected not only by the opening degree of the gate valve means but also by the wear and clogging of the passage means and head pressure of molten metal in the ladle, the relationship between the valve opening degree and the actual teeming rate must always be taken into account. Therefore, according to the present invention, the actual measurement of the teeming rate is compared with the programmed rate signal, that is, the primary rate control signal to modify the secondary rate control signal.
According to a further feature of the present invention, a particular method is employed in calculating the actual teeming rate. More specificallyl the teemed weight is measured at predetermined intervals, and the results of the measurements are all taken into account so that the average slope of the change in the teemed weight can be calculated. For the purpose, when the measurement is made by means of a crane scale which measures the weight of the ladle, the calculation is performed in accordance with the following formula:
~ (i 2 )W;
bn = ~ T n(n+l)(n+2) (1) where: bn is the calculated teeming rate;
Wj is an indication of the crane scale:
T is the interval of each two measurements;
n is the number of measurements substracted by one.
: According to a further feature of the present inven-tion, means are provided for calculating the relationship between the valve opening degree and the rate of teeming and modifying the second rate control signal before it is applied to the actuator means. For the purpose, an assumption may be made that there is a linear relationship between the valve opening degree and the teeming rate and the slope and con-stant in the linear equation is determined through calcula-tion.
In accordance with a further aspect of the present invention, there is provided apparatus for producing metal ingots including passage means with gate valve means for allowing molten metal to pa~s into a mould, teeming rate programming means for providing a primary control signal, feed forward circuit means connected with said programming means to receive the primary rate control signal thereform and produce a secondary rate control signal, actuator means operatively associated with said gate valve means for con-tr~lling the gate valve means in accordance with the second-ary rate control signal, means for measuring the teeming rate and producing a teeming rate signal, said teeming rate mea-~uring means including means for measuring moulded weight of metal and means for calculating the teeming rate in accordance with change~ in the moulded weight, modifying signal circuit mean for comparing the primary rate control ~ignal and the teeming rate signal and producing a modifying signal when there is any difference between the two signal~, said modify-ing ~ignal being used to modify the secondary rate control signal, characterized in that said weight measuring means is a 3Q crane scale for measuring weight of ladle means and that said teeming rate calculating means includes means for making calculations in accordance with an equation L~ .
I ~ ~ -4-~073540 12 ~ )Wj b = _ _ n(n+l)(n+2) where: bn is the calculated teeming rate, Wj is an indication o~ the crane scale:
T is the interval between each two measurements, n is one less than number of measurements.
In accordance with a further aspect of the present invention, there is provided apparatus for producing metal ingots including passage means with gate valve means for allowing molten metal to pass into a mould, teeming rate pro-gramming means for providing a primary control signal, feed forward circuit means connected with said programming means :
to receive the primary rate control signal therefrom and pro-duce a secondary rate control signal, actuator means operative- ~-ly associated with said gate valve means for controlling the gate valve means in accordance with the secondary rate control signal, means for mea~uring the teeming rate and producing a teeming rate signal, said teeming rate measuring means includ-ing means for measuring moulded weight of metal and means for calculating the teeming rate in accordance with changes in the moulded weight, modifying signal circuit means for comparing the primary rate control signal and the teeming rate signal and producing a modifying signal when there is any difference between the two signals, said modifying signal being used to modify the secondary rate control si~nal, characterized in that valve control signal generating means is provided between the feed forward circuit means and the actuator means so as to receive the secondary rate control signal and produce on the basis of the following equation a valve control signal which is applied to the actuator means to control the gate valve means:
.
! A ~ -4a-: ' .
~ `` 1073540 bn = PXn + q - wherein: bn represents the primary teeming rate control signal, Xn is the valve control signal:
p and q are constants.
In order that the present invention is more clearly understood, it will further be described by way of embodiments taking reference to the accompanying drawings, in which:
Figure 1 is a diagrammatical view of a ladle and a mould provided with teeming rate control means in accordance with one embodiment of the present invention:
Figure 2 is a block diagram showing one example of the control means in accordance with the present invention:
Figure 3 is a block diagram showing another example of the present invention:
Figure 4 is a diagram showing a typical example of the programmed pattern of the teeming rate control; and Figure 5 is a diagram showing the result of rate calculation in accordance with the present invention.
Referring now to the drawing~, particularly to Figure 1, there is 3hown an ingot making device comprising a pouring ladle 1 and a mould 2 located beneath the ladle 1.
As in conventional in the art, the ladle 1 is charged with molten metal which is teemed into the mould to make an ingot.
To control the rate of pouring or teeming, the ladle 1 is provided with a gate valve 7 : ' ', ~ 4b-' ' ~4 ' 1~73540 of which opening degree is controlled by means of a servo actuator 6.
The ladle 1 is suspended by means of suspending arms 3 of an overhead crane. In the embodiment, the suspending arms 3 are provided with weight measuring means, such as a crane scale 4, for measuring the weight of the ladle 1. The crane scale 4 is connected with teeming rate control means 5. The rate con-trol means 5 receives a weight signal from the crane scale 4 and produces an output which is utilized to control the servo actuator 6.
Referring to Figure 2, the control means 5 comprises a teeming rate programmer 10 in which a teeming rate pattern is programmed in terms of millimeter per second which represents the rising rate of the surface level of molten metal in the mould. The programmer 10 is connected with unit converting means 11 which receives a programmed signal from the programmer 10 and produces a first rate control signal in terms of kilograms per second. The unit converting means 11 is connected with a feed forward means 12 which receives the first rate control signal from the unit converting means 11 and produces a second rate control signal in accordance with the first rate control signal.
The second control signal is then applied to the servo actuator 6 which determines the opening degree of the gate valve 7 in accordance with the second control signal.
The control means 5 further includes a teeming rate signal generator 13 which is connected with the crane scale 4 to receive a weight signal therefrom and produces a teeming rate signal in accordance with a change in weight of the ladle 1. The teeming rate signal generator 13 is connected through a sampling device 14 with a hold circuit 15. The sampling device 1~ is in -~
the form of a switch which is closed at periodical intervals so that the teeming rate signal is allowed to pass therethrough -~
.:
1~73540 intermittently with predetermined intervals. The hold circuit 15 maintains a previously received teeming rate signal until a next signal is received. Further, the hold circuit 15 produces an output signal which is the same as that maintained therein and applied to modifying signal generator 18.
The modifying signal generator 18 also receives the first rate control signal from the unit converting means 11 and compares the first rate control signal with the teeming rate signal from the hold circuit 15 to produce a modifying signal which corresponds to the difference between the first rate con-trol signal and the teeming rate signal. The modifying signal is applied to the feed forward means 12 to modify the second rate control signal produced therein.
The output of the hold circuit 15 is also applied to unit converting means 16 which converts the signal in kilograms per second from the holding circuit 15 to a corresponding signal in terms of millimeters per second and the latter signal is utilized to effect a proper indication at an indicator 17.
There is also provided moulding weight setting means 19 which produces a signal corresponding to a desired ingot weight for each mould 2. The output of the setting means 19 is connected with a stop circuit 20 which also receives the teeming rate signal from the teeming rate signal generator 13. The circuit 20 integrates the teeming rate signal from the device 13 to obtain the weight of the moulded metal and, as soon as the weight becomes equal to the weight as determined by the device 19, it produces a stop signal which is applied to the servo actuator 6.
Referring to Figure 4, there is shown a typical pattern of the teeming rate program for rimmed steel. According to the pattern, the gate valve 7 is at first opened to the full open position for the first or leading mould 2 as shown by A so that 1~7354() an adequate passage is established for the molten metal. After a short period, the valve is closed to a restrlcted position as shown by B. Then, after a certain time interval, the gate valve is gradually opened along the line C to the position D and main-tained at the level for a certain period to the point E.
The period B and the gradual opening of the gate valve 7 are required for preventing turbulence at the bottom part of the mould 2 and avoid surface defects (so-called "scab") which may otherwise be produced near the bottom cide of the ingot.
During the period D, the teeming rate is maintained as high as possible within a limit in which surface defects such as "hair crack" can be avoided.
At the point E, the gate valve 7 is closed by a certain amount to decrease the rate of teeming as shown by F and after a certain period, it is further closed to decrease the rate as shown by G. As soon as the weight of the moulded metal reaches a desired value, the gate valve 7 is closed to the restricted position H to complete the teeming operation for the first mould 2. This stepped closing of the gate valve from the period E to H is required to prevent turbulence at the top portion of the poured metal and avoid surface defects which may otherwise be produced on the top surface of the weight.
Thereafter, a second mould 2 is placed beneath the pouring ladle and the gate valve 7 is gradually opened along the line I to a position J to conduct a second casting operation.
In operation, the programmer 10 produces a signal which varies as shown in Figure 4 and the signal is modified by the unit converting means 11 into the first teeming rate control signal. The first teeming rate control signal is received by the feed forward means 12 to be passed therethrough and applied a9 the second rate control signal to the servo actuator 6 to determine the opening degree of the valve in accordance with the ... . .. ...
programmed pattern.
The teeming rate signal generator 13 continuously calculates the rate of teeming and the output therefrom is inter-mittently passed through the sampling device 14 at predetermined intervals, for example, at every three seconds. T'nus, the teem-ing rate signal from the holding circuit 15 is renewed at the predetermined intervals and applied to the modifying signal generator 18.
The modifying signal generator 18 compares the rate signal from the holding circuit 15 with the first rate control signal from the device-ll and, if there is any difference there-between, it produces a modifying signal preferably in accordance with the following equation:
C = k (~b = 1 ~ t~b dt) (2) o wherein C : value of the modifying signal b : the difference between the rate signal from the the holding circuit 15 and the first rate control signal kp : proportional gain Tl : integral time.
The modifying signal thus produced is applied to the feed forward means 12 to modify the second rate control signal. When the cal-culated weight of the moulded metal reaches the programmed weight which is represented by the signal from the device 19, the stop circuit 20 produces a stop signal to close the gate valve to the restricted position to decrease the teeming rate to a minimum value as shown by H in Figure 4. As soon as a subsequent mould is located beneath the pouring ladle 1, the programmer 10 sends a further signal to repeat a subsequent moulding cycle~
One of the most important features of the present ~73540 invention is in the manner o~ calculating the rate of teeming.
More specifically, the circuit 13 intermittently conducts calcu-lations at time intervals of, for example, three seconds based on the equation (1) which has previously been referred to.
Through the calculations, it is possible to eliminate or at least decrease the effect of possible errors in the crane scale as shown in Figure 5.
Figure 3 shows another embodiment of the present inven-tion in which corresponding parts are designated by the same reference numerals as in Figure 2. In the embodiment, valve control signal generating means 21 is interposed between the feed forward means 12 and the servo actuator 6. The valve control signal means 21 functions to make calculations based on a pre-determined equation xn = f (bn) which represents the relation-ship between the teeming rate bn and the valve openlng xn.
Practically, the relationship may be assumed as being represented by a linear equation n PXn + q (3) wherein p and q are constants.
In the embodiment shown in Figure 3, calculating means 22 is ~rovided in order to obtain the constants p and q. The calculating means 22 receives signals from the valve control signal generating means 21 and the teeming rate signal generating means 13 and conducts a calculation based on the equation I = ~ n(bn - PXn q) wherein ~n = ~N n, ~ being constant smaller than one. For example, ~ ma~ be 0.99. The calculating means 22 intermittently makes calculations,~for example, at the time interval of three seconds to obtain the values p and q where the value I is the smallest.
The output of the means 22 is thus considered as _ g _ ' ' - j - . . .
: , 1~73540 representing the constants p and q and the output is then inter- ~
mittently applied to thinning-out means 23 which permits the ~-signal from the calculating means 22 to pass therethrough once per several times of signal inputs. The signal passed through the thinning-out means 23 is applied to the valve control signal generating means 21 to determine the relationship between the teeming rate control signal and the valve control signal. When the output of the calculating means 22 is directly applied to the valve control signal generating means 21, there may be a possibility of overshooting or hunting. Therefore, it is prefer-able to provide the thinning-out means 23 as shown, however, in some cases, it may be omitted.
Practically, the calculation of the teeming rate in accordance with the equation (1) does not always represent the actual rate Vj but there is a time lag which is estimated as being represented by the following equation n n(n+l)(n+2) (5) Therefore, it is necessary to have the valve control signal from the means 21 correspondingly modified before the calculation is performed by the calculating means 22. Such modification is recommendably made in accordance with the equation ~, j(n+l-j)xn Xn 6 n(n+l)(n+2) (6) Thus, the calculation should be made using the value ; Xn in the place of xn in the equations (3) and (4). According to the control of the present invention, the most desirable operating condition can be attained within a few minutes after starting of teeming operation and the adjustments or modifica-~ tions performed in previous teeming operation can all be :~ - 10 -.; .
~073540 utilized in the succeeding operation.
The invention has thus been shown and described with reference to specific embodiments which are shown in the accom-panying drawings, however, it should be noted that the invention is in no way limited to the details of the illustrated arrange-ment but changes and modifications may be made without departing from the scope of the appended claims. Although the present invention has been described with reference to an ingot making process in which the molten metal is poured from a ladle into the mould, it can also be applied to a process wherein molten metal is through an opening formed in the bottom of the mould.
Claims (10)
1. Apparatus for producing metal ingots including pas-sage means with gate valve means for allowing molten metal to pass into a mould, teeming rate programming means for providing a primary control signal, feed forward circuit means connected with said programming means to receive the primary rate control signal therefrom and produce a secondary rate control signal, actuator means operatively associated with said gate valve means for controlling the gate valve means in accordance with the secondary rate control signal, means for measuring the teeming rate and producing a teeming rate signal, said teeming rate measuring means including means for measuring moulded weight of metal and means for calculating the teeming rate in accordance with changes in the moulded weight, modifying signal circuit means for com-paring the primary rate control signal and the teeming rate signal and producing a modifying signal when there is any difference between the two signals, said modifying signal be-ing used to modify the secondary rate control signal, charac-terized in that said weight measuring means is a crane scale for measuring weight of ladle means and that said teeming rate calculating means includes means for making calculations in accordance with an equation (1) where: bn is the calculated teeming rate;
Wj is an indication of the crane scale;
T is the interval between each two measurements, n is one less than number of measurements.
Wj is an indication of the crane scale;
T is the interval between each two measurements, n is one less than number of measurements.
2. Apparatus in accordance with claim 1 in which valve control signal generating means is provided between the feed forward circuit means and the actuator means so as to receive the secondary rate control signal and produce a valve control signal which is applied to the actuator means to control the gate valve means.
3. Apparatus in accordance with claim 2 in which said valve control signal generating means is means for converting the secondary rate control signal to the valve control signal in accordance with the equation bn = pxn + q wherein: bn represents the primary teeming rate control signal, xn is the valve control signal;
p and q are constants.
p and q are constants.
4. Apparatus in accordance with claim 3 in which means îs provided for receiving the valve control signal from the valve control signal generating means and teeming rate signal from the teeming rate measuring means to output constant modi-fying signals to said valve control signal generating means, said constant modifying signals being calculated on the basis of the following equation:
wherein ?n = ?N-n, ? being a constant smaller than one, the calculations being performed to obtain the values p and q where the value becomes the smallest, the constant modifying signals being applied to the valve control signal generating means to modify the constants for the calculation.
wherein ?n = ?N-n, ? being a constant smaller than one, the calculations being performed to obtain the values p and q where the value becomes the smallest, the constant modifying signals being applied to the valve control signal generating means to modify the constants for the calculation.
5. Apparatus in accordance with claim 4 in which the calculations for obtaining the constant modifying signals are performed intermittently at predetermined time intervals.
6. Apparatus in accordance with claim 5 in which thinning-out means is provided between the constant modifying signal generating means and the valve control signal generat-ing means to allow the constant modifying signals to pass therethrough once for a predetermined number of signal inputs thereinto.
7. Apparatus for producing metal ingots including passage means with gate valve means for allowing molten metal to pass into a mould, teeming rate programming means for pro-viding a primary control signal, feed forward circuit means connected with said programming means to receive the primary rate control signal therefrom and produce a secondary rate control signal, actuator means operatively associated with said gate valve means for controlling the gate valve means in accordance with the secondary rate control signal, means for measuring the teeming rate and producing a teeming rate sig-nal, said teeming rate measuring means including means for measuring moulded weight of metal and means for calculating the teeming rate in accordance with changes in the moulded weight, modifying signal circuit means for comparing the primary rate control signal and the teeming rate signal and producing a modifying signal when there is any difference between the two signals, said modifying signal being used to modify the secondary rate control signal, characterized in that valve control signal generating means is provided between the feed forward circuit means and the actuator means so as to receive the secondary rate control signal and produce on the basis of the following equation a valve control signal which is applied to the actuator means to control the gate valve means:
bn = pxn + q wherein: bn represents the primary teeming rate control signal;
xn is the valve control signal;
p and q are constants.
bn = pxn + q wherein: bn represents the primary teeming rate control signal;
xn is the valve control signal;
p and q are constants.
8. Apparatus in accordance with claim 7 in which means is provided for receiving the valve control signal from the valve control signal generating means and teeming rate signal from the teeming rate measuring means to output constant modifying signals to said valve control signal generating means, said constant modifying signals being calculated on the basis of the following equation:
wherein ?n = ?N n, ? being a constant smaller than one, the calculations being performed to obtain the values p and q where the value becomes the smallest, the constant modifying signals being applied to the valve control signal generating means to modify the constants for the calculation.
wherein ?n = ?N n, ? being a constant smaller than one, the calculations being performed to obtain the values p and q where the value becomes the smallest, the constant modifying signals being applied to the valve control signal generating means to modify the constants for the calculation.
9. Apparatus in accordance with claim 8 in which the calculations for obtaining the constant modifying signals are performed intermittently at predetermined time intervals.
10. Apparatus in accordance with claim 9 in which thin-ning-out means is provided between the constant modifying signal generating means and the valve control signal generat-ing means to allow the constant modifying signals to pass therethrough once for a predetermined number of signal inputs thereinto.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA272,712A CA1073540A (en) | 1977-02-25 | 1977-02-25 | Teeming rate control in metal ingot making |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA272,712A CA1073540A (en) | 1977-02-25 | 1977-02-25 | Teeming rate control in metal ingot making |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1073540A true CA1073540A (en) | 1980-03-11 |
Family
ID=4108024
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA272,712A Expired CA1073540A (en) | 1977-02-25 | 1977-02-25 | Teeming rate control in metal ingot making |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1073540A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112275797A (en) * | 2020-09-03 | 2021-01-29 | 太原钢铁(集团)有限公司 | Method for eliminating surface defects of super austenitic stainless steel middle plate |
-
1977
- 1977-02-25 CA CA272,712A patent/CA1073540A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112275797A (en) * | 2020-09-03 | 2021-01-29 | 太原钢铁(集团)有限公司 | Method for eliminating surface defects of super austenitic stainless steel middle plate |
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