Note: Descriptions are shown in the official language in which they were submitted.
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.
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1073540
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
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1073540
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.
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1073540
: 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-
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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 -~
.:
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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
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1073540
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
N 2
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
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~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.
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