Information
-
Patent Grant
-
6588493
-
Patent Number
6,588,493
-
Date Filed
Friday, December 21, 200122 years ago
-
Date Issued
Tuesday, July 8, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Elve; M. Alexandra
- Lin; I.-H.
Agents
-
CPC
-
US Classifications
Field of Search
US
- 164 453
- 164 454
- 164 455
- 164 480
- 164 1544
- 164 1547
- 164 1555
- 164 1556
- 164 1552
- 164 413
- 164 414
- 164 428
- 164 1501
- 164 1514
- 164 1513
- 164 1511
-
International Classifications
-
Abstract
A model-based strategy is provided for determining casting roll operating temperature in a continuous thin strip casting process. A first temperature sensor produces a first temperature signal indicative of the temperature of cooling liquid supplied to the casting rolls and a second temperature sensor produces a second temperature signal indicative of the temperature of cooling liquid temperature exiting the casting rolls. A computer determines a heat flux value as a function of the first and second temperature signals, and computes the operating temperature of the casting rolls as a function of the heat flux value, the second temperature signal and a number of constants defined by fixed-valued operating parameters of the continuous thin strip casting process. A control strategy is also provided to modify one or more operating parameters of the continuous thin strip casting process as a function of the casting roll temperature.
Description
FIELD OF THE INVENTION
The present invention relates generally to processes for continuously casting thin steel strip, and more specifically to systems for determining casting roll operating temperature and controlling one or more thin strip casting process parameters as a function thereof.
BACKGROUND OF THE INVENTION
It is known to cast metal strip by continuous casting in a twin roll caster. In such a process, molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product which is delivered downwardly from-the nip between the rolls. The molten metal may be introduced into the nip between the two rolls via a tundish and a metal delivery nozzle system located beneath the tundish so as to receive a flow of metal from the tundish and to direct it into the nip between the rolls, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip. This casting pool may be confined between side plates or dams held in engagement with end surfaces of the rolls so as to dam the two ends of the casting pool against outflow, although alternative means such as electromagnetic barriers have also been proposed for this purpose.
When casting thin steel strip in a twin roll caster of the type just described, the molten steel in the casting pool will generally be at a temperature of the order of 1500° C. and above, and very high cooling rates are achieved over the surfaces of the casting rolls. To this end, the casting rolls are typically liquid cooled uniformly adjacent to their surfaces in order to promote rapid solidification of the thin metal strip. In the twin roll casting process, care must be taken to avoid excessive casting roll surface temperatures that may cause accelerated deterioration of the casting rolls, potentially leading to catastrophic explosions caused by leakage of the cooling liquid into the casting pool. Control of the surface temperature of the casting rolls is therefore critical to this thin strip casting process.
A primary obstacle to the successful control of casting roll surface temperature has been the difficulty in accurately measuring or estimating the surface or operating temperature of the casting rolls. Typical casting roll temperatures are of the order of 360° C. and above, and it is impractical to measure this temperature using currently available temperature sensors. Known techniques for estimating casting roll temperature, on the other hand, are bulky and not easily implemented with a computerized control system to provide on-line, instantaneous casting roll temperature information.
What is needed is a casting roll operating temperature determination system that is easily implemented in software and that accurately bases the casting roll operating temperature determination on easily measured operating conditions. Such a system would allow for on-line, real-time monitoring of casting roll operating temperature, and further provide a platform to implement casting roll operating temperature-based prognostic and diagnostic capabilities.
SUMMARY OF THE INVENTION
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a method is provided comprising the steps of determining an inlet temperature (T
I
) and an outlet temperature (T
O
) of cooling liquid circulated through a cooling system of the at least one casting roll, computing a heat flux value (Q) as a function of the inlet and outlet temperatures, the heat flux value indicative of an amount of heat removed from the at least one casting roll by the cooling system, and computing the surface temperature of the at least one casting roll (T
ROLL
) as a function of the heat flux value and the outlet temperature.
In accordance with another aspect of the present invention, a system is provided comprising a first temperature sensor producing a first temperature signal (T
I
) indicative of temperature of cooling liquid entering a cooling system of the at least one casting roll, a second temperature sensor producing a second temperature signal (T
O
) indicative of temperature of cooling liquid exiting the cooling system of the at least one casting roll, and a computer computing a heat flux value (Q) as a function of said first and second temperature signals, the heat flux value indicative of an amount of heat removed from the at least one casting roll by the cooling system, and computing the surface temperature of the at least one casting roll (T
ROLL
) as a function of said second temperature signal and said heat flux value.
In accordance with a further aspect of the present invention, a method is provided comprising the steps of determining an inlet temperature (T
I
) and an outlet temperature (T
O
) of cooling liquid circulated through a cooling system of the at least one casting roll, computing a heat flux value (Q) as a function of the inlet and outlet temperatures, the heat flux value indicative of an amount of heat removed from the at least one casting roll by the cooling system, developing a correlation between the surface temperature of the at least one casting roll (T
ROLL
), the heat flux value and the outlet temperature, mapping a first threshold surface temperature to a first threshold outlet temperature using the correlation, monitoring the outlet temperature, and generating a signal if the outlet temperature exceeds the threshold outlet temperature, the signal thereby indicative of the surface temperature of the at least one casting roll exceeding the first threshold surface temperature.
In accordance with yet another aspect of the present invention, a system is provided comprising a first temperature sensor producing a first temperature signal (T
I
) indicative of temperature of cooling liquid entering a cooling system of the at least one casting roll, a second temperature sensor producing a second temperature signal (T
O
) indicative of temperature of cooling liquid exiting the cooling system of the at least one casting roll, and a computer computing a heat flux value (Q) as a function of said first and second temperature signals, the heat flux value indicative of an amount of heat removed from the at least one casting roll by the cooling system, and correlating the surface temperature of the at least one casting roll (T
ROLL
) to the heat flux value and the second temperature signal, said computer mapping a first threshold surface temperature to a first threshold outlet temperature using the correlation and generating a control signal if the second temperature signal exceeds the threshold outlet temperature, the control signal thereby indicative of the surface temperature
The present invention provides a model-based system for determining casting roll operating temperature in a thin strip casting process.
The present invention also provides a thin strip casting control system for modifying one or more operating parameters associated with the steel casting process as a function of the casting roll operating temperature.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a diagrammatic illustration of one embodiment of a continuous thin strip casting apparatus.
FIG. 2
is a diagrammatic illustration showing some of the details of the twin roll strip caster of the apparatus of FIG.
1
.
FIG. 3
is a perspective view of the twin casting rollers of
FIGS. 1 and 2
illustrating a cooling system therefor.
FIG. 4
is a cross-sectional view of the twin rollers viewed along section lines
4
—
4
of FIG.
3
.
FIG. 5
is a block diagram illustration of a general purpose computer system operable to determine the operating temperature of at least one of the twin rollers shown in
FIGS. 1-4
and to provide strip casting process control information as a function thereof.
FIGS. 6A and 6B
comprise a flowchart illustrating one embodiment of a software algorithm for determining the operating temperature of at least one of the twin rollers shown in
FIGS. 1-4
and for providing strip casting process control information as a function thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to a number of preferred embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated embodiments, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
The present invention is based on producing steel strip in a continuous strip caster. It is based on extensive research and development work in the field of casting thin strip in a continuous strip caster in the form of a twin roll caster. In general terms, casting steel strip continuously in a twin roll caster involves introducing molten material between a pair of contra-rotated horizontal casting rolls which are internally liquid cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip delivered downwardly from the nip between the rolls, the term “nip” being used to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel from which it flows through a metal delivery nozzle located above the nip so as to direct it into the nip between the rolls, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip and extending along the length of the nip. This casting pool is usually confined between side plates or dams held in engagement adjacent the ends of the rolls so as to dam the two ends of the casting pool against outflow, although alternative means such as electromagnetic barriers have also been proposed. The casting of thin strip in twin roll casters of this kind is, for example, described in U.S. Pat. Nos. 5,184,668, 5,277,243 and 5,934,359, all of which are expressly incorporated herein by reference. Additional details relating to continuous thin strip casting of this type are described in co-pending U.S. patent application Ser. Nos. 09/967,163, 09/968,424, 09/966,184, 09/967,105, and 09/967,166, having Attorney Docket Nos. 29685-69008, 29685-69009, 29685-69010, 29685-69011 and 29685-68977 respectively, all of which are assigned to the assignee of the present invention and the disclosures of which are each expressly incorporated herein by reference.
Referring to
FIG. 1
, a continuous thin strip casting apparatus/process
50
is illustrated as successive parts of a production line whereby steel strip can be produced in accordance with the present invention.
FIGS. 1 and 2
illustrate a twin roll caster denoted generally as
54
which produces a cast strip
56
that passes in a transit path
52
across a guide table
58
to a pinch roll stand
60
comprising pinch rolls
60
A. Immediately after exiting the pinch roll stand
60
, the strip passes into a hot rolling mill
62
comprising a pair of reduction rolls
62
A and backing rolls
62
B in which it is hot rolled to reduce its thickness. The rolled strip passes onto a run-out table
64
on which it may be force cooled by water jets
66
and through a pinch roll stand
70
comprising a pair of pinch rolls
70
A and
70
B, and thence to a coiler
68
.
Referring now to
FIG. 2
, twin roll caster
54
comprises a main machine frame
72
which supports a pair of parallel casting rolls
74
and
74
′ having a casting surfaces
74
A and
74
B respectively. Molten material, e.g., molten metal, is supplied during a casting operation from a ladle (not shown) to a tundish
80
, and from the tundish
80
through a refractory shroud
82
to a distributor
84
via control of a tundish valve
81
. The molten metal is then passed through a metal delivery nozzle
86
into the nip
88
between the casting rolls
74
and
74
′. Molten material thus delivered to the nip
88
forms a pool
92
above the nip
88
and this pool
92
is confined adjacent the ends of the rolls by a pair of side closure dams or plates
90
which are applied by a pair of thrusters (not shown) comprising hydraulic cylinder units connected to the side plate holders. The upper surface of pool
92
(generally referred to as the “meniscus” level) may rise above the lower end of the delivery nozzle
86
so that the lower end of the delivery nozzle
86
is immersed within this pool
92
. The twin roll caster
54
may be of the kind which is illustrated and described in some detail in U.S. Pat. Nos. 5,184,668 and 5,277,243 or U.S. Pat. No. 5,488,988, the disclosures of which are each expressly incorporated herein by reference.
The casting rolls
74
and
74
′ are controllably cooled so that shells solidify on the moving roll surfaces and are brought together at the nip
88
between them to produce the solidified strip
56
which is delivered downwardly from the nip
88
between the rolls
74
and
74
′. Although the present invention contemplates controllably cooling the casting rolls
74
and
74
′ in accordance with any known technique therefore, casting rolls
74
and
74
′ are, in one illustrative embodiment, cooled by way of a cooling system configured to direct cooling liquid therethrough as illustrated in
FIGS. 3 and 4
.
Referring to
FIGS. 3 and 4
, a source of cooling liquid
110
is fluidly coupled to liquid inlet ends of rolls
74
and
74
′ via inlet conduit
112
, and liquid outlet ends of rolls
74
and
74
′ are fluidly-coupled to an outlet conduit
114
. Each of rolls
74
and
74
′ define a number of liquid passageways
116
therethrough, wherein liquid passageways
116
are in fluid communication at one end of rolls
74
and
74
′ with inlet conduit
112
, and at an opposite end of rolls
74
and
74
′ with outlet conduit
116
. In one embodiment, liquid passageways
116
are arranged in circular fashion generally adjacent to surfaces
74
A and
74
B of rolls
74
and
74
′ respectively as illustrated in
FIG. 4
, although the present invention contemplates other configurations of liquid passageways
116
.
In any case, liquid from the source of cooling liquid
110
is directed through conduit
112
, through the liquid passageways
116
of each casting roll
74
and
74
′, and from rolls
74
and
74
′ through conduit
114
. In one embodiment, the source of cooling liquid
110
is a cooling unit configured to supply chilled water. In this embodiment, outlet conduit
114
may be fluidly coupled at its free end to source
110
for re-cooling of the water passing through rolls
74
and
74
′. Alternatively, the source of cooling liquid
110
may be a conventional well or municipal water utility station operable to supply pressurized water in a known manner. In this embodiment, outlet conduit
114
may be re-cycled or otherwise directed away from apparatus/process
50
in the form of waste water. Alternatively still, the cooling liquid supplied by source
110
may be a conventional coolant liquid of known chemical composition such as that typically used in cooling internal combustion engines, or other known coolant liquid. In this case, conduit
114
is fluidly coupled to source
110
for re-cycling and re-cooling of the coolant liquid. In any case, the flow rate of liquid through rolls
74
and
74
′ is controlled via conventional means.
Regardless of the type of cooling liquid used or the structural arrangement of cooling liquid source
110
, inlet conduit
112
includes a first temperature sensor
118
of known construction in fluid communication therewith and electrically connected to a signal path
120
. A second temperature sensor
122
of known construction is disposed in fluid communication with outlet conduit
114
and is electrically connected to a signal path
124
. The temperature sensors
118
and
122
may each be positioned at any suitable location along conduits
112
and
114
respectively, wherein sensor
118
is operable to produce a first temperature signal indicative of the temperature of cooling liquid flowing from inlet conduit
112
into the liquid inlets of either, or both, of casting rolls
74
and
74
′, and sensor
122
is operable to produce a second temperature signal indicative of the temperature of cooling liquid flowing out of the liquid outlets of either, or both of, rolls
74
and
74
′ and through outlet conduit
114
.
A cooling liquid flow rate mechanism
115
is disposed in-line with the flow of cooling liquid supplied by source
110
and is electrically connected to signal path
117
. In one embodiment, mechanism
115
is a cooling liquid flow rate control mechanism of known construction and associated with the cooling liquid source
110
as illustrated in
FIG. 3
, wherein mechanism
115
may be controllably adjusted such that cooling liquid from source
110
is supplied to conduit
112
at a desired flow rate as is known in the art. In this embodiment, mechanism
115
also includes a conventional flow rate sensor that is operable to produce a flow rate signal on signal path
117
indicative of the flow rate of cooling fluid supplied from source
110
to conduit
112
. In an alternative embodiment, mechanism
115
does not include a flow control component, and the flow rate of cooling liquid supplied by source
110
may accordingly fluctuate. In this embodiment, mechanism
115
is a conventional fluid flow sensor that may be disposed at any suitable location in fluid communication with the cooling liquid flowing from source
110
, through conduit
112
, through either of the casting rolls
74
or
74
′, and/or through conduit
114
. The fluid flow rate sensor in either embodiment is operable to produce a flow rate signal on signal path
117
indicative of the flow rate of cooling fluid supplied from source
110
to conduit
112
. In one embodiment, the fluid flow rate sensor may include an orifice plate having one pressure sensor disposed in fluid communication with liquid on one side of the plate and another pressure sensor in fluid communication with liquid on the other side of the plate, wherein the rate of fluid flow through the orifice plate is a well known function of the difference between the pressure signals produced by the two pressure sensors and the cross-sectional area of the flow orifice defined through the plate. It is to be understood, however, that the present invention contemplates alternatively utilizing other known fluid flow rate sensors or sensing systems, and such other sensors or sensing systems are intended to fall within the scope of the present invention. Thus, while flow rate mechanism
115
may or may not include a control mechanism for regulating the flow rate of cooling fluid supplied by source
110
, it does in any case include a fluid flow rate sensor for monitoring the flow rate of cooling liquid flowing through the casting roll cooling system.
Referring now to
FIG. 5
, one illustrative embodiment of a system
150
for determining generally the operating temperature of either or both of casting rolls
74
and
74
′, and more specifically for determining the temperature of either or both roll surfaces
74
A and
74
B, in accordance with the present invention, is shown. Central to system
150
is a general-purpose computer
152
that may be a conventional desktop personal computer (PC), laptop or notebook computer, or other known general purpose computer configured to operate in a manner to be described subsequently. Computer
152
has at least three analog-to-digital (A/D) inputs, one of which is connected to signal path
120
, one of which is connected to signal path
117
, and the other of which is connected to signal path
124
. Computer
152
is thus configured to receive an analog flow rate signal produced by flow rate mechanism
115
as well as two analog temperature signals produced by temperature sensors
118
and
122
, although the present invention contemplates that temperature sensors
115
,
118
and
122
may alternatively be configured to produce digital signals in which case the inputs of computer
152
connected to signal paths
117
,
120
and
124
may be digital inputs.
System
150
further includes a conventional memory
154
for storing information and executable software algorithms therein as is known in the art. A keyboard
156
is electrically connected to computer
152
, and may be used to enter certain information relating to the operation of apparatus/process
50
into memory
154
as will be described in greater detail hereinafter. Computer
152
is also electrically connected to a conventional monitor
158
, wherein computer
152
is configured to display a computed temperature of either or both of the casting rolls
74
and
74
′. Monitor
158
may further be configured with touch-sensitive switches as an alternative means for entering into memory
154
information relating to the operation of apparatus/process
50
. An audible or other alarm
160
is also included, and is electrically connected to computer
152
, wherein alarm
160
may be activated under the direction of computer
152
in a known manner.
In one embodiment, as will be described in greater detail hereinafter, computer
152
may be configured to display information relating to the control of apparatus/process
50
based on the computed surface temperature of either, or both of, casting rolls
74
and
74
′. In this embodiment, an operator of apparatus/process
50
is required to monitor the displayed information and physically take whatever action is required by the displayed information to accordingly control apparatus/process
50
as a function of casting roll surface temperature. In an alternative embodiment, computer
152
is electrically connected to the continuous strip caster apparatus/process
50
via a number, N, of signal-paths, as shown by dashed-line connection in
FIG. 5
, wherein N may be any positive integer. In this embodiment, computer
152
is operable to automatically control one or more operating parameters associated with apparatus/process
50
in accordance with known control techniques, and computer
152
may be configured in this embodiment to automatically modify one or more of these operating parameters based on the computed casting roll surface temperature to accordingly control apparatus/process
50
as a function of the casting roll surface temperature as will be described in greater detail hereinafter. In either case, computer
152
is further operable to activate alarm
160
whenever the casting roll surface temperature exceeds a temperature threshold.
Referring now to
FIGS. 6A and 6B
, a flowchart is shown illustrating one preferred embodiment of a software algorithm
200
for determining the surface temperature of either or both of the casting rolls
74
and
74
′, and for providing information relating to the operation of apparatus/process
50
as a function of roll surface temperature, in accordance with the present invention. Algorithm
200
is stored in memory
154
and is executable by computer
152
in a known manner. Algorithm
200
begins at step
202
, and at step
204
computer
152
is operable to receive a number of fixed operating parameters (FOP) corresponding to fixed physical parameters associated with apparatus/process
50
in general and with the structure and operation of the casting rolls
74
,
74
′ and corresponding structure in particular. In one embodiment, an operator of apparatus/process
50
executes step
204
by entering such fixed operating parameter (FOP) information into memory
154
via keyboard
156
, touch-screen monitor
158
and/or any other known data entry mechanism. Alternatively, such information may already reside within memory
158
, and in this case step
204
may be omitted. In any case, fixed operating parameters that have been determined to be useful in determining the surface temperature of either or both of casting rolls
74
and
74
′, in accordance with the present invention, include, but are not necessarily limited to, the diameter, D, of the casting rolls
74
and
74
′ (typically in units of meters), the length, L, of the casting rolls
74
and
74
′ (typically in units of meters), the specific heat, SH, of the cooling liquid (typically in units of J/kg° C.), the density, DN, of the cooling liquid (typically in units of kg/m
3
) and a variable parameter, S, relating changes in roll temperature to changes in roll diameter (typically in units of ° C./m). The diameter, D, of the rolls
74
and
74
′ are, over time, subject to change due to wear, machining, and the like, and the parameter S is therefore included to account for changes in heat transfer of the rolls
74
and
74
′ with corresponding changes in roll diameter. Generally, D and L may be easily measured, SH and DN may be found in published tables and/or be provided by a supplier of the cooling liquid, and S may generally be measurable and/or be provided by a manufacturer of casting rolls. In any case, the foregoing operating parameters generally represent fixed-valued parameters that need only be measured or otherwise ascertained once, or in the case of roll diameter, D, whenever a significant change in roll diameter has occurred, and then entered into memory
156
at step
204
of algorithm
200
.
Algorithm
200
advances from step
204
to step
206
where computer
152
is operable to generate a base equation for computing caster roll surface temperature as a function of the physical and fixed operating parameter values FOP, as well as the temperature of coolant liquid entering rolls
74
and/or
74
′ and the temperature of coolant liquid exiting rolls
74
and/or
74
′. In accordance with the present invention, such a base equation for the operating surface temperature, Top, of the casting rolls
74
and/or
74
′ has been developed for one embodiment of the thin strip casting apparatus/process
50
, and is generally of the form:
T
OP
=1197
*Q/L
+27.3 +(
T
O
−35)
+S*
(
D
−0.5) (1),
wherein Q is the total heat removed from the roll surfaces by the cooling liquid (in units of Mwatts), and wherein the constants 1197, 27.3 and 35 reflect one specific embodiment of the thin strip casting apparatus/process
50
. Those skilled in the art will recognize that such constants may vary depending upon the particular thin strip casting a process in which the roll surface temperature determination system of the present invention is implemented, and that such constants will generally be readily ascertainable without undue experimentation. In any case, algorithm execution advances from step
206
to step
208
where the computer
152
is operable to measure the cooling liquid inlet temperature, T
I
, the coolant liquid outlet temperature, T
O
, (both
20
typically in units of ° C. ) and the flow rate of cooling liquid, FR, supplied by liquid source
110
(typically in units of m
3
/hr). In the embodiment described hereinabove with respect to
FIGS. 1-5
, computer
152
is operable to execute step
208
by reading the first and second temperature signals on signal paths
120
and
124
respectively, and by reading the cooling liquid flow rate signal on signal path
117
. It will be understood, however, that the present invention contemplates alternatively determining the temperature of cooling liquid entering rolls
74
and
74
′, the temperature of cooling liquid exiting rolls
74
and
74
′, and/or the flow rate of cooling fluid flowing through the caster roll cooling system via any other known mechanism or technique therefore. In any case, algorithm execution advances from step
208
to step
210
where computer
152
is operable to compute the total heat removed, Q, from the roll surfaces by the cooling liquid passing therethrough, hereinafter referred to heat flux or heat transfer, as a function of the flow rate of cooling fluid, FR, and a difference between T
I
and T
O
. In one embodiment, computer
152
is operable at step
210
to compute Q according to the equation:
Q=FR*DN*SH*
(
T
O
−T
I
) (2),
where DN and SH are constant terms defined hereinabove. However, those skilled in the art will recognize that computer
152
may alternatively be configured to determine Q in accordance with one or more predefined tables, charts and/or graphs relating appropriate values of Q to cooling fluid flow rate values, FR, and to temperature differential values T
O
−T
I
.
In any case, algorithm execution advances from step
210
to step
212
where computer
152
is operable to update three constants A, B and C used to define an iterative equation for computing the casting roll surface temperature, T
ROLL
that is based on equations (1) and (2) above. One embodiment of such an equation takes the form:
T
ROLL
=A*Q+B*T
0
+C
(3),
where Q and T
O
have been previously defined, and the constants A, B and C define the updatable constants. Initially, constants A, B and C are defined via appropriate algebraic manipulation of equation (1), and with each successive pass through algorithm
200
, the constants A, B and C are updated based on previous values therefore and also on current Q and T
O
values. In one embodiment, the constants A, B and C are updated using known recursive techniques, although the present invention contemplates using other known techniques for updating these constants to updated values A
U
, B
U
and C
U
. Following step
212
, algorithm
200
advances to step
214
where computer
152
is operable to compute the casting roll surface temperature, T
ROLL
, according to equation (3) using the updated constant values A
U
, B
U
and C
U
; i.e., according to the equation:
T
ROLL
=A
U
*Q+B
U
*T
O
+C
U
(4).
Computer
152
is further operable at step
214
to display the present value of T
ROLL
on the monitor
158
of system
150
.
Following step
214
, algorithm execution advances to step
216
where computer
152
is operable to compare the casting roll surface temperature T
ROLL
computed at step
214
to a first temperature threshold T
1
. As long as T
ROLL
is less than or equal to T
1
, algorithm execution loops back to step
208
. Thus, as long as T
ROLL
stays at or below T
1
, computer
152
is operable to continually compute T
ROLL
and display current values thereof on monitor
158
.
If, at step
216
, computer
152
determines that T
ROLL
has exceeded T
1
, algorithm
200
advances to step
218
where computer
152
is operable to compare the casting roll surface temperature T
ROLL
to a second temperature threshold T
2
. If T
ROLL
has exceeded T
1
but is less than T
2
, algorithm
200
advances to step
220
where computer
152
activates alarm
160
and issues an instruction to modify one or more operating parameters associated with the thin strip casting apparatus/process
50
. In one embodiment, for example, computer
152
is operable at step
220
to display a message on monitor
158
instructing an operator of apparatus/process
50
to take appropriate steps to reduce the level of the pool
92
(
FIGS. 2 and 4
) and/or reduce the rotational speed of the casting rolls
74
and
74
′. Alternatively, in embodiments wherein computer
152
is configured to automatically control the thin strip casting apparatus/process
50
, computer
152
is operable at step
220
to control apparatus/process
50
in such a manner as to reduce the level of the pool
92
and/or reduce the rotational speed of the casting rolls
74
and
74
′. Either or both of these measures are intended cause the casting roll temperature to drop below the desired threshold temperature T
1
. In any case, algorithm
200
loops back from step
220
to step
208
to compute a new casting roll surface temperature value T
ROLL
.
If, at step
218
, computer
152
determines that T
ROLL
has exceeded T
2
, algorithm
200
advances to step
222
where computer
152
is operable to compare the casting roll surface temperature T
ROLL
to a third temperature threshold T
3
. If T
ROLL
has exceeded T
2
but is less than T
3
, algorithm
200
advances to step
224
where computer
152
is operable to activate alarm
160
and to issue an instruction to modify another one or more operating parameters associated with the thin strip casting apparatus/process
50
. In one embodiment, for example, computer
152
is operable at step
224
to display a message on monitor
158
instructing an operator of apparatus/process
50
to take appropriate steps to close the pool feed gate; i.e., by closing nozzle
86
, tundish valve
81
(see
FIG. 2
) or the like. Alternatively, in embodiments wherein computer
152
is configured to automatically control the steel strip casting apparatus/process
50
, computer
152
is operable at step
224
to control apparatus/process
50
in such a manner as to close the pool feed gate as just described. This measure is intended to interrupt the flow of molten material to the pool
92
to thereby allow the cooling liquid flowing through the casting rolls
74
and
74
′ to reduce the surface temperature thereof. In any case, algorithm
200
loops back from step
224
to step
208
to compute a new casting roll operating temperature value T
ROLL
.
If, at step
222
, computer
152
determines that T
ROLL
has exceeded T
3
, algorithm
200
advances to step
226
where computer
152
is operable in one embodiment to display a message on monitor
158
instructing an operator of apparatus/process
50
to take appropriate steps to terminate the operation of apparatus/process
50
to thereby terminate the thin strip casting operation. Alternatively, in embodiments wherein computer
152
is configured to automatically control the steel strip casting apparatus/process
50
, computer
152
is operable at step
226
to automatically terminate the operation of apparatus/process
50
. Temperature threshold T
3
is generally chosen such that a casting roll surface temperature above T
3
indicates dangerous or uncontrolled operation of apparatus/process
50
requiring immediate termination of the apparatus/process
50
to prevent damage to and/or destruction of the apparatus/process
50
.
While the invention has been illustrated and described in detail in the foregoing drawings and description, the same is to be considered as illustrative and not restrictive in character, it being understood that only preferred embodiments thereof have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. For example, steps
216
,
218
and
222
may be modified to replace the casting roll surface temperature T
ROLL
with the cooling liquid outlet temperature T
O
, such that computer
152
is accordingly operable to monitor the outlet temperature of cooling liquid exiting the casting rolls
74
and
74
′ rather than the casting roll surface temperature. In this embodiment, the surface temperature thresholds T
1
, T
2
and T
3
described hereinabove would be mapped to appropriate outlet temperature thresholds T
1
-T
3
using the correlation equation (4) above. Steps
220
,
224
and
226
would then be executed if/when the cooling liquid outlet temperature exceeds the various outlet temperature thresholds T
1
-T
3
. Such modifications to algorithm
200
are well within the knowledge of a skilled artisan, and could easily be implemented without undue experimentation.
Claims
- 1. A method of monitoring surface temperature of at least one casting roll of a thin strip casting process, the method comprising the steps of:determining an inlet temperature (TI) and an outlet temperature (TO) of cooling liquid circulated through a cooling system of the at least one casting roll; computing a heat flux value (Q) as a function of the inlet and outlet temperatures, the heat flux value indicative of an amount of heat removed from the at least one casting roll by the cooling system; developing a correlation between the surface temperature of the at least one casting roll (TROLL), the heat flux value and the outlet temperature; mapping a first threshold surface temperature to a first threshold outlet temperature using the correlation; monitoring the outlet temperature; and generating a signal if the outlet temperature exceeds the first threshold outlet temperature, the signal thereby indicative of the surface temperature of the at least one casting roll exceeding the first threshold surface temperature.
- 2. The method of claim 1 further including the step activating an alarm if the outlet temperature exceeds the first threshold outlet temperature.
- 3. The method of claim 1 further including the step of reducing one of a pool level of molten material within the thin strip casting process and a casting speed of the at least one casting roll if the outlet temperature exceeds the first threshold outlet temperature.
- 4. The method of claim 3 further including the steps of:mapping a second threshold surface temperature greater than the first threshold surface temperature to a second threshold outlet temperature greater than the first threshold outlet temperature using the correlation; and activating an alarm if the surface temperature exceeds the second threshold outlet temperature.
- 5. The method of claim 4 further including the step of discontinuing a flow of molten material within the thin strip casting process if the surface temperature exceeds the second threshold outlet temperature.
- 6. The method of claim 5 further including the steps of:mapping a third threshold surface temperature greater than the second threshold surface temperature to a third threshold outlet temperature greater than the second threshold outlet temperature using the correlation; and terminating the thin strip casting process if the surface temperature exceeds the third outlet temperature threshold.
- 7. The method of claim 1 wherein the step of computing a heat flux value (Q) includes computing the heat flux value further as a function of a number of physical properties associated with the cooling liquid.
- 8. The method of claim 1 wherein the step of computing a heat flux value includes computing the heat flux value according to the equation Q=FR*DN*SH*(TO−TI), where FR is the flow rate of the cooling liquid, DN is the density of the cooling liquid and SH is the specific heat of the cooling liquid.
- 9. The method of claim 1 wherein the step of developing a correlation includes developing a correlation according to the equation TROLL=A*Q+B*TO+C, where A, B and C are constants dependent upon operating conditions of the thin strip casting process.
- 10. The method of claim 1 further including the step of causing the generated signal to vary operating parameters of the thin strip casting process to reduce the surface temperature of the at least one casting roll.
- 11. The method of claim 1 further including the step of determining a flow rate of the liquid circulated through the cooling system;and wherein the step of computing a heat flux value includes computing the heat flux value further as a function of the flow rate of the liquid circulated through the cooling system.
- 12. The method of claim 11 further including the step of generating a signal if the surface temperature exceeds a first threshold temperature.
- 13. The method of claim 12 further including the step of activating an alarm if the surface temperature exceeds the first threshold temperature.
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