FIELD OF INVENTION:
The present invention relates to a method of optimization of the intensity of cooling for the secondary cooling of the continuously cast billets for different casting parameters like the section sizes of casting strand for different grades of steel comprising variations of steel superheat temperatures and variation in casting speed and a system to carry out such method. The present invention also makes use of Programmable Logic Controller (PLC) based automation system. The automatic secondary cooling system (ASCS) is designed and developed to precisely control the water flow at desired rate in secondary cooling zones in each strand. The optimized cooling system so configured helps improving productivity by increasing the casting speed. The present invention is also directed to improve the quality of cast billet, including casting of crack prone grade of steel and control centerline segregation through intense cooling near crater end. The intensity of cooling at various secondary cooling zone is calculated through heat transfer model, which runs in two different modes : (i) the prediction mode specifying the heat transfer co-efficient in each secondary cooling zone from the targeted strand surface temperature of that zone and (ii) the simulation mode specifying temperature profile of the strand based on known heat flux boundary. The method includes user-friendly application software using the standard PLC and Human Machine Interface (HMI) programming software of Schneider platform for the core objective of desired flow control. The integrated system is adapted to run on continuous basis, with preferred control on water flow rate at each zone within ±1% of set point generated based on the modeling.
BACKGROUND ART:
It is well known in the art of continuous casting of steel, secondary spray cooling has a considerable influence on surface and internal defects in continuously cast products. Surface and internal quality depends on the surface temperature distribution of casting strand. The variation in surface temperature of billet strand can be controlled by water flow rate in secondary cooling zones at a particular casting speed and superheat. Control of water spray needs to be optimized to avoid excessive surface temperature rebound between different zones of secondary cooling. In addition, surface temperature of strand at unbending /straightening zone should avoid low ductility zone of steel. Another important aspect of optimizing secondary cooling is that the surface temperature profile of strand should not grossly vary with casting speed and superheat and the optimization of cooling requirements shall also take care of variations with respect to section size of strands and grade chemistry.
2

The existing secondary cooling zone consists of three zones viz MS zone (Multi-stage) just below the mould, zone-I & zone IIA. The total length of secondary cooling was only upto 4 meters. The water intensity in different zones remained same even with varying casting speed, superheat and grade. This improper secondary cooling led to inconsistency in billet quality in terms of internal crack. In order to circumvent this improper secondary cooling and associated defects induced in the cast products/billet, an improved system to eliminate the limitations as mentioned above was an extremely essential requirement in continuous caster of steel plants.
There was therefore a persistent need to develop an improved system for secondary cooling wherein the cooling method shall be optimized based on a heat transfer model with respect to variable process parameters like the casting speed, superheat of steel being cast, section size of strands and grade/chemistry and incorporating controlled varying flow rate of water accordingly, to obtain superior quality cast products eliminating defects such as internal crack and the like.
OBJECTS OF THE INVENTION:
The basic object of the present invention is therefore directed to a method of secondary cooling based on heat transfer model for superior quality concast billets incorporating desired cooling intensity with respect to variable process parameters like the section size of strands, casting speed, superheat and grade of steel and a PLC based automated system with human machine interface (HMI) to impose said precise control on the water flow rate optimized with respect to said process variables, at different zones of secondary cooling.
The basic object of the present invention is therefore directed to a method of secondary cooling for superior quality Concast billets incorporating desired cooling intensity based on heat transfer model, which runs in two modes e.g. either in prediction mode to predict the required heat transfer coefficient in each secondary cooling zone from the targeted strand surface temperature of that zone or in simulation mode to determine the temperature profile of the strand based on known heat flux boundary.
3

A further object of the present invention is directed to develop a cooling system for the secondary cooling with controlled flow rate of water to increase the productivity of caster through increasing casting speed.
A still further object of the present invention is directed to optimize the cooling intensity of casting /solidifying strands in different zones of secondary cooling of the caster with flow control of cooling water such that the quality of cast billet is improved and also to facilitate casting including the crack prone grade of steel.
A still further object of the present invention is directed to optimize the cooling intensity of casting /solidifying strands in different zones of secondary cooling of the caster, to control centerline segregation through intense cooling near crater end.
A still further object of the present invention is directed to optimize the cooling intensity of casting /solidifying strands in different zones of secondary cooling of the caster, by using computer hardware and software means to accommodate input data related to different process parameters at the different zones and necessary processing means, to effect said desired rate of cooling with controlled flow rate of water.
SUMMARY OF THE INVENTION:
The basic aspect of the present invention is thus directed to a method of secondary cooling based on heat transfer model for superior quality concast billets comprising :
Calculating water intensity of secondary cooling zones using model, which runs on either temperature or heat flux boundary conditions depending on a prediction or simulation mode of computation ;
inputting in a PC based HMI the heat numbers, section size and steel grade; loading the said input into a PLC as a recipe;
executing the spray cooling automation scheme in real time mode through said PLC as soon as the cast starts and starts receiving the casting speed data;
4

generating the set point of water flow in each zone for the strand based on last tundish temperature and the casting speed of the stand.
According to a further aspect of the present invention, a method of secondary cooling based on heat transfer model wherein, in said prediction mode, the model is adapted to predict required heat transfer coefficient in each secondary cooling zone from the targeted strand surface temperature of that zone while in simulation mode the model is adapted to calculate the temperature profile of the strand based on known heat flux boundary such as hereindescribed.
A still further aspect of the present invention is directed to a method of secondary cooling based on heat transfer model wherein the quantity of water in secondary cooling zones is computed based on specific requirement of strand surface temperature profile for said (a) casting speed, (b) superheat range (<30 C, 30-50 C and >50 C): difference between metal temperature and liquidus temperature (LT), section size (100X100, 125X125,150X150mm square), steel grade wise cooling intensity selected from hard cooling, medium cooling and soft cooling.
A still further aspect of the present invention a method of secondary cooling based on heat transfer model wherein after enabling the PLC operation the following control stages are followed:
(a) updating the measured tundish temperature and if the tundish temperature is more
than the liquidus temperature calculate the superheat temperature;
(b) select the look up table for the water flow for selective superheat for selected section
size and type of cooling;
(c) read casting speed to decide set point;
(d) controlling the flow control valve for water spray.
Said method of secondary cooling based on heat transfer model wherein if the ladle change signal is not enabled the steps (a) to (d) are repeated.
According to another aspect of the present invention said method of secondary cooling based on heat transfer model wherein if the ladle change signal is enabled the new grade is confirmed within specified time by reading grade, LT and type of cooling and thereafter repeating steps (a) to (d) above.
5

Another aspect of the present invention is directed to said method of secondary cooling based on heat transfer model wherein if the new grade is not confirmed within specified time and the sequence is completed or the casting is stopped the procedure is stopped with delay.
A further aspect of the present invention is directed to said method of secondary cooling based on heat transfer model wherein if the new grade is not confirmed within specified time and the sequence is not completed or the casting is not stopped repeating the above stages again.
According to yet another aspect of the present invention is directed to a system of secondary cooling based on heat transfer model for superior quality concast billets following the aforedescribed method comprising:
means for calculating water intensity of secondary cooling using model which runs on either temperature or heat flux boundary conditions depending on a prediction or simulation mode of computation ;
means for inputting in a PC based HMI the heat numbers, section size and steel grade; means for loading the said input into a PLC as a recipe;
means for executing the spray cooling automation scheme in real time mode through said PLC as soon as the cast starts and starts receiving the casting speed data;
means for generating the set point of water flow in each zone for the strand based on last tundish temperature and the casting speed of the stand.
A further aspect of the present invention is directed to a system of secondary cooling based on heat transfer model for superior quality concast billets, comprising an auto mode control to generate set points dynamically on inputs from periodically measured tundish temperature and instantaneous values of strand speed.
6

A further aspect of the present invention is directed to said system of secondary cooling based on heat transfer model for superior quality concast billets wherein,
analog feedback signal for speed of caster for individual strands are taken into strand-wise PLCs and temperature of the tundish is fed into one of the PLCs;
means to measure the water flow and pressure in each zone for logging into the system;
means to control the flow dynamically depending upon the strand speed, tundish temperature, section size and grade of steel.
According to a further aspect of the present invention said system of secondary cooling based on heat transfer model for superior quality concast billets wherein the flow is controlled through motorized control valve activated through an actuator card interfaced with PLC output, said PLC outputs being activated after execution of control loops within the PLC based on the control algorithms guided by the application requirement.
A further aspect of the present system of secondary cooling based on heat transfer model for superior quality concast billets wherein the system comprises Proportional +Integral + Derivative (PID) control loops for various zones of each strand.
A still further aspect of the present invention directed to a system of secondary cooling based on heat transfer model for superior quality concast billets wherein for each strand of the caster, one dedicated PLC is installed and one PLC used for interfacing with existing PLCs of the caster for common functions, all said PLCs are adapted to communicate on a data bus with speed of atleast 10 MBPS and said PLC system further comprising PC based engineering cum HMI system with interface to PLC.
A still further aspect of the present invention directed to a system of secondary cooling based on heat transfer model for superior quality concast billets wherein secondary cooling sections are extended through addition of additional zones, with length of secondary cooling zones and nozzle configuration as detailed in Table 2.
7

A still further aspect of the present invention directed to a system of secondary cooling based on heat transfer model for superior quality concast billets adapted to selectively operate in anyone of manual mode, semi-auto mode auto mode.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES:
Figure 1: is the graphical representation of typical surface temperature profile for modified system as compared to the pre-modified system drawn from model analysis.
Figure 2: is the illustration of schematic diagram of automatic secondary cooling system (ASCS) according to the present invention.
Figure 3: is the Flow diagram illustrating various control aspects for the cooling intensity corresponding to variations in process parameters, according to the present invention.
Figure 4: is the illustration of Automation system configuration comprising PLC and HMI and other hardware and software components of the system and their functional relationship used in the present invention.
Figure 5: shows the typical water spraying arrangement comprising spray nozzles for the secondary cooling in continuous caster.
Figure 6: is the illustration of the valve stand comprising flow meters and control valves for PLC controlled water spraying for desired cooling intensity in secondary cooling of the caster strands.
Figure 7: is the illustration of comparative macro images of billets cross-sections produced following the present system of optimized cooling intensity in secondary cooling of caster strands wherein the internal cracks are completely eliminated, as compared to the conventional practice.
DETAILED DESCRIPTION WITH REFERENCE TO ACCOMPANYING FIGURES AND EXAMPLES: Mathematical model for Secondary Cooling:
8

The secondary cooling zone consist of three zones in continuous billet caster strands viz. MS (multi-stage) zone just below mould, zone I and zone IIA. The total length of secondary cooling stretches normally only up to 4 meters. Water distribution pattern to achieve desired cooling intensity in the secondary cooling zone based on the requirement of the specific surface temperature profile for solidifying strand, has been developed following mathematical modeling of thermal phenomenon taking place during casting. The heat transfer model helps solving three-dimensional Fourier equation of heat transfer adopting control volume approach. For arriving at such solution, appropriate initial and boundary conditions were applied for different zones of cooling. The initial conditions are the metal temperature, casting throughput and section size of the strand. Savage-Pritchard Equation of heat flux, as given below, was used as boundary condition in mould:
q= (2.68 - 0.33Vtr) x 106;
where 'q' is the heat flux and tr is residence time of liquid metal in mould.
In the secondary cooling zones, either temperature or heat flux boundary condition has been applied depending on prediction or simulation mode of computation. In radiation cooling zone where water spray is not used for cooling purpose, Stefan-Boltzmann equation of heat transfer was applied as boundary condition.
Input and output of the heat transfer model:
The model as developed for the present invention to ascertain billet surface temperature profile by controlling cooling intensity at different zones, requires input in terms of metal properties, casting conditions and parameters for solution procedure. In material properties, the thermal conductivity of solid and liquid steel as function of temperature, liquidus and solidus temperature of the grade of steel material, latent heat of steel are being considered. The casting condition has been provided through cross-section of strand, length of each cooling zone, casting speed, superheat and the targeted surface temperature at the exit of each zone. The model calculates the effective heat transfer coefficients required in each zone of the secondary cooling to achieve targeted surface temperature at the exit of the zone. The temperature profile of the entire strand and shell thickness along the strand are also computed.
9

Reference is first invited to the accompanying figure 1 wherein a typical strand surface temperature profile and solidification profile as computed from the model as described, has been illustrated. Such a temperature profile could be achieved for the model analysis of the present invention following the methodology for solution of the respective heat transfer boundary conditions of different zones, as described below.
Solution Methodology:
To find solution to the heat transfer model according to the invention, the governing partial differential equation along relevant boundary conditions has been discretised into algebraic equations using control volume method. These algebraic equations are solved through implicit scheme. The algorithm is quite accurate for heat conduction problems and intrinsically stable. Grid independency tests were also carried out to ascertain the effect of mesh density on the computational results.
The model runs in two modes: Prediction and Simulation. In the prediction mode, the model predicts required heat transfer coefficients in each secondary cooling zone from the targeted strand surface temperature of that zone. In simulation mode, it calculates the temperature profile of the strand based on known heat flux boundary. The details of the calculation procedure involved in the solution are explained in the following steps:
The first step deals with calculation of temperature profile of strand up to mould region done through simulation mode with mould heat extraction through Savage-Pritchard equation of heat flux as strand surface boundary condition. The temperature profile of the cross-section at the exit of mould is the inlet temperature profile for first secondary cooling zone.
In the second step, the model runs in prediction mode for the first secondary cooling zone. The target mid surface temperature at the exit of the zone is one of the inputs to the model; in this step. Then the target surface temperature along the length of the zone is calculated through linear interpolation. The model then determines the required heat transfer co-efficient (hz) at various cross-sections of the strand at a very small increment along the casting direction to achieve target surface temperature of the strand.
In the third step, the average heat transfer coefficient (havg) is calculated for the zone, from the different heat transfer coefficients (hz), as obtained in the previous step.
10

The fourth step deals with determining the surface temperature profile of the strand in simulation mode, where heatflux from surface is determined from havg.
In the fifth step, the interpolated surface temperature profile as obtained in the second step, is compared with calculated temperature profile obtained in the fourth step. At particular distance (in casting direction) from the start of the zone, both the surface temperature are same. The heat transfer coefficient (hz) (determined in the second step) at that particular distance is the effective heat transfer coefficient (heff) for the entire zone.
In the sixth step, temperature profile of the strand is calculated with effective heat transfer coefficient (heff) in simulation mode. At the exit of the particular zone, the calculated mid surface temperature is same as the targeted surface temperature. The temperature profile at the exit cross-section of the zone is the inlet temperature profile for the next zone.
The seventh step determines the water flow rate required for the zone, from correlation between water flux and effective heat transfer coefficient (heff) through Nozaki's equation, given by:
heff = 1570 W0.55 [1 - 0.0075Twater ]/ 4;
where W is the water flux and Twater is temperature of water.
After the temperature profile and corresponding requirements of water flow rates are determined, next task is the preparation of water table for implementation of the secondary cooling in desired controlled manner.
The quantity of water in secondary cooling zones has been computed based on specific requirement of strand surface temperature profile, through aforedescribed procedure subject to the following conditions:
Casting speed in the range of 1.0 to 4.5 m/min, depending on the section size cast;
- Superheat range(<30° C, 30-50° C and > 50° C) indicating the difference between
the actual metal temperature and liquidus temperature for the grade;
- Section sizes(100xl00, 125x125 and 150x150 mm square);
11

Steel grade wise cooling intensity, such as hard cooling, medium cooling or soft cooling;
The specific consumption of water for hard cooling was obtained as 1.2 litre per kg of cast billet; while that for the medium and soft cooling were found to be 1.1 and 0.95 litres per kg respectively. Requirement of water in each secondary cooling zone have been computed for various casting speed at particular section size, cooling intensity and a range of superheat. A water table comprising the casting speeds versus the water flow rates at different zones has been prepared. An illustrative example of water table comprising a set of data corresponding to an embodiment of the present invention having 125x125 mm square section of casting subjected to hard cooling intensity and a superheat range exceeding 50°C is provided in the following Table 1.
For each section, nine water tables were generated considering three superheat range and three cooling intensities. Thus all together twenty seven water tables were generated to achieve optimum secondary cooling for different operating conditions.
Table 1:

Casting Speed (m/min) MS zone (Ipm) Zone I (Ipm) Zone IIA (Ipm) Zone IIB (Ipm) Zone III (Ipm)
3.5 130 255 120 50 34
3.3 130 240 110 50 34
3.1 130 225 100 50 34
2.9 130 210 90 50 32
2.7 130 200 85 48 30
2.5 130 190 80 46 28
2.3 130 185 75 44 26
2.1 130 180 70 42 25
1.9 130 170 60 40 25
1.7 130 170 60 40 25
1.5 130 170 60 40 25
12

The configuration of the secondary cooling zone for each of the six strands in a continuous caster, consist of three cooling zones namely, the MS zone, Zone-I and Zone-IIA. The metallurgical length of the caster was far beyond the existing/conventional secondary cooling region. This led to reheating of the billet at the end of secondary cooling zone resulting in internal cracks in billet. In order to avoid such situation and to intensify cooling at the crater end for controlling centerline segregation, secondary cooling zone has been extended by 3.1 meters through addition of two more zones such as Zone-lib and Zone-Ill, for the method of the present invention. The length of secondary cooling zones and nozzle configuration, according to the secondary cooling system of the present invention, in different zones are summarized in following Table 2. In the present system of secondary cooling of caster, the materials of all water pipe lines have been changed from mild steel to stainless steel to avoid nozzle choking due to rusting.
Table 2:

Zone Zone length, Meter Numbers of Nozzles Nozzle type
MS 0.30 4x4 7065 L
Zone-I 1.50 9x4 5065 L
Zone-IIA 1.90 9x4 3565 L
Zone-IIB 1.90 9x4 3565 L
Zone-III 1.20 4x4 3565 L
Example of nozzle: 7065 L 70 - indicates7.01 l/min at 2.8 bar pressure; 65 - indicates spray angle 65° at 2.8 bar; L - indicates full cone nozzle.
Automatic Secondary Cooling system(ASCS):
The control system for automatic control of water flow to achieve the desired cooling of billets according to the present invention, is based on the strand speed, superheat in the tundish, section size in a strand and product grade feedback. This is realized through a programmable logic controller based automation system comprising of PLCs, instruments for measurement of flow, pressure, control valves with actuator for flow controller, PLC
13

programming unit, a Human Machine Interface (HMI) station and allied accessories such as interposing relays, power supplies, stainless steel pipe lines, valve stand etc. The broad schematic diagram of the Automatic Secondary Cooling System (ASCS) of the present invention has been illustrated in the accompanying Figure 2.
The automation system is designed to operate in three different modes having the required system flexibility to suit desired controlled secondary cooling operations for casting strands.
The Manual mode comprises open loop system wherein no control through the PLC is done and the water flow control is achieved by manually setting the flow control valves either from the PLC or at the field through hand wheel of the control valve.
The system can also be operated in Semi-auto mode, which is a stand-alone closed loop control. The set points for flow in each zone of individual strand are fed into the PLC through HMI screen and this flow is controlled based on the flow feedback values.
The Auto mode for said heat transfer model based control of the present invention is capable for fully automatic mode of operation in which the set points are dynamically selected for each cast sequence based on periodically measured tundish temperature and instantaneous values of strand speed.
The analog feedback signal for speeds of caster for individual strand is fed into PLC in each strand and the temperature of tundish is fed into one of the PLCs. To achieve desired control in secondary cooling of caster strands, apart from using input data for the strand speeds and tundish temperature, the water flow and pressure in each zone are measured and logged into the system. Then the flow is controlled dynamically depending upon the strand speed, tundish temperature, section size and grade of cast steel. Such automatic flow control is achieved through operation of motorized control valve activated by means of an actuator card interfaced with PLC output. The PLC outputs are activated after execution of the control loops within the PLC based control algorithms guided by the application requirement. The control algorithm is represented through the flow diagram in the accompanying figure 3.
The flow control is guided by a database developed such as the water table already explained, comprising information about desired cooling parameters for different grades of end product for different input tundish temperatures, instantaneous strand speed values.
14

The database is integrated with the control software for fully automatic mode of operation. In all, the control system consists of Proportional +Integral +Derivative (PID) control loops for zone-I, zone-IIA, zone-IIB and zone-Ill of each strand. For each strand of the caster, one dedicated PLC has been installed and one PLC has been used for interfacing with existing PLCs of the caster for the common functions. All PLCs are communicating on a data bus with speed of at least 10 MBPS. The PLC system also consists of two PC based engineering cum HMI system with appropriate interface to the PLC.
Before the beginning of a sequence of casting, the operator inputs the heat number, section size and the steel grade into PC based HMI. The HMI then looks up the table and assigns the corresponding Water Table. This information is downloaded by HMI to the PLC as a receipe download. The PLC uses the downloaded data in the relevant memory address and is ready to execute the spray cooling automation scheme in real time mode as soon as the cast starts and also starts receiving the casting speed data. The set point for water flow in each zone for the strand is generated based on last tundish temperature and the casting speed of the strand.
Application software was developed using the standard PLC and HMI programming software of Schneider platform for the core objective of water flow control at different zones in each of the strands. Additionally the system incorporates various features for easy to use functionality such as on-line historical trending, control summary etc. The software is so designed that all the desired set points and selection of mode of operation etc can be done through user friendly HMI screens from where the parameters are downloaded to the PLC on giving a single key command. The accompanying Figure 4 illustrates the various aspects of the Automation System Configuration by means of a representative flow diagram. The integrated system is designed to run on continuous basis and the water flow rates in each zone is controlled with an accuracy of ± 1 % of set point generated based on the heat transfer model for a billet caster.
Figure 5 is the illustration of the typical arrangement of the water spraying in a caster strand comprising stainless steel pipe lines on which selective numbers of spray nozzles with specific orientation are mounted, such that the desired surface temperature of cast product in a particular zone is maintained and the cooling rate is consistently maintained within the range of accuracy mentioned.
15

Figure 6 is the illustration of a typical valve stand in a caster strand, comprising control valves flow meters and pressure transmitters that are controlled under auto mode according to the present invention by means of PLC controller and HMI interface means to measure the water flow and pressure in each zone for logging into the system; and means for effecting said automatic flow control of water, based on strand input data for the corresponding operating parameters for a grade and speed of caster, and at the different zones.
Figure 7 shows the comparative images of macro sections of billets produced following the present system of optimized cooling intensity in secondary cooling of caster strands wherein the internal cracks are completely eliminated for a Grade C-20 material having superheat of 48 °C, as compared to one obtained through the conventional practice.
16

WE CLAIM:
1. A method of secondary cooling based on heat transfer model for superior quality
concast billets comprising :
applying either temperature or heat flux boundary conditions depending on a prediction or simulation mode of computation ;
inputting in a PC based HMI the heat numbers, section size and steel grade; loading the said input into a PLC as a recipe;
executing the spray cooling automation scheme in real time mode through said PLC as soon as the cast starts and starts receiving the casting speed data;
generating the set point of water flow in each zone for the strand based on last tundish temperature and the casting speed of the stand.
2. A method of secondary cooling based on heat transfer model as claimed in claim 1
wherein in said prediction mode , the model is adapted to predict required heat transfer
coefficient in each secondary cooling zone from the targeted strand surface temperature of
that zone while in simulation mode the model is adapted to calculate the temperature profile
of the strand based on known heat flux boundary such as hereindescribed.
3. A method of secondary cooling based on heat transfer model as claimed in anyone of
claims 1 or 2 wherein the quantity of water in secondary cooling zones is computed based
on specific requirement of strand surface temperature profile for said (a) casting speed,(b)
superheat range (<30 C,30-50 C and >50 C): difference between metal temperature and
liquidus temperature, section size (100X 100,125X 125,150X150mm square), steel grade
wise cooling intensity selected from hard cooling, medium cooling and soft cooling.
4. A method of secondary cooling based on heat transfer model as claimed in anyone of
claims 1 to 3 wherein after enabling the PLC operation the following control stages are
followed:
(e) updating the measured tundish temperature and if the tundish temperature is more than the liquidus temperature calculate the superheat temperature;
17

(f) select the look up table for the water flow for selective superheat for selected section
size and type of cooling;
(g) read casting speed to decide set point;
(h) controlling the flow control valve for water spray.
5. A method of secondary cooling based on heat transfer model as claimed in claim 4
wherein
if the ladle change signal is not enabled the steps (a) to (d) are repeated.
6. A method of secondary cooling based on heat transfer model as claimed in claim 4
wherein if the ladle change signal is enabled the new grade is confirmed within specified
time by reading grade, LT and type of cooling and thereafter repeating steps (a) to (d)
above.
7. A method of secondary cooling based on heat transfer model as claimed in claim 6
wherein if the new grade is not confirmed within specified time and the sequence is
completed or the casting is stopped the procedure is stopped with delay.
8. A method of secondary cooling based on heat transfer model as claimed in claim 6
wherein if the new grade is not confirmed within specified time and the sequence is not
completed or the casting is not stopped repeating the above stages again.
9. A system of secondary cooling based on heat transfer model for superior quality concast
billets following the method as claimed in anyone of claims 1 to 8 comprising:
means for calculating water intensity of secondary cooling using model which runs on either temperature or heat flux boundary conditions depending on a prediction or simulation mode of computation ;
means for inputting in a PC based HMI the heat numbers, section size and steel grade; means for loading the said input into a PLC as a recipe;
means for executing the spray cooling automation scheme in real time mode through said PLC as soon as the cast starts and starts receiving the casting speed data;
18

means for generating the set point of water flow in each zone for the strand based on last tundish temperature and the casting speed of the stand.
10. A system of secondary cooling based on heat transfer model for superior quality concast
billets as claimed in claim 9 comprising an auto mode control to generate set points
dynamically based on inputs from periodically measured tundish temperature and
instantaneous values of stand speed.
11. A system of secondary cooling based on heat transfer model for superior quality concast
billets as claimed in anyone of claims 9 or 10 wherein
analog feedback signal for speed of caster for individual strands are taken into strandwise PLCs and temperature of the tundish is fed into one of the PLCs;
means to measure the water flow and pressure in each zone for logging into the system;
means to control the flow dynamically depending upon the strand speed, tundish temperature, section size and grade of steel.
12. A system of secondary cooling based on heat transfer model for superior quality concast
billets as claimed in anyone of claims 9 to 11 wherein the flow in controlled through
motorized control valve activated through an actuator card interfaced with PLC output, said
PLC outputs being activated after execution of control loops within the PLC based on the
control algorithms guided by the application requirement.
13. A system of secondary cooling based on heat transfer model for superior quality concast
billets as claimed in anyone of claims 9 to 12 wherein the system comprises Proportional
+Integral + Derivative (PID) control loops for various zones of each strand.
14. A system of secondary cooling based on heat transfer model for superior quality concast
billets as claimed in anyone of claims 9 to 13 wherein for each strand of the caster, one
dedicated PLC is installed and one PLC used for interfacing with existing PLCs of the caster
for common functions, all said PLCs are adapted to communicate on a data bus with speed
of atleast 10 MBPS and said PLC system further comprising PC based engineering cum HMI
system with interface to PLC.
19

15. A system of secondary cooling based on heat transfer model for superior quality concast
billets as claimed in anyone of claims 9 to 14 wherein secondary cooling sections are
extended through addition of additional zones with length of secondary cooling zones and
nozzle configuration as detailed in Table 2.
16. A system of secondary cooling based on heat transfer model for superior quality concast
billets as claimed in anyone of claims 9 to 15 adapted to selectively operate in anyone of
manual mode, semi-auto mode and auto mode.
20
17. A method of secondary cooling based on heat transfer model for superior quality
concast billets and a system for carrying out said method substantially as hereindescribed
and illustrated with reference to the accompanying figures and Tables.

A method of optimizing the intensity of cooling for the secondary cooling of the Concast billets for different casting parameters like the section sizes of casting strand, different grades of steel, variations of steel superheat temperatures and variation in casting speed and a system to carry out such method of controlled water cooling at different zones of a caster strand. The present invention also makes use of Programmable Logic Controller (PLC) based automation system; the automatic secondary cooling system (ASCS) adapted and developed to precisely control the water flow at desired rate in secondary cooling zones in each strand, the flow rates are being determined based on a input database, feed to the controller, generated and based on a heat transfer based mathematical model and its solution under selective initial and boundary conditions matching with the prevailing parameter values at different zones in a caster strand.