FIELD OF THE INVENTION
The present invention relates to a system for improved on-line control of hood annealing
process involving centralized monitoring and controlling all critical process parameters of
annealing cycle in various batch/hood annealing bases and furnaces in operation. More
particularly, the online control system in annealing furnace operation according to the
present invention is adapted for achieving improvement in quality throughput as well as
reduction in energy and protective gas consumption. The present system of centralized
control and monitoring critical annealing parameters on-line in all the annealing bases,
includes Programmable Logic Controller (PLC) based automation for controlling base
temperature and soaking time duration in an annealing cycle. The system of the invention is
further adapted to operate in cooperation with application software enabled processor
developed to control the flow of mixed gas and atmospheric air to maintain the heating
pattern of the annealing cycle in a hood-annealing furnace. The present system of
centralized on-line control of annealing process in hood annealing furnace/bases involve the
centralized control unit and a single power contactor panel interfaced with the field elements
like positioner and torque limit for each actuator of furnace operatively connecting the
control gears in the control room, unlike those kept conventionally in the enclosure placed
at the top of the furnace. The system also provides for alarm annunciation, fault diagnosis,
historical as well as on-line trending of vital process parameters and generates MIS reports
on demand. The centralized system of the present invention is thus directed to providing
operational efficiency, reduced manpower cost, simple and effective support to operation
and maintenance and improved productivity combined with economizing costs of
inputs/energy, favoring wide scale application in steel industry.
BACKGROUND ART
It is well known in the art of batch annealing of CR coils that to regain the mechanical
properties, which get lost during the thickness reduction by cold rolling in Tandem Mills the
appropriate annealing cycle has to be followed in batch annealing furnace/hood-annealing
bases.
In conventional batch annealing process, a number of coils are stacked in a base, the
number of coils varying depending on the width and weight of each coil. Each of such coil is
separated by a converter plate placed in between two coils. The stack is then covered with
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an inner cover and the charge is sealed with sand. All the air inside the inner cover is taken
out and substituted with nnixed gas such as Nitrogen and Hydrogen in desired proportion.
The annealing base furnace is usually lighted up using suitable burners and mixed gas as
fuel, to increase the tennperature of the coils to desired annealing temperature depending
on physical parameters such as the thickness, width and weight of the coil as well as the
grade, composition and its quality. The hood annealing process thus requires raising the
temperature of the coils to a predetermined annealing temperature following predetermined
temperature gradient and also soaking the coil for time duration at the elevated
temperature. The annealing cycles involve also gradual or controlled cooling of stack. The
time duration and the on-line control of temperature are of utmost importance in the
annealing process.
In batch annealing unit, the coils are placed in base and then a movable furnace is placed
for covering the coils for carrying out the desired process annealing cycle for the coils. The
annealing is carried out in an inert atmosphere. The furnace is lightened and the coils are
heated up accordingly.
When sheet steel are cold rolled in Tandem Mill for desired thickness reduction and coiling,
the grain structure of the steel gets elongated and heavy internal stresses are developed,
due to which the mechanical properties of the material becomes unfavorable for certain
application as the ductility is reduced and hardness is increased. To regain the mechanical
properties, the material is heated at a temperature of 68OOC - 7200C to restore favorable
property values by relieving locked up stresses due to cold deformation and recrystallisation
of deformed grains, following predefined annealing cycle for a given steel chemistry/size
and weight of stack of CR coil in furnace.
The CR coils, three or four in numbers, depending on the width of the strip are stacked on
the base and each coil being separated by one converter plate placed in between. The stack
is then covered with an inner cover and the whole charge is sealed with sand at the bottom
periphery of the hood seating on base. A movable furnace having burners around its circular
periphery is put over. Before lighting the burners, all air inside the inner cover is taken out
and the inner environment is substituted with mixed gases (96% of N2 and 4% of H2), to
avoid oxidation. The annealing temperature is then raised up to 650°C - 720°C depending
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on the wt. of charge, quality of steel, its use etc. Time duration of soaking & annealing are
pre-determined based on various parameters. When final annealing & soaking is completed,
the furnace is put off. Then the whole charge is allowed to cool down to 100°C
approximately, after which the coils are ready for transfer from the furnace.
In the existing system in the annealing line, the heat input to the furnace are controlled by
the actuators placed in furnace top. The control signals are generated by a single point
controller, where inputs are taken from the base temperature of the furnace. The power to
the actuator are made available at the boxes placed at the top of furnace near to actuator.
The control elements along with field limit & torque switches are also placed inside the
boxes near to the actuator. So the operation, of the actuators , limit switches etc was not
available earlier to the operator of the furnace.
These processes require on-line control over temperature and time element to produce
quality output. There exists various heating pattern, which depends on width, thickness,
and weight of the charged coils. Control of annealing operation is conventionally performed
through single point controller dedicated for each base. This needs very often the
intervention of operators for switching over from heating to soaking and cooling during the
annealing cycle which in turn lead to loss of quality and increase in specific energy
consumption and also specific consumption of protective gas. Once discontinued, a lot of
reconnections also are to be restored for putting a particular base back under annealing
cycle.
There has been thus a continuous need to develop an on-line control system for batch
annealing of CR coils in annealing bases that would on one hand to overcome the problems
experienced in the conventional manual control at each base operation by adopting an
improved PLC based automation scheme implemented to control all annealing furnaces from
a centralized control cabin avoiding human intervention and on the other hand optimize the
parameters e.g. the temperature, time etc for the annealing cycle for a particular grade of
CR steel to restore mechanical properties to desired levels which is lost/reduced after cold
reduction, in a simple and cost effective manner. The system automation for the process
parameters would thus use thermo couple output for base temperature and PG temperature
input to the PLC and application software to control the flow of mixed gas and atmospheric
air to maintain in a manner ensuring the predetermined heating/soaking pattern of the
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annealing cycle and would generating desired trending and reports of continuous monitoring
of status, to achieve desired results.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to provide a Programnnabie Logic
Controller (PLC) based centralized control and monitoring system for process parameters
such as the temperature and gradient of heating, time of soaking/holding at a desired
temperature for a particular quality/grade of steel, whereby such control can be
simultaneously executed at all bases and furnaces without individual human interference, so
as to favor improvement of the mechanical properties of the CR coils in a simple manner
and with optimized fuel consumption.
A further object of the present invention is directed to a centralized control and monitoring
system for process parameters for annealing of CR coils in hood annealing bases wherein
said system would be advantageously and favourably use individual field signals, both
analog and digital, brought to the centralized control unit along with provision of control
either through PG temperature or base temperature,
A still further object of the present invention is directed to a centralized control and
monitoring system for process parameters for annealing of CR coils in hood annealing bases
wherein desired control ramp during heating cycle and predetermined time for soaking help
achieving optimum heat input to the furnace commensurate with the batch characteristics in
terms of volume, weight and composition.
A still further object of the present invention is directed to a centralized control and
monitoring system for process parameters for annealing of CR coils in hood annealing bases
wherein the system provides an online integrated approach to fault diagnosis and analysis
of process parameters to achieve desired product quality and also reduce specific fuel
consumption.
A still further object of the present invention is directed to a centralized control and
monitoring system for process parameters for annealing of CR coils in hood annealing bases
adapted to provide historical and online trending of vital parameter values and status of
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inputs and outputs at any point during the annealing cycle and for any individual
furnace/annealing base.
SUMMARY OF THE INVENTION
Thus according to the present invention there is provided system for online control of hood
annealing process comprising:
a PLC based automation;
thermo couple output for base temperature and PG temperature provided as inputs to said
PLC; and
means for controlling the flow of mixed gas and atmospheric air such as to maintain the
desired heating pattern for the annealing cycle.
Advantageously, a system for online control of hood annealing process of the invention
comprises means for report generation.
In accordance with yet another aspect system for online control of hood annealing process
comprises:
centralized control for hood annealing furnace;
control of heat inputs to furnace such as to achieve desired control of ramp during heating
cycles and predetermined time for soaking cycle;
an integrated fault diagnosis and analysis of annealing parameters; and
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means to generate historical and on-line trending of all vital paranneters and status of inputs
and outputs.
Importantly, in the system for online control of hood annealing process the said
programmable logic controller provides for centralized control and monitoring of all bases
and furnaces; and
said centralized control unit is adapted to receive individual filed signals both analog and
digital and having means for control either through PG temperature or base temperature.
According to another aspect the system for online control of hood annealing process
comprises a single power contractor panel catering to each individual base having a required
interface with filed elements including positioner and torque limit for each actuator of the
furnace and removable of the control gears from top of the furnace to the control room.
Also, preferably the system for online control of hood annealing process of the invention
involves bifurcating the single bus catering to all the bases for ease of maintenance and
reducing downtime.
In accordance with yet another aspect the system for online control of hood annealing
process comprises alarm annunciation, fault diagnostics and monitoring of vital process
parameters and interfaces along with historical, on-line trending and MIS reports.
Advantageously, in the above system for online control of hood annealing process the input
signals for all the field control devices are provided with proper isolation and all digital input
and output are routed through interposing relays and contactor of matching specifications to
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control the flow of mixed gas and air at certain ratio such as to maintain the furnace
temperature;
said PLC processes the signal received from the filed and compares with actual
temperatures and set temperatures, in the instance there is difference in comparison the
PLC is adapted to output a command to the actuator of the valve either to open in case the
actual temperature is lagging behind with the set temperature or to close in case of actual
temperature is more than the set temperature, said command being received by relay
means defined for a particular base and accordingly said relay is adapted to act either to
open or close, a digital I/O in turn commands the designated contactor of the motor of the
valve, said working principle being implemented for all bases.
In accordance with yet another aspect the system for online control of hood annealing
process of the invention favours user friendly operation by way of the operators interface
through PC as well as through the operators panel view and display means providing for
display of all vital parameters.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: is the illustration of the schematic diagram for the PLC based centralized control of
annealing parameters for all furnaces/bases according to the invention.
Figure 2: is the illustration of the typical ideal annealing cycle comprising the desired
heating, soaking and cooling, having predetermined pattern.
Figure 3: is the actual profile maintained during the annealing cycle using the centralized
control and monitoring system of the present invention.
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DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
The present invention is directed to an online integrated system involving PLC based control
and feed back signals, analog or digital, analyzed through a processor for desired
monitoring and control of the vital process parameters during the annealing cycle for all the
hood annealing bases, instead of controlling individual furnace manually from independent
console. The heating temperature, soaking temperature and duration/holding time or the
cooling rate is optimally controlled based on input data from the individual bases through a
single bus bifurcated to cater all the bases and thereby facilitate maintenance and reduce
downtime as well. Thus the annealing cycle is maintained for a particular batch of CR coils
having given volume, weight and composition in an optimal way such that the mechanical
properties lost due to cold reduction is favorably restored in the end product.
Reference is first invited to accompanying Figure 1 that illustrates the schematic diagram
for the PLC based centralized control of annealing parameters for all furnaces/bases
according to the invention. According to an embodiment of the invention, the centralized
control system for controlling annealing process parameters for all bases from one control
point comprises a Programmable Logic Controller (PLC), interfaced with the Inputs/Outputs
modules and single contactor panel. The present system also comprises panel for controlling
the motorized valves, programming and operator terminal/workstation for operation of
customized software to interpret and analyze the input data, both analog and digital,
necessary communication cables, power & control cables and other interface equipment &
instruments like relays, actuators, thermocouple elements etc. are also present in the
system to operatively feed signal to the devices according to the value of individual field
signals, aniaog and digital brought to said centralized controller having provision of control
either through PG temperature or base temperature and the designed value for optimum
annealing cycle operation that is predetermined, corresponding to the batch in a particular
base. The operation and monitoring of parameter values performed continuously through
integration of all bases, bifurcating the single bus to cater all the bases and thereby favor
ease and time reduction for maintenance.
In the present embodiment of the system according to the invention, all the inputs from
limit switches and the torque switches of the actuator operation are brought to the central
PLC as input. This rearrangement facilitates smooth operation of the control gears and the
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contactors placed inside the control room, unlike those kept conventionally in the enclosure
placed at the top of the furnace. This modification makes the operations of the actuators
and its fault diagnostics very transparent to the operator & maintenance personal.
For improved on-line measurement and control of Hood annealing furnaces temperatures,
the most important consideration have been PID pulse output and integration with existing
power elements and actuators.
Input signals for all the field control devices has been taken to the system with proper
isolation. All digital input and output has been routed through interposing relays & contactor
of matching specification to control the flow of mixed gas and air at certain ratio to
maintain the furnace temperature.
As already described, the temperature of base & PG has been utilized in the present system
as input to PLC. The operator sets the set point according to the grade, width, weight etc.
that defines the temperature gradient and time settings for heating & soaking cycles. PLC
process the signal received from field; and it then compares the actual temperature and set
temperature. If there is difference measured from such comparison, the PLC outputs a
command to the actuator of the value either to open in case of actual temperature is
lagging behind with the set temperature or to close in case of actual temperature is more
than the set temperature. This command is received by a relay defined for a particular base
and accordingly the relay acts either to open or close. The digital I/O in turn commands the
designated contactor of the motor of the valve. The mixed gas and air flow rate is controlled
accordingly. The same working principal has been implemented for all bases identically. The
present system helps achieving lower specific fuel consumption and also reduced
consumption of protective gases.
Accompanying Figure 2 illustrates an ideal heating soaking pattern which is hardly possible
to be maintained rigidly in actual operation because of different variable parameters that
needs to be continuously monitored. Accompanying Figure 3 is the illustration of the actual
time-temperature distribution profile maintained during a complete annealing cycle in batch
annealing process in bases, comprising selective temperature and gradient for heating and
cooling and the soaking temperature and time duration, for desired transformation of grains
to obtain desired improved mechanical properties of the CR coils.
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Operators interface has been provided through the PC as well as through the operator panel
view. In normal operational mode operators' entry is made through the PC and the Panel
view is kept as standby for operations during failure of the PC. All screens for entry of input
data of heating, soaking cycles has been made user friendly. All facilities like extension,
stoppage or aborting annealing process has been incorporated. Display of all vital
parameters, trending, abnormalities, and alarms has also been developed in various screens
as required by the operation and quality personnel of the shop.
The improved PLC system for controlling annealing cycle installed to operatively interface
with a single contactor panel consisting of adequate number of contactors installed to
actuate different devices in the system upon receiving appropriate signals from the PLC, to
approach the optimum values. Compatible Input/Output modules and relays were
incorporated for fields I/Os. The above modules, relays and contactors were integrated and
commissioned to achieve the targeted objective.The system of the invention is further
capable to generate MIS reports for on-line measurement and control of Hood annealing
furnaces and may include either or more of the following:-
• Production report
• Monthly report
• Shift report (production/base position/delay/repair)
• Historical trend.
In addition to such reports, various screens have been developed for operator viewing and
control. The on-line and historical trending of vital parameters are utilized for quality
appraisal of annealed coils to standardize process and quality.
It is thus possible by way of this invention directed to a system of on-line integrated control
and monitoring all vital parameters for the annealing furnaces/ bases for batch annealing of
CR coils obtained after cold reduction, to restore some of the important mechanical
properties lost during the thickness reduction in tandem mills, by involving a PLC based
control of all vital annealing parameters in an predetermined annealing cycle under
operation by adaptive control of temperature, time and gas-air flow rates, such as to
optimize the heating or cooling temperatures and gradients and also to maintain reasonably
stable temperature for soaking for desired duration to obtain favored improved mechanical
properties in end product in a simple, reliable and cost effective manner and also achieve
favored reduced specific consumption of energy/fuel and also specific consumption of
protective gases used in the process.
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WE CLAIM:
1. A system for online control of hood annealing process comprising:
a PLC based automation;
thermo couple output for base temperature and PG temperature provided as inputs
to said PLC; and
means for controlling the flow of mixed gas and atmospheric air such as to maintain
the desired heating pattern for the annealing cycle.
2. A system for online control of hood annealing process as claimed in claim 1 comprising
means for report generation.
3. A system for online control of hood annealing process as claimed in anyone of claims 1
or 2 comprising:
centralized control for hood annealing furnace;
control of heat inputs to furnace such as to achieve desired control of ramp during
heating cycles and predetermined time for soaking cycle;
an integrated fault diagnosis and analysis of annealing parameters; and
means to generate historical and on-line trending of all vital parameters and status of
inputs and outputs.
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4. A system for online control of hood annealing process as claimed in anyone of claims 1
to 3 wherein said
programmable logic controller provides for centralized control and monitoring of all
bases and furnaces;and
said centralized control unit adapted to receive individual filed signals both analog and
digital and having means for control either through PG temperature or base
temperature.
5. A system for online control of hood annealing process as claimed in anyone of claims 1
to 4 comprising a single power contractor panel catering to each individual base having
a required interface with filed elements including positioner and torque limit for each
actuator of the furnace and removable of the control gears from top of the furnace to
the control room.
6. A system for online control of hood annealing process as claimed in anyone of claims 1
to 5 comprising bifurcating the single bus catering to all the bases for ease of
maintenance and reducing downtime.
7. A system for online control of hood annealing process as claimed in anyone of claims 1
to 6 comprising alarm annunciation, fault diagnostics and monitoring of vital process
parameters and interfaces along with historical, on-line trending and MIS reports.
8. A system for online control of hood annealing process as claimed in anyone of claims 1
to 7 wherein the input signals for all the field control devices are provided with proper
isolation and all digital input and output are routed through interposing relays and
13

conactor of matching specifications to control the flow of mixed gas and air at certain
ratio such as to maintain the furnace temperature.
said PLC processes the signal received from the filed and compares with actual
temperatures and set temperatures, in the instance there is difference in comparison the
PLC is adapted to output a command to the actuator of the valve either to open in case
the actual temperature is lagging behind with the set temperature or to close in case of
actual temperature is more than the set temperature, said command being received by
relay means defined for a particular base and accordingly said relay is adapted to act
either to open or close, a digital I/O in turn commands the designated contactor of the
motor of the valve, said working principle being implemented for all bases.
14
9. A system for online control of hood annealing process as claimed in anyone of claims 1
to 8 wherein the operators interface is through PC as well as through the operators
panel view and display means provides for display of all vital parameters.
10. A system for online control of hood annealing process substantially as hereindescribed
and illustrated with reference to the accompanying figures.

A system for improved on-line control of hood annealing process involving centralized
monitoring and controlling all critical process parameters of annealing cycle, directed to
achieve improvement in quality throughput as well as reduction in energy and protective
gas consumption. The control and monitoring of critical annealing parameters on-line in all
the annealing bases, comprise Programmable Logic Controller (PLC) based automation for
controlling base temperature and soaking time duration in an annealing cycle. The
application software enabled processor of the system developed to control the flow of mixed
gas and atmospheric air to maintain the heating pattern of the annealing cycle in a hood-
annealing furnace. The centralized control unit and a single power contactor panel of the
system interfaced with the field elements like positioner and torque limit for each actuator
of furnace operatively connecting the control gears in the control room. The system enable
fault diagnosis, historical/on-line trending of vital process parameters, improved
productivity, reduced inputs/energy, favoring wide scale application in steel industry.