Description:Title of Invention:
An advanced system for controlling temperature of heat treatment furnaces of railway wheels using PLC based heating system and method.
Field of the Invention:
The present invention relates to an advanced system and method for controlling temperature of heat treatment furnaces of railway wheels using PLC based cascaded programmed heating. More particularly the present invention is directed towards the advancement involving a cascaded air/ gas ratio control with lead-lag philosophy for precision temperature control for controlling temperature of heat treatment furnaces of railway wheels and to develop a system for centralized supervision and heating operation through customized PLC based human machine interface (HMI)
Background of the Invention:
Railway wheels are produced by forging and rolling of heated wheel blocks. In forging press the block is given the shape of wheel with punching hole at centre. After forging, wheels are treated in batch type reheating furnace and thereafter rolled in a mill, where wheels achieve proper profile & dimension in step by step rolling and marking. After getting the final shape, wheels are subjected to a heat treatment process comprising of heating, soaking, quenching and tempering. Tempered wheels are then cooled in air and stacked as black wheel. Subsequently, wheels are precisely machined, finished and quality assurance carried out.
After getting final shape of wheel, as mentioned above, through forging, rolling & dishing processes, wheels are subjected to heat treatment process in a heat treatment furnace. The reason is that, for getting final shape of wheel, steel stocks are subjected to repeat mechanical deformations like forging, rolling & dishing as well as repeated heating / cooling. This deteriorates the key mechanical properties of wheels. Achieving desired mechanical properties for strength & longevity of the finished wheel, depends upon the correct temperature at which the wheel is heated and soaked, heating time and cooling time cycle in the furnaces. Hence, the correct operation of the heat treatment furnace is a very vital link in wheel making process. There are a variety of continuous type furnaces used in industrial heat treatment process. Amongst them, Rotary Hearth type is an important and common type of furnace suitable for wheel heat treatment process and logistics. The rotary hearth furnace considered under subject invention uses Coke Oven (CO) gas as fuel with air for combustion.
As mentioned above, this type of heat treatment process involves a very precise temperature control inside the furnace as the temperature of the stock has to be maintained within a very close tolerance in order to achieve the desired mechanical characteristics of wheels. The rotary hearth heating furnaces have two temperature zones such as Heating Zone and Soaking Zone. Heating and Soaking zone temperatures of these furnaces needs to be maintained at around 920 and 880 degree Celsius respectively, so that final wheel temperature of 780 – 840 degree Celsius can be achieved. The desired set temperatures and final wheel temperature are dependent on type of wheels being heated, like for locomotive or coach. The retention time inside the furnace also depends on type of wheels. Furthermore, a precise thermal regime has to be adhered to involving heating, soaking, tempering and air cooling. A typical thermal regime to be maintained inside these furnaces is illustrated in Fig. 1. The precision temperature control requirement cannot be achieved merely by individual control of gas and air flow using standalone controllers.

Objective of the Invention:

It is thus the basic object of the present invention to provide for a system for controlling temperature of heat treatment furnaces for producing railway wheels and a method for controlling temperature of heat treatment furnaces involving the system of the present advancement.
According to an aspect the present advancement is to provide for said system and method wherein a cascaded air/ gas ratio control with lead-lag philosophy for precision temperature control for controlling temperature of heat treatment furnaces of railway wheels is attained and provided.
Another aspect of the advancement is to develop and provide for a complete instrumentation and control scheme including selective air and gas flow measurement sensors and control valves.
Yet another objective of the present invention is to develop a Programmable Logic Controller (PLC) based system for controlling temperature of heat treatment furnaces for producing railway wheels and a method for controlling temperature of heat treatment furnaces.
A still further objective of the present invention is to develop a system and method for centralized supervision and heating operation through customized PLC based human machine interface.

Summary of the Invention
Thus, according to the basic aspect of the present invention there is provided a system for controlling temperature of heat treatment furnaces for producing railway wheels comprising:
a PLC based controller with cooperative Human Machine Interface (HMI) adapted for controlling heat treatment based on type of wheel under heat treatment and maintaining of desired thermal regime including heating, soaking, tempering and air cooling inside the heat treatment furnace;
operatively connected input means for setting of desired temperature set point (SP) temperature and thermocouple means for generating actual temperature process values (PV) and difference temperature generator between said set point (SP) and actual temperature measurement from thermocouples;
gas flow controller means and air flow controller means for required control of heating gas and air flow including operative required flow control of the operating respective gas and air valves maintaining required air/gas ratio and lead/lag control including PLC based cascade controller for desired heat utilization.
According to another aspect the system as above comprises said PLC based controller operatively connected to plurality of said heat treatment furnaces and maintaining respective heat treatment regime;
Said cooperative Human Machine Interface (HMI)for monitoring and controlling of furnace heating through cooperative PCs and graphical user Interface (GUI);
According to yet another aspect of the present invention there is provided a system as above comprising manual or auto operability and include dedicated software based PID controllers including (i) temperature controller (ii) gas controller and (iii) air flow controller;
thermocouples and Temperature transmitters mean for measuring, monitoring and controlling the temperature;
means for measuring differences between set point (SP) and actual temperature measurement based on thermocouple means of said temperature process valve (PV);
valve opening controller means for operative controlled opening of the respective gas and air valves including filed mounted pneumatic actuators.
According to yet another aspect of the present invention there is provided for the system as above comprising auto adjustable type controllers for attaining desired air/gas ratio and lead/lag control for heating gas efficiency; and automated temperature control of heating and soaking zones with cascading air-gas ratio control means;
means to monitor furnace pressure, inlet air and gas pressure and process parameters including field devices comprising orifices, control valves and actuators;
thermocouple means, temperature transmitters, pressure transmitters and differential pressure transmitters;
said PLC based system including means for monitoring safety circuits of furnaces, PLC based cascade Air/Gas modulated ratio control and instrumentation means for precision heating of furnace;
field instrumentations operatively connected to analog and digital input/output cards;
combustion air and furnace pressure through microprocessor based pressure transmitters for real time measure of pressure of CO gas and air;
Yet another aspect of the present invention there is provided for a system as above comprising said PLC based controller generating PID temp, PID gas and PID air and set air/Gas ratio based control; and
includes cascade mode operability wherein gas and air valve operate as master and follower application based on temperature controller with temperature, gas and air valve operable in auto mode based on ratio set point and temperature set point.
According to yet another aspect of the present invention there is provided for the system as above comprising ratio mode operability wherein the gas and air valve operate as master and follower with gas and air both valves being auto operable, means for setting ratio Sel PB, ratio set point and set temperature increase or decrease options through HMI screen.

According to yet further aspect of the present invention there is provided for the system as above comprising:
said reheating furnace operatively connected to measurement means including thermocouple, temperature transmitters, air-gas flow transmitters, pressure transmitters, orifice plate and actuators;
said PLC based controller including PC based HMI and servers communicating with PLC Processors for controlling the temperature of the reheating furnace;
said PLC based controller adapted for selectively operating Lead/Lag control under (a) manual mode (b) auto mode (c) Ratio Mode and (d) Cascade Mode.

According to yet another aspect of the present invention there is provided for the system as above wherein said Lead/lag control includes selectively:
a) Manual control including means for set point and operability of said air/gas valves based on temperature modulations required;
b) Auto Mode control including auto set point for valve operations based on actual PV with PID parameters and operability fo valves individually;
c) Cascade Mode including gas and air valves as master and follower operable based on temperature controller, means to set gas and air valve in auto, means to set ratio of set point and temperature of set point;
d) Ratio mode including gas and air valve operable as master and follower application, gas and air both valves set in auto, means to set ratio mode by ratio sel pb, mean to set the ratio mode by ratio set point, means to set temp increase or decrease.

The above system is thus directed to production of Railway Wheels through forging and rolling of heated wheel blocks which are subjected to a heat treatment process comprising of heating, soaking, quenching and tempering in a heat treatment furnace such as a rotary hearth furnace using gaseous fuels such as CO gas and combustion air. The purpose of this heat treatment system is ensuring critical mechanical properties like hardness and reduce internal stresses generated through previous process. In order to achieve desired properties, accurate furnace temperature control is very crucial across all zones of the furnace. This is a complex process not achievable through standalone controllers and simple adjustment of air and gas flows in furnace.
To improve the furnace heating control, a state-of-the-art hot redundant PLC based system has been proposed as above. Accurate temperature control has been achieved through PLC based programmed heating incorporating cascade temperature and air-gas ratio control. To enhance the control efficacy, improved control valves and actuators has been introduced in both air and gas lines of both the heating as well as soaking zones of each furnace. The control system also includes field instrumentation like orifice, process transmitters etc. The entire system has been integrated for automated heating operation of the furnaces. Computerized Human Machine Interface (HMI) with interactive graphics, historical trends, reports etc. facilitates operators in efficient furnace heating control.
The system is capable of achieving very precise temperature control within±10 degree centigrade
According to yet another aspect of the present invention there is provided for a method for controlling temperature of heat treatment furnaces involving the system as above comprising:
i. Setting the desired temperature set point and Air / Gas ratio;

ii. Determining the difference between set point (SP) and the actual temperature measurement i.e. temperature process value (PV);

iii. Depending on the difference between set point (SP) and the actual temperature measurement i.e. temperature process value (PV)deciding the percentage of opening of respective gas and air valves;

iv. Regulating the opening / closing percentage of respective control valves by means of using field mounted pneumatic actuators;

v. Monitoring furnace pressure, inlet air and gas pressuretemperature, pressure, air / gas flow rates by means of using smart type microprocessor based pressure transmitters, differential pressure transmitters;

vi. Heating with precision control and optimum consumption of coke oven gas, is achieved involving PLC based cascade air/gas modulated ratio control and instrumentation system including lead/lag control and thereby enabling monitoring and controlling of heating furnace.

According to yet further aspect of the present invention there is provided for the method as above which is selectively operable in (a) manual mode (b) auto mode (c) Ratio Mode (d) cascade mode wherein
said manual mode includes steps of (i) selecting manual mode (ii) set point given ‘MV’ field, Checking MV fill in PID screen and checking valve open %;
said auto mode includes steps (i) selecting auto mode (ii) set point given to ‘SV’ to individual PID (gas and air) (iii) set ‘ML’ and ‘MH’ for maximum valve open/close range (iv) ‘MV’ change based on SV and PV upto maximum /minimum range;
said Ratio Mode including (i) set air and gas valve in auto mode, ratio set point given (iii) set temp increase or decrease wherein when set temp increase then set air SV followed by carrying out gas ‘SV’ automatically and generate based on computation with air PV and ratio SV and when Sel Temperature decrease, set gas SV, air ‘SV’ automatically and generate based on computed Gas PV and Ratio PV;
said cascade mode carried out including gas, air and temp controller set in auto mode, set ratio “SV”, set temp “SV”, thermocouple select for temp, temperature above 7000C;
thermocouple must select before switch over to cascade mode (Temp 1 or temp 2) and wherein carrying out selectively SV generation computation in Cascade mode and determination of cascade override.

The details of the invention, its objects and advantages are explained hereunder in relation to non-limiting exemplary illustrations wherein,
Brief Description of Accompanying Drawing:
• Fig 1 illustrates the Typical furnace thermal regime to be maintained during heat treatment process of railway wheels
• Fig 2 illustrates cascade Air – Gas ratio with Lead – Lag control philosophy used.
• Fig 3 illustrates the architecture of automation system
• Fig 4depicts the air and Gas flow measurement and control architecture
• Fig 5depicts a typical furnace heating control screen and modes of operation to achieve precision temperature control
• Fig 6A-6F provides details of Modes of operations and algorithm where in
• Fig 6A represents the pictorial view of manual mode of operation and algorithm,
• Fig 6B depicts the auto mode of operation and its algorithm,
• Fig 6C discloses the details of ratio mode of operation and algorithm through pictorial representation
• Fig 6D represents the cascade mode of operation and its algorithm,
• Fig 6E depicts the cascade mode switching operation and algorithm,
• Fig 6F represents the modes of operations and algorithm for cascade mode SV generation calculation,
• Fig 6G shows the modes of operations and algorithm for cascade mode override.

Detailed Description of the Invention in relation to the above accompanying figures:
As described earlier, precision temperature control requirement cannot be achieved merely by individual control of gas and air flow. Therefore, novel system for controlling temperature of heat treatment furnaces of railway wheels using PLC based cascaded programmed heating has been developed.
It is based on more complex cascade control concept based gas-air ratio control with lead–lag control feature. Such control is achieved by using programmed heating, wherein three dedicated software based PID controllers are used for controlling the temperature of individual zone. The dedicated controllers are i) Temperature Controller, ii) Gas Flow Controller and iii) Air Flow Controller. Operator inputs the desired temperature set point and Air / Gas ratio. Depending on the difference between set point (SP) and actual temperature measurement from thermocouples i.e. temperature process value (PV), the controller decides the percentage of opening of respective gas and air valves. The system output actually regulates the opening / closing percentage of respective control valves through field mounted pneumatic actuators. The controllers are auto adjustable type to cater the requirement of Air / Gas ratio and lead / lag control to achieve optimum heating gas utilization. Hence, heating with precision control and optimum consumption of coke oven gas, which is a scarce energy source, is achieved using such control philosophy.
The new control system is capable of achieving automatic temperature control of heating and soaking zones with cascaded air-gas ratio control. It facilitates the control of air and gas flow of each zone of furnace through cascaded air-gas ratio. In addition, the control system also controls and monitors the furnace pressure and combustion of air pressure. The system monitors furnace pressure, inlet air and gas pressure and other related process parameters. Field devices such as orifices, control valves and actuators have been introduced. For monitoring of the process parameters like temperature, pressure, air / gas flow rates etc. thermocouples, temperature transmitters, pressure transmitters and differential pressure transmitters have been used. The control system is based on PLC system programmed and installed to handle all functionalities of furnaces including various safety circuits of the furnaces. based cascade air / gas modulated ratio control and instrumentation system helps in precision heating of furnaces for maintaining the temperature variation within a band of ± 10 degree centigrade. (Refer Fig 2)
To ensure uninterrupted plant operation, PLC system is selected as high availability, fault tolerant and dual redundant configuration with respect to processor, power supply, communication and networking. The field instrumentation is connected with the system through various analog and digital input / output cards. Process Input /Outputs are linked with processors through redundant deterministic network. (Refer Fig3).
Details of instrumentation and flow control elements: To measure real time pressure of CO gas, Combustion air and furnace pressure smart type microprocessor based pressure transmitters have been used. Transmitters have built-in field indicator, three-way manifold and mounting accessories. For measurement of air and gas flow, Orifice plates are used. For controlling the gas and combustion of air, pneumatically operated butterfly type control valves are used. Microprocessor based temperature transmitters along with thermocouples are used for temperature measurement (Refer Fig 4).
A user friendly Human Machine Interface (HMI) enables plant operators to effectively monitor and control the furnace heating. It also facilitates the operator with informative graphics, historical trends, alarms etc. HMI has been implemented in two identical industrial grade PCs connected to PLC through dual Ethernet. The basic objective of HMI is to facilitate operator to control the temperature of C1 and C4 furnaces. HMI also depicts Graphical Users Interface (GUI) screen for monitoring various furnace parameters, wherein real-time values of all furnace parameters are displayed at a glance for assistance of operators. (Refer Fig.5)
Usefulness of the Invention:
The system can be implemented for any heat treatment furnaces using gas as fuel and where very precise temperature control is required.
Industrial Applicability of the invention:
The system as above would help precise temperature control within ±10 degC for all zones of furnaces and facilitating substantial increase in quality parameters of wheels. Similarly, it can be used in other industrial heat treatment/reheating furnaces
, Claims:We Claim:

1. A system for controlling temperature of heat treatment furnaces for producing railway wheels comprising:
a PLC based controller with cooperative Human Machine Interface (HMI) adapted for controlling heat treatment based on type of wheel under heat treatment and maintaining of desired thermal regime including heating, soaking, tempering and air cooling inside the heat treatment furnace;
operatively connected input means for setting of desired temperature set point (SP) temperature and thermocouple means for generating actual temperature process values (PV) and difference temperature generator between said set point (SP) and actual temperature measurement from thermocouples;
gas flow controller means and air flow controller means for required control of heating gas including operative required flow control of the operating respective gas and air valves maintaining required air/gas ratio and lead/lag control including PLC based cascade controller for desired heat utilization.

2. The system as claimed in claim 1 comprising said PLC based controller operatively connected to plurality of said heat treatment furnaces and maintaining respective heat treatment regime
said cooperative Human Machine Interface (HMI)for monitoring and controlling of furnace heating through cooperative PCs and graphical user Interface (GUI).

3. The system as claimed in anyone of claims 1 or 2 comprising manual or auto operability and include dedicated software based PID controllers including (i) temperature controller (ii) gas controller and (iii) air flow controller;
thermocouples and Temperature transmitters mean for measuring, monitoring and controlling the temperature;
means for measuring differences between set point (SP) and actual temperature measurement based on thermocouple means of said temperature process valve (PV);
valve opening controller means for operative controlled opening of the respective gas and air valves including filed mounted pneumatic actuators.

4. The system as claimed in anyone of claims 1 to 3 comprising auto adjustable type software based controllers for attaining desired air/gas ratio and lead/lag control for heating gas efficiency;
and automated temperature control of heating and soaking zones with cascading air-gas ratio control means;
means to monitor furnace pressure, inlet air and gas pressure and process parameters including filed devices comprising orifices, control valves and actuators;
thermocouple means, temperature transmitters, pressure transmitters and differential pressure transmitters;
said PLC based system including means for monitoring safety circuits of furnaces, PLC based cascade Air/Gas modulated ratio control and instrumentation means for precision heating of furnace;
field instrumentations operatively connected to analog and digital input/output cards;
combustion air and furnace pressure based microprocessor including pressure transmitters for real time measure of pressure of CO gas.

5. The system as claimed in anyone of claims 1 to 4 comprising said PLC based controller generating PID temp, PID gas and PID air and set air/Gas ratio based control; and
includes cascade mode operability wherein gas and air valve operate as master and follower application based on temperature controller with temperature, gas and air valve operable in auto mode based on ratio set point and temperature set point.

6. The system as claimed in anyone of claims 1 to 5 comprising ratio mode operability wherein the gas and air valve operate as master and follower with gas and air both valves being auto operable, means for setting ratio Sel PB, ratio set point and set temperature increase or decrease options.

7. The system as claimed in anyone of claims 1 to 6 comprising:
said reheating furnace operatively connected to measurement means including thermocouple, temperature transmitters, air-gas flow transmitters, pressure transmitters, orifice plate and actuators;
said PLC based controller including PC based HMI and servers communicating with PLC Processors for controlling the temperature of the reheating furnace;
said PLC based controller adapted for selectively operating Lead/Lag control under (a) manual mode (b) auto mode (c) Ratio Mode and (d) Cascade Mode.

8. The system as claimed in anyone of claims 1 to 7 wherein said Lead/lad control includes selectively:
a) Manual control including means for set point and operability of said air/gas valves based on temperature modulations required;
b) Auto Mode control including auto set point for valve operations based on actual PV with PID parameters and operability for valves individually;
c) Cascade Mode including gas and air valves as master and follower operable based on temperature controller, means to set gas and air valve in auto, means to set ratio of set point and temperature of set point;
d) Ratio mode including gas and air valve operable as master and follower application, gas and air both valves set in auto, means to set ratio mode by ratio select PB, means to set the ratio mode by ratio set point, means to set temp increase or decrease through HMI.

9. A method for controlling temperature of heat treatment furnaces involving the system as claimed in anyone of claims 1 to 8 comprising:
i. Setting the desired temperature set point and Air / Gas ratio;

ii. Determining the difference between set point (SP) and the actual temperature measurement i.e. temperature process value (PV);

iii. Depending on the difference between set point (SP) and the actual temperature measurement i.e. temperature process value (PV)deciding the percentage of opening of respective gas and air valves;

iv. Regulating the opening / closing percentage of respective control valves by means of using field mounted pneumatic actuators;

v. Monitoring furnace pressure, inlet air and gas pressure temperature, pressure, air / gas flow rates by means of using smart type microprocessor based pressure transmitters, differential pressure transmitters;

vi. Heating with precision control and optimum consumption of coke oven gas, is achieved involving PLC based cascade air/gas modulated ratio control and instrumentation system including lead/lag control and thereby enabling monitoring and controlling of heating furnace.

10.The method as claimed in claim 9 which is selectively operable in (a) manual mode (b) auto mode (c) Ratio Mode (d) cascade mode wherein
said manual mode includes steps of (i) selecting manual mode (ii) set point given ‘MV’ field, Checking MV fill in PID screen and checking valve open %;
said auto mode includes steps (i) selecting auto mode (ii) set point given to ‘SV’ to individual PID (gas and air) (iii) set ‘ML’ and ‘MH’ for maximum valve open/close range (iv) ‘MV’ change based on SV and PV upto maximum /minimum range;
said Ratio Mode including (i) set air and gas valve in suto mode, ratio set point given (iii) set temp increase or decrease wherein when set temp increase then set air SV followed by carrying out gas ‘SV’ automatically and generate based on computation with air PV and ratio SV and when Sel Temperature decrease, set gas SV, air ‘SV’ automatically and generate based on computed Gas PV and Ratio PV;
said cascade mode carried out including gas, air and temp controller set in auto mode, set ratio “SV”, set temp “SV”, thermocouple select for temp, temperature above 7000C;
thermocouple must select before switch over to cascade mode (Temp 1 or temp 2)
and wherein carrying out selectively SV generation computation in Cascade mode and determination of cascade override.

Dated this the 24th day of March, 2023
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199