Claims:WE CLAIM:

1. A system for controlling furnace entry side charging equipments of multi-strand rolling mill operations including billet feeding, pushing and discharge operations for a pusher type reheating furnace of said multi-strand rolling mill comprising
PLC and Digital DC Drive operated dual motor based furnace pusher to push the billets into the furnace one by one for heating
PLC and Digital AC Drive operated Ejector Ram (ERAM) to push the heated billets one by one out of the furnace into the rolling line;
PLC and Digital AC Drive operated motor based Draw in Roller to feed the billet into the furnace without jamming the mouth; and
said PLC for controlling said Draw in Roller, said furnace pusher and said ERAM operations through integrated control scheme involving interlocking and sequencing steps embedded in said PLC with automatic annunciations, forbiddance and permissions corresponding to remotely connected operator desks.

2. The system as claimed in claim 1, wherein the PLC and Digital DC Drives operated dual motor based furnace pusher includes two DC motors connective with respective DC drives, working in master/slave configuration, whereby one of said two DC motor drives is configured as master drive and running in speed mode, the other of said two DC motor drives is configured as slave drive and running in Torque mode.

3. The system as claimed in claim 1 or 2, wherein the master DC motor drive is connected to the PLC over profibus network for receiving speed set point as speed reference and acting torque value as torque reference from the PLC, whereby the master DC motor drive is connected to the slave DC motor drive through hardwiring involving analog output-1(Act. Torque) of the master drive connected to analog input-1(Torque Ref) of the slave drive for forwarding the torque reference to the slave drive.

4. The system as claimed in anyone of claims 1 to 3, wherein the PLC on receiving forward pushing (FP) command from the operator desk, take one complete cycle involving the drives starting and reference releasing based on pusher actual position feedback limit switches which are taken as digital inputs in the PLC;

said PLC stops involving reference withdrawal at defined home position and after removal of the FP command, the pusher drives remain "ON" for about 90 sec and after elapse of that time stops automatically to avoid creeping of the motors and ready for next forward/Reverse command

5. The system as claimed in anyone of claims 1 to 4, further comprising the PLC adapted for releasing corresponding digital output to hard wired AC drive of the ERAM including direction dependent digital output on receiving ERAM Forward/Reverse command from the operator desk, whereby based on the direction dependent digital output of the PLC, the ERAM moves forward or reverse direction.

6. The system as claimed in claim 5, wherein constant reference is set on the ERAM drive itself and when forward/reverse command is removed, the ERAM drive remain "ON" for 45 sec and after elapse of this time it will stops automatically to avoid the creeping of motor and ready for next forward/Reverse command.

7. The system as claimed in anyone of claims 1 to 6, further comprising setting reference speed and acceleration of the motor of the Draw in Roller from HMI station online, and the speed is set within a range of 1000-1200 RPM, typically at 1100 RPM for a billet length of 11 meters ensuring that the draw in roller can efficiently feed the billet into the furnace without jamming the mouth. The Speed and acceleration set point is transmitted to the drive from the PLC.

8. The system as claimed in anyone of claims 1 to 7, wherein the PLC with the remotely connected operator desks and HMI terminal enables efficient operation management including process monitoring, control and maintenance of charging section equipment in the rolling mill through complete real time visualization of the process, on-line display of status and electrical parameters of each equipment, on-line configuration & operation of equipment, on-line status of complete integrated process as well as historical trends of faults and critical parameters.
, Description:FIELD OF THE INVENTION:
The present invention relates to managing multi-strand rolling mill operation. More specifically, the present invention is directed to provide an improved control system for Billet Feeding, Pushing and Discharge operations for a pusher type reheating furnace of a multi-strand rolling mill.

BACKGROUND OF THE INVENTION:
A Wire Rod Mill is a continuous high capacity rolling mill used to produce Steel Wires and Rods of various dimensions from Billets. Such a rolling mill comprises of charging area to handle cold input material i.e. Billet, reheating furnace to heat cold billet to a temperature suitable for rolling through a train of rolling stands called the roughing & finishing stands followed by coil handling area. A multi-strand wire rod mill typically includes more than a single rolling train, generally 2-strand or a 4-strand. Such mills may typically have a common charging section having one or two charging platforms, roll tables, furnace and discharging sections, common train of roughing stands followed by individual finishing stands for each strand.
The existing furnace entry side charging equipments are adapted to operate based on relay logic and contactor control system which is difficult to maintain, trouble shoot and has no flexibility of operation. The absence of any effective speed control in the existing furnace entry side charging equipments also leads to frequent failure of the equipment motors.
Occurrence of billet jamming in DIR and ERAM are also common due to improper speed and torque control, complex control regime for Furnace pusher and ERAM.

Frequent stoppages of such sections due to above equipment failure affect the entire mill, also results in frequent F/c temperature regulation leading to rolling and quality issues, idle running of equipment.

It thus has been a need for developing an improved control system for the furnace entry side charging equipments of the multi-strand rolling mill which can address the above limitations.

OBJECTIVE OF THE INVENTION:
It is thus the basic object of the invention to develop an improved system for controlling furnace entry side charging equipments of multi-strand rolling mill operations including billet feeding, pushing and discharge operations for a pusher type reheating furnace of said multi-strand rolling mill.

Another object of the present invention is to develop an improved control system for furnace entry side charging equipments which would provide an effective speed control for the entry side charging equipment motors and thereby reduce frequent failure of the equipment motors as well as wear and tear of mechanical components the motors are driving.

Another object of the present invention is to develop an improved control system for furnace entry side charging equipments which would avoid occurrence of billet jamming in DIR and ERAM.

Another object of the present invention is to develop an improved control system for furnace entry side charging equipments which would avoid frequent stoppages of complete section due to the equipment failure.

SUMMARY OF THE INVENTION:
Thus according to the basic aspect of the present invention there is provided a system for controlling furnace entry side charging equipments of multi-strand rolling mill operations including billet feeding, pushing and discharge operations for a pusher type reheating furnace of said multi-strand rolling mill comprising
PLC controlled and Digital DC Drive operated dual DC motor based furnace pusher to push the billets into the furnace one by one for heating
PLC controlled and Digital AC drive operated AC Motor based Ejector Ram (ERAM) to push the heated billets one by one out of the furnace into the rolling line;
PLC controlled and Digital AC drive operated AC motor based Draw in Roller to feed the billet into the furnace without jamming the mouth; and
said PLC for controlling said Draw in Roller, said furnace pusher and said ERAM operations through integrated control scheme involving interlocking and sequencing steps embedded in said PLC with automatic annunciations, forbiddance and permissions corresponding to remotely connected operator desks.

In a preferred embodiment of the present system, the PLC operated dual motor based furnace pusher includes two DC motors with respective drives, working in master/slave configuration, whereby one of said two DC motor drives is configured as master drive and running in speed mode, the other of said two DC motor drives is configured as slave drive and running in Torque mode.

In a preferred embodiment of the present system, the master DC motor drive is connected to the PLC over profibus network for receiving speed set point as speed reference and acting torque value as torque reference from the PLC, whereby the master DC motor drive is connected to the slave DC motor drive through hardwiring involving analog output-1(Act. Torque) of the master drive connected to analog input-1(Torque Ref) of the slave drive for forwarding the torque reference to the slave drive.

In a preferred embodiment of the present system, the PLC on receiving forward pushing (FP) command from the operator desk, take one complete cycle involving the drives starting and reference releasing based on pusher actual position feedback limit switches which are taken as digital inputs in the PLC;

said PLC stops involving reference withdrawal at defined home position and after removal of the FP command, the pusher drives remain "ON" for about 90 sec and after elapse of that time stops automatically to avoid creeping of the motors and ready for next forward/Reverse command

In a preferred embodiment of the present system, the PLC on receiving ERAM Forward/Reverse command from the operator desk, release corresponding digital output to hard wired drive of the ERAM including direction dependent digital output whereby based on the direction dependent digital output of the PLC, the ERAM moves forward or reverse direction.

In a preferred embodiment of the present system, constant reference is set on the ERAM drive itself and when forward/reverse command is removed, the ERAM drive remain "ON" for 45 sec and after elapse of this time it will stops automatically to avoid the creeping of motor and ready for next forward/Reverse command.

In a preferred embodiment of the present system, reference speed and acceleration of the motor of the Draw in Roller is set from HMI station online, and the speed is set within a range of 1000-1200 RPM, typically at 1100 RPM for a billet length of 11 meters ensuring that the draw in roller can efficiently feed the billet into the furnace without jamming the mouth.

In a preferred embodiment of the present system, the PLC with the remotely connected operator desks enables efficient operation management including process monitoring, control and maintenance of charging section equipment in the rolling mill through complete real time visualization of the process, on-line display of status and electrical parameters of each equipment, on-line configuration & operation of equipment, on-line status of complete integrated process as well as historical trends of faults and critical parameters.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig 1 shows overall schematic representation of the billet feeding, pushing and discharging equipment for a rolling mill having a draw in roller, a furnace pusher and an ejector ram.

Fig 2 shows integrated architecture for seamless control of equipment in charging section in accordance with the present invention.

Fig 3 shows improved scheme for furnace pusher in accordance with the present invention.

Fig 4 shows improved control scheme for draw in roller and ejector ram in accordance with the present invention.

Fig 5A – 5D show operator interface designs for improved on-line monitoring calibration and diagnostics in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION:
Reference is first invited from the accompanying Figure 1 which depicts (Here a typical 4 strand mill with common charging, pusher type furnace and discharging section) furnace entry side charging equipment comprising of 2 nos. of Charging Grates (CG) 1-2 to store and transfer billets to roll table, 2 nos. of corresponding Billet Manipulators cum Rejectors (BR) 1-2 for proper placement of billet on roll tables and also rejecting defective billets, Roll Tables section (RT) 1-4 to transport billets on the charging line, one set of Draw In Rollers (DIR) to draw the billets into the pusher type furnace, Furnace Pusher (FP) 1-2 to push the billets into the furnace one by one for heating, Ejector Ram (ERAM) to push the heated billets one by one out of the furnace into the rolling line. All the operations are carried out at a very high speed as the simultaneous rolling goes on in four strands so the complete charging-furnace-discharging section is required to work non-stop and equipment operate at a high rate close to 120 operations per hour. All the systems of the zone are very critical for running of the Mill since these are the common equipment for all multiple rolling strands. Therefore, 100% availability of these equipment has to be ensured. The control scheme for Furnace Pusher and Discharge operations from the Reheating furnace are the most complicated, the former because of the large load it handles as furnace is always full under regular operation and the latter because it is to be ensured that the movement of the Ejector Ram should be adequate to push the billet completely into the rolling stand and thus avoid billet jamming at furnace door. The layout of such mills are very distributed and operations are carried out from operator desks in different areas requiring inter pulpit coordination.

The present invention provides an improved control system and related methodology for Billet Feeding, Pushing and Discharge operations for a pusher type reheating furnace and the equipments thereof (as discussed above) of a multi-strand rolling mill. The improved system has an integrated control scheme based on state of art programmable digital controllers and digital AC and DC drives and other components networked with each other. The control schemes have so been designed that they can very reliably operate the critical equipment at high speed and while handling large load specially the Furnace Pusher mechanism. Apart from the hardware design, the methodology employed for control of equipment also helps in fool-proof operation and quick troubleshooting as well as resolution of faults in any of the equipment of charging section.
Mechanism Existing Details New configuration
Draw In Roller DC Compound motor, 14 KW, 220Vdc, 1200/2300 RPM, 57 A, Flywheel moment: 1.7 kgm2 , S4 duty, Foot mounted, Frame:225, Operating speed range: 1200-1400 RPM, Field voltage and current: 220 V DC, 30 A • New inverter grade Squirrel Cage Induction motor, 45KW, 1471 RPM, 225S/M frame size
• New VVVF Drive, 94A
Ejector RAM DC Compound motor, 10.5 KW, 220V, 780/2300 RPM, 57 A, Flywheel moment: 1.7 kgm2 , S4 duty, Foot mounted, Frame:225, Operating Speed: 780 RPM, Field Voltage and Current: 220 V DC, 50 A, • New inverter grade Squirrel Cage Induction motor, 45KW, 1471 RPM, 225S/M frame size
• New VVVF drive, 94A ACS880 (Standby shall be common for DIR and ERAM)
Furnace Pushers 1,2 Motor Details: DC Separately excited 40 KW, 220V DC, 202 A , 620/1800 RPM, S4 Duty, Field voltage and current: 220V DC, 6A • New digital DC drives, 680A, one for each Furnace pusher motor to be operated in master slave configuration for torque sharing.
• Existing DC motors retained in the new control architecture
Controls & Operation • Controls of CG, BR, DIR, FP, ERAM are through relay logic and contactor control scheme.
• Operation of Charging equipment is from individual operator posts for CG & BR, 1-2, Furnace Pusher through Pulpit Post 1 (PP1), ERAM through ERAM post • New PLC system, with Remote I/o Stations for Drive commands and interlocks for Charging section and monitoring of RG and IG parameters
• Hardware interconnection with existing Schneider PLC system for display
• Hardware interconnection with GE Fanuc PLC system for command interlocks of DOR through I/O
• New ergonomic Operator Desk PP1, New Desks of CG, Retaining desks for PP2 and ERAM post
• New HMI cum engineering terminal
Methodology for control of complex mechanisms of Furnace Pusher, Draw In Roller and ejector RAM involving the present control system:
PLC and Digital DC Drives operated Furnace Pusher: Furnace pusher have two DC motor. The digital DC drives, workin master/slave configuration. One of the motor drive is taken as master drive and running in speed mode, the other motor drive is configured as slave drive and running in Torque mode. Master gets Speed Set point over the profibus network from PLC and its "Act torque" value taken as torque reference to Slave drive through hardwiring i.e. Analog output-1(Act. Torque) of master drive is connected to Analog Input-1(Torque Ref) of Slave drive. Whenever FP Forward command is given from operator pulpit it will take one complete cycle(Drive Starts and Reference released) based on the pusher actual position feedback Limit switches which are taken as digital inputs in the PLC, it will stop (Reference withdrawn) at defined home position. After Removal of Forward command Pusher drive will be "ON" continue for 90 sec and after elapse of that time stops automatically to avoid creeping of motors. As soon as forward/Reverse command is given from operator pulpit the above cycle is repeated again.

PLC and Digital AC drive operated Ejector RAM: Whenever ERAM Forward/Reverse command is given from the desk a command is released from PLC to the AC Drive through digital Output and one more digital output is released from PLC for the Direction. Based on the command and direction Digital output of PLC, ERAM move forward/Reverse. Constant Reference is set on the drive only. When forward/reverse command is removed drive will be still "ON" for 45 sec and after elapse of this time it will stops automatically to avoid the creeping of motor. As soon as forward/Reverse command is given the above cycle is repeated again.

PLC and Digital AC drive operated Draw in Roller: The reference speed and acceleration of the motor can be set from the HMI station online. The speed is set within a range of 1000-1200 RPM, typically at 1100 RPM for a billet length of 11 meters so that the draw in roller can efficiently feed the billet into the furnace without jamming the mouth. The Speed and acceleration set point is transmitted to the drive from the PLC.

The Roll table sections, Draw in Roller, Furnace Pusher and Ejector Ram operations are coordinated through interlocking and sequencing in the PLC with automatic annunciations, forbiddance and permissions to the concerned operator desks.
This system also has PLC connected remote operator desks and remote HMI terminal on Ethernet network, for centralized monitoring, maintenance and calibration of all equipment of charging section and includes features such as follows:
Efficient operation management system for process monitoring, control and maintenance of charging section equipment in a rolling mill through complete real time visualization of the process, on-line display of status and electrical parameters of each equipment, on-line configuration & operation of equipment, on-line status of complete integrated process as well as historical trends of faults and critical parameters.
Usefulness of the invention:
• Improved reliability of control system
• Improved man-machine safety
• Improved speed control leading to lesser wear and tear of mechanical components
• Enhanced operation & maintenance management
• Energy saving
The present system can also be implemented in similar charging sections for pusher type reheating furnaces or other similar applications having heterogeneous control system architecture and distributed equipment.