FORM 2
THE PATENTS ACT, 1970 (39 OF 1970)
&
THE PATENTS RULE, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION:
A SYSTEM FOR DETECTION AND CONTROL OF FAILURE OF TORQUE TRANSMISSION AND SKIDDING AND A METHOD THEREOF.
2. APPLICANTS:
(a) Name: STEEL AUTHORITY OF INDIA LIMITED;
(b) Nationality: A Govt, of India Enterprise;
(c) Address: Bhilai Steel Plant, Bhilai, State of Chattisgarh,India.
3. PREAMBLE TO THE DESCRIPTION
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The Present invention relates to a system for detection and control of failure of torque transmission and skidding in Twin-motor Two-high Rolling/blooming mill stand and a method of its implementation. More particularly, the present invention is directed to a detection and control system for torque transmission failure and skidding, involving an electronic circuit using standard components, developed to continuously monitor the difference in the currents drawn by the Top and Bottom motors of Main Drives. In case the difference is more than a predetermined setting for a pre-settable time which is indicative of skidding/spindle failure, the circuit operates a relay, which can be wired for tripping/stoppage of drive. The electronic circuit favours detecting the skids at very early stage and withdraws the speed reference from the main drives. Whenever the metal skids, the operator has to release the foot pedal anyway to attempt another bite so he does not even come to know that the skid circuit has operated and reference has been withdrawn and thus his rhythm of operation remains intact. Thus the innovative circuit detects skidding reliably without affecting the rolling rate and production. The Torque Transmission Failure and skidding detection and control system according to the present invention thus having prospect of wide scale advantageous application in 2-high horizontal stand of blooming mill equipped with individually driven rolls for early detection of failure of top/bottom motor spindle by measuring actual difference in top and bottom motor currents during normal rolling and during spindle broken conditions thereby minimizing chances of Spindle breakage on one hand by early detection of skidding and thus avoiding transmission of excessive mechanical forces and on the other hand to avoid possible extensive secondary damage of equipments by detection and immediate tripping of respective drive motor in case of occurrence of spindle breakage, maintaining roiling rate/production, enhance mill availability, saving on costs due to breakdown and spares.
BACKGROUND ART
It is experienced during the rolling of ingots in the Blooming Mill which is a 2-High horizontal stand, equipped with individually driven rolls, roll skidding and spindle failure is a common phenomena. Each roll is driven by 930V, 8MW, 0-80-100rpm, 9130Amps separately excited DC motor. There is no gearbox and the motor spindle is directly coupled to the rolls for transmission of torque. Average weight of steel ingots which are used for

rolling is 8 to 9 Ton. The length of Rolls is 2800 mm while diameter is 1150 mm (Min.1100mm and Max.1180mm).
Rolls are used in pairs. Each roll set is ground with the required pass design (4 pass design including the shaped beam pass). Usually, after rolling of about 1lakh ton, the rolls are changed. The used rolls are sent for redressing in Roll Turning Shop for further use.
The spindle head on the motor side is an integral part of the component (made of material steel 50) while that on the roll side is detachable part, made of alloy steel 60XH, having Chromium and Nickel for enhanced strength and toughness. This is mainly to protect the spindle from more severe condition of loading on roll side coupling. Since the top roll moves up and down in course of rolling process, the top spindle operates at varying inclinations due to which seventy of stress on top spindle is higher.
Due to the unbalanced load condition on motor spindle, incidents of breakage of spindles in blooming mill are quite common. Often the bottom motor spindle is broken which is associated with extensive secondary damage caused to the H-frame, 1- Frame, transverse beams of bottom spindle, H -frame Foundation column etc. Consequently, the mill remains shutdown for a substantial number of shifts and a huge production loss results, triggering the need for appropriate protection against such occurrences.
It is further observed in the related art that a significant difference between top and bottom motor armature currents develops immediately after the spindle breakage. However, detection of a mechanical parameter like breakage of materials by electrical means has been a very difficult proposition since it may not be very accurate, or it may cause false tripping. It is clearly apparent that such conditions indicate positive indication of failure of transmission of torque to one of the rolls. Thus it is realized that an online eariy detection of skidding occurrence and immediate precautionary measure can save larger damage due to spindle breakage and consequent secondary damages.
There has been therefore a need in the existing art relating to rolling operation in blooming mills in steel plants to developing a system for early detection of metal skidding at drive rolls and consequent failure of spindle due to excess/uneven loading, in a simple, compact and cost effective manner. The system would provide a protective means by tripping a relay based control circuit immediately after detection of spindle failure or detect

occurrence of skidding thus saving major damage of plant and equipment and ensure safe operation without interruption.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to developing a system for detection and control of failure of torque transmission and skidding for 2-High blooming mills involving an protective relay based electronic circuit adapted to detect spindle failure and skidding so as to immediately trip the drive motors and thus avoid large scale damage of equipments of rolling mill.
Another object of the present invention is directed to developing a system for detection and control of failure of torque transmission and skidding for 2-High blooming mills adapted to fast detection of failure of torque transmission due to breakage of spindle.
A further object of the present invention is directed to developing a system for detection and control of failure of torque transmission and skidding for 2-High blooming mills adapted to fast detection of Metal Skidding in 2-High Rolling Mills.
A still further object of the present invention is directed to developing a system for detection and control of failure of torque transmission and skidding for 2-High blooming mills which is simple and compact in design adapted for uninterrupted feeding of steel stock without affecting rolling rate and production.
A still further object of the present invention is directed to developing a system for detection and control of failure of torque transmission and skidding for 2-High blooming mills which would be capable of protecting the spindly stand housing and associated mechanical parts from severe mechanical stress developed due to skidding phenomenon which is one of the major contributors for mechanical failures in Rolling Stands.
A still further object of the present invention is directed to developing a system for detection and control of failure of torque transmission and skidding for 2-High blooming mills wherein fast detection of metal skidding and/or stopping the drive motors by a relay

operated tripping circuit immediately after spindle breakage avoid extensive secondary damage caused to the H-frame, I Frame, transverse beams of bottom spindle, H frame Foundation column etc.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a system for detection and control of failure of torque transmission and skidding in Twin-motor Two-high Rolling mill stand comprising:
thyristor converter circuitry providing the current feedbacks of top and bottom motors of the main drive in the rolling mill;
an electronic circuit operatively connected to continuously monitor the difference in the currents drawn by Top and Bottom motors of Main Drives in said rolling mill;
a relay means in said circuit adapted to operate based on a current difference exceeding a predetermined setting for a pre-settable time; and
means for tripping/stoppage of drive actuated by said relay.
Another aspect of the present invention is directed to a system for detection and control of failure of torque transmission and skidding comprising
said thyristor converter circuitry providing the current feedbacks of top and bottom motors of the main drive in the rolling mill;
diffrential amplifier means wherein said top motor current and said bottom motor current feedbacks are compared to thereby generate an IDIFF signal;

an absolute value generator means adapted to receive said IDIFF signal to generate an absolute value of the IDIFF signal;
a Comparator means receiving said absolute value of the IDIFF signal and camparing the same with a preset range and adapted to generate signal when the IDIFF signal is not within said preset range;
said relay means adapted to receive the Comparator output and get energized whenever the IDIFF is higher than the pre set range to further activate said means for tripping/stopping of drive.
A still further aspect of the present invention is directed to said system for detection and control of failure of torque transmission and skidding comprising:
applying a contact of said relay means to a timer means adapted to set time range;
timer means contact operatively conneceted to reference withdrawal circuit of said thyristor converter such that when the IDIFF signal exceeds the setting value for a timer set in the timer , the reference is automatically withdrawn and the motor stopped immediately.
According to yet another aspect of the present invention is directed to a system for
detection and control of failure of torque transmission and skidding wherein said
Comparator means is set with a settable reference preferably 2kA to 8kA for said
comparison and said timer setting is set for a time set range of 0 to 1 sec.
Advantageously, in said system for detection and control of failure of torque transmission and skidding, said circuit is adapted to detect the skids at very early stage and withdraws the speed reference from the main drives.
Still further aspect of the present invention is directed to a system for detection and control of failure of torque transmission and skidding wherein said circuit is adapted to operate every time skidding takes place during biting of metals in the rolls.

Importantly, said system for detection and control of failure of torque transmission and skidding is adapted such that chances of Spindle breakage is minimized by early detection of skidding and thereby avoiding transmission of excessive mechanical forces to equipments and support structures.
Also said system for detection and control of failure of torque transmission and skidding is adapted such that if the spindle breaks, the secondary damage to the equipment is minimized by fast initiation of tripping.
According to yet another aspect of the present invention is directed to a method for detection and control of failure of torque transmission and skidding using the system comprising the steps of
monitoring the difference in the currents drawn by Top and Bottom motors of Main Drives in twin motor two high rolling mill;
detecting occurrence of skid or spindle breakage by identifying said current difference (IDiff) value with a pre-determined set range for required activation of the said relay means;
withdrawing the speed reference from the main drives based on early skid detection to thereby minimize the chances of spindle breakage and secondary damage.
The present invention and its objects and advantages and described in greater details with reference to the following non limiting accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: is the graphical plot of the top and bottom motor current following spindle breakage.

Figure 2: is the graphical illustration of plot of the difference in top and bottom motor current against rolling time, during normal rolling operation without metal skidding or spindle breakage.
Figure 3: is the graphical presentation of the difference in top and bottom motor current against rolling time after spindle breakage has occurred.
Figure 4: is the schematic illustration of the electrical circuit diagram for skidding and/or torque transmission failure detection involving a torque transmission failure relay (TTFR).
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
As already described, the present invention is directed to providing a system for online detection and control of torque transmission failure and skidding in 2-High horizontal rolling stand of blooming mills. The detection and tripping of the drive motor of top/bottom roll to avoid spindle breakage and consequential secondary damage is achieved through a relay operated tripping circuit activated by sensing the substantial difference in motor armature current of the top and bottom drive motor, immediately after occurrence of metal skidding or failure of torque transmission due to spindle breakage. Thus the system of the invention is ensuring safe and longer rolling operation in blooming mill minimizing/avoiding spindle breakage or metal skidding and thereby enhancing rolling rate and production.
It is observed from the patterns of current recordings that a significant current difference between top and bottom motor armature currents develop immediately after the spindle breakage. Occurrence of such conditions is a positive indication of failure of transmission of torque to one of the rolls. This led to developing a detection method wherein spindle breakage is detected by continuous comparison of Top and Bottom motor currents. It is observed that during rolling at load and no-load, the maximum difference in the currents of the Top and Bottom motors is normally around 2 to 3.5kA. However, in the event of spindle breakage, the difference become much more than this, and if a tripping could be initiated during such a condition, spindle breakage is detected electrically and automatic

stopping of drives can be implemented. Study of the actual difference in top and bottom motor currents during normal rolling and during spindle broken conditions has been experimentally studied to evaluate the threshold value of current difference for presetting of the relay to ensure reliable tripping ensuring safe operation of rolling plant.
Reference is first invited to the accompanying Figure 1 that shows the plot of the top and bottom motor current for ID and 2D motor following the spindle breakage. The graph shows the current drawn by both the armature of top drive motor and the bottom drive motor independently along with the RPM plotted against time. It may be seen from the graph that the difference between the top and bottom motor current exceeds upto about 8KA during rolling time immediately following occurrence of spindle breakage.
Reference is invited to the accompanying Figure 2 that illustrates the graphical plot of the current difference of top and bottom drive motor against time when the rolling operation is Carried out under normal load/no load conditions, without occurrence of skidding or spindle breakage due to abnormal load/stress distribution. It is noted that the maximum current difference between load and no load condition under normal situation is contained within 2kAto 3.5kA.
Reference is now invited to the accompanying Figure 3 that illustrate the graphical plot of the current difference of top and bottom drive motor against time when there occurred skidding or spindle breakage. It may be observed that the difference of the top and bottom motor armature current is of much higher order when skidding/spindle breakage takes place. The present invention makes use of this current difference parameter for detection and control of the torque transmission failure and skidding detection in blooming mill.
Reference is now invited to the accompanying Figure 4 that schematically illustrate the electrical circuit diagram according to the invention for metal skidding and/or torque transmission failure detection involving a Torque Transmission Failure Relay (TTFR). An electronic circuit has been designed using standard components e.g. a Differential Amplifier, an Absolute Value Generator, a Comparator, a Relay Driver and a Timer.
The armature current feedback is necessary for the operation of closed loop thyristor converter controller for any DC motor. The current feedbacks for top and bottom motors

were therefore available in the existing circuit of the thyristor controller as depicted by the area enclosed within the dotted lines in the Existing Circuit. The current feedback signal of Top Motor (IT) and that of bottom Motor (IB) were tapped for this circuit.
The signals of Top motor current and Bottom motor current feedbacks are compared in the differential amplifier block. The output of the differential amplifier is the IDIFF signal which is positive when IT is more than IB and negative when IB is higher. The amplitude of the IDIFF signal represents the difference in the currents of Top and Bottom motors of the Main Drive.
The IDIFF signal so derived from the differential amplifier is applied to the input of an Absolute Value Generator block whose output is of the same polarity irrespective of whether IT is higher or IB is higher. The absolute value of the IDIFF signal is applied to a Comparator block which compares the value with a settable reference (range of setting 2kA to 8kA). The comparator output changes when the IDIFF becomes more than the setting.
The Comparator output is applied to a relay driver block. The relay energizes whenever the IDIFF is higher than the setting. A contact of this relays is applied to a Timer (Time setting range: 0 to lSec). The timer contact is wired to the existing Reference Withdrawal circuit of the Thyristor Converters. So whenever the IDIFF signal exceeds the setting value for a time set in the timer, the Reference is automatically withdrawn and the motors are stopped immediately.
This circuit continuously monitors the difference in the currents drawn by Top and Bottom motors of Main Drives. In case the difference is more than said predetermined setting for a pre-settable time, the circuit operates a relay, which can be wired for tripping/stoppage of drive. The circuit has been tested in lab under simulated conditions and is found to be 100% reliable. After satisfactory lab performance, the same is put into operation and connected up for control blockage.
The present circuit detects the skids at very early stage and withdraws the speed reference from the main drives. Whenever the metal skids, the operator releases the foot pedal to attempt another bite so he does not even come to know that the skid circuit has operated and reference has been withdrawn and thus his rhythm of operation remains

unaffected. The innovative circuit thus detects skidding reliably without affecting the rolling rate and production and the present scheme eliminates instances of failure of Torque Transmission; however the functionality of the circuit is checked regularly for satisfactory performance.
The innovative circuit of the detection and control system according to the present invention has been embedded in the Main drive Regulation scheme of Blooming and Billet Mill. The same system for detection and control of failure of torque transmission and skidding and its protective electrical circuit is equally suitable for Roughing and Finishing stand main drives of Plate mill.
After implementation, drive parameters and operation of circuit has been closely monitored. Recordings of parameters revealed that the circuit is operating whenever skidding takes place during biting of metals in the rolls.
The circuit detects loss of Torque Transmission to work roll due to failure of spindle and associated parts. The circuit also quickly detects skidding of Metal stock and withdraws speed reference to drive; thereby protecting the spindle, stand housing and associated mechanical parts from severe mechanical stress developed due to skidding phenomenon which is one of the major contributors for mechanical failures in Rolling Stands. In case of skidding occurrence, the operator immediately releases foot pedal and again feeds the stocks without affecting the rolling rate and production.
It is thus possible by way of the present invention to providing an innovative circuit serving dual purposes comprising:
(i) Minimizing chances of Spindle breakage by early detection of skidding and thereby avoiding transmission of excessive mechanical forces; and
(ii) If the spindle breaks at all due to any other reasons like material defects etc, the secondary damage to the equipment shall be minimized by fast initiation of tripping.

The system for detection and control of failure of torque transmission and skidding according to the present invention is thus capable of wide industrial application in steel plants to monitor and control rolling operation to automaticaily safe guard the drive motor and drive system comprising the spindle, stand housing and associated mechanical parts avoiding excess/uneven loading so as to ensure enhanced plant availability and increased production with reduced operation cost.

We Claim:
1. A system for detection and control of failure of torque transmission and skidding in
Twin-motor Two-high Rolling mill stand comprising:
thyristor converter circuitry providing the current feedbacks of top and bottom motors of the main drive in the rolling mill;
an electronic circuit operatively connected to continuously monitor the difference in the currents drawn by Top and Bottom motors of Main Drives in said rolling mill;
a relay means in said circuit adapted to operate based on a current difference exceeding a predetermined setting for a pre-settable time; and
means for tripping/stoppage of drive actuated by said relay.
2, A system for detection and control of failure of torque transmission and skidding as
claimed in claim 1 comprising
said thyristor converter circuitry providing the current feedbacks of top and bottom motors of the main drive in the rolling mill;
differential amplifier means wherein said top motor current and said bottom motor current feedbacks are compared to thereby generate an IDIFF signal;
an absolute value generator means adapted to receive said IDIFF signal to generate an absolute value of the IDIFF signal;
a Comparator means receiving said absolute value of the IDIFF signal and comparing the same with a preset range and adapted to generate signal when the IDIFF signal is not within said preset range;

said relay means adapted to receive the Comparator output and get energized whenever the IDIFF is higher than the pre set range to further activate said means for tripping/stopping of drive.
3. A system for detection and control of failure of torque transmission and skidding as
claimed in anyone of claims 1 or 2 comprising:
applying a contact of said relay means to a timer means adapted to set time range;
timer means contact operatively connected to reference withdrawal circuit of said thyristor converter such that when the IDIFF signal exceeds the setting value for a timer set in the timer, the reference is automatically withdrawn and the motor stopped immediately.
4. A system for detection and control of failure of torque transmission and skidding as claimed in anyone of claims 2 to 3 wherein said Comparator means is set with a settable reference preferably 2kA to 8kA for said comparison and said timer setting is set for a time set range of 0 to 1 sec.
5. A system for detection and control of failure of torque transmission and skidding as claimed in anyone of claims 1 to 4 wherein said circuit is adapted to detect the skids at very early stage and withdraws the speed reference from the main drives.
6. A system for detection and control of failure of torque transmission and skidding as claimed in anyone of claims 1 to 5 wherein said circuit is adapted to operate every time skidding takes place during biting of metals in the rolls.
7. A system for detection and control of failure of torque transmission and skidding as claimed in anyone of claims 1 to 6 wherein said system is adapted such that chances of Spindle breakage is minimized by early detection of skidding and thereby avoiding transmission of excessive mechanical forces to equipments and support structures.
8. A system for detection and control of failure of torque transmission and skidding as claimed in anyone of claims 1 to 7 wherein said system is adapted such that if the spindle breaks, the secondary damage to the equipment is minimized by fast initiation of tripping.

9, A method for detection and control of failure of torque transmission and skidding using he system as claimed in anyone of claims 1 to 8 comprising the steps of
monitoring the difference in the currents drawn by Top and Bottom motors of Main Drives
in twin motor two high rolling mill;
detecting occurrence of skid or spindle breakage by identifying said current difference (IDiff) value with a pre-determined set range for required activation of the said relay means.;
withdrawing the speed reference from the main drives based on early skid detection to thereby minimize the chances of spindle breakage and secondary damage.
10. A system for detection and control of failure of torque transmission and skidding in Twin-motor Two-high Rolling mill and a method of implementation thereof substantially as herein described and illustrated with reference to the accompanying drawings.