AN IMPROVED SYSTEM FOR AUTOMATIC CONTROL OF ROLL COOLANT IN
COLD ROLLING MILL.
FIELD OF THE INVENTION
The present invention relates to an improved control system for roll coolant emulsion
system of cold rolling mill. More particularly, the present invention relates automatic
control of emulsion in Tandem Mill of Cold Rolling Mill as per the requirement of mill
operation.
BACKGROUND AND PRIOR ART OF THE INVENTION
Research & Development Centre for Iron and Steel (RDCIS), Ranchi and Bokaro Steel
Plant (BSL), Bokaro have designed, installed and commissioned a project "Automatic
control of emulsion system in stand # 5 of Tandem Mill# 2, CRM, BSL." System is being
utilized successfully since commissioning from March 2015 at Tandem Mill#2, Cold
Rolling Mill, Bokaro Steel Plant.
Tandem Mill # 2 in Cold Rollin Mill, Bokaro Steel Plant is a 4hi five stand, 1420mm mill
commissioned in 1989. The roll coolant emulsion system of Tandem Mill (TM) #2 is
meant for cooling of work rolls only during roll bite to prevent heating of rolls. This
requires flow control of emulsion during threading and intermittent stoppages of mill. In
absence of flow control system, the motor were made to run at rated rpm during this
period and the emulsion was bypassed into the tank through bypass line. This resulted
in considerable wastage of electrical energy. Frequent starting and stopping of pumps
during intermittent stoppage is also not desirable as it would lead to motor failure due to
heating as these motors are continuous duty motors. Moreover, poor control of roll
coolant emulsion by the valves resulted in leakage & carryover of emulsion after stand
5. This contributed to considerable wastage of emulsion & quality problems like black
patches as well.

RDGIS commissioned a Variable voltage variable frequency (VWF) drive based
automatic control of emulsion system in stand #5. The new VWF drive system has
been interfaced with existing mill automation. The new system offers different variable
speeds to the emulsion pumps so as to run at different speeds as per requirements of
the mill operation. Mill speed is generated through Programmable Logic Controller
(PLC) system of mill automation. Mill speed is then compared with the set speed &
accordingly reference output is given to the drive. This system has helped in
considerable savings in electrical energy. The frequent start-stop, if required will not
damage the motor because of the soft starting feature (ramp time) inbuilt in the drive. It
will also help in increasing the life of the pumps and motors. Flow control of emulsion as
per different grades of CR sheets to be rolled is also feasible through this system.
In the prior art U.S. Pat. No. 5,201,132 discloses a system and an associated method
for cooling, heating, wiping or drying strip, such as metal strip. The disclosure of this
patent is incorporated herein by reference. It provides the use of a single unit or a pair
of units having a source of gas, a plenum, and a plurality of fixed nozzles which are
adapted to direct gas onto a passing strip.
Another prior art U.S. Pat. No. 4,076,222 discloses the use of a solid curtain of water to
cool metal strip stock emerging from a rolling mill. Another prior art U.S. Pat. No.
5,390,900 discloses a system wherein a curtain of water is employed to cool a metal
strip with air used intermittently to divert the water from cooling impingement on the
strip.
In another prior art U.S. Pat. No. 4,120,455 discloses cooling apparatus for cooling
metal sections through the spraying of a mixture of gas and liquid. This prior art system
provides an air inlet opening, a water inlet opening in communication with the air inlet
opening, and an outlet opening. Water droplets generated moves generally radially into
the axial air flow. In yet another prior art U.S. Pat. No. 4,226,108 discloses the use of
two hollow caissons, one inside the other, with sprayers adapted to effect atomizing of
the water by the air.

OBJECTS OF THE INVENTION
One object of the present invention is to overcome the disadvantages / drawbacks of
the prior art.
A basic object of the present invention is to provide automatic control of roll coolant in
cold rolling mill.
Another object of the present invention is to optimize the set points to synchronize
the speed of pumps with mill operation.
Yet another object of the present invention is to interface the VVVF drive with the
existing mill automation platform.
Yet another object of the present invention is to provide the VVVF drive controlled pump
systems which offer pressure control with energy savings and the ability to match the
flow consumption profile without waste.
These and other advantages of the present invention will become readily apparent from
the following detailed description taken in conjunction with the accompanying drawings.
According to one of the aspect of the present invention there is provided an improved
system for automatic control of roll coolant and the said system comprising: at least two
centrifugal Pumps means is substantially installed in the two emulsion networks of Roll
coolant circuits; at least two squirrel cage induction motors means substantially installed
with the pumps in two emulsion networks of Roll coolant circuits; at least two VWF
Drives means substantially installed to drive motors of the emulsion pumps in two
emulsion networks of Roll coolant circuits; at least one programmable logic controller
means installed in the control room for incorporating the operational logic of roll coolant
emulsion system & generating different speed reference for VWF drives; and at least
one controller means installed in the control room for the controlling and monitoring the
operation of emulsion system.
In an exemplary embodiment, the two centrifugal Pumps and two squirrel cage
induction motors are installed in the two emulsion networks. One emulsion network is
always kept as hot standby.

In another embodiment a VVVF Drive panel is provided comprising of drive controller,
Power modules, digital input & output cards, analog input & output card and
communication module. The VVVF drive is interfaced with PLC of mill automation
through cables. Mill speed is generated through PLC system of mill automation. Mill
speed is then compared with the set speed & accordingly reference output was given to
the VVVF drive.
In another embodiment VVVF Drive and the PLC is connected through networking by
means of communication cable and control cables. The control system further includes
a screen display for real time controlling and monitoring of entire emulsion network.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Other features as well as the advantages of the invention will be clear from the following
description.
Fig. 1 illustrates a table showing steps of speed as per mill operation in accordance with
the present invention;
Fig. 2 illustrates the control logic flow chart in accordance with the present invention;
Fig. 3 illustrates the single line diagram of the VVVF drive scheme in accordance with
the present invention;
Fig. 4 illustrates the Digital input & output connection of drive in accordance witn tne
present invention;
DETAILED DESCRIPTION
The present invention relates an improved system for automatic control of roll coolant in
cold rolling mill.
The present system consists of centrifugal Pumps, squirrel cage induction motors and
VVVF Drives interfaced with the existing mill automation. The basic design &

engineering of the VFD based automatic emulsion control system was carried out. The
operational logic was developed based on the shop logistic (Fig. 1). This figure depicts
a table showing different steps of emulsion pumps as per requirement of mill operation.
These steps offer pressure control of roll coolant with energy savings and the ability to
match the flow consumption profile without waste; it was decided to interface the new
VVVF drive with the existing automation platform in TM#2. Based on the scheme, digital
input & output was finalized so as to cater the requirement of mill operation and
interface the new drive system with existing automation system of the mill (Fig. 3 & 4).
Fig. 3 shows the single line diagram of the drive. This figure shows power circuit and its
components. As the pumps will run in variable speeds though drive, selection of pump
sets with inverter grade motors was made. The rating of the drive was selected so that
the drive is able to cater to 150% of the full load current of the motor. Dimension &
capacity of pump set was calculated based on parameters of existing emulsion network.
Digital & Analogue l/Os of drives were connected to the remote l/o panel of the existing
PLC (Fig. 4). Fig. 4 depicts connection of input & output connection of the drive. This
picture also depicts interfacing of the drive with mill automation. The input signals are of
control commands like start, stop, different steps of speed signals etc. Programme of
the existing PLC was modified to interface the new system in mill automation. Mill speed
is generated through PLC system of mill automation (Fig. 2). The said figure shows
control logic flow chart incorporated in PLC and depicts how the PLC gives control
command to the drive for start, stop & different steps of speeds. Mill speed is then
compared with the set speed & accordingly reference output is given to the drive. Finally
the total system was integrated & fine tuned including further appropriate change in PLC
and drive logic.
The following design parameters were taken into consideration in designing the an
improved system for automatic control of roll coolant in cold rolling mill.



Numerous modifications may be made to the present invention,
intended scope hereof. Thus, it should be apparent that there has been provided in
accordance with the present invention an improved system for automatic control of roll
coolant in cold rolling mill and advantages set forth above. Although the invention has
been described in conjunction with specific embodiments thereof, it is evident that many
alternatives, modifications and variations will be apparent to those skilled in the art.
Accordingly, it is intended to embrace all such alternatives, modifications and variations
that fall within the spirit and broad scope of the appended claims.

WE CLAIM
1. An improved system for automatic control of roll coolant in cold rolling mill, said
system comprising:
at least two centrifugal Pumps means is installed in the two emulsion networks
of Ro 11 coolant circuits;
at least two squirrel cage induction motors means installed with the pumps in two
emulsion networks of Roll coolant circuits;
at least two VVVF Drives means installed to drive motors of the emulsion pumps
in two emulsion networks of Roll coolant circuits;
at least one programmable logic controller means for incorporating the
operational logic of roll coolant emulsion system & generating different speed
reference for VVVF drives; and
at least one controller operably connected to the system for controlling and
monitoring of operation of roll coolant emulsion system.
2. The system as claimed in claim 1, wherein an appropriate monitoring and
automatic control system has been designed for roll coolant emulsion system.
3. The system as claimed in claim 1, wherein the operational logic has been
programmed for optimizing different steps of speed of emulsion pump as per
requirement of mill operation.
4. The system as claimed in claim 1 & 2, wherein a human machine interface
screen has been designed for monitoring & control of the roll coolant emulsion
system.

5. The system as claimed in claim 1, wherein emulsion pumps are controlled in
steps as per requirement of mill operation.
6. The system as claimed in claim 3, wherein the steps offer pressure control of roll
coolant with energy savings and the ability to match the flow consumption profile
without waste.