This document provides a summary of a project on wringer roll position control in a steel mill. It discusses the objectives of understanding the wringer rolling process, identifying potential problems, and controlling roll position electronically. It describes the wringer roll and its use in cold rolling steel sheets. It explains that linear variable differential transformers (LVDTs) are used to precisely measure the position of the wringer roll piston and ensure the proper tension is maintained on steel sheets passing through the roll. The LVDT converts displacement of the piston into a proportional voltage for monitoring on screens and controlling the process.

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Wringer roll Position control
Project by: Shashank kumar
(BIT Mesra, Ranchi)
VT Number: VT20152940
Project guide: Sumit Ganguly
Manager, Mills & Utilities, Electrical
Maintenance PLTCM,CRM
Company: Tata Steel Ltd. Jamshedpur.
Program: Prashikshan-2015.

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Contents:
1. What is Rolling ?
2. Types of Rolling and its uses.
3. Advantages of cold rolling over hot rolling.
4. Wringer roll and it‟s Working.
5. Position control methods in Winger roll
6. Why LVDT?
7. Control mechanism and working of LVDT
8. Application/Advantages of LVDT.
9. References

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Objectives:
# This project provides information about Wringer rolling process and its importance in steel
industry for manufacturing of high tensile strength and smooth surface iron sheets.
# Identification of potential problems occurring while rolling in wringer rolls due to friction
and other reasons and solution of the problem.
# Understanding electronics behind position control of Wringer roll.

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1. What is Rolling?
The process of plastically deforming metals into sheets by passing it betweens rolls is
generally referred as rolling. Rolling is the most widely used forming process, which provides
high production and close control of final product.The metal under roll is subjected to high
compressive stresses as a result of the friction between the rolls and the metal surface.[3]
2. Types of Rolling and its uses.
Rolling[2] can mainly be divided into two types:
1) Hot rolling 2) Cold rolling.
Hot rolling:
The initial breakdown of ingots into blooms and billets is generally done by hot-rolling .This is
followed by further hot rolling into plate, sheet, rod, bar, pipe, rail.
Cold rolling:
Cold rolling played a major role in industry by providing sheet, strip, foil with good surface
finishes and increased mechanical strength with closed control of product dimensions.

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3. Advantages of cold rolling over hot rolling.
When it comes down to making cold rolled sheets and hot rolled sheets, the method is quite
similar. They both are made from same materials and they both go from similar
manufacturing process except for one crucial part. Cold rolled steel is rolled, or passed
through at least two rollers at room temperature until it forms the desired shape and
dimensions. And hot rolled steel is rolled at or above its re-crystallization temperature,
which is at 1,700 °F.
The physical properties of hot rolled steel and cold rolled steel vary greatly.
4. Wringer rolls.
The production process of cold rolling steel/ stainless [1]
Steels annealing and pickling line consists of mainly following sections:
1. Entry section 2.Process section 3.Exit section 4.Shearing line section.
1.Entry section consists of Payoff reel, Threading belt/Double cut shear, Welding machine,
Entry loop tower, Side trimmer.
2.Process section consists of Cleaning Unit, Pickle Units, Plating Units, Strip Marking,
Wringer roll, Reflow Units, Chemical Treatment Units, Electrostatic Oiled.
3.Exit section consists of Exit Loop Tower, Mirror Inspection, Thickness Gauge & Pinhole
Detector, Tension Reel.
4.Shearing line section consists of Coil car and payoff reel, Mirror and automatic inspection
unit, Drum shear unit, Conveyor System, Pilling System Units, Delivery Roller Table.
*We are here interested in Wringer roll of process section.

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4.1. Working.
The wringer roll is subjected to rubber lining are constituted of a pair of the stepped wringer
rolls. The wringer rolls are thereby so constituted that the rolls can follow up a change in the
width of the strip.
Wringer rolls ensure minimal residual oil levels on strip surfaces in all kinds of cold rolling
mills. This allows you to run your duo, four-high, Z-high or 20 roll stand at top speed for
highest productivity. Furthermore, metal chips and other particles are absorbed by the
porous fibre structure of the nonwoven covering, preventing surface damage of the strip.
The high friction coefficient guarantees permanent synchronous running with the strip and
the risk of aquaplaning is eliminated. Wringer rolls provide exact strip speeds as measuring
rolls and draw even the oiliest of strips as in- feed drivers.

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5. Position control methods in Winger roll
In wringer rolling method, as we know that the roller of wringer roll is made up of an oil-
draining special covering made of non-woven synthetic fiber to ensure correct strip tension
on the running steel. This strip tension is responsible for the deformation of the rolling steel
into required Cold rolled stainless steel (AISI 200, 300, 400 series) with specific Thickness
(say 2-7.0mm HR, .3-5.0mm CR) and Width (say 600-1,550mm).Wringer roll‟s strip tension
is controlled by the double acting pneumatic cylinder with precise positioning and vertical
loading and this tension is fixed for the required production set (with particular specifications)
and expected to work accordingly for the fixed span of time
The pneumatic control systems have played the important roles in the industrial
automation equipments owing to the following advantages -low cost, clean of the working
environments, easy in power transfer, and so on. In recent years, high accuracy and high
speed systems are growing up rapidly, and are important in steel industry and other high-
tech industries.
Even though using pneumatic control systems there are some anomaly in the control
mechanism of wringer roll. This can be better understood with the help of example. Let‟s say
at the time of installation the radius to the roller was (x+a) cm but after some production
cycle due to friction force „F‟ between the surface of roller and the running steel ,the outer
surface of the roller start degrading and after some production cycle the roller‟s radius get
reduced to say x cm. Due to this reduction in the roller‟s radius, strip tension on the running

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steel decreases and so the vertical loading by the double acting pneumatic cylinder
increases by „a‟. The increment in the vertical loading is controlled by the pneumatic control
system which is beyond the scope of this project. Our main goal is the analysis of the
deformation in the wringer roll and continuous display of the any change in the piston
position of the pneumatic cylinder.
Here for the above goal we have applied LVDT for display of change in position of the piston
of pneumatic cylinders. Theory of the LVDT is explained later. In present case, when there is
„a‟ times decrement in the radius of the roller then piston of the pneumatic cylinder which is
attached to the axis of the roller (through which vertical load is provided) is also displaced to
„a‟ cm length in downward position. The core of LVDT, attached with the piston as in
following figure also moves „a‟ cm which converts the linear displacement into voltage form
which is then displayed on the screen via signal conditioners.
Signal conditioners amplify the voltage output from the LVDT to a desired value for proper
display and a limiting value of the decrement in the radius of the roller is also set in the
signal conditioner section and whenever value exceeds the limiting value(set by the
operator) then an alarm will be set and required action will be taken accordingly by the
responsible person.

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6. Why LVDT?
Linear Variable Differential Transformer
Introduction
LVDTs are robust, absolute linear position/displacement transducers; inherently frictionless,
they have a virtually infinite cycle life when properly used. As AC operated LVDTs do not
contain any electronics, they can be designed to operate at cryogenic temperatures or up to
1200 °F (650 °C), in harsh environments, under high vibration and shock levels. LVDTs have
been widely used in applications such as power turbines, hydraulics, automation, aircraft,
satellites, nuclear reactors, and many others. These transducers have low hysteresis and
excellent repeatability.
The LVDT converts a position or linear displacement from a mechanical reference (zero, or
null position) into a proportional electrical signal containing phase (for direction) and
amplitude (for distance) information. The LVDT operation does not require an electrical
contact between the moving part (probe or core assembly) and the coil assembly, but
instead relies on electromagnetic coupling.

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7. Control mechanism and working of LVDT
One type of positional sensor that does not suffer from mechanical wear problems is the
“Linear Variable Differential Transformer” or LVDT for short. This is an inductive type
position sensor which works on the same principle as the AC transformer that is used to
measure movement. It is a very accurate device for measuring linear displacement and
whose output is proportional to the position of its moveable core.
It basically consists of three coils wound on a hollow tube former, one forming the primary
coil and the other two coils forming identical secondaries connected electrically together in
series but 180o
out of phase either side of the primary coil.
A moveable soft iron ferromagnetic core (sometimes called an “armature”) which is
connected to the object being measured, slides or moves up and down inside the tubular
body of the LVDT.
A small AC reference voltage called the “excitation signal” (2 – 20V rms, 2 – 20kHz) is
applied to the primary winding which in turn induces an EMF signal into the two adjacent
secondary windings (transformer principles).
If the soft iron magnetic core armature is exactly in the centre of the tube and the windings,
“null position”, the two induced emf‟s in the two secondary windings cancel each other out as
they are 180o
out of phase, so the resultant output voltage is zero. As the core is displaced
slightly to one side or the other from this null or zero position, the induced voltage in one of
the secondaries will be become greater than that of the other secondary and an output will
be produced.
The polarity of the output signal depends upon the direction and displacement of the moving
core. The greater the movement of the soft iron core from its central null position the greater
will be the resulting output signal. The result is a differential voltage output which varies
linearly with the cores position. Therefore, the output signal from this type of position sensor
has both an amplitude that is a linear function of the cores displacement and a polarity that
indicates direction of movement.
The phase of the output signal can be compared to the primary coil excitation phase
enabling suitable electronic circuits such as the AD592 LVDT Sensor Amplifier to know
which half of the coil the magnetic core is in and thereby know the direction of travel.
When the armature is moved from one end to the other through the centre position the
output voltages changes from maximum to zero and back to maximum again but in the
process changes its phase angle by 180 deg‟s. This enables the LVDT to produce an output
AC signal whose magnitude represents the amount of movement from the centre position
and whose phase angle represents the direction of movement of the core.

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The Linear Variable Differential Transformer (Diagram)

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8. Application/Advantages of LVDT.
A typical application of a linear variable differential transformer (LVDT) sensor would be as a
Displacement transducer, where the small displacement is then converted into a readable
voltage signal by the sensor.
Advantages of the LVDT compared to a resistive potentiometer are that its linearity, that is
its voltage output to displacement is excellent, very good accuracy, good resolution, high
sensitivity as well as frictionless operation. They are also sealed for use in hostile
environments (such as in the wringer roll‟s environment).
The LVDT is designed with long slender coils to make the output voltage essentially linear
over displacement up to several inches (several hundred millimetres) long.
The LVDT can be used as an absolute position sensor. Even if the power is switched off, on
restarting it, the LVDT shows the same measurement, and no positional information is lost.
Its biggest advantages are repeatability and reproducibility once it is properly configured.
Also, apart from the uni-axial linear motion of the core, any other movements such as the
rotation of the core around the axis will not affect its measurements.
Because the sliding core does not touch the inside of the tube, it can move without friction,
making the LVDT a highly reliable device. The absence of any sliding or rotating contacts
allows the LVDT to be completely sealed against the environment.
LVDTs are commonly used for position feedback in servomechanisms, and for automated
measurement in machine tools (wringer roll) and many other industrial and scientific
applications.

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9. References
[1]The Difference Between Hot Rolled Steel & Cold Rolled Steel by capital steel and wire.inc
[2]Suction Roll Training by Bill Frawley
[3]Rolling of metals lecture IIT,mandi.
[4]Wikipedia.