1. BASICS OFBASICS OF
AUTO GAUGE CONTROLAUTO GAUGE CONTROL

2. ..
IntroductionIntroduction
RollingRolling is a is a metal formingmetal forming process in which metal stock is passed through a pair of rolls. process in which metal stock is passed through a pair of rolls.
Rolling is classified according to the temperature of the metal rolledRolling is classified according to the temperature of the metal rolled. If the temperature of the. If the temperature of the
metal is above its metal is above its recrystallizationrecrystallization temperature ( temperature ( RecrystallizationRecrystallization is usually accompanied
by a reduction in the strength and hardness of a material and a simultaneous increase in the
ductility), then the process is termed as then the process is termed as hot rollinghot rolling. If the temperature of the metal is below. If the temperature of the metal is below
its recrystallization temperature, the process is termed as its recrystallization temperature, the process is termed as cold rollingcold rolling
The term Cold Rolling is so called because it is working the metal below its recrystallizationThe term Cold Rolling is so called because it is working the metal below its recrystallization
temperature is around 0.4 Tm – 0.5 Tm (where Tm is melting point in degrees Kelvin) in mosttemperature is around 0.4 Tm – 0.5 Tm (where Tm is melting point in degrees Kelvin) in most
of pure metals. Usually Cold Rolling is done at ambient temperature. of pure metals. Usually Cold Rolling is done at ambient temperature.
Cold rolling is a process of reducing thickness of metallic strips by passingCold rolling is a process of reducing thickness of metallic strips by passing
it through rolling mill. The rolling mill consists mainly of rolls drives, bearings, mill-springit through rolling mill. The rolling mill consists mainly of rolls drives, bearings, mill-spring
and housing for these parts.and housing for these parts.
The electric motors drive the work rolls and the torque imparted by the rollsThe electric motors drive the work rolls and the torque imparted by the rolls
on metal provides the load to bring about reduction in thicknesson metal provides the load to bring about reduction in thickness .The reduction in thickness.The reduction in thickness
goes into increase in length without much lateral spread. Flow of coolant is applied togoes into increase in length without much lateral spread. Flow of coolant is applied to
prevent rolls from heating due to friction between rolls and strips.prevent rolls from heating due to friction between rolls and strips.
Frictional force acts on the work piece and is opposite in directionFrictional force acts on the work piece and is opposite in direction
to motion of strips .At entrance the frictional force acts in forward to motion of strips .At entrance the frictional force acts in forward
direction and draws a strip in to rolls. Tension from entrance asdirection and draws a strip in to rolls. Tension from entrance as
well as exit side helps to keep neutral point within the arc ofwell as exit side helps to keep neutral point within the arc of
contact so that metal just does not slip. Neutral point is thecontact so that metal just does not slip. Neutral point is the
point where opposite forces nullify each other.point where opposite forces nullify each other.

3. TYPES OF MILLSTYPES OF MILLS
1. Tandem1. Tandem
There is a payoff reel at the entry and a coiler at the exit. Between the stands areThere is a payoff reel at the entry and a coiler at the exit. Between the stands are
dancer rolls, and the speed of each stand is adjusted automatically .Tandemsdancer rolls, and the speed of each stand is adjusted automatically .Tandems
have two, three, or four mill stands, depending on the total reduction to perform.have two, three, or four mill stands, depending on the total reduction to perform.
However, the total reduction is performed in one passHowever, the total reduction is performed in one pass..
2 .Reversing mill2 .Reversing mill
If the production schedule has many different kinds of material, a reversing mill isIf the production schedule has many different kinds of material, a reversing mill is
better .The rolling direction is alternatively from left to right and from right to left.better .The rolling direction is alternatively from left to right and from right to left.
The payoff reel allows the operator to prepare the next strip during rolling. It isThe payoff reel allows the operator to prepare the next strip during rolling. It is
used as an uncoiler only during the first pass.used as an uncoiler only during the first pass.

4. There are two types of reversing 6-high mill:There are two types of reversing 6-high mill:
1. Two work rolls and four back-up rolls (type 1-2) .1. Two work rolls and four back-up rolls (type 1-2) .
The horizontal force due to the torque is absorbedThe horizontal force due to the torque is absorbed
by the back-up rolls in both rolling directions. Butby the back-up rolls in both rolling directions. But
the distribution of the R.S.F. on the back-up rolls isthe distribution of the R.S.F. on the back-up rolls is
not favorable. This design is rarely used now.not favorable. This design is rarely used now.
2. Six rolls on the same vertical axis . For example, two2. Six rolls on the same vertical axis . For example, two
work rolls (Dia=385), two intermediate rollswork rolls (Dia=385), two intermediate rolls
(Dia= 440), and two back-up rolls (Dia=1200)(Dia= 440), and two back-up rolls (Dia=1200)
( This dia is used in our Mill)( This dia is used in our Mill)

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6. AUTOMATIC GAUGE CONTROL
Many factors cause final thickness to vary. Therefore, in order to get aMany factors cause final thickness to vary. Therefore, in order to get a
thickness that falls within required tolerances, it is necessary to control it.thickness that falls within required tolerances, it is necessary to control it.
Corrections may be carried out by action either on the screwdownCorrections may be carried out by action either on the screwdown
or on the tension.or on the tension.
TensionTension
Back tension (at the entry side) and front tension (at the exit
side) are applied to the strip. The back tension has the reverse
action: force is moved downstream. The front tension increases the
FWD SLP, and force is moved upstream.
NOTE : Mills having small work rolls (for example, 20-high mills)
need high tensions.
USE OF TENSION
· to make easier reduction
· to improve flatness
· to keep the strip centered in the rolling axis (to avoid shifting)

7. ..
Manipulation of thickness through tension works as follows:Manipulation of thickness through tension works as follows:
· Increase the tension (back and front) if the exit thickness is larger· Increase the tension (back and front) if the exit thickness is larger
than required.than required.
· Decrease the tension (back and front) if the exit thickness is smaller· Decrease the tension (back and front) if the exit thickness is smaller
than required.than required.
Generally, tension variation is limited to 20%. If this limit is reached, anGenerally, tension variation is limited to 20%. If this limit is reached, an
action on the screwdown is triggered.action on the screwdown is triggered.
Manipulation of tension in order to alter thickness is rarely used.Manipulation of tension in order to alter thickness is rarely used.
It advantage is its high precision. But its drawbacks are many: onlyIt advantage is its high precision. But its drawbacks are many: only
small thickness variations can be corrected, especially on “hard”small thickness variations can be corrected, especially on “hard”
materials, and the correction speed is often slow. This method can onlymaterials, and the correction speed is often slow. This method can only
be used for “soft” materials and to correct small and rare variationsbe used for “soft” materials and to correct small and rare variations
(i.e., in very particular cases).(i.e., in very particular cases).
Therefore, we shall focus on the method that acts on the rollTherefore, we shall focus on the method that acts on the roll
gap, that is to say, alteration of the screwdown.gap, that is to say, alteration of the screwdown.

8. Roll Separating Force (R.S.F.)
The basis of understanding rolling is knowing the forces created by rolling, theThe basis of understanding rolling is knowing the forces created by rolling, the
main one being Roll Separating Force(R.S.F.). During rolling, the strip ismain one being Roll Separating Force(R.S.F.). During rolling, the strip is
deformed, but so is the mill housing. The difference isdeformed, but so is the mill housing. The difference is
that the deformation of the strip is permanentthat the deformation of the strip is permanent
(plastic) while the deformation of the mill is temporary(plastic) while the deformation of the mill is temporary
(elastic).(elastic).
Roll Separating force is directly proportionalRoll Separating force is directly proportional
to width of the sheet. The strip acts as a wedge betweento width of the sheet. The strip acts as a wedge between
the two rolls and creates the forcesthe two rolls and creates the forces FF andand FF (Fig 2) . This(Fig 2) . This
is the R.S.F.is the R.S.F.
All parts of the housing experience R.S.F. For a given Fig 2All parts of the housing experience R.S.F. For a given Fig 2
mill, the higher the reduction and the harder the material,mill, the higher the reduction and the harder the material,
the higher the R.S.F.the higher the R.S.F.
The R.S.F. is uniformly distributed along the width of the stripThe R.S.F. is uniformly distributed along the width of the strip
( Fig 3 ) and is proportional to the strip width.( Fig 3 ) and is proportional to the strip width.
Fig 3Fig 3

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The consequences of R.S.F. are:
· roll bending (Fig 4).
· a shearing effect on the necks of the rolls.
(Fig 4).
· roll flattening: the rolls are flattened where
they make contact with the strip as well as
with any other roll.
· deformation of the housing: some parts are in (Fig
4).
compression, others in tension.
. an axial force on the rolls ( Fig 5), if the strip is thicker on one side
than on the other.
Fig 5.Fig 5.

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With a constant passive gap, let’s say 1 mm, several strips thicker thanWith a constant passive gap, let’s say 1 mm, several strips thicker than
1 mm are rolled. For each case, the separating force and the exit1 mm are rolled. For each case, the separating force and the exit
thickness are plotted on a diagram.thickness are plotted on a diagram.

11. ..
Test aTest a::
The exit thickness is 1.2 mm.The exit thickness is 1.2 mm.
The separating force is 150 tons.The separating force is 150 tons.
Test b:Test b:
The exit thickness is 1.4 mm.The exit thickness is 1.4 mm.
The separating force is 300 tons.The separating force is 300 tons.
In test a, the rolling mill deformation was 0.2 mm (active gap –In test a, the rolling mill deformation was 0.2 mm (active gap –
passive gap). In test b, the deformation was the double: 0.4 mm; thepassive gap). In test b, the deformation was the double: 0.4 mm; the
separating force was also the double: 300 tons.separating force was also the double: 300 tons.
The rolling mill undergoes an elastic deformation since it comesThe rolling mill undergoes an elastic deformation since it comes
back to its original shape when the separating force is zero (otherwiseback to its original shape when the separating force is zero (otherwise
it would be destroyed). In all elastic deformation, the deformation isit would be destroyed). In all elastic deformation, the deformation is
proportional to the force. Therefore, the 1 mm abscissa (passive gap)proportional to the force. Therefore, the 1 mm abscissa (passive gap)
and points A and B are on a straight line.and points A and B are on a straight line.
The same series of tests performed with a different gap, i.e., 2The same series of tests performed with a different gap, i.e., 2
mm, gives a line parallel to the first line: always the same deformationmm, gives a line parallel to the first line: always the same deformation
under the same force.under the same force.

12. Gauge PLCMMS PC
Gauge PC
ABB PLC
HMI PC
(Wonderware &
Omni Server)
Profibus Cable
Com Port comm.
Ethernet Comm.
Ethernet Comm.
Gauge C-Frame &
RIO Panel
Screen Cable
Special Signal Cable
GAUGE TRANSFER SYSTEM

13. Hydraulic Automatic GaugeHydraulic Automatic Gauge
Control SystemsControl Systems
Conventional hydraulic gaugeConventional hydraulic gauge
control systems work on a complexcontrol systems work on a complex
electro-mechanical spindle principle.electro-mechanical spindle principle.
However, this is associated withHowever, this is associated with
relatively long response times,relatively long response times,
extensive maintenance and inaccurateextensive maintenance and inaccurate
gauge (roll gap) settings. Manygauge (roll gap) settings. Many
system operators are modernizingsystem operators are modernizing
their installations and convertingtheir installations and converting
them at the same time. Nowadaysthem at the same time. Nowadays
practically all modern systempractically all modern system
builders rely on automatic hydraulicbuilders rely on automatic hydraulic
gauge control systems.gauge control systems.

14. HAGC CylindersHAGC Cylinders

15. ..
What is Gauge?
GaugeGauge - is a measuring instrument for measuring and indicating a quantity such as- is a measuring instrument for measuring and indicating a quantity such as
the thickness of strips or the amount of oil etc.the thickness of strips or the amount of oil etc.
Thickness gages are used to make precise dimensional cross sectionThickness gages are used to make precise dimensional cross section
measurements on a wide variety of coatings and materials including steel, plastic,measurements on a wide variety of coatings and materials including steel, plastic,
glass, rubber, ceramics, paint, electroplated layers, enamels etc. There are manyglass, rubber, ceramics, paint, electroplated layers, enamels etc. There are many
mechanical gaging, nondestructive and destructive techniques available tomechanical gaging, nondestructive and destructive techniques available to
accomplish this task: IR or nuclear gauges, eddy current, magnetic particle, laser,accomplish this task: IR or nuclear gauges, eddy current, magnetic particle, laser,
ultrasonic, X-ray, are only a few of the many techniquesultrasonic, X-ray, are only a few of the many techniques
Automatic gauge control
Automatic Gauge Control (AGC) is a closed loop control function designed toAutomatic Gauge Control (AGC) is a closed loop control function designed to
regulate thickness at the exit of the rolling mill stand to increase the thicknessregulate thickness at the exit of the rolling mill stand to increase the thickness
accuracy. Auto gauge control is nothing but the gauge monitoring and the amountaccuracy. Auto gauge control is nothing but the gauge monitoring and the amount
of load to be applied by loading cylinder to get final thickness. To this process toof load to be applied by loading cylinder to get final thickness. To this process to
happen by automation we need some factors to be measured during rollinghappen by automation we need some factors to be measured during rolling
process. AGC mainly controls the loading of cylinder with respect to the thicknessprocess. AGC mainly controls the loading of cylinder with respect to the thickness
to be obtained.to be obtained.
AGC depends on main four factorsAGC depends on main four factors
 Thickness feed-forward controlThickness feed-forward control
 Thickness feedback controlThickness feedback control
 Mass flow control.Mass flow control.
 Speed feed-forward controlSpeed feed-forward control

16. Thickness feedback controlThickness feedback control ::
The basic control strategy is thickness feedback (monitor control) based on theThe basic control strategy is thickness feedback (monitor control) based on the
measured thickness deviation at the exit side of the mill.measured thickness deviation at the exit side of the mill.
The delay time, transport of the strip from the roll gap to theThe delay time, transport of the strip from the roll gap to the
thickness gauge, essentially determines the control system’s dynamicthickness gauge, essentially determines the control system’s dynamic
response, particular at low rolling speed. The software package provides with aresponse, particular at low rolling speed. The software package provides with a
predictive model based option to improve the dynamic behavior of thepredictive model based option to improve the dynamic behavior of the
thickness feedback controller significantly.thickness feedback controller significantly.
Thickness feed-forward controlThickness feed-forward control
With a thickness gauge at the entry side of the roll gap, theWith a thickness gauge at the entry side of the roll gap, the
thickness feed-forward control can be applied. It is able to compensate anythickness feed-forward control can be applied. It is able to compensate any
thickness deviation caused by changing entry thickness.thickness deviation caused by changing entry thickness.
Feedforward control employing entry thickness deviation andFeedforward control employing entry thickness deviation and
entry sheet speed measurements to improve AGC disturbance rejectionentry sheet speed measurements to improve AGC disturbance rejection
performance for incoming thickness variationsperformance for incoming thickness variations
Mass flow controlMass flow control
Using Mass Flow for Automatic Gauge Control to achieve better gaugeUsing Mass Flow for Automatic Gauge Control to achieve better gauge
control during the rolling process in Cold Rolling mills, requires the speed andcontrol during the rolling process in Cold Rolling mills, requires the speed and
thickness of the strip to be measured at the entry and exit of each mill stand.thickness of the strip to be measured at the entry and exit of each mill stand.
The mass of the steel strip flowing into the rolling stand equals the mass of theThe mass of the steel strip flowing into the rolling stand equals the mass of the
strip exiting the stand.strip exiting the stand.

17. ..
For Mass Flow Automatic Gauge control, a X-RAY gauge is used in conjunctionFor Mass Flow Automatic Gauge control, a X-RAY gauge is used in conjunction
with a thickness gauge to perform Mass Flow Automatic Gauge control. Thewith a thickness gauge to perform Mass Flow Automatic Gauge control. The
MFAGC is calculated by:MFAGC is calculated by:
Mass Entry = Mass ExitMass Entry = Mass Exit
Mass = Thickness (T) X Width(W) X Density(D) X Length(L)Mass = Thickness (T) X Width(W) X Density(D) X Length(L)
Length = Speed(S) X Time(T).Length = Speed(S) X Time(T).
Width, Density, and Time are constant.Width, Density, and Time are constant.
Therefore, substituting in the Mass formula;Therefore, substituting in the Mass formula;
TEntry X SEntry = TExit X SExit Or TEntry X (SEntry/SExit)= TexitTEntry X SEntry = TExit X SExit Or TEntry X (SEntry/SExit)= Texit
In summary, you can control the thickness out of a mill stand ifIn summary, you can control the thickness out of a mill stand if
you know the entry side thickness and speed and the exit speed.you know the entry side thickness and speed and the exit speed.
Speed feed-forward controlSpeed feed-forward control
With the speed feed forward control solution velocity depending processWith the speed feed forward control solution velocity depending process
variations are compensated, in particular in the acceleration and decelerationvariations are compensated, in particular in the acceleration and deceleration
phases.phases.

19. ..
Strip thickness controlStrip thickness control
The major difficulty in strip thickness control in cold rolling is the highThe major difficulty in strip thickness control in cold rolling is the high
speed combined with the high accuracy that is required from thespeed combined with the high accuracy that is required from the
control systemcontrol system. The control system will face a "new process" for each. The control system will face a "new process" for each
new strip entering the mill. The strip thickness, which is a major qualitynew strip entering the mill. The strip thickness, which is a major quality
variable, is disturbed by e.g. variations in mill speed, strip hardness,variable, is disturbed by e.g. variations in mill speed, strip hardness,
strip tension and thickness of the incoming strip. Changes in processstrip tension and thickness of the incoming strip. Changes in process
parameters may mean that the process will react in different ways toparameters may mean that the process will react in different ways to
control actions. The purpose of the adaptive functions is to compensatecontrol actions. The purpose of the adaptive functions is to compensate
for these disturbances automatically based on previous rollingfor these disturbances automatically based on previous rolling
experience.experience.

20. The control structure in the AGC system is shown belowThe control structure in the AGC system is shown below

21. ..
Roll gap preset functionRoll gap preset function
First Control has also added a special roll gap setup function basedFirst Control has also added a special roll gap setup function based
on an on-line learning network. The learning network is a form of neural networkon an on-line learning network. The learning network is a form of neural network
which is very fast and is capable of handling large input/output dimensions. Thewhich is very fast and is capable of handling large input/output dimensions. The
learning network will estimate the gap position and force in the next pass basedlearning network will estimate the gap position and force in the next pass based
upon data obtained from previous rolling. After each passupon data obtained from previous rolling. After each pass of rolling, the learningof rolling, the learning
network will be fed with setup data and data from the previous rolling pass. Basednetwork will be fed with setup data and data from the previous rolling pass. Based
on this data, a new roll gap position/roll force is predicted for the next pass or coil.on this data, a new roll gap position/roll force is predicted for the next pass or coil.
At the same time, the network will slightly modify itself depending on the outcomeAt the same time, the network will slightly modify itself depending on the outcome
in the previous pass. In this way, the network is made to ”remember” previousin the previous pass. In this way, the network is made to ”remember” previous
rolling to be used the next time a similar mill setup situationrolling to be used the next time a similar mill setup situation
arises. For the moment, the network is capable of estimating the roll force with anarises. For the moment, the network is capable of estimating the roll force with an
average error of about 6 tons, according to a test run made on data stored in theaverage error of about 6 tons, according to a test run made on data stored in the
production database. Work is still going on to improve the accuracy of prediction.production database. Work is still going on to improve the accuracy of prediction.
The predicted gap/force value is used to preset the roll gap position atThe predicted gap/force value is used to preset the roll gap position at
a starting point for the AGC so that the thickness will be as close to target asa starting point for the AGC so that the thickness will be as close to target as
possible when the rolling starts.possible when the rolling starts.

22. ..
The automatic AGC start up procedureThe automatic AGC start up procedure
The AGC start-up sequenceThe AGC start-up sequence
In order to maximize the amount of strip within tolerance, First Control has developed a newIn order to maximize the amount of strip within tolerance, First Control has developed a new
AGC start-up procedure that will quickly take the thickness to the correct target. NormallyAGC start-up procedure that will quickly take the thickness to the correct target. Normally
the thickness will be within a few μm from the correct target after only 2-5 m rolling, see thethe thickness will be within a few μm from the correct target after only 2-5 m rolling, see the
recording in fig 8. It has been estimated that as much as 20-40 m strip can be gained in thisrecording in fig 8. It has been estimated that as much as 20-40 m strip can be gained in this
way in the final pass. The adaptive control functions normally need about 2-5 m rolling to beway in the final pass. The adaptive control functions normally need about 2-5 m rolling to be
fully adjusted to the process parameters in the new strip. The operator activates thefully adjusted to the process parameters in the new strip. The operator activates the
automatic start-up sequence by switching on the AGC before the strip starts moving. Theautomatic start-up sequence by switching on the AGC before the strip starts moving. The
control system will then activate the different control functions in a specified sequence tocontrol system will then activate the different control functions in a specified sequence to
minimize the setting time to correct output thickness. The control system also uses anminimize the setting time to correct output thickness. The control system also uses an
adaptive mass flow preset function based on previous rolling, which essentially predicts theadaptive mass flow preset function based on previous rolling, which essentially predicts the
mass flow thickness before it can be seen (and corrected) at exit gauge.mass flow thickness before it can be seen (and corrected) at exit gauge.

23. ..
The thick end disturbance reduction.The thick end disturbance reduction.
The AGC stop sequenceThe AGC stop sequence
At the strip ends there are normally fairly large thickness disturbances originatingAt the strip ends there are normally fairly large thickness disturbances originating
from the thickness setting in the preceding passes (”thick end”) or from somefrom the thickness setting in the preceding passes (”thick end”) or from some
problems in the preprocessing. The thick end disturbances are mainly controlledproblems in the preprocessing. The thick end disturbances are mainly controlled
by efficient feedforward control. Since the feedforward control is self-adaptive, itby efficient feedforward control. Since the feedforward control is self-adaptive, it
can remove nearly 100% of the disturbance. Experience from rolling shows thatcan remove nearly 100% of the disturbance. Experience from rolling shows that
the AGC is capable to reduce thickness deviations of an magnitude of 10-30μmthe AGC is capable to reduce thickness deviations of an magnitude of 10-30μm
down to 1-4μm. In this way more strip will be kept within tolerances. Normally, thedown to 1-4μm. In this way more strip will be kept within tolerances. Normally, the
operator will keep the AGC in operation until the very stop of the mill to remove asoperator will keep the AGC in operation until the very stop of the mill to remove as
much thick end disturbances as possible.much thick end disturbances as possible. The AGC will be automatically switchedThe AGC will be automatically switched
off when the minimum speed is reachedoff when the minimum speed is reached..

24. THANKS