ROLL ECCENTRICITY EXPERT
Rolls in rolling mills are never completely round but haveeccentricity which can be caused by:• grinding inaccuracy• non-uniform thermal expansion• asymmetrical adjustment of bearing rolls shell via drive
keys
Each eccentricity consists of a base frequency whichis the rotary frequency of the roll and several harmonicfrequencies. Every roll of each roll stack can show sucheccentricities which lead to thickness and tension errors
which also lead to disturbances in neighboring stands.
The result is a mixture of many cyclic disturbances in theexit thickness that in most plants add up to a significant
percentage of the total thickness error.
CHALLENGE
The first step is to find out the degree of improvementof the exit thickness which can be expected by installingan eccentricity compensation. This is a challenge due thelarge number of different eccentricity frequencies which allchange with roll speed.
At high rolling speed the frequencies of eccentricities aremuch too high to be compensated by a closed loop control
such as a mass flow control or a strip tension control.
Moreover Roll Eccentricity Expert should compensate onlyroll eccentricities to avoid inappropriate reaction to otherkinds of disturbances. This is difficult as all the available
measurement signals contain many other disturbances.
Moreover there is no possibility of measuring theeccentricity directly.
Therefore the eccentricity needs to be determined byindirect measurement.

The best signal for determination of eccentricities is thestand exit thickness. This however is not available for moststands. Therefore a compensation has to use other, lessconvenient, signals.
Finally filtering a single eccentricity frequency is difficult asa pair of rolls has very similar diameters and therefore very
similar frequencies.
OUR SOLUTION
Primetals Technologies delivers hard- and software for
eccentricity compensation. The Roll Eccentricity Expert
is a fully digital model based control, which uses thefact that the eccentricity of each roll remains relatively
constant during rolling to model its shape over several
revolutions. Using an inverted plant model this modelled
eccentricity is transformed into a compensation setpoint
for the gap control (pre-control)moving the gap in a waythat eliminates the influence of the eccentricity on strip
thickness or tension.
As input the Roll Eccentricity Expert uses, depending on
availability, a combination of the exit thickness, entry strip
tension and roll force to extract the eccentricities.

Roll Eccentricity Expert

Control concept

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Exit gauge versus time depending on the eccentricity compensation status

Roll Eccentricity Expert

MAIN BENEFITS• Better strip quality - improved thickness
tolerances also at high rolling speeds• Maintenance friendly - using existing
thickness, roll load or strip tension
measurements as feedback for control, hence
no additional sensors or instrumentation areneeded• Less roll changes - applicable to compensate
backup-, intermediate- and work rolleccentricities• Fast ROI - easy to implement in existing basic
automation environments

Structure of the controller

PRODUCT FEATURES

Stability and high compensation rate:

Can be installed in:• For up to 4 harmonic frequencies per roll

• Every stand• For high speed levels (up to 22Hz)• For every roll

• For all strip types• All types of Cold and Hot Rolling Mills• During acceleration

Can work with all kinds of measurement setups. The
following possible input signals can be combined forbetter disturbance differentiation:• For changing eccentricities during rolling• Exit thickness

No need for additional sensors , e.g. for synchronizing• When other disturbances exist• Entry strip tension• Roll force

Primetals Technologies
Germany GmbHA joint venture of Mitsubishi Heavy
Industries and partners
Bunsenstr. 43 | 91058 Erlangen | Germany
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Order No. T10-1-N236-L2-P-V4-EN
Printed in Linz | © 2020

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