Upgrading of Hot Finishing Mill to 4-Stands,
and Replacement of Computer Control System
by Hiromi Hirono *, Toshio Sakai *, Shigeru Hishikawa *2, Hideshi Karakawa *3,
Hiroyuki Kobayashi *2, Takashi Sakai *4, Mamichi Tsuyuki *, Tomoaki Mizutani*and Hiroyuki Yanagisawa *Since 1994, in response to increasing demand for can body stock and other alumi-

ABSTRACT num strip products and to users' requirements for higher quality, work has been
going forward on a program to upgrade the hot finishing mill at the Fukui Works. Phase I of the
program involved expansion to 4 stands and introduction of a new computer control system, andwent into service in March 1997. The result has been the capability of high-speed rolling of thinner
strips providing increased capacity, together with significant improvements in thickness accuracy
due to the introduction of the new control technology as well as in the properties of the material andother aspects of quality. Phase II of the upgrade--introduction of a computer control system for therougher--went forward to completion in March 1998.

1.

INTRODUCTION

A program to upgrade the hot finishing mill at the Fukui
Works involving expansion to 4 stands and introduction ofa new computer control system went into service in March
1997.
The result has been increased hot rolling capacity andimproved yield, together with significant improvements inthickness accuracy as well as in the properties of thematerial and other aspects of quality. This paper provides
an overview of the hot finisher mill after the upgrade, anddescribes the new control technology and hot rolling process control system that were introduced.

2.

GENERAL DESCRIPTION

The hot rolling mill of the Fukui Works went into service inMay, 1983 as a world-class facility, equipped with large
rolling stands capable of producing wide, large-diametercoils and featuring the latest in computer control. Since
then, continuing improvements have been made in response to increasing demand for aluminum strip products--particularly can stock--and users' requirements for higher
quality in terms of dimensional accuracy, performance andstrip surface quality, but given the inadequate capacity of* Fukui FA Engineering Sec., Fukui Planning Dept., Plant& Facilities Div.
* 2 Rolling Technology Sec., Fukui Lab., R&D Div.
* 3 Production Engineering Sec., Production Dept., Fukui
Factory, Light Metals Div.
* 4 Planning Sec., Plant & Facilities Div.

the computer control system and the addition of further
stands by other players in the industry, we were faced withdifficulty in coping with the situation regarding aluminum
strip products. Accordingly a plan was developed to upgrade the Fukui hot finisher by expansion to 4 stands andby replacement of the computer control system. The plan
had the following objectives:
1) To address users requirements by increasing the number of finishing stands and the total reduction, thereby
improving the quality of aluminum strip products--specifically can body stock--and increasing product coildiameter.
2) To increase productivity by reducing the thickness of
hot-rolled coils, thereby effecting pass cutting in the
cold-rolling process.
3) To realize a high-productivity hot-rolling mill by replacing the computer control system with one of the latest
design that achieved a significant degree of automation.
The expansion of the hot finisher to 4 stands, which was
Phase I of the upgrade program, has been achieved. Figure 1 shows line layout.
2.1 Equipment Specifications
The hot finishing line was expanded by adding a fourth
stand (F0) upstream of the three existing stands (F1-F3).
Photo 1 shows the appearance of the finishing mill andTable 1 shows main specifications.
The newly installed F0 stand is of 4-high construction
with hydraulic screw-down, and to provide for the rolling of103

(5) Provision of a cold coolant sprayer mechanism to improve profile correction capability as thickness is decreased.
The F0 stand is powered by a high-response, low-maintenance AC motor (5,000 kW), with a large-capacity gate
turn-off (GTO) thyristor drive unit (10,000 kVA).

Photo 1

Table 1

Hot finishing millSpecifications of Hot Finishing Mill
F0

F1-F3

IHI/Toshiba

IHI/Fuji Denki/ToshibaStand no.
Manufacturer

2.2 Computer Control System
The plan to upgrade the hot finishing line also provided for
introducing a new computer control system, involving renovation of control for the expanded hot finishing stand andthe addition of process computers. This was accompanied by significantly augmented functions.
Figure 2 shows the configuration of the computer control system for the hot strip rolling mill. It was transitional,
having been completed with the renovation of the control
system for the rougher in March, 1998.

Type

Non-reversing 4-stands

Main motor rating

5000 kW AC

3750 kW DC

Max. rolling force

40.0 MN

31.2 MN

Max. rolling speed

112 m/min

175/270/360 m/min

Roll dimensions

Profile actuator

WR 800 x 2850 mm
WR 720 x 2850 mm
BUR 1620 x 2850 mm BUR 1520 x 2850 mm
TP 1620 x 2850 mm
WRB
TP roll (top / bottom)

WRB
TP roll (top)Cold coolant sprayer

high-quality aluminum products with high productivity it
has the following features:(1) Use of rollers with high power (5,000 kW) and highscrew down force (40 MN).
(2) Ample profile correction capability (large-capacity workroll bender (WRB) and taper piston (TP) roll).
(3) Adoption of high-response hydraulic screw-down system and high-response mill drive system to prevent
tension fluctuation between stands and improve thickness correction capability.
(4) Provision of side guides to prevent snaking of the strip--hydraulic at the entry side of hot finisher, F0 and F1and screw + pneumatic at the entry of F2 and F3.

2.2.1 Control System
The control system comprises a digital controller capableof high-speed, high-volume calculations, an operator guidance device operated by touch panels, and an FDDI-I compatible control system dataway with a data transmission
capacity of 100 Mbps, and having a wide scan transmission data region. Taking advantage of the features of thishigh-speed, high-capacity control system makes it possible to:(1) achieve high-precision rolling control, including tension
control and thickness control;(2) improve operating convenience by means of fully implemented operator guidance and use of touch panel operation for items of infrequent use; and(3) improve flexibility of control system structure and reduce the space occupied by electrical equipment
through use of remote I/Os.
2.2.2 Computer System
In the computer control system, a process computer dedicated to finisher set-up calculation/learning and finisher
process data gathering is introduced. In addition engineering workstations for dynamic profile control and high-speed
data gathering are connected to the control system
dataway, and EWSs for engineering data and the production database and an EWS for the process analysis database are connected to the information system LAN. All of
this data can be referenced and acquired at any time bypersonal computers connected to the on-site LAN.
HRT

HTM
38SH

150SH
EDM

TR

150SH : 150-mm cut shear
38SH : 38-mm cut shear
TR: Tension reel

EDM : Edger mill
HRM : Hot reversing mill
HTM : Hot tandem mill

Figure 1

104

Layout of hot rolling line

Furukawa Review, No. 18. 1999

Slab receiving place
Hot processcomputer

Operational
control database
Coil pay-out place
ProfileControl

HOT process computer
Mill line tracking,
Rougher set-up calculation/learning,
Rougher pre-setting,
Rougher process data gathering,
Hot production control
HT process computer
Finisher set-up calculation/learning,
Finisher pre-setting,Finisher process data gathering,
Hot production control,
Coil transfer line tracking

Figure 2

High-speed
data gathering

PSC1:
PC1:
Finisher mill control master,
Rougher master, table master
Temperature control
PC2:
PSC2:
Rougher sub-machine control master
Finisher thickness control
PC3:
PSC3:
Machines around rougher mill control master,
Coiler master
Automatic gauge control
PSC4:
PC4:
Spray control,
Slab cooling temperature control
Crown control actuator settings
PSC5:
Roll eccentricity elimination control

Configuration of computer control system for hot strip rolling mill

Roll thermal crown
calculation

GMC trace

ABS: Absolute AGC
ASC: Speed control
CC:
Current control
COL: Coolant spray control
DPC: Dynamic profile control
FiSUC: Fi stand ACG (successive)
HPC: Hydraulic position control

Figure 3

Finisher set-up
calculation/learning

LC:
Load cell
RTC:
Reel tension control
MAGC: Monitor AGC
T:
Thermometer
MCAGC: Mass flow AGC
TC:
Tension control
MMC:
Mill modulus control
TEMPC: Temperature control
MRH:
Master speed referenceTM:
Tension meter
OSM:
Optical shape meter
WRBC: WRB control
PM:
Profile meter
XRAY: X-ray gauge meterREC:
Roll eccentricity elimination control

Block diagram of control system for hot finisher

1053. CONTROL TECHNOLOGIES

3.1 Automatic Gauge Control
In addition to conventional methods such as monitor AGC,
thickness control for the hot finisher effects mass flow thickness control using a high-speed hydraulic screw-downsystem combined with positive methods such as absolute
AGC, thereby suppressing thickness amplitude of thesteady-state portion and reducing top-end off gauge length.
Further, with a view to automating the avoidance of rollingproblems in high-load rolling, a new excessive rolling force/
torque avoidance control function has been incorporated.
3.1.1 Thickness Control of Steady-State Portion
In controlling the thickness of the steady-state portion, a
combination of mill modulus control (MMC) to compensate for high-frequency thickness deviation, monitor AGC
to compensate for low-frequency deviation in steady-state
thickness, and roll eccentricity elimination control to compensate for periodic deviation in thickness due to the eccentricity of the rolls is used to improve thickness accuracy. Mass-flow AGC is also implemented to maintain thedrafting schedule at each of the intermediate stands, andthereby stabilize the properties of the rolled material.
3.1.2 Top-End Absolute AGC
With the objective of raising yield by reducing the off-gauge
length of the hot-rolled coils, top-end absolute AGC has
been newly implemented.
To assure thickness accuracy using absolute AGC, it isessential than accuracy be increased by gauge meterequation.1) To this end a function is newly incorporated
whereby the elastic curve of the mill is measured automatically and computer and controller data are constantly
updated. To obtain consistently accurate values for gaugemeter compensation (GMC), which is made up primarilyof thermal expansion of the rolls, the thermal expansion is
calculated by means of a mathematical thermal crownmodel, allowing the GMC value to be corrected at set intervals. This results in a significant reduction in the offgauge length of the top end compared to previously. Figure 4 shows the results of adopting absolute AGC.
3.1.3 Excessive Rolling Force/Torque Avoidance Control
In the case of material that is particularly hard or wide,
rolling requires greater rolling force and torque. Towards
the end of the strip this tendency gradually strengthens
due to the effects of cooling, and if rolling continues unchanged the excessive force/torque may result in mill stoppage. In the new AGC system, therefore, a new function
has been added whereby the drafting schedule is automatically changed when maximum rolling force or rolling
torque is approached, thus avoiding mill stoppage. The

106

Thickness deviation (µm)

27.0m

20sec
+50µm

– 50µm10.0m

Thickness deviation (µm)

Figure 3 is a diagram showing the control system. The
renovation described here introduced new techniques forgauge control, profile control and temperature control.
These techniques, and the results obtained, are discussed
below.

20sec
+50µm

– 50µmFigure 4

Thickness deviation at delivery side of F3 standbasic concept is to reduce the load on a given stand byclosing the roll gap of the upstream stand when there is amargin at the upstream stand and opening the roll gap of
the given stand when there is no margin at the upstream
stand.
3.2 Profile Control
In recent years there has been an increase in the accuracy demanded with respect to the thickness distribution(profile) and shape. Since the profile of the product is determined by the hot finisher, profile control is important for
quality but because it also involves the elastic deformation of the rolls and the plastic deformation of the rolledmaterial, automatic control is extremely difficult.1)
For the present system upgrade, new models were developed for both pre-setting and dynamic control. This system assures minimum profile error distribution at the delivery side of the final stand mainly by pre-setting and controlling the WRB force, and in addition to a mathematicalmodel, operator knowhow is factored in, thereby approaching the touch of a human operator. It features may be enumerated as follows:(1) Actuators are the WRB, TP roll and roll spray pattern.
(2) Sensors are the profile gauge at the delivery side of
the final stand and optical shape meters mounted between stands.
(3) The F3 delivery-side profile control sector is given aweighting and divided into 20 so that the edge portionis finely divided in the direction transverse to the strip,
and, based on the delivery-side target profile distribution and the delivery-side actual profile, a delivery profile deviation ∆ε(i) is obtained by∆ε(i) = PACT(i) – PREF(i).....(1)where:∆ε(i): Delivery-side profile deviation (zone i),
PACT(i): Actual delivery-side profile,

Furukawa Review, No. 18. 1999

PREF(i): Target delivery-side profile,Figure 5 shows a typical application of this control.

(4) The WRB control input for each stand is set so that theevaluation function Φ in Equation (2) is minimized.
Φ = Σ { ∆ε(i) – Σ αj(i) Fj }2+ Σ Wj n ∆Φj 2 .

.....(2)where:
Φ: evaluation function,∆ε(i):Delivery-side profile deviation (zone i),αj(i): WRB effect function for stand j (zone i),∆Fj: WRB control input for stand j
Wj: WRB control weighting coefficient for stand jn: number of divisions in transverse direction (20).
(5) The shape limits are set from the optical shape meterand information on WRB manual intervention by theoperator, and the initial settings of WRB force and automatic control during rolling are carried out in such a
way that these are not exceeded.

3.3 Temperature Control
In aluminum hot rolling, and particularly in hot finishing,accurate control of the temperature of the material is crucial to the quality of the finished product. In the present
project, a new material temperature model was developed
to optimize temperature control gain for each material to
be rolled, and a new type of radiance thermometer was
adopted, thereby increasing the accuracy of temperature
measurements.
3.3.1

High-Accuracy Exact-Solution Analytical Temperature Model
Generally speaking, the material temperature model madeuse of an approximation equation derived from the following one-dimensional thermal conduction equation at nonsteady-stateT = ( T0 – θ L) exp(–4a / h 2 . K . t ) + θ L.....(3)PC value (%)

where:
T : material temperature (°C ),T0 : initial material temperature (°C ),θ L : coolant temperature (°C),
a : temperature conduction rate (mm2/sec),h : strip thickness (mm),K : recovery coefficient,t : thermal conduction time (sec).
b) 2nd scan

Actual speed (mpm)

Previously, the approximation equation used in Equation (3) had a large error with respect to coefficient K, but
in the present work, by subjecting the one-dimensional
thermal conduction equation at non-steady-state to logical analysis and by determining the various coefficientsfrom experiments on the cooling capacity of coolants, it
was possible to raise the accuracy of the temperature prediction model. Figure 6 shows how it was possible, using
the new temperature model to obtain a predictive accuracy for rolling speed of approximately 90%, with an error
range of ±10%.

e)14th scan

Set speed (mpm)

Figure 5

Effects of dynamic profile control

Figure 6

Anticipated accuracy of temperature model(Stand F3)

107

3.3.2

New Type Of Two-Wavelength Radiance Thermometer
Until now, the radiance thermometer used was of the onewavelength type, but problems of temperature control accuracy were posed by the difficulty of setting the appropriate emissivity, and by susceptibility to the influence of the
strip surface conditions. Accordingly it was decided to adopt
a new type of two-wavelength thermometer, the ASTS®
from the LAND Corporation.
This thermometer is characterized by introducing, withrespect to the Wien's approximation equations (4) and (5)of Plank's law relating to heat radiation on two wavelengths
λ1 and λ2, a new relational equation (6) for two-wavelength
emissivity in aluminum. That is to say,
V1 = ε1λ1–5 exp(–C / λ1T )V2 = ε2λ2–5 exp(–C / λ2T )ln ε2 = A. ln ε1 + B.....(4).....(5).....(6)where:
V1, V2: thermometer output,
λ1,λ2: measuring wavelength,ε1:emissivity at wavelength λ1,ε2:emissivity at wavelength λ2,
T : material temperature (K),C:
constant (= 14,388 µmK).
From Equations (4) through (6), we obtain
1/T–1/T1=A' (1/T2–1/T1)+B'

alloys.
Through the adoption of this thermometer, it was possible to measure material temperature with good accuracy, without having to revise emissivity settings each time
the alloy was changed (Figure 8). Learning accuracy forthe setting calculations was also improved, in effect raising the predictive accuracy of the rolling model.
3.4 Hot Rolling Process Control System
The present renovation was accompanied by developmentof a variety of control and support systems, contributing tomaintaining and improving the quality of the rolled products, and to speeding up problem analysis thereby shortening equipment down-time. The main functions are described in the following.
3.4.1 Quality SPC System
The statistical process control (SPC) system gathers data
for strip thickness, strip profile and material temperature
at intervals of only 10 ms, and these data are then subjected to FFT analysis, profile waveform analysis and statistical analysis to allow the automation of quality decisions. As a result, in the event of a quality abnormality, theoperator is notified immediately as to thickness off-gauge
length, thickness amplitude, strip profile estimation values, off-temperature length, etc., to prevent continuanceof the abnormality.3).....(7)

If coefficients A' and B' are first determined experimentally using Equation (7), measurement of true temperature T can be made using the measurements of radiancetemperatures T1 and T2. Figure 7 shows the experimental
results, and good correlation was obtained for all main

Frequency

where:
T1: radiance temperature at λ1 (K)T2: radiance temperature at λ2 (K)Coil take-up temperature - target temperature (˚C )T

T

Frequencya) One-wavelength thermometer

Coil take-up temperature - target temperature (˚C )T

Figure 7

108

T

Relationship between radiance temperatures T1(at λ1) and T2 (at λ2) and true temperature T for
aluminum stripb) Two-wavelength thermometer
Figure 8

Histogram of temperature errors on one- and twowavelength radiation thermometers

Furukawa Review, No. 18. 1999

3.4.2 High-Speed Data Gathering/Analysis System
Using the high-speed, large-capacity control system
dataway, rolling process data and control output data ofall types is gathered at 50-ms intervals and stored in the
database, creating a system that supports graphic displays on personal computer screens. This makes it possible to analyze rolling phenomena as well as rolling problems due to control faults, so that causes can be identified. This contributes greatly to the rapid solution of the
problem, and to the prevention of its recurrence.
3.4.3 Quality Database System
At the Fukui Works a database is maintained containing
quality data generated at all stages of the production process. In the case of the hot rolling process, engineering
data gathered automatically by the process computers isstored automatically in the quality database. It is thus possible to analyze data across processes, contributing tohigher quality.
3.4.4

Automatic Hydraulic Screw-Down Step-Response
Measurement
Deterioration of the servo valve of the hydraulic screwdown system has an adverse effect on its response andinterferes with thickness control. To prevent this, routine
measurements of the system's step response must be
taken to evaluate the degree of deterioration. In the present
program, automatically performing step response measurement and data analysis at the time of roll gap zeroing
has made it possible to confirm deterioration quickly andeasily.

4. CONCLUSION
The Fukui Works is pressing ahead with Phase II of therenovation of the hot rolling line--upgrading the control
system of the hot rougher. The upgrade program was implemented in January 1998, and after on-line adjustment wascompleted on schedule in March of the same year. Thishas brought to completion Furukawa Electric's programof renovating the hot rolling line of the Fukui Works, creating a line that is fully responsive to the quality and productivity requirements of our customers.
We are committed to further advances in automationand further integration with the outstanding capabilities ofour staff, so as to achieve even higher levels of quality andproductivity.

REFERENCES

1) M. Kamata; "Continuous Rolling of Thin Strips", Trends in SteelTechnologies V, Supervised by Japan Steel Association, Chijin
Syokan, (1997), 139. (in Japanese)
2) H. Matsuyama; "Measurement and Control of Temperature",
Series of Practical Techniques in Energy Saving, Energy Saving
Center, (1989), 90. (in Japanese)
3) T. Iwashita et al.; Furukawa Electric Review, No.95 (1994), 94.
(in Japanese)
Manuscript received on July 17, 1998.

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