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Abstract—Hot rolling products with improved quality features
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such as thickness profile, strip width, flatness, and material me-
chanical properties, are in increasing demand. The project goal is
to improve the production quality in an existing hot rolling mill at
Aceralia Steel Company, Avilés, Spain. This paper describes the
design and implementation of a supervisory system for real-time
compensation of uneven thickness on both sides of a rolled strip.
The design is based on a multivariable process model, whose pa-
rameters are calculated online using measurement data from the
mill. As a result, a computer system was developed that corrects
the automatic gage control output from online acquired mill oper-
ation data. Previously, this task was done manually and periodi-
cally by a human operator.Manual correction is tedious and error
prone, since it is based on visual inspection.Moreover, the proposed
method leads to notorious improvement in the output strip quality,
as the correcting signalmay be continuously applied before the un-
even thickness effect is visible.6379
Index Terms—Automatic gage control, hot rolling mill, multi-
variable systems, system identification.I. INTRODUCTION
THIS PAPER describes the design and implementation of a
supervisory system for real-time compensation of uneven
thickness on both sides of a rolled strip. The project goal is to
improve an existing hot rolling mill at Aceralia Steel Company,
Avilés, Spain [1]. The design is based on amultivariable process
model, whose parameters are calculated online using measure-
ment data from the mill.
In a hot rolling mill the plate thickness is reduced, from an
initial thickness of about 25 cm to a final thickness of 5 cm, by
pulling the plate between two parallel rolls while moving the
upper work roll; see Fig. 1. Thickness reduction is achieved in
a series of passes. On each pass, a mechanical screw system
adjusts the unloaded roll gap before threading the plate in the
mill.
While material is being fed, and in order to keep the output
thickness within range, automatic gage control (AGC) systems
are applied. AGC corrections are made by using hydraulic po-
sitioning systems.
Paper PID01–37, presented at the 2001 IndustryApplications SocietyAnnual
Meeting, Chicago, IL, September 30–October 5, and approved for publication
in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Metal Industry
Committee of the IEEE Industry Applications Society. Manuscript submitted
for review October 15, 2001 and released for publication December 14, 2001.
J. C.Alvarez,A. B.Díez, andD.Alvarez arewith theDepartment of Electrical
and Computer Engineering, University of Oviedo, 33204 Gijón, Spain (e-mail:
juan@ieee.org; alberto@isa.uniovi.es; dalvarez@isa.uniovi.es).
J. A. González and F. Obeso are with the Centro de Desarrollo, Aceralia Steel
Company, 33480 Avilés, Spain (e-mail: jrodriguezg@aceralia.es; fobesoc@ac-
eralia.es).
Publisher Item Identifier S 0093-9994(02)02676-2.Fig. 2. Manual uneven thickness compensation: two identical hydraulic servo
systems control the position on both sides of the upper roll pack, according to
the AGC correction signal, and a human operator commands a tilting signal in
order to compensate for the unevenness between north and south sides.
Most operating AGCs in industry have been designed taking
into consideration the mean value of the plate thickness on both
sides. However, some factors may produce uneven thickness,
such as flatwedge profiles. They lead to visible shape deviations
in the rolling direction of the slab (for example, the camber or
sweep defect), occasionally causing the clogging of the strip in