| Summary: | HSS (high speed steel) rolls are among the latest technological addition to the hot
rolling process. Reduced wear, increased campaign times, increased life and better
control on the quality of the strip are some of the features of HSS rolls which transforms
directly into higher productivity making HSS a better roll material compared to
traditional roll materials (HiCr, IndefChill).
The introduction of HSS rolls to the Hot-Strip mill is a very recent event (1991)
and thus it presents a lot of areas and challenges which need to be studied and analyzed.
The objective of this investigation was to study the thermal behaviour of HSS rolls in the
finishing mill using the process modelling approach. The objective was achieved by
modifying and applying mathematical models developed at UBC. The steady-state
model (1-dimensional model) was used to study the thermal behaviour at the surface and
the transient model (2-dimensional model) was used to study the thermal behaviour of the
bulk of the roll. The 2-d transient model results were used to calculate the thermal crown.
Data for developing and validating the models was provided by Dofasco Inc., for a
campaign consisting of 208 bars over 9 hours. The comparison between the
measurements and prediction (for the temperature as well as the crown) showed excellent
agreement.
The model predictions showed that the rolls achieved steady-state in
approximately 200 minutes with the current campaign conditions and assuming no
excessively long delays between the processing of consecutive bars. Final roll gap profile was calculated by adding the thermal crown, mechanical crown and preground
crown. Other issues addressed in this work were prediction of the thermal behaviour
under conditions with mill pacing of 10 seconds; and proposition of a method of
controlling the thermal crown.
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