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K. LABER et al.: ANALYSIS OF THE TEMPERATURE CHANGE OVER THE CONTINUOUS INGOT LENGTH...
of temperature distribution over the casting length before
the fi rst rolling stand, the casting end temperature
during heating the casting in the heating furnace was
increased by 50 °C relative to the nominal casting temperature
(1 150 °C).
The rolling speed ranged from 0,10 m/s in the fi rst
stand to 7,0 m/s in stand no. 17; the roll temperature
was 60 °C, and ambient temperature 20 °C. The coeffi -
cient of heat exchange between the rolls and the band
was α = 3 000 W/m 2 K, and the coeffi cient of heat exchange
between the band and the air was α air = 100 W/
m 2 K. The friction coeffi cient and the friction factor were
assumed to be variable, being dependent on the band
temperature, and amounting to, respectively, µ =
0,3÷0,42 and m = 0,6÷0,8. The test material was steel
20MnB4 [4].
The following object’s parameters were assumed for
thermovision tests: emissivity, 0,82; distance from the
object, 3 m; ambient temperature, 20 °C; refl ected temperature,
20 °C; relative humidity, 50 % [5].
RESULTS AND DISSCUSION
Figure 1 shows example results of numerical computation
of temperature distribution for the starting and
end regions of the feedstock and for the end feedstock
part heated up by 50 °C before the fi rst rolling stand.
Unevenness of temperature occurring initially at the
beginning and end of the feedstock decreased as the
rolling process progressed in particular passes. The
main cause of this phenomenon was the contact of the
band with the rolls during the rolling process and the
generation of heat due to plastic deformation. The temperature
values computed numerically were compared
with the actual values measured with a thermovision
camera for all passes. For the feedstock upstream the
fi rst rolling stand (Figure 2) they amounted to, respectively:
15 °C (with a relative error of 1,4 %) for the
feedstock beginning, 12 °C (with a relative error of 1,2
%) for the feedstock end, and 11 °C (with a relative error
of 1,1 %) for the heated-up feedstock end.
From the obtained results it was found that the initial
temperature difference for the beginning and end of the
feedstock, being about 65 °C, decreased to about 30 °C
after rolling stand no 17. Whereas, when examining the
temperature change on the feedstock surface before the
Figure 1 Distribution of temperature over the feedstock
surface before stand no. 1, as computed numerically:
a) feedstock beginning, b) feedstock end, c) heatedup
feedstock end
Figure 2 Thermogram before stand no. 1, a) feedstock
beginning, b) feedstock end, c) heated-up feedstock
end
fi rst rolling stand for the heated-up feedstock end, as compared
to the temperature of the feedstock beginning it was
determined that the existing feedstock surface temperature
difference, being about 47 °C, decreased to about 15
°C after rolling stand no 17. Heating up the feed stock end
by 50 °C resulted in a decrease in the band surface temperature
difference after rolling stand no 17 by more than
twofold, compared the rolling of the feedstock end heated
up to the nominal temperature (1 150 °C).
Figures 3 and 4 represent the variation of temperature
in the core and on the surface of band after individual
passes.
By analyzing the change of temperature in the band
core (Figure 3) is established that during rolling of the
initial band region in rolling stands nos. 1÷3 a constant
temperature existed, whereas for both the band end and
the pre-heated band end, a drop in temperature occurred
in these stands. This is due to the fact that during rolling
the band end and the heated-up band end, very large temperature
differences exist between the core temperature
(Figure 3) and the lateral band surface temperature (Figure
4) values. Downstream rolling stand no 1, the differences
in temperature for the heated-up end of the band
between its core and lateral surface were greater by as
much as 50 % compared to the beginning of the band.
Figure 3 Change of feedstock core temperature after each
pass
Figure 4 Change of feedstock surface temperature after each
pass
40 METALURGIJA 52 (2013) 1, 39-42