WELDING RESEARCH Fig. 4 — Heating sections along the roll axial direction. Fig. 5 — Furnace roll chamber temperature as a function of time. A B A tures. When the temperature is lower than 600C, MO-RE®1 has the lowest yield strength, tensile strength, and elongation among the three materials. There is an increase in the yield strength of materials MO-RE®1 and N117 from 600 to 800C. This phenomenon is known as yield strength anomaly (YSA) in which the yield strength actually increases at elevated temperatures. The mechanism of YSA could be attributed to the phase transformation and the precipitates at 800C. The roll was heated by heat convection 434-s WELDING JOURNAL / NOVEMBER 2016, VOL. 95 Fig. 7 — Mesh for the cooling system design. A — Overall design; B — holes at the end; C — cooling channels near the journal. from hot air inside the furnace. Surface heat convection (qs) was calculated using Equation 2: qs = h(T–Ts) (2) where h was heat convection coefficient (h), and Ts was the air temperature inside the furnace. T was the temperature on the outer and inner surfaces of the furnace roll. Since Ts and T were changed with the time and the location on the roll surface, a user subroutine was developed to automatically calculate the heat flux (qs). The user subroutine was developed on the platform of ABAQUS (Ref. 27). For a given time and location on the roll surface, ABAQUS provided a temperature (T) to the subroutine. The subroutine determined Ts based on the heating zone shown in Fig. 4 and the heating process diagram shown in Fig. 5 and then calculated a heat flux (q). By inputting the heat flux to ABAQUS, a new temperature (T) was calculated and inputted to the subroutine. This looping process was done for all time increments and locations on the roll in the thermal analyses. As the roll temperature reached the furnace air temperature, the heat flux approached zero. By using the subroutine, the heat flux distributions on the roll and the heat flux transient changes during heating and cooling were modeled during the thermal analyses. The typical heat convection coefficient (h) for air is between 10 and 1000 W/(m2K). Several heat transfer analyses were conducted to determine the heat convection coefficient to heat the roll based on the input furnace temperature, as shown in Fig. 5. It was found that the roll can be heated to the designated temperature according to the time specified in Fig. 5 in 24 h by inputting the heat convection coefficient, 20 W/m2C. After heating for Fig. 6 — Mechanical boundary and loading conditions. A — Forces on the roll; B — pressure on the roll; C — modeling contacts. B C C
Welding Journal | November 2016
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