| OCR Text |
Show 9 whereas billets are moving through the furnace in the direction of their length. Results a n d Discussion Investigation of forced heating effect (8) A consecutive three cycles of forced heating by high-speed burner and natural cooling in air is shown in Fig.8. Apparently, each cycle shows consistent heating and cooling patterns, respectively, and the corresponding point of each cycle is deviated only in a range of 40°C, which indicates the results can be used to analyze the effect of heating speed on billets. The temperature distribution of measured points in-between 400 to 460 seconds interval is further elucidated in Fig.9, which indicates the billet surface (Dl) exhibits a faster temperature ascending and descending as compared that of the internals. The burner begins fired as the surface drops to a minimum while the internals show a continuous temperature descending. In other words, the internals is found to exhibit temperature minimum 10 seconds later than the surface, which is caused by the internals are continuously losing heat to the surface either in axial or longitudinal direction. The inconsistency of curves is diminished when the surface and the internals are brought to a close temperature, and since then all curves b e c o me ascending synchronously. The time lag increases as the billet diameter enlarges, due to heat at the surface is being conducted into the internals that results in temperature further rising gets more difficult. From the temperature ascending results shown in Fig.9,the curve shows a gradual temperature rising until 10 seconds later, then the rising slope becomes steeper and stabilised, however, the rising speed is always smaller than 2 °C/sec. The billet transport speed is significantly reduced to 0.2-0.4 m/sec as the billet head begins entering billet mill, a length 2 m forced heating zone could provide maximum 10 seconds heating time to lift up the billet tail portion. Based this result, a prediction of temperature profile by the furnace with forced heating is sketched in Fig. 10. Apparently, the portion from the middle through the tail is able to be brought close to designate temperature range, based on a bench result mentioned |
