| OCR Text |
11 above, but the magnitude of the lift-up m a y depend on forced heating segment as well as the cross section area of billets. Therefore, a possible curve shown in Fig. 10 predicts the addition of forced heating has a potential to heal the temperature non-uniformity, without mention surface overheating. Demonstration of designed holding furnace Since a 14.4m furnace appears to be longer than the available space, shown in Fig.l, thus it suffers to reconstruct the passage existed in-between the primary mill and the billet mill, in order to install the furnace at the right position. Bearing this demand, a billet guide arrangement centered in-between two mills has been moved 2 m toward the primary mill, which actually creates few operational difficulties. In other words, because the billets m a y impinge the guide earlier while they are hot as plastic, which results in a bending head portion occurring a lot of easier for the longer and smaller cross-sectional billets. That has a potential to eject billets out of the passage before entering the furnace or to d a m a g e the furnace front and the inside refractory during discharged into the furnace. Therefore, a special design has been m a d e on the furnace to prevent that abovementioned operational risky (9) . A computational modelling of temperature profile as billets are transported through the furnace is shown in Fig.l 1, whereas few billets (refer to Table 1) , are selected to investigate the effect of the exposed tails and the thickness on the temperature profile of billets. From the result shown in Fig.l 1, regardless the furnace length or billet cross section area, a sharp rising inevitably appears at the earlier of the temperature profiles indicates surface overheating occurs in the section sitting inside the furnace outlet, which caused by 10 seconds crops shearing. As the furnace length is increased, the temperature profile shows a much better uniformity across the entire length, as compared both of curve C and D. In other words, an increasing of furnace length not only provides holding a longer billet portion inside the furnace before entering the billet mill, moreover, as the transport speed is significantly reduced to 0.2 m/sec, a longer furnace is also able to heal the temperature drop effectively at the tail portion of the billet. However, the object of the holding furnace is to obtain a more uniformly temperature profile across the billet length, although a lift up of the tail portion by increasing the furnace length does heal the temperature non-uniformity, that m a y suffer a rise at the head portion simultaneously, this phenomena is also shown in Fig.l 1 despite of |
