OCR Text |
Show 2 enough in order to keep pace with set-up operation condition of milling machines (2). In other words, a holding or reheating furnace is needed to raise the temperature of steel in the course of processing until it is sufficiently hot to be plastic enough for economic reduction by rolling to the desired section (3) . It is often found and quite economical to roll ingots directly through the billet stage into more refined steel products. The primary mill stage in the production from ingots consist of a serious of operations (4) , whereby the ingot cross-section is reduced to a square or oblong having rounded corners, and that of dimensions approximate to nominal specified size, and the length of the ingot is increased, corresponding to the decrease in cross-section. Next, w h e n the still hot product coming from the primary mill is immediately rolled in a succeeding billet mill, and the concluding operations cut a relatively short length called crop from each end of the rolled piece as scrap, and cut the remaining long piece into multiples to suit the required lengths for final products (5) . In the ideal case without reheating, the primary mill just keep the billet mill busy, in this connection, the billet mill must be performed rapidly to retain as much heat as possible in the ingot to keep its temperature high enough for good quality rolling. However, because the long ingots with smaller cross-section area often suffer a substantial heat loss before introduced to billet mill, and since the more critical grades of steel with their restricted range of rolling temperatures, have b e c o m e more widely used, some of newer installations have provided reheating facilities to roll a wide variety of steel products (6) . In this presentation for a local steel industry (GHIC) producing special alloys, since the billet mill was not able to perform a faster speed, the longer square ingots were being exposed in the air, as discharged from the primary mill, which results in a temperature non-uniformity happened across the ingots. Apparently, it requires first designing and installing a holding furnace to heal the temperature difference. Further, a two-dimensional unsteady mathematical model is developed to predict the temperature distribution of the ingots. Several alloys, with various cross section area and length, are charged into the furnace to investigate the temperature distribution improvement against that without the furnace. Finally, the demonstration results are brought to compare that obtained by computation modelling in order to optimise the furnace operating conditions. |