OCR Text |
Show 7 section areas. An individual experiment, using one 15><104 Btu/hr burner directly fired on a 48.5mm diameter round bar, was carried out to investigate the surface temperature profile change. As shown in Fig.6, at the rear surface of the burner flame, 4 thermocouples are wired into the round bar, at a radial direction, to measure the temperature variation of depth at the same cross section during forced heating and natural cooling. Furthermore, 4 additional measuring points, with 5cm interval between two adjacent points at the longitudinal direction, are m a d e at the centre of the bar to simulate the effect of transport time on the different cross-sectional points. During a cycle, the testing bar is first heated up to a temperature where all centre line points (H1-H4 and D4) indicate over 1000°C, and then cooled in air to allow a temperature homogenised across the bar, until the surface of Dl is dropped to 950°C the heating is then restarted. The measured temperatures on each point is recorded against the time in each cycle, as the temperature of measured points of a cycle at certain time shows a difference within a range of 40°C with the precede and succeed cycles, that of the heating and cooling patterns are selected to evaluate the effect of heating speed on the bar. Description of designed holding furnace Since direct heating onto the billets surface may cause an irreversible d a m a g e of steel quality (7) , a roller-heath furnace with 14.4m is finally designed and demonstrated for the holding performance of the billets. It is known that the flow of the heat through a thick body of steel is relatively slow compared to surface absorption in high temperature furnaces. Therefore, the holding temperature, depending on alloy billets, is cautiously regulated to prevent the surface overheating while bringing the temperature inside the material up to the required level. In order to keep the exhaust gas temperature below 260°C, the furnace is installed with eight pairs honeycomb ceramic regenerative burners, 15><104 Kcal/hr per pair (NFK model DL-1) , to maximize the heat recovery. The pitch of rollers is designed as 600mm, whereas roller shell material is m a d e by a special material (Kubota KHRSA) and is able to tolerate the furnace temperature up to 1200°C. A cross-section of the roller-hearth holding furnace is shown in Fig.7, the regenerative burners fire across the furnace above rollers to heat the surface of billets, |