| OCR Text |
Show 5 but economical holding furnace. In this manner, a mathematical modelling of unsteady two-dimensional heat conduction, in terms of finite difference and fully implicit method with only thermal radiation loss, is first developed to simulate the temperature distribution of billets. Few assumptions stated as following, are used to match the blank test without the furnace first, and then proceed to simulate the heating results: 1. Uniform boundary conditions; 2. Neglect energy change through the rolling mill; 3. Radiative heat exchange dominates the heat transfer inside the furnace; 4. Emissivity of round bar is 0.8 and ambient temperature is 30°C. Experimental At the beginning, a 9.6m long furnace, located at 2 m away from the pendulum, is designed to heal the temperature distribution across the billet, Fig.4 shows a computational modelling temperature profile of a billet with 27.65m with/without the furnace, the blank test without the furnace apparently indicates that the temperature difference across the billet is over 150°C. As long as the furnace is applied, also shown in Fig.4, this longest billet, with the smallest cross-section area, shows that the head throughout the center half has a significantly improvement of temperature uniformity, due to those are kept in the furnace without heat release. Unfortunately, since the transport speed has been reduced 10 times slower, those tail portions exposed at the front of the furnace only gains temperature slightly. Moreover, it is found an increase of furnace temperature improves slightly on the temperature profile of the billet, which indicates the heating characteristic of hot alloy billets must be taken into consideration. The effect of direct heating on billets To solve the temperature decay happened at the billet tails, the first approach was to reserve 2 m at the front of 9.6m furnace and to install two high-speed burners, whereas 8 pair of regenerative burners were squeezed at the remaining furnace, as shown in Fig.5. Based on this concept, the burners flame is directly fired onto the surface of incoming billets, but is only selectively heated at the tail portions of smaller cross- |
