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Show 3. Emergency Heater An emergency electric heater, which is mounted on the furnace lid, is on to keep the temperature of the molten aluminum if the burner tube is cracked. However, the heater is only available for emergency purposes because its capacity is as small as 6 kw. 4. Performance We tested the furnace under the following conditions. Conditions Holding capacity Holding temperature Aluminum material Holding time Results Unit heat Heating up rate 580 kg 680°C ADC12 111.15 h 21.4 kcallkg-h 22.9°C/h Other heat loss 5025 kcal/h (40.5%) Heat loss from the furnace wall 4079 kcal/h (32.8 %) Exhaust loss 3324 kcal/h (26.7%) Heat of combustion 12428 kcal/h Fig. 2 Chart of Heat Balance s. Comparison of Holding Performance Figure 3 shows the comparison of holding performances between the conventional crucible furnace, the immersion bath type holding furnace, and the immersion holding crucible furnace. More than 70 kcal/kg-h of heat units are held with the conventional crucible furnace, whereas the bath-type furnace shows a considerably lower value of about 25 kcal/kg-h. Between these is the value for an immersion-type crucible furnace, but it is still close to that of the bath-type furnace. It should be noted that the thermal load applied to the conventional crucible is considerably higher than that applied to the immersion-type crucible furnace. This is because the former is heated directly by flame and exhaust gas, whereas the latter is heated through the molten aluminum. The reduced thermal load helps extend the life of the crucible. 9 |