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Show 1. Immersion Burner 1-1 Description of Immersion Burner The immersion-tube burner is a single end type as shown in Figure 1. The burner nozzle, because it becomes hot, uses a heat resistant material. The outer tube is made of ceramic. 1-2 Performances Required of the Immersion Burner Nozzle Ceramic outer Lube Fig. 1 Structure of the Immersion Burner Because it heats molten aluminum from the inside, the burner is exposed to more severe conditions, thermally and mechanically, than conventional methods. The outer tube, therefore, must be of a higher quality. Table 1 shows the requirements for the outer tube material, followed by a detailed description of each. Table 1 Requirements for outer tube material 1) Excellent thermal shock resistance 2) Inactive with molten aluminum and exhaust gas 3) Excellent thermal conductivity and mechanical strength, and moldable into a thin-walled tube 4) Available at a reasonable price 1) Excellent thermal shock resistance The outer tube is exposed to a combustion gas and should be resistant to the thermal shock when the burner is ignited. There will be a temperature difference of about 1,100°C between inand outside the outer tube in the air, and about 400°C even in the molten aluminum. In addition, tensile stress occurs because the outer tube is heated from the inside. Therefore, the outer tube material should have excellent thermal conductivity and thermal shock resistance. 2) Inactive with molten aluminum and exhaust gas Molten aluminum is highly corrosive, thus prohibiting the use of ordinary metals for the outer tube. Even if it is ceramic, those containing Si02, which are normally used as bricks, cannot be used for a long period. 2 |
