OCR Text |
Show IT ceramic as SiC, S~N4 and SIALON, are used for the outer tube, it would still be corroded by flux (NaCI, etc.) used for degassing or eliminating impurities in the molten aluminum, resulting in the invasion of Al (or Al20 3 ) into the tube wall, and it would finally crack. When exposed to the high-temperature combustion gas, materials such as C, Si3N4 , SiC are oxidized. 3) Excellent thermal conductivity and mechanical strength, and moldable into a thin-walled tube Because the outer tube conducts heat between exhaust gas and molten aluminum, its characteristics have a direct influence on the efficiency of the burner. The outer tube material should have excellent thermal conductivity and be moldable into a thin-wall tube. It should also be mechanically strong, and easy to handle. 4) Available at a reasonable price The price of one outer tube ranges from forty or fifty thousand through to more than one million yen, depending on the materials used and the assembly methods. Considering both price and properties required, the material currently in use mostly consists of SiC and C in the following configuration: Above slag line Slag line Fig. 2 Material (SiC / C) Configuration Table 2 Required Properties for Different Segments of the Heater Tube Segment Required Properties Material Configuration Above slag line 1) Resistant to oxidation SiC: 47% 2) High mechanical strength C:30% 1) Resistant to corrosion by slag SiC: 46% Slag line 2) Resistant to thermal shock C: 33% 3) Resistant to oxidation 1) Inactive with molten aluminum SiC: 45% Below slag line 2) Resistant to thermal shock C: 350/0 3) High thermal conductivity 3 |