| 摘要 |
PURPOSE:To contrive to enhance corrosion resistance of a heat exchanger and prevent harmful substances from being mixed into dew water, by a method wherein an Sn-Bi base alloy having a Bi content in a specified range is used as a surface-treating material for a heat exchanger for a high efficiency type water heater. CONSTITUTION:The surface of the heat exchanger is coated with an Sn-Bi base alloy. A comparison of corrosion losses of Sn-Bi base alloys having different Bi contents shows that an alloy having a higher Bi content is corroded more easily, so that a desirable Bi content is 0.1-40wt%, preferably about 5wt%. By applying a surface-treating material consisting of such an Sn-Bi base alloy to a secondary heat exchanger 2, corrosion resistance and durability can be enhanced, as compared to the case of using a Pb-Sn base alloy for the same purpose. Further, when a primary heat exchanger 1 is also coated with the Sn-Bi base alloy, harmful substances are not mixed into dew water formed on the surface of the secondary heat exchanger 2, so that acidic dew water formed can be discharged by only conducting a neutralizing treatment. |
