| 摘要 |
The surfaces of steel sheet or strip are prepd. prior to coating by immersion in a hot molten metal bath (M) without using a flux. Prepn. consists of feeding the strip through two successive heating zones (a,b); and then through a cooling zone (c) with a protective atmos. in which the strip is cooled to ca. the temp. of bath (M). The capacity of the steel strip to absorb radiant heating energy in zones (a,b) is increased by forming a visible coating (a1), contg. iron oxide, in zone (a), and preserving layer (a1) in zone (b). Layer (a1) is pref. completely reduced in zone (c) by an atmos. contg. by vol. min 10% H2. Layer (a) may consist of iron oxysulphide,obtd. by using combustion gases in zone (a) contg. max. 2% free O2 and 0-36 g of sulphur per m3, esp. by burning fuel in air to attain min. 1205 degrees C in zone (a), the colour of layer (a1) being dark yellow to blue. Zone (b) is pref. separate from zone (a) and contains below 5% H2. See also 2375335. Used for all types of metal (M), e.g. Al or its alloys; Zn or its alloys; Pb-Sn alloys. Coke oven gas contg. sulphur can be used in the process and a substantial increase in thermal efficiency is obtd. |
