A novel conversion treatment for iron and steel parts was developed by combining the phosphating and two-step oxidation processes. The phosphating bath composition and process conditions are as follows: zinc dihydrogen phosphate 30-40 g/L, zinc nitrate 90-120 g/L, manganese nitrate 10-20 g/L, total acidity 80-90, free acidity 2-3, normal temperature, and time 10 min. The first oxidation is carried out in a bath containing NaOH 550-600 g/L and NaNO2 100-150 g/L at temperature 130-150 °C for 25-35 min. The secondary oxidation is carried out in a bath containing NaOH 600-650 g/L and NaNO2 150-200 g/L at temperature 135-140 °C for 25-35 min. The obtained composite film is smooth, thick and corrosion resistant (even after being abraded for a long time), having both advantages of phosphating film and oxidation film.%将钢铁件磷化与氧化(双槽)两大工艺结合起来,开发了一种新型转化膜生产工艺.磷化液配方和工艺条件为:磷酸二氢锌30 ~ 40 g/L,硝酸锌90 ~ 120 g/L,硝酸锰10 ~ 20 g/L,总酸80 ~ 90点,游离酸2 ~ 3点,常温,时间10 min.第一槽氧化液配方和工艺条件为:NaOH 550 ~ 600 g/L,NaNO2100 ~ 150 g/L,温度130 ~ 150 °C,时间25 ~ 35 min.第二槽氧化液配方和工艺条件为:NaOH 600 ~ 650 g/L,NaNO2150 ~ 200 g/L,温度135 ~ 140 °C,时间25 ~ 35 min.该复合转化膜具备磷化膜与氧化膜的优点,平整光滑,厚而耐腐蚀,经过长久磨损后依旧耐腐蚀.
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