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      发黑处理特点：
（1）发黑安全不用电，用碱性高温发黑需100%用电。
（2）提高工效：共需1-2小时。
（3）发黑成本低，设备简单，操作方便；对发黑时间作了严格的控制。
（4）工艺适应性强：解决了球墨铸铁不能发黑的难题。
      发黑处理是一种轴承套圈倒角及挡边的发蓝防锈处理工艺。轴承套圈在热处理后经过除油脱脂，然后在氢氧化钠、亚硝酸钠、硝酸钠和水的混合溶液中进行变色处理，其配比为2-3∶1，其余加水；加水量以温度在 135℃-145℃为合适；时间15-25分钟；取出套圈用清水冲洗后进行钝化处理，钝化处理用重铬酸钾溶液作为填充液，其浓度为12%-18%；在室温下 1-2分钟；经钝化处理并干燥后，放入105℃-120℃的机油或防锈油中 1-3分钟，至气泡完全消失后取出，停放10-15分钟后检验。本发明生成的氧化物薄膜性能稳定，在常温下可长期保护套圈倒角、挡边处不生锈，轴承的外观质量得到明显改善。A3钢用碱性发黑好一些。实际操作中，需要注意的是工件发黑前除锈和除油的质量，以及发黑后的钝化浸油。发黑质量的好坏往往因这些工序而变化。

Black finish features:(1) black security is not electricity, use high temperature alkaline black 100% utilization.(2) improve the working efficiency, need 1 to 2 hours.(3) black low cost, simple equipment, easy to operate;Make the strict control on black time.(4) the process adaptability is strong, solved the difficult problem of nodular cast iron can not black.Black finish is a kind of bearing ring chamfer and bluing antirust processing technology of the guard.Bearing ring after oil removal after heat treatment, and then in a mixture of sodium hydroxide, sodium nitrite and sodium nitrate and water color processing in the solution, the ratio of 2-3:1, the rest of the water.Add water to the temperature at 135 ℃ to 145 ℃ for appropriate;15 to 25 minutes;Take out the ring after wash passivation treatment, passivation treatment with potassium dichromate solution for filling liquid, the concentration of 12% to 12%;1 to 2 minutes at room temperature;After passivation treatment and drying oil is put in the 105 ℃ to 120 ℃ or rust-proof oil 1-3 minutes, to take out after bubble disappear entirely, park 10 to 15 minutes after the inspection.This invention generated oxide film performance is stable, at room temperature can be long-term protection ring chamfer, guard not rusting, the appearance of the bearing quality is obviously improved.A3 steel with alkaline black better.In practice, it is important to note the quality of the workpiece cleaning and degreasing before dark, and the passivation oiled after dark.Black quality often change because of these processes.