The surface of the steel parts is blackened, also known as bluing.Blackening treatment now commonly used methods have the traditional alkaline heating blackening and the appearance of late room temperature blackening two kinds.But the blackening process at room temperature is not very good for low carbon steel.A3 steel is better blackened with alkalinity.The basic blackening is subdivided, and there is the difference between one blackening and two blackings.The main components of black liquor are sodium hydroxide and sodium nitrite.Blackening requires a wide range of temperatures, between 135 and 155 degrees Celsius to get a good surface, but it takes a little bit longer.In practical operation, it is necessary to pay attention to the quality of rust removal and oil removal before blackening the workpiece, and passivated immersion oil after blackening.The quality of blackening often varies with these processes.
Metal "blue" liquid medicine
Alkaline oxidation or acid oxidation is used.An oxide film is formed on the metal surface to prevent corrosion of the metal surface. This process is called "bluing".The oxide film formed by the "bluing" treatment on the surface of ferrous metal is mainly ferric tetroxide in outer layer and ferrous oxide in inner layer.
I. Alkaline oxidation "bluing" solution
1.Formula: sodium nitrate 50 ~ 100g sodium hydroxide 600 ~ 700g sodium nitrite 100 ~ 200g water 1000 g
2.Method: after measuring according to the formula, under the stirring condition, add each material in turn, dissolve, mix evenly.
3.Description:
(1) The metal surface must be cleaned and dried before "hair basket" treatment.
(2) The "bluing" treatment condition of metal devices is related to the carbon content in the metal, the temperature of "bluing" liquid and the treatment time of metal devices.
(3) Every week or so to analyze the contents of sodium nitrate, sodium nitrite and sodium hydroxide in the solution on schedule, in order to timely supplement the relevant components.Generally use half a year after the replacement of all solutions.
(4) After the metal "bluing" treatment, it is better to rinse with hot soapy water for several minutes, and then rinse with cold water.Then, rinse with hot water and blow dry.
Second, acid oxidation method "blue" solution
1.Formula: 3 ~ 10 g calcium nitrate phosphate 80 ~ 100 g manganese peroxide 10 ~ 15 g water 1000 g
2.Method: after measuring according to the formula, add phosphoric acid, manganese peroxide and calcium nitrate in turn under the condition of constant stirring, dissolve and mix evenly.
2.Description:
(1) The metal devices should be cleaned and dried before "bluing" treatment.
(2) The protective film obtained by this method is black, and its main composition is composed of calcium phosphate and iron oxide. Its corrosion resistance and mechanical strength are both higher than those obtained by alkaline oxidation method.
4. The working temperature of "bluing" is 100℃, and the treatment time is 40 ~ 45 minutes.In the treatment of carbon steel, the content of phosphoric acid in the liquid was controlled at 3 ~ 5 g/l.The phosphoric acid content is controlled at 5 ~ 10 g/l when alloy or cast steel is processed.Attention should be paid to periodic analysis of the content of phosphoric acid in the liquid.
5. The cleaning method of metal components after "bluing" treatment is the same as above.