Blackening

Blackening is a common means of chemical surface treatment. The principle is to produce an oxide film on the metal surface to isolate the air and achieve the purpose of rust prevention. Blackening treatment can be used when the appearance requirements are not high. The surface blackening treatment of steel parts is also called bluing.

There are two common methods of blackening treatment: traditional alkaline heating blackening and late room temperature blackening. However, the effect of room temperature blackening process on low carbon steel is not very good. Alkaline blackening is subdivided, and there is the difference between one blackening and two blackening. The main components of black liquor are sodium hydroxide and sodium nitrite. The temperature difference required for blackening is not large. A good surface can be obtained between 135-155 ℃, but it takes a little time.

(1) Blackening is safe without electricity, and 100% electricity is required for alkaline high-temperature blackening. (2) improve work efficiency: it takes 1-2 hours in total. (3) blackening cost is low, equipment is simple and operation is convenient; blackening time is strictly controlled. (4) strong process adaptability: the problem that nodular cast iron can not blacken is solved.

The utility model relates to a bluing antirust treatment process for chamfering and retaining edges of bearing rings. The bearing ring is degreased after heat treatment, and then discolored in the mixed solution of sodium hydroxide, sodium nitrite, sodium nitrate and water. The ratio is 2-3 ∶ 1, and the rest is added with water; The appropriate amount of water is 135 ℃ - 145 ℃; Time: 15-25 minutes; Take out the ferrule and rinse it with clean water for passivation treatment. Potassium dichromate solution is used as the filling solution for passivation treatment, and its concentration is 12% - 18%; At room temperature for 1-2 minutes; After passivation and drying, put it into engine oil or antirust oil at 105 ℃ - 120 ℃ for 1-3 minutes, take it out after bubbles completely disappear, and park it for 10-15 minutes before inspection. The oxide film produced by this process has stable performance, can protect the ring chamfer and retaining edge from rust for a long time at room temperature, and the appearance quality of the bearing has been significantly improved.

A3 steel is better blackened with alkali.

In actual operation, attention should be paid to the quality of rust removal and oil removal before blackening and passivation and oil immersion after blackening. The blackening quality often changes due to these processes.