BLACK OXIDE COATING is a method for surface protecting, it is the target to make an oxidized film on the surface of the slewing bearing to isolate the air to achieve the purpose of anti-rust. Let’s briefly introduce the defects commonly found in the process of slewing bearing surface machining..
1. Light color on surface
(1) When the blackening treatment is performed, the bath temperature is low, which made oxidation insufficient, so that the oxide film indicate light color.
(2) This phenomenon occurs are caused of NaOH in the blackening bath is few and the content of NaNO2 is too high, so that the temperature of the blackening bath is difficult to rise, and the temperature required for blackening is not completely achieved, and the oxidation rate is reduced. the oxide film is thinner, the surface of the slewing bearing is light evently.
2.Red color on surface
(1) Reason 1: When the temperature of the slewing bearing groove too high at first or the last stage too high, the oxidation rate is increased, and the formed film is thin, and red iron oxide is formed. If the bath temperature is too high, the formed Fe3O4 oxide film is immediately destroyed to become red Fe2O3 while met the oxygen, causing the slewing rings to become red.
(2) Reason 2: The bath concentration is too high, especially that with high NaOH is high while NaNO2 is low, the temperature of the blackening bath is increased, the solubility of the oxide film is easily, and the oxide film is destroyed. The surface easily turn red.