Benefits of using black oxidized bearings in wind applications

Benefits of using black oxidized bearings in wind applications

During operation, wind turbines are subjected to a wide range of varying temperatures, wind speeds and loads. These operating conditions, in combination with potential detrimental influences from solid contamination and tribochemical attack due to oil chemistry and water contamination, could result in bearing damage (fig. 1) , which would considerably shorten bearing service life.

One of the requiremets  to prevent these failures is superior surface performance that favours  the running-in process, is resistant to corrosion and is inert against  unfavourable reactions from aggressive lubricant chemistry. Through  SKF’s long involvement with the wind energy industry, the company has  identified black oxidation as one of many solutions to improve  operational reliability.

Black oxidation process

Black oxide is a surface treatment that is formed by a chemical  reaction at the surface layer of the bearing steel and is produced when  parts are immersed in an alkaline aqueous salt solution operating at a  temperature between approximately 130 and 150 °C. The reaction between  the iron of the ferrous alloy and the reagents produces an oxide layer  on the outer layer of the bearing components, consisting of a  well-defined blend of FeO, Fe2O3 and resulting Fe3O4. The result is a  dark-black surface layer of approximately 1–2 μm in thickness. The total  process consists of about 15 different immersion steps, in many of  which it is possible to vary chemical contents, concentrations,  temperatures, immersion times and fluid behaviour within the tanks.