What are the small holes on the surface of the bearing rings? How are they formed?

I wonder if bearing manufacturers have encountered this situation during the production of bearings. What is going on? How are these small holes formed? Below, China Bearing Network (abbreviated as: Huazhou Network) will share how the small holes on the surface of the bearing ring are formed and what are the characteristics of this small hole corrosion based on its understanding of bearings.

What are the small holes on the surface of the bearing ring?

The small holes on the surface of the bearing ring, such as the small holes on the surface of the bearing ring in Figure 1, are corrosion holes. In various stages of bearing production, single-point or multi-point quasi-circular or oblong black dot defects often appear on the surface of the bearing ring. In many cases, people often mistake this defect for a material defect.

How is the small hole corrosion on the surface of the bearing ring formed?

Under normal circumstances, there is a passivation film on the metal surface to protect the metal from oxidation and corrosion, but due to the uneven chemical or physical properties of the metal surface, such as large component fluctuations, non-metallic inclusions, foreign matter adhesion, mechanical damage, cracks in the oxide film, etc., the surface passivation film may be destroyed.

The metal surface without the passivation film is in an active dissolution state. At this time, if it encounters an electrolyte solution of a certain concentration, the corrosive anions (such as Cl-) in the electrolyte solution will be electromigrated by the active metal surface cations and enriched on the metal anode surface, causing the corrosion potential of the metal electrode to increase; when the metal anode corrosion potential is high to a certain extent and reaches the critical value for the formation of corrosion nuclei, the anode begins to dissolve, the anode current increases sharply, and pits are formed on the metal surface.

Prevention and treatment of small hole corrosion on the surface of bearing rings

Generally speaking, small hole corrosion is not easy to occur on smooth, clean and dry surfaces. There are many reasons for the corrosion of bearing parts. The most common ones are erosion by humid air, sea breeze and seawater, sweat, oxidation and deterioration of rust-proof oil (grease), and various chemical treatment processes (such as pickling, acid printing, etc.) between processes. Failure to neutralize and clean in time, etc.; In addition, some areas are currently seriously polluted, acid rain and acid mist occur frequently, and the rich nitric acid and hydrochloric acid in them greatly increase the tendency of parts to produce small hole corrosion.

In the bearing production process, many links may cause pinhole corrosion, especially the storage and turnover links after the ring is turned. Sometimes the ring is not immediately heat treated after turning, and the passivation film on the surface is relatively fragile and prone to pinhole corrosion; because the turned parts are blank parts, they are often not given the necessary surface protection, providing a good storage environment, and avoiding bumps and scratches, which also leads to the occurrence of pinhole corrosion; as the storage time of the turned parts continues, deeper corrosion holes may be generated, so that grinding cannot eliminate these pinholes.

Impact of pinhole corrosion on the surface of bearing rings

Pinhole corrosion not only affects the accuracy and surface roughness of the bearing, but also reduces its service life and even leads to scrapping, so it should be given full attention. Especially in humid, hot, and offshore climate environments, it is even more important to avoid the occurrence of pinhole corrosion. Strictly follow the cleaning and rust prevention procedures to carry out rust prevention on the bearing rings during processing. The cleaning liquid and rust-proof oil (liquid) used should meet the requirements of the process technology regulations; at the same time, speed up the turnover speed in the production link to prevent various bumps and scratches.