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What are the small holes on the bearing ring surface

wallpapers News 2020-12-15
The small holes on the surface of the bearing ring are corroded small holes. In all stages of bearing production, such as single-point or multi-point quasi-circular or oblong black dot-like defects often appear on the surface of the bearing ring. In many cases, people often mistake this kind of defect as being caused by material defects.
 
How does the small hole corrosion on the surface of the bearing ring form?
 
Under normal circumstances, there is a passivation film on the metal surface to protect the metal from oxidation and corrosion. However, due to the uneven chemical or physical properties of the metal surface, such as large composition fluctuations, non-metallic inclusions, foreign matter adhesion, Mechanical damage, oxide film cracks, etc., make the surface passivation film may be destroyed.
 
The metal surface that has lost the passivation film is in an active dissolved state. At this time, if it encounters a certain concentration of electrolyte solution, the corrosive anions (such as Cl-) in the electrolyte solution will be electromigrated by the active metal surface cations. Concentrated on the surface of the metal anode, causing the corrosion potential of the metal electrode to rise; when the corrosion potential of the metal anode is high to a certain level, reaching the critical value for the formation of corrosion nuclei, the anode begins to dissolve, the anode current increases sharply, and a depression is formed on the surface pit.
 
Prevention and Treatment of Small Hole Corrosion on the Surface of Bearing Ring
 
Generally speaking, pinhole corrosion is unlikely to occur on smooth, clean and dry surfaces. There are many reasons for the corrosion of bearing parts. The most common ones are the erosion of moist air, sea breeze, seawater, sweat, oxidation and deterioration of rust-preventing oil (grease), and various chemical treatment processes (such as pickling, acid printing, etc.) It can be neutralized and cleaned in time, etc.; and in some areas, the environment is seriously polluted. Acid rain and acid fog frequently occur. The rich nitric acid and hydrochloric acid make the parts have a tendency to corrode.
 
In the bearing production process, many links may produce pinhole corrosion, especially the storage and turnover links after the ring turning. Sometimes after the ferrule is turned, the heat treatment is not performed immediately. At this time, the passivation film on the surface is relatively fragile and is prone to pinhole corrosion; because the turned parts are rough parts, they often do not pay attention to the necessary surface protection to provide a good storage environment To avoid bumps and bumps, it also leads to the occurrence of pinhole corrosion; as the storage time of the car parts continues, deeper corrosion holes may be generated, so that the grinding process cannot eliminate these small holes.
 
The effect of small hole corrosion on the surface of the bearing ring
 
The pinhole corrosion not only affects the accuracy and surface roughness of the bearing but also reduces its service life and even leads to scrap. Therefore, people should pay full attention to it. Especially in a humid, hot, offshore climate, it is necessary to avoid problems such as pinhole corrosion. Strictly follow the cleaning and rust prevention procedures for the rust prevention treatment of the bearing rings during the processing. The cleaning fluid and rust prevention oil (liquid) used should meet the requirements of the technical regulations; at the same time, accelerate the turnover rate in the production process to prevent various Knock and bruise.

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