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Electrolytic corrosion (galvanic corrosion)

Describes electrolytic corrosion which is one of the causes of wear of OILES bearings.

The term “electrolytic corrosion” here refers to galvanic corrosion (contact corrosion between dissimilar metals). In each industry, most machines and structures consist of a combination of dissimilar metals in a certain form; few of them generally consist of a single metal.
If an electrolyte solution (water, sea water, etc.) intervenes in the combination of metallic materials, galvanization is generated, selectively corroding a material with lower potential peculiar thereto.
Accordingly, when combining metallic materials, it is necessary to combine those with lower mutual potential difference as much as possible. Generally recommended is a combination of 100 mV or less.
The specific potential of the material numerically differs depending on the type, PH value, contamination and flow velocity of an electrolyte solution such as water, sea water, etc. To grasp accurate corrosion data, it is necessary to measure a peculiar potential with a potentiometer.
OILES bearings related to galvanic corrosion include OILES #500 (solid lubricant embedded bearings), etc.

Photo 1 shows an example of galvanic corrosion of OILES #500.
The solid lubricant embedded in OILES #500SP-SL1 is of graphite and results in a potential difference of approx. 0.9 V from carbon steel of the mating shaft.
In the example of galvanic corrosion shown in Photo 1, the damaged seal of the grease enclosed bearings allowed in rain water, resulting in trouble.
As mentioned above, you can see that graphite (solid lubricant) with higher peculiar potential is selectively corroding carbon steel (mating material) with lower peculiar potential.

Pin;Quenched S45C Bush;Oiles 500SP-SL1

Photo. 1. Example of Galvanic Corrosion

Galvanic corrosion is seen more remarkably in a dry-wet repeating condition than when completely immersed in water.
In the atmosphere, galvanic corrosion is generated by an entry of rain water in outdoor use and under high humidity.
If the contact surface is protected by oils and fats such as oil and grease, however, galvanic corrosion is greatly inhibited.
To prevent galvanic corrosion, it is necessary to protect the contact surface with oils and fats such as oil and grease or decrease the specific potential difference of the material.
When using OILES #500SP-SL1 or OILES #500SP-SL2 bearings with embedded graphite-based solid lubricant in a corrosive environment, it is recommended to periodically lubricate them as one of galvanic corrosion preventive measures.
Since polytetrafluoroethylene has no peculiar potential, OILES #500SP-SL4 bearings, where polytetrafluoroethylene-based solid lubricant has been embedded, are highly resistant to galvanic corrosion.

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