Many purchasers and maintenance technicians assume that stainless steel bearings will never rust once selected. In their understanding, stainless steel, as the name suggests, does not rust and can fully resist water, moisture and corrosion.
However, many users encounter pitfalls in practical applications. Even with stainless steel bearings, rust spots and dark marks appear on the surface soon. Pitting corrosion, rotation jamming may occur, and the bearings eventually wear out and fail. Is this a product quality issue, or a result of cutting corners by suppliers?
The answer is straightforward. We misunderstood the meaning of "stainless steel" from the start. Stainless does not mean rust-proof forever.
The rust resistance of stainless steel bearings relies on a dense passive film on the surface. This protective film isolates moisture and air, and can basically prevent rust in dry indoor environments. Nevertheless, the passive film is not robust. When exposed to accumulated water, salts, acids and alkalis, especially chloride ions, the protective film will be damaged rapidly.
Corrosion caused by chloride ions features strong permeability. It does not only stay on the surface but penetrates deep into the metal and forms pitting corrosion. At the initial stage, only tiny dark spots appear, which are hard to detect. As corrosion worsens, bearing precision drops, abnormal noise and jamming occur, and the failure will disrupt the normal operation of the whole equipment.
Selecting bearings based solely on price is a major misconception when using stainless steel bearings. Different working conditions require completely different materials; there is no universal grade.
• 201 / 304 stainless steel bearings: Suitable for conventional scenarios with dry indoor environment, no corrosion and no salt, featuring excellent cost performance to meet basic rust prevention requirements.
• 316 stainless steel bearings: With stronger resistance to salt and chloride ions, they are suitable for mildly corrosive environments such as outdoor humid conditions, rain wash and food processing.
Even if 316 material is selected, it can only delay rusting and cannot completely eliminate corrosion. Under extreme working conditions such as seawater immersion, high salt, high acid and alkali, and heavy chemical corrosion, the passive film of all types of stainless steel will keep failing, and corrosion problems still exist. The final selection guide is as follows to avoid unnecessary costs.
• Dry indoor and conventional working conditions: Choose 304 stainless steel bearings for cost-effectiveness;
• Outdoor humid, light salt spray and food industry applications: Choose 316 stainless steel bearings for enhanced corrosion resistance;
• Seawater immersion, high salt, high acid & alkali and heavy corrosion working conditions: Select full ceramic bearings for a permanent solution.
Stainless steel is only rust-resistant, not absolutely rust-free. Properly distinguishing material properties and selecting bearings accurately according to on-site working conditions can avoid corrosion problems from the source and reduce extra losses caused by equipment maintenance and downtime. Kent Bearing has supplied more than 200 million sets of motor bearing solutions for over 500 motor manufacturers worldwide. If your motors are troubled by bearing issues, or you want to prevent bearing problems in advance, please contact the Kent technical service team at 19957028916. We will help you quickly locate the root cause of problems, easily resolve motor faults, cut after-sales losses and retain key customers steadily!
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