The Importance of Clean Bearings
Dirt is one of the biggest problems that can affect bearings. An accumulation of dirt on a bearing can lead to slower operations, a reduction of efficiency, and a higher potential for permanent damage to a machine. Therefore, it’s essential that you regularly clean and grease your bearings.
Here are some pre-emptive measures you can take to prevent dirt from getting on your bearings when handling them, before you start to clean and grease the bearings:
- Wear clean elastomer gloves.
- Use clean, lint-free bags.
- If using compressed air, use filtered and dry – but make sure to not spin the bearings using the air.
How To Clean Bearings
All traces of existing greases and preservatives on bearings must be cleaned before applying Krytox™ greases, as they could otherwise form carbon deposits that lead to bearing failure.
Cleaning bearings can be broken down into 4 simple steps:
- Use a prying tool to carefully remove the seal, by prying between it and the inner ring, without touching any other parts of the bearing.
- Place your bearings in a clean wire basket, then carefully lower the basket into a container of clean solvent. Use a solvent appropriate for the type of lubricant that’s present on the bearing. Avoid chlorinated solvents as they can cause corrosion. Fluoridated solvents are usually unnecessary for hydrocarbon lubricants.
- Physically agitate the parts, or have cleaning fluid pumped through the bearing. Maintain the solvent temperature under its flash point. An ultrasonic cleaner can also be used.
- Dry the bearings by blowing hot air through them or by heating them to 93.3°C for 10 minutes. Allow to cool to room temperature. To remove heavier solvents, volatile solvents may also be used as a final rinse; although they are flammable and so extra care should be taken around them.
How To Grease Bearings
Once your bearings are clean, they should be lubricated immediately, by hand, with a specified Krytox™ lubricant.
Greasing bearings can be broken down into 4 simple steps:
- Weigh the correct amount of grease on a gram balance and transfer it to a syringe (to calculate how much grease to put in a bearing, see next section).
- Inject half of the grease in the cavities between the rolling elements; one half from either side of the bearing.
- Carefully rotate the bearing, by hand, to spread and distribute the grease across the rolling elements sufficiently.
- Carefully replace shields or seals, stopping any grease from leaking out prematurely.
How Much Grease To Use
It’s important to use a sufficient amount of grease in bearings, as too little grease could lead to premature failure while too much grease could lead to the overheating of bearings. The application and operating speed of the bearing determine the amount of grease applied, as described below.
- Conveyor belts and low-speed machinery with DN values under 50,000, use 60-75% of the free volume.
- Medium-speed applications with DN values between 50,000-200,000, use 35-50% of the free volume.
- High-speed applications, use 25-35% of the free volume.
- Extreme-speed applications, use 10-15% of the free volume.
Remember to consider Krytox™ grease’s high density when determining the fill quantity by weight. The specific gravity of Krytox™ grease is about 2.0 mg/L. Contact your bearing manufacturer for the capacity of the specific bearing you are using.
Furthermore, make sure you use a dedicated grease gun that matches the fitting. Grease fittings should be changed to a different style, such as button-head or pin type, to stop other types of grease from accidentally going inside the bearing.
Speed Factor (DN)
The speed factor (DN) of a bearing determines the available speed range for the grease inside a bearing. The DN value is calculated by multiplying the inner race i.d. (in millimeters) by the RPM. DN values of 100,000-400,000, and higher, have been achieved at temperatures of 204 °C- 260 °C using Krytox™ greases. Special break-in runs might be required to further spread the grease to avoid overheating, at these speeds.
The speed factor is ultimately a measure of the lubricant’s internal friction, dependent on the type of bearing, its load, speed, precision, and lubrication system, and is a key factor when determining how to clean and grease bearings.