Grease selection for high-speed bearings

1. Define bearing and operating conditions

• Rotational speed (rpm): Rotational speed is particularly important for high-speed bearings. The grease's DN value (rotational speed x bearing diameter) must be below a certain limit.
  • For example: DN = d(mm) × n(rpm)
  • For high speeds, greases with low viscosity and a thin structure are preferred.
• Load: Is the load on the bearing light, medium, or heavy?
  • If the load is light, thin and low-viscosity grease is suitable.
  • If the load is heavy, more adhesive grease with EP additives may be required.
• Temperature: High-speed bearings typically heat up. Therefore, the grease's maximum operating temperature and thermal stability are important.

2. Consider the basic components of the grease

• Base oil (mineral, synthetic):
  • For high speeds, synthetic base oils (PAO, ester) are preferred because they have lower viscosity and do not degrade at high temperatures.
• Thickener:
  • Lithium complex (Li-Complex) and aluminum complex bearing greases are suitable for high temperature and high speed.
  • Standard lithium soap is good for low speeds, but at high speeds, the grease may splatter or melt.
• Additives:
  • Antioxidant, EP, and anti-wear additives increase bearing life.
  • In high-speed applications, excessive EP additives may be unnecessary and can increase the grease's viscosity.

3. Viscosity and consistency class

• Low viscosity, low NLGI grade should be appropriate for the bearing speed.
  • Generally, NLGI 1 or 2 is preferred.
  • For very high speeds (e.g., >20,000 rpm), NLGI 0 or 00 can even be used.
• ISO VG (base oil viscosity)
  • For high speed, ISO VG 32–100 is ideal (varies depending on temperature).

4. Typical high-speed greases

• Lithium complex based synthetic greases (PAO based) → common use, withstands up to 150–180 °C.
• Polyester or ester based synthetic greases → can withstand up to 200 °C.
• NLGI 1–2, low viscosity types → reduce splashing and heating at high speed.

5. Application tips

• Do not apply more grease than necessary to the bearing; excessive grease increases friction and heat at high speeds.
• The bearing's lubrication interval and grease purge should be checked regularly.
• If necessary, use a lubrication system (e.g., drip or centralized lubrication) because manual greasing may be insufficient at high speeds.

📌 Summary table:

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