Learn what bearing preload is, why it's critical for angular contact bearings, and the difference between factory and spring preload. Discover how to select the right preload for optimal rigidity and performance.
What is Bearing Preload?
Bearing preload is a predetermined axial or radial force applied to eliminate internal clearance, creating a state of controlled "negative clearance." This intentional stress elastically deforms the raceways and rolling elements, locking them together to enhance performance.
While standard radial bearings often operate with clearance, angular contact bearings require preload to maintain constant contact between the balls and raceway.
Why Use Preload? Key Benefits
Applying the correct preload optimizes bearing performance by:
1.Increasing Rigidity: Eliminates play, making assemblies stiffer for machine tool spindles.
2.Improving Accuracy: Ensures high running precision, even with changing loads.
3.Reducing Noise & Vibration: Prevents axial resonance, especially in small electric motors.
4.Preventing Skidding: Optimizes ball spin to reduce sliding friction and wear.
Types of Bearing Preload: Factory vs. Spring
Choosing the right preload method depends on your application's need for stiffness versus thermal stability.
1. Factory Preload (Built-in)
Applied during manufacturing via a calculated axial offset between rings, labeled as Light, Medium, or Heavy.
Pros: Extremely high rigidity; ideal for stable operating conditions.
Cons: Sensitive to thermal expansion; requires precise mounting.
Example: A GMN S6005 C bearing requires 130 N of force to achieve its Medium preload.
2. Spring Preload (External)
Uses components like wavy washers or Belleville springs to apply continuous force.
Pros: Excellent thermal compensation (force stays constant during shaft elongation); allows for looser housing tolerances.
Cons: Less rigid than factory preload.
Best For: Applications with significant temperature changes or where cost-effective housing machining is a priority.
| Feature | Factory Preload | Spring Preload |
| Rigidity | Very High | Moderate / Flexible |
| Thermal Compensation | Poor | Excellent |
| Mounting Complexity | High Precision Required | More Forgiving |
How to Select the Right Preload
Follow these steps to choose the optimal preload for your application:
1.Define Requirements: Do you need maximum stiffness (e.g., grinding spindles) or precise positioning under light/variable loads? If yes, preload is necessary.
2.Analyze Conditions:
Temperature: If the shaft runs hotter than the housing, a back-to-back (DB) arrangement is less sensitive to thermal growth than a face-to-face (DF) setup.
Speed: Spring preload is common for high speeds but verify it meets stiffness needs.
3.Calculate Force (for Springs):
Use the empirical formula to estimate the required preload force:
F = k × d
Where: F = Force (kN), d = Bore Diameter (mm), k = Factor (0.005–0.01 for motors; 0.02 for anti-vibration).
Conclusion
Proper bearing preload is essential for high-precision performance. Use Factory Preload for maximum rigidity and Spring Preload for superior thermal stability. Always validate your selection through testing to account for real-world operating conditions.
