What is the importance of preloading in bearings?

Short Answer:

The importance of preloading in bearings lies in its ability to eliminate internal clearance, reduce vibration, and improve positioning accuracy. Preloading means applying a small intentional force on the bearing during installation to keep the rolling elements tightly in contact with the raceways. This helps in improving stiffness, stability, and noise reduction in rotating systems.

Preloading is especially important in precision machines, such as CNC machines, robots, and electric motors. Without proper preload, the bearing may suffer from looseness, noise, uneven wear, or reduced service life. Proper preloading ensures smooth operation, higher accuracy, and better performance of the bearing.

Detailed Explanation:

Importance of preloading in bearings

In rotating machines, bearings support shafts and reduce friction between moving parts. For bearings to perform smoothly and accurately, they must be installed in a way that reduces looseness and increases stability. This is done by applying preload, which is a deliberate internal force that pushes the rolling elements (balls or rollers) against the raceways even when there is no external load.

Preload removes internal clearance, enhances contact, and improves the mechanical behavior of the bearing during actual operation. It is especially important in high-precision and high-speed applications where even small movements can affect performance.

What is preload in bearings?

Preloading means applying a small internal force on the bearing during assembly. This can be achieved in two ways:

  • Axial preload: Used in angular contact and tapered roller bearings by pushing the inner and outer rings towards each other.
  • Radial preload: Used in some applications by using oversized rolling elements or tight fits.

Preloading can be applied using:

  • Springs
  • Axial screws or nuts
  • Solid spacers
  • Matched pair bearings with offset

Benefits of preloading in bearings

  1. Eliminates internal clearance

Most bearings have a small amount of clearance between the rolling elements and raceways to allow easy rotation. However, this clearance can cause vibration, looseness, and inaccuracy.

Preload fills this gap, reducing internal play and improving performance.

  1. Increases stiffness

Stiffness means how much a system resists movement when a load is applied. Preloading makes the bearing more rigid, reducing deflection under load.

  • Important in CNC machines, spindles, and measuring equipment
  • Improves precision and repeatability
  1. Reduces vibration and noise

A loose bearing may cause the rolling elements to rattle or bounce, producing noise and vibration. Preloading holds the elements in position, reducing motion and noise.

  • Useful in medical devices, fans, and electric motors
  • Ensures smooth, quiet operation
  1. Improves positioning accuracy

In machines that need precise movements (like robotics or servo systems), any looseness in the bearing can lead to errors. Preload improves accuracy by minimizing backlash or delay in motion transfer.

  • Helps maintain correct shaft position
  • Critical in high-speed and positioning-sensitive systems
  1. Increases bearing life

Preload keeps the load evenly distributed across the rolling elements, reducing stress on individual parts. This avoids shock loads, uneven wear, and damage.

  • Promotes uniform wear
  • Reduces fatigue and failure

However, too much preload can increase friction and heat, so it must be applied carefully.

Where preload is important

  • Machine tool spindles
  • High-speed motors
  • Precision gearboxes
  • Robotic arms and actuators
  • Optical and medical equipment

How to determine correct preload

  • Use manufacturer recommendations
  • Follow assembly procedures carefully
  • Measure axial displacement or torque after assembly
  • Avoid over-preloading (can cause overheating and early failure)

Modern systems may use preload sensors or adjustable mechanisms to maintain optimal load during operation.

Conclusion

Preloading in bearings is very important to ensure tight contact, reduce clearance, and improve performance in critical machines. It helps achieve better stiffness, less noise, accurate motion, and longer bearing life. Preload is especially useful in high-precision and high-speed applications. However, it must be applied correctly to avoid excessive force. Understanding and applying the correct preload ensures the bearing works efficiently, smoothly, and reliably.