Self-lubricating bearings are widely used in applications where external lubrication is limited or not feasible. These bearings rely on embedded solid lubricants—such as PTFE or engineered composite materials—to reduce friction and wear.

However, under dry running conditions, where no additional lubrication is present, their performance can change significantly. Many engineers and buyers notice that friction, wear, and service life vary more than expected.

Understanding why self lubricating bearings perform differently in dry running is essential for evaluating material behavior and predicting performance in real operating conditions.

Self-Lubricating Bearings in Dry Running Conditions: Basic Mechanism

Self-lubricating bearings operate by forming a transfer film on the mating surface during sliding motion.

• The sliding layer releases solid lubricant (such as PTFE)

• A thin transfer film forms between the bearing and shaft

• This film reduces direct metal-to-metal contact

Under stable conditions, this mechanism enables low friction without oil or grease. In dry running bearings, however, the formation and stability of this transfer film become the key factors affecting performance.

Why Self-Lubricating Bearings Perform Differently in Dry Running

The performance of self lubricating bearings in dry running depends on how effectively the transfer film can form and remain stable during operation.

Transfer Film Stability

• Stable film → consistent low friction and reduced wear

• Unstable film → increased friction and surface damage

Dry running conditions make it more difficult to maintain a stable film, especially during startup, load variation, or intermittent motion.

Material Behavior Under Dry Friction

Different composite materials respond differently under dry running conditions. For a detailed comparison of material performance, see PTFE vs fiber vs metal-backed bearings in dry running.

• PTFE-based materials provide low friction but may wear faster under high load

• Reinforced composites offer improved wear resistance

• Metal-backed structures help support load and dissipate heat

These differences explain why dry running bearings performance can vary even when the design appears similar.

Load, Speed, and PV Limits in Dry Running Bearings

One of the most important factors affecting self lubricating bearings in dry running is the PV value (Pressure × Velocity).

• Higher load increases contact pressure

• Higher speed increases frictional heat

• The combined effect accelerates wear

When the PV limit is exceeded:

• The transfer film becomes unstable

• Friction rises rapidly

• Wear increases significantly

This is a primary reason why dry running bearings may perform differently compared to lubricated conditions.

Temperature Effects on Dry Running Bearings Performance

In dry-running conditions, heat generation becomes more significant due to the absence of liquid lubrication.

• Friction generates heat at the contact surface

• Limited heat dissipation increases operating temperature

• Elevated temperature affects material properties

If the temperature exceeds material limits, the sliding layer may soften or degrade, leading to unstable performance and accelerated wear.

Performance Characteristics of Dry Running Bearings

Due to the combined effects of transfer film behavior, load, speed, and temperature, dry running bearings performance typically shows the following characteristics:

• Higher sensitivity to operating conditions

• Greater variation in friction and wear

• More dependence on material design

These characteristics explain why self lubricating bearings require more careful evaluation in dry-running environments compared to lubricated systems.

Practical Implications for Dry Running Applications

In practical applications, differences in performance are often linked to operating conditions rather than fundamental material failure.

For example, unstable transfer film formation, excessive PV values, or high operating temperatures can all lead to increased wear in dry running bearings.

Recognizing these influencing factors helps engineers better understand performance variations and evaluate suitability for specific applications.

Conclusion

Self-lubricating bearings in dry running conditions behave differently primarily due to the stability of the transfer film and the interaction between load, speed, and temperature.

By understanding these mechanisms, it becomes easier to interpret performance changes, compare materials, and make informed decisions in dry-running applications.

For complex applications involving high load or challenging dry-running conditions, further technical evaluation may be required to ensure reliable performance.