Thermal Expansion: A Key Consideration in Material Selection for Plane Bearing Design

We are all aware that plastics expand and contract at different rates. However, in bearing design, thermal expansion is not just a material property, it is a critical material selection decision that directly impacts performance, fit, and service life.

When designing plastic plane bearings, one of the most critical considerations is understanding how material selection influences thermal behavior across the full operating environment. Engineers must design not only for normal operating temperatures, but also for minimum and maximum extremes.

Poor material selection can lead to:

• Loss of press fit in cold temperatures

• Excessive expansion and shaft seizure at elevated temperatures

• Changes in running clearance and alignment

• Premature wear or catastrophic failure

Selecting the right bearing material ensures dimensional stability and consistent performance across temperature fluctuations.

What Is Thermal Expansion?

“Thermal expansion is the tendency of matter to change in shape, area, and volume in response to changes in temperature.”

At a practical engineering level, thermal expansion reflects how molecular activity increases with temperature, causing materials to expand and contract as temperatures drop.

For bearing applications, this behavior must be carefully matched between the shaft, housing, and bearing material to maintain proper fit and clearance.

Expanding (pun intended) on that, the Wikipedia page for thermal expansion offers some solid information, like how expansion is a result of the change in kinetic energy of molecules.

Why Thermal Expansion Is Critical to Material Selection

Thermal expansion becomes especially important when working with dissimilar materials, such as:

• Steel shafts

• Aluminum housings

• Polymer or composite bearings

Each material expands at a different rate.

If material selection does not account for these differences:

• Clearances may close completely under heat (leading to seizure)

• Press fits may loosen under cold conditions

• Bearing geometry may distort under load

This is why thermal expansion should always be evaluated early in the material selection process, not after design is finalized.

Understanding CLTE: A Core Material Selection Metric

The Coefficient of Linear Thermal Expansion (CLTE) is one of the most important metrics used in bearing material selection.

CLTE measures:

• How much a material expands per unit length

• Per degree of temperature change

It is typically expressed as:  in/in/°F (or mm/mm/°C)

In practical terms, CLTE allows engineers to predict how a bearing will behave across temperature ranges and whether it will maintain proper fit and clearance.

Expert Note from TriStar: Thermal expansion is one of the most common causes of bearing failure when material selection is rushed or based on assumptions. Our engineers evaluate CLTE alongside load, speed, and press fit to ensure bearings maintain proper clearance and performance across the full operating temperature range; not just at room temperature.

CTLE Material Comparison

Material Selection: Why Some Materials Perform Better Than Others When it Comes to Thermal Expansion

Not all bearing materials respond equally to temperature changes. This is where material selection becomes critical.

For example:

• CJ composite bearings

  • Have a thermal expansion rate similar to steel

  • Allow for tighter tolerances and press fits

  • Maintain dimensional stability from cryogenic temperatures up to 350°F

• High-performance materials like Torlon® and polyimides

  • Offer relatively low thermal expansion

  • Perform well in high-temperature environments

• UHMW (Ultra-High Molecular Weight Polyethylene)

  • Can expand up to 13x more than steel

  • May not be suitable for high-temperature or tight-tolerance applications

These differences highlight why material selection cannot rely on general assumptions about “plastics”; each formulation behaves differently.

Here is a breakdown of linear expansion in some of the key materials from our tier one product line along with some other common materials.

Why Thermal Expansion Impacts More Than Just Fit

Thermal expansion doesn’t just affect dimensions; it influences:

• Friction and heat generation

• Wear rates over time

• Lubrication effectiveness (especially in self-lubricating materials)

• Overall bearing service life

A well-selected material will maintain stable performance across temperature swings, while a poorly selected one may degrade rapidly even if it performs well at room temperature.

We can Help

Thermal expansion is just one piece of the material selection puzzle, but it’s one of the most important.

If you’re designing a bearing for:

• High-temperature environments

• Wide temperature swings

• Tight tolerance applications

• Metal-to-polymer interfaces

TriStar’s engineering team can evaluate your application and recommend the optimal material based on real-world operating conditions. Contact our engineers for customized guidance on material selection. 

Let us review your materials, tolerances, and design criteria to ensure long-term performance and reliability.