Understanding Internal Clearance

Bearings are designed with a specific internal clearance that measures the space between
the rings and the rolling elements. This clearance enables smooth rotation of the rolling
elements, compensates for thermal expansion, and ensures optimal load distribution.

It is crucial to choose the correct internal clearance as it directly influences noise, vibration,
heat, and fatigue life, while factors such as impact loads, severe vibration, and ring fit also
affect the internal clearance. Achieving the ideal internal clearance for a specific application
requires a careful balance of these parameters.

Differences Between Radial and Axial Internal Clearance

Internal clearance in bearings can be classified into two types: radial and axial clearances.
Radial clearance is determined by the difference between the diameter of the ball or roller
and the space between the inner and outer rings. It is measured perpendicular to the shaft
and changes as the bearing rings expand or contract.

Axial clearance, on the other hand, refers to the total displacement that can occur between
the rings in an axial direction. As the radial clearance increases, so does the axial clearance.
A larger radial clearance means there is more room between the balls and rings, allowing
greater freedom of movement for the individual elements in relation to each other.

Choosing the Right Specification for the Job

Internal clearances are categorized using a scale from C1 (tightest) to C5 (loosest) or even
larger. As the numerical value increases, the radial clearance also increases. Greater
clearance allows for better tolerance to external heat. Conversely, lower clearances are
required when minimizing noise and vibration is important. The ideal internal clearance
depends on the specific application and the prevailing operating conditions.

“Standard” and “Normal” Internal Clearance for Electric Motors

It is crucial to differentiate between “normal” and “standard” clearances, especially as
new standards emerge for modern electric motors that operate at higher temperatures
and speeds. In the case of electric motors, the commonly specified clearances are C2 for
situations where noise control is of utmost importance, and either C3 or C4 when exposed
to elevated ambient temperatures. The term “normal clearance” is also interchangeably
referred to as C, CO, or “standard” clearance.

Key takeaway: The ideal internal clearance depends on the specific application and operating conditions. If you’re unsure of which clearance number to use, contact your Bartlett representative and a member of our highly knowledgeable team will be able to troubleshoot with you.


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