Managing Shaft Expansion: Effective Bearing Strategies for High‑Heat Machinery

Axial shaft expansion is a critical concern in machines that either generate or are exposed to high temperatures during operation. In industrial hot‑gas fans, heat is transmitted through the shaft itself, while in paper‑machine drying cylinders, hot steam travels through a hollow shaft that runs directly through the bearing bore.

There are several proven methods to allow bearings to accommodate the linear expansion of a shaft. The most common approaches are:

1. Fix one bearing in the housing, giving the opposite bearing axial freedom (non‑locating).

2. Select bearing types that internally allow one bearing to act as the locating element while the other accommodates shaft expansion, preventing axial movement of both outer rings.

SKF’s CARB (Compact Aligning Roller Bearing) is specifically engineered to absorb linear expansion, misalignment, and heavy loads simultaneously.

What expansion can we expect from a paper‑machine drying cylinder? Roughly 6 microinches (0.000006″) per degree Fahrenheit per inch of shaft length—typical for gray cast iron.

Using this rate, a temperature rise of 200 °F (111 °C) in a machine with bearings spaced 400 in (10.2 m) apart yields:

0.000006″/°F/″ × 200 °F × 400 ″ = 0.480″, or just under ½″ (≈ 12 mm).

Other strategies exist to accommodate thermal expansion. Contact your local SKF Applications Engineering Service for expert guidance.