In machines that generate or use heat during operation, axial shaft expansion can be a problem. In industrial hot air fans, heat is transferred through the shaft. In the paper machine dryer, the hot steam passes directly through the hollow shaft through the bearing hole. There are many ways to allow the bearing to handle the linear expansion of the shaft. The most common are: 1. Position (fix) one bearing in the bearing housing and allow the other bearing to be axially free (non-positioning).

2. The selected bearing type allows one bearing to act as a locating bearing, allowing the other bearing to adapt to the expansion of the shaft internally. Prevent axial movement of the outer rings of the two bearings.

CARB (SKF's compact spherical roller bearings) bearings can simultaneously adapt to linear expansion, misalignment and heavy loads. What is the expansion rate of the paper machine dryer? For every 1 degree Fahrenheit, the shaft length per inch is approximately 6 microinches (0.000006"). (This expansion rate depends on the material used; gray cast iron is typical.) Using the expansion rate above, the shaft can grow if available How many machines have the temperature risen by 200 degrees Fahrenheit (111 degrees Celsius) and the distance from the center to the center of the bearing is 400 inches (10.2 meters)? Just multiply the numbers: 0.000006" /°F / "x 200" x 400" = 0.480", or slightly less than 1/2" (~12mm) There are other ways to adapt to thermal expansion. Please contact your local SKF Application Engineering Service Department for help.