Why might one bearing locate a shaft while another allows axial movement?

The short answer

A locating/non-locating bearing arrangement can support a wind-generator shaft while accommodating its axial thermal movement. The locating support establishes axial position; the non-locating support provides the specified displacement path. Axial freedom at the intended interface is therefore different from uncontrolled assembly looseness.

Trace expansion to a permitted interface

Shaft and housing temperatures can differ, and their materials and lengths can produce different expansions. If both ends constrain all relative axial movement, that difference can create additional axial forces. The designer must decide where movement is accommodated. SKF describes arrangements in which displacement occurs inside a suitable bearing or at a specified ring-to-seat interface; neither method should be assumed from a photograph.

Check the complete axial chain

Identify shoulders, covers, locknuts, spacers, seals and couplings that could unintentionally constrain the intended movement. A nominally floating support can cease to float if another part bottoms against it. Conversely, simply removing axial restraint can undermine a locating function. The review needs both the permitted travel and the retained load path, including how thrust in each direction reaches the designated support.

Request an arrangement section

Ask the generator supplier to mark the locating support, non-locating support, movement direction and allowable displacement on its assembly drawing. Clarify the cold-to-running dimensional change used in that design. SKF arrangement guidance explains the concept, not a MARSTON bearing layout or allowable travel. The practical decision is whether the supplied axial chain preserves the intended expansion path; it is not an instruction to loosen a cover, change a fit or adjust bearing preload. A locating bearing’s function should be identified for both thrust directions. Otherwise an apparently available expansion path may coexist with an unresolved reverse-load path that becomes relevant in a different rotor condition.