False brinelling

Damage from standing still while vibrating. Urgency

Chemical attack from water, or micro-movement that keeps stripping the protective oxide.

What false brinelling looks like

• Shallow, shiny or rust-stained marks on the raceway at exact ball or roller spacing
• Often several sets of marks, because the bearing was shifted slightly between idle periods
• Edges are soft and the surface looks worn away, not pressed down like a true dent

Rotec AI schematic illustration. It shows the typical pattern and is not a photograph of a real bearing.

How false brinelling develops

When a stationary bearing is shaken (shipping, a neighbouring machine, a standby unit), the rolling elements rock a tiny amount in the same spots. The lubricant is squeezed out and the steel wears away by fretting. Nothing rolls, so fresh lubricant never gets back into the contact.

How fast it progresses: Damage accrues while the machine is not even running. It shows up later as noise and vibration, and can seed fatigue.

Causes of false brinelling

Mounting, handling & storage

• Vibration during transport or long storage

Operating conditions

• Standby machines next to running equipment; machines idle for long periods while the structure vibrates

Bearing selection

• Lubricant or design not suited to vibratory duty

How to confirm it is false brinelling

• Marks at exact element spacing, plus a history of idle vibration or shipping
• Edges look worn, not pushed in; compare with true overload dents (below)
• A reddish tint is common, but not required

How to fix and prevent false brinelling

• Keep bearings from vibrating while stopped: isolate, damp or lock the rotor for transport
• Rotate standby machines at regular intervals so fresh lubricant reaches the contacts
• Use a grease with good anti-fretting properties for vibratory duty
• Choose a design suited to vibration where it cannot be avoided

Easily confused with

• Overload deformation (true brinelling): True brinelling dents have raised, sharp edges and no wear; false brinelling marks are worn flat and often reddish.
• Moisture corrosion: Moisture etching is chemical and often frosted; false brinelling is mechanical and polished.

Worth knowing

How to tell it from true brinelling

False brinelling wears away the surface texture and leaves no raised edges, often with brown corrosion in the marks and a sharp edge to the damaged area. A true brinell dent keeps the original grinding marks in the bottom of the depression, because the metal was pushed down, not worn away. Marks from rough mounting have raised edges.

Shipping and standby are the usual causes

Vibration while the bearing is not turning lets the rolling elements rock in the raceway with no oil film to protect them. Long road, rail or sea transport, and standby machines near running ones, are the classic cases. Lock rotors for transport, take weight off the bearings, and turn standby machines regularly.

Spring preload for motors that stand or travel

An axial spring on the floating bearing keeps the balls loaded and greatly reduces false brinelling. The handbook rule is F = k × d (newtons, bore in mm). Quiet running needs k of 5 to 10; to resist false brinelling use k of 20. A 25 mm bore then needs about 500 N. The Load Calculator has a spring preload tool.

Other corrosion modes

Questions about false brinelling