Advanced rolling contact fatigue in which cracks starting just below the surface, near the depth of maximum shear stress, join up and release flakes of metal, leaving rough, deep cavities. In rolling bearings it is the classic end-of-life failure, often brought on early by contamination dents, misalignment or poor lubrication. It throws large fatigue particles into the oil, high PQ readings and clear bearing defect frequencies in vibration data.
Outer race is spalled across a third of the load zone, that bearing comes out this weekend.
Also heard as
- flaking
- spall
Related terms
Pitting
Rolling contact fatigue that leaves visible craters on gear teeth or bearing races.
Analytical ferrography
Microscope study of wear particles pulled from oil by a magnet, used to identify how a machine is wearing.
PQ index
Magnetic measure of total ferrous debris in an oil sample, including large particles that spectrometers miss.
Glitter
Visible sparkling metal flakes in drained oil or a cut-open filter, a red flag for serious wear.
Same word, different worlds
Flakes or chunks of coating breaking away from the surface, typically under thermal cycling or impact.
Refractories & Furnace LiningsCracking off of pieces or layers from the hot face of a refractory lining.
Gear EngineeringLarge, irregular flakes broken out of a tooth surface, usually where pits have grown and joined.
Concrete & CementChunks or flakes breaking away from a concrete surface or edge, often from corroding rebar beneath.
Sealants & WaterproofingConcrete, brick or stone breaking off in flakes or chunks at the surface.