Surface damage in which pieces of metal much larger than single pits break away, leaving shallow, irregular craters. It often grows from progressive pitting as pits link up, and on case-hardened gears it can start deeper, near the case-core boundary, when the case is too shallow for the load. Spalled teeth throw debris into the oil, which damages bearings and other gears.
Pits have joined up into spalling on the pinion, there's flakes the size of a fingernail on the magnet.
Also heard as
- spall
- spalled
Related terms
Pitting
Surface fatigue of gear teeth that breaks out small craters, typically on the flank just below the pitch line.
Case depth
How deep the hardened surface layer of a gear tooth goes, usually measured to a set hardness such as 50 HRC.
Fuzz
Shop word for the fine metallic paste that collects on a magnetic drain plug from normal gear wear.
TIFF
Tooth interior fatigue fracture: a crack that starts deep inside a case-hardened tooth, not at its surface.
Same word, different worlds
Flaking of large chunks from a bearing race or gear tooth after fatigue cracks below the surface link up.
Thermal SprayFlakes 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.
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.