# Why Grease Churn Heat Outruns Oil-Air Above dN 1e6

When spindle dN climbs past about 1,000,000, grease churning heat rises faster than conduction can dump it. Balls plow through excess grease, viscosity spikes locally, and the outer ring temperature climbs until clearance collapses. Oil-air metering avoids that trap: micro-doses of oil ride a clean air stream that also cools the raceway.

For high-speed spindles, TFL Bearing summarizes when grease still works and when oil-air becomes the safer default. Read the field notes on oil-air lubrication for high-speed spindles before you change grease grade or fill volume.

Shandong TFL Bearing Co., Ltd publishes spindle application notes so maintenance and design share one vocabulary on dN limits, NBU15 fills, and run-in.