Most Bearings Fail at Installation, Not in Service

A bearing that is perfectly made can be ruined in the few minutes it takes to fit it. Correct mounting - fit, clearance, heating and alignment - is the single biggest controllable factor in achieved service life.

Fits and Tolerances

The shaft/housing fit depends on which ring rotates. The rotating-load rule: the ring that carries the rotating load must be mounted with an interference (tight) fit so it cannot creep, while the stationary ring uses a sliding (loose) fit to allow slight movement and even wear. Typical shaft tolerances are k5 / m6 / n6 / p6 and housing tolerances H7 / J7 / K7 / N7, chosen by load and speed.

Internal Clearance Classes

Bearings are supplied with a defined internal clearance (the slack between rolling elements and raceways): C2 (less than normal), CN / C0 (normal), C3 (greater than normal), C4 (still greater). Because an interference fit on a warm shaft removes clearance, higher operating temperatures normally call for a larger initial clearance (e.g. C3) so the bearing does not end up preloaded or seized in service.

Heating: Induction, Not a Blowtorch

For interference fits the ring is heated to expand it. An induction heater is preferred: it heats evenly, demagnetises the part, and avoids the local hotspots and contamination of an oil bath or blowtorch. A practical guide is to heat to roughly ΔT ≈ 80°C above ambient to gain the needed expansion (Δd ≈ α × d × ΔT, with α ≈ 11×10⁻⁵/°C for steel); for most sizes this means a bearing temperature around 100-110°C. Do not exceed 120°C for grease-filled (sealed) bearings - beyond that the grease degrades. For sealed bearings, 80-90°C is the safe ceiling.

Cold Fitting, Alignment and Torque

Smaller interference fits can be pressed on with a hydraulic / mechanical press and a supporting sleeve that loads the ring evenly (never press on the wrong ring - you would damage the raceway). After mounting, check alignment (misalignment causes edge loading) and use a torque wrench to the specified seating force. Finally, confirm the bearing turns freely before the machine is started.

How KMK Bearing Applies This

At KMK Bearing (SINO BEARINGS, KMK brand) these principles guide every order we manufacture in Chengdu, China. Our in-house process chain - forging, heat treatment, precision grinding, superfinishing and cleanroom assembly - is built to the standards described above, whether the part is a standard catalog bearing or a custom-engineered solution.

• 20+ years of precision bearing manufacturing
• Materials from chrome steel to 17-4PH stainless steel and full ceramic (ZrO2, Si3N4)
• In-house heat treatment and metrology to P4/P2 (ABEC 7/9) precision
• Custom designs and low-MOQ prototyping from drawings or samples

Discuss your application with kevin@sinoti.com or browse our bearing catalog.

SINO BEARINGS (KMK) - Perfect Quality -- Great Service -- Customized.

Source: SINO BEARINGS