Image: Gearbox — Rohloff AG (gfdl).

Surface Finish Is a Performance Feature

To a bearing engineer, surface finish is not cosmetics - it is a load-carrying, lubrication-controlling, noise-determining property. The last two machining operations, grinding and superfinishing, decide it.

Grinding to Micrometre Tolerances

After heat treatment the ring is too hard to cut, so it is ground. Face, outer-diameter, raceway (track) and bore grinding each control specific features: ovality, roundness, taper, eccentricity and roughness. Modern CNC grinders hold sizes to roughly ±1 µm, and raceway profile error is typically held within a couple of micrometres so the loaded contact area is even.

Superfinishing: The Mirror Pass

Superfinishing (sometimes called superfinishing stone polishing or micro-finishing) uses fine abrasive stones under low pressure with oscillation to remove the microscopic peaks left by grinding. It produces a characteristic cross-hatch and drives raceway roughness down to Ra ≤ 0.05 µm. The benefits are concrete: better lubricant film retention, lower friction and running temperature, reduced vibration and noise, and longer rolling-contact fatigue life.

Why Roughness Numbers Matter

As a rule of thumb, grinding leaves raceways around Ra 0.1-0.2 µm while superfinishing takes them below 0.05 µm. Balls are taken even further: after hard grinding they are lapped between cast-iron plates to roundness errors under 0.5 µm and surface roughness near Ra 0.01 µm, reaching precision grades such as G10-G5.

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