Bearing-Pair Preload
Preload Rings

A preload ring (preload collar) is a precision spacer specifically designed to set the axial preload in a bearing pair — typically angular contact or taper roller bearings arranged back-to-back (DB) or face-to-face (DF). The ring sits between the inner or outer races of the two bearings and determines the preload force. Preload rings are supplied in matched lengths (±0.005 mm or tighter) and sometimes in graduated size sets to allow field adjustment of preload.

Two types of preload: Rigid preload — a fixed spacer (preload ring) of precise length locks in a fixed preload force. Good for stable temperature conditions. Resilient (spring) preload — a disc spring or wave spring applies a force-controlled preload that maintains consistent force despite thermal expansion. For machine tool spindles: rigid preload via precision spacer rings is standard — the ring length is ground to ±0.002 mm. For general gearboxes: ±0.005 mm is sufficient.

Too high preload: excess friction → heat generation → thermal expansion → further increase in preload (positive feedback) → bearing seizure. Also: reduced fatigue life, higher motor current. Too low preload: balls skid (slip instead of roll) at high speed → smearing of raceway → premature failure. Preload window is specified by the bearing manufacturer — the preload ring length must be matched to put the assembly within this window.

Yes — HXC regularly supplies preload rings as matched sets sorted by length into ±0.001 mm bins. This allows the assembler to select the exact ring length needed to achieve the target preload during assembly. For spindle rebuilds where the bearing pair and housing have worn to specific dimensions, matched preload ring sets allow restoring the original preload without replacing the bearings.

Prototype (1–5 pcs, ground + lapped): 3–5 days. Small batch (10–50 pcs): 5–9 days. Production (100–1,000 pcs): 7–12 days. Matched sets (sorted into ±0.001 mm bins): add 2–3 days. Stainless or ceramic: add 2–4 days. Rush production available.

100Cr6 (SUJ2 / GCr15) through-hardened bearing steel HRC 60–62 — the standard choice for spindle preload rings. 42CrMo4 induction hardened — gearbox and industrial applications. SUS440C hardenable stainless — clean-room, surgical, semiconductor. Si3N4 ceramic (HV 1500) — high-speed motorised spindles where thermal expansion of steel rings would shift the preload. ZA bronze — sliding and vibration-damping applications.

ID / OD bearing-fit surfaces: Ra 0.4 µm standard. Ring faces (bearing-race contact): Ra 0.2 µm standard, Ra 0.05 µm lapped on request. Length tolerance: ±0.005 mm standard, ±0.002 mm precision, ±0.001 mm matched-set. Face flatness: ≤ 0.003 mm standard, ≤ 0.001 mm lapped. All measured by contact profilometer and CMM, reported on the inspection certificate.

Yes — beyond plain spacer rings, HXC machines stepped rings (one face larger diameter than the other, for split-race designs), wave-spring grooves cut into the ring, threaded preload nuts integral to the ring, and dual-purpose rings combining preload and seal-retainer functions. Submit your section drawing and we machine to the exact contour.

The required ring length depends on the bearing pair's contact angle, ball pitch diameter, target preload force, and the housing / shaft tolerances. The bearing manufacturer's catalogue gives the preload force vs spacer-length relationship for the specific bearing pair. For new designs, supply the bearing part number and target preload class (Light / Medium / Heavy per the bearing maker) and HXC will compute and propose the spacer length.