Slewing Ring Calculator — Static Safety, L10 Life & Friction Torque (ISO 76 / ISO 281)

The static load check follows ISO 76:2006 (basic static load ratings and equivalent static load). The rating life uses the L10 power law of ISO 281:2007 on the dynamic equivalent load of the public yaw and pitch bearing design guideline (an estimate); the static check keeps the manufacturers' comparative load. The equivalent-load formula that converts the tilting moment to an axial load uses the manufacturer comparative method from slewing-ring technical handbooks, which is geometry-specific and not fixed by a single public standard. The calculator therefore carries an engineering-estimate disclaimer and should be validated against the manufacturer's own selection software and, for safety-critical applications, reviewed by a licensed professional engineer.

s₀ = C₀ / Feq, where C₀ is the ring's basic static load rating and Feq is the equivalent comparative load combining axial force, radial force and tilting moment. On the C₀ ratio the calculator reads CHECK below 2 and FAIL below 1, or below your own higher requirement. The application factors the makers publish (crane 1.45, excavator / turntable / radar / medical / machine tool 1.5, measuring, wind and solar tracker 2.0 — the top of each range) belong to their limiting-load curves, so the calculator applies them there: paste the raceway and bolt curves, the maker's load conversion and the mounting, and it reports how far the load point can grow before it leaves each curve — below the factor it reads FAIL. The hero, sketch chip, PDF report and Excel all show ONE governing verdict — the worst of s₀, moment safety, the curve reserves and the element checks when entered, the rating life, the service findings and the engine warnings such as raceway speed — with s₀ as the headline value and the governing check named, so they can never disagree.

The tilting moment M (kN·m) is converted using Feq_M = k · M / Dpw, where Dpw is the raceway pitch diameter (enter the maker's value; left blank it is assumed ≈ 0.85 × OD and the verdict is capped at CHECK) and k is a moment-lever factor that depends on the contact geometry: 4.4 for four-point contact ball rings, 4.1 for cross-roller rings and 5.0 for double-row axial ball rings; an eight-point ring (two four-point rows) carries 1.1 times the four-point form because its two rows share the load. A three-row roller ring converts the moment on each axial row separately — the main row Fa + k_main·M/Dpw, the retaining row k_ret·M/Dpw ∓ Fa — with the levers solved for the two rows as rigid rings (never below 4.1), while its radial row carries Fr alone (s₀ = C₀_rad/Fr). This factor follows the rigid-ring load distribution for each ring type and matches the values published in slewing-ring manufacturers' handbooks. It is an engineering estimate — no single ISO clause fixes k for an arbitrary ring geometry.

For the STATIC load check and the ring-type comparison, yes. For the LIFE, enter the oscillation (frequency and stroke) or a duty spectrum: the calculator counts the travel of each oscillation (2θ/360 of a revolution, with the guideline's k_osc 0.85 for this simplified method) on the guideline's dynamic equivalent load, and flags a stroke below half the critical stroke, where false brinelling and fretting — not rolling-contact fatigue — govern. Enter the element geometry for the contact-pressure and case-depth checks the guideline asks for at the extreme load. A final design still needs the turbine's load spectrum from the load simulation, the finite-element check of the ring in its flexible structure, and the ring maker's own acceptance criteria.

Because fatigue and static overload are different failure modes. The static check uses the comparative load, which is built to be conservative for the most loaded element under the extreme load (moment lever 4.4, radial factor 5.046 on ball rings). Fatigue accumulates over the whole raceway, so the public yaw and pitch bearing design guideline rates life on a lighter dynamic equivalent load, Pa = 0.75·Fr + Fa + 2.5·M/Dpw, matched to finite-element results — a life on the static load would read several times too short and oversize the ring. For a radially loaded ring the calculator uses a conservative envelope instead, because that approximation assumes the axial and moment load dominate.

Open Mounting → In service and enter the measured increase of the tilting clearance since installation (measured the same way each time), the as-installed value if you have it, and the number of bolts found below 80 % preload at the last re-tightening. The wear limit comes from the element size (ball rings the smaller of 0.035·Dw + 0.6 mm and 0.07·Dw, crossed rollers 0.017·Dw − 0.024 mm, from Dw 10 mm), and the total clearance may not exceed 4 × the as-installed value — the maker's own limit wins when entered. At the limit the ring reads FAIL (stop and replace); above 75 % of it, measure every 300 operating hours instead of 700. Each loose bolt is replaced with both neighbours; when 20 % or more are loose, replace them all.

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