Bearing life discussions often mix a calculated rating life with a target service duration. The basic dynamic rating life L10 is calculated from the bearing’s dynamic load rating and equivalent dynamic load. Application tables, by contrast, give planning guidance for broad equipment categories. A machine’s target life should be chosen for its duty, maintenance strategy, downtime cost, and governing requirement. The SKF ranges below are copied as source-specific guide categories from its 2018 publication; they are not mandatory values or guarantees.

Bearing Design Life by Application

Basic L10 equation

The basic relationship is L10=(C/P)^p, where C is the basic dynamic load rating, P is equivalent dynamic bearing load, and p is 3 for ball bearings or 10/3 for roller bearings. The result is in millions of revolutions. Under constant speed n in revolutions per minute, the basic hours conversion is L10h=1,000,000/(60n) times (C/P)^p. Increasing load relative to rating capacity can reduce calculated life sharply because the load ratio is raised to the bearing exponent. Check the bearing type and load calculation before using the equation.

What the 90 percent means

ISO 281 defines the dynamic load rating and rating-life framework. Basic rating life is associated with 90% reliability for a population of apparently identical bearings operating under the same conditions. That is a statistical rating convention; it does not promise that an individual bearing will run for the calculated duration, nor does it account for every real-world failure cause. A higher reliability target requires an appropriate life adjustment method and usually a different selection. State the reliability basis when presenting a calculated result.

Interpreting the guide ranges

SKF’s 2018 table places household, agricultural, instrument, and medical-technology applications in a 300–3,000 h guideline range. Short or intermittent operation and certain tools and construction equipment are shown around 3,000–8,000 h. Machine tools used for about eight hours each day are listed at 20,000–30,000 h, while continuous 24-hour service is shown at 40,000–50,000 h. Waterworks, furnaces, and similar long-running equipment appear at 60,000–100,000 h. Keep the utilization description with the range when comparing applications.

Conditions that change real life

The basic equation does not by itself capture lubrication film, contamination, corrosion, mounting errors, misalignment, vibration, temperature, or shock loading. Static overload and brinelling are not dynamic fatigue-life questions. A bearing can fail well before its calculated L10 if the operating environment or installation is poor; a well-maintained system may perform differently from a nominal guide category. Check the current bearing manufacturer method for modified rating life, lubricant selection, fits, internal clearance, sealing, and maintenance interval.

A sound selection process

Define the duty cycle and speed, calculate radial and axial loads, choose an equivalent dynamic load method appropriate to the bearing, then determine basic rating life. Compare the result with a justified application target and note the reliability basis. Review static safety, lubrication, sealing, contamination control, thermal limits, mounting, and maintainability separately. Use the current supplier catalog and governing project requirements because methods and product data can change. Treat the table as an early planning reference, not a replacement for a complete bearing and lubrication analysis. For variable-speed or intermittent operation, use the actual load and speed spectrum instead of assuming one constant operating point. Document the assumptions so later maintenance or redesign can revisit them.

Sources and verification

Equation and guide ranges are from SKF Bearings and Mounted Products (2018), bearing life section and Table 3. The reliability framework is within ISO 281:2007; check the currently applicable edition and supplier method for a design.

This table is a reference aid, not a substitute for the governing design code, product specification, qualified engineering review, or measurements from the actual component and service conditions.