Calculation Parameters
Based on ISO 281 and bearing manufacturer standards
How the Calculator Works
Basic Dynamic Load Rating
The basic dynamic load rating C is calculated using:
C = P × fL / (fT × a1)
where:
- C — basic dynamic load rating (N)
- P — equivalent dynamic bearing load (N)
- fL — life factor
- fT — temperature factor
- a1 — reliability factor
Equivalent Dynamic Load
For combined radial and axial loads:
P = X × Fr + Y × Fa
where X and Y are factors dependent on the Fa/Fr ratio and bearing type.
Life Factor Calculation
The life factor is calculated from the required life:
fL = (L10h × n × 60 / 10⁶)^(1/p)
where p = 3 for ball bearings and p = 10/3 for roller bearings.
Temperature Effects
Operating temperature affects bearing capacity:
- Up to 150°C (302°F): fT = 1.0
- 200°C (392°F): fT = 0.90
- 250°C (482°F): fT = 0.75
- 300°C (572°F): fT = 0.60
Bearing Type Selection Guide
- Ball Bearings: High speeds, moderate loads, low friction
- Cylindrical Roller: High radial loads, moderate speeds
- Spherical Roller: Heavy loads, misalignment capability
- Tapered Roller: Combined loads, high stiffness
- Needle Roller: High radial loads, compact design
Important Considerations
- Always consider safety factors for critical applications
- Account for shock loads and vibration
- Proper lubrication is essential for achieving calculated life
- Contamination can significantly reduce bearing life
- Consider bearing arrangement (fixed/floating) for thermal expansion
Usage Examples & Value Selection Guide
Example 1: Electric Motor Bearing
Scenario: 30 kW motor with belt drive
- Bearing Type: Ball bearing (deep groove)
- Radial Load: 2500 N (belt tension)
- Axial Load: 200 N (minor thrust)
- Speed: 1480 RPM
- Required Life: 40000 hours
- Temperature: 70°C
- Reliability: 90%
- Result: C ≈ 35 kN → Select 6309 (C = 52.7 kN)
Example 2: Pump Shaft Bearing
Scenario: Centrifugal pump with overhung impeller
- Bearing Type: Spherical roller bearing
- Radial Load: 8000 N (impeller weight + hydraulic)
- Axial Load: 3000 N (thrust load)
- Speed: 2950 RPM
- Required Life: 50000 hours
- Temperature: 85°C
- Reliability: 95%
- Result: C ≈ 125 kN → Select 22218 (C = 170 kN)
Example 3: Gearbox Output Shaft
Scenario: Industrial gearbox with heavy radial loads
- Bearing Type: Tapered roller bearing
- Radial Load: 15000 N
- Axial Load: 5000 N (helical gear thrust)
- Speed: 150 RPM
- Required Life: 100000 hours
- Temperature: 90°C
- Reliability: 98%
- Result: C ≈ 220 kN → Select 32220 (C = 298 kN)
How to Choose Values
Bearing Type Selection
- Ball Bearings:
- Speeds up to 20,000 RPM
- Light to moderate loads
- Low friction requirements
- Fa/Fr < 0.5 typical
- Cylindrical Roller:
- High radial loads only
- No axial load capacity (except NJ, NUP)
- Allow free axial movement
- High speed capability
- Spherical Roller:
- Very heavy loads
- Misalignment up to 2°
- Combined loads OK
- Lower speed limits
- Tapered Roller:
- High combined loads
- High stiffness needed
- Usually paired
- Fa/Fr up to 1.5
Load Calculation Tips
- Belt Drives: Radial load = 1.5-2.5 × belt tension
- Gear Drives: Include separating forces and dynamic factors
- Overhung Loads: Calculate moment loads at bearings
- Dynamic Factors:
- Light shock: × 1.2-1.5
- Moderate shock: × 1.5-2.0
- Heavy shock: × 2.0-3.0
Life Requirements by Application
- 8,000-12,000 hours: Household appliances, hand tools
- 20,000-30,000 hours: 8-hour daily operation machines
- 40,000-50,000 hours: 16-hour daily operation
- 60,000-100,000 hours: 24-hour continuous operation
- 100,000-200,000 hours: Critical equipment, no failures
Temperature Considerations
- Standard bearings: -30°C to +120°C
- High-temp bearings: Up to 200°C with special grease
- Stabilized bearings: Up to 250°C (S1 suffix)
- Special bearings: Up to 350°C (S2, S3 suffix)
- Note: Higher temps require special lubricants
Reliability Factor Selection
- 90% (a1=1.0): Standard industrial applications
- 95% (a1=0.62): Important equipment
- 96% (a1=0.53): Critical processes
- 97% (a1=0.44): Safety-critical
- 98% (a1=0.33): Aerospace, medical
- 99% (a1=0.21): Ultra-critical, no failure allowed