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Lube Interval Calculator - SKF-Based Bearing Regreasing Intervals for Rotating Equipment

Calculate grease relubrication frequency and quantity for ball and roller bearings by size, speed & temperature

Calculate bearing relubrication intervals using the SKF regreasing interval formula. Enter bearing type, bore diameter, operating speed, and temperature to determine the recommended hours between grease applications. Supports deep groove ball bearings, angular contact, cylindrical roller, spherical roller, and tapered roller bearings. Includes grease quantity calculations based on bearing width, correction factors for contamination, vibration, vertical shafts, and high-humidity environments. Results follow SKF, NSK, and FAG recommended practices.

Pro Tip: Over-greasing causes more bearing failures than under-greasing. When you pump too much grease, the bearing churns it and generates heat that breaks down the grease base oil, leaving hardened thickener that insulates instead of lubricating. The correct volume per application is 0.114 × D (mm) × B (mm) in cubic centimeters - usually just a few grams. Use a calibrated grease gun (know how many grams per pump stroke) and count your strokes. A grease gun at 10,000 psi will blow out seals in seconds.

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Lubrication Interval Calculator
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How It Works

  1. Enter Bearing Information

    Input the bearing type (ball, cylindrical roller, spherical roller, tapered roller), bore diameter, and outer diameter. The calculator uses standard bearing dimension tables to determine the mean bearing diameter (d + D) / 2 for the regreasing formula.

  2. Specify Operating Conditions

    Enter the shaft speed in RPM and the bearing operating temperature. Higher speeds and higher temperatures both shorten the regreasing interval. Temperature above 160°F (70°C) is the primary driver of grease degradation.

  3. Apply Correction Factors

    Select applicable correction factors: heavy contamination (dust, moisture), vertical shaft orientation, vibration severity, food-grade grease, and humid environment. Each factor multiplies the base interval downward.

  4. Review Interval and Quantity

    See the recommended regreasing interval in operating hours or calendar time, plus the correct grease volume per application in grams or ounces. The calculator also shows the maximum extended interval if ultrasonic monitoring confirms grease condition.

Built For

  • Maintenance planners building PM schedules with data-driven grease intervals for each bearing
  • Reliability engineers optimizing lubrication routes to prevent both over-greasing and under-greasing
  • Millwrights determining grease quantity for initial fill of new bearing installations
  • Vibration analysts correlating lubrication condition with bearing defect frequency trends
  • Plant operators verifying correct grease intervals for equipment in contaminated environments
  • CMMS administrators entering calculated intervals into computerized maintenance management systems
  • Training staff on proper relubrication techniques and volume calculations

Features & Capabilities

SKF Regreasing Formula

Uses the industry-standard SKF regreasing interval equation with speed factor (n × dm), temperature correction, and bearing type multipliers. Results match SKF Dialset and maintenance handbook recommendations.

Contamination Correction Factors

Adjusts intervals for real-world conditions including heavy dust (0.5×), moisture exposure (0.5×), vertical shaft (0.5×), high vibration (0.5×), and food-grade grease with lower performance characteristics (0.5-0.7×).

Grease Volume Calculation

Calculates the precise relubrication quantity using Gp = 0.005 × D × B (grams) for replenishment and 0.114 × D × B (cc) for initial fill, where D is outside diameter and B is bearing width in mm. Converts to grease gun pump strokes based on selectable gun output.

Calendar Conversion

Converts operating-hour intervals to calendar-based schedules based on the machine's typical running hours per day or week. Generates route-friendly scheduling that integrates with weekly, monthly, and quarterly PM cycles.

Ultrasonic Monitoring Integration

Shows how ultrasonic grease monitoring (dB level trending) can extend or shorten calculated intervals by confirming actual grease condition in real time, allowing condition-based rather than time-based lubrication.

Comparison

Bearing Type Speed Factor Range Base Interval (hrs) Temp Correction at 180°F Typical Application
Deep Groove Ball < 500,000 8,000 - 20,000 0.5&times; Motors, pumps, fans
Angular Contact Ball < 400,000 6,000 - 15,000 0.5&times; Pumps, spindles
Cylindrical Roller < 350,000 5,000 - 12,000 0.5&times; Gearboxes, conveyors
Spherical Roller < 250,000 3,000 - 8,000 0.5&times; Crushers, vibrating screens
Tapered Roller < 200,000 2,000 - 6,000 0.5&times; Wheel hubs, rolls

Frequently Asked Questions

The SKF method calculates the base interval from the speed factor (n × dm, where n is RPM and dm is mean bearing diameter in mm) and bearing type. Ball bearings have the longest base intervals because rolling contact generates less heat than line contact in roller bearings. This base interval is then multiplied by correction factors for temperature (halved for every 15°C above 70°C), contamination, orientation, vibration, and grease type. The result is the number of operating hours between grease applications.
The replenishment quantity formula is Gp = 0.005 × D × B, where D is bearing outside diameter and B is bearing width, both in millimeters, giving the result in grams. For example, a 6310 bearing (110mm OD, 27mm width) needs about 15 grams per application. A standard manual grease gun delivers approximately 1-1.5 grams per pump stroke, so this bearing would need roughly 10-15 strokes. Over-greasing by even 50% can cause overheating and premature failure.
Excess grease causes the rolling elements to churn through the grease, generating frictional heat that raises bearing temperature 20-40 degrees above normal. This heat oxidizes the grease base oil, leaving behind hardened thickener that acts as an insulator rather than a lubricant. The bearing runs hot, the seals may blow out spraying grease, and ultimately the bearing fails from overheating. Over-greasing is the number one cause of electric motor bearing failure in many industrial plants.
Grease life follows a chemical degradation curve: for every 15°C (27°F) increase in bearing temperature above 70°C (158°F), the relubrication interval is cut in half. A bearing running at 100°C needs grease four times more often than the same bearing at 70°C. Above 120°C, standard greases degrade rapidly and high-temperature synthetic greases (polyurea or PFPE based) are required. Always measure actual bearing temperature rather than assuming it matches ambient conditions.
Yes. Ultrasonic monitoring is the gold standard for condition-based lubrication. A bearing in good lubrication condition produces a baseline dB level on an ultrasonic detector. As grease degrades, the dB level rises due to increased metal-to-metal contact and friction. When the dB reading increases 8-12 dB above baseline, it is time to add grease. Adding grease one pump at a time while monitoring allows you to stop at the optimal fill level. This approach eliminates both over-greasing and under-greasing.
Most electric motor manufacturers recommend NLGI Grade 2 polyurea grease for standard applications or lithium complex grease as an alternative. Polyurea grease has excellent high-temperature stability and long service life in the 60-150°C range typical of motor bearings. Never mix grease types without confirming compatibility - mixing polyurea with lithium complex can cause softening, hardening, or oil separation. When in doubt, completely purge the old grease before switching to a new type.
Apply a 0.5× correction factor (halve the calculated interval) for each severe contamination condition: heavy dust or particulate, water spray or high humidity, corrosive atmospheres, or outdoor exposure. Combine multiple factors multiplicatively. A bearing in a dusty, wet environment would use 0.5 × 0.5 = 0.25× the clean-condition interval. Consider upgrading to sealed bearings, adding labyrinth seals, or improving bearing housing sealing before simply greasing more often, as contaminated grease accelerates wear.
Disclaimer: Relubrication intervals are estimates based on the SKF regreasing formula and general industry guidelines. Actual intervals depend on grease type, bearing condition, seal effectiveness, operating loads, and environmental conditions. Always follow the bearing and equipment manufacturer's specific lubrication recommendations. ToolGrit is not responsible for bearing life, lubrication outcomes, or equipment reliability.

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