Bearing Selection for Rotating Equipment

Understanding the Critical Role of Bearings in Rotating Equipment

Bearings are the unsung heroes of rotating machinery, quietly supporting shafts, reducing friction, and enabling the smooth operation of everything from small electric motors to massive industrial turbines. For industries across Nova Scotia and the broader Atlantic Canada region—including pulp and paper, seafood processing, mining, and manufacturing—proper bearing selection can mean the difference between reliable operation and costly unplanned downtime.

The Maritime climate presents unique challenges for rotating equipment. High humidity, salt air exposure in coastal facilities, and significant temperature variations throughout the year all influence bearing performance and longevity. Understanding these factors, combined with sound engineering principles, enables facility managers and engineers to make informed decisions that optimise equipment reliability while controlling maintenance costs.

This comprehensive guide explores the fundamental principles of bearing selection, examining the various types available, key selection criteria, and practical considerations specific to industrial applications in our region.

Types of Bearings and Their Applications

Rolling Element Bearings

Rolling element bearings are the most common type found in industrial rotating equipment. They utilise balls or rollers to support loads while minimising friction. The primary categories include:

• Deep groove ball bearings: The most versatile bearing type, capable of handling radial and moderate axial loads. Suitable for speeds up to 10,000 RPM in standard configurations, they're ideal for electric motors, pumps, and fans commonly found in Atlantic Canadian processing facilities.

• Angular contact ball bearings: Designed to handle combined radial and axial loads, typically arranged in pairs for bidirectional thrust capacity. Common in machine tool spindles and high-speed applications requiring precise positioning.

• Cylindrical roller bearings: Excellent for high radial loads with speeds up to 6,000 RPM. Frequently specified for gearboxes, large electric motors, and conveyor systems in mining and material handling operations.

• Spherical roller bearings: Self-aligning design accommodates shaft deflection and misalignment up to 2-3 degrees. Essential for heavy-duty applications in pulp and paper mills, crushers, and vibrating equipment.

• Tapered roller bearings: Handle combined radial and axial loads in one direction. Predominantly used in wheel hubs, gearboxes, and applications requiring adjustable preload.

Plain Bearings (Journal Bearings)

Plain bearings operate through sliding contact between surfaces, typically with a lubricating film separating the shaft from the bearing surface. They offer several advantages in specific applications:

• Hydrodynamic bearings: Generate a supporting oil film through shaft rotation, suitable for high-speed turbomachinery and large rotating equipment where loads exceed rolling element bearing capacities.

• Hydrostatic bearings: Use externally pressurised lubricant to support loads at any speed, including zero RPM. Specified for precision machine tools and heavy slow-speed equipment.

• Sleeve bearings: Simple, cost-effective solution for moderate loads and speeds. Common in fractional horsepower motors and auxiliary equipment.

Specialty Bearing Types

Certain applications demand specialised bearing solutions. Magnetic bearings, which levitate the shaft using electromagnetic fields, eliminate mechanical contact entirely and are gaining traction in high-speed compressors and turbines. Ceramic hybrid bearings, featuring silicon nitride rolling elements, offer superior performance in high-temperature or electrically sensitive applications, such as variable frequency drive (VFD) motors increasingly common in Nova Scotia's energy-conscious industrial facilities.

Key Selection Criteria and Engineering Calculations

Load Analysis

Accurate load determination forms the foundation of proper bearing selection. Engineers must consider:

• Radial loads: Forces perpendicular to the shaft axis, typically from belt tension, gear mesh, or gravitational effects

• Axial (thrust) loads: Forces parallel to the shaft axis, from helical gears, propellers, or process forces

• Combined loads: Most applications involve both components, requiring calculation of equivalent dynamic load (P) using the formula: P = XFr + YFa, where X and Y are load factors specific to bearing type

• Dynamic vs. static loads: Impact, shock, and vibration can multiply effective loads by factors of 1.5 to 3.0, depending on severity

Speed Considerations

Bearing speed capability is typically expressed as the DN value (bearing bore in millimetres multiplied by rotational speed in RPM). Standard steel ball bearings can operate up to DN values of 500,000, while precision spindle bearings may exceed 2,000,000. For a typical 50mm bore bearing in a 3,600 RPM motor, the DN value of 180,000 falls well within normal operating parameters.

Excessive speed generates heat through churning losses in the lubricant and friction at contact surfaces. The limiting speed—maximum recommended operating speed—varies significantly based on bearing type, precision class, lubrication method, and cooling provisions.

Life Expectancy Calculations

Bearing life is statistically predicted using the L10 life formula, representing the number of revolutions (or hours at constant speed) that 90% of a bearing population will achieve or exceed:

L10 = (C/P)^p × 10^6 revolutions

Where C is the dynamic load rating, P is the equivalent dynamic load, and p equals 3 for ball bearings or 10/3 for roller bearings. Modern calculations incorporate modification factors for lubrication effectiveness (a1), material quality (a2), and operating conditions (a3), enabling more accurate predictions.

For critical equipment in continuous process industries—common throughout Atlantic Canada's pulp, paper, and seafood processing sectors—engineers typically specify bearings with L10 lives exceeding 100,000 hours, providing comfortable safety margins against premature failure.

Lubrication Strategies for Maritime Conditions

Grease Lubrication

Approximately 90% of rolling element bearings operate with grease lubrication due to its simplicity and effectiveness. Key considerations for proper grease selection include:

• Base oil viscosity: Must be appropriate for operating temperature and speed. ISO VG 100-150 mineral oils suit most general industrial applications, while synthetic bases extend temperature range and service intervals.

• Thickener type: Lithium complex greases offer excellent all-around performance. Polyurea thickeners provide superior high-temperature stability, while calcium sulphonate complex greases excel in wet environments—a significant consideration for coastal Nova Scotia facilities.

• Additive package: Corrosion inhibitors are essential in Maritime environments. EP (extreme pressure) additives protect against metal-to-metal contact during boundary lubrication conditions.

Relubrication intervals depend on bearing size, speed, temperature, and environmental contamination. A 100mm bore bearing operating at 1,800 RPM and 70°C might require regreasing every 2,000-3,000 hours, while the same bearing in a clean, cool environment could extend to 8,000 hours or more.

Oil Lubrication

Oil lubrication becomes necessary when operating conditions exceed grease capabilities—typically at high speeds (DN > 400,000), elevated temperatures (> 120°C), or when heat removal is required. Methods include:

• Oil bath: Simple, effective for moderate speeds with oil level maintained at rolling element centre

• Circulating systems: Provide cooling and filtration for demanding applications

• Oil mist: Delivers precise quantities with minimal heat generation, suitable for high-speed machinery

• Oil-air systems: Combine minimal oil quantities with cooling air flow for precision spindles

Environmental and Application-Specific Considerations

Contamination Protection

Contamination is the leading cause of premature bearing failure, responsible for up to 40% of all bearing problems. Effective sealing strategies are paramount, particularly in the dusty, wet, or corrosive environments common to Atlantic Canadian industries:

• Contact seals (lip seals): Provide excellent contamination exclusion but generate friction and heat, limiting speed capability to approximately 70% of open bearing values

• Non-contact seals (shields): Allow higher speeds with reduced protection; suitable for clean environments

• Labyrinth seals: Combine contamination protection with minimal friction through tortuous paths that exclude particles

• External sealing arrangements: Housing-mounted seals, bearing isolators, and air purge systems provide additional protection for severe service

Temperature Extremes

Nova Scotia's climate subjects outdoor and unheated equipment to temperature ranges from -30°C to +35°C annually. Low-temperature considerations include:

• Grease stiffening and increased starting torque below -20°C

• Clearance reduction from differential thermal contraction

• Potential for condensation and ice formation

Solutions include synthetic lubricants with low pour points, increased internal clearance (C3 or C4 fits), and bearing heaters for startup assistance.

Corrosion Resistance

Coastal facilities throughout the Maritime provinces face accelerated corrosion from salt-laden air. Stainless steel bearings (AISI 440C) provide moderate corrosion resistance for light loads, while ceramic hybrid bearings offer superior corrosion immunity with excellent load capacity. Proper sealing, corrosion-inhibiting lubricants, and controlled storage conditions extend bearing life significantly in these challenging environments.

Installation, Monitoring, and Maintenance Best Practices

Proper Installation Techniques

Studies indicate that 16% of premature bearing failures result from improper installation. Critical practices include:

• Cleanliness: Work in clean environments; even particles as small as 5 microns can initiate fatigue damage

• Proper fitting: Apply mounting force only to the tight-fit ring—never through the rolling elements

• Thermal mounting: Heat bearings uniformly to 80-120°C above ambient for interference fit installation; induction heaters provide controlled, even heating

• Alignment: Verify shaft and housing alignment within bearing tolerance; misalignment of 0.001 inches per inch of bearing width can halve bearing life

• Preload adjustment: Set proper preload for angular contact and tapered roller bearings per manufacturer specifications

Condition Monitoring

Modern predictive maintenance programs utilise multiple technologies to detect bearing degradation before failure:

• Vibration analysis: Identifies characteristic frequencies associated with inner race, outer race, ball, and cage defects. Baseline readings and trending enable early detection of developing problems.

• Temperature monitoring: Sudden temperature increases often indicate lubrication breakdown or contamination. Continuous monitoring via RTDs or infrared thermography provides early warning.

• Oil analysis: For oil-lubricated bearings, particle counting and spectrographic analysis reveal wear metals and contamination levels.

• Ultrasonic monitoring: Detects high-frequency emissions from metal-to-metal contact, lubrication issues, and early-stage defects before vibration amplitudes increase significantly.

Failure Analysis

When bearings fail, thorough investigation prevents recurrence. Common failure modes include:

• Fatigue spalling: Normal end-of-life failure appearing as flaking on raceway surfaces

• Abrasive wear: Dull, scratched surfaces indicating contamination ingress

• Adhesive wear (smearing): Material transfer from skidding, often due to inadequate load or lubrication

• Corrosion: Pitting and etching from moisture or chemical exposure

• Electrical erosion: Characteristic cratering from current passage, increasingly common with VFD installations

Economic Considerations and Total Cost of Ownership

Bearing selection decisions should consider total cost of ownership rather than initial purchase price alone. A premium bearing costing twice as much but lasting three times longer represents significant savings when installation labour, downtime costs, and secondary damage risks are factored in.

For critical equipment where unplanned downtime costs thousands of dollars per hour—not uncommon in Atlantic Canada's continuous process industries—specifying high-quality bearings with conservative safety factors provides excellent return on investment. Conversely, non-critical auxiliary equipment may justify standard-grade bearings with shorter replacement intervals.

Energy efficiency also merits consideration. Low-friction bearing designs, precision tolerances, and proper lubrication can reduce parasitic losses by 10-30%, providing ongoing operational savings that compound over equipment lifetime.

Partner with Sangster Engineering Ltd. for Your Rotating Equipment Needs

Proper bearing selection requires careful analysis of loads, speeds, environmental conditions, and economic factors—expertise that comes from years of hands-on engineering experience. At Sangster Engineering Ltd., our team of professional engineers has been supporting industrial clients throughout Nova Scotia and Atlantic Canada with practical, cost-effective solutions for rotating equipment challenges.

Whether you're specifying bearings for new equipment, troubleshooting premature failures, or developing predictive maintenance programmes for your facility, we provide the technical expertise you need. Our understanding of local conditions—from the salt air of coastal processing plants to the demanding environments of inland manufacturing facilities—ensures recommendations that perform reliably in real-world Maritime conditions.

Contact Sangster Engineering Ltd. today to discuss your bearing selection challenges, equipment reliability concerns, or rotating machinery engineering needs. Our Amherst-based team is ready to help you optimise equipment performance and minimise costly downtime.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.