How to Select the Right Sliding Bearing for Your Project

When designing mechanical systems, one of the most critical decisions engineers face is selecting the right bearing. Sliding bearings—also known as plain bearings, sleeve bearings, bushings, or journal bearings—are among the most versatile and widely used components in industrial applications. Unlike rolling-element bearings that use balls or rollers, sliding bearings operate through a sliding action between two surfaces, making them suitable for applications ranging from automotive engines to construction machinery.

This guide will walk you through the essential factors to consider when selecting the optimal sliding bearing for your specific application.

Sliding Bearing Basics

Sliding bearings are mechanical components designed to constrain, guide, or reduce friction in rotary or linear applications. They function via a sliding action between the bearing surface and the shaft or mating component, rather than the rolling action of ball bearings -2. This fundamental difference gives sliding bearings distinct advantages, including:

• High load-carrying capacity
• Compact design with minimal space requirements
• Cost-effective manufacturing
• Quiet operation
• Suitability for high-speed precision applications (often preferred over ball bearings above 3,600 RPM) 

The bearing's performance is determined by the coefficient of friction between the two materials and the loads transferred to the bearing assembly. These properties can be significantly enhanced through proper lubrication .

Key Selection Factors

1. Assess Your Application Requirements

The selection process always begins with a thorough evaluation of your intended application. Key questions to consider include:

• What type of motion is involved—rotary, oscillating, or linear?
• What are the operating environmental conditions (temperature, humidity, chemical exposure)?
• Is the application subject to impact loading or vibration?
• What are the required speeds and loads?

Proper selections include evaluating environmental factors such as aggressive chemicals, contamination, high or low operating temperatures, and wash-down requirements—particularly relevant in food and beverage applications . Each application will suggest specific materials for optimal performance.

2. Calculate the PV Value

The PV value—the product of specific load (pressure) and sliding speed—is perhaps the most critical parameter in sliding bearing selection. It measures the bearing material's ability to accommodate the temperature limit generated by frictional energy during operation .

Pressure (p) Calculation:

p = F / (L × D)

Where F = load/force, L = bearing length, and D = shaft diameter.

Velocity (V) Calculation:

V = π × D × n / (60,000)

Where n = rotational velocity .

The PV value has a significant influence on bearing service life—the lower the PV value, the longer the bearing's life . When evaluating materials, compare your calculated design PV against the material's rated PV value. For design purposes, the calculated PV should be multiplied by a safety factor before comparing with material ratings .

3. Determine Proper Clearance

Diametral clearance is crucial for proper bearing operation. The clearance must accommodate:

• Thermal expansion of the bearing and shaft materials
• Manufacturing tolerances
• Lubrication film requirements

Typical clearances for plain bearings range from 0.001 to 0.002 times the bearing diameter . For polymer bearings, running clearance typically falls between 0.002 and 0.004 inches, with housing bore and shaft tolerance also factoring into the calculation .

In applications involving plastic bearings, it is also important to consider how swelling may affect clearances in humid or underwater environments .

4. Consider Length-to-Diameter (L/D) Ratio

The length-to-diameter ratio influences both load capacity and alignment. For full-film hydrodynamic bearings, a common L/D ratio ranges from 0.35 to 1.5 . The longer the bearing, generally, the better the performance in terms of load distribution and alignment stability .

5. Evaluate Mating Shaft Requirements

The shaft surface roughness often has a significant influence on service life. A surface roughness greater than 0.4 µm may have a negative effect on bearing performance . General guidelines include:

• The heavier the load, the harder the shaft should be
• Higher risk of embedded contaminants requires harder shafts

Shaft materials should be steel, with bearing materials such as steel or hard brass; aluminum or wood should never be used for sliding members as they cause stick-slip performance and tendency to jam.

Material Selection Guide

Steel-Backed Multilayer Bearings

For demanding industrial applications, EPEN's EX series tri-layer plain bushings represent an advanced solution. These bearings feature a steel backing that provides structural integrity and thermal conductivity, onto which a porous bronze layer is sintered. Acetal copolymer (POM) or PTFE mixtures are impregnated into the bronze layer, with lubrication indents stamped into the surface .

Material characteristics include:

Parameter	Value
Static Load Capacity	250 N/mm²
Dynamic Load Capacity	140 N/mm²
Max Sliding Speed (Pre-lubricated)	2.0 m/s
PV Value	2.8 N/mm²·m/s
Coefficient of Friction	0.05~0.20
Operating Temperature	-40°C to 110°C

These bearings are suitable for rotary and oscillating movement with self-lubricating, anti-wear, low-friction, and low-noise performance .

Bronze Bearings

Bronze bearings offer high load-carrying capacity and can handle pressures from 25,000 to 40,000 psi in oscillating or rotary applications . Copper-based composites provide good wear resistance and can be tailored with various alloying elements:

• Tin and aluminum additions improve strength and hardness
• Zinc additions allow operation without continuous lubrication
• Lead additions reduce hardness for improved embeddability

Self-Lubricating Bearings

Self-lubricating or oil-impregnated bearings eliminate the need for external lubrication. Sintered bronze can be impregnated with oil that is released as the bearing warms up. Solid lubricants can also be incorporated into the bearing matrix .

Advantages of self-lubricating bearings include:

• Elimination of oil holes and grooves (reducing machining costs)
• Lower maintenance requirements
• Simplified mechanical design
• Safer operating environment without dependence on oil lubricants 

Polymer Bearings

Plastic and composite bearings offer several compelling benefits:

• Corrosion resistance in harsh environments
• Vibration damping and shock absorption
• Weight reduction of 25% or more compared to metallic alternatives
• Cost-effective manufacturing
• Low coefficient of friction (0.05 to 0.15) without external lubrication 

However, polymer bearings have specific design considerations. The coefficient of friction (typically 0.15-0.30 μ for dry-running applications) means that for every 10 lbf of load, 1.5 to 3 lbf of drive force is required to move the bearing .

Lubrication Strategies

Lubrication is critical to safe and efficient bearing operation. Poor lubrication can lead to fast material wear and machinery breakdowns .

Hydrodynamic Lubrication

In hydrodynamic systems, the shaft rides on a continuously flowing layer of lubricant. This is common in high-speed applications where speeds above a few hundred RPM are needed to pump oil through the bearing. Operating temperature must be calculated into viscosity considerations to ensure proper lubrication and minimum film thickness .

Boundary Lubrication

In boundary lubrication conditions, the bearing surfaces are separated by a very thin film of lubricant. EX sleeve bushings are commonly recommended for intermittent operation and boundary lubrication environments, particularly with oil hole designs for continuous or repeated refueling occasions .

Dry Operation

For dry-running applications, bearings with solid lubricants embedded in the bearing material are essential. These bearings have a solid lubricating film created by the transfer of material from the bearing layer to protect the mating component .

Application-Specific Considerations

Automotive Engine Applications

In demanding engine environments where extreme pressures, high temperatures, and rapid movements are the norm, bearings require exceptional fatigue strength. Critical applications include connecting rod bearings, main bearings supporting the crankshaft, and thrust washers controlling axial movement .

Hydraulic and Construction Machinery

These applications typically require bearings capable of handling heavy loads under intermittent operation, often with boundary lubrication conditions .

High-Temperature or Extreme Environments

Bearings operating in extreme temperatures, humidity, shock, or vibration require materials that are durable and dependable. The full range of ambient operating temperatures must be considered, as changing temperatures can affect the distance between the bushing and housing or between the bushing and shaft .

Practical Selection Checklist

Before finalizing your sliding bearing selection:

• Define operating conditions – Load, speed, temperature range, environment
• Calculate PV value – Compare with material ratings
• Determine required clearance – Account for thermal expansion and tolerances
• Select appropriate L/D ratio – Balance load capacity and alignment
• Choose lubrication strategy – Hydrodynamic, boundary, or self-lubricating
• Evaluate cost considerations – Initial cost vs. maintenance and lifecycle costs
• Consult with manufacturers – Leverage technical expertise for specialized applications

Conclusion

Selecting the right sliding bearing requires careful consideration of multiple factors, from the basic application requirements to sophisticated calculations of PV values and clearances. With options ranging from high-performance steel-backed multilayer bearings to self-lubricating polymers, there is a solution for virtually every application—from automotive engines to heavy construction machinery.

When in doubt, consulting with manufacturers like EPEN Sliding Bearing can provide valuable insights into new materials and material properties, ensuring you select the optimal bearing for your project. requirements.

FAQ

What factors most significantly impact sliding bearing lifespan?

How long a sliding bearing lasts depends on the type of material used, how well it is oiled, the load it is under, and its surroundings. Bearings that are properly oiled and working within their design load limits can last for decades. Bearings that are overloaded or not properly oiled, on the other hand, fail very quickly. Corrosive conditions, abrasive pollution, and thermal cycling all speed up wear by a large amount. Bronze bearings don't handle minor lubrication as well as composite materials that have oils built in.

How do I determine whether my application needs sliding bearings or rolling element bearings?

Plain bearings work best in places where there are big loads, shocks, swaying motion, or limited access to grease. Rolling element bearings work best when they are continuously rotating at a high speed and are under modest loads. When there is pollution in the environment, plain bearings are often chosen because they can handle particles better. Your ability to do upkeep and your budget also play a role in this choice.

Can plain bearings perform reliably in high-speed applications?

How fast something can go depends on the materials used and how well they are oiled. Self-lubricating materials usually only work at mild speeds. Hydrodynamic bronze bearings that use pressurized oil to lubricate them work well at high speeds. The PV maximum for the material you've picked tells you how fast to go based on the operating pressure.

Partner with Epen for Your Sliding Bearing Solutions

Choosing the optimal sliding bearing solution becomes straightforward when you work with experienced manufacturers who know your industry challenges. Jiashan Epen Bearing Co., Ltd. specializes in metal-plastic composite bearings, bimetal designs, and single-metal plain bearings serving construction machinery, mining equipment, marine applications, and agricultural systems across 30 industries. Our research team can analyze your application, help you choose the right material, and create a custom bearing that fits your exact needs. As a dedicated sliding bearing manufacturer, we deliver both standard catalog products and customized solutions at competitive pricing without compromising quality. Contact our technical specialists at epen@cnepen.cn to discuss your project requirements, request product samples, or access our comprehensive catalog with detailed specifications.

References

Khonsari, M.M. and Booser, E.R., "Applied Tribology: Bearing Design and Lubrication," John Wiley & Sons, Third Edition, 2017.

Neale, M.J., "The Tribology Handbook," Butterworth-Heinemann, Second Edition, 1995.

American Society of Mechanical Engineers, "ASME B18.23.1 - Plain Washers and Bearing Materials Standards," ASME International, 2018.

Budynas, R.G. and Nisbett, J.K., "Shigley's Mechanical Engineering Design," McGraw-Hill Education, Eleventh Edition, 2020.

Society of Automotive Engineers, "SAE J459 - Bearing and Bushing Alloys - Chemical Composition," SAE International Standards, 2019.

Hamrock, B.J., Schmid, S.R., and Jacobson, B.O., "Fundamentals of Fluid Film Lubrication," Marcel Dekker, Second Edition, 2004.