Plain Bearing Selection: Materials, Fits and OEM Costs
Table of Contents
Plain bearing selection starts with the load and motion, then matches the bearing material, lubrication method, installed fit, and shaft surface to that duty. Use pressure-velocity data to screen a specific grade under its stated conditions, and validate temperature, friction, wear, and dimensional stability in the application. Compare OEM costs over the same service requirement, including installation, maintenance, replacement, and downtime.
1. Define the Bearing Function Before Choosing a Material
1.1 What This Plain Bearing Guide Covers
This guide focuses on cylindrical sleeve bushings and related flanged bushings that support a shaft through sliding contact. Their performance depends on the bearing material, the mating shaft, the fit, and the operating conditions together. A material name alone cannot establish load capacity, running clearance, or service life. Begin with the required motion and support function, then compare specific grades and constructions against the same duty.
1.2 Distinguish Radial Bushings from Other Plain Bearings
A straight radial bushing supports load across the shaft axis. A flanged design may also support an axial reaction at its flange when that surface is designed and rated for the duty. Thrust washers, spherical plain bearings, and hydrodynamic journal-bearing systems have different geometries and selection methods. Do not apply a radial sleeve's projected-area or fit rules to those products without checking the appropriate design guidance.
1.3 Turn the Application into a Supply Requirement
Explain which dimensions, materials, and maintenance conditions are fixed and which remain open to a proposal. Identify the shaft, housing, retention features, and available space on an assembly drawing. FHD's self-lubricating bearing product page is a starting point for an inquiry, with the exact construction and operating requirements to be confirmed in writing. Keep a preliminary material recommendation separate from approval of a production part.
2. Record the Load and Motion over a Complete Cycle
2.1 Normal Loads, Peaks and Static Holds
Supply the radial force at each bearing position, including peaks and their duration. Distinguish a short impact from a sustained load and identify long stationary holds. For a mechanism with multiple supports, provide the geometry used to determine bearing reactions. A material that survives the maximum force briefly still needs review for deformation and wear during the rest of the duty.
2.2 Rotation, Oscillation and Start-Stop Service
Record rotational speed or the angle and frequency of oscillation, together with dwell time and direction changes. A small repeated arc exposes the same contact region differently from continuous rotation. Include starting frequency and how the machine accelerates under load. These details help the supplier assess friction and lubrication during the actual cycle rather than selecting from the highest speed alone.
2.3 Temperature and Exposure History
List bearing-location temperatures during startup, steady operation, shutdown, and cleaning. Identify moisture, process fluids, abrasive particles, and chemicals that can reach the contact. Describe the housing's cooling conditions and any nearby heat source. Where measurements are missing, mark them as open inputs and assign responsibility for obtaining them before the design is released.
3. Compare Material Families by Their Complete Construction
3.1 Use the Comparison Table as a Shortlist
The table below helps compare the construction, lubrication, and interface questions behind a material shortlist. It does not rank every bronze, composite, or polymer grade, and an advantage demonstrated by one grade should not become a promise for its whole family. Select candidates against the same duty and maintenance constraints, then obtain the data for each exact proposal before accepting a quotation.
| Material family | Construction to identify | Selection question | Purchasing detail to confirm |
|---|---|---|---|
| Solid bronze | Specified alloy; any grooves or solid-lubricant features | How will lubrication reach the contact under the required duty? | Supply/finish-machining sequence and shaft pairing |
| Oil-impregnated sintered bronze | Porous metal grade and supplied lubricant | Does the load-motion-temperature cycle suit this grade and oil? | Handling, approved finishing and replenishment instructions |
| Metal-backed PTFE composite | Backing, supporting layer and exact PTFE-based sliding material | Are shaft surface, wear and proposed dry/lubricated conditions suitable? | Liner condition, installed bore and permitted finishing |
| Metal-backed POM composite | Backing and exact polymer sliding layer or lubricant-retention features | What initial or service lubrication does this design require? | Lubrication and installation instructions for the actual product |
| Bulk or reinforced polymer | Named compound, reinforcement and manufacturing form | How do load, temperature and moisture affect fit and wear? | Installed dimensions, environmental conditioning and shaft requirements |
3.2 Specify More than a Generic Material Name
Terms such as bronze, PTFE composite, and engineering plastic leave important details unresolved. Ask for the material designation, backing or reinforcement, sliding layer, and lubricant where applicable. State whether substitutes need engineering approval and what document identifies the supplied construction. Include that identity on the controlled specification. A visual description may help identify a sample, but it cannot control the composition of a repeat order.
3.3 Keep Qualification Separate from Availability
A supplier's catalog can help identify a candidate, but the quotation must define what will actually be supplied. Confirm dimensions, material, required finishing, inspection scope, and any manufacturing limitation for that proposal. Avoid assuming that every grade discussed in a technical guide is available from FHD. Approve the proposed part only after its application requirements and supply details have been reconciled.
4. Solid Bronze Bushings: Grade and Lubrication Matter
4.1 Identify the Alloy and Sliding Arrangement
For a solid bronze bushing, name the alloy or ask the supplier to propose one for a defined duty. Different bronze grades have different mechanical and sliding characteristics. Show whether the design uses external oil or grease, a specified solid-lubricant feature, or another approved lubrication arrangement. The word bronze does not establish dry-running suitability or eliminate the need to review the shaft pairing.
4.2 Review Grooves and Lubricant Delivery
An externally lubricated bronze bushing needs a practical path for lubricant to reach the working contact, with oil holes, grooves, supply points, and load orientation shown on the drawing. Have the supplier review those features for the proposed construction rather than copying a groove pattern from an unrelated assembly. The supply also needs accessible replenishment and a way for maintenance staff to check that it remains effective.
4.3 Control Machining and Final Geometry
Clarify whether the bushing is supplied finished, installed and finish-machined by the machine builder, or manufactured to another agreed sequence. Final machining requirements affect tooling, inspection, and the responsibility for the running bore. Show the finished datum scheme and any alignment requirement across multiple supports. Ask the quotation to identify which manufacturing and measurement steps are included before comparing unit prices.
5. Oil-Impregnated Sintered Bronze Requires Its Own Review
5.1 Understand the Oil-Carrying Construction
Oil-impregnated sintered bronze uses a porous metal structure containing lubricant. The supplied oil and the material grade are part of the specification, not incidental packaging details. GGB's BP25 sintered-bronze datasheet illustrates a manufacturer-specific construction whose properties depend on the lubricant. Use it as an example of the information to request, not as evidence of FHD's material limits or product equivalence.
5.2 Confirm Handling and Finishing Instructions
Ask how the oil-impregnated part may be stored, cleaned, and installed without changing its intended condition. Clarify the finishing sequence before requesting a tighter bore. Reaming or other machining needs approval for that specific grade and process. Record the supplied lubricant and whether further preparation is required before assembly. A replacement bushing that looks similar may arrive with a different oil or handling requirement.
5.3 Evaluate the Service Cycle and Replenishment Plan
Review speed, load, temperature, and rest periods against the supplier's data for the oil-impregnated grade. Confirm whether the proposed duty requires supplementary lubrication or another maintenance action. Do not assume that stored oil provides unlimited lubricant life under every exposure or operating condition. Include the relevant cycle in the application trial and define the condition that would trigger replacement or servicing.
6. Metal-Polymer Composites and Engineered Polymers
6.1 Identify the Backing and Sliding Layer
A metal-backed composite combines structural support with a separate sliding surface. Specify both parts of the construction, because the backing and liner perform different jobs. FHD's article on self-lubricating bearing materials and manufacture provides related background; use the proposed grade's technical data for the selection itself. Check whether the lining may be machined and how the part must be installed before defining the finished dimensions.
6.2 Do Not Treat PTFE and POM as Identical
Different sliding layers can have different preparation and maintenance requirements. For example, SKF's composite plain-bearing catalog distinguishes its PTFE composite from POM composite designs that require initial lubrication. That distinction belongs to the specified products and should not be generalized into a rule for every similar-looking bushing. Ask the supplier to identify the lubrication instructions for the exact construction being quoted.
6.3 Review Polymer Grade and Dimensional Stability
For a bulk or reinforced polymer bushing, request the exact compound and manufacturing form, then assess deformation under sustained load, thermal expansion, and moisture response where relevant to that grade. Those effects can change the installed bore as well as wear performance. Include the actual shaft, housing material, and environmental conditioning in the review rather than selecting from a generic plastic description.
7. Estimate Contact Pressure with the Correct Geometry
7.1 Use Projected Area for a Radial Sleeve
For a cylindrical radial sleeve, a common nominal-pressure screen is p = F / (d × L). Here F is radial force, d is nominal bearing bore diameter, and L is bearing length. Force in newtons and dimensions in millimeters give pressure in newtons per square millimeter (N/mm²), equivalent to megapascals (MPa). GGB's composite-bearing engineering handbook explains this projected-load approach and the related sliding-speed calculation. The result is a nominal screening pressure, not the local peak pressure at an edge.
7.2 Check Uneven Loading and Misalignment
A bending shaft, distorted housing, or misaligned pair of seats can concentrate contact over part of the bearing length, so increasing nominal area does not guarantee uniform load distribution. Supply shaft deflection, support spacing, and alignment information where those effects are significant. When the projected-pressure calculation appears acceptable but contact is likely to be uneven, review the geometry instead of simply specifying a longer bushing.
7.3 Separate Static and Moving Load Conditions
Use the applicable material limits for stationary, intermittent, and continuously moving conditions. A maximum static pressure does not automatically describe allowable pressure while sliding. Sustained loading may also require a deformation review, particularly for materials whose dimensions change with time under load. Compare the actual conditions with the supplier's definitions before assigning a single allowable load to the machine.
8. Sliding Speed, Starting Friction and Motion Quality
8.1 Convert Shaft Speed into Sliding Speed
For uniform rotation, shaft surface speed can be calculated as v = π × d × n / 60,000 when diameter is in millimeters and speed is in revolutions per minute. The result is in meters per second. Oscillation and varying motion need a cycle-specific description that includes travel angle, frequency, and dwell. Confirm which speed definition the material supplier uses so an average does not hide a demanding part of the cycle.
8.2 Define Starting Torque and Running Resistance
State any limit on breakaway torque as well as the running-friction requirement. Startup after a long loaded stop can be different from established motion with the same bearing and shaft. The actuator must satisfy the required starting condition. Specify load, temperature, rest time, lubricant condition, and the test arrangement when friction is an acceptance characteristic. A catalog friction coefficient is not a guaranteed starting-torque result for the complete mechanism.
8.3 Check Slow Motion and Reversals
Tell the supplier when the machine must move smoothly at low speed or reverse through a small angle. Friction variation can matter to positioning and actuator sizing even when the average running resistance appears acceptable. Assess any stick-slip tendency in the representative assembly under the conditions that affect the process. Use the trial to verify motion quality rather than assuming all plain-bearing materials behave the same at low speed.
9. Use PV as a Screen, Then Review Heat and Wear
9.1 Interpret the Pressure-Velocity Product
PV combines nominal pressure with sliding velocity and is often used to screen a material's operating range. igus's explanation of PV and lubrication shows why the permissible value depends on application conditions. Check the individual pressure and velocity limits alongside any applicable PV curve. A satisfactory product of the two numbers does not, by itself, establish acceptable wear, deformation, or temperature.
9.2 Do Not Multiply Independent Catalog Maxima
Published maximum pressure and maximum speed may come from different test conditions, so their product is not a permitted operating point unless the manufacturer says those conditions can occur together. Match the proposed combination to the grade's documented operating envelope, lubrication state, and temperature conditions. At zero speed the numerical PV value becomes zero, but static deformation and subsequent starting behavior still require review.
9.3 Account for Heat Removal and Duty Cycle
Sliding friction generates heat that must leave through the shaft, bearing, housing, and surrounding environment. Housing material, wall geometry, cooling, and nearby heat sources therefore belong in the evaluation. Intermittent running may provide cooling time, but its benefit depends on the actual cycle and thermal response. Measure temperature during validation and ask the supplier how the tested conditions compare with the basis of its published limits.
10. Specify the Installed Bore and Running Fit
10.1 Measure the Bushing in Its Intended Housing
Pressing a bushing into a housing can change its inner diameter. igus's guidance on installing and checking plain bearings describes the importance of assessing dimensions after installation for its products. Request the housing requirements and installed-bore limits for the proposed grade and size. A free-state bore measurement may answer a different question from whether the assembled part has the required running clearance.
10.2 Include Housing Material and Assembly Conditions
The housing is part of the fit specification. Provide its bore, tolerance, material, wall thickness, and features that affect stiffness. Explain whether it is split, coated, heated during assembly, or tightened after the bushing is installed. These conditions can influence retention and the installed bore. Have the supplier define the appropriate fit and installation method rather than applying one housing tolerance to every metal, composite, and polymer bushing.
10.3 Define Clearance under the Relevant Conditions
Specify the shaft size and the installed bearing bore together with the temperature and conditioning state used for inspection. Review the clearance after expected thermal change, moisture exposure, and assembly effects where applicable. A rolling-bearing clearance class does not define a sleeve bushing's shaft-to-bore running fit. Agree on the actual dimensional limits and measurement method instead of requesting either an undefined tight fit or universal zero clearance.
11. Treat the Shaft Surface as Part of the Bearing System
11.1 Specify Material, Hardness and Coating
Identify the shaft material, any heat treatment, surface hardness, and coating in the RFQ. Ask the bearing supplier to review that counterface with the proposed sliding material and operating conditions. Some grades permit different shaft treatments, but an example from one material cannot establish another grade's requirements. Include coating thickness and finishing responsibility when the coating affects the running diameter.
11.2 Use a Defined Surface-Finish Requirement
State the surface-finish parameter and relevant inspection method on the shaft drawing, using the proposed material's recommended range. Ra and Rz describe different characteristics and should not be substituted by copying the same numerical value. A general instruction to polish the shaft leaves the required finish unresolved; record any specified grinding direction or texture as well, so machining and inspection can work to an agreed requirement.
11.3 Inspect Geometry and Entry Features
Check shaft roundness, straightness, alignment, and the entry geometry used during assembly. Burrs or damaged edges can harm a sliding layer before the machine begins operating. Define shoulders, chamfers, and lead-in features from the supplier's installation requirements without assuming one shape or size suits every bushing. Protect the finished shaft surface during handling and inspect it before fitting trial parts.
12. Match Lubrication and Environmental Protection
12.1 Clarify What Self-Lubricating Means
Self-lubricating can describe different constructions, including stored oil or a sliding material containing solid lubricants. Request the exact requirement for initial preparation, supplementary lubrication, and service maintenance. The term does not automatically mean every application can run dry or that inspection is unnecessary. Put the approved lubrication condition on the specification so production and maintenance teams use the same instructions.
12.2 Review Fluids and Chemicals by Grade
List process liquids, cleaners, concentrations, temperatures, and exposure times where available. Include immersion, repeated wash cycles, and drying between cycles when they occur. Chemical or moisture exposure may affect the liner, backing, lubricant, and dimensions differently. Ask for suitability of the complete proposed construction, including any coating, rather than relying on the base material's general reputation.
12.3 Control Abrasive Contamination
Describe the size and source of particles that can reach the sliding interface. A bushing should not be assumed to seal the assembly simply because its material can run with little external lubricant. Show covers, seals, scrapers, and drainage paths where the surrounding design uses them. Material selection alone may not control wear if the shaft repeatedly brings abrasive contamination into contact. Include representative contamination in testing when it is a critical service condition.
13. Set a Service-Life Target That Can Be Verified
13.1 Define Wear and Positioning Limits
Express the required life in operating hours, cycles, or travel under a stated duty. Define the condition that ends useful service, such as excessive play, shaft-position error, rising torque, or damage to the mating surface. Measure the initial installed condition so later observations have a meaningful reference. A dimensional change should be evaluated for wear, deformation, or environmental effects rather than automatically attributed to one cause.
13.2 Distinguish Estimates from Qualification
Ask the supplier to identify the material data, test method, and application factors behind a life estimate, noting any difference in shaft surface, temperature, or motion pattern. A calculation can help compare candidates, but production approval needs evidence appropriate to the machine and its risks. Keep estimated performance, observed sample results, and accepted requirements identifiable in the project records.
13.3 Run a Representative Trial
Test the proposed bushing with the intended shaft, housing, installation procedure, and lubricant condition. Include starts, stops, static holds, and environmental exposure that control the actual service requirement. Record temperature, friction or torque, wear indicators, and functional performance using agreed methods. Review deviations with the responsible engineer before deciding whether the design is qualified for production.
14. Compare OEM Costs over the Same Service Requirement
14.1 Start with the Complete Installed Cost
The bearing's unit price is only one entry in an OEM cost comparison. Include tooling, setup, special inspection, housing preparation, shaft finishing, and installation work that the proposed design requires. Record each supplier's assumptions so an inexpensive part does not hide a costly interface change. The cost template below uses project inputs rather than invented prices or promised savings.
| Cost item | Candidate A | Candidate B | Evidence or assumption |
|---|---|---|---|
| Initial bearing purchases | [Initial quantity × quoted unit price] | [Initial quantity × quoted unit price] | Approved configuration and purchasing quantity |
| Tooling and setup | [Quoted one-time cost] | [Quoted one-time cost] | Included work, ownership and repeat-order terms |
| Interfaces and assembly | [Shaft/housing/installation cost] | [Shaft/housing/installation cost] | Actual machining, finishing and assembly requirements |
| Maintenance | [Labor, lubricant and inspection] | [Labor, lubricant and inspection] | Agreed tasks and intervals under the stated duty |
| Replacement and restoration | [Replacement parts, access and rework] | [Replacement parts, access and rework] | Validated life or clearly labeled life scenarios |
| Downtime | [Plant-specific estimate] | [Plant-specific estimate] | Confirmed stoppage duration and internal costing basis |
| Validation and documentation | [Trial/report costs] | [Trial/report costs] | Required tests, samples and records |
| Total for the common period | [Sum with stated assumptions] | [Sum with stated assumptions] | Keep uncertain inputs visible; do not claim unverified savings |
14.2 Include Maintenance and Replacement Work
Use the organization's own records to estimate lubrication, inspection labor, replacement access, and shaft or housing restoration. Compare candidates over the same duty and evaluation period. A material change may shift work between initial machining and later maintenance, so include both in the comparison. If service life is uncertain, show scenarios and label their assumptions rather than assigning an unsupported life advantage. Keep downtime costs traceable to the machine's actual production and maintenance conditions.
14.3 Account for Supply and Change Costs
Request sample, release, and forecast quantities along with price validity and any minimum order requirement. Ask how material substitutions, drawing changes, special packaging, and repeat-order identification will be handled. Consider the effort of validating an alternate part when comparing continuity of supply. A fair comparison includes only confirmed supply terms and clearly marked planning assumptions.
15. Build the RFQ and Acceptance Plan Together
15.1 Send the Application and Interface Data
Attach the bearing and assembly drawings, load-motion cycle, shaft specification, housing details, and environmental conditions. Identify the preferred material or explain the requirements that a proposed grade must satisfy. Include sample and production quantities, target arrival date, and the technical contact. Ask suppliers to return their proposed construction, operating assumptions, dimensional requirements, and exceptions against the same RFQ checklist.
| Input | Buyer supplies | Supplier response requested |
|---|---|---|
| Function and geometry | [Radial sleeve/flanged design; drawings and revision] | Exact construction, scope and proposed changes |
| Load and motion | [Radial/axial loads, peaks, static holds, speed and oscillation] | Pressure/speed/PV review and any missing duty data |
| Material and lubrication | [Mandatory grade or selection needs; lubricant condition] | Named grade, backing/liner, lubricant and maintenance requirements |
| Shaft and housing | [Materials, dimensions, finish, hardness, stiffness and assembly] | Counterface requirements, fits and installed-bore limits |
| Environment | [Temperature, moisture, chemicals and contaminants] | Suitability and relevant restrictions for the complete construction |
| Life and acceptance | [Hours/cycles, failure criteria, measurement and trial plan] | Selection basis, test scope, documentation and remaining validation |
| Order stages | [Samples, production releases, forecast and arrival date] | Prices, one-time charges, minimum quantity and schedule assumptions |
15.2 Agree on Inspection before Ordering Samples
Choose measurable checks for the construction, installed fit, shaft surface, and functional requirements that matter to the machine. FHD's related bearing inspection article can support the quality discussion, while the agreed methods must suit the selected plain bearing. Define whether each dimension is checked before mounting, in a specified test housing, or in the production assembly. Require results linked to the inspected samples and resolve unclear acceptance criteria before testing starts.
| Check | Define in advance | Evidence retained |
|---|---|---|
| Material and construction | Grade, backing/liner, supplied lubricant and revision | Specified documents linked to the delivered batch |
| Dimensions and fit | Free-state or installed condition; housing and conditioning state | Measured results using agreed methods and limits |
| Shaft counterface | Material, treatment, coating, finish and geometry | Actual mating-part inspection record |
| Assembly | Permitted installation/finishing sequence and retention | Approved method and recorded trial configuration |
| Application performance | Duty, environment, temperature, friction and wear criteria | Test observations, results and exception disposition |
| Release and changes | Approval owner and controlled production specification | Written release and review requirements for substitutions |
15.3 Control the Approved Production Configuration
Record the material grade, sliding layer, lubricant, dimensions, mating-surface requirements, and approved installation method. Retain the trial results and the disposition of technical exceptions with the drawing revision. Require review of changes that could affect installed clearance, friction, chemical compatibility, or wear. Release repeat orders against that controlled package so a familiar part number does not conceal an unreviewed construction change.
16. Buyer FAQs on Plain Bearing Selection
16.1 Which Plain Bearing Material Is Best?
The best choice depends on the load, motion, shaft pairing, environment, lubrication, and required life. Solid bronze, oil-impregnated sintered bronze, metal-polymer composites, and engineered polymers solve different application problems, so compare named grades under the same conditions and confirm the installed geometry. The material family alone is not a performance specification.
16.2 Is Passing a PV Limit Enough?
No, PV is a screening measure rather than a complete qualification. The proposed pressure and speed must also satisfy the applicable individual limits, operating envelope, temperature, and lubrication conditions. Friction at startup, static deformation, shaft compatibility, and wear may still control the selection. Validate the candidate against the service requirement and the supplier's grade-specific guidance.
16.3 What Should You Send FHD for a Quotation?
Send the application, load and motion cycle, drawings, shaft and housing specifications, lubrication condition, and environmental exposure through FHD's contact page. Add the required quantities, service-life criterion, acceptance checks, and target arrival date. Request confirmation of the exact material and construction, installed-bore requirements, documentation, and commercial terms. Approve the application review and sample results before authorizing the production configuration.
