SF-1 PTFE Composite Rod-Guide Bushings for Oil-Filled Shock Absorbers
For an SF-1 PTFE composite sleeve in an oil-filled shock absorber’s piston-rod guide, review the exact lining formulation, installed clearance and local oil-flow conditions together. Dry-friction or PV data alone cannot establish resistance to cavitation and flow erosion. Specify a validation programme that reproduces the damper’s stroke, frequency, side load, fluid and temperature.
This guide addresses the bearing layer in an existing rod-guide arrangement. It does not approve a vehicle suspension component or replace the damper designer’s hydraulic, structural and durability requirements. A pneumatic rod-guide replacement and an oil-filled damper require different evidence.
Write the complete composite material into the enquiry
Obtain the backing metal, porous interlayer, sliding-layer composition, thickness, outside coating and applicable substance restrictions. SF-1 is a purchasing-family description; it does not establish a proprietary formulation, a test history or lead-free compliance. Identify the offered supplier material and documentation explicitly.
GGB’s DU page describes its own steel-backed bronze-interlayer bearing with PTFE and lead. Its DU designation is protected. Treat it as a documented manufacturer example rather than an alternate name for every SF-1 sleeve.
[1]GGB separately publishes DP4 and DP4-B data with distinct material identities. The presence of PTFE in two products does not establish the same fluid-erosion behaviour. A proposed replacement needs evidence for the supplied material and the actual damper assembly.
Separate surface damage mechanisms before changing the bearing
GGB’s DP4 handbook describes cavitation and flow-erosion damage in oil-lubricated strut rod-guide linings and presents separate evaluation rigs. Its comparisons belong to DP4 under the stated tests; they are not SF-1 or BONIU ratings.
[2]| Observation | Question to investigate | Useful evidence |
|---|---|---|
| Long axial scoring | Did debris or a damaged rod pass through the guide? | Particle analysis, rod condition and seal inspection |
| Local edge wear | Is the rod tilted or the guide seat distorted? | Installed bore, alignment and side-load history |
| Pitting or loss of lining near an oil path | Could cavitation or local flow contribute? | Damage map, fluid circuit and operating record |
| High breakaway force | Is clearance, temperature or counterface condition involved? | Cold/hot friction checks and dimensional measurements |
| Loose sleeve or fretting backing | Is housing retention adequate? | Seat measurements and retention inspection |
These are diagnostic questions, not visual proof of a single cause. Several mechanisms can coexist. Preserve the guide orientation and damaged part before cleaning, and correlate photographs with the oil feed, seal position and load direction.
Use the motion waveform, not only average rod speed
For a sinusoidal rod displacement with full peak-to-peak stroke S and frequency f, peak speed is π × f × S and mean absolute speed is 2 × f × S. Use metres and seconds. These kinematic relations describe motion, not a bearing load or erosion limit.
| Quantity | Cycle A | Cycle B |
|---|---|---|
| Full stroke S | 80 mm | 20 mm |
| Frequency f | 2 Hz | 8 Hz |
| Peak rod speed πfS | 0.503 m/s | 0.503 m/s |
| Mean absolute rod speed 2fS | 0.320 m/s | 0.320 m/s |
| Reversals per second 2f | 4 | 16 |
Both cycles have the same peak and mean sliding speed, but Cycle B reverses four times as often and sweeps a shorter rod region. A single average-speed entry hides that difference. Pressure histories and local oil motion require the damper’s hydraulic model or measurements; they cannot be calculated from this table alone.
State whether the waveform is sinusoidal, triangular, impact-driven or measured in service. Include dwells, temperature stabilisation and transient events. Keep side load and pressure aligned to the relevant point in the stroke rather than pairing independent maxima without explanation.
Review the fluid circuit and installed gap as one assembly
Send the oil specification, viscosity information at operating temperature, additives, filtration and fluid-conditioning procedure. Identify nearby restrictions, oil feeds, pressure chambers and venting. Avoid describing the guide as dry-running when its intended environment is an oil-filled damper.
Specify the rod diameter limits and the mounted guide bore limits, including the reference temperature. Housing fit, thin-wall closure, rod finish, straightness and coating condition affect the interface. An apparent bore before pressing is not acceptance of the installed clearance.
Do not change a feed hole, add a groove or enlarge the running gap as a general cure for erosion. These changes can alter guidance, leakage and the local flow field. Evaluate the design change with the damper engineer before releasing production parts.
Separate assembly inspection from duty validation
Use a supported housing and an insertion tool that loads the backing without damaging the sliding layer. Deburr approved entry features and align any specified seam and feed location. Check seating, bore and cleanliness after installation. Do not ream, hone or burnish the lining unless that exact bearing construction permits the operation.
Define two acceptance stages. Dimensional inspection confirms the component and its installed geometry. A representative assembly test evaluates the damper’s friction, leakage, temperature response and durability under an agreed sequence. Record test duration, load and waveform, fluid condition, pass criteria and the post-test examination method.
GGB’s handbook distinguishes wear/friction testing from cavitation and flow-erosion evaluations. Copying one test’s duration or a relative graph into an SF-1 order would leave the rest of the application unqualified.
[2]Agree what constitutes unacceptable lining loss, friction change, leakage or rod damage before testing. The required evidence may include supplier material tests and a damper-level programme. This guide provides no life estimate or assurance of suspension-system fitness.
Frequently asked questions
Does a dry-running PV rating qualify a damper guide?
It does not establish fluid-erosion resistance or damper durability. Review the exact lining, local oil environment and representative assembly evidence.
Are SF-1, DU and DP4 interchangeable names?
No. Obtain the actual material specification. DU and DP4 identify manufacturer products with their own constructions and published data.
Can equal average rod speeds be treated as equal duty?
Stroke, reversal rate, load waveform, pressure and temperature can differ even when average speed is the same. Preserve those variables in the validation plan.
Request a drawing review
Provide the rod-guide and housing drawings, installed limits, rod material and finish, complete lining identification, side-load history, stroke waveform, frequency, fluid and temperature data, oil-circuit section, failure photographs if available, validation criteria and order quantity.
Send your drawing for review or email sales@boniubushing.com. BONIU reviews material availability, manufacturing feasibility and inspection scope for each enquiry. This article does not confirm stock, application approval, certification or BONIU testing.
Technical references
- GGB: DU metal-polymer bearings. Proprietary material identity and construction.
- GGB: DP4 and DP4-B handbook. Printed pages 12–15 distinguish strut wear/friction, cavitation and flow-erosion tests. No proprietary numerical rating transferred.
Published manufacturer information belongs to its source and applies to the stated product or material. Original calculations and checklists here are engineering analysis using declared assumptions. They are not BONIU specifications or test results. Release the supplied component against the approved drawing.