SF-1 PTFE Composite Sleeve Bushings for Scroll-Compressor Eccentric Drive Hubs
An SF-1-labelled PTFE sleeve should be considered for a scroll-compressor eccentric drive hub only against a compressor-specific material and validation specification. The orbiting scroll’s lack of self-rotation does not mean zero sliding at the drive journal. Define the rotating pin, hub motion, lubrication circuit and exact lining before comparing suppliers.
Separate scroll orbit from local journal sliding
Copeland describes its scroll mechanism as a fixed scroll working with an orbiting scroll that moves in a small circle without rotating. This explains the overall compression motion; the bearing review still needs a section of the actual eccentric drive arrangement.[1]
Engineering analysis: in an idealized arrangement with a rotating cylindrical crankpin inside a non-spinning orbiting hub, the pin and bore centres share the orbital translation. That common motion does not remove the pin’s rotation relative to the bore. Identify any drive bush, compliance mechanism or other intervening member before calculating the contact speed.
Scope: this is a design-enquiry guide, not a recommendation to retrofit a sealed compressor or substitute an unapproved sleeve. No BONIU compressor approval, hermetic-system qualification or tested service life is asserted. SF-1 and DU-type are family descriptions, not proof of equivalence to a named compressor bearing.
Use the journal diameter in the defined relative-motion example
Assume a 25 mm journal rotating at 3,000 rpm relative to the idealized non-spinning hub. The circumferential sliding speed is π × 0.025 × 3,000 ÷ 60, approximately 3.93 m/s. This is a kinematic illustration, not a recommended SF-1 speed or operating point.
The orbital radius is not the journal radius. Substituting orbital travel speed into this journal calculation would answer a different motion question. Equally, one motor-speed figure does not identify the load vector, start/stop sequence, oil supply or the local speed if an intervening drive component moves relative to both parts.
Submit a motion diagram with each member’s angular and translational movement. The compressor designer should confirm the bearing load and contact model. A high-speed application cannot be approved from a generic static-load value or a dry-running product label.
Compare actual lining construction and processing
GGB’s primary white paper on scroll-compressor bearings compares slurry-, powder- and film-based PTFE overlays. It reports that conventional thin-overlay constructions and a thicker film-based construction have different post-installation sizing capabilities. Its results belong to the named materials and tested methods, not to every SF-1 sleeve.[2]
| Specification item | Why it matters | Required evidence |
|---|---|---|
| Backing, porous layer and overlay | Defines the actual composite construction | Controlled material designation and section specification |
| PTFE formulation and fillers | Affects the tested sliding and fluid behaviour | Traceable formulation reference and relevant compatibility data |
| Overlay thickness and process | Determines the available running layer and permitted finishing route | Supplier-controlled construction and sizing instruction |
| Installed dimensions and datums | Connects the journal support to compressor geometry | Drawing tolerances, assembled inspection and measurement method |
| Fluid and lubrication state | Defines the environment at the sliding interface | Refrigerant/oil identity, mixture conditions, temperature and supply sequence |
Do not authorize reaming because another PTFE material is machinable. Obtain written permission for the exact supplied lining and finishing process. A dimensional improvement that removes the intended running layer can change tribological behaviour.
Read the test method before using a performance claim
The GGB paper separates flat-specimen tests from compressor-manufacturer bushing tests. Its latter tests used a 30 mm bore × 20 mm length specimen and a stated oil/R410A mixture; the paper also defines seizure stop criteria. Those conditions are test definitions, not a BONIU allowable pressure, temperature, speed or compatibility statement.[2]
| Evidence | Useful question | What it cannot establish alone |
|---|---|---|
| Material identification and section inspection | Was the specified layered material supplied? | Compressor operating life or seizure margin |
| A defined laboratory tribology test | How did specimens compare under those conditions? | Behaviour at every refrigerant, mixture ratio or shaft finish |
| Installed dimensional inspection | Does the mounted bearing meet the drawing? | Lubricant supply during startup or transient operation |
| Approved compressor-level validation | Does the specified assembly meet its acceptance programme? | Automatic approval of another grade, process or supplier |
Request the relevant conditions, specimen geometry, counterface, sample definition and acceptance criteria with a supplier comparison. A wear or seizure ranking cannot be transferred to an altered journal size and fluid circuit by matching the PTFE label.
Keep refrigerant, oil and startup in the duty definition
Identify the refrigerant and oil grades, their relevant mixture conditions, temperatures, expected supply path and operating sequence. A material compatible with one neat oil has not thereby been demonstrated in every refrigerant/oil mixture. State whether a claimed test represents a flat coupon, a bushing rig or the assembled compressor.
Map first startup, routine starts, stopped dwell, speed changes and the approved operating envelope separately. Include the designer’s expected journal loading and lubrication conditions for each state. Do not combine the highest numbers from unrelated tests into one operating rating.
Damage morphology needs investigation before a material change. Record where overlay loss, exposed interlayer, scoring or other damage occurs relative to the housing, oil passages and load direction. Appearance alone does not establish cavitation, starvation or fatigue as the cause.
Installation and fit checks
- Use the approved housing fit, chamfer, tooling and insertion direction. Protect the sleeve edges and PTFE running surface during pressing.
- Verify the installed bore, roundness and alignment to the compressor datums. Record the measurement condition, part revision and the mating journal condition.
- Preserve the intended oil passages and drawing-defined seam orientation. Do not add a groove, feed hole or relief by assumption.
- Follow the specified cleanliness and assembly-lubrication procedure. Keep particle control separate from the dimensional pass.
- Treat a change in lining process, supplier, sizing method or fluid exposure as a change for the responsible compressor qualification process.
Frequently asked questions
Does an orbiting scroll mean its drive bushing has no relative rotation?
No. The overall scroll motion and the local pin/bore motion are different. Identify all drive members before deriving the contact speed.
Can a generic SF-1 sleeve be substituted for a branded compressor bearing?
Not on the family name alone. Construction, formulation, sizing, fluid conditions and application validation must match the approved requirements.
Can I use the white paper’s test conditions as BONIU ratings?
No. They describe specific specimens and methods. BONIU performance or approval would require evidence for the proposed supplied component.
Is a tighter installed bore always better?
No. The approved clearance, geometry and thermal/fluid conditions control the requirement. Fix the cause of an out-of-tolerance installation through an authorized process rather than arbitrarily removing lining material.
Technical sources
- Copeland: How scroll compression technology works. Manufacturer explanation of fixed and orbiting scroll motion; not a BONIU component endorsement.
- GGB: The evolution of polymer bearing processing for scroll compressor performance and life enhancement. Primary manufacturer paper comparing named lining processes and explicit test methods. No published results are assigned to SF-1 generally or to BONIU.
Request a drawing review
Send the eccentric drive section and motion diagram, sleeve and journal drawings, installed tolerance requirements, exact lining specification, counterface details, loads and speed sequence, refrigerant/oil conditions, lubrication route, cleanliness requirements, quantity and qualification plan. Ask BONIU to confirm manufacturing scope and available material evidence. Compressor suitability remains subject to the responsible designer’s approval and validation.