Self Lubricating vs Oil Impregnated Bronze: How to Choose

Self-Lubricating vs Oil-Impregnated Bronze: Structure and Duty Limits

Self-lubricating bronze is not one product. It is two structures that fail in opposite ways: oil-impregnated sintered bronze stores SAE 30 oil in 19–27 % interconnected porosity and works to roughly 105 °C, while graphite-plugged cast bronze carries solid graphite plugs across 20–30 % of the sliding surface and keeps running to 250 °C with peaks near 300 °C. Choose oil-impregnated when pressure stays under about 14 N/mm², sliding speed is measurable, and the housing is sealed and cool. Choose graphite-plugged when pressure is high, motion is slow, oscillating or start-stop, and the position is hot, wet, dusty or impossible to reach with a grease gun. If you cannot state P, V and peak temperature for the position, neither should be ordered yet.

1. The naming problem: “self-lubricating” describes two different structures

Both families are sold as self-lubricating bronze, and that is where most mis-orders start. They store lubricant in completely different ways.

Oil-impregnated sintered bronze (powder metallurgy). A CuSn10 powder mix is pressed, sintered to a controlled density, sized, then vacuum-impregnated with oil — conventionally SAE 30. The interconnected pore network is the reservoir: oil bleeds to the surface under rotation and is drawn back when the shaft stops.

Graphite-plugged cast bronze (solid-lubricant-embedded). A solid casting or continuous-cast bar — typically C86300 manganese bronze, C95400/C95500 aluminium bronze, or C93200 tin bronze — is drilled in a staggered pattern and the holes are filled with compressed graphite. Coverage of the sliding surface is normally 20–30 % (some suppliers publish 25–35 %). During running, frictional heat and pressure push graphite out of the plugs; it transfers to the shaft as a film roughly 0.5–2 µm thick and re-forms after local damage. The matrix is specified under ASTM B505/B505M (continuous cast), ASTM B22 (C86300 castings), ASTM B271 (centrifugal cast) or ISO 4382-1 (cast copper alloys for plain bearings); EN 1982 and GB/T 1176 are the usual European and Chinese references.

One trap worth naming: the “graphite” in sintered bronze is a powder addition capped at about 0.5 wt % in the mix. It is not the same quantity as the 20–30 % surface coverage provided by solid graphite plugs. If a drawing calls for “graphite bronze,” confirm which one is meant before quoting.

2. The numbers that decide the order

Six numbers settle most self-lubricating bronze selections: lubricant content or coverage, hardness, load, speed, PV and temperature. All values below are published typical ranges for guidance. Catalogue values differ by supplier, casting route and test method — treat them as screening limits and confirm against the mill certificate and the supplier’s own test data before release.

Parameter	Oil-impregnated sintered bronze (SAE 841 / ASTM B438 Gr.1 Type 2)	Graphite-plugged cast bronze (C86300 base)
Lubricant reservoir	Oil in 19–27 vol % interconnected pores (ASTM B438 minimum ≥ 18 %)	Solid graphite plugs over 20–30 % of sliding area
Density	6.4–6.8 g/cm³	≈ 8.0 g/cm³
Hardness	HRH 45–60 apparent (≈ HB 30–70); porous structure is not Brinell-tested	≥ 190–210 HB (C86300 continuous cast typically ≈ 225 HB at 3000 kgf)
Tensile strength	≈ 96 MPa (14,000 psi); K constant ≥ 26,000 psi (≈ 180 MPa) radial crush	≥ 750 MPa (C86300)
Max pressure P	≈ 14–15 N/mm² dynamic (2,000 psi)	≈ 100 N/mm² dry; 50 N/mm² oil-lubricated — confirm static vs dynamic basis
Max sliding speed V	≈ 6.0 m/s (1,200 sfpm)	0.3–0.5 m/s dry; up to 1.0 m/s oil-lubricated
PV ceiling	≈ 1.6–1.8 N/mm²·m/s (50,000 psi·ft/min)	1.65 N/mm²·m/s dry as commonly published; some catalogues list 2.5–3.8 — verify
Friction coefficient µ	0.07–0.15 (oil film)	0.12–0.16 dry; 0.03–0.08 oil-lubricated
Temperature range	−10 to +105 °C with standard SAE 30 oil (≈ 10–220 °F); synthetic oil to ≈ 150 °C, special oils beyond	−40 to +250 °C; short peaks to +300 °C
Shaft finish	Ra 0.2–0.8 µm	Ra 0.4–0.8 µm
Shaft hardness	200–300 HB	≥ 200 HB; 50–55 HRC recommended against C86300
Governing standards	ASTM B438-25, ASTM B439-25 (iron-base), MPIF Standard 35, ISO 5755, DIN 1850, GB/T 5143	ASTM B505/B505M, ASTM B22, ASTM B271, ISO 4382-1, EN 1982, GB/T 1176

Two observations cut through the marketing of both self-lubricating bronze families. First, the porous structure that makes sintered bronze self-lubricating is also what caps it: roughly one third of the volume is void, so pressure capacity is an order of magnitude below a solid casting. Second, the graphite plug does not care about temperature the way oil does — the temperature ceiling of a sintered bearing is the oil’s ceiling, not the bronze’s, which is why the published range ends near 105 °C while the graphite-plugged range extends past 250 °C.

3. Product feature → what you actually get on the plant floor

A self-lubricating bronze bushing earns its place by removing work from the maintenance plan, not by adding a line to the specification. This is what each property changes in your plant.

Product feature	Value you receive
Graphite plugs covering 20–30 % of the sliding surface	No lubrication point at that position — no grease line, no access platform, no confined-space permit for a re-lube round
Solid cast matrix, ≥ 750 MPa tensile (C86300)	Survives shock, edge loading and impact that would crack or spall a porous sintered body
≥ 190–210 HB against a hardened shaft	Holds up to abrasive iron-oxide scale instead of being polished away by it
Published dry PV ceiling of ≈ 1.65 N/mm²·m/s	Service life you can estimate before purchasing, instead of discovering after a failure
−40 to +250 °C, peaks to +300 °C	Keeps working where grease carbonises and impregnating oil dries out
Self-replenishing transfer film	Tolerates start-stop and oscillating duty; reduces stick-slip in screw-down and adjustment mechanisms
No oil or grease to wash out	Unaffected by cooling-water spray and steam on the caster and runout table
No oil to drain or wipe	Cleaner product surface — matters on strip lines where drips cause quality rejects
Machined to your drawing (split halves, flanges, wear plates, spherical)	Drop-in replacement at the next planned shutdown, with no housing modification
Lead-free base option (C86300 ≤ 0.20 % Pb versus C93200 at 6–8 % Pb)	RoHS / REACH-compliant builds where your customer’s specification requires it

4. Grade → application → benefit

Read the table as: which self-lubricating bronze grade, at which position, and for what reason. Four solid-lubricant grades plus the sintered baseline cover the large majority of enquiries we receive.

Grade (base + lubricant form)	Typical application	Key benefit	Reference numbers
C86300 / CuZn25Al5Mn4Fe3 + graphite (ZCuZn25Al6Fe3Mn3, “JDB-1” type)	Screw-down screws and thrust washers, mill-housing window liners, roll-change car pivots, heavy pivot joints	Highest load capacity of the common graphite-plugged grades; absorbs shock and misalignment	≥ 750 MPa tensile, ≥ 210 HB, dry P ≈ 100 N/mm², V ≤ 0.5 m/s dry, PV 1.65 N/mm²·m/s dry, −40…+250 °C (peaks 300 °C). Requires a hardened shaft
C95400 / C95500 aluminium bronze + graphite (CuAl10Fe3 / CuAl10Ni5Fe4)	Hot runout-table rollers, coiler mandrel pivots, caster segment supports, flying-shear cranks	Retains strength and corrosion resistance under radiant heat, water and steam	C95400 ≈ 517–586 MPa, 170–210 HB; graphite-plugged versions published to 300–400 °C; strong resistance to oxidation and cooling water
C93200 (SAE 660) + graphite	Guide and adjustment bushings, medium-load linkages, general plant machinery	Lowest material cost, best embeddability (dirt tolerance), easiest machining	240–310 MPa, 60–75 HB, Pb 6–8 % gives emergency lubricity. Not RoHS-compliant because of the lead content
CuSn8 / CuSn8P wrapped bronze with lubrication indents (DIN 1494 / ISO 3547)	Hydraulic cylinder eyes, agricultural and construction linkages	Lower cost than solid castings where periodic re-lubrication is possible	Higher load capacity than sintered bronze at a comparable price point; needs a re-lube schedule
SAE 841 oil-impregnated sintered bronze (ASTM B438 Gr.1 Type 2)	Small motor and fan shafts, enclosed gearboxes, conveyors in clean areas, appliances	Near-net-shape, quiet, low unit cost at volume	≥ 18 % oil by volume, K ≥ 26,000 psi, PV 50,000 psi·ft/min, −10…+105 °C with standard oil

5. Run the PV check before you send the enquiry

Every self-lubricating bronze order should start here. PV is pressure × sliding velocity. Check P first, then V, then PV — the binding constraint is usually not the one buyers expect.

Case A — roll-change car pivot, P = 40 N/mm², v = 0.03 m/s → PV = 1.20 N/mm²·m/s. Sintered bronze fails on pressure: 40 N/mm² is nearly three times its 14–15 N/mm² ceiling. Graphite-plugged C86300 passes all three checks (P ≤ 100, V ≤ 0.5, PV ≤ 1.65). Specify graphite-plugged.

Case B — fan shaft, P = 2 N/mm², v = 0.8 m/s → PV = 1.60 N/mm²·m/s. Sintered bronze passes all three checks (P ≤ 14, V ≤ 6.0, PV ≤ 1.75). Graphite-plugged fails on speed: 0.8 m/s exceeds the 0.3–0.5 m/s dry ceiling, and there is no margin. Specify oil-impregnated.

Case C — caster position at 260 °C, P = 30 N/mm², v = 0.02 m/s → PV = 0.60 N/mm²·m/s. The oil in a sintered bearing oxidises and dries out well below 260 °C, so the material is disqualified on temperature regardless of the PV result. Specify graphite-plugged, and confirm the graphite grade for sustained high temperature.

For shock and impact duty, apply a safety factor of at least 2 to the PV ceiling and increase wall thickness rather than line speed. Graphite’s film-forming ability also depends on adsorbed moisture in the surrounding air; in high vacuum or extremely dry gas, specify MoS₂ or PTFE-based plugs instead and validate by test.

6. Standards, size range, custom options and the default fit system

What you can order, and the fit system shipped with a self-lubricating bronze bushing unless your drawing overrides it.

Standards covered. Oil-impregnated sintered: ASTM B438-25 and ASTM B439-25 (iron-base), MPIF Standard 35, ISO 5755, DIN 1850 / W.Nr 2.1177, GB/T 5143. Graphite-plugged and solid: ASTM B505/B505M (continuous cast), ASTM B22, ASTM B271, ISO 4382-1, EN 1982, GB/T 1176. Material certification to EN 10204 3.1 on request.

Standard range. Catalogued graphite-plugged straight sleeves typically start at 8 mm ID, with flanged bushings, thrust washers, wear plates and spherical bearings in the same series. Above the catalogue ceiling, self-lubricating bronze parts are made to drawing by centrifugal or sand casting.

Custom capability.

• Plug pattern (staggered, diamond, aligned) and coverage between 20 % and 35 %

• Plug material: graphite, graphite-PTFE, or MoS₂ composite

• Forms: straight, flanged, double-flanged, thrust washer, wear plate, spherical, split half-bearings, worm wheels

• Oil grooves, figure-eight or spiral grooves, debris-flushing grooves

• Steel-backed bimetal construction and segmented designs for large diameters

• Machining to your drawing or reverse-engineering from a sample

Default fit system (applied unless your drawing states otherwise):

Element	Default	When to change it
Housing bore	H7	Verify bore roundness on thin-wall or welded housings
Bushing OD	r7	Move to s7 for light-alloy (aluminium) or thin-wall housings
Shaft	g6	Shift to f7 or e7 above ≈ 100 °C; bronze expands more than the steel shaft and is constrained by the rigid housing, so clearance closes as temperature rises
Shaft roughness	Ra 0.4–0.8 µm	Ra > 1.6 µm machines the bronze; Ra < 0.1 µm gives the graphite film no valleys to anchor in
Shaft hardness	≥ 200 HB	50–55 HRC (e.g. 42CrMo, GCr15) recommended against graphite-plugged C86300

Running clearance after press fit. A bushing with an r7 OD pressed into a rigid H7 steel bore collapses inward; the F7 internal tolerance is designed to absorb that collapse.

Shaft Ø (mm)	Total running clearance (mm)
30	0.027 – 0.065
50	0.034 – 0.080
80	0.043 – 0.097
100	0.050 – 0.112
150	0.061 – 0.131

Above 150 mm, size the total diametral clearance at roughly 0.05–0.10 % of the shaft diameter. Always defer to the OEM drawing where one exists, and do not tighten a specified clearance in pursuit of efficiency — the seizure risk is not acceptable in continuous process plant.

7. FAQ — the questions we actually receive in enquiries

Below are the self-lubricating bronze questions that arrive in the inbox most often, with the answers we send back.

Are oil-impregnated bronze and self-lubricating bronze the same thing? No. Oil-impregnated sintered bronze is one subset of self-lubricating bronze: SAE 841 powder-metal bronze with oil held in 19–27 % interconnected porosity per ASTM B438-25. The other subset is solid-lubricant-embedded bronze, where graphite plugs cover 20–30 % of a solid cast surface. Different structure, different limits.

What does “25 % graphite coverage” mean, and can I get more? It is the share of the sliding surface occupied by graphite plugs, not a percentage of the alloy. Standard coverage is 20–30 %; up to 35 % is available for slow, high-load duty. More coverage means more lubricant but less load-bearing metal, so it is specified against the duty calculation, not requested by default.

What PV can we run at? Our screw-down does 55 MPa at 0.02 m/s. PV = 1.10 N/mm²·m/s, inside the ≈ 1.65 N/mm²·m/s dry ceiling for a self-lubricating bronze bushing in C86300 with graphite plugs, and P = 55 N/mm² is inside the ≈ 100 N/mm² limit. Sintered bronze is disqualified at that pressure — its dynamic ceiling is about 14–15 N/mm². Verify the plug grade for the temperature at that position.

What shaft finish and hardness do you need? Shafts ground to Ra 0.4–0.8 µm at ≥ 200 HB. Against graphite-plugged C86300 we recommend hardened 42CrMo or GCr15 at 50–55 HRC. Too rough and the shaft machines the bronze; too smooth and the graphite film has nothing to anchor to.

Will it survive 260 °C near the caster? Graphite-plugged bronze is rated −40 to +250 °C with short peaks to +300 °C, so sustained 260 °C is at the top of the range and needs the high-temperature graphite grade confirmed. Oil-impregnated bronze is not suitable — standard SAE 30 oil is limited to roughly 105 °C.

Do you have a lead-free option for a RoHS-compliant build? Yes. C86300 manganese bronze contains ≤ 0.20 % lead and is the usual lead-free choice for graphite-plugged parts. C93200 (SAE 660) contains 6–8 % lead, chosen for its embeddability, and is not RoHS-compliant.

Can you make a split half-bearing to our drawing instead of a catalogue number? Yes. Split halves, flanged and double-flanged bushings, thrust washers, wear plates and spherical bearings are all produced to drawing or reverse-engineered from a sample. Send the drawing with the fit system, shaft specification and duty data.

What is the MOQ and lead time for non-standard sizes? [PLACEHOLDER — MOQ] and [PLACEHOLDER — lead time]. One-off and sample parts are accepted for validation; machined-to-drawing parts generally take longer than catalogue sizes because of the casting route.

What clearance should we machine for? For a default H7 housing, r7 bushing OD and g6 shaft, expect the running clearances in the table in section 6. If the position runs above ≈ 100 °C, move the shaft to f7 or e7 so thermal growth does not close the clearance.

How long will it last compared with the greased bronze we use now? A self-lubricating bronze bushing removes the re-lube task, but wear life still depends on P, V, temperature, contamination and shaft condition — not on the brochure. Send the duty data and we will calculate PV against the grade ceiling and quote an expected interval. Where a graphite-plugged bushing replaces a grease-lubricated one, the usual gain is the elimination of the re-lube task, not a guaranteed multiple on wear life.

Are these genuine OEM parts? No. These are compatible replacement parts manufactured to your drawing or sample specification; they are not OEM-branded products and are not supplied by the original equipment manufacturer.

8. Conclusion

Self-lubricating bronze selection is a duty calculation, not a preference. If pressure stays below roughly 14 N/mm², sliding speed is above about 0.3 m/s, and the housing is sealed and below 100 °C, oil-impregnated sintered bronze per ASTM B438-25 gives quiet, near-net-shape, low-unit-cost performance. If pressure is high, motion is slow or oscillating, and the position runs hot, wet or out of reach of a grease gun, graphite-plugged cast bronze is the defensible specification. Send P, V, peak temperature, shaft specification and the drawing, and the grade and fit system can be confirmed before you commit.

Send your drawing and duty data for a PV check and a quotation