Self-Lubricating Flanged Bronze Bushings — Graphite-Plugged High-Strength Brass (CuZn25Al6Fe3Mn3)

A flanged bronze bushing carries radial load and locates the assembly axially in one part. Plug it with graphite and it runs dry, indefinitely, in places nobody can reach with a grease gun. This page covers the JFB flanged series in CuZn25Al6Fe3Mn3 high-strength manganese brass (GB ZCuZn25Al6Fe3Mn3, nearest UNS equivalent C86300) — full dimension and tolerance tables, verified material data, and a cast copper-alloy grade cross-reference you can actually specify from.

1. What a self-lubricating flanged bushing is

A flanged bushing (flange bushing, flanged sleeve bearing) is a plain bearing with an integral flange at one end. The cylindrical bore carries the radial load; the flange face takes the axial thrust and, just as often, simply stops the bushing walking out of its housing under vibration. That combination is why flanged designs show up wherever a pin, trunnion or pivot both rotates and needs to be located.

A self-lubricating (oilless, maintenance-free) flanged bushing goes one step further: solid lubricant — here, graphite — is embedded directly into the bearing body. As the shaft turns, a thin graphite transfer film forms on the counterface and is continuously replenished from the plugs. There is no oil film to squeeze out, no grease to wash away, and no grease to bind with dust into abrasive paste. For a bushing buried in a pivot point behind a guard, that is the difference between a service interval and a service life.

The trade-off is honest and worth stating plainly: graphite-plugged bronze is a high-load, low-speed solution. Its limiting factor is PV — contact pressure multiplied by sliding velocity — not load alone. Specify it for slow, heavy, oscillating duty and it will outlast almost anything else you could put in the hole. Specify it for a fast continuous shaft and it will run hot. Section 7 covers the selection logic.

2. Material: CuZn25Al6Fe3Mn3 high-strength manganese brass

The body alloy is a cast high-strength manganese brass — in Chinese practice often called “高力黄铜”. It is a Cu–Zn–Al–Fe–Mn multi-element alloy, strengthened by solid solution and grain refinement rather than by heat treatment, which is precisely why it holds its hardness in a thick section. In the GB/T 1176 casting designation it is ZCuZn25Al6Fe3Mn3; the same composition appears as CuZn25Al6Fe3Mn3 under ISO 1338. The nearest UNS designation is C86300 — “nearest” being the operative word, as the next section explains.

2.1 Chemical composition

GB/T 1176 values as tabulated in the source specification sheets. C86300 values are the published figures for continuous-cast product.

2.2 Mechanical properties — and why the casting method matters

This is the single most important line on the page. Cast copper alloys are not like rolled steel: the same nominal composition gives measurably different properties depending on how it was cast and how thick the section is. Sand casting cools slowly and coarsely; centrifugal and continuous casting cool fast and fine, and produce a denser wall. Always state the casting method when you specify.

^* Marked as a reference (non-mandatory) value in GB/T 1176.

Cross-check against the UNS designation. Published continuous-cast C86300 data gives tensile strength 758 MPa minimum, yield strength 427 MPa minimum, elongation 14 % minimum and 223 HB typical. The strength and elongation figures sit close to the GB/T 1176 centrifugal/continuous values above, which is what you would expect from two specifications describing the same alloy family. The hardness figures do not line up as neatly: GB/T 1176 lists 160–170 HB as a reference value, while published C86300 data and supplier test data for this alloy both sit in the 210–270 HB band.

2.3 Physical and service properties

Where two columns disagree, use the published C86300 figure for preliminary design and confirm against the material test certificate for the actual batch.

The machinability rating is worth dwelling on: at roughly 8 % of free-cutting brass, this alloy is not free-machining. Expect meaningful tool wear and plan for carbide tooling, low cutting speeds and generous feed. That is the price of the hardness that makes it wear well — and it is also why finished bushings are supplied net-shape or near-net wherever the geometry allows.

3. Grade nomenclature and cross-reference

Cast bearing bronzes are specified under at least six national systems, and the equivalences between them are approximate. The table below is a working cross-reference for the alloys most often encountered in plain-bearing work.

^† ZCuSn10P1 is not chemically interchangeable with C90700. GB/T 1176 specifies phosphorus at 0.8–1.1 %, whereas the corresponding UNS C90700 composition limits phosphorus to a much lower maximum. The two are grouped in general reference tables, but the phosphorus contents are not the same. Specify the composition, not the cross-reference.

^‡ ZCuZn26Al4Fe3Mn3 is listed against C86300 in some reference tables. It should not be: its aluminium range (2.5–5.0 %) does not overlap C86300’s (5.0–7.5 %) at all. A lower-aluminium manganese brass such as C86200 is the chemically closer match. Verify before substituting.

A note on terminology. Casting designations carry a leading letter in some systems and not others. ZCuZn25Al6Fe3Mn3 is the GB/T 1176 casting form; drop the leading “Z” and you have the ISO 1338 form CuZn25Al6Fe3Mn3. German practice prefixes the process route (G-CuZn25Al5 for sand cast). Japanese bearing bronzes use a functional code (HBsC4C). None of this changes the alloy — but it does mean a part number, a drawing callout and a mill certificate can describe the same material in three different ways.

4. JFB series: dimensions and tolerances

The JFB series is the standard graphite-plugged flanged bushing: plain cylindrical bore, integral flange, graphite plugs distributed over the sliding surface. Bore is produced to E7 and outside diameter to r6, giving a controlled interference fit in an H7 housing. All dimensions in millimetres.

Bore and outside-diameter tolerance bands are ISO 286 values. Flange thickness is subject to a −0.10 mm tolerance. Length tolerance and plug pattern are confirmed at order.

5. JDBB flanged series and JZW bushes

5.1 JDBB flanged bushings

The JDBB series is the lighter-duty flanged pattern, supplied in the same graphite-plugged high-strength brass. Note that for a given bore the JDBB outside diameter runs roughly 2 mm smaller than the JFB — so the two series are not interchangeable in an existing housing. Measure the housing bore before substituting.

Flange thickness follows the difference between overall length and body length (5 mm from d16 to d40, 6 mm at d50, 7 mm at d60). The 12 mm bore breaks that progression at 4 mm — check this dimension if flange thickness is critical to your assembly.

5.2 JZW bearing bushes

The JZW series covers larger half-bearing and bush geometries for heavily loaded pivot points.

Chamfer and step dimensions (L₂, r) are only specified for some sizes in the source data. Sizes not shown are machined to drawing — send us the print.

6. How graphite plugging delivers maintenance-free running

The mechanism is simple and it is worth understanding, because it explains both the strengths and the limits of the product.

1. Plugs are embedded, not coated. Solid graphite is pressed into holes or pockets machined into the bearing wall, typically covering around a quarter of the sliding area. There is no surface layer to wear through — the lubricant reservoir runs through the full wall thickness.
2. A transfer film forms on first movement. Sliding smears graphite onto the shaft counterface. Friction then occurs between graphite and graphite rather than between bronze and steel.
3. The film self-replenishes. As the film is consumed, more graphite is exposed at the surface. The bearing is not “lubricated for X hours” — it is lubricated for as long as there is plug material left, which for a correctly sized bushing is its whole service life.
4. Heat is carried away through the bronze. The brass body conducts frictional heat out to the housing. This is why the alloy’s thermal conductivity matters, and why a loose fit in the housing — which breaks that heat path — is a common cause of premature failure.

Two consequences follow. First, graphite-plugged bronze genuinely prefers dry running: adding grease attracts grit and defeats the point. Second, it is not a high-speed bearing. The PV limit arrives quickly as velocity rises, so the design envelope is high load at low to moderate sliding speed, and it is at its best under oscillating or intermittent motion where a hydrodynamic oil film could never establish itself anyway.

Indicative performance envelope

These are indicative figures for preliminary selection only. Actual capacity depends on PV, duty cycle, temperature, counterface finish and hardness, and the rigidity of the housing. Final selection is confirmed against your operating conditions.

7. Design and installation guidance

7.1 Fits

• Housing bore: H7. This is what the r6 outside diameter is designed against, and it is also the heat path out of the bearing — do not compromise it.
• Bore: produced to E7 as tabulated. Remember the bore closes up when the bushing is pressed into the housing; the finished running clearance is smaller than the free-state bore.
• Shaft: select by duty — e7 for light-load running, f7 where better guidance accuracy is needed, g6 for high-precision intermittent duty.

7.2 Counterface

• Shaft hardness: harder shafts resist abrasion and hold the transfer film better. A work-hardened or through-hardened journal is worth the cost on heavily loaded pivots.
• Surface finish: aim for Ra in the region of 0.4–1.6 µm. Too smooth and the graphite film has nothing to key into; too rough and you machine the plugs away in the first hour.
• Geometry: chamfer the shaft end and break all housing edges. Most installation damage happens in the first 50 mm of press travel.

7.3 Installation

• Press the bushing in square, using a mandrel that loads the flange face — never drive on the bore or the sliding surface.
• Do not ream or machine the bore after fitting unless the design specifically allows for it; you will remove the plug pattern that the bearing depends on.
• Where the housing is thin or the fit is heavy, chill the bushing rather than increase press force.
• Confirm axial clearance against the flange thickness tolerance (−0.10 mm) and the stack-up of the surrounding parts.

8. Applications

Graphite-plugged flanged bushings earn their place where load is high, motion is slow or oscillating, and access for relubrication is poor. Typical installations:

• Construction and mining machinery — excavator and loader boom and bucket pivots, hydraulic cylinder eyes, conveyor and crusher linkages, where dust and shock load destroy grease films.
• Hydraulic equipment — cylinder trunnions, pump and motor mounting pivots, valve linkages.
• Metallurgical and steel plant — continuous-caster roll tracks, furnace-door mechanisms, ladle trunnions, rolling-mill equipment operating at elevated temperature.
• Marine and port equipment — deck cranes, hatch covers, winch and sheave bearings exposed to salt spray and wash-down.
• Dies, moulds and machine tools — guide pillars and bushings, wear plates, tilt and ejector mechanisms.
• General industrial machinery — textile, rubber, printing, packaging, lifting and water-conservancy equipment; anywhere a maintenance round currently includes a grease nipple nobody can reach.

9. How graphite-plugged bronze compares

Figures are indicative of each family. Where your duty sits near a boundary, send us the load, speed, duty cycle and temperature and we will size it properly. See also self-lubricating bronze bushings and bronze wear plates.

10. Frequently asked questions

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