Self Lubricating Brass Bushings: Where They Fit, and When to Choose Bronze
Self lubricating brass is a copper-zinc alloy body carrying a solid lubricant — graphite, MoS₂ or PTFE — so the bearing builds its own lubricating film instead of waiting for a grease gun. It is worth understanding separately from self-lubricating bronze, because the two families solve overlapping but different problems. Brass machines faster, costs less per kilogram at equal strength, and handles clean, moderate-duty work well. It also carries a hard limit that bronze does not: dezincification. This page covers the grades, the numbers behind them, how the lubricant reservoir is designed, and the conditions where specifying brass is a mistake.
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Brass and bronze are not interchangeable
Self-lubricating brass alloys represent a significant advancement in bearing materials, combining the inherent properties of brass with embedded lubricants to reduce friction and wear without the need for external lubrication. This innovation is particularly beneficial in applications where maintenance is challenging or impractical.
The names are used loosely in purchasing, which is where most specification errors start. The metallurgical distinction is simple:
- Brass is copper-zinc. Bearing grades add lead, aluminium, manganese, iron or silicon to that base. Free-machining brass such as CuZn39Pb3 contains roughly 2.5–3.5% lead, which is what gives it its cutting behaviour and its tolerance of marginal lubrication.
- Bronze is traditionally copper-tin. Modern bearing bronzes extend that to aluminium bronze, manganese bronze and leaded tin bronze, but the tin-based family remains the reference for plain bearings.
- Manganese bronze (C86300) is a brass, not a bronze. It sits in the copper-zinc-aluminium system. It is sold under a bronze name because of its strength and bearing heritage, and it behaves like a high-tensile brass in service.
That last point matters because a drawing that says “bronze” usually means a tin bronze such as C93200, while a drawing that says “manganese bronze” means a zinc-based alloy with a different corrosion profile and roughly double the strength. Both are stocked; the composition on the mill certificate is what settles it. A plain-language version of the distinction is in bronze as an alloy of copper, and the wider material set is compared in the bushing material overview.
Grades used for self-lubricating brass parts
Values below are typical for cast or hot-worked stock at room temperature. Composition ranges follow the common ASTM and EN designations; the certificate supplied with the order governs.
| Designation | Common equivalent | Nominal composition, typical ranges | Tensile strength, typical | Hardness, typical | Where it is used |
|---|---|---|---|---|---|
| CuZn39Pb3 (CW612N, ≈C38500) | Free-machining leaded brass | Cu 57–59%, Pb 2.5–3.5%, Zn balance | 340–440 MPa (49–64 ksi) | 90–110 HB | Small bushings, appliance and light machinery parts, high-volume turned work |
| CuZn40Pb2 (CW617N) | Leaded brass for hot work | Cu 57–59%, Pb 1.5–2.5%, Zn balance | 360–450 MPa (52–65 ksi) | 95–120 HB | Hot mill and furnace-adjacent equipment — see CuZn40Pb2 bushes for hot mill equipment |
| C86300 | Manganese bronze / high-tensile brass | Cu 60–66%, Zn 22–28%, Al 5–7.5%, Fe 2–4%, Mn 2.5–5% | 760–860 MPa (110–125 ksi) | 225–280 HB | Heavy static load, low speed, shock and abrasive conditions — see C86300 manganese bronze bushings |
| CuZn25Al5Mn4Fe3-C (EN CC762S class) | High-tensile aluminium brass | Cu 60–67%, Al 3–6%, Mn 2.5–5%, Fe 2–4%, Zn balance | 700–800 MPa (100–116 ksi) | 200–240 HB | Slide blocks, lifting and heavy plant where load and wear both matter — see CuZn40Al2 slide blocks |
| C86500 and C85700 class | Leaded and cast brasses | Cu 55–65%, Zn 30–42%, with Al, Fe, Mn and Pb additions | 450–620 MPa (65–90 ksi) | 120–180 HB | General cast brass bushings and machined fittings |
C93200 is frequently listed alongside brass bushings because it is supplied in the same size range and machined on the same equipment. It is a leaded tin bronze, not a brass, and is covered separately under tin bronze bushings.
Maximize Efficiency with Self Lubricating Brass Bushings
Maximize your machinery’s performance and efficiency with self lubricating brass bushings, designed to minimize friction and wear without external lubrication
How the self-lubricating version works
Solid lubricant is held inside the brass body in one of three ways: plugs pressed into drilled or cast pockets, a dispersion of lubricant through a sintered matrix, or a polymer liner bonded to a metal backing. As the shaft turns or oscillates, a small quantity of lubricant transfers to the counterface and forms a film. The film is thin and is continuously consumed and reformed, which is why these bearings have a finite life even though they never need greasing.
Under dry running, a self-lubricating brass bushing typically holds a coefficient of friction in the 0.15–0.25 band for free-machining grades, and down toward 0.08–0.16 where graphite plugs cover a meaningful share of the contact area. Those are ranges, not guarantees: pressure, velocity, counterface finish and temperature all move the number. The comparison between the two common lubricant routes is set out in MoS₂-impregnated bronze versus graphite-plugged bronze, and impregnated construction is described under graphite-impregnated bronze bushings.
Operating envelope and where each route stops working
| Parameter | Free-machining brass with grooves | Graphite-plugged brass or high-tensile brass | Graphite-plugged tin bronze, for comparison |
|---|---|---|---|
| Dry friction coefficient, typical | 0.15–0.25 | 0.10–0.18 | 0.08–0.16 |
| Allowable static pressure, typical | 25–40 MPa (3.6–5.8 ksi) | 60–100 MPa (8.7–14.5 ksi) | 70–100 MPa (10–14.5 ksi) |
| Sliding speed, typical ceiling | 0.5–1.0 m/s (100–200 ft/min) | 0.3–0.5 m/s (60–100 ft/min) | 0.3–1.5 m/s (60–300 ft/min) |
| Continuous body temperature, typical | to 150–200 °C (300–390 °F) | to 200–250 °C (390–480 °F) | to 250–300 °C (480–570 °F) |
| Graphite film useful to, in air | not applicable | about 450–500 °C (840–930 °F) | about 450–500 °C (840–930 °F) |
| Water and brine | dezincification risk above roughly 60 °C (140 °F) | same alloy limitation | bronze is the safer choice |
Two things follow from that table. First, the brass body limits temperature more than the lubricant does: graphite survives far hotter than the alloy around it, so the body sets the ceiling. Second, in any wet or chloride-bearing service, tin bronze removes a failure mode that brass carries permanently.
Groove and pocket design
Where the part carries a solid lubricant, the reservoir geometry decides how long it lasts. Practical rules that hold up in service:
- Groove width of at least one-tenth of the shaft diameter, and depth no less than one-thirtieth of the shaft diameter. Narrower or shallower and the reservoir empties before the film stabilises.
- V-shaped grooves suit oil, because the wedge helps build a film. Rectangular cross-section suits grease and solid lubricants, giving more volume and better retention.
- Do not groove the loaded zone where it can be avoided. Break the groove short of the edge or run it parallel to the load line so the bearing does not lose contact area at the point of peak pressure.
- Deburr every groove edge. A raised lip at the groove mouth wipes the film off the shaft on every pass.
- Plug coverage is normally quoted as a percentage of the bearing surface; layout depends on travel per cycle and expected life. Sizing is explained in calculating plug size for graphite-plugged bronze bearings.
When not to specify self-lubricating brass
- Any wet, chloride-bearing or ammonia-containing service. Brass loses zinc selectively — dezincification — leaving a porous copper sponge with little strength. It accelerates with temperature and with stagnant or low-flow conditions. Above roughly 60 °C (140 °F) in water, or in any ammonia environment including some fertiliser and refrigeration duties, use tin bronze or aluminium bronze.
- Seawater and marine splash zones. Same mechanism, faster. Bronze is the standard answer here, and the alloy choice interacts with the other metals in the assembly.
- Sustained temperature above about 200 °C (390 °F). The brass body softens and creeps well before the graphite gives out. Specify bronze.
- High sliding speed. Brass has lower thermal conductivity than the tin bronzes, so frictional heat stays in the contact. Speeds above roughly 1 m/s sustained are better served by bronze or a composite liner.
- Heavy shock loading. Free-machining brass grades are relatively brittle. Where impact is present, C86300 or a tin bronze carries it better.
- Potable water or RoHS-restricted equipment where the lead content in free-machining grades is not acceptable. Use a low-lead or lead-free alloy and accept the small change in machinability.
For the reverse case — duties where brass is genuinely the sensible pick — the rolling mill and steel plant examples are representative: clean, dry, moderate temperature, high volume, and where machinability matters. See the notes on oil-free brass bushings in rolling mills and the brass bushing service page.
Selection shortcut. If the service is dry, below 150 °C (300 °F), lightly to moderately loaded and cost-sensitive, brass is usually right. If it is wet, hot, shock-loaded or continuous-run, bronze is usually right. Where two options look equally workable, price both against the drawing and against the cost of a second failure.
Why Choose Self-Lubricating Brass for Your Industrial Needs
brass alloy
Learn why self-lubricating brass is a top choice for industries seeking durability, corrosion resistance, and low-maintenance solutions in machinery parts.
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Self lubricating brass alloy Comparison with Bronze
While both brass and bronze can be engineered for self-lubrication, bronze is more commonly associated with this property due to its frequent use with graphite inserts. However, self-lubricating brass offers unique advantages, including better machinability and corrosion resistance, making it suitable for specific applications where these properties are beneficial.
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Applications of Self-Lubricating Brass
- Automotive Industry: Used in steering mechanisms and suspension systems to enhance performance and reduce maintenance.Wikipedia
- Industrial Machinery: Employed in conveyor systems and pumps where continuous operation is required.
- Marine Equipment: Chosen for its corrosion resistance in marine environments.
- Home Appliances: Utilized in devices like washing machines and fans for quiet and efficient operation.
- Heavy Machinery: Suitable for high-load applications requiring strength and wear resistance.
self-lubricating brass alloys offer significant benefits in reducing maintenance needs and enhancing the durability of components across various industries. Understanding their properties, design considerations, and appropriate applications is essential for optimizing performance and achieving cost-effective solutions.
