Custom plain bearings
The demand for custom non-standard plain bearings is increasing. We can manufacture copper alloy materials to meet China’s national standards as well as the ASTM (UNS, SAE), EU, and JIS standards.
Bespoke plain bearings
viiplus collaborates with customers to find tailored solutions, offering plain bearings in various materials, sizes, tolerances, and designs.
Timely Delivery
Committed to meeting tight deadlines without compromising on quality, we ensure reliable and efficient production timelines.
Versatility
Capable of handling both small-scale and high-volume orders, we provide seamless support for projects of any size. Additionally, we can develop custom copper alloy materials based on specific customer requirements and drawings.
Specialized in Graphite Plugged Bronze Bearings
A graphite plugged bronze bearing carries load on a cast bronze body and lubricates itself from graphite plugs embedded in the sliding surface. This guide sets out how the transfer film works, how to choose between C93200, C86300 and C95500, what pv and temperature envelope to design to, and which shaft finish, fit and installation method protect the bearing from day one.
Custom Machined Bronze Parts & Bearings
Key takeaways
- Plugged bronze runs dry at high load and low speed — typically below 0.5 m/s — where oil films cannot form.
- Load capacity is set by the bronze body, not by the plugs: C86300 manganese bronze is the strongest of the common bearing bronzes.
- Plug grade follows the environment: wet-service plugs for water and humidity, high-temperature plugs for hot, dry duty.
- Self-lubricating does not mean fit-and-forget: an initial grease film at assembly is still recommended to bridge the break-in period.
- Published pv and friction figures apply only under optimal conditions. Confirm final values against the mill certificate for your order.
Oilless Bushing Material, Machining Parts
What a graphite plugged bronze bearing is
A graphite plugged bronze bearing — also sold as a solid-lubricant bronze bushing, graphite bronze bushing or maintenance-free bronze bearing — is a cast bronze sleeve with a machined pattern of recesses in the sliding surface. The recesses are filled with plugs of solid graphite-based lubricant. The bronze carries the mechanical load; the plugs supply the lubrication.
The construction is deliberately simple, and that is the point. There is no oil circuit, no grease nipple, no seal to fail, and no risk of lubricant leaking into the product or the environment. The bearing is at its best in exactly the places where oil lubrication struggles: slow oscillating motion, high static load, shock loading, contaminated or dusty air, and temperatures that would cook a conventional grease.
Two design decisions dominate performance. The first is the bronze alloy, which sets load capacity, corrosion behaviour and temperature ceiling. The second is the lubricant coverage and plug grade, which set the friction coefficient and whether the bearing survives in water.
How the solid lubricant transfer film works
The mechanism is a transfer film, not a reservoir. On the first movements, a thin layer of graphite is smeared from the plugs onto the counterface. After that, most of the sliding happens between the graphite film on the shaft and the graphite film on the plug surface, rather than between bronze and steel. Measured dry friction coefficients fall in the range of roughly 0.11 to 0.16 for plugged bronze depending on alloy and plug grade — an order of magnitude better than unlubricated bronze-on-steel, though still higher than a full hydrodynamic oil film.
Because the film has to be built by running, the break-in period matters. Do not put a freshly installed plugged bearing straight into full-load service. Start unloaded or lightly loaded and build up, so that the microscopic high spots on shaft and bore polish down and the load spreads across the whole pressure area instead of concentrating on a few points. Skipping break-in is one of the most common causes of shortened service life in solid-lubricant bearings.
The film also needs somewhere to live. That is why a very smooth shaft is not the goal: a mirror finish gives the graphite little to key into and slows film formation. The roughness band recommended in section 9 is deliberately a “ground, not polished” finish.
Break-in: what actually goes wrong
Shaft and bore look smooth to the eye but are not geometrically perfect, and a small misalignment is normal. Initial contact is therefore local. Under full load, those local contact points overload the film before it has formed, and the bearing scores. A short, progressive break-in at reduced load lets the entire pressure area come into contact before the load is raised.
Plugs, grooves and plug patterns
Solid lubricant can be applied to a bronze bearing in two ways, and the choice is application-driven rather than cosmetic.
| Feature | Plug type (drilled recesses + plugs) | Filled-groove type |
|---|---|---|
| Construction | Recesses machined through or partly through the wall, then filled with solid lubricant plugs | Grooves machined into the surface, filled with lubricant compound, then cured |
| Lubricant volume | High — plugs are deep and can be large | Lower — limited by groove cross-section |
| Best for | Heavy load, shock, long unattended service, high temperature | Light to medium duty, thin wall sections, cost-critical parts |
| Wall thickness | Needs enough wall to host the plug | Works in thin walls |
| Directionality | Pattern is laid out to suit the motion (rotating, linear or oscillating) | Pattern designed per application |
Plug pattern and coverage
Plug layout is not decorative. A good pattern puts lubricant across the full swept area of the counterface without ever leaving a continuous unlubricated band along the direction of motion. The plugs are deliberately staggered rather than aligned on a single axis, so that no line of the shaft travels over bronze without crossing a lubricant source. Coverage is normally expressed as a percentage of the sliding area and is matched to duty: heavy, slow, oscillating applications take a higher coverage than light, faster ones.
The pattern is specified to the motion. For a rotating shaft, plugs are distributed around the bore. For linear or oscillating motion, the layout is designed so that the full stroke passes over lubricant. Because the pattern is machined, it can be adapted to almost any geometry — one of the practical advantages of this bearing type over wrapped or moulded alternatives.
Bronze alloy selection
Four copper alloys cover the overwhelming majority of plugged bronze bearing applications. The trade-off is consistent: tin bronzes give embeddability and conformability, manganese bronze gives raw strength, and aluminium bronzes give corrosion and temperature resistance.
| UNS | Common name | Cu | Sn | Pb | Zn | Al | Fe | Ni | Mn |
|---|---|---|---|---|---|---|---|---|---|
| C93200 | Leaded tin bronze (SAE 660) | 81.0–85.0 | 6.3–7.5 | 6.0–8.0 | 2.0–4.0 | ≤0.005 | ≤0.20 | ≤1.0 | — |
| C95400 | Aluminium bronze | ≥83.0 | — | — | — | 10.0–11.5 | 3.0–5.0 | ≤1.5 | ≤0.50 |
| C95500 | Nickel-aluminium bronze | ≥78.0 | — | — | — | 10.0–11.5 | 3.0–5.0 | 3.0–5.5 | ≤3.5 |
| C95510 | Ni-Al bronze (AMS 4880 data) | ≥78.0 | ≤0.20 | — | ≤0.30 | 9.7–10.9 | 2.0–3.5 | 4.5–5.5 | ≤1.5 |
| C86300 | High-strength manganese bronze | 60.0–66.0 | ≤0.20 | ≤0.20 | 22.0–28.0 | 5.0–7.5 | 2.0–4.0 | ≤1.0 | 2.5–5.0 |
Single values are maximums unless shown as a range or minimum. For C93200 and C86300 the copper minimum may be calculated as Cu + Ni; the Ni value includes Co. Cu plus the sum of named elements is 99.0 % minimum for C93200 and 99.5 % minimum for the others.
Which alloy for which job
- C93200 leaded tin bronze. The general-purpose bearing bronze. Good anti-friction behaviour, tolerant of shaft imperfections, excellent machinability, and reasonable resistance in seawater and brine. Choose it for moderate loads where embeddability and cost matter more than peak strength.
- C95400 / C95500 aluminium bronzes. Higher strength, hardness and corrosion resistance than the tin bronzes, with useful strength retention at elevated temperature. C95500 adds nickel for seawater and cavitation resistance. Choose them for marine, chemical and high-temperature service, and accept the harder counterface requirement.
- C86300 high-strength manganese bronze. The strongest of the common bearing bronzes, with good fatigue and shock resistance. It is the default for heavy, slow, shock-loaded bearings and wear plates. One restriction: it is not recommended for seawater service.
Lead content: a specification checkpoint for EU, UK and North American markets
C93200 is a leaded bronze containing 6.0–8.0 % lead by weight. The RoHS Directive (2011/65/EU) Annex III exemption for copper alloys is limited to 4 % lead by weight, so C93200 sits outside that exemption. Lead is also a REACH substance of very high concern and is listed under California Proposition 65. If the end product is placed on an EU, UK or North American regulated market, confirm the applicable exemption or specify a lead-free alternative before releasing the drawing.
Mechanical and physical properties
The values below are specification minimums for continuously cast material unless noted, which makes them a conservative basis for comparison. They are not guaranteed values for a finished bushing.
| UNS | Tensile strength min. MPa |
Yield strength min. MPa |
Elongation min. % |
Brinell hardness HB |
Density g/cm³ |
CTE 10⁻⁶/°C |
|---|---|---|---|---|---|---|
| C93200 | 241 | 138 | 10 | 65 typ. | 8.91 | 17.3 |
| C95400 | 586 | 221 | 12 | 170 typ. | 7.45 | 15.5 |
| C95500 | 655 | 290 | 10 | 190 min. | 7.53 | 15.5 |
| C95510 (AMS 4880) | 655–740 | 386–440 | 9–12 | 175–230 | 7.53 | 15.5 |
| C86300 | 758 | 427 | 12 | 223 typ. | 7.83 | 20.7 |
Yield strength measured at 0.5 % extension under load; elongation measured over 2 in. or 50 mm. Brinell values are typical unless marked as a minimum. Coefficient of thermal expansion is quoted over 20–300 °C for the aluminium and manganese bronzes and 20–100 °C for C93200. C95510 figures are published ranges for continuously cast, quench-hardened and temper-annealed material above 102 mm section, quoted from AMS 4880 reference data (see disclaimer).
Section size reduces the guaranteed minimums
ASTM B505/B505M permits minimum tensile and yield strength to be reduced by 10 % for cast bar with a cross-section, thickness, diameter or wall of 102 mm (4 in.) or more. Large-diameter plugged bushings and thick wear plates frequently fall into this category. If strength is critical, state the section size at the enquiry stage and ask for the actual test values.
Operating envelope: load, speed, pv, temperature
These are the numbers that decide whether a plugged bronze bearing will work. All of them are interdependent — raising the speed eats into the allowable load, and vice versa — so treat them as an envelope rather than as four independent limits.
| Bronze | p static N/mm² |
p dynamic N/mm² |
Dry friction µ | Max. speed m/s |
Max. pv N/mm²·m/s |
Max. temp. °C |
|---|---|---|---|---|---|---|
| CuSn7ZnPb (C93200 class) | 80 | 40 / 30 | 0.11–0.14 | 0.4 / 0.5 | 1.2 / 1.0 | 80 / 250 |
| CuSn12Pb | 100 | 70 / 25 | 0.11–0.14 | 0.4 / 0.15 | 2.0 / 1.6 | 80 / 250 |
| CuAl10Ni (C95500 class) | 150 | 90 / 80 | 0.13–0.16 | 0.4 | 1.5 | 80 / 350 |
| CuZn25Al5 (C86300) | 150 | 100 / 90 | 0.13–0.16 | 0.4 / 0.15 | 1.5 / 1.0 | 80 / 300 |
Where two values are shown, the first applies to the wet-service plug grade and the second to the high-temperature plug grade. Maximum temperature is shown in the same order. These figures are valid only under optimal operating conditions; higher sliding speed, poorer shaft finish, misalignment or contamination all reduce them.
Reading the pv limit
pv is contact pressure multiplied by sliding speed, and it stands in for the frictional heat generated per unit of bearing area. In dry-running bronze, heat is almost always the limiting factor rather than static strength — which is why a bearing comfortably inside its 150 N/mm² static rating can still fail if pv is exceeded.
pv = p × v with p in N/mm² and v in m/s
Example: a bushing loaded to 90 N/mm² running at 0.015 m/s gives pv = 1.35 N/mm²·m/s — within the published dry limit for most plugged bronze grades, but with little margin if the speed doubles.
Why occasional lubrication still helps
Even though the bearing is designed to run dry, occasional greasing measurably extends service life. It raises the allowable pv, lowers the friction coefficient, carries heat away, flushes out wear and foreign particles, protects the shaft from corrosion, and adds a margin of reliability at start-up. Where a product is already designed with a lubrication point, using it once in a while costs nothing and buys a lot of life. Where lithium-based grease is used above about 150 °C, a polyurea- or bentonite-thickened grease is the safer choice.
Solid lubricant grades
Plug compound selection is driven by the environment, and getting it wrong is a common cause of premature failure. The two generic families below cover most industrial duty.
| Service condition | Recommended plug family | Upper temperature | Caveat |
|---|---|---|---|
| Dry, elevated temperature | Graphite-based high-temperature compound | ≈ 300–350 °C | Not for water or steam service |
| Water, humidity, submerged | Wet-service compound, very low friction | ≈ 80 °C | Low temperature ceiling by design |
| Marine / salt water | Wet-service compound + aluminium or tin bronze body | Per grade | Avoid high-strength manganese bronze |
| Dusty or abrasive | Graphite-based compound, high coverage | Per grade | Add seals and surface-harden the shaft |
Plug compounds are normally high-density blends of graphite with PTFE and metallic additives, and they are oriented to the direction of motion. Because the orientation is machined in, the motion direction must be stated with the order. A bearing built for rotation may not lubricate correctly if it is installed in a linear application.
Chemical resistance
The chart below is a screening aid for alloy selection against common media. It is not a substitute for immersion testing under your own concentration, temperature, aeration and contamination conditions, and it is not a service-life prediction.
| Medium | Concentration % | Temperature °C | C93200 | C95400 | C86300 |
|---|---|---|---|---|---|
| Strong acids | |||||
| Hydrochloric acid | 5 | 20 | X | O | X |
| Hydrofluoric acid | 5 | 20 | O | O | X |
| Nitric acid | 5 | 20 | X | X | X |
| Sulfuric acid | 5 | 20 | O | R | X |
| Phosphoric acid | 5 | 20 | O | O | X |
| Weak acids | |||||
| Acetic acid | 5 | 20 | X | O | X |
| Formic acid | 5 | 20 | X | R | X |
| Boric acid | 5 | 20 | X | R | X |
| Citric acid | 5 | 20 | X | R | X |
| Bases | |||||
| Ammonia | 10 | 20 | X | X | X |
| Sodium hydroxide | 5 | 20 | O | R | O |
| Potassium hydroxide | 5 | 20 | O | R | O |
| Solvents | |||||
| Acetone | — | 20 | O | R | O |
| Carbon tetrachloride | — | 20 | O | O | O |
| Ethanol | — | 20 | O | R | O |
| Glycerin | — | 20 | O | R | O |
| Salts | |||||
| Calcium chloride | — | 20 | R | R | R |
| Magnesium sulfate | — | 20 | R | R | R |
| Sodium chloride | — | 20 | R | R | R |
| Zinc chloride | — | 20 | X | O | X |
| Gases | |||||
| Chlorine | — | 20 | X | X | X |
| Sulfur dioxide | — | 20 | O | O | X |
| Hydrogen sulfide | — | 20 | O | O | O |
| Fuels & oils | |||||
| Paraffin | — | 20 | R | R | R |
| Petroleum | — | 20 | R | R | R |
| Diesel fuel | — | 20 | R | R | R |
| Mineral oil | — | 70 | R | R | R |
| Other | |||||
| Fresh water | — | 20 | R | R | O |
| Sea water | — | 20 | O | R | X |
| Hydrocarbon | — | 20 | R | R | O |
“O” means resistance depends on construction and operating detail — oxygen content, temperature, aeration, flow velocity and contaminants all shift the result. Where a medium is rated X, do not specify that alloy without immersion test data for the actual service condition.
type of Custom Bearings & Bushings, Flanged Bearings, Custom Oilless Bronze Bushings, Custom Sliding Bearing
Custom Bearings & Bushings Materials & Alloys We Machine
Shaft and counterface requirements
A solid-lubricant bearing is only half of a tribological system. The shaft is the other half, and it is usually the cheaper half to get right at the design stage.
| Parameter | Tin bronzes (C93200 class) | High-strength bronzes (C86300 / C95500) |
|---|---|---|
| Minimum shaft hardness | ≈ 180 HB | ≈ 300 HB |
| Hardness difference vs. bushing | ≥ 100 HB recommended | |
| Surface roughness Ra | 0.2 – 0.8 µm | 0.2 – 0.8 µm |
| Preferred shaft condition | Hardened and ground to size | |
| Housing bore tolerance | H7 | H7 |
| Bore after mounting | r6 / E7 (other on request) | r6 / E7 (other on request) |
| Shaft tolerance | f7 / h6 | |
Counterface selection scales with contact pressure. At low pressure a plain carbon or alloy steel is adequate. As pressure rises, the shaft needs surface hardening and then additional treatment:
- Up to 24.5 N/mm² — carbon or alloy structural steel (C45, 42CrMo4); HB 150 or over; Ra better than 1.6 µm. In a corrosive environment use a corrosion-resistant steel such as X20Cr13; in seawater use super-duplex or a nickel alloy.
- 24.5 to 49 N/mm² — add surface hardening such as induction hardening or carburising; HB 250 or over.
- 49 to 98 N/mm² — surface hardening plus nitriding or hard chromium plating; HRC 50 or over.
Surface treatment of the shaft serves three purposes: improved corrosion resistance, improved surface hardness, and improved smoothness for better lubricity. Whichever route is chosen, keep the finish inside the recommended Ra band — too rough and it abrades the plugs, too smooth and the graphite transfer film cannot establish.
Material Selection
Bronze Alloy Composition
Casting
Centrifugal casting, continuous casting
Machining
Precision Machining
Quality Inspection
Material Testing, Surface Inspection
