Oil Free Bushing Center Flanged Self-Lubricating Bronze Bushings
A center flanged bronze bushing carries radial load through its cylindrical body while a flange at the midpoint of its length seats into a groove in the housing bore, locating the shaft axially in both directions. Available in graphite-plugged, tin bronze, aluminum bronze and manganese bronze, in metric and inch sizes.
What Is a Oil Free Bushing Center Flanged Bronze Bushing?
A center flanged bronze bushing is a plain bearing with an integral radial flange positioned at the midpoint of its length rather than at one end. The cylindrical body carries the radial load, while the central flange sits in a matching groove machined into the housing bore and provides axial location in both directions.
This geometry differs from the more common end flange design, where the flange lies flush against the mounting face. Because a center flange is captured inside the housing, the bushing can be installed from either end and resists axial movement in both directions without a separate thrust washer or retaining ring. In assemblies where shaft position must be held accurately under reversing loads, this reduces part count and simplifies the housing.
The flange also acts as a thrust face. When a shaft shoulder or rotating component bears against either side of the flange, axial thrust transfers into the housing instead of into a separate component. For this reason center flanged bushings are frequently specified at pivot joints, linkage points and oscillating bearings where axial loads reverse during the working cycle.
A center flanged bushing is specified by four principal dimensions: inside diameter after fitting (d), outside diameter (D), overall length (L), and flange diameter and thickness.
Flange Position: Center vs. End vs. Double Cut Edge
Selecting a flange position is usually the first decision in specifying a flanged bushing. The three common options serve different assembly constraints.
| Feature | Center flange | End flange | Double cut edge |
|---|---|---|---|
| Flange location | Midpoint of length | One end | Midpoint, flats milled on both sides |
| Axial location | Both directions | One direction | Both directions |
| Housing requirement | Groove machined in bore | Flush mounting face | Groove plus clearance for flats |
| Thrust faces | Two | One | Two |
| Installation | From either end | From the plain end | From either end, oriented to flats |
| Space efficiency | Moderate | Good | Suited to confined envelopes |
| Anti-rotation | Provided by flange in groove | Provided by flange face | Enhanced by the milled flats |
| Typical use | Reversing axial loads, oscillating pivots | Standard thrust location | Tight assemblies, clearance for adjacent parts |
Center flange. Requires a groove in the housing bore, which adds a machining step, but delivers location in both directions from a single component. It is the usual choice where axial load reverses during operation — for example at a boom pivot or a linkage that pushes and pulls.
End flange. The most widely used arrangement: the flange seats against the mounting face and provides a single thrust face. It is simpler to fit and to house. Where one-directional location is sufficient, this is normally the more economical option — see our flanged bronze bushings page for that geometry in detail.
Double cut edge. A center flange with flats milled across the flange on both sides. The flats let the bushing clear adjacent components such as bolt heads or ribs, allow fitting into a confined envelope, and improve resistance to rotation in the housing. See double cut edge center flanged bushings where space is constrained.
Housing and servicing considerations
A center flange needs a groove cut into the housing bore, which adds a machining operation compared with an end flange. Where the housing is already designed for an end flange, or where the joint is easy to reach and the axial load is light, the simpler arrangement is usually preferable. Consider also how the bush will be removed at overhaul: a flange captured in a groove is more awkward to extract than one sitting against a face, so allow access or a withdrawal feature when the housing is designed.
Custom Your Oil Free Bushing Flanged Bronze Bushing
Graphite flange bearings offer self-lubricating performance using a copper-based alloy. VIIPLUS bearings eliminate the need for oil or grease by creating a graphite film between surfaces for reliable lubrication. Available in standard metric and imperial sizes, or custom-manufactured to your specifications. Graphite-filled grooves and wear plates are also available. Oilless Bearings can be produced from various bronze alloys to suit specific application needs.
oil free bushing center flanged Bushing Material Options
Load capacity, wear life and temperature limit depend heavily on the alloy. Four material families cover the majority of center flanged applications.
Graphite-plugged bronze
A tin bronze body with solid graphite plugs embedded in the bearing surface. As the shaft rotates, a thin graphite film transfers to the counterpart and provides continuous solid lubrication. This makes the bushing maintenance-free and suited to low-speed, high-load duty, to locations that cannot be regreased, and to elevated temperatures. Continuous service to roughly 250 °C, with higher intermittent peaks. Sliding speed under dry running is typically up to 0.5–1.0 m/s.
Tin bronze
CuSn8 and CuSn10 grades (comparable to C90700 / C90500 compositions) are the general-purpose choice. They offer good wear resistance, resistance to seizure against steel, and straightforward machinability, at a moderate cost. Tin bronze bushings are normally grease- or oil-lubricated and suit moderate loads and speeds.
Aluminum bronze
Grades such as C95500 nickel aluminum bronze and C95200 combine higher strength with strong resistance to seawater and chemical attack. They are specified for heavy loads and for marine, hydraulic and chemical environments. Note that aluminum bronze calls for a harder, well-finished shaft — see shaft recommendations in the FAQ.
Manganese bronze
High-tensile manganese bronze (C86300 type) carries higher loads than tin bronze and absorbs shock and impact well. It is used at heavily loaded, slow-moving pivot points in construction and mining equipment. Machinability is lower than tin bronze, which is reflected in cost and lead time.
Matching the alloy to the environment
Temperature and corrosion often decide the alloy before load does. Graphite-plugged bronze keeps its lubricating film where grease would carbonise or wash out, which is why it is used in ovens, dryers and furnace equipment. Aluminum bronze resists seawater and many process chemicals, so it is preferred for marine and hydraulic service. Where the shaft is relatively soft or the finish is coarse, a softer tin bronze is more forgiving than a hard, high-strength alloy, which will score an unprepared shaft.
Dimensions and Size Range
The tables below show representative sizes from our standard tooling range. Center flanged bushings are very frequently produced to drawing, so the figures are indicative of common proportions rather than a fixed catalogue — bore, outside diameter, length, flange diameter and groove position can all be adjusted to suit the housing design.
Choosing the proportions
Wall thickness. Wrapped bushings use a thin wall, typically 1.0–2.5 mm depending on bore, which keeps the outside diameter small and helps heat flow into the housing. Solid and centrifugally cast bushings use a heavier section where the load is high or the housing bore is already fixed by an existing design. A thinner wall also means the bore closes less during press-fitting.
Flange diameter. The flange sets the thrust area, so a larger flange carries more axial load and wears more slowly. The practical limit is usually the space available in the housing and the diameter of groove that can be machined. Where axial loads are modest, a standard flange diameter keeps the housing compact.
Length. Bearing length is normally between 0.5 and 1.5 times the bore diameter. A longer bush lowers the bearing pressure and improves guidance, but it demands better alignment — if the shaft deflects or the housing bore is not concentric, a long bush will edge-load and wear at its ends.
| d (bore) | D (OD) | Flange Ø | Flange thickness | L (length) |
|---|---|---|---|---|
| 10 | 12 | 18 | 1.5 | 10–20 |
| 12 | 14 | 20 | 1.5 | 12–25 |
| 15 | 17 | 23 | 1.5 | 15–30 |
| 20 | 23 | 30 | 2.0 | 20–35 |
| 25 | 28 | 35 | 2.0 | 25–40 |
| 30 | 34 | 42 | 2.0 | 30–50 |
| 35 | 39 | 48 | 2.0 | 35–55 |
| 40 | 44 | 54 | 2.5 | 40–60 |
| 50 | 55 | 66 | 2.5 | 50–70 |
| 60 | 65 | 78 | 3.0 | 60–80 |
| d (bore) | D (OD) | Flange Ø | Flange thickness | L (length) |
|---|---|---|---|---|
| 1/2″ | 5/8″ | 7/8″ | 0.062″ | 1/2–3/4″ |
| 3/4″ | 7/8″ | 1-1/8″ | 0.062″ | 3/4–1″ |
| 1″ | 1-1/8″ | 1-1/2″ | 0.078″ | 1–1-1/2″ |
| 1-1/4″ | 1-3/8″ | 1-3/4″ | 0.078″ | 1-1/4–1-3/4″ |
| 1-1/2″ | 1-5/8″ | 2″ | 0.093″ | 1-1/2–2″ |
| 2″ | 2-1/8″ | 2-1/2″ | 0.093″ | 2–2-1/2″ |
| 2-1/2″ | 2-5/8″ | 3″ | 0.125″ | 2-1/2–3″ |
Custom dimensions
Center flanged bushings are commonly manufactured to customer drawings across a wider envelope than the tables show — typically from 8 mm bore up to 300 mm bore, with wall thickness, flange thickness, groove position and length set to the housing design. Options include oil grooves and holes (diamond, figure-eight, circular or straight patterns), chamfers, and split or welded constructions for larger diameters.
Oil grooves and running clearance
Grooves are optional on graphite-plugged bushes, since the graphite itself provides the lubrication, but they are normally specified on tin bronze bushes that run greased. The pattern is chosen according to the motion — rotating, oscillating or linear — and is arranged so the groove does not run through the loaded zone. Standard manufacturing tolerances apply to the outside diameter and to the bore before fitting; the running clearance is achieved after fitting, as described below. If your application needs a specific clearance rather than a standard tolerance, state it on the drawing so it can be allowed for during manufacture.
Load, PV Limit and Speed
Bearing life is governed largely by the PV value — the product of the bearing pressure and the sliding velocity. It is a measure of heat generated at the sliding surface, and exceeding the limit for a given material raises temperature, accelerates wear and can lead to seizure.
| Performance Parameter | Specification |
|---|---|
| Static Load Capacity | 100–200 MPa |
| Dynamic Load Capacity | 40–70 MPa |
| PV Limit — Dry | 1.2–1.6 MPa·m/s |
| PV Limit — Lubricated | 2.0–2.8 MPa·m/s |
| Maximum Speed — Graphite, Dry | 0.5–1.0 m/s |
| Maximum Speed — Oil-Lubricated | Up to 2.5 m/s |
| Continuous Service Temperature | −40 to +250 °C |
| Maximum Intermittent Temperature — Graphite | Up to 300 °C |
These are typical engineering ranges for bronze bushing alloys in normal industrial service. The achievable value for a specific bush depends on the alloy, wall thickness, housing stiffness and heat dissipation, shaft surface finish and hardness, and whether lubrication is present.
Pressure. Calculated on the projected bearing area (bore × length). Intermittent peak loads above the dynamic figure are usually acceptable if the mean load stays within range.
Speed and duty. Self-lubricating graphite-plugged bushings are designed for slow sliding. At higher speeds, or where heat cannot escape, a lubricated tin bronze bushing with oil grooves will typically carry a higher PV. Oscillating duty — a joint that rocks through a small angle rather than rotating continuously — generally gives longer life than continuous rotation at the same nominal PV, because the load is distributed and the lubricant film has more opportunity to recover.
Working out the PV value
As an example, a bush with a 40 mm bore and a 40 mm length carrying a radial load of 12 kN has a projected area of 40 × 40 = 1,600 mm², giving a bearing pressure of 7.5 MPa. If the shaft surface speed is 0.3 m/s, the PV is 7.5 × 0.3 = 2.25 MPa·m/s. That figure sits within the lubricated range but above the dry-running range for graphite-plugged bronze, so this duty would call for a lubricated tin bronze bush, a larger bearing area, or a reduced speed. We will check the PV for you if you send the load, speed and duty cycle.
Installation and Press-Fit Tolerance
Most premature failures of flanged bushings trace back to fitting rather than to material. Two points matter most: the interference fit must be correct, and the press force must never be applied to the flange.
| Feature | Recommendation | Note |
|---|---|---|
| Housing bore | H7 | Break the entry edge with a chamfer to avoid shearing material |
| Shaft | f7 or g6 | h7 where closer guidance is required |
| Interference on OD | 0.03–0.08 mm | Increases with diameter; thin-wall bushings take less |
| Groove width | Flange thickness + 0.1–0.2 mm | Flange must seat without being pinched |
| Groove depth | (Flange Ø − D) / 2 | Flange sits below the bore surface |
| Housing bore finish | Ra 1.6 μm | — |
| Shaft finish | Ra 0.4–0.8 μm | Rougher shafts shorten bushing life |
Fitting procedure
- Inspect and cleanCheck the housing bore size and the groove width and depth. Deburr all edges and clean the bore and the bushing. Any swarf left in the groove will prevent the flange seating squarely.
- Verify the grooveConfirm the flange drops into the groove with clearance and is not pinched when the bushing is in position. A flange clamped tightly in its groove can distort and bind the shaft.
- Align the bushingStart the bushing square to the bore. A mandrel or a fitting sleeve of the same outside diameter helps keep it aligned during the first few millimetres of travel.
- Press on the outside diameterUse an arbor press and apply the force through a sleeve that bears on the outer wall, not on the flange. Press in one smooth, continuous movement.
- If force must reach the flangeSupport the whole flange face with a dedicated fitting sleeve so the load is distributed. Never strike the flange with a hammer — it is the part most likely to crack or bend.
- Check the bore after fittingPress-fitting closes the inside diameter, typically by 60–80% of the interference. Verify with a plug gauge or bore gauge and ream, burnish or hone to the final clearance if required.
- Lubricate and run inApply a thin film of grease before assembly, including on graphite-plugged bushes, and run in at reduced speed and load. This improves the transfer film and early wear behaviour.
Typical Applications
Cranes and lifting equipment
Boom pivots, slew ring connections, sheave bearings and drum supports work at low speed under heavy load, often oscillating through a limited arc and exposed to weather. A center flange holds the pin axially in both directions as the load reverses through the lifting cycle, and graphite-plugged bronze removes the need to reach greasing points at height. Graphite-plugged bronze or C95500 nickel aluminum bronze is normally specified for these joints. Oscillation angles are often small — from a few degrees to roughly 30° — so the load stays concentrated on a limited arc of the bearing surface, where a material holding a solid lubricant film performs better than one relying on grease that can be squeezed out. See graphite oilless bearings on a large crane for a worked example.
Agricultural machinery
Harvester cutter drives, tractor linkage points, seeder openers and front axle pivots combine shock loading with abrasive dust and long idle periods. Self-lubricating bronze does not depend on a grease film that can dry out or attract grit between seasons, and maintenance-free operation matters most during a short harvest window. Shock loading and long idle periods make grease unreliable in this duty. Graphite-plugged bronze is the usual choice, with manganese bronze where impact loads are severe. Because the working window is short, a joint that runs a full season without attention is worth more than a lower-cost bush that needs weekly greasing.
Packaging machinery
Cam followers, rocker arms, sealing jaws and transfer fingers run at moderate speed in repeated cycles, frequently in food or pharmaceutical lines where oil leakage is unacceptable. Solid-lubricated bronze keeps the area clean, and the two flange faces maintain axial position in mechanisms that reciprocate. Tin bronze with oil grooves suits lubricated designs, while graphite-plugged bronze is used where product contact rules out grease. Holding axial position matters here: any drift in the mechanism affects registration and cut quality, so the two thrust faces of a center flange are doing useful work rather than simply locating the bush.
Conveyors and material handling
Idler rolls, take-up units, chain guides and sorting mechanisms run slowly and continuously, often in dust, with limited maintenance access. Long service life without regreasing reduces the number of line stoppages, which is usually the dominant cost in a conveyor installation. Tin bronze with grooves works well where the line follows a scheduled lubrication routine; graphite-plugged bronze suits sealed or inaccessible runs. Because the bush is captured in a groove, it cannot walk out of the housing under vibration — a failure mode worth designing out on long conveyor runs.
