Solid-Lubricant Bronze Bearings: Application Location Matrix

Most bearing catalogues start from a part number. This article starts from the other end: it takes the physics of a sliding interface, derives the duty envelope the physics allows, and then maps that envelope onto the specific locations inside real machines where a solid-lubricant bronze bearing is the rational choice — and where it is not.

Article type: engineering reference · Scope: cast and machined copper-alloy plain bearings with embedded solid lubricant · All numerical values are reference values and are subject to the disclaimer at the end of this page.

1. Start with the physics, not a catalogue

1.1 A plain bearing is a film-management device

Strip away the part numbers and a plain bearing has exactly one job: keep two solid surfaces apart with a layer of something that shears easily. The bronze is not the bearing in the functional sense. The bronze is the structure that holds and supports the film. Everything that follows — the speed ceiling, the load ceiling, the choice of alloy, the reason a plug pattern covers a quarter of the surface — falls out of that single statement.

There are three ways to make the film. A fluid film is generated by motion dragging a viscous medium into a converging gap. A boundary film is a molecular layer adsorbed on the surface. A solid film is a layer of a low-shear-strength solid smeared onto the counterface. Oil-lubricated design spends its whole life trying to stay in the first regime. Solid-lubricant bronze bearings are deliberately designed to live in the third, and that is the entire point of the technology.

1.2 Why fluid films abandon you exactly where you need them

Consider the heat balance. The frictional power dissipated per unit of apparent contact area is:

q  =  μ · p · v
where μ is the friction coefficient, p the mean contact pressure and v the sliding velocity. The product p · v is the familiar PV term.

That heat has to leave through the bearing shell, the shaft and the surrounding structure. Temperature rises until the heat leaving equals the heat generated. Two failure routes follow directly:

  • Velocity too low. A hydrodynamic wedge needs entrainment velocity. Below the transition speed the oil is never dragged in fast enough to separate the surfaces, so the interface stays in the boundary regime no matter how much oil is supplied. Low speed and high load is precisely the corner of the map where oil lubrication is structurally weakest.
  • PV too high. Once generation exceeds removal, temperature climbs, oil viscosity collapses, the film thins, contact becomes metallic, friction climbs further, and the loop closes on itself until the surfaces seize.

This is why the classic application territory for solid-lubricant bronze bearings reads like a list of places where oil lubrication struggles: slow, heavy, oscillating, hot, dirty, submerged, or inaccessible.

1.3 What a solid lubricant changes

A lamellar solid such as graphite, or a low-surface-energy polymer such as PTFE, does not need entrainment velocity to become a film. It needs relative motion — any relative motion — plus a modest amount of frictional energy to smear material onto the counterface. Once a transfer film a few micrometres thick exists on the shaft, the interface is graphite on graphite rather than bronze on steel, and the shear now happens inside the film instead of at the asperities.

Two design consequences follow, and they explain the geometry of every product in this family:

  1. The reservoir must be volumetric, not superficial. A coating wears off. A plug pressed into a hole drilled through part of the wall keeps exposing fresh lubricant as the surface wears down. That is the whole argument for drilling and plugging rather than coating.
  2. The supply rate is self-regulating. The bronze matrix has a higher coefficient of thermal expansion than the graphite insert. As the interface warms, the matrix expands slightly more than the insert; on cooling it contracts again. This expansion-and-contraction cycle meters the lubricant out during running and lets the insert sit flush when stopped. It is not a mechanism that has to be switched on; it is a consequence of the material pair.

1.4 The 25 to 30 percent rule, derived

The source data sheet states that the lubricant reservoirs cover about 25 to 30 percent of the sliding surface. That number is not arbitrary, and it is worth reconstructing, because it is the single most useful number for judging a supplier’s design.

Two failure modes bound the range from either side:

  • Too little coverage. The transfer film forms only where an insert has passed. If the insert pitch is too coarse relative to the contact width, stretches of the surface run unfilmed during part of each stroke or each revolution, and the unfilmed stretches score.
  • Too much coverage. Every square millimetre given to a graphite plug is a square millimetre of bronze removed from the load path. The plugs carry almost no load. Raise the coverage and the real contact pressure on the remaining bronze rises in proportion, which accelerates creep, embeds the plug edges and eventually dislodges them.

The band quoted in the source data — 25 to 30 percent — sits inside the 20 to 35 percent range commonly published for this construction. It is a compromise, and it is worth treating as one: if a duty is very slow and lightly loaded, coverage toward the upper end is defensible; if it is near the pressure ceiling, coverage toward the lower end with a stronger matrix is the more robust choice.

1.5 The envelope that falls out

Putting the heat balance and the coverage argument together gives the duty envelope that this construction can occupy. The values below are the ones stated in the source data sheet, with the unit conversion made explicit because the source mixes units:

Table 1 — Duty envelope stated in the source data sheet.
Parameter Steel-backed construction Solid cast bronze construction Note
Static surface pressure 150 N/mm² 150 N/mm² Stated as a movement-static figure
Dynamic surface pressure 90 N/mm² 90 N/mm² The material property table lists 100 N/mm² — see footnote
Sliding speed, dry < 0.5 m/s < 0.3 m/s 30 m/min and 18 m/min respectively
Sliding speed, oil-lubricated < 1.0 m/s < 1.0 m/s Adding oil roughly doubles the usable speed
Friction coefficient 0.03 – 0.20 0.03 – 0.20 See footnote on the lower bound
PV limit (dry, published practice) around 1.6 N/mm²·m/s Not stated in the source; widely published for this construction

Footnotes. (a) The data sheet’s product section gives 150 N/mm² static and 90 N/mm² dynamic, while the same document’s material property table gives a permitted load of 100 N/mm² for the matrix. The two figures are on different bases — an ultimate or short-term limit versus a permissible working value. Design to the lower, permissible figure and ask the supplier which basis each number rests on. (b) A friction coefficient of 0.03 is at the optimistic end of the 0.05 to 0.15 range commonly published for dry running of this construction, and is realistic only once a mature transfer film exists. Use the upper half of the band for thermal calculations. (c) 15 m/min, the permitted speed listed for the manganese brass row of the material table, equals 0.25 m/s and is consistent with the 0.3 m/s dry ceiling; 20 m/min equals 0.33 m/s.

2. Three constructions, three cost curves

The source document describes three ways of making a copper-alloy plain bearing. They are not competing grades of the same thing; they sit at different points on a cost-versus-capability curve, and the curve is driven by geometry.

Construction How it is made Lubrication Where it wins Where it loses
Machined copper-alloy bearing Turned or milled from wrought or continuously cast bar, tube or plate, always to a customer drawing Designed for external lubrication; grooves, holes and pockets to drawing Tight tolerances, small radial envelope, low weight, arbitrary geometry, any copper alloy Needs a lubrication supply and a maintenance regime; life is governed by the lubrication regime
Cast bronze bearing with embedded solid lubricant Cast bronze body, plain or flanged; holes drilled in a pattern and filled with solid lubricant Carries its own lubricant reservoir; intended to run without routine re-lubrication Low speed, high load, oscillation, temperature extremes, inaccessible or dirty locations Speed-limited; a share of the surface is given over to non-load-bearing insert
Steel-backed cast bronze bearing with embedded solid lubricant Bronze cast onto a steel shell to produce an integral metallurgical bond, then plugged as above As above Large diameters; high load with reduced material cost; the shell carries the structural job Bimetal interface introduces a bond-integrity check; repair of a damaged shell is not straightforward

Table 2 — construction comparison. All three are made to drawing or to a stated standard; none is an off-the-shelf catalogue item in the sense that a rolling bearing is.

2.1 Why the steel shell changes the economics above about 100 mm

The source data sheet claims a considerably reduced material cost for bearings with a diameter over 100 mm. The claim is worth unpacking, because it is a genuine first-principles result and not marketing.

A solid bronze bushing is sized by two constraints that pull against each other. The bore is fixed by the shaft. The wall must be thick enough to be cast soundly, to be pressed into the housing without collapsing, and to carry the hoop stress of the press fit. As bore diameter grows, wall thickness has to grow with it, so the bronze volume grows approximately with the square of the diameter.

But the load-carrying job in a bearing is done by a thin layer at the sliding surface. Bronze buried at mid-wall depth is doing structural work, not bearing work. Bronze is several times the cost of structural steel per kilogram.

Bonding a bronze lining metallurgically onto a steel shell separates the two functions: steel takes the hoop stress and the press-fit load, bronze is only as thick as the bearing function requires. Required bronze volume now scales with the sliding surface area rather than with the cross-section. The larger the diameter, the larger the gap between the two curves — hence the 100 mm crossover. The exact crossover for a given design depends on required wall thickness, load, section and batch quantity, so treat it as a rule of thumb to be checked against a quotation, not as a constant.

3. The five alloy systems

The source data sheet lists five copper-alloy systems. The designations below describe the alloys by their metallurgy rather than by any commercial code, and the values have been cross-checked against publicly published data for the corresponding standard designations.

Alloy system Nominal composition (weight %) Comparable standard designation 0.2 % proof stress, MPa Tensile strength, MPa Brinell hardness Density, g/cm³ Machinability (free-cutting brass = 100)
High-strength manganese–aluminium brass Cu 62–68; Zn balance (about 25); Al 5.0–7.5; Mn 2.5–5.0; Fe 2.0–4.0 CuZn25Al5Mn4Fe3, comparable to EN CC762S and UNS C86300 350–460 750–820 210 min 7.7 8
Leaded tin–zinc bronze Cu about 85; Sn about 5; Pb about 5; Zn about 5 CuSn5Pb5Zn5, comparable to EN CC491K and UNS C83600 90–138 241–280 60–85 8.8–8.94 84–90
Nickel–aluminium bronze Cu about 80; Al about 10; Ni about 5; Fe about 5 CuAl10Fe5Ni5, comparable to EN CC333G and UNS C95500 260–470 500–800 150–234 7.5–7.6 50
Tin bronze, about 12 % tin Cu about 88; Sn about 12 CuSn12, comparable to EN CC483K and UNS C90800 150–190 270–360 90–120 8.6–8.8 30–40
Leaded tin bronze, about 10 % tin / 10 % lead Cu about 80; Sn about 10; Pb about 10 CuSn10Pb10, comparable to EN CC495K and UNS C93700 100–138 210–310 60–90 8.86–9.0 High; the lead phase is responsible

Table 3 — alloy systems and cross-checked reference properties. Ranges shown span the published minimum and typical values for the corresponding designations. Where a range is given, the lower figure is normally a published minimum and the upper a typical value; the two are not interchangeable.

Alloy system Permitted surface pressure, N/mm² Permitted sliding speed (as stated), m/min Equivalent speed, m/s Temperature range in source data, °C
High-strength manganese–aluminium brass 100 15 0.25 −100 to +300
Leaded tin–zinc bronze 60 10 0.17 −100 to +400
Nickel–aluminium bronze 50 20 0.33 −100 to +400
Tin bronze, about 12 % tin 70 10 0.17 −100 to +400
Leaded tin bronze, 10 % Sn / 10 % Pb 60 10 0.17 −100 to +400

Table 4 — duty figures as stated in the source data sheet, with the unit conversion made explicit.

Data verification notes. Four items in the source spreadsheet differ from publicly published data and were corrected or annotated in the tables above:

  1. Corrupted cell. The iron content of the manganese–aluminium brass was stored as a spreadsheet date rather than a range: the intended value “2–4” was auto-converted on data entry. It has been restored to the 2.0–4.0 % window that corresponds to the published composition of this alloy.
  2. Density. The source lists 8.0 g/cm³ for the manganese–aluminium brass. Published values for the corresponding alloy are 7.70 g/cm³. The published value is used above; the difference is about 4 % and matters if mass is estimated from volume.
  3. Upper temperature limit. The source lists −100 to +400 °C for four of the five systems, including both lead-bearing bronzes. Lead melts at 327 °C, and published maximum mechanical-temperature figures for the 10 % lead tin bronze are close to 140 °C. The +400 °C figure is defensible as the capability of the solid lubricant system and the short-term envelope of the assembly, but it is not a strength limit for a lead-bearing matrix. Design the matrix to its elevated-temperature property curve.
  4. Tin bronze strength. The source lists a tensile minimum of 270 MPa for the 12 % tin bronze. Published figures for the corresponding alloy are ≥300 MPa for continuous cast and ≥280 MPa for centrifugal cast. The source figure is consistent with centrifugal cast and slightly conservative for continuous cast.

4. The application location matrix

A location matrix is a lookup from a place in a machine to a bearing specification. It is more useful than a material chart because the same machine contains locations with completely different duty signatures, and a single “material for this machine” answer is almost always wrong somewhere.

The matrix below is built on two derived axes rather than on tradition:

  • Axis 1, motion type — because it determines whether a fluid film can exist at all.
  • Axis 2, temperature band — because it determines which failure mechanism is rate-controlling.

Every location then resolves to four outputs: construction, alloy system, insert type, and the failure mode that will appear if the choice is wrong.

4.1 Axis 1: motion type

Motion What it does to the film Consequence for selection
Continuous rotation, moderate to high speed A converging wedge forms and a hydrodynamic film is sustained above the transition speed Oil-lubricated machined bronze is usually the more economical answer. A solid-lubricant bearing is over-specified and speed-limited here; use it only where relubrication is genuinely impossible
Continuous rotation, slow Entrainment velocity is below the transition speed; the interface stays in the boundary regime The core territory for solid lubricant inserts. Select the matrix for pressure, not for speed
Oscillation through a small angle The film is squeezed out at each reversal and never re-establishes; the contact never travels far enough to bring fresh lubricant in Solid-lubricant inserts plus a staggered plug pattern, so that every point of the contact passes over an insert within a fraction of the stroke
Reciprocation, linear Velocity passes through zero at each stroke end; the boundary regime is entered twice per cycle As above, plus attention to edge loading at the stroke ends, where the contact reverses under load
Intermittent, with long dwell Oil drains from the contact during dwell and may oxidise or be washed out; start-up occurs with a dry, possibly corroded interface This is where embedded solid lubricant earns its cost: the reservoir is always present at the interface, regardless of how long the machine has stood

Table 5 — motion type as the primary selection axis.

4.2 Axis 2: temperature band

Band Rate-controlling mechanism Practical implication
Below −40 °C Differential thermal contraction between insert and matrix; stiffening of any residual grease Copper alloys retain ductility at low temperature, so the metallurgy is rarely the limit. The insert retention and the startup film are the items to verify. The −100 °C lower bound quoted in the source data should be confirmed for the specific insert and fit
Ambient to 150 °C Normal adhesive and abrasive wear All five alloy systems are usable; selection is driven by load and environment rather than by temperature
150 to 260 °C Oil and grease oxidise, coke and lose film strength This is the band where an oil-lubricated design starts to fail for chemical rather than mechanical reasons. A graphite-based insert is unaffected. PTFE-based inserts approach their usual continuous-service ceiling near 260 °C
260 to 400 °C Matrix strength and creep, not lubrication Use a matrix with genuine hot strength: nickel–aluminium bronze, or high-strength manganese–aluminium brass. Avoid lead-bearing matrices in this band — see the verification note above
Above 400 °C Outside the stated envelope of this construction Not covered by the source data and not claimed here

Table 6 — temperature band as the secondary selection axis.

4.3 Continuous casting machine

A caster is the textbook application: slow, heavy, hot, water-sprayed, dust-laden and running for months without a stop. Almost every bearing location on the machine is a boundary-lubrication problem.

Location Motion Duty signature Construction Alloy system Insert Dominant failure mode if wrong
Mould oscillation table guides Small-amplitude sinusoidal oscillation at casting frequency High frequency, short stroke, reversing load, warm and wet Cast bronze with inserts Tin bronze, about 12 % tin — impact resistance is the reason Graphite-based Fretting and plug edge breakdown from the reversal frequency
Segment roll pins and roll neck bushes Slow continuous rotation, often under spray water Very high radial load, very low speed, water plus scale Steel-backed cast bronze with inserts Nickel–aluminium bronze where water is continuous; manganese–aluminium brass where it is mainly load Graphite-based above water; PTFE-based where submerged Abrasive wear from scale ingress, then ovalisation
Dummy-bar guide and withdrawal unit Intermittent, high starting load Start-up under load after long dwell Cast bronze with inserts High-strength manganese–aluminium brass Graphite-based Start-up seizure during the first stroke
Ladle turret trunnion and slewing ring bushes Very slow oscillation under very high load Extreme static load, near-zero velocity, radiant heat Steel-backed cast bronze with inserts, large diameter High-strength manganese–aluminium brass Graphite-based Creep and extrusion of the matrix under sustained static load
Torch cutting carriage and discharge roller table Slow rotation with frequent stops Moderate load, hot, radiant heat, dust Cast bronze with inserts, flanged where thrust is present High-strength manganese–aluminium brass Graphite-based Heat soak lifting the interface above the matrix limit

Table 7 — continuous casting machine, location matrix.

4.4 Rolling mill and roller tables

Rolling mills share the caster’s load and speed signature but add shock loading and, in the welding and cooling zones of tube and pipe mills, alternating heat and water.

Location Motion Duty signature Construction Alloy system Insert Dominant failure mode if wrong
Forming and sizing horizontal roll chocks Slow continuous rotation Highest radial load on the mill, plus axial thrust; the reason a flanged form is used Steel-backed cast bronze, flanged Manganese–aluminium brass for load; nickel–aluminium bronze where water is present Graphite-based Flange root fracture from unrestrained axial thrust
Vertical roll bushes Slow rotation, side-force dominated Medium load, side loading, moderate temperature Cast bronze, flanged Manganese–aluminium brass Graphite-based Uneven wear from a side load the plain sleeve was never meant to carry
Turks-head, guide and squeeze rolls Oscillating combined with rotation Small bushes, frequent reversal, lubrication access poor Cast bronze with inserts, small bore Tin bronze, about 12 % tin Graphite-based Plug dislodgement from repeated reversal at the edge of the contact
Welding and cooling zone rolls Slow rotation Heat plus water spray, alternating Cast bronze with inserts Nickel–aluminium bronze PTFE-based insert with molybdenum disulphide and carbon fibre Corrosion-assisted wear; graphite alone is the weaker choice in continuous water
Screw-down nuts and press screws Slow, heavily loaded translation Very high load, very low speed, often vertical Machined copper-alloy, externally lubricated High-strength manganese–aluminium brass Not applicable — grooved and oil-fed Thread galling; a solid lubricant insert cannot be plugged into a thread flank

Table 8 — rolling mill, location matrix. Note the exception in the last row: solid lubricant inserts are drilled into a sliding surface, so threaded and screw locations belong to the machined, externally lubricated family.

4.5 Shipboard deck and hull equipment

Deck machinery combines long idle periods with infrequent but heavily loaded operation, in a salt-laden atmosphere. The idle periods are the dominant design input: a bearing that stands for months and then has to move under full load is a start-up lubrication problem.

Location Motion Duty signature Construction Alloy system Insert Dominant failure mode if wrong
Deck crane slewing, luffing and boom foot pins Slow oscillation, long dwell between operations High load at very low velocity, salt atmosphere, poor relubrication access Cast bronze with inserts; steel-backed above about 100 mm Nickel–aluminium bronze for the salt environment Graphite-based above the waterline Start-up seizure after a long idle period; corrosion creep at the housing interface
Rudder stock and pintle bushes Slow oscillation, small angle High load, continuous seawater immersion Cast bronze with inserts, large diameter Nickel–aluminium bronze PTFE-based, water-capable grade Corrosion and dealloying of an unsuitable matrix; graphite alone performs poorly when continuously submerged
Hatch cover hinge and linkage bushes Slow rotation, long dwell Moderate load, exposed, intermittent use Cast bronze with inserts Tin bronze, about 12 % tin, or leaded tin bronze Graphite-based Corrosion bonding of the pin to the bush during the idle period
Stern tube and propeller shaft bearings Slow to moderate continuous rotation Continuous water immersion, high load, long service interval expected Cast bronze with inserts where the duty is within the speed ceiling; otherwise a water-lubricated machined bronze or composite Nickel–aluminium bronze or manganese–aluminium brass PTFE-based, water-capable grade Speed above the dry ceiling; the location often exceeds what this construction allows
Winch, windlass and capstan bearings Slow rotation, intermittent, load reversals High shock load, salt spray Steel-backed cast bronze with inserts Manganese–aluminium brass Graphite-based Shock cracking of a matrix selected for load but not for impact

Table 9 — shipboard equipment, location matrix.

4.6 Hydro turbine and gate machinery

Hydraulic machinery is the clearest case for this technology in the source literature: submerged, slow, very heavily loaded, and expected to work after years of standing still. It is also where the water-capable insert earns its place.

Location Motion Duty signature Construction Alloy system Insert Dominant failure mode if wrong
Dam gate trunnion bushes Very slow rotation through a small arc, sometimes once a year Very high static load, submerged or splash zone, years of dwell between movements Steel-backed cast bronze with inserts, large diameter Manganese–aluminium brass for load; nickel–aluminium bronze for submerged service PTFE-based, water-capable grade Start-up seizure: the gate will not lift, which is a safety issue, not a maintenance issue
Gate hoist and lifting-link pins Slow rotation under load High load, intermittent, exposed to weather Cast bronze with inserts Manganese–aluminium brass Graphite-based Fretting at the pin-to-bush interface during load reversals
Turbine wicket gate and guide vane stems Slow oscillation through a limited arc High load, submerged, precise positioning required Cast bronze with inserts, often flanged Nickel–aluminium bronze PTFE-based, water-capable grade Stick-slip and cavitation-assisted wear on the stem
Turbine main shaft and guide bearings Continuous rotation Moderate speed, water-lubricated Usually outside this construction; a machined, water-lubricated bronze is the normal answer Tin bronze or leaded tin bronze Not applicable Running a plugged bearing above its dry speed ceiling
Trash rack and screen rake guides Linear reciprocation Low load, submerged, abrasive Wear plates and slide pads rather than bushes Nickel–aluminium bronze PTFE-based Abrasive wear from grit held at the interface

Table 10 — hydro turbine and gate machinery, location matrix.

4.7 Offshore and submerged structures

Offshore locations add two constraints to the marine set: intervention cost is very high, and the environment is continuously wet or splash-cycled. Here the maintenance interval, not the bearing unit price, drives the specification.

Location Motion Duty signature Construction Alloy system Insert Dominant failure mode if wrong
Riser and conductor guide bushes Slow vertical sliding or oscillation Continuous immersion, high load, no intervention possible Steel-backed cast bronze with inserts Nickel–aluminium bronze PTFE-based, water-capable grade Corrosion-assisted wear and galvanic interaction with the surrounding steel
Crane pedestal and slew ring bushes on platforms Slow oscillation, long dwell High load, salt atmosphere, infrequent use Steel-backed cast bronze with inserts Nickel–aluminium bronze Graphite-based where above the splash zone Start-up seizure, and corrosion creep where the bronze meets the housing
Jack-up leg chord and rack guides Slow linear translation, very high load Extreme static pressure, intermittent, exposed Wear plates and slide pads, steel-backed Manganese–aluminium brass Graphite-based Creep of the matrix under sustained pressure above the permissible figure
Subsea valve actuator stems and linkage Very slow rotation, very long dwell Submerged, high load, fail-to-operate is unacceptable Cast bronze with inserts, small bore Nickel–aluminium bronze PTFE-based, water-capable grade Corrosion bonding during a multi-year dwell

Table 11 — offshore and submerged structures, location matrix.

4.8 Mobile and off-highway machinery

Forest machines, dumpers and agricultural machines share a signature: high shock load, low speed, contaminated environment, and a maintenance regime that is honoured imperfectly. This is where an embedded lubricant reservoir is worth more than a marginal improvement in material strength.

Location Motion Duty signature Construction Alloy system Insert Dominant failure mode if wrong
Excavator and loader boom, arm and bucket pivots Slow oscillation under shock High load, frequent reversal, dust and impact, relubrication often missed Cast bronze with inserts, flanged where thrust is present Manganese–aluminium brass Graphite-based Impact cracking, then ovalisation that takes the pin with it
Dumper body and hoist pivots Slow rotation, loaded cycles High shock load at loading, long dwell when parked Steel-backed cast bronze with inserts Manganese–aluminium brass Graphite-based Brinelling from impact at the load zone
Forestry crane and grapple pivots Frequent oscillation, shock Moderate load, very high cycle count, contaminated Cast bronze with inserts Tin bronze, about 12 % tin, for impact resistance Graphite-based Plug edge breakdown at high reversal frequency
Agricultural implement linkage and folding frame pivots Slow oscillation, seasonal dwell Moderate load, seasonal use, weather exposure, minimal maintenance Cast bronze with inserts or machined bronze externally lubricated Leaded tin–zinc bronze where load is moderate Graphite-based Corrosion bonding over a winter of standing
Hydraulic cylinder eye and clevis bushes Slow oscillation, high thrust High load, misalignment tolerated, poor lubrication access Cast bronze with inserts, flanged Manganese–aluminium brass Graphite-based Edge loading from misalignment, then extrusion of the bush ends

Table 12 — mobile and off-highway machinery, location matrix.

4.9 Furnace, kiln and hot-zone equipment

Above roughly 260 °C, the selection logic inverts: lubrication is no longer the problem, matrix strength is. This is the band where the two lead-bearing alloy systems must be set aside in favour of the nickel–aluminium bronze or the manganese–aluminium brass.

Location Motion Duty signature Construction Alloy system Insert Dominant failure mode if wrong
Furnace car and bogie wheel bushes Slow rotation, thermal cycling High load, repeated heating and cooling, scale Cast bronze with inserts Nickel–aluminium bronze Graphite-based Oxidation-assisted wear and loss of interference as the housing relaxes
Kiln and dryer support roller bearings Slow continuous rotation High load, sustained high temperature, dust Steel-backed cast bronze with inserts Nickel–aluminium bronze Graphite-based Creep of the matrix under sustained load at temperature
Injection moulding machine toggle link bearings Oscillation, high cycle rate High load, rapid reversal, moderate temperature Cast bronze with inserts Manganese–aluminium brass Graphite-based Fretting at high cycle counts
Continuous furnace roller hearth bushes Slow rotation Sustained high temperature, moderate load Steel-backed cast bronze with inserts Nickel–aluminium bronze Graphite-based Scaling and seizure where a lead-bearing matrix was used above its limit

Table 13 — furnace, kiln and hot-zone equipment, location matrix.

5. From duty signature to selection

The seven location matrices above collapse into a compact decision table. Use it as a starting point for a discussion with a supplier, not as a final specification.

If the dominant condition is Start with Because
Very high static or dynamic load at low speed, large diameter Steel-backed cast bronze, manganese–aluminium brass, graphite insert The steel shell takes the structural load; the brass has the highest strength of the five systems
Continuous water contact or immersion Nickel–aluminium bronze with a PTFE-based insert The matrix resists seawater corrosion and the insert is the grade intended for wetted service
Shock or impact loading Tin bronze, about 12 % tin Impact resistance is the distinguishing property of this system among the five
Sustained temperature above 260 °C Nickel–aluminium bronze, graphite insert Hot strength and creep resistance; the lead-bearing systems are excluded
Low load, ease of machining and cost Leaded tin–zinc bronze, externally lubricated if speed allows Highest machinability of the five and the lowest strength — match them
Poorly hardened or unhardened shaft Leaded tin bronze, 10 % tin / 10 % lead, with inserts The soft lead phase tolerates a softer counterface and embeds foreign particles
Tight tolerance, small radial envelope, external lubrication available Machined copper-alloy bearing to drawing Machining allows tolerances a wrapped thin-wall bearing cannot reach, and the envelope can be minimised
Oscillation with a stroke shorter than the contact width Staggered plug pattern, coverage toward the upper end of the 25 to 30 % band Every point of the contact must pass over an insert within a fraction of the stroke

Table 14 — compact selection table.

6. Choosing the solid lubricant insert

The source data sheet offers two insert families. The choice is almost entirely an environment decision, and the temperature figures quoted for each are lower than the matrix figures — which is the correct order of priority, since the insert is the element that actually forms the film.

Insert family Composition as described Stated behaviour Typical locations Caution
Graphite-based Graphite with additives High resistance to chemical attack; low friction; stated capability up to 400 °C General industrial locations above the waterline: casting machines, roller tables, furnace equipment, press die guides The stated temperature is an insert capability, not a matrix limit — see the verification note in section 3
PTFE-based PTFE with molybdenum disulphide and carbon fibre Low friction; performs well in water; stated capability up to 300 °C Submerged or in-contact-with-water locations: ships, dam gates, turbines, cranes PTFE-based compositions are commonly quoted with a continuous-service ceiling near 260 °C. The 300 °C figure should be treated as a short-term upper bound

Table 15 — solid lubricant insert families. The source data sheet notes that several alternative lubricant materials and, for the solid cast construction, several alternative base materials are available beyond the two listed here.

7. Fits, tolerances and geometry

The source data sheet gives a complete fit system. Note that the outside diameter does not “conform” to the housing in a standards sense — it takes the shape of the housing bore once pressed in, which is why the outside-diameter tolerance is stated as a press fit.

Element Stated tolerance Comment
Housing bore H7 The bore determines the final inside diameter of a pressed bushing; a bushing pressed into an H7 bore finishes close to the bore size
Cylindrical bushing Inside F7, outside m6 m6 gives the press fit. The finished bore is normally machined or burnished after pressing where a precise clearance is needed
Flanged bushing Inside E7, outside r6 The larger interference of r6 reflects the axial location duty of a flanged form
Shaft d8, e7 or f7 recommended Published practice for this construction also cites g6 and h7; the choice sets the running clearance, which must allow for the thermal expansion of the bronze
Shaft hardness Not stated in the source; published practice is above about 150 HB A soft counterface is damaged by the hard bronze and machines the transfer film off as it forms
Shaft roughness Not stated in the source; published practice is Ra 1.6 µm or finer, some sources Ra 0.4 to 0.8 µm Roughness controls both film formation and abrasion; it is usually the cheapest life improvement available

Table 16 — fits and tolerances. The source data sheet states that bearings are manufactured according to the drawing or to a standard, so the values above are the default and are negotiable on a drawing.

Geometry notes

  • Plain versus flanged. Use a flanged form wherever axial thrust or axial location is present. Substituting a plain sleeve at a thrust location moves the load to the press fit, which it is not sized for.
  • Thrust washers and slide plates. Pure axial locations take a thrust washer; linear and oscillating guides take a wear plate or slide pad. Both are offered in the same materials and with the same inserts.
  • Plug orientation. Where the load is directional, orient the plug pattern so that plugs enter the load zone; where the load reverses, a regular staggered pattern is the safer choice.
  • Running clearance. Bronze has a coefficient of thermal expansion around 18 × 10−6 per kelvin. In a hot location, size the cold clearance so that the hot clearance is still positive; more bearings are lost to thermal closure of the clearance than to wear.

8. Machining and installation notes

  • Press, do not strike. Drive the bushing in with a press or an arbor that loads the full end face. Striking a plugged bronze bushing can dislodge inserts and crack a steel-backed shell.
  • Finish after pressing where the tolerance demands it. Because the outside diameter takes the shape of the housing bore, the final inside diameter of a thin-walled bushing is set by the bore. Machine or burnish afterwards where the running clearance is critical.
  • Do not machine the plugs flush with a blunt tool. The inserts are meant to sit slightly below or flush with the surface and to be exposed by wear. Smearing bronze over the plug faces during finishing defeats the mechanism at start-up.
  • Apply a thin film of grease or oil at assembly. This protects the interface for the first few cycles, before the transfer film has been established. After that the bearing is intended to run without routine re-lubrication within its envelope.
  • Stress relieving. Where a machined manganese–aluminium brass component is heavily worked or asymmetric, published practice is a stress relief around 260 °C held for about one hour per 25 mm of section. This is a fabrication note, not a service limit.
  • Dust and grit. Solid lubrication does not attract grit the way grease does, but it does not exclude it either. In contaminated locations a shield or wiper is the cheapest extension of life.
  • Check the counterface, not just the bearing. In a majority of premature-wear investigations the shaft condition, not the bushing material, is the finding.

9. Reading a failed bearing

A returned bearing is a record of which axis of the matrix the specification got wrong. The correlation is worth keeping:

Observation Most likely cause Which axis was misread
Discoloured or heat-tinted surface, transfer film absent, matrix smeared PV exceeded; heat destroyed the film faster than it was replenished Load or speed, or both — refer to Table 1
Plugs proud of the surface, bronze worn back around them Sustained overheating; the matrix expanded and did not recover Temperature band
Plugs missing, holes empty and rounded at the edge Excess coverage for the pressure, or shock loading Coverage versus load; impact not accounted for
Scoring in bands, aligned with the sliding direction Counterface too rough, or abrasive ingress Environment and shaft condition
Bore ovalised, wear concentrated at the load zone only Normal wear at end of life, or sustained static load above the permissible figure Load
Bushing rotated in the housing Insufficient interference, or thermal relaxation of the housing Fit and temperature
Cracked flange root Axial thrust carried by a form not sized for it Geometry
Corrosion products at the interface, bush seized to the pin Matrix not matched to the medium, or a long idle period in a corrosive environment Environment

Table 17 — failure signature to root cause. This table is a diagnostic aid for an investigation, not a substitute for one.

10. Frequently asked questions

What does “solid-lubricant bronze bearing” actually mean?

Why is the sliding speed limit so low compared with a rolling bearing?

Why are solid lubricant inserts limited to roughly a quarter of the surface?

When is a steel-backed construction preferable to a solid cast bronze bushing?

Which base alloy should be used where water is present?

Can a lead-bearing bronze be used at 400 degrees Celsius?

Do these bearings need any lubrication at installation?

What is the most common cause of premature failure?

11. Technical disclaimer

  1. All figures in this article are engineering reference values only. They are not specification limits and must not be used as acceptance criteria or as the sole basis for a design calculation.
  2. Actual properties depend on the casting method (sand, centrifugal or continuous), section thickness, cooling rate, and any stress-relieving or tempering treatment. Values obtained from a separately cast test bar are not representative of a thick section of the same heat.
  3. Values are variously published as minimum or as typical, and the two are not interchangeable. Where this article shows a range, the lower figure is normally a published minimum and the upper a typical value. Where the source data sheet and publicly published data disagree, the difference is annotated in the table footnotes.
  4. The material test certificate (MTC) supplied with each delivery, issued for example to EN 10204, is the only document that defines the chemical composition and mechanical properties of the material actually delivered. Where the certificate and this article differ, the certificate governs.
  5. Cross-standard equivalences between EN, DIN, UNS, JIS and AS designations are approximate. A designation described here as comparable is similar but not identical, and any substitution requires independent verification against the applicable standard and the service conditions.
  6. This article contains no claim of conformity to, certification to, qualification to, or approval under any specification, standard or regulatory regime.
  7. This article reaches no conclusion regarding military or defence application, automotive application, food-contact application, medical application, nuclear application, or airworthiness. Equipment in those fields is subject to separate qualification regimes that are outside the scope of this document.
  8. Named standards and specification systems (ASTM, EN, DIN, JIS, AS, SAE and AMS) are cited solely as published data sources for the property values shown, and for no other purpose.
  9. Where an SAE or AMS specification is named, it is referenced only as a source of published material property data. It constitutes no claim of conformity, qualification, approval or airworthiness of any kind.
  10. The application locations listed in the matrices are illustrative of general industry practice. Whether a given location is suitable for a particular installation depends on the actual load, speed, temperature, environment, alignment and maintenance regime, and must be assessed by the equipment designer or the responsible engineer.
  11. Figures marked as not stated in the source data (shaft hardness, shaft roughness, PV limit, insert coverage outside 25 to 30 percent) come from general published practice for this construction, are approximate, and should be confirmed for the specific product.
  12. Nothing in this article constitutes a warranty, a representation of fitness for a particular purpose, or engineering advice for a specific installation.