2. Grade cross-reference

Equivalences between standard systems are approximate. Two alloys listed as equivalent can differ in impurity limits, in whether the property values apply to cast or wrought product, and in heat-treatment condition. Confirm the equivalence against the specification named on the drawing before substituting a grade.

Cast and wrought grades with similar names are not interchangeable. CuAl10Fe as a wrought designation and C95400 as a cast designation have different specification bases and different property values.

3. Chemical composition by grade

Values below are the limits published in the cited specification. Single values are maximum limits unless a range or minimum is shown.

For continuously cast and centrifugally cast CuSn12-C, EN 1982 raises the allowable copper content to 89.0% and lowers the minimum tin content to 10.5% (castings) or 10.7% (ingots). Continuous-cast C93200 and C93800 permit phosphorus up to 1.5%.

4. Mechanical properties

Property values are condition-specific: casting method, section size and heat treatment all move the numbers. Where a design calculation uses these values, take them from the specification covering the actual product form.

Machinability rating is expressed relative to free-cutting brass C36000 = 100. The spread from C86300 at 8 to C93800 at 80 is a direct consequence of lead content and matrix hardness, and should be reflected in machining cost estimates. CuSn8 is a wrought strip alloy normally formed rather than machined from solid.

Wrought temper designations for CuSn8

Higher tempers raise spring properties and strength but reduce formability. Wrapped bushings are produced from strip in a temper compatible with the rolling and forming steps; final dimensional accuracy comes from the subsequent sizing operation.

5. Load, speed and allowable limits

Allowable load, sliding speed and PV are not intrinsic constants of an alloy. They depend on the lubrication regime, shaft hardness and surface finish, running clearance, heat dissipation, duty cycle and contamination. Published values for the same alloy can differ by a factor of two between a grease-lubricated bushing and a dry-running one.

The trend across the families is consistent enough to guide shortlisting:

• Higher hardness alloys (manganese bronze, aluminium bronze) carry higher static loads before plastic deformation, but demand a harder, finer-finished shaft and reliable lubrication.
• Leaded tin bronzes tolerate lubrication interruption better because lead smears across the contact surface and limits seizure damage.
• Aluminium bronzes and manganese bronze retain useful strength at temperatures where tin bronzes soften; nickel aluminium bronze adds resistance to cavitation and seawater.
• Wear rate rises steeply once the contact temperature exceeds what the lubricant and alloy can dissipate, which is a function of PV rather than load alone.

 Heat treatment and temper designations

Aluminium bronzes

Aluminium bronzes respond to heat treatment. The usual routes are solution treatment in the 870–915 °C range followed by water quench, then tempering; and stress relieving, typically around 315 °C, to reduce residual stress before finish machining. Quench-and-temper conditions raise tensile and yield values above the as-cast figures in Table 4. Because the transformation is sensitive to section thickness and cooling rate, the heat-treatment cycle belongs on the drawing and on the inspection plan.

Tin bronzes

Cast tin bronzes are generally used as-cast. Stress relieving may be applied to stabilise dimensions before finish machining. For wrought CuSn8 the condition is set by cold work and annealing, expressed as the R-tempers in Table 5 rather than as a heat-treatment callout.

Temper designations

• F — as fabricated.
• O — annealed, used for wrought products to obtain the softest condition.
• H — cold worked (strain hardened), with a second digit indicating the degree of hardening (H02 quarter-hard through H10 extra-spring).
• TQ50 — quench hardened and temper annealed, used for aluminium bronze castings.
• R-values — EN convention for wrought copper alloys, where the number is the minimum tensile strength in MPa (R540 = 540 MPa minimum).

A temper designation is meaningless without the product form and standard behind it. H04 on a strip and H04 on a tube do not describe the same amount of cold work.

Corrosion behaviour

Manganese bronzes and other high-zinc alloys can suffer dezincification in stagnant or hot saline water. Where that risk exists, specify a dezincification-resistant grade or an aluminium bronze. Galvanic coupling matters too: a bronze bushing in a steel or aluminium housing under an electrolyte will drive corrosion of the less noble metal, and the housing material and coating have to be considered alongside the alloy.

8. Solid lubricants: graphite, MoS₂ and PTFE

Where oil or grease cannot be supplied reliably, the lubricant is built into the bearing material. Three mechanisms are used:

• Graphite inserts — plugs of graphite are pressed into drilled holes in a bronze matrix. As the shaft turns, graphite transfers to the contact surface and forms a film. Coverage ratio, plug diameter and hole pattern are design variables; base alloys include CuZn25Al5, CuSn8, C95400 and CuAl10Ni5Fe4. See graphite-plugged bronze bearings.
• MoS₂ (molybdenum disulfide) — a layered solid with low shear strength, used as a coating, as an additive in a polymer matrix, or embedded in a metal matrix. Effective at higher loads than graphite in some conditions; oxidation in air above roughly 400 °C degrades it.
• PTFE — used as a lining on a steel or bronze backing, or as a fibre in a composite. Lowest coefficient of friction of the three, with lower allowable load and a temperature ceiling set by creep. See PTFE composite bearings.

Solid-lubricant bearings change the selection logic: allowable load and speed are set by the lubricant film as much as by the bronze matrix, and the base alloy is chosen for load support, corrosion resistance and machinability rather than for sliding behaviour.