Leaded Tin Bronze for Plain Bearings and Bushings
Manufacture and application of bronze rings, particularly in machinery and equipment.
Leaded Tin Bronze Bearings and Bushings
Leaded tin bronzes trade a share of strength for a quality that many bearing jobs need more: soft, distributed lead particles that let the lining conform to the shaft, embed dirt, and survive marginal lubrication. This page covers the family used for cast sleeve bearings — C93200, C93700 and C93800 above all — with composition limits, lead levels, duty guidance and the trade-offs that decide between them.
What lead does in a bearing bronze
In a leaded tin bronze, the tin builds the hard Cu–Sn matrix that carries load and resists wear, while lead does not dissolve in the copper matrix at all — it solidifies as discrete globules between the dendrites. Those globules act as a built-in solid lubricant:
- Conformability. Lead-rich areas smear slightly under load, so the lining beds into the shaft geometry instead of running edge-loaded for its whole life.
- Embeddability. Hard debris from dust or wear is pressed into the lead rather than ploughing through the shaft surface.
- Anti-seizure margin. When the oil film breaks down, lead smears across the asperity contacts and delays galling long enough for the machine to be stopped or the film to recover.
The cost is strength and hardness. Every point of lead added is a point of load-bearing matrix removed, which is exactly why the three commercial grades form a ladder: more lead, more forgiving, less load capacity.
The grades in this family
| UNS | Common name | Cross-reference | Nominal Pb | Family position |
|---|---|---|---|---|
| C83600 | Leaded red brass, “85-5-5-5” | SAE 40, EN CC490K (CuSn5Zn5Pb5) | 5% | Entry level; valves and fittings heritage |
| C92200 | Leaded tin bronze, “Nialite” | SAE 622 | 1.5% | Low-lead; moderate loads, good casting behaviour |
| C93200 | High-leaded tin bronze, “85-5-5-5 bearing bronze” | SAE 660, CuSn5Zn5Pb5 (near equivalent) | 7% | The general-purpose bearing bronze |
| C93700 | High-leaded tin bronze | SAE 64, CuSn10Pb10 (near equivalent) | 9.5% | Heavy duty; softer shafts, oscillating motion |
| C93800 | High-leaded tin bronze | SAE 67, CuSn7Pb15 (near equivalent) | 14.5% | Maximum embeddability; lowest loads |
Cross-references to EN designations are near equivalents: composition limits differ between systems, so a drawing naming an EN grade cannot automatically be filled with a UNS grade. Verify limit by limit before substituting.
Composition limits
| UNS | Cu | Sn | Pb | Zn | Fe | P | Ni |
|---|---|---|---|---|---|---|---|
| C83600 | 84.0–86.0 | 4.0–6.0 | 4.0–6.0 | 4.0–6.0 | ≤0.30 | ≤0.05* | ≤1.0 |
| C92200 | 86.0–89.0 | 5.5–6.5 | 1.0–2.0 | 3.0–5.0 | ≤0.25 | ≤0.05* | ≤1.0 |
| C93200 | 81.0–85.0 | 6.3–7.5 | 6.0–8.0 | 2.0–4.0 | ≤0.20 | ≤0.15 | ≤1.0 |
| C93700 | 78.0–82.0 | 9.0–11.0 | 8.0–11.0 | ≤0.50 | ≤0.15 | ≤0.05* | ≤1.0 |
| C93800 | 75.0–79.0 | 6.3–7.5 | 13.0–16.0 | ≤0.50 | ≤0.15 | ≤0.05* | ≤1.0 |
*Where phosphorus is specified as a deoxidiser in sand castings; continuous cast product is typically P-deoxidised at lower residual levels. Single values are maximum limits.
Mechanical properties (continuous cast)
| UNS | Tensile, MPa | Yield (0.5% ext), MPa | Elongation, % | Brinell | Machinability rating* | Density, g/cm³ |
|---|---|---|---|---|---|---|
| C83600 | 255 | 115 | 30 | 75 | 90 | 8.83 |
| C92200 | 240 | 105 | 25 | 70 | 70 | 8.75 |
| C93200 | 240 | 125 | 20 | 65 | 70 | 8.93 |
| C93700 | 240 | 125 | 16 | 60 | 80 | 8.86 |
| C93800 | 210 | 105 | 15 | 55 | 80 | 9.25 |
*Machinability relative to free-cutting brass C36000 = 100. Values are reference minima for the continuous cast condition; sand cast and centrifugal cast product differs.
Density matters when you quote by weight
C93800 at 9.25 g/cm³ is roughly 3.6% heavier than C93200 at 8.93 g/cm³ for the same volume. For a large cast bushing ordered by finished weight, using a generic 8.8 g/cm³ figure for the whole family systematically understates material weight — and therefore cost.
Choosing between C93200, C93700 and C93800
The ladder from C93200 to C93800 is a trade of load capacity for forgiveness. Use these rules of thumb:
- C93200 (SAE 660) — the default. Steady loads to roughly 15–20 MPa on the projected area at moderate speeds with clean oil. Hardened shafts preferred (≥300 HB), but it tolerates softer ones better than most bronzes.
- C93700 (SAE 64) — where the shaft is softer (through-hardened steel below 300 HB, or stainless), where motion is oscillating rather than continuous rotation, and where edge loading is hard to avoid. The extra lead gives a wider anti-seizure margin.
- C93800 (SAE 67) — for dirty environments, infrequent lubrication, or starts-and-stops duty, at reduced loads (roughly up to 10 MPa). It embeds debris and conforms where a stronger lining would score the shaft.
A boundary condition to check before selecting
Leaded tin bronzes are lining materials, not structural ones. When calculated compressive stress on the bearing project area exceeds roughly 20 MPa (or impacts occur), step up to an aluminium bronze or a graphite-plugged bronze instead of climbing the lead ladder — a higher-lead grade will not fix a load problem; it will only defer it.
Lead content and regulatory context
Lead in these alloys is metallic, dispersed and bound in the casting — not a surface coating. Still, the family sits inside tightening regulatory scrutiny of lead:
- Drinking-water contact is the strictest case: low-lead alternatives (C89833 family and similar bismuth/tin alloys) have replaced leaded grades in many plumbing products. Bearings are generally outside that scope, but food-machinery applications should be checked against food-contact requirements case by case.
- RoHS / ELV / end-of-life rules treat copper alloys with lead as exempt for many uses today, with declared lead content. Export documentation may require declaring the Pb percentage — the Table 2 limits are what to cite.
- Worker exposure during machining is a shop-floor matter: standard dust extraction and hygiene practice for lead-containing alloys.
Regulatory orientation only — confirm the current status for your market and application with the applicable authority.
Duty limits and lubrication
| Grade | Load, MPa | Speed, m/s | PV, MPa·m/s | Notes |
|---|---|---|---|---|
| C93200 | 15–20 | up to 5 | 1.0–1.8 | Good grease retention in standard oil-groove patterns |
| C93700 | 15–20 | up to 4 | 1.0–1.6 | Oscillating duty, softer shafts |
| C93800 | 8–12 | up to 3 | 0.7–1.2 | Erratic lubrication, dirty environments |
These envelopes assume boundary lubrication with periodic greasing through a standard groove pattern. Hydrodynamic film conditions raise the permissible values substantially; dry running is not a design condition for this family — if the duty is dry or maintenance-free, move to graphite-plugged bronze or steel-back PTFE composite.
FAQ
- Is C93200 the same as SAE 660?
- C93200 is the UNS number for the alloy standardised as SAE J461 660. In practice “SAE 660 bearing bronze” and C93200 refer to the same composition class. The EN near-equivalent CuSn5Zn5Pb5 (CC491K) has different limit values, so treat them as similar, not identical.
- Which leaded bronze should I use for an intermittently greased bushing in a dusty yard application?
- That is the C93800 profile: low-to-moderate load, contamination, uncertain lubrication. The high lead content embeds grit and bridges dry starts. If loads exceed roughly 12 MPa, redesign the interface or move to graphite-plugged bronze instead.
- Can leaded tin bronze run against a soft (unhardened) shaft?
- C93700 and C93800 are the family members chosen for softer shafts, because their lead content limits shaft scoring. C93200 prefers a hardened shaft but tolerates 250–300 HB. Always check surface finish: a rough shaft will wear any bronze lining quickly.
- Why is C93800 heavier than other bronzes?
- Lead has a density of 11.34 g/cm³, higher than copper. At 13–16% Pb, C93800 reaches about 9.25 g/cm³ versus 8.93 g/cm³ for C93200. Weight-based quotations must use the grade-specific density.
- Are these alloys suitable for food machinery?
- Only after a case-specific review. Lead-containing copper alloys face restrictions in food-contact surfaces under several jurisdictions. Where food contact or wash-down zones are involved, use the low-lead or lead-free alternatives and verify the applicable regulation.
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