CuSn5Zn5Pb2-C Bronze Bushing
CuSn5Zn5Pb2-C Bronze Bushing
Self-lubricating bronze bearings are engineered for applications where external lubrication is impractical. Solid lubricants are compressed and molded directly into the bearing to guarantee a maintenance-free product. No additional lubrication is necessary.
CuSn5Zn5Pb2-C Bronze Bushings (CC499K)
CuSn5Zn5Pb2-C is the cast leaded gunmetal known by its EN material number CC499K — roughly 5% tin, 5% zinc, 2% lead, balance copper. It is the general-purpose gunmetal for cast bushings, pump and valve parts, and marine fittings where lubrication is available. This page is the specification reference: composition, mechanical properties by casting process, bearing limits, and where the grade does and does not belong.
Two things this grade is regularly misunderstood on. First, the -C in the designation does not mean carbon — it marks the composition as a cast product in the EN system, and the alloy contains no carbon as an alloying element. Second, CC499K is not a self-lubricating alloy: the lead improves emergency running and machining but the bearing needs a supplied film of oil or grease. Dry running requires graphite plugs.
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What CuSn5Zn5Pb2-C Is
CuSn5Zn5Pb2-C is a cast copper–tin–zinc–lead alloy, defined in EN 1982 and identified by the material number CC499K. It sits in the gunmetal group — the copper alloys that carry zinc and lead alongside the tin, and which have been the default casting material for pumps, valves, marine hardware and general engineering bushings for over a century.
The name reads straight off the chemistry — roughly 5% tin, 5% zinc, 2% lead, balance copper. Against the familiar 85-5-5-5 gunmetal (CC491K) it carries less lead, so it is slightly stronger and less prone to smearing under load. Against the high-tin bearing bronzes such as CuSn11Pb2-C it is softer and more ductile, with better castability and better machinability.
What the grade is chosen for is castability, pressure tightness and machinability. It fills thin sections, casts sound, passes a pressure test, and machines at a rating well above the unleaded bronzes. Where a bushing is large, cast to shape and runs oil-lubricated at moderate load, CC499K is usually the economical choice.
Chemical Composition — EN 1982 / CC499K
The limits below are those for CC499K in cast product form. Copper is the balance, and the minor elements are maximum limits rather than target additions. Values vary between editions of the standard and between foundries, so the certificate for your order governs.
| Element | Range | Role in the alloy |
|---|---|---|
| Copper (Cu) | 84.0 – 88.0 | Matrix. Carries thermal and electrical conductivity. |
| Tin (Sn) | 4.0 – 6.0 | Principal strengthener. Raises hardness, wear resistance and seawater corrosion resistance. |
| Zinc (Zn) | 4.0 – 6.0 | Deoxidiser and cheapener. Improves fluidity and casting soundness. |
| Lead (Pb) | 1.0 – 3.0 | Insoluble soft particles. Free machining, embeddability, emergency running. |
| Nickel (Ni) | ≤ 2.0 | Grain refiner. Adds strength and corrosion resistance. |
| Phosphorus (P) | ≤ 0.10 | Residual deoxidiser. Above a trace it embrittles the casting. |
| Iron (Fe) | ≤ 0.30 | Residual; controlled to avoid hard inclusions that damage the shaft. |
| Antimony (Sb) | ≤ 0.25 | Residual. |
| Sulphur (S) | ≤ 0.10 | Residual; kept low to avoid hot shortness. |
| Aluminium (Al) | ≤ 0.01 | Kept at trace level — it forms hard oxides and hurts casting soundness. |
| Silicon (Si) | ≤ 0.01 | Kept at trace level for the same reason. |
Mechanical Properties by Casting Process
EN 1982 lists minimum properties against the casting route, because the cooling rate changes the grain structure and therefore the strength. Continuously cast and centrifugally cast stock cools faster and comes out finer-grained and stronger than sand-cast material of the same composition.
| Casting process | EN suffix | Tensile Rm, min | 0.2% proof Rp0.2, min | Elongation A, min | Brinell HBW, min |
|---|---|---|---|---|---|
| Sand casting | GS | 200 MPa | 90 MPa | 13 % | 55 |
| Continuous casting | GC | 250 MPa | 110 MPa | 13 % | 65 |
| Centrifugal casting | GZ | 250 MPa | 110 MPa | 13 % | 65 |
These are minimums. Measured values on production stock normally sit above them — centrifugal and continuous cast bar commonly returns 250–320 MPa tensile with 70–90 HBW — but the exact figure depends on section thickness, which is the variable most often overlooked. A thick section cools slowly and will not reach the properties a thin test bar does. If a design is strength-critical, tell us the ruling section and we will quote against it rather than against a table.
Physical and Thermal Properties
| Property | Typical value | Why it matters in a bearing |
|---|---|---|
| Density | 8.8 g/cm³ | Mass of a cast part; relevant to rotating balance. |
| Solidification range | ≈ 855 – 1010 °C | Wide freezing range — the reason the alloy feeds well in thin sections. |
| Thermal conductivity | ≈ 70 W/m·K | Carries frictional heat out of the contact. Roughly a third of steel’s figure. |
| Electrical conductivity | ≈ 12 % IACS | Only relevant where the part also carries current. |
| Thermal expansion, 20–300 °C | 18 ×10−6 /K | Roughly half as much again as steel — dominates hot running clearance. |
| Elastic modulus | ≈ 100 GPa | About half of steel. Governs press-fit and housing calculations. |
| Continuous service ceiling | ≈ 200 – 230 °C | Set by the lead phase, not the copper matrix. |
The temperature ceiling catches people out. Lead melts at 327 °C, and long before that it softens and smears out of the matrix. A lead-free bronze would be sound at 400 °C but is not interchangeable with CC499K on a hot duty — above roughly 230 °C continuous, move to a lead-free alloy.
Reading the Designation: -C, CC499K, GS / GC / GZ
EN designations carry four pieces of information, and all four affect what you actually receive. Taking EN 1982 – CuSn5Zn5Pb2-C-GZ as the full form:
- CuSn5Zn5Pb2 — the chemistry. Copper with roughly 5% tin, 5% zinc and 2% lead.
- -C — the product form. In the EN copper system, -C marks a cast composition and -W a wrought one. It has nothing to do with carbon.
- CC499K — the material number. CC is the copper-casting block; the 49x series is the CuSnZnPb gunmetal group. This number is independent of the casting process, so it is the safest way to name the material on a drawing.
- -GZ — the process suffix. GS sand cast, GC continuous cast, GZ centrifugal cast.
Two practical consequences. If a drawing says only “CuSn5Zn5Pb2-C” with no process suffix, the properties in Table 2 are undefined — you have named a composition, not a quality level. And if a specification quotes “CuSn5Zn5Pb2 with 0.2% carbon”, the carbon is not part of this alloy and should be queried before manufacture.
What Each Alloying Element Does
The gunmetal composition is a compromise between four requirements; each element is there for a specific reason rather than by tradition.
Tin — strength and corrosion
Tin dissolves in the copper and strengthens it, and it is what gives the alloy its resistance to seawater and brine. More tin means higher hardness and better wear resistance but lower ductility and a wider freezing range, which makes casting harder. At 4–6% the alloy casts reliably and still has useful strength.
Zinc — soundness and cost
Zinc deoxidises the melt, which is what makes gunmetal castings pressure-tight rather than porous, and improves fluidity so thin sections fill. It is also cheaper than tin. Below about 15% the alloy is not susceptible to dezincification.
Lead — machinability and emergency running
Lead is almost insoluble in copper and sits as fine discrete particles through the structure. Those particles break chips as the tool cuts — which is why gunmetal machines freely — and they smear under local pressure, letting the bearing survive a momentary loss of oil film. They also absorb grit rather than letting it score the shaft. The cost is real: lead lowers strength and ductility and sets the temperature ceiling.
Nickel and phosphorus — residuals with an effect
Nickel up to 2% refines the grain and adds strength and corrosion resistance, and is sometimes a deliberate addition. Phosphorus is a leftover from deoxidation; a trace is harmless but excess makes the casting brittle, which is why it is capped at 0.10%.
How CC499K Compares with the Alternatives
| CC499K | CC491K | CuSn11Pb2-C | C93200 (SAE 660) | |
|---|---|---|---|---|
| EN / UNS | CuSn5Zn5Pb2-C | CuSn5Zn5Pb5-C | CuSn11Pb2-C | C93200 |
| Tin, % | 4 – 6 | 4 – 6 | 10 – 11.5 | 6.3 – 7.5 |
| Zinc, % | 4 – 6 | 4 – 6 | ≤ 0.5 | 1 – 4 |
| Lead, % | 1 – 3 | 4 – 6 | 1 – 2.5 | 6 – 8 |
| Tensile, MPa (typ.) | 250 – 320 | 200 – 260 | 260 – 320 | 240 – 290 |
| Machinability | Good | Very good | Moderate | Very good |
| Embeddability | Moderate | Good | Low | Good |
| Pressure tightness | Very good | Good | Very good | Moderate |
| Load capacity | Moderate | Moderate | High | Moderate |
| Usual choice for | General cast bushings, pump and valve parts | Fittings, low-pressure valve bodies | Heavily loaded bearings, worm wheels | General US-specification bushings |
When to Specify CC499K — and When Not To
Where it fits
- Cast bushings and sleeves running on oil or grease at moderate load and speed.
- Pump and valve components where pressure tightness and castability matter more than peak strength.
- Marine hardware in seawater or brackish service.
- Large or irregular parts where casting to shape costs less than machining from bar.
- Parts that need a lot of machining — the lead pays for itself in tool life and cycle time.
Where it does not
- Dry running. Use a graphite-plugged bronze instead; the base alloy should then be chosen for strength, not for bearing properties.
- High PV or heavy shock. Move to CuSn11Pb2-C, C95500 nickel aluminium bronze, or manganese bronze C86300.
- Sustained temperature above about 230 °C. The lead phase governs; use a lead-free alloy.
- Potable water contact. Restricted in several markets — see below.
- Thin-wall, high-volume bushes. A wrapped CuSn8 strip bushing is cheaper and dimensionally better; see wrapped bronze bushings.
Casting and Machining Notes
Three routes are available. Continuous cast bar and tube is the most economical start for a bushing: sound, fine-grained and close to size, so machining allowance is small. Centrifugal casting gives the densest grain and suits larger diameters and hollows carrying real load. Sand casting suits one-offs, large parts and shapes that cannot be spun.
Machinability is good, in the region of 60–70 on the C36000 = 100 scale, and the lead gives short broken chips rather than the stringy swarf the unleaded bronzes produce. Three points are worth passing to the shop: the first cut on a casting has to get under the cast skin or tool wear rises sharply; thin-walled parts need full-length support, since a sleeve gripped in three jaws goes out of round when released; and lead-bearing swarf should be collected separately.
Lubrication, PV Limits and Solid-Lubricant Variants
CC499K needs a supplied film. The lead gives it better behaviour under a momentary loss of oil than a lead-free alloy, which is useful in equipment started cold or run intermittently — but that is emergency running, not self-lubrication. Sizing figures for continuous oil or grease lubrication are typically:
| Parameter | Oil or grease lubricated | Graphite plugged, dry |
|---|---|---|
| PV, continuous | 1.6 – 2.2 MPa·m/s | 1.0 – 1.4 MPa·m/s |
| PV, short peaks | up to ≈ 2.6 MPa·m/s | up to ≈ 1.8 MPa·m/s |
| Max sliding speed | 2.0 – 2.5 m/s | 1.0 – 1.5 m/s |
| Max static pressure | 50 – 70 MPa | 50 – 70 MPa |
A 50 mm bore × 50 mm long bushing carries 20 kN radial load at 150 rpm.
Option A — 50 mm long. Projected area = 2,500 mm², so P = 20,000 / 2,500 = 8.0 MPa. V = π × 50 × 150 / 60,000 = 0.39 m/s. PV = 3.14 MPa·m/s — above the 2.2 ceiling, so it would run hot.
Option B — 80 mm long. Area = 4,000 mm², so P = 5.0 MPa; V is unchanged. PV = 1.97 MPa·m/s — inside the band, though without much margin.
Reading the result. Nothing about the alloy changed — the bearing just got longer. Because the limit is thermal, adding area is usually cheaper than upgrading to a higher-tin bronze. If 80 mm will not fit, the next moves are better heat removal or a change of grade.
Where dry running is required, we plug the bush with graphite and the limit comes from the plug coverage and grade rather than the base alloy. See graphite bronze bushings, and groove patterns for the lubricated case.
Typical Applications
Pumps and valves
Shaft sleeves, gland bushes, stem bushes and wear rings. Pressure tightness, castability and corrosion resistance in water are why this family has dominated pump and valve work. The zinc keeps castings sound enough to pass a pressure test without impregnation.
Marine and offshore
Rudder and pintle bushes, deck machinery, seawater pump sleeves and general shipboard hardware. Gunmetal resists seawater and biofouling better than the plain tin bronzes and tolerates the intermittent motion of deck equipment. See sliding bearings for marine and offshore.
General engineering
Gearbox bushes, linkage pivots, conveyor and packaging bearings, and cast wear parts. Where load is moderate and lubrication real, CC499K gives long service at lower cost than the high-tin bronzes.
Hydraulic and water control
Cylinder gland bushes, gate and valve bushings, and hydro-mechanical pivots. For parts in contact with raw water, note the potable-water restriction below.
Agriculture and construction equipment
Pivot bushes on implements, linkages and slow oscillating joints, where shock loading combines with dust and long idle periods. Where the part cannot be regreased, a graphite-plugged variant is the usual answer.
