ZCuPb17Sn4Zn4 — 17-4-4 lead bronze in older shorthand, ZQPb17-4-4 on legacy drawings — is a cast copper alloy built around a high lead content. The lead exists as discrete soft particles in a copper-tin-zinc matrix that smear across the bearing surface under load, giving a low-shear film. That makes it forgiving: it tolerates marginal lubrication and embeds grit instead of scoring the shaft. It is also soft, temperature-limited and increasingly constrained by substance rules. This page gives the composition and property ranges we work to, where the alloy fits, and how to enquire.

Reading the designation

The GB numbering is literal: a cast (Z) copper (Cu) alloy carrying roughly 17% lead (Pb), 4% tin (Sn) and 4% zinc (Zn), with copper the remainder. Tin strengthens the matrix; zinc improves castability and lowers cost. Neither changes the character of the alloy, which is set by the lead.

Chemical composition

Element	Content (%)	Note
Lead (Pb)	14.0 – 20.0	Forms the soft lubricating phase
Tin (Sn)	3.5 – 5.0	Strengthens the matrix
Zinc (Zn)	2.0 – 6.0	Castability
Phosphorus (P)	0.05 max	Impurity limit
Aluminium (Al)	0.05 max	Impurity limit
Iron (Fe)	0.4 max	Impurity limit
Silicon (Si)	0.02 max	Impurity limit
Antimony (Sb)	0.3 max	Impurity limit
Total impurities	0.75 max	Combined limit
Copper (Cu)	Remainder	Base metal

Composition follows GB/T 1176 for cast copper alloys. Where a drawing cites an older or proprietary designation we ask for the standard revision before quoting, since trade names in this family are not tied to one fixed analysis. See bronze bearing material standards.

Mechanical and physical properties

Property	Value	Comment
Tensile strength σb	≥ 175 MPa (≥ 25 ksi)	Chosen for conformity, not strength
Elongation δ5	≥ 7%	Enough ductility for press fitting
Brinell hardness	Typically 55 – 70 HB	Tables vary; the inspection report governs
Maximum sliding speed	Confirm against PV	Soft matrix limits heat generation capacity
Practical PV, boundary or dry running	Roughly 0.5 – 1.0 MPa·m/s (14,000 – 29,000 psi·ft/min)	Higher with good lubrication and cooling
Continuous service temperature	Commonly kept below about 200 °C (390 °F)	Lead softens well below its 327 °C (621 °F) melting point
Machinability	Good	Lead gives free cutting and good finish

Why the lead is there

Lead is almost insoluble in solid copper, so as the casting freezes it separates as fine particles through the matrix. Three things follow:

• A low-shear film. Under load, lead at the surface spreads into a thin film on bore and journal. Friction drops and the bearing survives short periods with no external lubricant, which is why leaded bronzes are still specified for machines greased inconsistently.
• Conformability and embeddability. The soft matrix accommodates misalignment and swallows grit rather than driving it into the shaft. Against an aluminium or manganese bronze this is the decisive advantage on equipment with a soft or worn journal.
• Free machining. Lead breaks the chip, which is why this alloy is also used for machined components beyond plain bearings.

Comparison with neighbouring lead bronzes

Alloy	Lead content	Character	Typical pick
ZCuPb17Sn4Zn4 (17-4-4)	14 – 20%	Higher zinc, lower lead; better wear and self-lubricating behaviour than 15-8; harder to cast	Wear-resistant bushings, machinery bearings
ZCuPb15Sn8 (15-8)	13 – 17%	Higher tin, lower zinc; casts more easily, takes higher loads	Heavy bearings with dependable oil supply
ZCuPb30 (30 lead bronze)	≈ 30%	Very high lead; low boundary friction, lowest strength, segregates readily	Light-load and high-speed sleeves
C93200 / C93700 (leaded tin bronze)	≈ 7 – 10%	Higher strength, moderate lead; North American general-purpose grades	General bushings where a UNS grade is required
C89835 bismuth tin bronze	Lead-free	Substitute where lead is restricted	Lead-restricted specifications at moderate load

Against a tin bronze such as C90500, this alloy trades strength for conformability and emergency-running behaviour. See also common bronze bearing materials page.

Casting and machining notes

This alloy has a reputation for difficult foundry behaviour, and it is deserved. Lead is denser than the rest of the melt and barely soluble in it, so it settles while the casting is still liquid — lead segregation, or lead sweat. The result is a lead-rich band with poor properties and a tendency to weep in service.

• Melt and pouring temperatures. Heating to roughly 1,180 – 1,220 °C (2,156 – 2,228 °F) and pouring at 1,150–1,200 °C (2,102–2,192 °F) is the conventional window. Pouring too hot makes segregation worse; pouring too cold risks misruns in thin walls.
• Sand casting is the common route for bushings and blanks. Where the geometry is a plain cylinder, centrifugal casting gives a denser wall and more even lead distribution; we prefer it for thin-walled sleeves.
• Cooling rate matters. Faster solidification keeps lead particles finer and more evenly distributed; use chills on thicker sections.
• Machining is easy. Lead gives free cutting, good finish and long tool life. Sharp tools and modest speeds are enough; the risk is smearing rather than cutting.
• Inspection. Check bore and wall at 20 °C (68 °F) — see reading and measuring of bearing tolerance.

Typical applications

• Plain bearings and bushes in general machinery where lubrication is intermittent
• Machine tool slide and spindle support bushings
• Automotive and agricultural bushings with a soft counterface

Common shapes include straight sleeves, flanged bushings, thrust washers, bushings with countersunk fixing holes and linear bushings. Where the load case points away from a leaded alloy, see C86400 cast bronze bushings.

When not to specify this alloy

• RoHS or similar substance restrictions. The copper-alloy exemption permits up to 4% lead by weight; at 14–20% Pb this alloy sits far outside it. For RoHS compliance a bismuth or silicon bronze substitute is required.
• Potable water contact. Many jurisdictions restrict lead leaching in drinking water; check the local requirement first.
• Elevated temperature. Keep continuous service below roughly 200 °C (390 °F); above that the lead phase loses its supporting role and creep governs.
• High load, high speed or shock. With tensile strength about 175 MPa and hardness under 70 HB, this is not the alloy for heavy or impact loads; use a leaded tin bronze, manganese bronze or aluminium bronze.
• Thin-walled castings. Segregation risk makes very thin or very large sections harder to produce soundly.
• Fully dry, high-PV running. The lead film gives emergency capability, not maintenance-free life; for dry duty above modest PV, use graphite-plugged bearings.

How to request a quotation

Every bushing on this page is made to drawing. There is no web form: enquiries go to the engineering mailbox, which keeps technical questions attached to the drawing.

1. Send the drawing. PDF, DWG or DXF, or a dimensioned sketch with ID, OD, length and any flange or groove detail. A photograph of the worn part with callipers in frame is acceptable.
2. Add the duty. Radial load, speed or oscillation angle and cycle rate, temperature range, and how the bearing is lubricated — or that it runs dry.
3. Add the counterface. Shaft material, hardness and finish. On a soft journal this alloy is often right; on a hardened one we may suggest otherwise.
4. Add the commercial detail. Quantity per order and per year, target delivery, and any certification requirement.
5. Email it to una@viiplus.com. We confirm material availability, flag any specification issue such as a lead restriction, and quote against the drawing. Samples and small batches are accepted; lead time depends on size and casting route.

Machining capability and inspection are covered under machined bronze bushings and CNC machining of bronze.

Frequently asked questions

Is ZCuPb17Sn4Zn4 the same as C93200?

No. C93200 is a UNS leaded tin bronze with roughly 7% lead and about 7% tin, giving considerably higher strength. ZCuPb17Sn4Zn4 has roughly double the lead and less tin, so it is softer and more conformable but carries much less load. They are not drop-in substitutes.

Can it run completely dry?

For short periods at low PV, yes — that is what the lead film is for. As a permanent dry-running solution, no; specify graphite-plugged bronze.

Why do some datasheets show a hardness of 590?

That figure is the value without its decimal point; the intended reading is around 59 HB, consistent with a lead-rich cast bronze. Published tables vary, so the hardness on the inspection report is the figure to work from.

Is the alloy RoHS compliant?

No. The exemption allows up to 4% lead and this alloy contains 14–20%. For lead-restricted applications we supply bismuth or silicon bronze alternatives with comparable behaviour at moderate load.