C932 Bearing Bronze (SAE 660)
Also: C93200, CDA 932, UNS C93200, SAE 660, bearing bronze, high-leaded tin bronze, 83-7-7-3 bronze, Alloy 932, cast bronze bushing stock, QQ-C-390 C932
C932 (SAE 660) is the general-purpose bearing bronze: 7% tin, 7% lead, cast into bar and bushing stock. Machines at 70% of C360 and runs against steel shafts. As cast.
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At a glance
| Density | 8.91 g/cm³ (0.322 lb/in³) |
|---|---|
| Tensile strength | 240-275 MPa (35-40 ksi); ASTM B505 minimum 240 MPa (35 ksi) |
| Yield strength | 140-170 MPa (20-25 ksi) at 0.5% extension; ASTM B505 minimum 140 MPa (20 ksi) |
| Hardness | 60-70 HB (500 kg load) |
| Elongation | 10-20% (minimum 10%) |
| Modulus of elasticity | 100 GPa (14.5 Msi) |
| Thermal | Melts at 855-975 °C (1570-1790 °F); thermal conductivity ~58 W/m·K; electrical conductivity about 12% IACS; expansion ~18 um/m·K; bearing service to about 230 °C (450 °F) |
| Composition | 81-85% Cu, 6.3-7.5% Sn, 6-8% Pb, 1-4% Zn, up to 1% Ni |
Typical values, As continuous cast (M07), ASTM B505; sand castings (M01, ASTM B584) run about 10-15% lower. Confirm against the mill certificate and the purchase spec.
- MachinabilityExcellent
- About 70% of C360: the lead breaks the chip and the alloy cuts dry or with light oil at high speed with excellent finishes. Sharp carbide or HSS, slightly positive rake; bore and ream to size, the lead smears if the tool rubs.
- WeldabilityNot recommended
- Seven percent lead makes it hot-short and porous under the arc; fusion welds crack. Soft solder works, silver brazing is marginal (the lead sweats out). Repair by sleeving, not welding.
- FormabilityPoor
- A cast alloy with 10-20% elongation: it is not bent, drawn or coined. Light press fits and staking are the only cold work it sees. Shapes come from the casting or the lathe.
- Corrosion resistanceGood
- Good in atmosphere, fresh water, mineral oils, greases and most lubricants, and moderate in seawater. Attacked by ammonia, acids and sulfur-bearing oils. The lead limits it to non-potable water and to lubricants without aggressive additives.
C932 is the most stocked bearing bronze in North America, usually called SAE 660. It is a tin bronze with about 7% lead and 3% zinc, cast into solid and cored continuous-cast bar, rectangles and tubes, and into sand and centrifugal castings. The tin gives strength and wear resistance, the lead gives conformability, embeddability and dry-start tolerance, and the zinc makes it pour and machine cleanly. Bushings, sleeve and thrust bearings, wear plates, gears in light service, pump and valve parts and general utility castings are made from it.
As cast it gives about 240-275 MPa (35-40 ksi) tensile, 140-170 MPa (20-25 ksi) yield, 10-20% elongation and 60-70 HB, enough for medium loads at moderate speeds with oil or grease lubrication; typical bearing practice keeps steady loads under about 20-28 MPa (3,000-4,000 psi) with a hardened, ground steel journal. It machines at about 70% of C360 with short, clean chips and holds the tight bores and finishes bushings need. It is not hardenable, not weldable, not formable and not for potable water because of the lead.
Its neighbours are C954 aluminum bronze for heavier loads, shock and slow speeds (three times the strength, no lead, harder on the shaft), C954 or C863 manganese bronze for gears, C836 (85-5-5-5) for plumbing castings, and C89835 or similar lead-free bronzes for water. Plastic and composite bushings (Delrin, PTFE-lined) replace it where lubrication is absent and loads are light.
Heat treatment
None. C932 is used as cast; there is no hardening treatment and no useful anneal. A stress relief at about 260 °C (500 °F) is occasionally specified on heavily machined thin-wall bushings to keep them round. Do not exceed about 230 °C (450 °F) in service; the lead phase softens and the bearing loses load capacity.
Tempers and conditions
- As cast (M07 continuous cast)
- As cast (M01 sand cast)
- As cast (M02 centrifugal cast)
Stock forms
- Continuous-cast solid round bar
- Continuous-cast cored (hollow) bar and tube
- Continuous-cast rectangles and plate
- Sand castings
- Centrifugal castings
- Finished stock bushings and thrust washers
Relative cost
Tier 4 of 5. Continuous-cast bar runs about 1.5-2x C360 brass per pound, and cored bar reduces the machining waste. A stock bushing from a catalog is usually cheaper than machining one for small quantities; custom sizes and long lengths are where a machine shop earns its keep.
Typical applications
- Sleeve bushings and bearings for pumps, gearboxes and machine tools
- Thrust washers and wear plates
- Hydraulic pump and motor components
- Gears and worm wheels in light service
- Valve and pump bodies and guides
- Piston pins and connecting-rod bushings
- General-purpose bronze castings and fittings
Process compatibility
How C932 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | ExcellentExcellent | Bushings, bores and thrust faces machine fast and clean; hold press-fit sizes with reamers or fine boring and keep the lead from smearing. |
| CNC Turning | ExcellentExcellent | Cored bar turns into bushings with minimal waste; buy the cored size closest to the finished bore. |
| Screw Machining | GoodGood | Small bushings and spacers run from solid bar on multi-spindle machines; short chips, high rates. |
| Sand Casting | ExcellentExcellent | Custom bearing housings, gears and valve bodies pour readily; expect 10-15% lower properties than continuous-cast bar and specify ASTM B584. |
| CNC Grinding | FairFair | Bronze loads wheels; grind only when a bore must be under about 5 um (0.0002") tolerance, with open-structure wheels and plenty of coolant. Boring and honing are the norm. |
| Vibratory Finishing | GoodGood | Deburrs machined bushings and washers gently; mild media so the lead does not smear. |
| Plating | FairFair | Rarely plated; the lead complicates adhesion and a bearing surface is left bare. A copper strike before nickel works for cosmetic parts. |
| Welding | Not recommendedNot recommended | Hot-short and porous from the lead; sleeve or replace a worn bearing instead of building it up. |
| Heat Treating | Not recommendedNot recommended | No hardening response; used as cast. For a harder bronze specify C954 (170 HB as cast, 195 HB heat treated). |
| Press Brake Forming | Not recommendedNot recommended | A cast alloy with no useful ductility for bending; shapes come from the casting and the lathe. |
Compare C932
Design and sourcing tips
- Specify "C93200 per ASTM B505, continuous cast" for bar-machined bushings; sand castings (B584) are weaker and should be called out separately.
- Design bushings for a press fit of about 0.001 mm per mm (0.001 in per in) of outside diameter and expect the bore to close by roughly the same amount; finish-bore or ream after pressing when the running clearance matters.
- Run C932 against a hardened, ground steel shaft (at least 300 HB, Ra 0.4 um or better) and provide oil or grease; it tolerates dry starts but not dry running.
- Keep steady bearing pressure below about 20-28 MPa (3,000-4,000 psi) and the temperature under about 230 °C (450 °F); move to C954 for heavier or hotter loads.
- Buy cored bar sized just over the finished bore; solid bar wastes half the material as chips on large bushings.
- Do not use C932 in potable water or food contact because of the lead; specify a lead-free bronze such as C89835 there.
Frequently asked questions
- What is SAE 660 bronze?
- The SAE designation for C93200, the 83% copper, 7% tin, 7% lead, 3% zinc bearing bronze. The two names are used interchangeably on drawings and in catalogs; ASTM B505 is the spec for the continuous-cast bar most bushings are machined from.
- Does C932 bearing bronze contain lead?
- Yes, 6-8%. The lead is what gives it conformability, embeddability and tolerance of marginal lubrication, and it is why it machines so well. It also rules the alloy out for potable water and food contact, where lead-free bronzes such as C89835 or a bismuth-bearing grade are used instead.
- What is the difference between C932 and C954 for bushings?
- C932 is a soft, leaded tin bronze (60-70 HB) that conforms, embeds debris and forgives poor lubrication, for medium loads and moderate speeds. C954 aluminum bronze is three times stronger and much harder (170 HB), for heavy loads, shock and slow speeds, but it demands a hardened shaft, clean oil and good alignment. Start with C932; go to C954 when it wears or deforms.
- Can bearing bronze be welded?
- No. The lead makes C932 hot-short and porous under the arc, and repair welds crack. Worn bearings are sleeved, re-bored to an oversize shaft or replaced. Soft soldering works for non-structural attachment.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM B505 and ASTM B584
- Copper Development Association (CDA) alloy data for C93200
- ASM Handbook, Volume 2 (cast copper alloys) and Volume 18 (friction, lubrication and wear)
- Continuous-cast bronze producer data sheets (National Bronze, Concast Metal Products)
