Babbitt Bearing Metals
Babbitt is a soft white metal — tin or lead carrying hard cuboids of SbSn and needles of Cu₆Sn₅ in a ductile matrix — cast as a 1–5 mm lining inside a steel or bronze shell and bored to the shaft. Hardness is only 17–27 HB and compressive yield 25–45 MPa at room temperature, but that softness is the point: the lining conforms to misalignment, embeds grit instead of scoring the journal, and wipes or melts before the shaft is damaged when the oil film fails. ASTM B23 covers the tin-base grades 1, 2 and 3 and the lead-base grades 7, 8, 13 and 15.
Popular babbitt grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| Babbitt Grade 2 (Tin-Base) | 42 | 66 | 7.39 | Excellent | Poor | Turbines, compressors, high-speed journals |
| Babbitt Grade 1 (Tin-Base) | 30 | 66 | 7.34 | Excellent | Poor | Softest tin grade for well-aligned shafts |
| Babbitt Grade 3 (Tin-Base) | 45 | 70 | 7.46 | Excellent | Poor | Heavier loads at lower speed |
| ZSnSb11-6 | 55 | 90 | 7.35 | Excellent | Poor | GB tin-base grade on imported turbines |
| SnSb12Cu6Pb | 60 | 95 | 7.4 | Excellent | Poor | Medium-duty babbitt lining |
| WJ3 | 46 | 80 | 7.4 | Excellent | Poor | Lowest-cost JIS white metal |
| B23 Grade 15 | 45 | 62 | 10.1 | Excellent | Poor | Hardest lead-base babbitt |
Choose babbitt for
Hydrodynamic journal and thrust bearings in steam and gas turbines, generators, large compressors and gearboxes, marine propulsion, paper machines, cement and sugar mills — anywhere a shaft is too large or too critical for rolling bearings, the bearing must tolerate dirt and misalignment, and a failure must be repairable by re-lining rather than replacing the shaft.
Look elsewhere when
Bearing-metal temperature will exceed about 120 °C or unit load exceeds about 7 MPa (a leaded or aluminum bronze such as C93200 or C95400, or a bimetal steel-backed shell), the bearing runs dry or boundary-lubricated (bronze, or a PTFE-lined or oil-impregnated polymer bearing), the shaft is small and fast enough for a rolling bearing, or lead is prohibited — the tin-base grades are lead-free but the lead-base grades are not.
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Babbitt by application
- Turbine and generator bearings
- Babbitt Grade 2 (Tin-Base) spun-cast onto steel shells, 1.5–3 mm thick, with embedded thermocouples in the pad; ZSnSb11-6 or WJ2 when re-lining equipment built to GB or JIS drawings.
- Mill, pump and marine shafts
- ASTM B23 Grade 7 for slow, heavily loaded, dirty service where cost matters; Babbitt Grade 3 (Tin-Base) when the same bearing must also run warm.
- Engine and compressor crankshafts
- ASTM B23 Grade 15 or a thin-wall tin-base lining on a bronze or steel shell — a lining under 0.5 mm carries roughly twice the fatigue load of a 3 mm one.
- Repair and re-babbitting
- Match the original grade from the drawing or a hardness check: Babbitt Grade 2 (Tin-Base) for anything that ran fast and hot, ASTM B23 Grade 7 for slow mill and pump bearings.
Working with babbitt
- Casting and bonding
- The shell is degreased, pickled, fluxed and tinned with pure tin at 280–300 °C, then the babbitt is poured at 400–450 °C for tin-base (350–400 °C for lead-base) either statically or by spinning the shell so the metal freezes from the bond outward. Chill the shell from the back to drive directional solidification; a slow cool gives shrinkage porosity at the bond. Bond integrity is checked by ultrasonic scan and dye penetrant, and the lining is cast 2–3 mm oversize.
- Boring and finishing
- Babbitt machines like a soft, gummy metal: sharp positive-rake carbide or HSS, high speed, light feed, and a fine finishing pass to leave 0.4–0.8 µm Ra. Bore to a diametral clearance of about 0.15 % of shaft diameter for oil-lubricated journals, then cut oil grooves and relief, and blue-check or lightly scrape to the journal. Do not burnish or peen — a smeared surface closes the pores that hold oil.
- Load, speed and temperature
- Tin-base babbitt runs safely to a bearing-metal temperature of about 120 °C with an alarm at 110 °C; compressive yield halves between 20 °C and 100 °C, so the lining thickness and unit load are chosen together. Typical hydrodynamic unit loads are 1.5–3.5 MPa, with 7 MPa the practical ceiling for thin linings. Lead-base grades give up about 15 % strength and 10–20 °C of temperature for lower cost.
- Handling and lead
- Tin-base grades contain no lead and are the choice where the shop or the product must be lead-free; lead-base grades need fume extraction at the pot and dross handling as hazardous waste. Keep the pot below 480 °C and skim dross before pouring — overheated tin-base babbitt oxidizes and loses copper as hard segregates that scratch the journal.
Other solder & low-melting alloy series
Babbitt Bearing Metals — frequently asked
What is babbitt?
Babbitt is a soft white metal — tin or lead carrying hard cuboids of SbSn and needles of Cu₆Sn₅ in a ductile matrix — cast as a 1–5 mm lining inside a steel or bronze shell and bored to the shaft. Hardness is only 17–27 HB and compressive yield 25–45 MPa at room temperature, but that softness is the point: the lining conforms to misalignment, embeds grit instead of scoring the journal, and wipes or melts before the shaft is damaged when the oil film fails. ASTM B23 covers the tin-base grades 1, 2 and 3 and the lead-base grades 7, 8, 13 and 15.
Which grade of babbitt should I use?
Babbitt Grade 2 (Tin-Base) is the default for turbines, compressors and high-speed machinery: about 24 HB, the best fatigue strength of the tin grades and a wide casting window. Babbitt Grade 1 (Tin-Base) is softer and more conformable for lightly loaded, well-aligned journals; Babbitt Grade 3 (Tin-Base) is harder with 8 % copper for heavier unit loads at lower speeds. ASTM B23 Grade 7 is the general lead-base bearing metal for mills, pumps and slow shafts where cost governs, and ASTM B23 Grade 8 is its lower-tin sibling; ASTM B23 Grade 15 is the arsenic-strengthened automotive grade that holds hardness at 100 °C. ZSnSb11-6, ZSnSb8-4 and WJ2 are the Chinese and Japanese tin-base equivalents seen on imported equipment; SnSb12Cu6Pb is the DIN grade.
Which grade of babbitt is the strongest?
SnSb12Cu6Pb has the highest yield strength in the series at 60 MPa; ZSnSb11-6 follows at 55 MPa. Values are for each grade's default condition.
Which grade of babbitt is easiest to machine?
B23 Grade 14 (machinability excellent, 92/100), then Babbitt Grade 3 (Tin-Base) (92/100).
Tin-base or lead-base babbitt?
Tin-base (Babbitt Grade 2 (Tin-Base) and its neighbours) for anything that runs fast, hot or critical: better fatigue strength, better corrosion resistance to acidic oil and a 10–20 °C higher working temperature. Lead-base (ASTM B23 Grade 7 and Grade 8) for slow, heavily loaded, dirty and cost-sensitive service such as mills, pumps and line shafts. Both bond the same way and machine the same way; the drawing should name the ASTM grade.
How thick should the babbitt lining be?
As thin as the shell accuracy allows. Fatigue strength rises steeply as the lining gets thinner — a 0.5 mm lining on a rigid steel shell carries roughly twice the cyclic load of a 3 mm one — but a thin lining cannot embed large particles or absorb misalignment. Turbine pads typically run 1.5–3 mm after boring; large slow mill bearings and re-lined repairs run 3–6 mm because they need the conformability more than the fatigue margin.