Oil-mist and air-oil for rolling bearings
Pure oil-mist (reclassified) or metered air-oil for a rolling bearing. Airflow follows Alemite’s bore × rows factors. Oil rate, reclassifier holes, chock vent area, κ and mistability are separate results. A high κ does not clear a delivery problem.
Timken’s unheated band near VG 100 is 0.4–0.6. 0.50 is the example midpoint, not a VG 320 guarantee.
Speed
Strip or line speed and roll barrel diameter estimate shaft RPM assuming no slip. Barrel diameter is not the bearing bore.
Air-oil metering
Oil consumption is dose × cycles/hour × points. Carrier air is separate. Do not apply d×rows/14 as a certified air-oil oil rate. Timken cites about 0.2–0.3 bar in the chock.
Oil at 40 °C and cup temperature
This is not the cup temperature. Mist and air-oil remove almost no heat, so the cup can run far hotter.
Chock vents (clear area, not pipe callout)
A mill blueprint may show 1-1/4 in inlet couplings (Snap-Tite plain nipple) and 1-1/2 in vent elbows. Those callouts are not the 0.067 in reclassifier orifice, and an elbow or mist collector can cut the clear area. Enter measured minimum clear ID only.
Startup sump and wet-mill checks
No ASTM D1401 minute limit is attributed to the Timken rolling-mill text. Positive purge does not by itself remove water risk.
Assumptions & sources
- Alemite rolling-element oil mist: BI = d(in) × rows; moderate BI/40, heavy BI/20, mill BI/14. Lip-seal points use one moderate row at the seal diameter.
- Reclassifier table is Alemite 2018 at 20 in H₂O for a 0.067 in × 1.38 in spray fitting (0.30 SCFM per hole). 0.30 × holes is a preliminary count; the fitting table is preferred. Square-root pressure scaling is not used.
- Vent rule: clear vent area ≥ 2 × total reclassifier hole area (Timken Rolling Mill Catalog). Header velocity guidance is about 5 m/s (15–20 ft/s), not above 24 ft/s.
- κ uses ISO 281 ν₁ (branch at 1000 RPM, same as Minimum Viscosity) and this site’s ASTM D341 / D2270 fit. κ ≥ 4 full-film target, 1 ≤ κ < 4 mixed, κ < 1 boundary (EP such as Timken OK load ≥ 35 lb may be required). κ is not a measured film thickness.
- LubriMist Model EXP (about 0.65 in³/h/SCFM and 0.018 in³/h per BI) is a different system and is not mixed into the Alemite factors.
- This is an engineering screen, not an approved mill lubrication design.
How this calculator works
Oil-mist air demand for a rolling bearing is Alemite’s bearing inch: bore in inches times the number of rows. Moderate service divides by 40, heavy or continuous thrust by 20, and a rolling-mill work or backup roll by 14. Each specifically purged lip seal adds its own diameter divided by 40. Oil volume is that standard airflow times an editable mist concentration. The default 0.50 in³/h per SCFM is the midpoint of Timken’s 0.4–0.6 band for unheated oil near VG 100, and 34 in × 4 rows / 14 at that midpoint is about 80 cm³/h.
Reclassifier holes use the published Alemite spray-nozzle table at 20 in of water, about 0.30 SCFM for one 0.067 in hole. Chock vents must keep at least twice the total hole area clear so backpressure does not collapse the pressure drop across the nozzle. Viscosity ratio κ is computed at the temperature you enter and at hotter cup temperatures, because mist oil does not carry the heat away.
Inputs explained
Bore, not outside diameter, is the Alemite D. Rows come from the multi-row sidecar when a mill assembly is loaded. Service class is chosen explicitly; a mill design pre-selects the /14 factor and does not infer it from RPM. Seal count is not guessed from the row count.
Air-oil mode asks for injector dose, cycles per hour, points and carrier air. It does not pretend the mist formula is an air-oil oil rate. Cup temperature and header temperature are different questions: one is the film, the other is whether the oil stays a mist in a cold header.
Worked example
L289400 is a 4-row tapered assembly, 59.0551 × 75.3937 × 43.5039 in. Mill class, no seals, 0.50 in³/h per SCFM: 16.87 SCFM and about 138 cm³/h (3.32 L/day). At 20 RPM on nominal VG 320 / VI 100, ν at 110 °F is about 263 cSt and κ is about 2.90 (mixed film). At 5 RPM, κ drops below 1. The same oil at 100 RPM meets the κ ≥ 4 target at 110 °F and still carries the high-viscosity mist caution. Three or four single 0.067 in holes (0.9–1.2 SCFM) do not feed 16.87 SCFM.
Frequently asked questions
What airflow does a rolling-element oil-mist bearing need?
Alemite’s rolling-element factors use SCFM = bore in inches times rows divided by 40 for moderate service, by 20 for heavy or continuous thrust, and by 14 for rolling-mill work and backup rolls. Each lip-seal purge point adds seal diameter divided by 40 SCFM. Those factors are not an air-oil injector oil rate.
Why can kappa look fine while the mist still fails?
Kappa is oil viscosity at the cup temperature divided by the ISO 281 required viscosity. Oil-mist and air-oil remove almost no heat, so a roll-neck cup can run much hotter than the chock skin or the external coolant. A separate card judges atomization, header fallout and the reclassifier. A high kappa does not pass that card.
How many reclassifier holes does a large chock need?
At 20 inches of water, Alemite’s 0.067 inch by 1.38 inch spray fitting passes about 0.30 SCFM per hole. Three or four single-hole fittings pass only 0.9 to 1.2 SCFM. A large backup-roll chock needs many holes, usually multi-hole nozzles at the cups, and clear vent area at least twice the total hole area. Nominal pipe size is not the orifice.
When should I switch from pure oil-mist to air-oil?
Above about 460 cSt at 40 °C, Timken’s cited roll-neck pure oil-mist scope no longer applies. Air-oil meters liquid droplets in carrier air and does not use the mist d times rows over 14 factor as the oil rate. Enter the supplier dose, cycles per hour and lube points. Specialist heated mist systems exist only with explicit vendor engineering.