AGMA 9005

Gear oil viscosity for an industrial gearbox

The grade on an enclosed industrial gearbox is the viscosity that still carries the tooth load at the temperature the oil actually reaches, without giving the heat and the churning loss back. AGMA 9005-F16 is the general method when the OEM plate does not already name the oil.

This page is the pitch-line-velocity approach in steps. The numerical chart in AGMA 9005 is copyrighted and is not reproduced here. Open the standard, or follow the gearbox manual, for the grade the chart would name.

Pitch-line velocity

Pitch-line velocity is the speed of the tooth at the pitch circle. Both members of a gearset share it.

v (m/s) = π × d × n / 60,000

d is the pitch diameter in millimetres and n is the speed in revolutions per minute. A 200 mm pitch diameter at 600 rpm is 6.28 m/s. In inch units, v (ft/min) = π × d × n / 12 with d in inches. For a set, use either member. Geometry for the diameter and the ratio is the work of gearcalculators.com, and the gear practice behind it is Evolvent Design.

The method, without the chart

1. Name the gear type. Spur, helical, and bevel use one family of recommendations in AGMA 9005-F16. A cylindrical wormgear uses another, because the contact slides. Worm oils are on the worm gear page.
2. Calculate pitch-line velocity at the mesh you care about.
3. Use the bulk oil temperature in service. A splash-lubricated box often runs well above the room. Ambient temperature is the wrong input.
4. Take those two inputs into AGMA 9005-F16. The shape of the recommendation is physical: higher pitch-line velocity, lower viscosity grade, because a thick oil at speed churns and heats; higher oil temperature, higher viscosity grade, because the oil in the mesh has to stay thick enough after it has thinned.
5. Read the candidate oil at 40°C and 100°C and put those points in the converter. The ISO VG name is the 40°C grade. The film depends on the viscosity at the bulk temperature you used in step 3.
6. Follow the OEM lubricant specification when one exists. AGMA 9005 is the general method for the gearbox whose plate has gone missing.

Orientation while you go get the standard

These bands are shop orientation for a conversation. They are not the AGMA 9005 chart, and they are not a substitute for the nameplate.

• Slow, heavily loaded enclosed gears, on the order of a couple of metres per second, often end up at ISO VG 460 to 1000 once the sump is hot.
• General enclosed industrial reducers in the middle of the speed range are commonly ISO VG 150 to 320.
• High-speed sets, up around 15 m/s and beyond, are commonly ISO VG 68 to 150, particularly when the oil is circulated and cooled.

Splash lubrication has to live with the oil it is throwing. Forced circulation can run a lower grade because the oil is directed and can be cooled. A grade that foams or overheats in splash service is sometimes the wrong viscosity, and sometimes a circulation problem. The ISO VG chart and the pages for 220, 320, and 460 show how far a named grade moves between 40°C and 100°C.

Oil comparisons across brands live on oilviscositychart.com.

Get a lubricant recommendation for your gearbox

Send the gearbox type, the oil temperature it actually runs at, and what is in it now. A gear engineer at Evolvent Design can point you at a viscosity grade. The form is not live yet: it posts to a placeholder address in the site config, and nothing is stored.

Company website

Name Work email Company Gearbox type Select Spur or helical Bevel Worm Planetary Not sure Bulk oil temperature (°C) Pitch-line velocity or speed Current oil What the gearbox is doing

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Questions

Should I pick the ISO VG by the ambient temperature?

Pick it by the bulk oil temperature in service and by the pitch-line velocity. Ambient temperature matters because it pushes the sump temperature, and because the oil has to be movable at a cold start. The film in the mesh is the hot number.

Do I add EP additive just by going up a grade?

No. The viscosity grade and the additive system are separate specifications. AGMA 9005 distinguishes inhibited (R&O) oils, extreme-pressure oils, and compounded oils. The gear type and the OEM decide which family, and the viscosity selection decides the grade inside it.