IDB-LUB-033
Lubrication · oil ISO VG · grease NLGI · regimes
Lubrication & grease guide
Choosing oil or grease for bearings, gears and slides — lubrication regimes, ISO VG and NLGI grades, thickener types, additives, and compatibility with seals and plastics.
Abstract
The right lubricant cuts friction and wear, carries heat away, keeps contaminants out and stops corrosion. Choosing it means matching the lubrication regime, the oil viscosity (ISO VG) or grease consistency (NLGI) and thickener, and the additives — while staying compatible with the seals and plastics it touches.
Section 1 covers how lubricants work and the regimes. Section 2 is oil vs grease. Section 3 is oil viscosity (ISO VG). Section 4 is grease (NLGI and thickeners). Section 5 covers additives and special lubricants. Section 6 is a selection and re-lubrication checklist.
1.How lubricants work — the regimes
A lubricant separates surfaces with a film. How complete that film is defines the lubrication regime (the Stribeck curve), and it drives friction and wear:
| Regime | Film | Friction & wear | Where |
|---|---|---|---|
| Boundary | none — asperities touch | high friction, high wear | start/stop, low speed, high load |
| Mixed | partial film | moderate | transition speeds |
| Elastohydrodynamic (EHL) | thin film in concentrated contacts | low | rolling bearings, gears |
| Hydrodynamic | full film, surfaces separated | lowest friction, ~no wear | journal bearings at speed |
The goal is to run in EHL/hydrodynamic and survive the boundary phase at start-up — which is what anti-wear (AW) and extreme-pressure (EP) additives are for.
2.Oil vs grease
- Grease (≈ oil + thickener + additives) stays in place, seals out contaminants, and needs no circulationideal for sealed-for-life bearings, slow/intermittent motion, and inaccessible points. Limited cooling; can churn at high speed.
- Oil cools and cleans (it carries heat and debris away), suits high speed and high temperature, and is easy to filter and changebut needs a sump, seals or a circulation system.
Default to grease for most rolling bearings and slides; choose oil for high speed, high heat, or where the oil must also cool (gearboxes, engines).
3.Oil viscosity (ISO VG)
Pick viscosity so the film survives at the operating temperature: higher load or temperature → higher VG; higher speed → lower VG (less churning/drag). Industrial oils use ISO VG (cSt at 40 °C):
| ISO VG | Typical use |
|---|---|
| 32 | Hydraulics, high-speed spindles |
| 46 | Hydraulics, general bearings |
| 68 | Bearings, light gearing |
| 100–150 | Gearboxes |
| 220–320 | Heavy / slow gears, worm drives |
(Engine oils use the SAE grades, e.g. 5W-30; the "W" number is cold-flow, the second is hot viscosity.)
4.Grease — NLGI and thickeners
Two choices: consistency (NLGI) and thickener + base-oil.
| NLGI grade | Consistency | Use |
|---|---|---|
| 000 / 00 | fluid / semi-fluid | gearboxes, centralised systems |
| 0 / 1 | soft | low temperature, centralised lube |
| 2 | "normal" | most rolling bearings — the default |
| 3 | stiff | high speed, vertical shafts, sealing |
| 4–6 | block | special applications |
| Thickener | Max temp | Water resistance | Notes |
|---|---|---|---|
| Lithium 12-OH | ~120 °C | good | general-purpose default |
| Lithium complex | ~150 °C | good | higher temp, EP versions |
| Calcium sulfonate | ~150 °C+ | excellent | inherent EP + corrosion protection |
| Polyurea | ~150 °C | good | long-life sealed bearings (e.g. motors) |
| PTFE / PFPE | very high | excellent | chemical / extreme temp; expensive |
| Clay (bentonite) | high (no melt) | moderate | non-melting, but no true dropping point |
Match the base-oil viscosity to the application just like a straight oil — a stiff grease with thin base oil still under-lubricates a slow, heavy contact. And don't mix incompatible thickeners (e.g. lithium with polyurea) — they can soften and run out; purge fully when changing.
5.Additives and special lubricants
- AW (anti-wear) and EP (extreme-pressure)protect during boundary/shock loading (gears, heavily loaded bearings). EP additives can be corrosive to yellow metals (brass/bronze) — check compatibility.
- Corrosion / oxidation inhibitorsextend life and protect idle parts.
- Food-grade (NSF H1)for incidental food contact (food, pharma, packaging machinery).
- Dry-film (PTFE, MoS₂, graphite)where oil/grease can't stay or attracts dirt; vacuum, dusty, or very slow high-load.
- Plastics / elastomer-safemany oils and EP greases attack plastics and swell elastomers; for plastic gears and seals use a verified plastics-compatible grease (often PTFE-thickened, synthetic base). Always check seal/O-ring compatibility (see the O-ring guide).
6.Selection and re-lubrication checklist
- Speedhigh ndm favours oil or NLGI 2/3 with lower base-oil viscosity; low speed favours grease and higher viscosity.
- Load & shockadd AW/EP; raise viscosity/VG.
- Temperaturebase-oil viscosity at temp; thickener max temp and dropping point with margin.
- Environmentwater (calcium sulfonate), dust (sealing grease or dry film), chemical (PFPE).
- Compatibilityseals, elastomers, plastics, and yellow metals (EP).
- Special needsfood-grade (H1), low-noise (filtered greases for quiet bearings).
- Re-lubeset an interval from speed/temp (it falls fast as both rise); don't over-grease sealed bearings (churning, blown seals).