Industrial Grease — NLGI Grades, Thickener Types, and Selection (with Compatibility Table)

Grease is the most-used lubricant in a factory — bearings, motors, pumps, gears, joints — yet the most misunderstood. Many plants pick grease by just the "NLGI number" or color, then mix brands → bearings fail early for no obvious reason.

The truth: two NLGI 2 greases can be worlds apart. This article explains NLGI grades, thickener types, and the compatibility rule that prevents bearing failure.

1. NLGI Grade = Stiffness (Not Quality)

The NLGI consistency grade measures grease "stiffness" via ASTM D217 (cone penetration at 25°C), in 9 levels:

NLGI states only stiffness — not the thickener or temperature range, which matter more.

2. Thickener — What Actually Sets the Properties

The thickener is the "structure" that holds the base oil — it sets temperature, water resistance, and load capacity:

Dropping point (ASTM D2265 / ISO 2176) = the temperature at which grease starts to flow as a liquid — the application must stay well below it, not just match the NLGI.

3. The Iron Rule — Compatibility

flowchart TD
  A[Choose grease] --> B[1. Speed+load
-> base oil viscosity]
  A --> C[2. Operating temp
-> thickener + dropping point]
  A --> D[3. Water/moisture
-> Ca-sulfonate if wet]
  A --> E[4. NLGI grade
-> 2 general]
  B --> F{Change brand/
thickener?}
  C --> F
  D --> F
  E --> F
  F -->|Different thickener| G[Purge the old fully
do NOT mix!]
  F -->|Same thickener| H[Top up OK]
  G --> I[Long bearing life]
  H --> I

The most dangerous mistake: mixing different thickeners — e.g., lithium + polyurea. When mixed, the grease structure collapses into a liquid and runs out of the bearing → the bearing loses lubrication → it fails.

Rule: change thickener = purge the old grease completely first; never pump over it.

4. How to Choose (4 Variables)

1. Speed + load → sets base-oil viscosity (fast = light, slow/heavy = heavy)
2. Operating temperature → choose a thickener with a dropping point well above it
3. Water/moisture → wet = calcium sulfonate
4. NLGI grade → 2 general, 1 low temperature, 3 anti-drip/vertical

5. Checklist Before Ordering/Changing Grease

1. Identify the current thickener before switching brands — prevents incompatibility
2. Compare dropping point to operating temperature, not just NLGI
3. Select base-oil viscosity by speed/load
4. Wet work → water-resistant thickener (Ca-sulfonate)
5. Changing thickener = purge old fully — never pump over

We supply industrial grease across all thickeners (lithium, lithium complex, calcium sulfonate, polyurea) and NLGI grades, with guidance on choosing by the real speed/temperature/water of the application and verifying compatibility before a brand change — preventing bearing failures from wrong grease mixing.

Talk to our engineering team to match grease to your machinery — call 02-096-2118 or LINE OA @sahawatt1988.

Summary

• NLGI grade = stiffness only (ASTM D217) — NLGI 2 = the bearing standard
• Thickener sets the real properties — lithium (general), Ca-sulfonate (water/load), polyurea (long life/motors)
• Dropping point (ASTM D2265) gives the temperature range, not NLGI
• Never mix different thickeners — the structure collapses, grease runs out, bearings fail
• Choose by 4 variables: speed/load · temperature · water · NLGI

Right grease + no random mixing = bearings last many times longer, cutting downtime and repair cost.