⛽ Penetration of lubricating greases
Determination of consistency (hardness) of lubricating greases by cone penetration method. Measurement of penetration depth of standard cone under its own weight.
Overview
Cone penetration is the basic method for assessing the consistency (hardness) of lubricating greases and technical petrolatum. The penetration result serves to classify grease according to the NLGI (National Lubricating Grease Institute) system into 9 consistency classes — from class 000 (semi-fluid) to class 6 (very hard block). NLGI classification is the universal language for describing grease consistency worldwide.
The method involves measuring the depth of penetration (in tenths of a millimeter) of a standard metal cone of specified mass (102.5 g or 9.38 g for reduced cones) into a grease sample during 5 seconds at 25°C. The deeper the penetration, the softer the grease. The standard distinguishes unworked grease penetration (P0), grease penetration after working for 60 double strokes in a grease worker (P60), and penetration of grease worked longer.
NLGI classes and P60 penetration ranges: 000 (445–475), 00 (400–430), 0 (355–385), 1 (310–340), 2 (265–295), 3 (220–250), 4 (175–205), 5 (130–160), 6 (85–115). The most commonly used in automotive and industry is NLGI class 2 (P60 = 265–295 × 0.1 mm).
Grease penetration is a key parameter in selecting grease for specific applications — too soft grease flows out of the bearing, too hard grease does not deliver lubricant to the friction zone. Test results are required in all grease technical data sheets (TDS) and form the basis for quality control in grease production.
Method principle
A grease sample is placed in a standard container (cup) with diameter 77 mm and depth 58 mm. For worked penetration (P60), the grease is previously worked for 60 double strokes in a grease worker. The container with grease is thermostated to 25°C, then placed under the penetrometer. A standard metal cone (30° angle, mass 102.5 g including shaft) is positioned so its tip touches the grease surface. The cone is released and after 5 seconds from release, the penetration depth is read on the penetrometer scale with 0.1 mm accuracy (1 penetration unit = 0.1 mm).
Applications
- Classification of greases according to NLGI system (classes 000–6)
- Quality control in lubricating grease production
- Testing mechanical stability of greases (P0 vs P60 vs P100000)
- Selection of greases for specific applications (bearings, gears, screws)
- Acceptance control of greases in automotive and aviation industry
- Testing temperature effect on grease consistency
- Monitoring aging and degradation of greases in service
Key parameters
| Parameter | Value |
|---|---|
| Result unit | × 0.1 mm (e.g., 265 = 26.5 mm) |
| Cone mass with shaft | 102.5 g (full cone) |
| Penetration time | 5 ± 0.1 s |
| Test temperature | 25 ± 0.5°C |
| NLGI 2 (typical) | P60 = 265–295 × 0.1 mm |
| Repeatability | ±4 penetration units (full cone) |
Standard
- Standard number
- PN-EN ISO 2137:2020
- Title (PL)
- Przetwory naftowe i srodki smarowe — Oznaczanie penetracji stozkowej smarow plastycznych i wazeliny
- Title (EN)
- Petroleum products and lubricants — Determination of cone penetration of lubricating greases and petrolatum
Step-by-step procedure
1. Sample preparation
Thoroughly mix grease in original container. Avoid aeration. Take representative sample.
2. Worker filling (P60)
Fill worker container with grease, avoiding air bubbles. Insert perforated plate.
3. Grease working
Perform 60 double strokes of worker at rate approx. 1 stroke/s. For P0 skip this step.
4. Penetration cup filling
Transfer worked grease to penetration cup. Level surface with spatula, avoiding air bubbles.
5. Thermostating
Place cup with grease in water bath 25 ± 0.5°C. Thermostat minimum 1 hour (or until reaching 25°C throughout mass).
6. Penetrometer setting
Place cup under penetrometer. Lower cone until tip touches grease surface. Zero the scale.
7. Penetration execution
Release cone and simultaneously start stopwatch. After exactly 5 seconds, lock cone. Read penetration depth.
8. Measurement repetition
Perform minimum 3 penetrations at different cup locations (distance min. 10 mm). Calculate average.
9. Result calculation
Result = average of minimum 3 measurements, expressed in units × 0.1 mm. Assign NLGI class based on table.
10. Equipment cleaning
Clean cone, shaft and containers with white spirit, then toluene. Dry and store in protective packaging.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Laboratory penetrometer | Anton Paar PNR 500, Koehler K95500, Normalab NPM 440 | 15,000–50,000 PLN |
| Penetration cone (full) | Steel cone 30°, mass 102.5 g with shaft, per ISO 2137 | 1,000–3,000 PLN |
| Half / quarter cone | For small samples — mass 9.38 g (half), 2.34 g (quarter) | 800–2,000 PLN |
| Grease worker | Koehler K19500, container + perforated plate, manual or automatic | 5,000–15,000 PLN |
| Thermostatic bath | Julabo CORIO CD-200F, for thermostating grease containers (25°C) | 5,000–12,000 PLN |
| Grease container (cup) | ISO 2137 penetration cup (d = 77 mm, h = 58 mm), stainless steel | 300–800 PLN |
| Laboratory thermometer | Pt100 or liquid-in-glass thermometer 0–50°C, accuracy 0.5°C | 200–1,000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| White spirit / naphtha | 8032-32-4 | For cleaning cone, shaft and containers after testing |
| Toluene | 108-88-3 | Solvent for removing resinous grease residues |
| NLGI reference grease | — | Grease with certified penetration, for penetrometer verification |
Health and safety (OHS)
- Penetration cone — sharp tip, risk of injury during manipulation
- White spirit — flammable, work under fume hood
- Toluene — toxic by inhalation, use respiratory protection
- Protective gloves when handling grease (skin irritation)
- Safety glasses and laboratory coat mandatory