⛽ Penetration of lubricating greases

Petrochemistry PN-EN ISO 2137

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

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.

   ⏱ Time: 5 min

2. Worker filling (P60)

   Fill worker container with grease, avoiding air bubbles. Insert perforated plate.

   ⏱ Time: 5 min

3. Grease working

   Perform 60 double strokes of worker at rate approx. 1 stroke/s. For P0 skip this step.

   ⏱ Time: 2 min • 🌡 Temperature: 25°C

4. Penetration cup filling

   Transfer worked grease to penetration cup. Level surface with spatula, avoiding air bubbles.

   ⏱ Time: 3 min

5. Thermostating

   Place cup with grease in water bath 25 ± 0.5°C. Thermostat minimum 1 hour (or until reaching 25°C throughout mass).

   ⏱ Time: 60 min • 🌡 Temperature: 25°C

6. Penetrometer setting

   Place cup under penetrometer. Lower cone until tip touches grease surface. Zero the scale.

   ⏱ Time: 2 min

7. Penetration execution

   Release cone and simultaneously start stopwatch. After exactly 5 seconds, lock cone. Read penetration depth.

   ⏱ Time: 5 s • 🌡 Temperature: 25°C

8. Measurement repetition

   Perform minimum 3 penetrations at different cup locations (distance min. 10 mm). Calculate average.

   ⏱ Time: 5 min

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

Reagents, media and consumables

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

Frequently asked questions