⛽ Dropping point of greases

Petrochemistry PN-ISO 2176

Overview

Dropping point is the temperature at which a lubricating grease liquefies sufficiently that the first drop falls from the test cup under test conditions. It is one of the most important parameters characterizing thermal resistance of grease and serves as one of the criteria for classifying greases according to thickener type.

Different thickener types give greases different dropping points: calcium (Ca) greases — approx. 80–100°C, sodium (Na) greases — approx. 150–180°C, lithium (Li) greases — approx. 180–200°C, lithium complex (Li-complex) greases — approx. 250–280°C, polyurea greases — over 300°C. Dropping point does NOT mean maximum grease operating temperature — the upper limit of operating temperature is significantly lower (usually by 30–60°C).

The ISO 2176 method uses a classic apparatus with a test cup having an opening in the bottom, test tube, and heating bath. Grease fills the cup, and the entire assembly is slowly heated. The temperature at which the first drop of grease falls through the cup opening is recorded as the dropping point.

The result has great practical significance — grease whose dropping point is too close to operating temperature may "leak out" of the bearing, leading to mechanical damage. The standard forms the basis for grease specifications in automotive, steel, paper, and food industries.

CORRECTION OF THE DESIGNATION (23.09.2026): THIS ENTRY GAVE A STANDARD THAT DOES NOT EXIST. It read "PN-EN ISO 2176:1995" here, whereas the PKN catalogue card knows the document without the EN element and with a different year: **PN-ISO 2176:2011**, Polish version, published 15-07-2011, 11 pages, KT 222/PK 3 for Lubricants, implements ISO 2176:1995 [IDT] together with the corrigendum ISO 2176:1995/Cor 1:2001 [IDT], supersedes PN-C-04139:1984 — Polish version. The year 1995, which stood in the previous wording, is the year of the INTERNATIONAL document, not of the Polish standard; the Polish one appeared sixteen years later. The card has the "Superseded by" and "Date of withdrawal" fields empty, so the document is in force.

THE SCALE OF CITATIONS AND PROOF THAT THE PREVIOUS DESIGNATION WAS DEAD. In the accreditation scopes (read on 23.09.2026) the string "PN-EN ISO 2176" does not occur EVEN ONCE — the "Laboratories" tab at this entry showed zero. After the key was corrected to "PN-ISO 2176", matching by the beginning of the string gives 3 entries at 3 laboratories, and all forms with the core 2176 — 4 entries at 4 laboratories. AN ANCHOR IS NECESSARY HERE, and this is a warning of greater weight than the number itself: the string "2176" without a boundary on the left gives 36 entries at 27 laboratories, because it also catches PN-EN 12176 and PN-ISO 12176 — A COMPLETELY DIFFERENT standard, on the determination of the pH of sewage sludge, present in 32 entries at 23 laboratories. A core without an anchor would therefore inflate the count ninefold here. The shorter the number of the standard, the more dangerous a core without a boundary — with four-digit numbers one must always anchor. The same measurement on a second, independent copy of the scope database gave the same figures. The distribution is instructive: two laboratories write "PN-ISO 2176:2011+A1:2021-07", i.e. with the amendment sheet from 2021, one "PN-ISO 2176" without a date, one "PN-EN 50326:2003 PN-ISO 2176:2011" (two designations in one value), and one cites the international document directly — "ISO 2176:1995+AC1:2001+ Amd1:2020". The predecessor PN-C-04139 does not occur in the scopes even once.

Method principle

The test grease is placed in a small test cup (nipple) with a bottom opening of approximately 2.8 mm diameter. The cup is mounted in a test tube, and the entire assembly is placed in a heating bath (metal block or liquid). The assembly is heated at a constant rate of approximately 1–2°C/min. A thermometer placed inside the cup records the grease temperature. When the grease liquefies sufficiently that the first drop falls through the cup opening, the thermometer temperature is read — this is the dropping point. The result is corrected for deviation of heating rate from nominal value.

Applications

• Classification of lubricating greases according to thickener type
• Selection of grease for high-temperature applications (bearings, furnaces, dryers)
• Quality control in grease production — specification parameter
• Comparison of thermal resistance of different grease formulations
• Testing thermal stability of greases after long storage
• Automotive specifications (e.g., DIN 51825 classification KP, K, KPF)

Key parameters

Standard

Standard number

PN-ISO 2176:2011 + A1:2021-07 (wersja polska; wprowadza ISO 2176:1995 [IDT] oraz ISO 2176:1995/Cor 1:2001 [IDT])

Title (PL)

Przetwory naftowe — Smar plastyczny — Oznaczanie temperatury kroplenia

Title (EN)

Petroleum products — Lubricating grease — Determination of dropping point

Step-by-step procedure

1. Test cup preparation

   Wash cup with white spirit and acetone. Dry. Check bottom opening patency (d = 2.8 mm).

   ⏱ Time: 5 min

2. Cup filling with grease

   Fill cup with grease using spatula. Remove air bubbles. Grease should reach cup edge but not cover opening from outside.

   ⏱ Time: 5 min

3. Thermometer mounting

   Insert thermometer into cup with grease so bulb is approx. 2 mm above bottom opening. Do not touch walls.

   ⏱ Time: 2 min

4. Apparatus mounting

   Place cup with thermometer in test tube. Mount entire assembly in heating bath. Set second thermometer for bath temperature measurement.

   ⏱ Time: 3 min

5. Preliminary heating

   Start heating at constant rate. When temperature reaches approx. 30°C below expected dropping point, reduce heating rate to 1–2°C/min.

   ⏱ Time: 20–60 min

6. Observation

   Observe opening in cup bottom. Note temperature at which grease begins to deform. Continue heating.

   ⏱ Time: 10–30 min

7. Dropping point reading

   Record thermometer temperature at moment when first drop of grease falls from cup opening into test tube. This is the dropping point.

   ⏱ Time: 1 min

8. Determination repetition

   Perform second determination with new sample. Difference between two results should not exceed repeatability value (±5°C).

9. Cleaning

   After cooling, wash cups, test tubes and thermometers with white spirit and acetone.

   ⏱ Time: 10 min

10. Result reporting

    Report result as average of two determinations, rounded to 1°C. Include information about grease type and expected thermal class.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Hot bath and cups — temperature up to 300°C, risk of burns, use thermal gloves
• White spirit — flammable, work away from ignition sources
• Toluene — toxic (respiratory tract), work under fume hood
• Mercury thermometers — risk of mercury contamination if broken, use mercury-free thermometers
• Safety glasses and laboratory coat required

Frequently asked questions