⛽ Dropping point of greases
In short
Determination of temperature at which lubricating grease passes from semi-solid to liquid state and first drop falls from test cup. The test is performed according to PN-EN ISO 2176:1995; Measurement range: 60–300°C (depending on apparatus). The procedure comprises 10 steps (about 56 min–1 h 56 min in total); it is used for: 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.
At a glance
- Standard: PN-EN ISO 2176:1995
- Category: Petrochemistry
- Procedure steps: 10
- Total time of stages: 56 min–1 h 56 min
- Measurement range: 60–300°C (depending on apparatus)
- Heating rate: 1–2°C/min (near dropping point)
- Lithium grease (typical): 180–200°C
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.
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
| Parameter | Value |
|---|---|
| Measurement range | 60–300°C (depending on apparatus) |
| Heating rate | 1–2°C/min (near dropping point) |
| Lithium grease (typical) | 180–200°C |
| Li-complex grease | 250–280°C |
| Repeatability | ±5°C |
| Reproducibility | ±12°C |
Standard
- Standard number
- PN-EN ISO 2176:1995
- Title (PL)
- Przetwory naftowe — Smar plastyczny — Oznaczanie temperatury kroplenia
- Title (EN)
- Petroleum products — Lubricating grease — Determination of dropping point
Step-by-step procedure
-
Test cup preparation
Wash cup with white spirit and acetone. Dry. Check bottom opening patency (d = 2.8 mm).
-
Cup filling with grease
Fill cup with grease using spatula. Remove air bubbles. Grease should reach cup edge but not cover opening from outside.
-
Thermometer mounting
Insert thermometer into cup with grease so bulb is approx. 2 mm above bottom opening. Do not touch walls.
-
Apparatus mounting
Place cup with thermometer in test tube. Mount entire assembly in heating bath. Set second thermometer for bath temperature measurement.
-
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.
-
Observation
Observe opening in cup bottom. Note temperature at which grease begins to deform. Continue heating.
-
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.
-
Determination repetition
Perform second determination with new sample. Difference between two results should not exceed repeatability value (±5°C).
-
Cleaning
After cooling, wash cups, test tubes and thermometers with white spirit and acetone.
-
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
| Equipment | Example | Indicative price |
|---|---|---|
| Dropping point apparatus | Mettler Toledo DP70, Anton Paar PetroTest, Lin-Tech DP211 | 15,000–40,000 PLN |
| Test cups (nipple) | Metal cup with opening d = 2.8 mm, disposable or reusable | 200–600 PLN / 50 pcs |
| Glass test tubes | Test tubes for apparatus per ISO 2176 (d = 27 mm) | 50–150 PLN / 10 pcs |
| Thermometers (2 pcs) | Test tube thermometer and bath thermometer, range 0–400°C | 200–800 PLN / pc |
| Heating bath / heating block | Aluminum block with PID controller (included with apparatus) | included with apparatus |
| Spatula / knife for filling | Steel spatula for filling cup with grease | 20–50 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| White spirit | 8032-32-4 | For cleaning test cups and apparatus from grease residues |
| Acetone | 67-64-1 | For final rinsing and quick drying of cups |
| Toluene | 108-88-3 | Solvent for removing difficult grease residues |
| Reference grease | — | Grease with certified dropping point for apparatus validation |
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
Which standard describes this test?
The test is performed according to PN-EN ISO 2176:1995 — “Petroleum products — Lubricating grease — Determination of dropping point”.
How does this method work?
The test grease is placed in a small test cup (nipple) with a bottom opening of approximately 2.8 mm diameter.
What is the measuring range and accuracy?
Measurement range: 60–300°C (depending on apparatus); Heating rate: 1–2°C/min (near dropping point); Lithium grease (typical): 180–200°C; Li-complex grease: 250–280°C.
How long does the test take?
The times given for the individual stages add up to approximately 56 min–1 h 56 min. The procedure comprises 10 steps.
What equipment is required?
Dropping point apparatus, Test cups (nipple), Glass test tubes, Thermometers (2 pcs), Heating bath / heating block, Spatula / knife for filling. Indicative cost of the core instrument (Dropping point apparatus): 15,000–40,000 PLN.
Where is this test used?
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).
What safety precautions apply?
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.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 2176.