⛽ Foaming characteristics of oils
In short
Determination of the foaming tendency and foam stability of lubricating oils: air is blown through a diffuser in the sample in a graduated cylinder for five minutes, and the foam volume is read at the end of blowing and after ten minutes of settling. The test is performed according to PN-ISO 6247:2009 (Polish version; adopts ISO 6247:1998 [IDT] and Cor 1:1999); Sequences: I — 24 °C; II — 93.5 °C; III — 24 °C after sequence II (clause 4). The procedure comprises 8 steps; it is used for: Lubricating oils — foaming tendency and foam stability at 24 °C and 93.5 °C (clause 4), Evaluating oils for systems with high-speed gearing, high-volume pumping and splash lubrication (ASTM D892), Stored oils in which the dispersion of the foam inhibitor may have changed — option A with mixing before the test (8.5).
At a glance
- Standard: PN-ISO 6247:2009 (Polish version; adopts ISO 6247:1998 [IDT] and Cor 1:1999)
- Category: Petrochemistry
- Procedure steps: 8
- Sequences: I — 24 °C; II — 93.5 °C; III — 24 °C after sequence II (clause 4)
- Bath temperature: test temperature ± 0.5 °C (6.2)
- Air: 94 ± 5 ml/min for 5 min ± 3 s; total 470 ± 25 ml (6.3, 8.2)
Overview
STATUS (as of 30.10.2026). PN-ISO 6247:2009 — Polish version, published 16.12.2009, implements ISO 6247:1998 and its corrigendum ISO 6247:1998/Cor 1:1999 [IDT]; it replaced PN-C-04055:1985. The PKN catalogue card has no withdrawal note — the standard is current; Polish title according to the card: “Przetwory naftowe — Oznaczanie charakterystyk pienienia olejów smarowych”. ISO 6247:1998 is the first edition. The American method on the same subject is ASTM D892.
SIGNIFICANCE (ASTM D892). The tendency of oils to foam can be a serious problem in systems with high-speed gearing, high-volume pumping and splash lubrication — inadequate lubrication, cavitation and overflow loss of lubricant can lead to mechanical failure.
PRINCIPLE (clause 4). The sample at 24 °C is blown with air at a constant rate for 5 min and then allowed to settle for 10 min; the foam volume is measured at the end of each period. The test is repeated on a second portion at 93.5 °C and then, after the foam has collapsed, at 24 °C.
RESULT AND PRECISION (clauses 10–11). The result is reported to the nearest 10 ml as the foaming tendency (foam volume at the end of blowing) or the foam stability (volume at the end of settling), with the sequence number and an indication of whether the sample was tested as received or after mixing according to option A. When the foam does not completely cover the oil and an “eye” of clear oil is visible, the foam volume is reported as zero. Repeatability: r = 15 + 0.33 X for sequence II and r = 10 + 0.22 X for the others (X — mean of the results compared); there are no precision data for option A.
WHAT WE DO NOT GIVE HERE. The available preview of the standard lacks clause 1 and definition 3.1 and the description of the flowmeter and volume meter (6.4–6.5), and the text ends with the repeatability — we do not give the reproducibility or the annexes (diffuser measurement, thermometer requirements). We do not give foaming requirements for particular oils — they are set by the specifications of those oils.
Method principle
In a 1000 ml graduated cylinder immersed in a bath at the test temperature, clean dry air is blown through a diffuser at the bottom at 94 ± 5 ml/min for 5 min. The foam volume is read immediately after the air is stopped (foaming tendency) and after 10 min of settling (foam stability). Sequence I: 190 ml of sample at 24 °C; sequence II: a second portion of 180 ml at 93.5 °C; sequence III: the same portion after collapsing the foam and cooling, again at 24 °C (clauses 4, 8).
Applications
- Lubricating oils — foaming tendency and foam stability at 24 °C and 93.5 °C (clause 4)
- Evaluating oils for systems with high-speed gearing, high-volume pumping and splash lubrication (ASTM D892)
- Stored oils in which the dispersion of the foam inhibitor may have changed — option A with mixing before the test (8.5)
Key parameters
| Parameter | Value |
|---|---|
| Sequences | I — 24 °C; II — 93.5 °C; III — 24 °C after sequence II (clause 4) |
| Bath temperature | test temperature ± 0.5 °C (6.2) |
| Air | 94 ± 5 ml/min for 5 min ± 3 s; total 470 ± 25 ml (6.3, 8.2) |
| Settling | 10 min ± 10 s (8.2) |
| Test portions | 190 ml (sequence I), 180 ml (sequences II and III) (8.2–8.4) |
| Result | foam volume to the nearest 10 ml, with the sequence number (10.1) |
Standard
- Standard number
- PN-ISO 6247:2009 (Polish version; adopts ISO 6247:1998 [IDT] and Cor 1:1999)
- Title (PL)
- Przetwory naftowe — Oznaczanie charakterystyk pienienia olejów smarowych
- Title (EN)
- Petroleum products — Determination of foaming characteristics of lubricating oils
Step-by-step procedure
-
Cleaning the cylinder
The cylinder is rinsed with toluene, then heptane, washed with detergent solution, rinsed in turn with water and acetone and dried in a stream of clean, dry air; water must drain from the walls without forming drops. Thorough cleaning after each use removes traces of additives from the previous test (7.1–7.2).
-
Cleaning the diffuser
The diffuser is washed with toluene and heptane, forcing about 300 ml of solvent through it back and forth at least 5 times; after the last heptane wash the tube and diffuser are dried by blowing clean, dry air, and the tube is wiped; the diffuser is not wiped (7.3).
-
Assembly
The air inlet tube is adjusted so that the diffuser touches the bottom of the cylinder approximately at its centre; the air outlet is connected to the flowmeter through a copper coil in the cold bath, and the apparatus is checked for leaks (7.4).
-
Sample preparation
About 200 ml of sample is poured without shaking into a 600 ml beaker, heated to 49 ± 3 °C and allowed to cool to 24 ± 3 °C. Each step of the test is carried out within 3 h of completing the previous one (8.1).
-
Sequence I
Sample is poured into the cylinder up to the 190 ml mark and the cylinder is immersed in the 24 °C bath at least to the 900 ml mark. When the oil has reached the bath temperature, the stopper with the diffuser is inserted and the diffuser is left to soak for about 5 min; then the flow is set to 94 ml/min and air is passed for 5 min ± 3 s, counted from the first bubbles. The foam volume (total volume minus liquid volume) is read immediately; the total air volume is 470 ± 25 ml. After 10 min ± 10 s of settling, the foam volume is read to the nearest 10 ml (8.2).
-
Sequence II
A second portion is poured into a clean cylinder up to the 180 ml mark and immersed in the 93.5 °C bath; when the oil reaches 93 ± 1 °C, a clean diffuser is inserted and the procedure of sequence I is followed (8.3).
-
Sequence III
The foam remaining after sequence II is collapsed by stirring, the sample is cooled below 43.5 °C at room temperature, then placed in the 24 °C bath and, once at temperature, tested as in sequence I with a clean diffuser (8.4).
-
Result
The foaming tendency and foam stability are reported to the nearest 10 ml, with the sequence number and information on option A; when the foam does not completely cover the oil surface, the foam volume is reported as zero (clause 10).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| 1000 ml graduated cylinder | graduated in 10 ml intervals; distance from the bottom to the 1000 ml mark 335–385 mm; circular top (6.1.1) | — |
| Stopper | rubber or other suitable material, with a central hole for the air inlet tube and an off-centre hole for the air outlet tube (6.1.2) | — |
| Diffuser | spherical, of fused alumina, 25.4 mm in diameter, or cylindrical, of sintered porous stainless steel (porosity 5 µm); maximum pore diameter 80 µm, permeability 3000–6000 ml/min — measured according to Annex A (6.1.3) | — |
| Thermostatic baths | allowing immersion of the cylinder at least to the 900 ml mark, maintaining the temperature ± 0.5 °C, transparent; the 93.5 °C bath should be placed in a clear container able to hold the liquid if the cylinder breaks (6.2) | — |
| Air supply | 94 ± 5 ml/min through the diffuser; the air passes through a 300 mm drying column (cotton, desiccant, moisture indicator) (6.3) | — |
| Timer and temperature sensor | timer accurate to 1 s; temperature sensor according to Annex B or an equivalent calibrated sensor (6.6–6.7) | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Heptane | 142-82-5 | for cleaning the cylinder and the diffuser (5.1, 7.2–7.3) |
| Toluene | 108-88-3 | for cleaning the cylinder and the diffuser (5.2, 7.2–7.3) |
| Acetone | 67-64-1 | for rinsing the cylinder after water (5.3, 7.2) |
| Propan-2-ol | 67-63-0 | reagent from the list in the standard (5.4) |
| Non-ionic, water-soluble detergent | — | for cleaning the cylinder (5.5, 7.2) |
| Butyl phthalate | — | for the flowmeter, if needed (5.6) |
Health and safety (OHS)
- The 93.5 °C bath should be placed in a clear container able to hold the liquid if the cylinder breaks (6.2, Note 5)
- Toluene, heptane and acetone are flammable — according to their safety data sheets
- Hot oil and the 93.5 °C bath are a burn hazard
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-ISO 6247:2009 (Polish version; adopts ISO 6247:1998 [IDT] and Cor 1:1999) — “Petroleum products — Determination of foaming characteristics of lubricating oils”.
How does this method work?
In a 1000 ml graduated cylinder immersed in a bath at the test temperature, clean dry air is blown through a diffuser at the bottom at 94 ± 5 ml/min for 5 min. The foam volume is read immediately after the air is stopped (foaming tendency) and after 10 min of settling (foam stability).
What is the measuring range and accuracy?
Sequences: I — 24 °C; II — 93.5 °C; III — 24 °C after sequence II (clause 4); Bath temperature: test temperature ± 0.5 °C (6.2); Air: 94 ± 5 ml/min for 5 min ± 3 s; total 470 ± 25 ml (6.3, 8.2); Settling: 10 min ± 10 s (8.2).
How long does the test take?
The procedure comprises 8 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
1000 ml graduated cylinder, Stopper, Diffuser, Thermostatic baths, Air supply, Timer and temperature sensor.
Where is this test used?
Lubricating oils — foaming tendency and foam stability at 24 °C and 93.5 °C (clause 4); Evaluating oils for systems with high-speed gearing, high-volume pumping and splash lubrication (ASTM D892); Stored oils in which the dispersion of the foam inhibitor may have changed — option A with mixing before the test (8.5).
What safety precautions apply?
The 93.5 °C bath should be placed in a clear container able to hold the liquid if the cylinder breaks (6.2, Note 5); Toluene, heptane and acetone are flammable — according to their safety data sheets; Hot oil and the 93.5 °C bath are a burn hazard.
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-ISO 6247.