If I understand correctly the foaming tendency of oil (as measured using ASTM D892) is due to seperation of dissolved air in the oil. Is this correct?
Is there some analytical relationship between foaming tendency and solubility?

I can say that foaming gets worse the higher that additive leveal. heat and water contamination also impact foaming
bruce

Shishir,

Foaming tendency for new oils are mainly done on hydraulic, gear and turbine oils. For used oils, it is normally used to confirm that there is a foaming problem ie a persistant foam. But it needs to be used in conjunction with other analysis such as ICP, FTIR, TAN, water to determine the overall condition of the oil and possible cause of foaming ie contamination.

Most of the foaming problems I have come across is due to dirt ingression and water contamination. Components running hot combined with dirt ingression can also cause the oil to foam.

However, if the ISO VG grade of the oil is much higher than what the OEM intended or conditions determine, then the oil can foam as well due to cavitation of pumps. The component also runs hot under such conditions. Sometimes in these cases, the foam test will show everything is within specification.

I think the foaming tendency test is normally used to confirm if it is an oil problem (ie contamination or oil condition) or system/mechanical induced foam. So it needs to be used with other analytical techniques including checking the component running conditions and OEM requirements.

Hi,Shishir,

High and low oil level also leads forming in the system.

Thanks alot Mr. Menon, for your reply. I could not understand your reply completely, do you mean that in a closed container :
1) If oil is completely filled than it would have lower foaming tendency (when pressure gradient is introduced)
2) If oil is partially filled (say 3/4th ) than it would have higher foaming tendency
3) If oil is still less filled (say half) than it would have still higher foaming tendency

Dear Mr.Shishir,

In some cases, foaming is not a concern. But in many cases, it is very serious and can leads to lubrication failure and then premature failure of the machines. Mainly, there are two reasons for foam generation in the system. One is oil related and other is mechanical problem. Mechanical problem means. Over agitation, low oil level, excessive aeration and air detrainment problem etc….

Oil manufacturing companies are supposed to incorporate their oil with antifoam agents like silicone fluids and some polymers, which will retard the stable foam formation in the system during machine operation. All these are suicidal type of additives and will deplete slowly while doing its duty.

Your oil must have good air releasing property and good foam resistive property. Surface tension also has some effect on this.

The antifoam additive must not be dissolved in the oil; rather it must be in the dispersed small droplets form in the oil.

Thanks Alot Mr. Menon, for your elaborate reply. It gives me a good understanding of the phenomenon of solubility w.r.t. my application.

yes, don't confuse foaming with air release.....