The Foam test measures a lubricant's foaming tendency and stability.
According to the Foam test the tendency of oils to foam can be a serious problem in systems such as high-speed gearing, high-volume pumping, and splash lubrication. Inadequate lubrication, cavitation, and overflow loss of lubricant can lead to mechanical failure. This test evaluates oils for such operating conditions.
Foaming is a fundamental physical property of a lubricating fluid. Foam can degrade the fluid’s life and performance as well as that of the equipment being lubricated. Even though foam performance often is a defined specification for the new fluid, it’s often ignored on used fluid. You need to understand the reasons for loss in foam control and the methods of controlling this property in a used fluid.
Air is forced through a diffuser within a portion of oil creating foam. After 5 minutes of blowing, the amount of foam is recorded. Then, the sample is observed for the clearing of generated foam. Then either time of full dissipation is recorded or amount of foam remaining after 10 minutes.
Foaming tendency results are reported as a series of values, starting with the volume of foam (in ml) after 5 minutes of blowing air through the oil, followed by the volume of foam (in ml) after 10 minutes without air. The time (in seconds) until total foam dispersion is also reported.
For example: 20/0 (120) means 20 milliliters of foam tendency was measured after 5 minutes of aeration followed by no foam stability (0 ml) after the 10 minute settling time, and it took only 120 seconds to reach total foam dispersion. Most new oil specifications require 10 to 50 milliliters tendency maximum and 0 milliliters stability.
The tendency of lubricants to foam can cause serious issues in systems with high-speed operations. Not only can foam cause inadequate lubrication but also other problems such as overflowing reservoirs.