Behavior of Silicone Antifoam Additives in Synthetic Ester Lubricants

Abstract

The behavior of silicone (polydimethylsiloxane, PDMS) antifoamants as a function of PDMS viscosity in non-foaming and foaming synthetic ester turbine engine lubricants or model esters is described. Ten parts-per-million additions of PDMS with viscosities in the excess of about 5000 mm²s⁻¹ (cSt) are very effective antifoamants. At intermediate PDMS viscosities of 10-5000 mm²s⁻¹, the additive is profoamanl. At very low PDMS viscosities of less than about 10 mm²s⁻¹, the additive appears to be ineffectual either as pro- or antifoamant under the test conditions. The results provide a more complete understanding of additive-ester foaming behavior resulting in the development of a hypothesis for such partially miscible systems based upon the limited solubility of PDMS in esters and that effect on surface tension as influenced by variables such as PDMS molecular weight, concentration, and temperature. The hypothesis aids in explaining much of the previous, often conflicting, data and conclusions about foaming in such systems.

Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Diego, California, October 19–21, 1992

Notes

Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Diego, California, October 19–21, 1992