Wear debris in aerospace hydraulic fluid systems (Buna-N rubber particulates)

Abstract

The various sources of O-ring and bearing wear debris in aerospace hydraulic fluid systems are reviewed. The control of these particulates is discussed. Emphasis is placed on dynamic Buna-N (butadiene-acrylonitrile copolymer) rubber O-rings as generators of objectionable black elastomeric, carbon black, and light-colored polycrystalline bloom and fillers, as solid contaminants. Experimental results are presented which show that the range of the starting or static friction is 0.178-0.274. Kinetic coefficients of friction (ƒ) varied from 0.022-0.175. The data reveal that for anodized and bare T-6 aluminum surfaces (17–67 r.m.s. μin.) from 252,000–500,00 O-ring particles of less than 100 μ/100 ml of petroleum hydraulic fluid are produced by 5,000 strokes. It is concluded that further explorations and exploitation of other O-ring materials and improved metal surfaces as demonstrated, will be beneficial in accomplishing substantial reductions in the counts of particulates in the fluids. A maximum of 24,000 particles of 5–10 micronic sizes is considered as a generally desirable goal. These data should be of interest to the designers of missile hydraulic guidance systems, and those charged with the important responsibility of establishing the limiting cleanliness requirements of the fluids in these systems.