Carl E. Snyder

Characterization of Model Perfluoropolyalkylethers by Miniaturized Thermal Oxidative Techniques—Part I: Modified Oxidation-Corrosion Test

The metal catalyzed thermal oxidative stability of commercially available and model perfluoropolyalkylether (PFPAE) fluids was investigated by oxidation corrosion tests. Using model PFPAE fluids, prepared via direct fluorination of hydrocarbon analogues, a wider variety of specific molecular structures were available for study than previously available from more conventional PFPAE chemistry synthesis procedures. Because of a limited supply of the model fluids, a miniaturized oxidation corrosion test, using only 6 ml of fluid, was devised. This test, conducted at constant temperatures, was compared to a similar test using 20 ml of fluid on the more abundant commercial fluids and then extended to the model fluids. Details of the miniaturized test procedure and apparatus are presented. Also presented are the chemical structure-thermal oxidative stability relationships of the fluids as derived from this study. The destabilizing effect of an -OCF 2 - group is confirmed and other more subtle effects are noted.

Hydraulic System Component Storage with Military Hydraulic Fluids

In the military aerospace community, most hydraulic fluid pumps and components are currently being stored in rust inhibited fluids containing barium dinonylnaphthalene sulfonate (BSN). Fluids containing barium are hazardous waste after use, with expensive disposal, and have caused operational problems in aircraft hydraulic systems including helicopters and fighter aircraft. In this program, bearings and pistons were stored in jars containing both operational hydraulic fluids (MIL-PRF-83282, MIL-PRF-87257, and MIL-PRF-5606) and rust-inhibited hydraulic fluids containing BSN (MIL-PRF-46170 and MIL-PRF-6083). In addition, hydraulic pumps were filled with MIL-PRF-83282, MIL-PRF-87257, and MIL-PRF-46170. Hydraulic pumps were not filled with MIL-PRF-5606 or MIL-PRF-6083 because these hydraulic fluids are being phased out of military aerospace applications as operational and storage fluids, respectively. Jars, containing bearings and pistons, as well as hydraulic pumps, were stored for up to three years in a laboratory environment to determine if operational fluids would protect them from rusting during storage. After each year, the bearings, pistons, and pumps were inspected for corrosion. At the end of three years of storage, pumps were endurance tested using fresh operational fluid, MIL-PRF-83282. The bearings, pistons, and pumps showed no rusting for the duration of storage with either operational or storage fluids. The pumps stored with the operational fluids, MIL-PRF-83282 and MIL-PRF-87257, were in better condition than the pump stored with the rust-inhibited fluid. The operational hydraulic fluids, MIL-PRF-83282 and MIL-PRF-87257, provided excellent protection against rusting during storage. Manuscript contributed February 1, 2005 Review led by Paul Bessette

Behavior of perfluoropolyalkylethers under simulated dynamic bearing conditions

Perfluoropolyalkylether (PFPAE) fluids are of interest to the United States Air Force as potential high temperature liquid lubricants in gas turbine engines. PFPAE fluids have desirable thermal and oxidative stability, and favorable temperature/viscosity characteristics. However, their performance depends on the specific base fluids, additives, bearing material used as well as contact conditions and environments. Screening tests using a modified ball‐on‐rod type rolling contact fatigue (RCF) tester were conducted to study the effects of the above variables and lubricant circulation on fatigue life, wear and performance of PFPAE. Post test lubricant samples were analyzed for changes in physical and chemical properties. Traditional testing for viscosity, acid number and weight changes was performed. Fluid degradation was studied using Fourier transform infrared spectroscopy (FTIR), gas chromatography with atomic emission detector (GC‐AED) and supercritical fluid chromatography (SFC). Elemental analysis of the deposits formed at the tribocontact were determined by Auger electron spectroscopy (AES).

Effects of Contamination on Aerospace Hydraulic Component and System Performance

Most papers concerning hydraulic systems contamination cover primarily the adverse effects of particulate contamination on hydraulic component and system performance. While that is a valid concern, the effects of other contaminants can also be serious. This paper concentrates on the adverse effects of water, free air, and chemical contaminants on military aerospace hydraulic component and systems performance. The hydraulic fluids used in the military aerospace systems are both the mineral oil-based MIL-PRF-5606 [1] and the synthetic hydrocarbon-based fire resistant hydraulic fluids MIL-PRF-83282 [2], and MIL-PRF-87257 [3]. Examples will be provided where each of the contaminants were responsible for some adverse effect and the recommended solution for the problems will be provided. Some of the problems encountered were stuck valves, spongy controls, “burnt” hydraulic fluid, and erratic actuator performance. The methodology used to identify the source of the problem will be presented. Based on the problems found, limits for these contaminants were recommended and, when followed, solved the problems for the aircraft involved. The major significance of this paper is to enlighten the aerospace hydraulic system community to the potential problems caused by contamination other than particulate contamination and to suggest solutions for these problems.