Determination of Polymeric Sealing Principles Atul Rana Tribology Section, Imperial College of Science, Technology & Medicine Supervisor : Dr Ritchie Sayles Sponsors : Smiths Aerospace Actuation Systems TISPP UK Ltd. (Dowty Seals) Department of Trade & Industry

Introduction n Airplane Controls/Landing Gear controlled by a system of Hydraulic Linear Motion Actuator Assemblies n Leakage problems on runways etc. not understood. n An experimental study on the Tribology of Reciprocating seals in actuators n Study to back up a previous theoretical study of the same project. Determination of Polymeric Sealing Principles

The Reciprocating Seal (O-ring)

n Extreme Temperature conditions (-54C to +135C), difficult to achieve in test conditions n Severe Oil Pressure Loading conditions (35MPa Oil Pressure System) n Seal Behavior completely different at extreme conditions n Little research been done for such seals especially under these extreme conditions Determination of Polymeric Sealing Principles The Problems

n Surface roughness of contacting surfaces (elastomer and steel rods) n Static Contact Conditions n Friction Characteristics n Film Thickness n Contact Area Mapping n Leakage Determination of Polymeric Sealing Principles Parameters to Study

n To study the Tribology of the problem under realistic conditions using a seal specific rig n Supporting the theoretical model to study leakage under controlled conditions n Explain the behavior of the real seals in aerospace applications Determination of Polymeric Sealing Principles Objectives

n CVJ rig modified to model seal behavior n Contact observed visually through a microscope and Video equipment. n Dynamics of seal observed n Friction Tests carried out on seal with surfaces of varying roughness Preliminary Experimental Rig Determination of Polymeric Sealing Principles

n Nature of Static Dry Line contact, asperities in contact seen. n Unlubricated dynamic behavior shows nature of deflections n Lubricated seal shows some evidence of cavitation in the line contact region n Friction is fairly independent of stroking speed (for the machine’s speed range) n Friction depends on the roughness of the reciprocating surface Determination of Polymeric Sealing Principles Observations so far

n Image unclear in lubricated conditions n No Computer image capturing device being used n Clamping pressure and hence loads are small n Processing of available images difficult due to complexity of images n A method of successfully measuring film thickness not yet established Problems with Experiments Determination of Polymeric Sealing Principles

Preliminary Rig Arrangement Determination of Polymeric Sealing Principles Clamped Seal Direction of motion Computer Force transducer Data logger Sliding plate Microscope, light and camera Motor and gears Weight

Friction Measurements from Reciprocating Rig (Slider Roughness and Stroke Speed varied) Determination of Polymeric Sealing Principles

Images of Contact - “Footprint” Determination of Polymeric Sealing Principles Wet Conditions - Dark Spots represent contact Dry Conditions