There is a growing trend in the replacement of the babbit facing in thrust pad bearings with a composite PTFE surface layer. The PTFE faced bearings have been shown to allow a greater specific pressure, reduce thermal crowning, and in some cases negate the need for an oil-lift (jacking) system. These designs of bearing require new methods for the measurement of oil film thickness both to assist in their development and for plant condition monitoring. In this work, an ultrasonic method of oil film measurement is evaluated for this purpose. An ultrasonic transducer is mounted on the back face of the thrust pad. Pulses are generated and transmitted through the pad material, bonding interlayer, and PTFE surface layer. The proportion of the wave that reflects back from the oil film layer is determined. This is then related to the oil film thickness using a series of calibration experiments and a spring stiffness model. In practice the reflected signal is difficult to distinguish, in the time domain, from other internal reflections from the pad. Signals are compared with reflections when no oil film is present and processing is carried out in the frequency domain.Experiments have been performed on a full size PTFE-faced thrust pad destined for a hydroelectric power station turbine. The instrumented pad was installed in a test facility and subjected to a range of loading conditions both with and without oil lift. Whilst there were some problems with the robustness of the experimental procedure, oil films were successfully measured and used to study the effect of the oil lift system on film formation.
High performance optical metering structures in airborne and space applications need to exhibit dimensional stability in demanding thermal and mechanical environments. Materials for this application should have a low coefficient of thermal expansion, high thermal diffusivity, high specific stiffness and exhibit good ductility. Current materials are limited in one or more of these properties. Common choices are invar, carbonfiber composite, and silicon-carbide. The former has low specific stiffness and thermal diffusivity and the latter choices are brittle materials that require special care and have slow manufacturing processes. In this work, the development of a thermally invariant metal matrix composite will be described along with its incorporation into a high performance optical metering structure. The material is a composite of super-elastic NiTi ribbons and aluminum, where the ribbons are embedded using ultrasonic additive manufacturing. Measurements and modeling of the thermo-elastic response will be presented followed by the design and manufacture of a metering structure. The metering structure design eases integration with an optical bench and lens bezels while leveraging the advantageous properties of this new metal matrix composite.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.