M.S.

Deep groove and angular con tact 25 and 30 mm bore ball bearings were tested to high speeds using air-oil mist lubrication. Test conditions included cooling air flow rates of 1.5, 3.0, and 6.0 scfm (0.05, 0.10, and 0.20 kg/min), thrust loads of 50, 75, and 100 lb (222, 334, and 445 N), and a constant radial load of 25 lb (111 N). Steady-state bearing outer race temperature was recorded at various speeds under each set of test conditions. Maximum ON values of 1.9 x 10⁶, 1.5 x 10⁶, 1.4 x 10⁶, and 1.26 x 10⁶ were achieved on the 30 mm deep groove, the 25 mm deep groove, the 25 mm angular contact, and the 30 mm angular contact bearings, respectively. Tests were usually terminated when the stabilized outer race temperature reached approximately 200°F (366 K) although the 30 mm deep groove bearing was operated to 240°F (389 K). A cooling air flow rate of 1.5 scfm (0.05 kg/min) was judged not adequate for high speed bearing operation under the tested conditions. An outer-race temperature prediction equation, based on a regression analysis of the test results, is presented for each test bearing. / M.S.

Advanced ceramic materials have found many new applications in the automotive and other industries. To satisfy demands of higher temperatures and inert surfaces, new lubrication methods for these ceramics need explored and evaluated. This thesis focuses on a boundary lubrication method termed tribopolymerization -- the formation of polymers at the tribological interphase. The research evaluated new high-temperature classes of anti-wear additives. The work involved experiments on steel and alumina material pairs with a pin-on-disk tribometer used to explore the anti-wear capabilities of selected additives in the liquid phase at concentrations of 1% by weight in hexadecane. New additives included aromatic compounds with various pendant groups adding the design functionality necessary for in-situ polymerization. The amino, hydroxyl, acid, and ester functional groups underwent studies across several aromatic molecular compositions while new heterocyclic additives, in particular the readily available lactams, underwent exploratory tests as a new class under the tribopolymerization design approach. In concentrations of 1%, additives showed significant wear reductions of up to 99.9 %. Anti-wear behavior persisted in select cases at concentrations as low as 0.1% by weight. Compounds from two new classes demonstrated anti-wear behavior at 6x the frictional heat generation of standard exploratory conditions. This surprising effect partially filled a void in the effective range of operating conditions between 0.25 m/s, 40 N and 1.0 m/s, 160 N. Earlier work by Tritt found a complete absence of anti-wear behavior for the previous additive classes at the high-speed conditions. In addition, several individual compounds constituent to an A-R-A + B-R'-B condensation polymerization reaction demonstrated significant anti-wear behavior when used alone. In particular, the compound BTDA from DuPont's Kapton® exhibited higher wear reductions than any other new additive. These findings support tribopolymerization as an effective approach to boundary lubricant design. Low wear was often associated with an attached reaction debris layer. This finding is consistent with previous work involving tribopolymerization anti-wear additives with ceramics. Further research into the roles of the debris layer and tribochemistry will help in understanding the complex anti-wear behavior of these new high-temperature additive classes. / Master of Science

Electric charges are often found in naturally or artificially formed droplets, such as raindrops and those generated by Kelvin's water dropper. In contrast to the impact of neutral droplets on a flat solid surface upon which a thin convex lens shape layer of the gas film is typically formed, I show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets both experimentally and numerically. As the charge level is raised above a critical level of about 1% of the Rayleigh limit for representative impact conditions, the Maxwell stress overcomes the gas pressure buildup to deform the droplet bottom surface. A conical liquid tip forms and pierces Through the gas film, leading to a circular contact line moving outwards that does not trap any gas. The critical charge level only depends on the capillary number based on the gas viscosity. The deformation applies to common liquids and molten alloy droplets. Even dielectric surfaces can also induce conical deformation. The charged droplets can also deform upon hydrophobic surfaces, and increase the contact time on hydrophobic surfaces or even avoid bouncing. / Doctor of Philosophy / Electric charges are often found in naturally or artificially formed droplets, such as raindrops, waterfall, and inkjet printer. Neutral droplets impact on flat surfaces will usually trap a bubble inside because of the viscosity of air. The air bubble entrapped can be ignored if the droplet is water because the air bubble will eventually pinch-off. However, if the droplet is metal or some other viscous liquid, the air bubble will stay inside the liquid. This entrapped air bubble is undesired under some circumstances. For example, the existence of air bubble during metal 3D printing can influence the physical property. I show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets both experimentally and numerically. As the charge level is raised above a critical level of about 1% of the maximum charges a droplet can carry for representative impact conditions, the electric stress will dominate the deformation of droplet. A conical liquid tip forms at the droplet bottom, avoiding the entrapment of air bubble. The critical charge level is experimentally proved to be only dependent on the gas viscosity and impact velocity. The deformation applies to common liquids and molten alloy droplets. Even dielectric surfaces can also induce conical deformation. The charged droplets can also deform upon hydrophobic surfaces, and increase the contact time on hydrophobic surfaces or even avoid bouncing.

In a jet engine air and oil are mixed during removal from the bearing chamber. Before the oil can be recycled back into the system it must be separated from the air. This is accomplished through use of a de-aerator and breather. The oil air mixture enters the de-aerator first. The de-aerator is a vertical cylinder in which the air and oil enter from the top of the system. Gravity then pulls the oil down as it circulates along the outer wall of the de-aerator. The air is forced out through a top hole and sent to the breather where any oil droplets which remain are furthered separated. A pedestal is located near the bottom of the de-aerator. The pedestal creates a gap between itself and the de-aerator wall. Ideally this gap should be large enough to allow oil to flow through the gap without pooling on the pedestal, but small enough so that air does not flow through the gap. The oil will pool up on the pedestal and reduce the efficiency of the system. In this research, a 30° conical pedestal with a gap of 10.7% was tested. The results showed that the pedestal gap of 10.7% is too large and allows air to flow through the gap. The maximum water was 8.5% and the average water thickness was 5.11%. After studying both the previous experimental data and current CFD data, it is recommended further testing be conducted on pedestal gaps between 8.5% and 9.5%. / Master of Science

The analysis of ring type seals is of great concern for the designer of high speed and high pressure centrifugal compressors. Computers now play a major role in allowing for a quick evaluation of the floating ring seal. Since the accuracy of the rotor shaft stability evaluation depends on the validity of the dynamic seal characteristics, every step in the evaluation must be carefully scrutinized and updated to include the latest in theory and practical operating experience. This thesis presents the theory and results of one such extension to the current published analysis of oil ring seals. The new analysis includes the influence of the sealing fluid temperature gradients on the leakage flow rate and seal dynamic characteristics for multi-ring and/or multi-land ring configurations. Using classical short bearing theory but allowing for temperature and pressure dependent viscosity variations across the seal, the resulting pressure profiles have been determined numerically utilizing a finite difference solution technique. This thesis discusses the method used to calculate the flow and pressure profiles for oil seals, their influence on the seal dynamic characteristics, and the importance of their consideration on actual turbomachinery stability. / Master of Science

Introduction: At the present time there are, on the market, numerous lubricating aids which are designed to improve the lubricating qualities of the various mineral lubricating oils, especially those intended for automotive use. The manufacturers of some of these make statements concerning them that to any fair-minded individual are startling. With this in mind, it has been the purpose of the author to try to verity these claims or else disprove them. It would be impossible in the time allowed to test allot these aids; so a representative few were chosen which covered the field quite thoroughly. From the results shown by the use of these aids in an internal combustion engine, as well as those shown by the physical property tests in the laboratory, it seems as though their suitability for industrial use would be demonstrated. In other words, the results should show which of the arguments put forth by the manufacturers of the various products are of sound basis and which are stated merely for the sake of advertising and publicity. / Master of Science

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Masters of Science in Engineering, 2016 / This research is focused on optimizing the surface integrity of Ti-6Al-4V using advanced carbide inserts and minimum quantity lubrication (MQL). Experiments were designed to machine twenty Ti-6Al-4V blocks under dry and MQL lubricating conditions using innovative cemented carbide inserts produced by Liquid Phase Sintering (LPS) and Spark Plasma Sintering (SPS). The cutting speed, feed rate, and depth of cut, were considered as machining parameters, while the cutting force, temperature, tool wear, surface roughness and residual stress were considered as performance characteristics. The results obtained for surface roughness and residual stress measurements were used to analyze the surface integrity of the machined Ti-6Al-4V samples. The influence of sintering techniques and milling parameters on performance characteristics and surface integrity were investigated from experimental results obtained. Discrepancy in behavioral trends with respect to lubricating conditions was also investigated. The analyses of milling results showed that cutting speed played a major role in the optimization of surface integrity of the Ti-6Al-4V work pieces followed by the depth of cut. The results also showed that the LPS inserts performed better than the SPS inserts due to their better mechanical properties (higher fracture toughness (KIC) and transverse rupture strength). The application of MQL was also observed to significantly reduce milling temperatures resulting in better surface integrity. However, an optimized surface integrity of the Ti-6Al-4V samples was achieved during MQL milling with the 10Co-L insert at a low finishing speed of 75m/minute and a reduced depth of cut of 0.5mm.

by Lam Yip-mou Charles. / Thesis (M.B.A.)--Chinese University of Hong Kong, 1981. / Bibliography: leaves 104-106.

"Two most important events in the history of lubrication theory are attributed to Reynolds and Sommerfeld. Reynolds derived the governing equations for lubricating films in simplifying the Navier-Stokes equations considering thin-film effects. Sommerfeld obtained a closed form analytical solution to the Reynolds equation for the long bearing (one-dimensional case) with fixed constant eccentricity which results in a point symmetric pressure profile compared to an arbitrary (ambient) level. In attempting to reconcile with experimental evidence, Gumbel advanced the argument that sub-ambient pressure in a fluid film is not possible. On the basis that the fluid film would rupture, he put forth that the sub-ambient portion of the Sommerfeld solution should be discarded, a proposition that is commonly recognized as the half-Sommerfeld solution (of Gumbel). Ever since Gumbel suggested this improvement, much interest remains regarding the physical process of rupture in bearing lubricating films. In lubrication literature, cavitation is used interchangeably with rupture to indicate a condition in which an abundance of a gas phase, essentially ambient air, is present in a portion of the bearing clearance. A cogent two-phase morphology for addressing cavitation in long bearings is postulated in order to predict time-dependent fluid behavior from an initial state that is a generalization of Gumbel’s half-Sommerfeld solution. The ultimate steady-state is presumed to satisfy the hypothesis of Swift and Stieber that an ambient condition is reached by the rupture point at an unspecified location simultaneously with a vanishing pressure gradient. A trans-rupture continuity equation, as proposed by Olsson, determines a formula for the speed of a moving rupture point requiring a specific model of the two-phase flow in the rupture region. Employing an adhered film model, sequential application of Olsson’s equation to the rupture points of the intermediate states between the half-Sommerfeld and Swift-Stieber states renders an interpretation of a time-dependent progression towards a steady-state solution. Closed form analytical formulas, which readily combine to provide an exact solution to the Reynolds equation are derived with the start (formation point) of the full-film other than the customary bearing maximum gap and with the rupture point at any assigned intermediate location. Each valid solution for an intermediate state yields an invariant flux that must satisfy a window of constraints to exclude the possibility of sub-ambient pressures. A complete set of such valid solutions exists for each fixed eccentricity and can be depicted as a contour plot of the invariant flux with formation and rupture points as coordinates. The method can readily be extended to two-dimensions, offering a promising alternative to the Elrod cavitation algorithm, which is commonly used in more comprehensive bearing analyses."