The object of this research was to study the effect of initial surface -finish and finish mark orientation on intermetallic friction under unlubricated sliding contact conditions. The metal used was mild steel and the parameters investigated were sliding speed and load. Qualitative assessments of wear were also made. The basic apparatus consisted of a rotating disc and an elastically supported slider. The disc and slider each had the same-initial surface finish. Six different surface finishes were examined ranging in roughness from a peak to valley distance of 6.9 thousandths of an inch to 35 microinches R.M.S. Speed was varied from 1.25 to 60 inches per second and normal load from 1.025 to 3.075 pounds. No significant correlation was found, between the theory of Ernst and Merchant and the experimental results. Friction was more dependent on surface parameters affecting load concentration than, on the particular details of each surface asperity. The effects of finish mark orientation were only significant when they produced appreciable load concentration. Friction was found to increase as "wear-in" progressed and remain approximately constant once wear-in was complete. No relation between friction and velocity could be deduced. Wear-in was found to be influenced by initial surface geometry. The sufaces which gave high load concentration at sharp protuberances "wore-in" more quickly than those-with low load concentration. Smooth compatible surfaces which required little surface alteration also wore-in rapidly. Wear debris was found to influence both friction and wear-in. Evidence of mechanical working of debris between the surfaces was obtained. A quasi-harmonic oscillation of the slider supporting system was observed to result from wear-in. The frequency of vibration was a function of disc speed and load. The amplitude of the vibration increased linearly with disc speed up to a maximum value. The magnitude-of this maximum was dependent on normal load. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

<p dir="ltr">This thesis presents an investigation into the mechanism of friction generation and lubrication of cages used in modern Deep Groove Ball Bearings (DGBBs). Although cages provide a necessary function, e.g., ensuring proper spacing between rolling elements during assembly and operation, they also serve as an undesirable source of friction to the overall assembly. Cage friction originates primarily from two sources: i) localized cage pocket friction between the balls and the rollers and ii) churning losses from excess lubricant inside the bearing cavity. Localized cage pocket frictional losses were characterized through the development of a novel Bearing Cage Friction Test Rig (BCFTR). This rig was designed and developed to replicate the orientation and relative motion of a fully assembled bearing in steady state operation while measuring cage friction. The BCFTR uses a six-axis load cell to record forces and torques generated due to a rotating ball inside of a rigidly fastened cage segment. The test rig can be set up in two different configurations: i) a load control configuration where a friction coefficient is calculated due to a constant force applied between the ball and the cage segment and ii) a position control configuration where frictional torque is measured for specific positions of the ball relative to the cage. </p><p dir="ltr">In order to gain a deeper understanding of the relationship between cage position, lubrication, and friction, an acrylic cage segment with an exact cage pocket geometry was developed and tested on the BCFTR over a broad range of operating conditions. The clear acrylic cage allowed for the visualization of lubricant flow inside the cage pocket. Videos of oil flow revealed that the quantity of oil inside the pocket correlates closely with the measured frictional torque. Oil volume information from the videos was then used as an input to a cage pocket lubrication model. The model uses the finite difference method to solve the Reynolds and film thickness equations over a spherically defined cage pocket domain. The model was developed primarily to estimate cage pocket friction and corroborate with the results from the BCFTR; however, the model was also used to investigate the pressure distribution and lubricant shear stress in a variety of cage pocket shapes. The finite difference model uses oil volume fraction data to estimate frictional torque and corroborate experimental friction measurements. The results obtained from the model and experiments are in good agreement, proving that the key information required to estimate cage friction is the quantity of oil inside of the cage pocket.</p><p dir="ltr">The main contribution of overall cage friction in DGBBs can be attributed to local drag from inside the cage pocket; however, there remains an appreciable amount of friction and drag losses due to the interaction of the outside of the cage with oil in the bearing cavity. Because DGBB cages reside in the space between the rolling elements and have a significant effect on the churning behavior of the oil, it is paramount to understand how the size and shape of these cages affect the lubricant flow. To achieve this objective, a series of Computational Fluid Dynamics (CFD) models were developed. A full-scale simulation of the inner cavity of a DGBB was developed to observe fluid flow as a function of bearing geometry, operating conditions, and cage shape. Considerable effort was taken to perform optimization studies of the solution method. In addition, an efficient CFD model covering only three rolling elements was also used to investigate fluid flow in a bearing. This model utilized symmetry, periodic boundary conditions, and rotating reference frames to produce equivalent results to the full bearing simulation with a great reduction in computational effort. Results from the model were analyzed both qualitatively and quantitatively through the generation of contour maps of pressure and wall shear stress and the calculation of force and drag coefficient values for each cage.</p><p dir="ltr">The final development presented in this thesis is a high-fidelity Dynamic Bearing Model (DBM) capable of resolving local pocket and external cage lubrication effects of bearings in operation. In this dynamic simulation, the motion of the cage was determined using the finite difference method to solve for the pressure generation and resultant forces inside of each cage pocket at each time step. The computational domain of the finite difference model was designed to reflect the specific cage pocket geometry of four common cage designs. Additional testing on the bearing cage friction test rig was performed to characterize the lubrication state inside of each cage. An inverse distance weighting scheme was utilized to predict starvation parameters for a general ball position inside of the cage pocket. Additionally, the fluid drag losses associated with cage lubrication outside of the cage pocket were included in select dynamic simulations in the form of a drag torque applied to the cage. Results from the dynamic simulation reveal new knowledge on the effect of cage geometry and lubrication on dynamic behavior. Compared to simulations without cage lubrication, results from the new DBM demonstrate a reduction in median ball-cage contact force and improved stability in the trajectory of the center of mass of the cage.</p>

No description available.

Yes / The torque-tension relationship of threaded fasteners affects almost all engineering disciplines. Tribological processes at fastener interfaces manifest as the system's friction coefficient. Lubrication-related influences are usually described empirically using K or μ. The drive towards lightweight fastener materials in engineering systems and lubricants with reduced environmental impact is challenging existing knowledge and industrial practice in a range of applications, many safety critical. More comprehensive understanding is needed to achieve repeatable friction during assembly and re-assembly, resistance to loosening and fretting during operation, and effective anti-seize for disassembly with a growing range of materials and lubricants. The lubricants considered showed three predominant lubrication mechanisms: plastic deformation of metal powders; burnishing/alignment of molybdenum disulphide, MoS2; and adhering/embedding of non-metal particles. Multivariate analysis identified key sensitivities for these mechanisms. Assembly generated changes at fastener surfaces and in the lubricating materials. Re-assembly exhibited significant reductions in friction. / The full-text of this article will be released for public view at the end of the publisher embargo on 07 Dec 2024.

The primary purpose of this study is to assess the effectiveness and utility of laser-based sensors for measuring, quantitatively, the presence and extent of top-of-rail (TOR) friction modifiers that are commonly used in the railroad industry for reducing friction between railcar wheels and rail. Modifying the friction between the wheel and rail is not only important for significantly reducing rolling resistance, but it also contributes to reducing wheel and rail wear, lowering rolling contact fatigue, and potentially curving resistance. It is common to monitor rail lubrication empirically by manually observing the sheen of the rail and tactically sensing any residues that may be present on the rail. Often performed by experienced railroad engineers, such methods are highly subjective and do not provide a quantitative assessment of how lubricated or unlubricated the track may be. A new, quantitative measurement method for accurately assessing the state of lubrication of rail is developed and studied in depth. The method takes advantage of the light reflection and dispersion properties of laser-based optical sensors to provide a repeatable, verifiable, and accurate measure of the presence of TOR friction modifiers on the rail. The measurement system is assembled in a self-contained, portable rail cart that can be pushed on the rail at walking speeds. Various TOR states are assimilated in the lab for assessing the effectiveness of the laser system. Additionally, the laboratory results are repeated in the field on various tracks, including revenue service track. The results of the tests indicate that the developed system is able to accurately measure the presence of TOR friction modifiers from none to fully-saturated, but is not affected by environmental factors such as rain, sunlight, type of rail, and top-of-rail condition. The measurements provide the means for classifying the state of rail friction in an indexed manner. The results of the study will not only have a significant effect on more efficient use of TOR friction modifiers for promoting better fuel efficiency, but they can also have a major impact on braking practices in applications such as Positive Train Control (PTC). / Ph. D.

Oil feed grooves are implemented in reciprocating compressor piston applications to assure a constant supply of lubricating oil on bearing surfaces and decrease friction loss. In a hermetically sealed compressor, due to small clearances encountered, oil supply becomes critical in order not to operate in boundary lubrication regime. Due to the small size of the piston and small piston &ndash / cylinder clearance, a partial lubrication regime is present. In the current study, a model that solves Reynolds&rsquo / equation for piston-cylinder lubrication and the average Reynolds&rsquo / equation that considers the effect of roughness on partially lubricated bearing for a compressor piston with oil feed grooves is developed. A parametric study is carried out to investigate the effects of piston design parameters and then arrive at an improved piston performance by using alternative designs for oil feed groove and the other design parameters.

No description available.

This master’s thesis describes design and realization of a wayside unit for top-of-rail lubrication (TOR). TOR lubricant application causes wear reduction and lower noise emission. Firstly, patent analysis was provided and critically evaluated according to which requirements for developed device were specified – accurate dosage of small lubricant volume and high repeatability. On the basis of concept design, an experimental rig was created and used for lubricant application verification and spray lubrication parameter identification. Acquired results are considered in the final design of wayside unit with a technical facility. Two utility models were created within this master’s thesis.

LD2668 .T4 1941 S91 / Master of Science

No description available.