Lubricant Leakage Research Articles

Analyses of both steady behavior and dynamic tracking of non-contacting spiral-grooved gas face seals

The analyses for steady and unsteady sealing behaviors of spiral-grooved gas face seals are presented by finite element method. The element with nine nodes and four quadratic cures is used. And for avoiding the film thickness discontinuity over the grooves, two of them coincide with the circular arcs and the others approximate to the spiral lines. In steady-state analysis, the steady-state Reynolds equation is used, and different element meshes are utilized for different sealed pressures. The load capacity and the lubricant leakage on gas face seals are shown for different compressibility numbers and sealed pressures. Thus the optimal sealed pressure and the gas amount needed in actual applications can be determined according to the numerical results. For the dynamic tracking of the stator, the direct-dynamic analysis is used, and the explicit form of the unsteady compressible Reynolds equation is found by weighting the film thickness in each element. The initial pressure profile and the initial closing force are determined at the given sealed pressure. The dislocations due to the external shock disturbances are considered, including the rotor runout only, the stator misalignment only, and the mixed dislocations. The possibility of face contact, the detectable central clearance between stator and rotor, and the leakage under unsteady operation are concerned.

Design and Testing of an Adjustable Linkage for a Variable Displacement Pump

A variable displacement hydraulic pump/motor with high efficiency at all operating conditions, including low displacement, is beneficial to multiple applications. Two major energy loss terms in conventional pumps are the friction and lubrication leakage in the kinematic joints. This paper presents the synthesis, analysis, and experimental validation of a variable displacement sixbar crank-rocker-slider mechanism that uses low friction pin joints instead of planar joints as seen in conventional variable pump/motor architectures. The novel linkage reaches true zero displacement with a constant top dead center position, further minimizing compressibility energy losses. The synthesis technique develops the range of motion for the base fourbar crank-rocker and creates a method of synthesizing the output slider dyad. It is shown that the mechanism can be optimized for minimum footprint and maximum stroke with a minimum base fourbar transmission angle of 30 deg and a resultant slider transmission angle of 52 deg. The synthesized linkage has a dimensionless stroke of 2.1 crank lengths with a variable timing ratio and velocity and acceleration profiles in the same order of magnitude as a comparable crank-slider mechanism. The kinematic and kinetic results from an experimental prototype linkage agree well with the model predictions.

Lubrication Leakage Alarm of Wind Power Gearbox Based on K-nearest Neighbor and Back Propagation Neural Network

Lubrication Leakage Alarm of Wind Power Gearbox Based on K-nearest Neighbor and Back Propagation Neural Network

Influence of Surface Roughness Lay Directionality on Scuffing Failure of Lubricated Point Contacts

The influence of roughness lay directionality on scuffing failure is studied considering different roughness lay direction combinations of the contacting surfaces of a ball-on-disk contact. Using a recently developed scuffing model Li et al., (2013, “A Model to Predict Scuffing Failures of a Ball-On-Disk Contact,” Tribol. Int., 60, pp. 233–245)., the bulk temperature and flash temperature are predicted for each roughness lay combination within the load range from 0.76 GPa to 2.47 GPa in a step-wise manner under the rolling velocity of 10 m/s and slide-to-roll ratio of −0.5 to show substantial impacts of roughness lay directionality on scuffing resistance performance (SRP). It is found (i) the lay direction combination that results into contacts of asperities with small contact radii leads to increased local contact pressures and frictional heat flux, reducing SRP; (ii) the continuous asperity contact along the sliding direction leads to continuous surface temperature rise and lowers SRP; and (iii) the lubricant side leakage caused by the pressure gradient in the direction normal to the sliding direction leads to reduced SRP. With these main mechanisms in effect, the SRP of a contact decreases as the deviation between the roughness texture orientations of the two surfaces increases. The surfaces with their roughness lay directions both perpendicular to the sliding direction exhibits best SRP. The surfaces with one roughness lay direction positioned in line with the direction of sliding and the other positioned perpendicular to the sliding direction shows worst SRP.

Design and Materials Selection for Environmentally Friendly Ship Propulsion System

The selection of the material regarding specific design of the stern tube journal bearings in vessels is critical taking into account the lubrication system, whether oil or water based, and the consequent lubricant leakage. Therefore, the present study examines the feasibility and the advantages of implementing water lubricated polymer shaft bearings instead of conventional white metal bearings lubricated by oil. The investigation method is related to the numerical model and the software application based on finite difference method and isoviscous model. Results, based upon data collected from three different types of actual vessels in service, have shown that power loss in polymer bearings is at least 6 times less than in conventional white metal ones indicating that polymer journal bearings are significantly more energy efficient and environmentally friendly.

Simulation-based fabrication of micro-helical grooves in a hydrodynamic thrust bearing by using ECMM

In hydrodynamic thrust bearing, common micro-grooves with helical or herringbone forms are generally to ensure the bearing load capacity and reduce leakage of lubricant, consistent with the design or size requirements of grooves. In this investigation, the electrical field distribution and anodic dissolution of helical grooves in electrochemical micro-machining process can be predicted by using COMSOL MultiphysicsTM software. The processing equivalent is based on the chemical composition of the workpiece. The micro-helical grooves are hollowed out of hydrodynamic thrust bearing using a DC and pulse power supply, and experiment results are compared with simulation results. The experimental results demonstrate that the fine surface of helical grooves can be obtained with a depth of 4.9 μm in machining time of 3 s by using a pulse power supply of 5 kHz. To eliminate the effect of such factors as flush flow, temperature difference between workpiece and tool, and formation of hydrogen bubble barriers, the k values of these factors are considered for amendment to get more accurate simulation results.

S112032 流体動圧軸受端部に設けられたテーパーシールに関するメカニズムの解明 : 衝撃を受けたときのテーパーシールにおける流体表面の挙動([S11203]機械要素の設計・製造・応用技術(3))

To clarify the mechanism of the taper seal at the end of the fluid dynamic bearing used in the spindle motor of a hard disk drive, the behavior of the fluid surface in the seal when subjected to a shock is analyzed and solved. As a multi-phase flow, the behavior of the fluid surface in the seal is analyzed and numerically solved by using VOF method in consideration of the response of the rotor, the inertia force and the surface tension acting on the fluid, and the influence of the pressure from the bearing. The influences of the eccentricity of the rotor, the oil barrier film coated on the seal wall, the shock strength and the taper seal shapes on the behavior of the fluid surface are discussed. As a result, it is clarified that decreasing the eccentricity of the rotor, decreasing the mass of the rotor, increasing the stiffness and damping of the bearing, making a suitable seal shape are effective countermeasures against lubricant leakage from the seal.

Identification of Force Coefficients in a Squeeze Film Damper With a Mechanical Seal: Large Contact Force

Squeeze film dampers (SFDs) aid to reduce excessive vibration levels due to rotor imbalance and to raise stability thresholds in rotor-bearing systems. SFDs commonly include end seals to increase their damping capability with a lesser lubricant flow. Seals also aid to reduce the occurrence of air ingestion/entrapment that severely reduces the damper forced performance. However, most conventional end seals do not completely eliminate lubricant side leakage, which limits their effectiveness to prevent air ingestion. A novel end seal arrangement incorporates a spring loaded, contacting mechanical seal that effectively prevents lubricant side leakage and air ingestion. The mechanically sealed damper is intended for use in power engines for unmanned aircraft vehicles. The test damper journal is 2.54 cm in length and 12.7 cm in diameter, with a radial clearance of 0.127 mm. Prior literature reports dynamic load tests on the seal-SFD and measurements of orbital motions to characterize the mechanical parameters of both the mechanical seal and squeeze film damper section. The test data to date include damper operation for a single contact load (90 N) closing the mechanical seal. Presently, measurements of damper dynamic load performance are conducted with a larger contact force (260 N). A nonlinear parameter identification method in the frequency domain determines simultaneously the squeeze film damping and inertia coefficients and the seal dry-friction force. The test results show that the system equivalent viscous damping coefficients are twice as large as those obtained earlier with the smaller contact force. On the other hand, as expected, the squeeze film damper coefficients are nearly identical for both test configurations. Predicted squeeze film damping coefficients, from an improved model that includes the flow in the damper feed and discharge grooves, correlate well with the test data for small and moderate orbit radii. The experimental fluid added mass coefficients are in par with the actual mass of the bearing housing and accurately predicted.

Squeeze Film Damper With a Mechanical End Seal: Experimental Force Coefficients Derived From Circular Centered Orbits

The paper presents parameter identification measurements conducted on a squeeze film damper (SFD) featuring a nonrotating mechanical seal that effectively eliminates lubricant side leakage. The SFD-seal arrangement generates dissipative forces due to viscous and dry-friction effects from the lubricant film and surfaces in contact, respectively. The test damper reproduces an aircraft application that must contain the lubricant for extended periods of time. The test damper journal is 2.54cm in length and 12.7cm in diameter, with a nominal clearance of 0.127mm. The damper feed end opens to a plenum filled with lubricant, and at its discharge grooved section, four orifice ports evacuate the lubricant. In earlier publications, single frequency force excitation tests were conducted, without and with lubricant in the squeeze film land, to determine the seal dry-friction force and viscous damping force coefficients. Presently, further measurements are conducted to identify the test system and SFD force coefficients using two sets of flow restrictor orifice sizes (2.8mm and 1.1mm in diameter). The flow restrictors regulate the discharge flow area and thus control the oil flow through the squeeze film. The experiments also include measurements of dynamic pressures at the squeeze film land and at the discharge groove. The magnitude of dynamic pressure in the squeeze film land is nearly identical for both sets of flow restrictors, and for small orbit radii, dynamic pressures in the discharge groove have peak values similar to those in the squeeze film land. The identified parameters include the test system damping and the individual contributions from the squeeze film, dry friction in the mechanical seal and structure remnant damping. The identified system damping coefficients are frequency and motion amplitude dependent due to the dry-friction interaction at the mechanical seal interface. Squeeze film force coefficients, damping and added mass, are in agreement with simple predictive formulas for an uncavitated lubricant condition and are similar for both flow restrictor sizes. The SFD-mechanical seal arrangement effectively prevents air ingestion and entrapment and generates predicable force coefficients for the range of frequencies tested.

Free boundary of lubricant film in ferrofluid journal bearings

The growing interest in ferrofluid bearings is caused by their excellent self-sealing ability. The understanding of behaviour of ferrofluid film boundary adjacent to ambient air is crucial for the proper design of the sealing unit of ferrofluid bearings. This paper is the first attempt to predict the shape of a ferrofluid free boundary in the presence of a static load and magnetic field. Analysis involves simultaneous integration of the Reynolds equation and the free boundary equation using perturbation technique with respect to shaft eccentricity. Magnetic field is shown to flatten ferrofluid free boundaries as well as to reduce cavitation region; both effects diminishing lubricant leakage.

Identification of Force Coefficients in a Squeeze Film Damper With a Mechanical End Seal—Centered Circular Orbit Tests

The damping capability of squeeze film dampers (SFDs) relies on adequate end sealing to prevent air ingestion and entrapment. The paper presents the parameter identification procedure and force coefficients of a test SFD featuring a mechanical seal that effectively eliminates lubricant side leakage. The test damper reproduces an aircraft application intended to contain the lubricant in the film lands for extended periods of time. The test damper journal is 2.54cm in length and 12.7cm in diameter, with a nominal clearance of 0.127mm. The SFD feed end is flooded with oil, while the discharge end contains a recirculation groove and four orifice ports. In a companion paper (San Andrés and Delgado, 2006, ASME J. Eng. Gas Turbines Power, 119, to be published) single frequency–unidirectional load excitation tests were conducted, without and with lubricant in the squeeze film lands, to determine the seal dry-friction force and viscous damping force coefficients. Presently, tests with single frequency excitation loads rendering circular centered orbits excitations are conducted to identify the SFD force coefficients. The identified parameters include the overall system damping and the individual contributions from the squeeze film, dry friction and structural damping. The identified system damping coefficients are frequency and motion amplitude dependent due to the dry friction interaction at the mechanical seal interface. Identified squeeze film force coefficients, damping, and added mass, are in good agreement with predictions based on the full film, short length damper model.

Collets and friction

Conical sleeves, known as collets, have long been used for clamping sliding bodies to cylindrical columns in any desired position. Quantitative expressions for their properties are presented. Of particular interest is the ability of a collet to hold a shaft stationary against axial forces in either direction, and yet be able to release its grip with a minimum of additional force. This treatment relates the firmness of grip, the ease of release and the interface stresses to the cone angle, the coefficients of friction and the applied axial forces. The central part played by hysteresis is revealed. Experiments employing a test model give good support to the theoretical conclusions. They show that, up to the interface pressures reached, about 250 MPa, the friction between lubricated hardened steel and mild steel surfaces is independent of pressure. The strong dependence of friction on surface roughness is demonstrated. The possible adaptation of the collet test equipment to the measurement of friction at high interface pressures is touched upon. It could be a complementary alternative to the more flexible pin-on-disc method. With much larger working areas, it should have the advantages of better defined areas of contact, reduced ploughing effects and less leakage of lubricant.

Optimum Gas Journal Bearing with Open Bearing Ends and Feeder Slot

The optimum design of the cylindrical outer contours of a gas journal bearing is obtained using the methods of the calculus of variations with allowance for the lubricant leakage through the bearing ends and the feeder slot when the lubricant mass in the working gap is conserved. The variational problem of designing the clearance shape giving the maximum bearing load capacity is formulated and solved. A modified Elrod-Burgdorfer condition for the pressure is used.

Design of high-speed magnetic fluid bearing spindle motor

A high-speed magnetic-fluid bearing spindle motor for hard disk drive is introduced. Some design challenges and considerations of its load capacity, stiffness, power consumption, lubricant leakage and shock resistant capability are addressed. The prototypes were fabricated and the test results of the prototypes are presented and discussed. The results show that the magnetic-fluid bearing spindle motor is very promising for use in future hard disk drives.

Energy loss due to misalignment of journal bearings

An analysis of a journal bearing describing a maximum allowable value of misalignment at a length to diameter ratio of unity is presented. The journal misalignment is allowed to vary in direction up to a direction normal to the axial plane containing the load vector. The results demonstrate that journal misalignment influences bearing behaviour. For the same load carrying capacity, a misaligned bearing consumes more power due to friction than an aligned one. An optimum position of misalignment has been found to be almost along the axial plane containing the load vector since it produces lower frictional losses and less lubricant leakage than any other.

Overall Characteristics of Bearings Lubricated With Ferrofluids

Using the results shown in some previous papers, the overall characteristics of bearings lubricated with ferrofluids are calculated. First, the load carrying capacity of infinitely long sliding and journal bearings is considered. The pressure center and the attitude angle are also determined. Then, similar characteristics of finite bearings are obtained. In both cases, the new boundary conditions and the actual film extent under magnetic stresses are taken into account. It is shown that friction forces are mainly affected by the change in viscosity due to magnetic particle suspensions, while magnetic stresses modify friction only under special conditions which usually are not met in lubrication. In addition, the flow rates and the side flow coefficients are calculated. It is shown that the lubricant leakage can be reduced and even avoided when proper measures are taken. For short bearings, diagrams are given for the film extent, the film boundaries, the load carrying capacity, and the attitude of the journal center.

Film Lubrication of Finite Curved Surfaces

In treating film lubrication, Reynolds and Sommerfeld confined themselves to surfaces of infinite width, for mathematical reasons. Michell obtained the solution for a plane surface of finite width; the importance of this lies in the fact that leakage of lubricant through the lateral edges of a finite bearing reduces considerably the load supportable by the bearing. Solutions are obtained here for general cases of rectangular bearings with surfaces curved in both directions; for the Michell sector type of thrust bearing plate, in a case which allows consideration of the effect of the variation of film thickness with the radial distance from the center of rotation; and for the fitted finite journal bearing. General methods are exhibited suitable for handling other cases. In particular, the equations for the finite journal bearing in the general case are partially developed. Solutions for the journal bearing are shown to require laborious computation, so that an approximation to the film thickness is preferable; such an approximation, which can be handled relatively easily, is treated, and the solution obtained.