Foil bearings - Performance testing of foil journal bearings - Testing of static load capacity, friction coefficient and lifetime

2019 ◽  
Keyword(s):  
Friction Coefficient ◽  
Static Load ◽  
Load Capacity ◽  
Performance Testing ◽  
Journal Bearings ◽  
Foil Bearings

Experimental Investigation of Prototype Water-Lubricated Compliant Foil Bearings

2011 ◽  
Vol 490 ◽  
pp. 97-105 ◽  
Author(s):  
Artur Olszewski ◽  
Michał Wodtke ◽  
Piotr Hryniewicz
Keyword(s):  
Experimental Investigation ◽  
Friction Coefficient ◽  
Gas Turbines ◽  
High Speed ◽  
Journal Bearings ◽  
Radial Load ◽  
Sliding Speed ◽  
Good Tolerance ◽  
Foil Bearings ◽  
Water Pumps

First gas-lubricated compliant foil bearings (CFBs) were built in the 1950s. Due to their significant advantages, such as oil-free operation, good tolerance to bearing misalignment and very low maintenance, they have been penetrating the bearing applications for high speed compressors, air-cycle machines and gas turbines. The work presented here investigates a novel idea of water-lubricated compliant foil bearings, which could be used in applications where environmentally friendly lubrication is desired, for example in hydroelectric turbines or water pumps. Experimental results collected for three prototype water-lubricated foil journal bearings are presented. The tests were conducted under steady radial load and with the sliding speed varied incrementally. A sequence of design improvements is presented, with the best bearing demonstrating friction coefficient of about 0.01 at the sliding speed of about 4 m/s and the radial load of about 300 kPa. Encountered difficulties, research methodology and the testing equipment are also described.

Evaluation of Coated Top Foil Bearings: Dry Friction, Drag Torque, and Dynamic Force Coefficients

2018 ◽  
Author(s):  
Luis San Andrés ◽  
Wonbae Jung
Keyword(s):  
Friction Coefficient ◽  
Dry Friction ◽  
Loss Factor ◽  
Static Load ◽  
Sliding Friction ◽  
Dry Sliding ◽  
Drag Torque ◽  
Specific Load ◽  
Foil Bearings ◽  
Mos2 Coating

Despite their many advantages, bump-type foil bearings (BFBs) have issues of dry-friction during sliding contact at rotor start/stop cycles. To prevent premature wear of both shaft and the BFB, the proper selection and application of a coating on the top foil is of importance to ensure bearing long life. This thesis presents measurements characterizing the static and dynamic load performance of a Generation I BFB having uncoated and coated (VN, TiSiN, MoS2) top foils. The bearing, with length L and diameter D = 38 mm, integrates a 360° 0.127 mm thick top foil made of Inconel X-750, and a 27 bumps strip layer, 0.47 mm in height, made of the same stock as for the top foils. The VN and TiSiN coating, 0.005 mm thick, applies to the front and back surfaces of a top foil. The MoS2 coating, 0.020 mm thick, is sacrificial. The tests were conducted at room temperature (21°C), determined by the existing test facility. The dry-sliding torque (T) increases linearly with an increase in applied static load, max W/(LD) = 25.6 kPa. The bearing with a VN coated top foil shows the largest turning torque. The dry-sliding friction factor f = T/(½WD) decreases as the specific load (W/(LD)) increases. As expected, journal rotation towards the top foil free end (clockwise) produces a larger f than for rotations in reverse. A test-rig records the BFB drag torque during rotor acceleration and deceleration procedures to/from 70 krpm (138 m/s). The vertical load applied into a bearing equals W/(LD) = −8.0 kPa, 0 kPa and 8.0 kPa. In general, the bearing with a coated top foil shows a lesser drag torque than that of the uncoated top foil bearing. Among the coated foil bearings, the one with VN coating shows the highest drag torque, whereas another with MoS2 coating shows the lowest. When the rotor starts up, the dry-sliding friction coefficient (f) of the bearing with VN coating is ∼0.4 while f for the bearing with TiSiN coating is 0.3∼0.4. The uncoated bearing shows the largest f ∼0.6, and the MoS2 coated one has the lowest f = 0.2∼0.3. The drag torque, increasing with an increase in applied static load, is small when the rotor is airborne (lesser than ∼10% of peak torque). Dynamic load tests spanning excitation frequencies (ω) from 200 Hz to 400 Hz serve to identify force coefficients for the test BFBs with a specific load of 16 kPa and operating with shaft speed at 50 krpm (833 Hz). Baseline measurements correspond to a null applied load and no shaft rotation. The test bearings show a remarkable behavior with nearly isotropic direct coefficients and very small cross-coupled ones. The bearing direct stiffnesses (K) increase with frequency whereas the direct damping coefficients (C) quickly decrease. The bearing material loss factor, γ = ωC/K, represents best the BFB ability to dissipate mechanical energy. Over the excitation frequency range, γ = 0.34, 0.28, and 0.12 for the uncoated top foil, VN coated and TiSiN coated bearings. The test data show the bearing loss factor correlates with the dry friction coefficient as γ ∼ (0.71 × f) at a rotor speed of 50 krpm (95 m/s). Since the top foils with VN or TiSiN are coated on both sides, kinetic friction between the back of a top foil and the bumps’ crests likely lessens during sustained contact.

Performance Analysis of Double-Bumped Air Foil Bearings

2007 ◽  
Author(s):  
Y. C. Kim ◽  
D. H. Lee ◽  
K. W. Kim
Keyword(s):  
Theoretical Model ◽  
Friction Coefficient ◽  
Performance Analysis ◽  
Active Region ◽  
Load Capacity ◽  
Equivalent Stiffness ◽  
Vertical Deflection ◽  
Foil Bearings ◽  
Damping Coefficients ◽  
Stiffness And Damping

This paper presents a theoretical model for the analysis of double-bumped Air Foil Bearings (AFBs). The stiffness and damping coefficients of the double bump vary depending on the external load and its friction coefficient. The double bump can be either in the single or double active region depending on vertical deflection. The equivalent stiffness and damping coefficients of the bump system are derived from the vertical and horizontal deflection of the bump, including the friction effect. The results of the performance analysis for a double bumped AFB are compared with those obtained for a single bumped AFB. This paper successfully proves that a double bumped AFB has higher load capacity, stiffness, and damping than a single bump AFB in a heavily loaded condition.

Misalignment Effect on the Static and Dynamic Characteristics of Hydrodynamic Journal Bearings

1995 ◽  
Vol 117 (4) ◽  
pp. 717-723 ◽  
Author(s):  
Z. L Qiu ◽  
A. K. Tieu
Keyword(s):  
Dynamic Characteristics ◽  
Reynolds Equation ◽  
Static Load ◽  
Load Capacity ◽  
Vertical Direction ◽  
Journal Bearings ◽  
Static And Dynamic Characteristics ◽  
Flow Friction ◽  
The Stability ◽  
Side Flow

This paper solves the Reynolds equation by the finite difference method in a fixed coordinate system with the static load acted in the vertical direction. All static and dynamic characteristics (including load capacity, attitude angle, side flow, friction force, misaligned moments, and eight linear force coefficients) of a horizontally grooved bearing under different eccentricity and misalignment conditions are presented and compared with available experimental data. The effects of misalignment on all these bearing characteristics and on the stability of the rotor-bearing system are analyzed.

Performance Characteristics of Compliant Journal Bearings

1991 ◽  
Vol 113 (3) ◽  
pp. 639-644 ◽  
Author(s):  
C. R. Lin ◽  
H. G. Rylander
Keyword(s):  
Friction Coefficient ◽  
Load Capacity ◽  
Journal Bearings ◽  
Performance Characteristics ◽  
Coefficient Increase ◽  
Minimum Film Thickness ◽  
Final Design ◽  
Deformation Coefficient ◽  
Behavior Characteristics ◽  
Two Sides

This investigation of compliant journal bearings is directed toward the fundamental behavior characteristics which are necessary when compliance is factored into the final design. Analytical determintation of performance characteristics are shown as a function of the bearing flexibility. As the deformation coefficient increases, load capacity decreases, the cavitation angle and friction coefficient increase, attitude angle may increase or decrease, stability is improved for attitude angles less than 0.8, and minimum film thickness will occur near the two sides of the bearing.

The Static Performance Analysis of Air Foil Journal Bearings Considering Three-Dimensional Structure of Bump Foil

2005 ◽  
Author(s):  
Dong-Hyun Lee ◽  
Young-Cheol Kim ◽  
Kyung-Woong Kim
Keyword(s):  
Finite Element ◽  
Load Capacity ◽  
Three Dimensional ◽  
Element Model ◽  
Journal Bearings ◽  
Dimensional Structure ◽  
Suggested Model ◽  
3 Dimensional ◽  
Foil Bearings ◽  
Static Performance

The calculation of bump foil deflection is very important to predict the performance of foil bearings more accurately, because the foil bearings consist of top foil and its elastic foundation usually called bump foil. For the purpose of this, a finite element model considering 3-dimensional structure of the bump foil is developed to calculate the deflection of inter-connected bump. The results obtained from the suggested model are compared and analyzed with those from the previous proposed deflection models. In addition, load capacity of the foil bearings is analyzed by using this model.

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