On the Design, Manufacture and Premature Failure of a Metal Mesh Thrust Bearing: How Concepts That Work on Paper, Actually Do Not

2018 ◽  
Author(s):  
Travis A. Cable ◽  
Luis San Andrés
Keyword(s):  
Thrust Bearing ◽  
Ambient Air ◽  
Material Damping ◽  
Rotor Speed ◽  
Metal Mesh ◽  
Premature Failure ◽  
Foil Bearings ◽  
Light Load ◽  
Design And Manufacturing ◽  
Foil Thrust Bearing

Oil-free micro turbomachinery (OFT) implements compliant foil bearings because of their minute drag and ability to operate in extreme (high or low) temperature. Prominent to date, bump-type foil bearings integrate an underspring thin metal structure that provides resilience and material damping; and while the rotor is airborne, acts in series with the stiffness and damping of the gas film. The design and manufacturing of foil bearings remains costly as it demands of extensive engineering and actual experience. Alternative foil bearing configurations, less costly and easier to manufacture, are highly desirable to enable widespread usage of OFT. This manuscript details the design and manufacturing of a novel Rayleigh-step metal mesh foil thrust bearing (MMFTB) as well as its testing on a dedicated rig. Metal mesh structures offer significant material structural damping and can be easily procured at a fraction of the cost of a typical bump foil strip layer. The MMFTB consists of a solid carrier, a number of stacked annular Copper mesh sheets (wire diameter = 0.25, 0.3 and 0.41 mm), and a steel top foil (0.127 mm thick) that makes six pads (ID = 50.8 mm, OD = 2 ID), each 45° in extent. A 3 μm polymer coats each pad and a photo-chemical process etches a step 20 μm in height. Static and dynamic load measurements (without rotor speed) demonstrate the MMFTB has structural stiffness and material damping similar to that of a publicized bump-type foil thrust bearing. A maiden test of the MMFTB with rotor speed of Ω = 15 krpm (∼80 m/s at bearing outer diameter) proved briefly the bearing operation when applying a tiny thrust load. Further tests with ambient air, a rotor speed of 40 krpm (∼212 m/s at bearing OD), and a very light load/area < 7 kPa failed several of the prototype bearings, all exhibiting significant wear on one or more pads. The source of the failure is the inherent unevenness of the metal mesh stacked substructures, thus causing the pads to bulge towards the rotor collar surface before a load applies. A deficient anchoring method exacerbates the unevenness. Incidentally, a high rotor speed induced large windage that lifted the top foils pushing them against the spinning collar. As the bearing moved towards the rotating collar to begin applying thrust, the local high spots rubbed against the collar, before a hydrodynamic wedge could form to separate the surfaces. Without a robust sacrificial coating, metal-to-metal contact quickly disfigured the contacting top foil pads, erasing the etched step, and leading to failure. In concept, and on paper, the mesh sheets and the top foil lay flat against the bearing carrier, giving a false sense of uniformity in the design process. In actuality, a designer must consider the manufactured states of the individual components and how they assemble. A redesign of the bearing intends to overcome the existing flaws (highlighted herein) by incorporating a thicker top foil that is well anchored (to better withstand the effects of windage), a robust sacrificial coating, and a hydrodynamic wedge accomplished via a circumferential taper on each pad.

On the Design, Manufacture, and Premature Failure of a Metal Mesh Foil Thrust Bearing—How Concepts That Work on Paper, Actually Do Not

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Travis A. Cable ◽  
Luis San Andrés
Keyword(s):  
Thrust Bearing ◽  
Ambient Air ◽  
Material Damping ◽  
Rotor Speed ◽  
Metal Mesh ◽  
Premature Failure ◽  
Foil Bearings ◽  
Light Load ◽  
Design And Manufacturing ◽  
Foil Thrust Bearing

Oil-free microturbomachinery (OFT) implements compliant foil bearings because of their minute drag and ability to operate in extreme (high or low) temperature. Prominent to date, bump-foil thrust bearings integrate an underspring thin metal structure that provides resilience and material damping, and while the rotor is airborne, it acts in series with the stiffness and damping of the gas film. The design and manufacturing of foil bearings remain costly as it demands extensive engineering and actual experience. Alternative foil bearing configurations, less costly and easier to manufacture, are highly desirable to enable widespread usage of OFT. This paper details the design and manufacturing of a novel Rayleigh-step metal mesh foil thrust bearing (MMFTB) as well as its testing on a dedicated rig. Metal mesh structures offer significant material structural damping and can be easily procured at a fraction of the cost of a typical bump-foil strip layer. The MMFTB consists of a solid carrier, a number of stacked annular copper mesh sheets (wire diameter = 0.25, 0.3, and 0.41 mm), and a steel top foil (0.127 mm thick) that makes six pads (ID = 50.8 mm, OD =2 ID), each 45 deg in extent. A 3 μm polymer coats each pad, and a photochemical process etches a step 20 μm in height. Static and dynamic load measurements (without rotor speed) demonstrate that the MMFTB has structural stiffness and material damping similar to that of a publicized bump-type foil thrust bearing. A maiden test of the MMFTB with rotor speed of Ω = 15 krpm (∼80 m/s at bearing outer diameter (OD)) proved briefly the bearing operation when applying a tiny thrust load. Further tests with ambient air, a rotor speed of 40 krpm (∼212 m/s at bearing OD), and a very light load/area <7 kPa failed several of the prototype bearings, all exhibiting significant wear on one or more pads. The source of the failure is the inherent unevenness of the metal mesh stacked substructures, thus causing the pads to bulge toward the rotor collar surface before a load applies. A deficient anchoring method exacerbates the unevenness. Incidentally, a high rotor speed induced large windage that lifted the top foils pushing them against the spinning collar. As the bearing moved toward the rotating collar to begin applying thrust, the local high spots rubbed against the collar before a hydrodynamic wedge could form to separate the surfaces. Without a robust sacrificial coating, metal-to-metal contact quickly disfigured the contacting top foil pads, erasing the etched step, and leading to failure. In concept, and on paper, the mesh sheets and the top foil lay flat against the bearing carrier, giving a false sense of uniformity in the design process. In actuality, a designer must consider the manufactured states of the individual components and how they assemble. A redesign of the bearing intends to overcome the existing flaws (highlighted herein) by incorporating a thicker top foil that is well anchored (to better withstand the effects of windage), a robust sacrificial coating, and a hydrodynamic wedge accomplished via a circumferential taper on each pad.

Experimental Studies on Air Foil Thrust Bearing Load Capabilities Considering the Effect of Foil Configuration

2015 ◽  
Vol 813-814 ◽  
pp. 1007-1011
Author(s):  
R.N. Ravikumar ◽  
K.J. Rathanraj ◽  
V. Arun Kumar
Keyword(s):  
High Speed ◽  
Thrust Bearing ◽  
Experimental Studies ◽  
Ambient Air ◽  
Outer Edge ◽  
Foil Thickness ◽  
Foil Bearings ◽  
Load Carrying ◽  
Turbo Machinery ◽  
Foil Thrust Bearing

Abstract. Foil bearings are self-acting hydrodynamics bearings used to support lightly loaded high speed rotating machinery. The advantages that they offer to process fluid lubricated machines usingworking fluid as a lubricant (ambient air) physically non-contacting high speed operation. Foil bearings have been considered as an alternative to conventional bearings with the capacity to cater for high-speeds and hostile environment (high temperature). However, the lack of load carrying capacity at relatively lower speeds limits their applications in heavy turbo machinery and as such are highly suitable in lightly loaded, high speed turbo machinery like small gas turbines.This paper discusses the design and assessment of dynamic characteristics in terms of load carrying capabilities as a function of speed, gap between the bearing and the runner as well as shape of foils for an air foil thrust bearing. The effects of various bearing parameters like foil thickness, number of foils fixed circumferentially and along the axis of rotation and with foil geometry configuration. Characteristics of performance defined essentially in terms of load carrying capabilities and static stiffness have been used for evaluation. Experiments were conducted both for angular foils (with inner edge height less than outer edge height) and square foils by varying number of foils. The experimental results shows that the effect of foil configuration enhances the load carrying capabilities of air foil thrust bearing.

Development of Foil Thrust Bearings with Simple Structure for Micro Turbines

2011 ◽  
Vol 368-373 ◽  
pp. 1392-1395 ◽  
Author(s):  
Quan Zhou ◽  
Yu Hou ◽  
Ru Gang Chen
Keyword(s):  
High Speed ◽  
Simple Structure ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Complicated Structure ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Rotational Systems ◽  
Micro Turbine ◽  
Foil Thrust Bearing

Because of the low power loss and high stability, foil bearings are suitable lubrication components for high speed rotational systems. At present, the foil bearings used in actual applications almost have complicated structure and are hard to manufacture. In this paper, two kinds of foil thrust bearings with simple structure are presented. Configurations of these two foil thrust bearings are introduced; meanwhile, the load capacity and running stability are also tested in a high speed micro turbine. It is shown that viscoelastic supported foil thrust bearing has higher load capacity and hemisphere convex dots supported foil thrust bearing is more stable in high speed operational condition.

Experiments With Scaled Foil Bearings in a Test Compressor Rotor

2013 ◽  
Author(s):  
Oscar De Santiago ◽  
Víctor Solórzano
Keyword(s):  
Ambient Air ◽  
Stable Configuration ◽  
Metal Mesh ◽  
Promising Technology ◽  
Foil Bearings ◽  
Compressor Rotor ◽  
Gas Compression ◽  
Full Speed ◽  
Gas Seals ◽  
Run Up

Gas bearings are a promising technology for rotor support due to their inherent ability to work with process fluids in gas compression turbomachines. This feature has potential for eliminating oil systems, providing a clean operation and substantially reducing operating costs. This paper presents initial experiments of a 59 kg (130 lb) test compressor rotor supported on a pair of 90.20 mm (3.551 in) diameter metal-mesh foil bearings lubricated with ambient air in a rotordynamic test rig running at 9,000 rpm without gas compression. The configuration includes relocation of the bearing supports inboard of the gas seals to reduce bearing span, favoring a more stable configuration of the rotor-bearing system. Test foil bearings are designed to support static loads due to rotor weight and remnant imbalance levels. Test results show that the bearings are capable of supporting design loads and running at moderate vibration levels. A slow-growing subsynchronous vibration appears after a stable period at full speed as a result of top foil damage in the free end bearing during the run-up. This damage is due to lack of axial rotor constraints. The results of the experiments indicate that metal mesh foil bearings are a promising technology towards oil-free supported turbomachinery at larger scales than previously utilized.

The Static Characteristics of Bump Foil Thrust Bearing Considering Tilting Condition

2009 ◽  
Author(s):  
Tae-Young Kim ◽  
Dong-Jin Park ◽  
Yong-Bok Lee
Keyword(s):  
High Efficiency ◽  
Thrust Bearing ◽  
Numerical Models ◽  
Load Capacity ◽  
Static Characteristics ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Foil Thrust Bearing ◽  
Thrust Pad ◽  
Air Film

Air foil thrust bearings are the critical component available on high-efficiency turbomachinery which needs ability to endure the large axial force. Previous investigations about the static characteristics were obtained over the region of the thin air film using finite-difference method and the characteristics of the corrugated bump foil using finite-element method. Moreover, a recent study demonstrated that bearing performance is sensitive to tilting thrust pad condition. In this study, experimentally measured bearing static characteristics are compared with the numerical model of the foil thrust bearing considering tilting pad condition. Three geometrically different type foil bearings were tested to measure their load capacity under tilting conditions that have continuous angles from zero to 0.0002 rad. These data are presented for use i1n the development of more accurate foil thrust bearing numerical models.

Application of Materials on Foil Thrust Bearings for Micro Turbines

2011 ◽  
Vol 201-203 ◽  
pp. 2759-2762
Author(s):  
Quan Zhou ◽  
Yu Hou ◽  
Ru Gang Chen
Keyword(s):  
Thrust Bearing ◽  
Load Capacity ◽  
Bearing Surface ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Soft Surface ◽  
Static Part ◽  
Micro Turbine ◽  
Foil Thrust Bearing

Foil bearing that has a soft surface is a kind of air bearing. The performances of foil bearings are greatly affected by the materials of bearing surface, which is called foil element. In order to estimate the performance of foil bearings, two kinds of foil thrust bearings that are made of different materials respectively were tested in a micro turbine system, which contains rotation part and static part. Load capacity and stability of these foil thrust bearings were investigated in experiments. The results show that bearing which contains rubber has higher load capacity and bearing which contains copper foil has higher stability. According to the work in this paper, applications with different requirements can adopt suitable foil thrust bearing.

Effects of wedge curvature on performances of foil thrust bearing and the profile design in compressor system

2020 ◽  
pp. 135065012097552
Author(s):  
Hao Li ◽  
Haipeng Geng ◽  
Lei Qi ◽  
Lu Gan
Keyword(s):  
Reynolds Equation ◽  
Thrust Bearing ◽  
Dynamic Performance ◽  
Testing System ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Set Up ◽  
Foil Thrust Bearing ◽  
Excellent Stability

Foil thrust bearings have attracted considerable attention in small-sized turbo machines with its excellent stability, high compliance, temperature durability. Geometric structure play an important role on the performance of foil thrust bearings. However, the current research on the structure mainly focuses on the underlying foil type, such as bump foil, protuberant bump. In fact, the foil profile, especially in the convergent region has significant influence. In this paper, foil thrust bearings were classified into convex, slope and concave types according to the profile curvature. A numerical model of six pads foil thrust bearing was established by combining the shell model and Reynolds equation. The static and dynamic performance of thrust bearings with different curvature was calculated. The results showed that the convex convergent possessed higher capacity and was not sensitive to displacement disturbance. A stiffness testing system for thrust foil bearing was set up, and the results verified that the foil with convex wedge had higher stiffness. The experiment also indicated that all the thrust foil bearings had typical damping hysteresis. The axial force of a 10 kW on-board compressor was calculated. Based on the conclusion of this paper, the design scheme of curvature value β = 0.6 and gas thickness h2=15 µm was given in consideration of bearing capacity and machining robustness.

A New Structural Stiffness Model for Bump-Type Foil Bearings: Application to Generation II Gas Lubricated Foil Thrust Bearing

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Abdelrasoul M. Gad ◽  
Shigehiko Kaneko
Keyword(s):  
Thrust Bearing ◽  
Rotation Speed ◽  
Analytical Models ◽  
Structural Stiffness ◽  
Static Characteristics ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Compliant Structure ◽  
Stiffness Model ◽  
Foil Thrust Bearing

A new structural stiffness model for the compliant structure in foil gas bearings is introduced in the first part of this work. The model investigates the possibility that the flat segment between bumps, in bump foil strip, may deflect laterally and separate from the rigid bearing surface, and it also considers the interaction between bumps in the bump foil strip, the friction between the bump foil, and the surrounding structure. The validity of the analytical solution was verified through direct comparison with previous numerical and analytical models. In the second part of this work, the introduced bump foil model is used to investigate the static characteristics of generation II gas foil thrust bearing. The numerical simulations of the coupled fluid-structure interactions revealed that the foil thrust bearings share many features with their rigid bearing counterpart and the results showed clearly that the load carrying capacity of foil thrust bearings increases nonlinearly with the rotation speed and is expected to reach an asymptote as the rotation speed exceeds a certain value. The effects of ramp height and interface friction (i.e., friction at bump foil/rigid bearing interface and bump foil/top foil interface) on the static characteristics of generation II foil thrust bearings are investigated.

Numerical and experimental studies on the thermal and static characteristics of multi-leaf foil thrust bearing

2021 ◽  
pp. 135065012110110
Author(s):  
Yu Guo ◽  
Yu Hou ◽  
Qi Zhao ◽  
Xionghao Ren ◽  
Shuangtao Chen ◽  
...  
Keyword(s):  
High Speed ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Failure Process ◽  
Experimental Studies ◽  
Elastic Model ◽  
Static Characteristics ◽  
Bearing Load ◽  
Foil Thrust Bearing ◽  
Cooling Air

Foil bearing is considered to be a promising supporting technology in high-speed centrifugal machinery. Due to the high-speed shearing effect in the viscous lubricant film, heat generation could not be ignored. In this paper, a thermo-elastic model of the multi-leaf foil thrust bearing is proposed to predict its thermal and static characteristics. In the model, modified Reynolds equation, energy equation, and Kirchhoff equation are solved in a coupling way. The contact area between the foil and welding plate is taken into account. Besides, the effect of cooling air on the bearing temperature is investigated. The ultimate load capacity and transient overload failure process of the bearing is analyzed and discussed. The effect of rotation speed on the bearing temperature is more obvious than that of the bearing load. The bearing temperature drops obviously by introducing the cooling air, and the cooling effect is improved with the supply pressure. The transient overload failure of the bearing occurs when the bearing load exceeds the ultimate value.

Experimental Evaluation of the Structure Characterization of a Novel Hybrid Bump-Metal Mesh Foil Bearing

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Kai Feng ◽  
Yuman Liu ◽  
Xueyuan Zhao ◽  
Wanhui Liu
Keyword(s):  
Excitation Frequency ◽  
Structure Characterization ◽  
Viscous Damping ◽  
Metal Mesh ◽  
Equivalent Viscous Damping ◽  
Foil Bearings ◽  
Damping Characteristics ◽  
Foil Bearing ◽  
Mesh Density ◽  
Load Tests

Rotors supported by gas foil bearings (GFBs) experience stability problem caused by subsynchronous vibrations. To obtain a GFB with satisfactory damping characteristics, this study presented a novel hybrid bump-metal mesh foil bearing (HB-MMFB) that consists of a bump foil and metal mesh blocks in an underlying supporting structure, which takes advantage of both bump-type foil bearings (BFBs) and MMFBs. A test rig with a nonrotating shaft was designed to estimate structure characterization. Results from the static load tests show that the proposed HB-MFBs exhibit an excellent damping level compared with the BFBs with a similar size because of the countless microslips in the metal mesh blocks. In the dynamic load tests, the HB-MFB with a metal mesh density of 36% presents a viscous damping coefficient that is approximately twice that of the test BFB. The dynamics structural coefficients of HB-MFBs, including structural stiffness, equivalent viscous damping, and structural loss factor, are all dependent on excitation frequency and motion amplitude. Moreover, they exhibit an obvious decrease with the decline in metal mesh density.

Sign in / Sign up

Export Citation Format

Share Document