Main Shaft Bearings Research Articles

A 5MW direct-drive generator for floating spar-buoy wind turbine: Development and analysis of a fully coupled Mechanical model

This work forms the first of a two-part investigation aimed at identifying the challenges and opportunities of implementing a direct-drive generator for a spar-buoy type floating wind turbine. Preliminary specifications are presented for a fully coupled aero-hydro-servo-elastic model of a floating wind turbine with a 5 MW direct-drive generator. The drive-train model uses a low-speed, high-torque radial flux permanent magnet generator supported by two main-shaft bearings. The mechanical properties of the drive-train, including the main dimensions, mass of major nacelle equipment and details for the hub/nacelle assembly are presented. The rationale behind the adjustments to the tower and platform properties and the motivation to selection of best arrangement that is appropriate for supporting the developed system is explained. A discussion on the development of the variable speed-variable pitch control system suitable for the direct-drive system including modifications to avoid negative damping and blade-pitch instability are presented. Fully coupled simulations for the developed aero-hydro-servo elastic model were carried out in HAWC2 for the normal operating conditions of the wind turbine. The aerodynamic response of the model was verified and compared with that of a geared floating wind turbine system. Some initial results comparing the main shaft loads of the land-based and floating versions of the direct-drive wind turbine suggest satisfactory dynamic behaviour of the drive-train. The results prompt further research using a detailed drive-train model to verify the internal response, loading and durability of the components to assess their compatibility with a floating wind turbine system.

풍력발전시스템의 주 베어링용 0.18C-3.5Ni-1.5Cr-0.2Mo강의 침탄 표면특성

Characteristics of carburized surface layers in 0.18C-3.5Ni-1.5Cr-0.2Mo steels for main shaft bearings of wind turbines have been analyzed and evaluated before and after rolling contact fatigue tests. Mixed microstructure consisting of retained austenite and tempered martensite has been formed with compressive residual stresses in the surface hardened layers of the specimens showing uniform hardness distribution with value about Hv700 after vacuum carburizing and tempering. It has been found on the raceway of the layers of the specimens after rolling contact fatigue tests that the amount of retained austenite decreased and compressive residual stresses increased, resulting from cyclic contact stresses applied during the tests. It has been also revealed that higher durability of the bearings can be obtained through controlling the amount of the retained austenite in the surface of the bearing steels to be lower in this study.

Research on the Arrangement of Main Shaft Bearing in the Late-Model High-Stiffness CNC Lathe with AHP

The paper provided a feasible method for selecting the scheme of arrangement of main shaft bearing. It presented the common arrangement of main shaft bearing. According to the characteristics of high stiffness CNC lathe, selecting the scheme of arrangement of main shaft bearing by means of AHP. And then, it has chosen the optimum matching scheme in the common arrangement of main shaft bearing.

Experimental Study of Failure Performances of 51306-Coated Bearings under Lubricant Interruption Condition

Some terrible disasters of aircrafts were caused by inadequate lubrication or interruption of lubricant delivery of the gas turbine engine mainshaft bearings. This paper introduces the design of the test equipment, performs the experiments of failure performance for 51306 coated bearings to respond to oil interruption under the actual situation. The main failure performance of test coated bearings has been demonstrated to be the cage damage of the test coated bearing. The failure mechanism model of the damaged cage of test coated bearings under oil interruption condition is established for the failure analysis of damage cages. The failure mechanism of the damaged cages is revealed. The main reason for the damages of test coated bearing cages under lubricant interruption condition is that the perpendicular component force acted on the cage increases continually to go with the increase of the friction force between the balls and the cage due to inadequate lubrication until the cage is broken.

Fatigue Life of Main Shaft Bearing of Direct Drive Wind Turbine

A calculation method of fatigue life for main shaft bearing of direct drive wind turbine was proposed. The statics models of the bearing were established and a set of equilibrium equations were obtained. By solving the equilibrium equations, the displacements of the inner ring were obtained, and the rolling element loads were calculated further. Based on the load distribution of the rollers, the fatigue life of the bearing was calculated and the influences of the clearances on it were researched. Results show that the clearances of the bearing can influence its service life distinctly. Zero axial clearance is recommended for the bearing.

Models of Wind-Turbine Main-Shaft Bearings for the Development of Specific Lightning Protection Systems

One of the main cause of damages for wind turbine power plants is certainly constituted by lightning. Direct and indirect events can indeed produce damages and malfunctions of electrical and mechanical components. Concerning mechanical components, blades and bearings are the most involved parts. In particular, lightning-damages produced at bearings positioned at the mechanical interface between rotating parts of the wind turbine, can result in high costs, considering the difficulties involved in the replacement of such components. The paper presents a numerical and an analytical model of wind turbine main shaft bearings aimed at calculate their electrical impedance along with their experimental validation. These models provide useful criteria for the design of wind turbines lightning protection systems (LPS). In this respect, the paper presents also the development of a specific LPS for the protection of wind turbine bearings and the relevant effectiveness analysis obtained by means of experimental tests.

Optimal Design of Mainshaft Bearing for Wind Turbine

Working conditions, characteristics, and development about the mainshaft bearing for wind turbines are investigated and mathematical model based on the rated dynamic load is proposed in this paper. With the help of the nonlinearly minimum function, viz., fmincon, in MATLAB toolbox, the constrained optimization method for the main parameters of the bearing is studied in order to improve the bearing life.

Tribological advancements for reliable wind turbine performance

Wind turbines have had various limitations to their mechanical system reliability owing to tribological problems over the past few decades. While several studies show that turbines are becoming more reliable, it is still not at an overall acceptable level to the operators based on their current business models. Data show that the electrical components are the most problematic; however, the parts are small, thus easy and inexpensive to replace in the nacelle, on top of the tower. It is the tribological issues that receive the most attention as they have higher costs associated with repair or replacement. These include the blade pitch systems, nacelle yaw systems, main shaft bearings, gearboxes and generator bearings, which are the focus of this review paper. The major tribological issues in wind turbines and the technological developments to understand and solve them are discussed within. The study starts with an overview of fretting corrosion, rolling contact fatigue, and frictional torque of the blade pitch and nacelle yaw bearings, and references to some of the recent design approaches applied to solve them. Also included is a brief overview into lubricant contamination issues in the gearbox and electric current discharge or arcing damage of the generator bearings. The primary focus of this review is the detailed examination of main shaft spherical roller bearing micropitting and gearbox bearing scuffing, micropitting and the newer phenomenon of white-etch area flaking. The main shaft and gearbox are integrally related and are the most commonly referred to items involving expensive repair costs and downtime. As such, the latest research and developments related to the cause of the wear and damage modes and the technologies used or proposed to solve them are presented.

Design and Development of a High-Speed Bearing Test Apparatus

Abstract A bearing test apparatus was developed to test high-speed rolling element bearings such as the main-shaft bearings of gas turbine engines. The apparatus design was focused on the evaluation of the lubrication characteristics of bearings in an environment similar to that of gas turbine engines, such as the same bearing support structure, the lubrication method, the squeeze film damper, and the operating conditions. Using the module design of the system, both ball and roller bearings can be tested, and the bearings can be tested up to 42 000 rpm and 19 600 N axial and 1960 N radial load. The testing was successively carried out with the bearings up to 30 000 rpm.

Sonochemical synthesis and characterization of nanostructured iron and its alloys

Nanostructured iron and its alloys are industrially important materials. For example M50 steel (4.0% Cr, 4.5% Mo, 1.0% V, 0.8% C and balance Fe) due to its resistance to tempering, wear and rolling contact fatigue has extensive applications in the aircraft industry as main shaft-bearings in gas turbine engines [1, 2]. On the other hand, ultrafine iron dispersions have applications in ferrosuids, magnetic memory systems and catalysis [3, 4]. Conventional compacted M50 steel contains large micrometer sized carbide particle [5-8] dispersed in a body-centred tetragonal martensite phase and the former can act as fatigue crack initiation sites. In contrast, the nanostructured steels which would not have the large carbide particles would therefore be expected to exhibit superior mechanical properties. Several physical and chemical methods exist for the synthesis of nano-structured powders [9-11] such as metal evaporation [12], spray pyrolysis [13, 14], laser ablation [15,16], decomposition of metalorganics [17], chemical reduction [18, 19] and solgel processing [20, 21]. Decomposition of transition metal carbonyls using ultrasound has earlier been used to synthesize transition metal nanopowders [22,23] and some groups have reported the preparation of ultrafine iron dispersions in functional polymers by the thermal decomposition of Fe(CO)5 [24, 25], however, there have been no reports in the literature on the compaction of sonochemically produced nanometric iron powders and their characterization. The chemical effects of ultrasound are numerous and it can dramatically improve the rates and yields of stoichiometric and catalytic reactions [26, 27]. This property of ultrasound is utilized in this work to synthesize, characterize and subsequently consolidate nanometer-sized iron particles and nanophase M50 steel powders by the decomposition of organometallic precursors. The iron and M50 steel powders were synthesized in a one-step reaction by the sonochemical decomposition of the organometallic precursors in a high boiling point solvent, namely decalin. The powders

The effect of ion implantation on the fatigue life and corrosion resistance of M50 steel bearings

With the overall objective to improve the service life and reliability of gas turbine engine bearings by increasing their corrosion resistance, a collaborative project under the EEC BRITE/EURAM programme was initiated. The project was aimed at developing an ion implantation technique to implant bearing components with metallic species and to optimize the process to improve the service life of bearings in situations in which salt water contamination of the lubrication oil might occur. As part of the programme of work, testing was carried out to assess the effect of chromium implantation on the rolling contact fatigue (r.c.f.) life of bearings, made in M50 aero bearing steel, operating under conditions similar to those experienced by gas turbine engine main shaft bearings during aircraft take-off. Implantation of chromium did not adversely affect the r.c.f. life of bearings made in M50 material. Following testing, non-implanted and chromium-implanted bearing components were corrosion tested to determine whether the improvement in corrosion resistance of M50 material, produced by implantation with chromium, was maintained after the bearing had been run. The improvement in the corrosion resistance of M50 material achieved by implantation with chromium was maintained after the bearings had been run for 1000 h.

Analysis of Bearing Incidents in Aircraft Gas Turbine Mainshaft Bearings

An examination of approximately 200 bearing incidents in current aircraft engines has shown that damage in the bearing is initiated at the surface. Twenty-one cases were studied in detail, and five typical incidents are presented here. The initial damage was produced by abrasive particles, dents, grinding scores, skidding, large carbides and corrosion pits. The first phase of the failure mechanism appeared to be by peeling, where microscopic regions about 0.13 mm (0.005 in) were removed from the surface, and the peels eventually developed into spalls. These mechanisms of failure are a consequence of the partial EHD lubrication utilized in these bearings, and the consequent sharing of the load by the asperities and the EHD film. Failures of this type were reproduced in lest bearings run under typical engine conditions, and these tests were used to study the peeling mechanism. Techniques for the minimization of surface-initiated fatigue are also discussed. Presented at the 45th Annual Meeting In Denver, Col...

Real time simultaneous in-line wear and lubricant condition monitoring

An in-line complete oil breakdown rate analyzer (COBRA) and quantitative debris monitor (QDM R) were installed in the oil system of an aircraft turbine engine lubricant simulator. The in-line COBRA readings correlated well with those of a standard laboratory model COBRA and total acid number of the deteriorating lubricant. Increases in QDM R particle counts corresponded with increases in trace iron content which reflected abnormal wear occurring in the simulator. Analytical and direct reading ferrographic data confirmed the rapid increase and eventual modest decrease in wear debris concentration. After test completion it was determined that a mainshaft bearing had experienced abnormal wear. Thus for the first time successful capability for real time simultaneous in-line wear and lubricant condition monitoring was demonstrated.

4731684 Pivotable changeover mechanism for loading and ejecting functions in cassette tape recorder: Shoji Suzuki, Iwaki, Japan assigned to Alpine Electronic Ltd

Continuous operation at Mach 2 means higher oil system temperatures than in conventional aircraft powerplants. Consequently, a new type of lubricant is required and new methods of evaluating lubricants.The main requirements for a lubricant for the Concorde engines are defined in terms of bulk thermal stability, resistance to breakdown in a hot bearing, oil mist coking and gear load carrying. The rigs used to evaluate these various properties are described in detail, and some of the reasons for the choice of these particular rigs are given.Problems which may arise on mainshaft bearings are split into two groups, fatigue at high load and wear due to skidding at low load. The test rigs and methods used to explore both these phenomena are described. It is claimed that fatigue is relatively well understood but skidding at low loads is a much more complex matter and there is scope for more work to establish the important parameters.Minor lubricant problems have arisen on early standards of engine but these have now been overcome and performance of the oils is satisfactory. It is therefore concluded that the oil evaluation methods are successfully screening out unsatisfactory oils.

Fatigue crack propagation in carburized X-2M steel

The growth rates of fatigue cracks propagating through the case and into the core have been studied for carburized X-2M steel (0.14 C, 4.91 Cr, 1.31 Mo, 1.34 W, 0.42 V). Fatigue cracks were propagated at constant stress intensities, ΔK, and also at a constant cyclic peak load, and the crack growth rates were observed to pass through a minimum value as the crack traversed the carburized case. The reduction in the crack propagation rates is ascribed to the compressive stresses which were developed in the case, and a pinched clothespin model is used to make an approximate calculation of the effects of internal stress on the crack propagation rates. We define an effective stress intensity, Ke = Ka + Ki, where Ka is the applied stress intensity, Ki = σid i 1/2 , σi is the internal stress, and di is a characteristic distance associated with the depth of the internal stress field. In our work, a value of di = 11 mm (0.43 inch) fits the data quite well. A good combination of resistance to fatigue crack propagation in the case and fracture toughness in the core can be achieved in carburized X-2M steel, suggesting that this material will be useful in heavy duty gears and in aircraft gas turbine mainshaft bearings operating under high hoop stresses.

Flange Loads Measurements in a Cylindrical Roller Bearing

A method of measuring the forces between a roller and the guide flange in a turbine main shaft bearing has been developed. Experimental measurements of these forces were made for a nonpreloaded bearing with nominally balanced rollers and also intentionally unbalanced rollers. The bearing was radially loaded and measurements of the flange forces were made with the rollers, both in and out of the loaded region. Two different lubricants were studied, and significantly different flange forces were measured as a result of the change in viscosity. Using a MIL-L-23699 lubricant, edge loads in the range of 70–90 N (15–20 lb) were measured for both the balanced and the unbalanced rollers. However, when a light mineral oil (kerosene) was substituted for the higher viscosity military oil, higher edge loads (110–135 N) were measured for the unbalanced roller, but the end forces were reduced for the balanced roller.

Rolling element fatigue life

ROLLING‐element bearings for aircraft turbine engine mainshaft applications are generally specified to be made of AISI M‐50 steel. Current aircraft turbine engine manufacturers' material specifications require a double vacuum melted (VIM‐VAR, for vacuum induction melt, vacuum arc smelt) AISI M‐50 steel for mainshaft bearings. With this material, ball bearing fatigue lives of nearly 100 times AFBMA predicted life have been obtained. Reduction in inclusion content, trace elements, and interstitial gas content is considered responsible for a major portion of this life advancement. AISI M‐50 also has the hot hardness and hardness retention ability for long‐life rolling‐element bearing operation at temperatures up to 588 K (600°F).

Closure to “Discussions of ‘Endurance and Failure Characteristic of Main-Shaft Jet Engine Bearing at 3 × 106 DN’” (1977, ASME J. Lubr. Technol., 99, pp. 137–138)

Closure to “Discussions of ‘Endurance and Failure Characteristic of Main-Shaft Jet Engine Bearing at 3 × 106 DN’” (1977, ASME J. Lubr. Technol., 99, pp. 137–138)

Endurance and Failure Characteristic of Main-Shaft Jet Engine Bearing at 3 × 106 DN

Groups of thirty 120-mm bore angular-contact ball bearings were endurance tested at a speed of 12 000 and 25 000 rpm (1.44 × 106 and 3.0 × 106 DN) and a thrust load of 66 721 N (5000 lb). The bearings were manufactured from a single heat of VIM-VAR AISI M-50 steel. At 1.44 × 106 and 3.0 × 106 DN, 84 483 and 74 800 bearing test hours were accumulated, respectively. Test results were compared with similar bearings made from CVM AISI M-50 steel run under the same conditions. Bearing lives at speeds of 3 × 106 DN with the VIM-VAR AISI M-50 steel were nearly equivalent to those obtained at lower speeds. A combined processing and material life factor of 44 was found for VIM-VAR AISI M-50 steel. Continuous running after a spall has occurred at 3.0 × 106 DN can result in a destructive fracture of the bearing inner race.

Roller bearing slip and skidding damage

Currently main shaft bearings are running at DN values in excess of two million. Within the next decade, it is reasonable to consider bearings operating at DN values of three million and higher. With slip being the primary parameter correlated to failure, it will become more troublesome at the higher DN values. Slip occurs in a cylindrical roller bearing when the radial load is inadequate to develop a frictional (tractional) drive force between rolling elements and rotating raceway to overcome drag forces. In order to predict the occurrence and magnitude of slip, an analytical method was developed to determine the cage speed through a series of force and torque balances. When excessive slip is predicted, there are several bearing designs that can be used to minimize it. However, the most successful has been to increase the applied load on the bearing with an out-of-round bearing which can have either a bilobe or trilobe. A main shaft bearing used in a particular helicopter engine had been a continued source of trouble. Although several bearing designs and materials were evaluated, the elliptical bearing was the most significant in reducing slip and skid damage.