Micropitting in Wind Turbine Gearboxes: Calculation of the Safety Factor and Optimization of the Gear Geometry

2011 ◽  
Vol 86 ◽  
pp. 898-903
Author(s):  
Hanspeter Dinner
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Wind Turbine ◽  
Contact Pressure ◽  
Safety Factor ◽  
Lubricant Film Thickness ◽  
Metallic Contact ◽  
Small Cracks ◽  
Gear Geometry ◽  
Specific Sliding

If the contact pressure between mating flanks of a gear set is increased, the lubricant film thickness in between is reduced to a level where the asperities of the flanks start to touch. This case where the surface roughness is of similar value as the EHD film thickness is called “mixed friction”. Due to the metallic contact of the asperities and the movement of the flanks with respect to each other, the flanks are damaged. The damaged flanks appear dull or greyish, hence the name “grey-staining” (or “Graufleckigkeit” in German), see e.g. [4] or [1]. Micropitting are small cracks on the surface of the gears (as opposed to pitting, where the cracks form below the surface), which grow into the material. The size of the damages is about 10-20 mm depth, 25-100 mm length and 10-20 mm width. Micropitting is mainly observed with case carburized gears but may also be found in nitrided, induction hardened or through hardened gears. Micropitting mainly occurs in areas of negative specific sliding. Negative specific sliding is to be found along the path of contact between point A and C on the driving gear and between point C and E on the driven gear.

A Mixed-Lubrication Study of Journal Bearing Conformal Contacts

1997 ◽  
Vol 119 (3) ◽  
pp. 456-461 ◽  
Author(s):  
Qian (Jane) Wang ◽  
Fanghui Shi ◽  
Si C. Lee
Keyword(s):  
Film Thickness ◽  
Contact Pressure ◽  
Contact Area ◽  
Numerical Solutions ◽  
Mixed Lubrication ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Lubricant Film Thickness ◽  
Asperity Contacts

Numerical analyses of finite journal bearings operating with large eccentricity ratios were conducted to better understand the mixed lubrication phenomena in conformal contacts. The average Reynolds equation derived by Patir and Cheng was utilized in the lubrication analysis. The influence function, calculated numerically using the finite element method, was employed to compute the bearing deformation. The effects of bearing surface roughness were incorporated in the present analysis for the calculations of the asperity contact pressure and the asperity contact area. The numerical solutions of the hydrodynamic and asperity contact pressures, lubricant film thickness, and asperity contact area were evaluated based on a simulated bearing-journal geometry. The calculations revealed that the asperity contact pressure may vary significantly along both the width and the circumferential directions. It was also shown that the asperity contacts and the lubricant film thickness were strongly dependent on the bearing width, asperity orientation, and operating conditions.

Lubrication of 2D Soft Elasto Hydrodynamic Contacts: Extension of the Amplitude Reduction Theory

2011 ◽  
Author(s):  
F. Mora ◽  
P. Sainsot ◽  
A. A. Lubrecht ◽  
Y. le Chenadec
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Quantitative Prediction ◽  
Reduction Theory ◽  
Lubricant Film Thickness

This paper is an extension of the Amplitude Reduction Theory to soft ElastoHydrodynamic contacts. The ART permits a quantitative prediction of the influence of surface roughness on the lubricant film thickness modification as a function of the operating conditions.

The Effects of Three-Dimensional Model Surface Roughness Features on Lubricant Film Thickness in EHL Contacts

2003 ◽  
Vol 125 (3) ◽  
pp. 533-542 ◽  
Author(s):  
Jian W. Choo ◽  
Romeo P. Glovnea ◽  
Andrew V. Olver ◽  
Hugh A. Spikes
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Three Dimensional ◽  
Lubricant Film ◽  
Imaging Method ◽  
Dimensional Model ◽  
Lubricant Film Thickness ◽  
Model Surface ◽  
Three Dimensional Model ◽  
Spacer Layer

The Spacer Layer Imaging method has been used to investigate the influence of three-dimensional roughness features on the thickness and shape of elastohydrodynamic (EHL) films. An array of near-hemispherical bumps was employed to represent asperities. A micro-EHL film developed at the bumps whose orientation depended on that of the inlet boundary at the location at which the bump had entered the contact. Rolling-sliding conditions induced a micro-EHL film with a classical horseshoe shape at the bumps. The flow of lubricant around the bumps appeared to differ between thin and thick films.

Prediction of wind turbine gear micropitting under variable load and speed conditions using ISO/TR 15144-1: 2010

2012 ◽  
Vol 227 (9) ◽  
pp. 1898-1914 ◽  
Author(s):  
Issa S Al-Tubi ◽  
Hui Long
Keyword(s):  
Film Thickness ◽  
Wind Turbine ◽  
Rotational Speed ◽  
Gear Tooth ◽  
Lubricant Film ◽  
Tooth Surface ◽  
Variable Load ◽  
Lubricant Film Thickness ◽  
Wind Turbine Gearbox ◽  
Tooth Flank

Wind turbine gearbox operates under a wide array of highly fluctuating and dynamic load conditions caused by the stochastic nature of wind and operational wind turbine controls. Micropitting damage is one of failure modes commonly observed in wind turbine gearboxes. This article investigates gear micropitting of high-speed stage gears of a wind turbine gearbox operating under nominal and varying load and speed conditions. Based on the ISO standard of gear micropitting (ISO/TR 15144-1:2010) and considering the operating load and speed conditions, a theoretical study is carried out to assess the risk of gear micropitting by determining the contact stress, sliding parameter, local contact temperature and lubricant film thickness along the line of action of gear tooth contact. The non-uniform distributions of temperature and lubricant film thickness over the tooth flank are observed due to the conditions of torque and rotational speed variations and sliding contact along the gear tooth flanks. The lubricant film thickness varies along the tooth flank and is at the lowest when the tip of the driving gear engages with the root of the driven gear. The lubricant film thickness increases with the increase of rotational speed and decreases as torque and sliding increase. It can be concluded that micropitting is most likely to initiate at the addendum of driving gear and the dedendum of driven gear. The lowest film thickness occurs when the torque is high and the rotational speed is at the lowest which may cause direct tooth surface contact. At the low-torque condition, the varying rotational speed condition may cause a considerable variation of lubricant film thickness thus interrupting the lubrication which may result in micropitting.

Thermoelastic Instability With Consideration of Surface Roughness and Hydrodynamic Lubrication

1999 ◽  
Vol 122 (4) ◽  
pp. 725-732 ◽  
Author(s):  
J. Y. Jang ◽  
M. M. Khonsari
Keyword(s):  
Thermal Conductivity ◽  
Surface Roughness ◽  
Film Thickness ◽  
Hot Spots ◽  
Critical Speed ◽  
Hydrodynamic Lubrication ◽  
Lubricant Film Thickness ◽  
Governing Equations ◽  
Thermoelastic Instability ◽  
Liquid Lubricant

An idealized model consisting of a surface with high thermal conductivity separated by a film of liquid lubricant from a rough surface with low thermal conductivity is developed to study thermoelastic instability. The governing equations are derived and solved for the critical speed beyond which thermoelastic instability leading to the formation of hot spots is likely to occur. A series of dimensionless parameters is introduced which characterizes the thermoelastic behavior of the system. It is shown the surface roughness and the lubricant film thickness both play an important role on the threshold of instability. [S0742-4787(00)00104-1]

Pitting of Gears and Discs

1974 ◽  
Vol 188 (1) ◽  
pp. 673-682 ◽  
Author(s):  
R. A. Onions ◽  
J. F. Archard
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Surface Finish ◽  
Lubricant Film ◽  
Lubricant Film Thickness ◽  
Probable Reason ◽  
Controlled Conditions

Pitting tests using 127 mm (5 in) centres distance gear rig under controlled conditions are described. These are compared with similar disc tests using the same materials and lubricants. Tests of both types confirm Dawson's conclusion that an important factor influencing pitting life is the ratio of surface roughness to the calculated lubricant film thickness. It has been shown that using a hunting tooth ratio, particularly when associated with a rough harder surface and a surface finish oriented normal to the motion, increases the likelihood of wear. Most importantly, the results show that using disc tests can greatly overestimate the pitting life of gears. These experiments and other evidence from the literature suggest that the most probable reason for these differences between gears and discs lies in dynamic gear loads.

Pressure Calculation From Experimentally Evaluated Lubricant Thickness Within EHL Contacts

2007 ◽  
Author(s):  
M. Vrbka ◽  
M. Vaverka ◽  
R. Poliscuk ◽  
I. Krupka ◽  
M. Hartl
Keyword(s):  
Film Thickness ◽  
Contact Pressure ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
Solution Technique ◽  
Lubricant Film Thickness ◽  
Smooth Contact ◽  
Friction Surfaces

This paper is concerned with elastohydrodynamic lubrication, especially determination of lubricant film thickness and contact pressure within a point contact of friction surfaces of machine parts. A new solution technique for numerical determination of contact pressure is introduced. Direct measurement of contact pressure is very difficult. Hence, input data of lubricant film thickness obtained from the experiment based on colorimetric interferometry are used for calculation of pressure using the inverse elasticity theory. The algorithm is enhanced by convolution in order to increase calculation speed. The approach gives credible results on smooth contact and it is currently extended to enable the study of contact of friction surfaces with dents.

The Influence of Surface Roughness on Elastohydrodynamic Traction

1987 ◽  
Vol 201 (2) ◽  
pp. 145-150 ◽  
Author(s):  
C R Evans ◽  
K L Johnson
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Rheological Properties ◽  
Root Mean Square ◽  
Contact Pressure ◽  
Viscosity Index ◽  
Root Mean Square Roughness ◽  
Mean Square ◽  
Sliding Surfaces ◽  
The Mean

If the ratio λ of the nominal elastohydrodynamic film thickness h0 to the root-mean-square roughness is greater than about 5, the traction between two rolling and sliding surfaces is negligibly influenced by surface roughness. The traction is then primarily a function of the parameter α0[Formula: see text], as described in reference (4), where[Formula: see text] is the mean contact pressure and αo is the pressure–viscosity index of the lubricant. When λ lies in the range 0.5–6, it is shown that the effect of asperity interaction is for the traction to still be governed by the bulk rheological properties of the oil, but at a pressure corresponding to the mean contact pressure of the asperities.

Theoretical Investigation of Surface under Soft Mixed Lubrication

2016 ◽  
Vol 851 ◽  
pp. 326-332
Author(s):  
Jesda Panichakorn
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Contact Pressure ◽  
Load Capacity ◽  
Contact Region ◽  
Surface Friction ◽  
Mixed Lubrication ◽  
Multilevel Methods ◽  
Surface Velocity ◽  
Film Pressure

This paper presents the effect of surface roughness in line contact under isothermal soft mixed lubrication with non-Newtonian based on Power law viscosity model. The time independent modified Reynolds equation, elasticity equation and the load capacity of asperities equation were numerically solved using finite different method, Newton-Raphson method and multigrid multilevel methods to obtain the film pressure profiles, film thickness profiles and contact pressure in the contact regions. The simulation results showed that the the amplitude of surface roughness has a significant effects on the film pressure, film thickness and surface contact pressure in the contact region. The minimum gap between surface, friction coefficient and asperity load increase when the amplitude of surface roughness increases. For increasing surface velocity, the minimum gap between surface increases but asperity load decreases.

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