Tribotechnical Systems in the Automotive Technique - Lubricant ...

Tribotechnical Systems in the Automotive Technique 

Rolling Bearing Damages in Traction Motors 

Causes and their Elimination 

Dipl.-Ing. Peter Stephan 

LUBRICANT CONSULT GMBH 

Key-Account / OEM 

Bahn- und Verkehrstechnik 

www.lubcon.com 

ÖTG – Symposium 2005, FH Joanneum Gesellschaft mbH, Graz 

LUBRICANT CONSULT GMBH – Technology Center Schweinfurt (TZS) Page 1 

Graz 2005 – 16.08.2005 – St

Rolling bearing failures in Traction Motors – Causes and their Elimination 

Contents of the report: 

Lubrication / Grease Lubrication / Relubrication 

Bearing Failure in Electric Machines 

Damages and failures caused by wrong lubrication 

Bearing failures caused by current passage 

Relubrication system for electric machines in practise 


Graz 2005 – 16.08.2005 – St

LUBRICANT CONSULT GMBH, Maintal (bei Frankfurt/M.) 

Manufacturer of special lubricants 

greases, oils, pastes 

for demanding applications and / or 

extreme critical ambient conditions 

Lubricant + 

Lubrication Engineering = Customer‘s advantage 

LUBCON Service+Systems GmbH, Maintal + Schweinfurt 

Manufacturer / supplier of respective lubrication technique 

lubricators, central lubrication systems 

customer specific solutions (OEM and maintenance) 


Graz 2005 – 16.08.2005 – St

Manual Lubrication – Risk ?! 

Deficient lubrication Overfeeding lubrication 

Possibilities : increased intervals 

forgotten lubricating intervals 

Wrong relubrication quantity 

Mixing up of grease 

Danger of contamination 


Overfeeding is as dangerous as 

deficient lubrication! 

Possibilities : reduced intervals 

additional lubricating intervals 

Graz 2005 – 16.08.2005 – St

Automatic Relubrication – the better solution 

Advantages: Deficient and overfeeding lubrication can be avoided 

the correct lubricant is guaranteed 

contamination is nearly impossible 

lubrication into the running bearing is possible 

lubrication intervals are automatically secured 

reliable lubrication also at difficult accessible points 


Graz 2005 – 16.08.2005 – St

Failure Reasons of Rolling Bearings – General Failure Statistics 

Cause of failures : 

Assembly faults 

Liquid contaminations 

Operating condition, 

interpretation, production 

10% 

Solid dirt contaminations 

20% 

5% 5% 

Quelle: antriebstechnik 18 (1979) Nr.3 

Following failures 

15% 

20% 

20% 


5% 

Deficient lubricant 

Outdated lubricant 

Unsuitable lubricant 

More than 50% of all rolling bearing failures are caused by wrong lubrication! 

Graz 2005 – 16.08.2005 – St

Bearing Failure at Electric Motors – Main Reasons 

Lubrication / Relubrication 

wrong grease, deficient lubrication, overfeeding lubrication 

Too high priming force caused by the belt 

increased load, overturning, cage failure 

Bracing caused by the couplings / cardan shaft 

additional dynamic forces, increased loads 

Current transfer during operation with FU 

Contamination 

failures on running path, grease aging 

liquid (water, steam), solid (dirt), reduction of lifetime 

Break down of the sealings 

Assembly mistake 

„normal“ aging, sealing reaction with the grease 

Down time problems 


Is mostly valued as 

deficient lubrication ! 

But: 

Knowing the right 

cause, it is possible 

to eliminate it! 

Graz 2005 – 16.08.2005 – St

Bearing Failure – Lubrication – Wrong Grease (1) 

1 2 

3 

Bearing is no longer regreasable ( 1+2 ) 

Grease residues are sticked so much onto the 

slideway that they cannot be wiped away. ( 3 ) 

Cause: Despite of correct lubricating intervals, 

it is not possible to re-lubricate the bearings 

with a sufficient quantity of fresh grease ! 

Cause : wrong initial greasing ! 


Graz 2005 – 16.08.2005 – St

Bearing Failure – Lubrication – Deficient lubrication (1) 

1 2 

3 

Cause: Exceeding of service life, no relubrication. 

This bearing showed deficient grease lubrication at 

first delivery (1). The extracted grease sample is 

dry, mixed with particles and has no lubricity (2). 

The raceways are partly polished and changed. 

On the inner ring a typical spalling is visible (3). 


Graz 2005 – 16.08.2005 – St

Bearing Failure – Lubrication – Deficient lubrication (2) 

1 2 

3 

At delivery the bearing kept brown grease 

residues incapable of lubricating (1). 

On the raceways (2) and the lateral bearing 

surfaces (3) material spalling was visible, which is 

typical for deficient lubrication. 

Cause: Grease contamination during operation, no relubrication was effected 


Graz 2005 – 16.08.2005 – St

Bearing Failure – Lubrication – Overfeeding lubrication 

1 2 

This motor showed grease in good quality in the winding (1) the bearing 

and the clearance around the bearing were completely filled (2). 

The bearing was overheated, the additional lubrication caused a further 

temperature increase (grease-worked friction). 

Cause: Overfeeding lubrication with an automatical lubricator 


Graz 2005 – 16.08.2005 – St

Bearing Failure – Current Flow 

Reasons: 

Cyclic current flow 

Unsufficient earthing 

Capacitive flows 

HF caused by frequency 

changer set 

PWM principle by IGBT 


Graz 2005 – 16.08.2005 – St

Bearing Failure – Current Flow – the Damage Report 

Damages of the 

raceway 

Current flow with two effects 

1. 2. 

Aging of the lubricant 

Particles cause aging 

of the lubricant 

Smallest melting craters high thermal load 

Dramatic increase of numbers Coking of the oil / soap 

Complete destroying of the surface Aging due to mixing 

Roughness causes metal contacts Particles thicken the lubricant 

Permanent contorting of particles and show catalytic effects 

In case of higher current: Grooving Mixed friction conditions 

Complete failure of the rolling bearing 


Graz 2005 – 16.08.2005 – St

Current Flow - Mechanism 

Low speed 

Mixed friction area 

Excellent conductivity 

Metallic contact onto 

niveau of surface 

roughness 

R ~ 1 - 10 5 

Friction Coefficient 

Relative Speed 


F N 

F R 

s ~ 0,25 µm 

High speed 

p 

p 

Hydrodynamic friction 

No conductivity 

Lubricant as insulator, 

lightning discharge 

R >> 10 6 

Graz 2005 – 16.08.2005 – St

Bearing Failure – Current Flow – Pictures of the Damage(1) 

Optical expertise 

The damage of this deep groove ball bearing is very advanced and is clearly 

visible. The outer ring shows the typical grooving and also the grey colour of the 

raceway is visible. (1). 

All balls are equally grey discoloured (2). 

Reason: continious, relative strong current flow 

1 2 


Graz 2005 – 16.08.2005 – St

Bearing Failure – Current Flow – Pictures of the Damage (2) 

Microscopical Expertise 

V=50x 

Still not 

convincing ! 


Graz 2005 – 16.08.2005 – St

Bearing Failure – Current Flow – Pictures of the Damage (3) 

Expertise with Surface Electronic Microscope REM 

Original 45 x 

1000 x 

3µm 


4000 x 

Graz 2005 – 16.08.2005 – St

Bearing Failure – Current Flow – Grease Damage 

In the main load area the grease is already 

themally damaged – dark colouring ! 

The grease life time is drastically reduced! 

The inner ring shows the typical rotating 

dark coloured raceway. 

Problem: Reduction has not be concerned in the calculation ! 


Graz 2005 – 16.08.2005 – St

Relubrication Technique for Electric Machines 

Correct lubricating quantity 

Correct lubricant 


Continous fresh grease application 

Automatical relubrication into the 

operating bearing 

Long-term maintenance interval 

(Supply of the bearing up to 5 years) 

Graz 2005 – 16.08.2005 – St

Relubrication Technique – Practical Example „Traction Motor“ 

Quelle: HAVAG (Halle/S.), NBE 

Articulated bogie, tramway 


2 driving motors with 105kW each: 

1 movable bearing each with grease 

lubrication 

Solid bearings operate in oil bath 

Problem: 

Bearing failures, bearing noises 

Distinct low deviation of the 

indicated relubrication period 

Solution: 

16 months defined permanent 

lubrication with MicroMax 120 

Graz 2005 – 16.08.2005 – St

MicroMax 120 – the Functional Description 

120 cm³ grease measured in 0,12cm³ for max. 5 years 

Switch 


Micro-contolled system of the driving motor 

1000 single hubs for the grease supply 

Function independent of temperature 

Pressure build-up 0…10 bar 

Completely sealed ( IP68) 

Graz 2005 – 16.08.2005 – St

Grease Selection and Grease Operatig Time in Traction Motors 

Special requirements: 

Long-term lubrication / minimum quantity lubrication 

High vibration resistance – stability of the soap structure, structure stability 

Wide temperature range (-30°C…120°C) 

Speed index maximum nxdm = 400.000 

Excellent corrosion protection properties 

Electrical conductivity in ideal case (without graphite !) 

Conductivity of a grease: 

is able to reduce potential voltage 

reduction of the typical current passage effects (e.g. craters) 

LUBCON-ELC-line (conductive additive in nanotechnology) 


Graz 2005 – 16.08.2005 – St

Survey 

-Damages on rolling bearings caused by current passage in electrical machines 

will play a larger role in the future, when up-dated revolutionary controlling 

devices will be used. 

-High frequency current passage reduces the grease life-time. 

-The insulating measures decided by the manufacturer of electrical machines are 

successful. 

-A continous relubrication of the bearings with grease is a successful measure to 

a plain increase of the life time. 

-The usage of electrical conductive greases causes an advantageous reduction of 

the voltage potential between the bearing rings. 

-By now there are existing permanent lubrication devices on the market, which 

secure an extremely long running-time with minimum grease quantity. 


Graz 2005 – 16.08.2005 – St

Tribotechnical Systems in the Automotive Technique - Lubricant ...

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