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Environmental challenges in
maintaining low floor tram
traction gearboxes Dr.-Ing. N. Ritter
Dr.-Ing. M. Christ
Page 2
Table of content
• Introduction 3
• Gearbox Design (low floor trams) 4
• Typical damages due to
contamination 7
• Oil contamination 10
• Borescope inspection 12
• Sequence of contamination 14
• Preventive Measures 15
Page 3
Low floor tram gearboxes are operating close to
street surface
Page 4
70 % Low floor Tram traction
2-stage helical gear unit – Type Flender ASZA
ASZA 418 “Tango
BoGeStra“
input side
output side
Page 5
100 % Low Floor Tram
2-stage bevel-helical gear unit – Type Flender AKEA
AKEA 326
“Cityrunner“
input side
output side
Page 6
Traction Gearboxes with Contactless Seals for Wear-
free Operation
Seals are working while rotating (running vehicle)
Seals are „open“ when not in operation (stopped vehicle)
Seals are located down to 120 mm upon track level
Outside contamination may consist of
- Dust (concrete)
- Dust (brake )
- Water, even salted due to ice condition on roads in Northern hemisphere
Page 7
Railway Gearbox Problems / Failures Gear damages
Corrosion
Water inlet during operation in winter
Mixture of snow and salt (H20 - NaCl)
damages internal parts
Root cause: corrosion due to
environmental influences
Page 8
Railway Gearbox Problems / Failures Gear damages
Environmental influences /
Electrical erosion (fluting)
Grey shading
Root cause: Electrical current flow,
bad shielding concept of VFC drive
Page 9
Railway Gearbox Problems / Failures Bearing damages
Environmental influences /
Electrical erosion (fluting)
Point wise melted areas due to
point contact between ball and
race
decreased surface hardness
spalling
Root cause: Electrical current flow,
poor shielding concept of VFC drive
Page 10
Oil contamination discovered on Overhaul
Mud in inlet for oil channel
pinion
Page 11
Oil contamination discovered on Overhaul
Pinion „Polished“ after cleaning
Page 12
Inside gearbox after water passage
Page 13
Typical ranges of contamination
Contaminations
recommended by
oilcheck institutes measured in fleets
Silicium 100 mg/kg 30 – 160 (up to 500) mg/kg
Water 0,12% < 0.05%
Iron 15 – 850 mg/kg 200 – 700 ( up to 2000) mg/kg
Page 14
Typical sequence of contamination
1. Inflow of „dirty“ water by splashing or diving:
- oil level increasing due to additional water inflow, possibly leaking through sealing
- water is evaporating during continued service
2. Later in service
- Remaining oil level too low
- Sand and other contamination remaining in gearbox
- Gears getting polished
3. Damage risk
- Blocking oil channels
- Destroying bearing raceways resulting in early bearing failure
Page 15
Preventive measures
- Check oil samples for fleet-typical contamination levels
- Keep breathers clean and permeable
- Avoid access of abrasive material into the gearbox by:
- More frequent oil changes
- Protection against splash water (brushes)
- Avoidance of any stop in diving position of labyrinth seal diameter
- Use water detection system to perform early oil change on demand
- Check for sudden unexpected oil leakage as consequence of high
water level inside the gearbox
Page 16
Preventive measures
Brushes to reduce inlet
of dust and splash water
Water sensor (e.g. Hydac)
Page 17
Thanks for paying attention …
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