Environmental challenges in

maintaining low floor tram

traction gearboxes Dr.-Ing. N. Ritter

Dr.-Ing. M. Christ

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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

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Low floor tram gearboxes are operating close to

street surface

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70 % Low floor Tram traction

2-stage helical gear unit – Type Flender ASZA

ASZA 418 “Tango

BoGeStra“

input side

output side

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100 % Low Floor Tram

2-stage bevel-helical gear unit – Type Flender AKEA

AKEA 326

“Cityrunner“

input side

output side

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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

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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

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Railway Gearbox Problems / Failures Gear damages

Environmental influences /

Electrical erosion (fluting)

Grey shading

Root cause: Electrical current flow,

bad shielding concept of VFC drive

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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

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Oil contamination discovered on Overhaul

Mud in inlet for oil channel

pinion

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Oil contamination discovered on Overhaul

Pinion „Polished“ after cleaning

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Inside gearbox after water passage

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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

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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

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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

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Preventive measures

Brushes to reduce inlet

of dust and splash water

Water sensor (e.g. Hydac)

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Thanks for paying attention …