Key Concepts:
- Axle box: Component allowing smooth wheel rotation on train tracks.
- Degraded grease: Deteriorated lubricant within the axle box bearings.
- Overheating: Elevated temperature of the axle box due to friction from degraded grease.
- Chevron springs: Suspension components absorbing shocks and vibrations.
- Hot axle box detection system: System monitoring axle box temperatures.
- KHI fleet: SMRT's first-generation train fleet from the late 1980s.
- Overhaul: Comprehensive maintenance and repair process for trains.
Incident Overview:
An axle box detached from a train, disrupting services between Girong East and Bonav Vista for six days. The Land Transport Authority (LTA) investigated the incident for approximately eight months.
Likely Cause: Degraded Grease
The LTA report indicates that the likely cause was degraded grease within the axle box. While a definitive root cause couldn't be established due to the extent of damage to recovered parts, the degraded grease between the bearings was identified as a significant factor. Degraded grease leads to increased wear and tear, ultimately causing overheating and failure.
Overheating and Component Failure:
The hot axle box detection system recorded a temperature of 118°C on the day of the incident, nearly double the typical 65°C. This extreme overheating likely burned the rubber of the chevron springs, which are designed to absorb shocks and vibrations. The damaged chevron springs then detached, leading to the eventual detachment of the axle box from the train.
Train Details and Maintenance Delays:
The train involved was part of SMRT's 66 first-generation KHI fleet, dating back to the late 1980s. The train was overdue for an overhaul, delayed by over a year due to the COVID-19 pandemic. It had also exceeded its stipulated maintenance requirement of 500,000 km.
Preventive Measures and Timely Overhaul:
The LTA emphasizes that a more timely overhaul would have allowed for inspection of the axle box conditions and replacement of any degraded grease. This proactive maintenance could have prevented the incident.
Conclusion:
The axle box detachment was likely caused by a combination of degraded grease, leading to overheating and subsequent failure of the chevron springs. Delayed maintenance due to the pandemic contributed to the incident. The incident highlights the importance of timely overhauls and regular inspections to prevent component failures and ensure the safe operation of trains.
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