MRT EAST-WEST LINE MIS-HAP - IT'S THE BALL BEARINGS, STUPID

AI rendention of a dislodged axle box and mis-aligned bogie being dragged along.

So we have the spectacle of another train mis-hap on Sep 25 and the standard knee-jerk emotional reactions. Within minutes the same cacophony is all over town. Predictably, the regular whipping boys of generals and million-dollar salaried ministers get paraded on social media. I think it is alright for Singaporeans to speak up, but be adults in the room. By all means, say something useful and meaningful. Spare us all the nonsense speak. The public ought to show concern and want some answers. However, verbal bashing of folks many times removed from the chain of command is juvenile. It is alright for the minister and other top honchos to turn up at the scene, indeed they need to. But it is not alright for them to take it as a photo-op and take selfies for their own Facebook posts. I think humility of those in charge is sorely absent in Singapore in the way we see displayed in Japan.

I congratulate Straits Times for this report on Sep 27 and updated Sep 30 which described the event and the damages very well. We have all been told the fault points to an axle box which had been dislodged which in turn caused the bogie to be dragged along under the carriage, damaging tracks and trackside devices. We have been shown the 'what' but not the 'how' and 'why'. In this light I humbly blog, not as a pseudo-technical expert, but sharing what we can learn from the experience of others.

The axle is a solid rod that connects and aligns two wheels, enabling them to rotate together. The axle box is the protective housing containing bearings that support the axle and allow it to rotate smoothly, while also supporting the train's weight and protecting the axle from damage.

The bogie is a specific undercarriage assembly located beneath the main body of the vehicle and consists of wheels, axles, suspension, and sometimes motors or brakes. The bogie provides support, suspension, and stability while allowing the train to move smoothly along the tracks. Its primary role is to distribute the coach's weight, absorb shocks and vibrations, navigate curves and for powered bogies, provide braking and traction.

There is an underframe or car body, which sits atop the bogie. This supports the body work of the coach just like the chasis of a vehicle.

It's the bearings, stupid! 

As the 1st-gen trains are older Kawasaki Heavy Industries models, they use plain bearings. Most modern trains now use roller bearings (either cylindrical or tapered) which offer lower friction, greater load-bearing capacity, and better durability compared to the old plain bearings. The critical function of the bearing is to reduce friction between the rotating axle and the fixed frame of the train.

You have heard the "Diddy" Combs bombshell story in US. He stores 1,000 bottles of lubricants in his mansion for his regular wild parties for celebrities and high society names. If anything needs lubricants, lots of them, it's them bearings. They need to be lubricated to reduce friction and prevent wear. Regular maintenance is required to replenish the lubricant to ensure the longevity of the bearings and reduce heat from friction. As the old plain bearings have higher friction, they require more lubrication.

Exogenous contaminants such as dust, dirt and moisture can also increase friction with the bearings. The axle box prevents these contaminants from entering. Leakage or poor box maintenance may allow contaminants to enter.

Bearing overload is when the trains carry loads that exceed the design capacity of the axle box and bearings. Excessive loads cause higher rolling resistance and increase friction between the bearing components, resulting in overheating. Weight overload is more an issue with cargo trains.

Misalignment of axle box with the axle or wheelset can happen due to poor maintenance, mechanical failure or damage to axle box components,and overheating of bearings. When this happens, it can cause uneven pressure on the bearings leading to more stress and increased friction.

There are other causes for overheated roller bearings, including fatigue cracking, water damage, mechanical damaging, a loose bearing or a wheel defect.

So what is the problem with increased friction of the bearings. Friction causes heat build-up in the axle box, a situation called a 'hotbox'. This is very dangerous because overheating causes bearing seizure where bearings lock up and stop rotating. This is extremely dangerous because the axle and wheels cannot rotate freely, leading to even more friction and heat generation. A seized bearing can cause the axle rod to seize which causes the wheels to be dragged. This leads to severe damage to both the train and the tracks and possible derailment as well as fire to coach and surrounding equipment.

What are the telltale signs of a hotbox

With overheated bearings there is of course increased temperature. But this is unlikely to be noticed even by passengers.

Over heating leads to smoke, an acrid burning odor, or visible signs of burnt grease or oil.

Overheated bearings cause increased friction which causes excessive noise, including grinding or squealing sounds.

Once overheated, the increased friction. causes vibrations, indicating that the bearings are not functioning smoothly.

Overheated bearings may lead to hotbox fires

Smoke was reported in the Buona Vista mis-hap. Passengers were unlikely to notice the heat. The passengers in the affected coach most likely heard the squealing noises and felt the vibration. I have not seen or heard anyone talking about this in social media. Has anyone spoken to someone who was in that particular coach?

A chain reaction from a hotbox

Overheating (often called a hotbox) causes the bearings to seize, which in turn could seize the axle rod  causing the whole wheelset or bogie to be thrown out of alignment and dragged along. This results in significant friction between the train and the track and tremendous vibration which will cause other components such as suspension systems and clamps or parts that hold the axle box to collapse. The axle box then get dislodged. If the train is moving at high speed, the train could derail. As the axle box and bogie get dragged along, serious damage will be caused to the rails and sidetrack equipment.

In most cases, as hotbox problem builds up, it is usually at the bends when dislodgement of axle box and bogie occurs. In this particular incident, it is worth nothing the severe damages near to the Buona Vista station and the turn into the Ulu Pand depot. These are the bends where the train switched tracks. Three switch gears were damaged.

It is possible the axle box could get dislodged without a hotbox incident. The fault could be the parts that hold the axle box in place could be broken due to wear and tear or damage. I think this is less likely because these parts are easily observable in regular inspections.

What history shows:

These are some of the examples where tragic train crashes were due directly to hotbox incidents.

Coxville Train Wreck (USA, 1910)
Wheaton Train Wreck (USA, 1924)
Altoona Train Derailment (USA, 1950)
Białośliwie Train Accident (Poland, 1983)
Amundsen Express Derailment (Norway, 1990)
Severn Tunnel Rail Accident (UK, 1991)
Zeebrugge Freight Train Derailment (Belgium, 1999)
Pécrot Train Collision (Belgium, 2001)
Liaoning Freight Train Derailment (China, 2010)
East Palestine Train Derailment (USA, 2023)

There have been many other train accidents which were not due directly to hotbox and axle boxes but investigations suggested they may have played a role in damaging tracks that led to the disasters.

Use of sensors

In modern trains, temperature sensors are often installed in axle boxes to detect overheating and trigger alarms.. These 1st-gen trains do not have such sensors.

Some train systems install heat detection sensors on the tracks at intervals of a few miles. These allow undercarriage heat situation to be detected and real time data to be fed to control systems.

Trackside hotbox detection sensors have been found to be ineffective in a study in 2019 by Constantine Tarawneh et al. The “major shortcoming” of these detectors is that they can’t distinguish between healthy and defective bearings, and temperature alone is not a good indicator of bearing health. Moreover, temperature is reactive in nature. That means by the time the sensors pick up a high temperature in a bearing, it’s too late, the bearing is already in its final stages of failure.

In the East Palestine Train Derailment (USA, 2023) hotbox sensors detected that a wheel bearing was heating up miles before it eventually failed and caused the train to derail. But the detectors didn’t alert the crew until it was too late. 30 miles outside East Palestine a sensor recorded a temperature of 38 degrees F above ambient and did not set off alarms because the operator's threshold was set at 170 degrees F above ambient. 10 miles later the next sensor recorded 103 degrees F above ambient.  Video of the train recorded in that area shows sparks and flames around the rail car. Still, no alert went to the crew. 20 miles later just as the train reached East Palestine, a hot box detector recorded the bearing’s temperature at 253 degrees F above ambient and sent an alarm message instructing the crew to slow and stop the train. That's when it derailed.

Tarawneh et al researchers developed a new system to better detect a bearing issue long before a catastrophic failure. The key is measuring the bearing’s vibration in addition to its temperature and load. Tarawneh sensors can be placed on board each rail car, near the bearing, to continuously monitor its vibration throughout its travels. The vibration of a failing bearing begins intensifying thousands of miles before a catastrophic failure. The Tarawneh sensor is a sort of accelerometer on a bearing that monitors vibration levels. The minute a defect happens in the bearing, the accelerometer will sense an increase in vibration, and that could be, in many cases, up to 100,000 miles before the bearing actually fails.

Costs of installing the Tarawneh technology device on every coach is an issue. Some suggest the alternative of installing sidetrack acoustic devices that can monitor vibration and noises.

The Investigative Panel of experts have an important job on their plate. Some of the areas they need to look into are :

* Was the OEM standard of maintenance of the ball bearings followed or did the regime change because cost considerations got in the way of trying to find a balance between over- and under- maintenance.
* Although load is not so much an issue in passenger trains, did a system designed for 3 million population create fatal stress on bearings serving 6 millions. SMRT trains has a remarkable 3 minute turnaround time. Does this increase stress on the bearings.
* Since the 1st gen trains do not have heat sensors on the axle box, are there trackside hotbox detection sensors? 

* The tracks and trackside equipment damages have all been replaced. These are all visible damages at the final stages of hotbox where the bearings have degraded, the axle box dislodged and the bogie collapsed. During this stage, severe vibrations and uneven movement of the wheels caused significant damage to the rail, such as deep gouges, cuts, or railhead deformation. However, as the study on the East Palestine incident shows, bearing heating started some 30 miles earlier. As bearing gets heated, friction increased and bearings degrade. This leads to bearing seizure which then degrades the axle box and the axle rod. This caused misalignment of wheels which damage and degrades the rails. In other words, the rails kilometres eastward of Buona Vista could have been stressed and degraded. The panel needs to determine how far back the tracks need to be stress tested.
* To confirm the new generation trains indeed come with hotbox detection sensors.
* To consider installation of Tarawneh new technology vibration detector in train cars.


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