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09/06/2010
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Trains, especially freight trains, need to be weighed. But how?
Just as overloaded heavy goods vehicles can damage roads, trains or railway wagons that are too heavy can damage rails. Worse than that, they can result in track subsidence and trains coming off rails. There have, in addition, been train crashes recorded in the US as a consequence of trains that have been too heavy for their braking power descending a long downhill gradient.
Such happenings result in a fearsome amount of expenditure to put right, assuming that there have been no human deaths or injuries. And if wagons contains bulk materials – stone, sand, coal, gypsum or grain, it is necessary to know how much they carry in order to assess the value of their cargo in the interests of commerce, or to know how much to charge for carrying them.
There is also the issue of whether wagons are loaded evenly. On a heavy goods vehicle on a road, it is usually fairly easy to see if a load is lop sided, since springs will be visibly more depressed where the weight is greatest, but the same is not true of a railway wagon. Nonetheless, a badly distributed load is equally problematic, potentially resulting in excessive stress to wheel profiles, axle boxes, bearings, gear boxes, final drive units and suspension components. The problems are much the same, regardless of whether the train is going on the national rail network, or is purely being used to move heavy items or minerals on a privately owned network in a steelworks, power station or mining or quarrying operation.
The Challenge
It is possible to build a weighbridge for rail wagons, in the same way that it is possible to build a weighbridge for trucks, but these are large items, expensive, and take some time to install.
If a potential problem with a possibly overweight train or badly loaded wagon is suspected, there may not be a weighbridge in the vicinity to make measurements before launching the train into the railway system. Hence, as well as a weighbridge, there needs to be some way to weigh wagons, wholly or by axle, or whole trains, using some simple system that can either be quickly installed or is portable.
Scales suitable for weighing a whole train are clearly impractical, but a specialist British company has come up with systems that allow wagons and trains to be weighed using units that are relatively simple to install. It has even developed a package that can be transported in the back of a car, carried to where it is needed by two men, and installed in 15 minutes. It does make use of modern technology to give and record accurate results, but its basis is extremely simple. Victorian engineers could have developed it too, if any of them had thought of it.
The solution will be described fully in Eureka's July 2010 edition. See if you can come up with anything better.
Solution to Last Month's Coffee Time Challenge
The solution to our challenge to design a commercially viable wave powered vessel exists in the form of the 'Wave Glider' a small autonomous surface vessel developed by Liquid Robotics, formed by a group of Silicon Valley engineers in Palo Alto, California. Intended for ocean surveying, monitoring and warning tasks, it is 2m long, but has a towing unit on a 7m long, streamlined, umbilical tether, which works below the waves. This has 12 wings which flex up and down as the vessel rises and falls, lifting and lowering the towing unit, which is deep enough to be below normal wave motion. As the wings flex, they have the effect of pulling the vessel forwards. The towing unit has a rudder, so the vessel can maintain or change direction.
Although it looks simple, director of scientific and commercial business, Justin Manley said, "There's a lot of mechanical complexity in there." Solar panels provide the small amount of power required to power the rudder motors and the electronics. A phase II development plans to use the rising and falling motion to provide the electric power also.
It communicates data and receives instructions via the Iridium satellite phone system. Manley said that, "We listen into the AIS network and we are pretty good at figuring out ways of keeping it out of the way of ships, even if they are fast and we are slow. If ships are not AIS, this adds complexity, but most of its work is targeted in the middles of oceans where ships don't go." This work is to monitor the environment, ocean currents, cosmic rays, tsunamis and undesirable activities. The vessels can be made to keep station, relying on GPS navigation, at a small fraction of the cost of a buoy with a long enough mooring line to attach it to the bed of the ocean. The US military and security services have uses for them, since they are relatively small, cheap, easily deployable and can be made hard to find. Tests so far include 60,000 nautical miles of voyaging, including one individual journey of 6,200 nautical miles over 430 days and station keeping to an accuracy of 50m in Monterey Bay. Average speed is 1.5 knots.
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Author
Tom Shelley
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