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Post by q8 on Oct 15, 2005 9:05:26 GMT
A thing that has always intrigued me is why do train bogies and wheelsets always have to have a solid axle?
Some modern trams have axleless trucks and cars have no axle but independent suspension. So why must trains have axles when other forms exist?
Another thing. I have read somewhere on the net (I forget where) that some plastics are actually stronger than steel and with better adhesion properties too.
This article also said that in principle there was no bar to making rail lines and train wheels of the stuff with a metal strip in the tread/railhead for track circuit purposes. Is it feasible or wishfull thinking by a plastics manufactory?
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Post by russe on Oct 15, 2005 11:31:41 GMT
A thing that has always intrigued me is why do train bogies and wheelsets always have to have a solid axle? Axles can be hollow, but machining the bore is expensive! Usually, there is little advantage is saving any weight on such a component, particularly on a drive bogie. Traditional wheelsets have axles because that is the easiest way of maintaining the close back-to-back and runout tolerances, typically 1.5mm or even less for high-speed wheelsets. The suspension and steering requirements for a car, and the weights and forces they have to carry, are very different to those of a train. I'm not aware of axleless trams. 'Strength' encompasses many different qualities. Plastics are not as hard as most steels, so would wear more and quicker. Plastics would grip better than steel, but traction at the tyre is always dependent on the weight impinging on the tyre and the coefficient of friction at the interface, so steel is still an optimum engineering choice for hardness, strength, cost and ease of manufacture. Plastic tyres, once worn, would be a throwaway, whereas steel can be reprofiled and can be recycled when beyond its useful life. (Metal is far more 'green' than plastic!) I'm sure all that is possible for lightweight applications, but it sounds extremely expensive, and I can't see any obvious benefit except perhaps for some reduction in running noise. Russ |
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Post by igelkotten on Oct 16, 2005 13:47:42 GMT
Actually, quite a few modern vehicles uses hollow axles. They are quite lighter, and are apparently actually more resistant to certain types of damage than solid-core ones. They are very common in high-speed applications, where you want to reduce the unsprung mass to an absolute minimum.
Axle-less wheel mountings and single-axle bogies etc are also something that has become more and more common lately, especially on low-floor trams and metro/urban rail vehicles. The idea behind the axle-less wheel mounting is that you can get the wheel to fit in a much smaller space, and does not have to worry about an axle clearance. Thus, you can build low-floor vehicles with full-width gangways throughout, giving lots of room for seats or prams or whatever.
The disadvantage is that it is an expensive and somewhat complicated method of construction. And it seems as if the wheels can have ride quality problems from time to time. This is not really surprising, considering the small space available for the suspension etc. Of course, on a low-speed tram, intended for short journeys, the requirements for a stable ride and excellent track-following qualities are not as strict as for a high-speed mainline train, so the trade-off can definately be well worth it.
While it has mainly been used for trailer wheels, I believe there are a few applications where single-wheel mounts are also powered, and controlled via a very sophisticated control system, with individual traction control for every single wheel on the vehicle.
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