OT- Why do trains have solid axles?

Pete F · Sep 18, 2013

I know there are quite a few people here involved with the railways, so I thought I'd throw this question out there?

I recently came across a little tidbit in reading where it said that trains need more power to pull through corners as the wheels on the carriages are mounted to solid axles. As a result the inside wheel needs to slip, resulting in increased power requirements, tyre and wear.

First of all I need to confirm this is in fact correct, and then the obvious question is why? Why not have a non-rotating axle and the bearing in the wheel, just as in road transport? In this day it seems like a terrible waste to require extra energy to haul, and I'm sure that would add up quickly on anything other than dead straight track. One way or the other there needs to be a bearing(s) in there.

Just curious.

Pete

johnoder · Sep 18, 2013

Rubbish. The wheel treads are tapered - shifting the two wheels and their axle occurs naturally (in curves) in relation to the gauge of the track and the taper works in effect as a differential. Been that way way over 100 years.

(My 7th edition American Machinist's Handbook details this on page 1170. The taper is 1" in 20")

michiganbuck · Sep 18, 2013

Interesting question Pete,

I had to look it up

Comparison of train and tram tracks - Ask.com Encyclopedia

With both tram and train wheels, this happens naturally because the tires are cone shaped sloping surfaces: the inside diameter is a few millimeters larger than the outside. As the track starts to curve, the train tries to run straight. The wheel flange presses against the side of the curved rail so the "contact point" between rail and wheel moves a few millimeters outwards, making the effective diameter of the outer wheel temporarily larger, and equally opposite: the effective diameter of the inner wheel effectively becomes temporarily smaller.

Buck

craigS · Sep 18, 2013

Pete,
It's a little more interesting than that. I was watching a video by my favorite physicist, Richard Feynman he gave a common man explanation of a trains wheels.

With a solid axle one would think a train could not go around a bend because the outside wheel would need to turn farther than the inside whee, which can't happen with a solid axle. That is why cars have a differential between the drive wheels. Also most folks think the flanges on the wheels are what keeps the train on the tracks which is not the case. The answer turns out to be that the wheel (tires) are not flat like most assume but are conical in shape. When the train goes around a bend the the axle shifts side to side and the outside wheel rides on a slightly larger radius and the inner on a smaller radius to compensate for the bend. This is also what keeps the train on the tracks, if it wonders to one side the larger diameter will force it back to the center. Sort of like a flat belt on a crown pulley. Feynman does such a good job with his explanations he is a joy to listen to, there are quite a few of his physics lectures up on YouTube, great fun if you have any interest in science explained to the common man.

Craig

Pete F · Sep 18, 2013

John I wouldn't know, hence the question. However this is where I first saw the information, and the explaination seemed quite confident given that it provided a formula to calculate the additional power required for different curve radii.
Tractive Effort & Power Calculations for Locomotive Sizing

Heavey Metal · Sep 18, 2013

Rail Curve Grease - UltraLube lubricants

abarnsley · Sep 18, 2013

When walking along a long curve, on our only mainline up here...

I was amazed at the amount of metal swarf on the inside edges of rail..

I mean a 1/4 in thick layer, a couple inches wide..

Chipmaking takes power...

Big B · Sep 18, 2013

abarnsley said:
When walking along a long curve, on our only mainline up here...

I was amazed at the amount of metal swarf on the inside edges of rail..

I mean a 1/4 in thick layer, a couple inches wide..

Chipmaking takes power...

Here come the scrappers.

Big B

Spud · Sep 18, 2013

Pic from link about "radially steering wheelsets" in modern trains

.

I thought bogies always allowed some diagonal movement of the axle to reduce wear and tear during a curve; didn't realise it is a modern invention.

Wheels and Bogies

steve45 · Sep 18, 2013

craigS said:
I was watching a video by my favorite physicist, Richard Feynman he gave a common man explanation of a trains wheels.

...Feynman does such a good job with his explanations he is a joy to listen to, there are quite a few of his physics lectures up on YouTube, great fun if you have any interest in science explained to the common man.

Craig

I LOVE Feynman! What an amazing and interesting man he was! Not only was he a brilliant physicist, but a comedian and a bongo player. I've read many of his books, but some are over my head.

I particularly like his proof of the Pythagorean Theorem. Wonder why they never explained it like that in school.

S_W_Bausch · Sep 18, 2013

Because Honda hasn't entered that market, yet.

Honda's just now wrapping up the Honda Jet R&D.

JST · Sep 18, 2013

abarnsley said:
When walking along a long curve, on our only mainline up here...

I was amazed at the amount of metal swarf on the inside edges of rail..

I mean a 1/4 in thick layer, a couple inches wide..

Chipmaking takes power...

UP tracks up the hill from work, next to where I take a walk everyday at lunch. Never seen any swarf at all normally.

I've seen a curl of steel on the inside top edge of the rail, though. Looked to be about 10mm wide off the edge of the rail, and I don't know how thick.

Pretty soon after that the rail grinder came through, and the curl of steel was gone. Maybe that is how the swarf got on the tracks you saw. I didn't look for any ground-off material when I saw the grinder train, but it must be there, a lot got taken off.

The rail grinders are very powerful, there is a car or two of big diesel generators, and the grinder cars have motors that look to be 25 to 50 HP each on the spindles. They reshape the head of the rail in one pass, moving at maybe 10 mph... considerably faster than you can walk.

eKretz · Sep 18, 2013

Don't mistake the fact that the conical wheels ride up or down their diameter in a turn as a complete friction-reducing or eliminating mechanism. Of course it will still take more power than traveling on straight rail. The entire weight of the train is being shoved over and lifted at the same time as gravity is trying to re-center it, so there's definitely going to be some force/friction exerted there.

As far as the OP's original query; I think it likely that they use solid axles so they can support more weight without needless complexity. Not to mention the cost of changing all the existing infrastructure and repair facilities (which are normally setup explicitly for and ONLY doing train wheels and axles).

Mechanola · Sep 19, 2013

A solid axle brings rigidity at a moderate price, that’s what’s needed with railways. The rail-wheel geometry explanation is fine but the speed difference between the inner and the outer wheel can become bigger than the radii level. A given bogie has its curve radius at which the speed difference equals rail-wheel geometry.

By the way, a train never runs straight on a straight track. There’s the momentum from earth that shifts trains west, most on north-south lines, and then the waggons actually sway in endless circles to and fro due to the indifferent concept of an even number of wheels. Bogies with three wheels would run stable but that’s not a proposal from me.

Mark Rand · Sep 19, 2013

Another reason for solid axles is for somewhere to put the brake disks on modern trains. Express coaches have serious brakes on them.

Pete F · Sep 19, 2013

Thanks guys. I'm having trouble imagining why having a bearing on a wheel should support less weight, these things aren't transporting a Saturn 5 around and a bearing that size could support a crap load.

I didn't ever realise the taper to the wheels was for the curves, I always thought it was to get the trucks to run straight when on straight tracks. Maybe the metal seen by some on the ballast is from the flanges? I know there's a couple of curves close to where I used to live and the wheels would squeal like stuck pigs as they went around them.

Pete

Anvil Jenkins · Sep 19, 2013

JST said:
UP tracks up the hill from work, next to where I take a walk everyday at lunch. Never seen any swarf at all normally.

I've seen a curl of steel on the inside top edge of the rail, though. Looked to be about 10mm wide off the edge of the rail, and I don't know how thick.

Pretty soon after that the rail grinder came through, and the curl of steel was gone. Maybe that is how the swarf got on the tracks you saw. I didn't look for any ground-off material when I saw the grinder train, but it must be there, a lot got taken off.

The rail grinders are very powerful, there is a car or two of big diesel generators, and the grinder cars have motors that look to be 25 to 50 HP each on the spindles. They reshape the head of the rail in one pass, moving at maybe 10 mph... considerably faster than you can walk.

I walked a lot of miles on tracks with curves (switches a lot of the time) and I agree no piles of swarf ever.

I have seen, heard, and smelled the rail grinders at work (really cool at night) and I agree that might be the source of the swarf.

I did a quick google and saw that a modern boxcar can weight 263,000 gross.....interesting that is roughly the same PAYLOAD that a Saturn V could carry :-). But at 263,000 and 8 wheels I come up with 32,875 per wheel and 65,750 per axle. The PSI where the wheel touches the rail must be truly astronomical.

Bill

BobRenz · Sep 19, 2013

One other factor is that railroad curves are not corners - they are very gradual, long radius curves.

Bill D · Sep 19, 2013

A big part of the equation is that the railroad does not own the cars. The car owners do not really care how much fuel it costs to haul. Before ball bearings became common trains used friction bearing with oil boxes at each wheel. I guess the car owners had to pay someone to check the oil and repairs were needed more often then ball bearings. I do not think the railroad will give a discount for a more modern car.
Not really sure how it works but I see strings of box cars on a siding being repaired by the local traction company and/or a subcontractor. Some how a bill for repairs and inspection gets sent to the owner. It is possible for individuals to buy a single car and rent it out. Same idea as a rental house except you will never see it again.
Bil lD.

Anvil Jenkins · Sep 19, 2013

Bill D said:
A big part of the equation is that the railroad does not own the cars. The car owners do not really care how much fuel it costs to haul. Before ball bearings became common trains used friction bearing with oil boxes at each wheel. I guess the car owners had to pay someone to check the oil and repairs were needed more often then ball bearings. I do not think the railroad will give a discount for a more modern car.
Not really sure how it works but I see strings of box cars on a siding being repaired by the local traction company and/or a subcontractor. Some how a bill for repairs and inspection gets sent to the owner. It is possible for individuals to buy a single car and rent it out. Same idea as a rental house except you will never see it again.
Bil lD.

What does it cost if your car has an issue that stops the train though ??

Bill

OT- Why do trains have solid axles?

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