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derailment on curves

vulcanworks

Joined: 31-01-17

Topics: 15

Replies: 21

Posted: Sun 10th Dec 2017, 7:15am
derailment on curves

Hi,
Im trying to investigate the cause of a rear coach derailing on a curve and wondered if there might be any insight from the community.

We have a temporary 26ft radius curve on tarmac. Its relatively flat with a slight camber towards the inside of the curve. 5 panels make up the 90ish degree curve, connected by fish plates.

Overtime during a running day the joints become slightly distorted and i have to realign the curve.

Yesterday for the first time we had 3 derailments, all involving the last bogie on the last coach, and all at roughly the same point on the curve.

Apart from the slight distortion at the joints which doesnt misalign the rails, we cant see what could be causing this to suddenly start happening.

If anyone has any thoughts it would be greatly appreciated.

Just to add, weve noticed some aluminum dust below the outside rail along the whole curve. The rolling stock is an 0-3-0 battery electric loco plus a 4ft coach followed by 2 5ft coaches all rated to be able to take a curve less than 20ft.
 

Replies To This Post

Xz

Joined: 1-01-92

Topics: 17

Replies: 249

Posted: Sun 10th Dec 2017, 10:02am

First you don't say whether bogie coaches or not, or if they were loaded, it can make a difference, though the basic problem is probably still the same, lack of flexibilty across the corners of the vehicle/bogie. It is most easily demonstrated in the small gauges which have no suspension at all. If there is a twist in the track so that all wheels cannot stay in contact with the rail and one whell is able to lift its flange to railhead then it will pop out of the groove especially on a bend. On a straight you might never notice! Bogie coaches without sufficient play in the pivots can suffer when the individual bogies are perfectly Ok.

I hope this helps your deliberations. Perhaps some plywood packing might help.

Bob G.
 

vulcanworks

Joined: 31-01-17

Topics: 15

Replies: 21

Posted: Sun 10th Dec 2017, 9:10pm

Hi
They are bogie coaches, and the derailments only occured when carrying passengers, but not every trip. Today I discovered the bar couplings had very little play, so through the curve they had lateral movement but precious little vertical movement. I replaced the bolts holding the bar to the clevis coupler with smaller ones to give more vertical motion, which has improved the situation, but not solved it. Im just thinking of an alternative coupling method as well as packing the track.
 

George Coles

Joined: 4-08-09

Topics: 19

Replies: 99

Posted: Mon 11th Dec 2017, 8:40am

Two thoughts:-
1) You say you have a slight inward camber on the curves. As Bob says, if the track is uneven and the coach is laterally stiff, there is a good chance that a wheel will lift above the rail. Have you tried taking out the camber?

2) I have found that with a short bogie coach and only one passenger on it, if the passenger is close to one end and leans back the other end lifts, derailing the bogie at the unloaded end. A bit like riding a surf-board?

George C
4973
 

MartynRedfearn

Joined: 1-01-94

Topics: 18

Replies: 114

Posted: Thu 14th Dec 2017, 4:21pm

A good way of just giving some extra movement is a washer on on of the bogie pivot pins, it just gives some easy twist before you have compress springs.
 

vulcanworks

Joined: 31-01-17

Topics: 15

Replies: 21

Posted: Sat 16th Dec 2017, 10:21pm

Well, an update. Things have improved after modifying the couplings and shimming the track level. However I now have a constant problem referred to by George. If the coaches are unevenly loaded bias towards one bogie, the opposite bogie will derail at some point on the curve (This does not happen on any straight section). I have mitigated this to a point by putting ballast inside the coaches over one bogie (a 12v 25kg battery to be exact). However this hasn't completely eliminated the problem.

There must be a way to solve this. It's not impossible for me to seat people so derailing doesn't happen as I only have a 3 coach train, but surely this isn't done on commercial railways with up to 10 coaches ?? and to be honest it doesn't look professional having to walk the train asking people to move.
 

vulcanworks

Joined: 31-01-17

Topics: 15

Replies: 21

Posted: Sun 24th Dec 2017, 2:11pm

Well, I've had to call it a day, as I've not been able to reliably solve the problem. Im big enough to admit defeat and ask for more direct help. If there is anyone local to the St Helens area, and might be able to come down and help diagnose our issues before the track is taken up in the new year, please PM me. Thank you
 

George Coles

Joined: 4-08-09

Topics: 19

Replies: 99

Posted: Sun 24th Dec 2017, 3:57pm

I think the 'surfing' issue only arises on shortish coaches, not longer ones as used on most 'commercial' (club or otherwise) railways.
Hope you get sorted.
Relax and enjoy your Christmas

George C
4973
 

Xz

Joined: 1-01-92

Topics: 17

Replies: 249

Posted: Sun 24th Dec 2017, 9:12pm

The solution is to get the weight nearer the centre of gravity, instead of outside the wheel-base. I other words, get the bogies as close to the ends of the coach as possible, any weight beyond the bolster will naturally tend to lift the other end. Your added weight over the bogies is unfortunately therefore only partly the answer. I have seen the problem on longer coaches where the bogies are closer together than desirable.
 

vulcanworks

Joined: 31-01-17

Topics: 15

Replies: 21

Posted: Fri 29th Dec 2017, 10:03pm

Thank you for all the replies. I've attached an image of one of the bogies. These are the same on all coaches. As you can see there is a centre spring on these bogies. I noticed from Martyn's reply that its suggested to place washers on the pivot. I can see how that would help I think. What about the opposite, if I removed the spring altogether ? The good news for me now is I don't have any further bookings for some time, so hopefully I can solve this problem in the mean time. Just need space to set up a test track.
 

George Coles

Joined: 4-08-09

Topics: 19

Replies: 99

Posted: Sat 30th Dec 2017, 6:12pm

Unfortunately your photo hasn't appeared. However, if you mean that there is a spring around the central pivot pin, then you may have found the source of your problem! I would suggest taking it out and testing the ride without the spring.
Perhaps you could try posting the pic again? If you have problems with the pic, try reducing its size. If all else fails email it to me and I'll try posting it. I am in the address book.

George C
4373
 

ivanhewlett

Joined: 1-01-85

Topics: 8

Replies: 54

Posted: Wed 3rd Jan 2018, 6:33pm

Hi

I think your problem has been solved, but in response to the question of asking people to sit in specific places I would say that I see no problem with this. On railways I have been involved with over the years it has always been the case that we will politely ask people to move towards the centre of an empty carriage in order to ensure a more equal balance between bogies. Don't forget that our loads (full scale people) on our small scale trains are effectively very large and should not be surprised by the effects of this.

Hope this helps in some way.

Kind Regards, Ivan (1065)
 

HauteSaoneFrance

Joined: 2-01-14

Topics: 30

Replies: 102

Posted: Sun 18th Feb 2018, 5:44pm

This thread has alerted me to a problem or maybe it's not a problem? Currently I'm building 3 No items of rolling stock all with chassis 3 m long 600 mm wide running on close coupled bogies fitted close to the ends of each chassis, these bogies have no springing to the axles with the bearing housings fixed rigidly to the bogie side plates, the springing is accomplished by the top plate which has a central bolt to attache the bogie to the chassis. I have seen bogies that have double springing i.e. axles sprung as well as the fixing plate being sprung is this a superior option and how real is the risk of derailing when the axles themselves aren't sprung?
 

Peter Beevers

Joined: 9-10-01

Topics: 3

Replies: 141

Posted: Sun 18th Feb 2018, 7:23pm

How real is the risk of derailing if the axles can't move up or down independent of each other?? Huge, unless your track is bowling green smooth.
 

Mick

Joined: 1-01-89

Topics: 7

Replies: 123

Posted: Mon 19th Feb 2018, 8:25am

I agree with Peter. I've attached a photo of the Cromar White bogies which are fitted to their 3 metre carriages - this one being serviced. We have eleven of these carriages. All our rolling stock at Sheffield is serviced regularly and recorded as such. The bogies are interchangeable and we always have a spare just in case. Note the springing, which is two stage i.e. first the carriage and then with passengers! Each wheel can withstand a 1" deflection. The axle weights on a fully loaded 3 metre carriage may well exceed those of your loco!
I agree with Peter. I've attached a photo of the Cromar White bogies which are fitted to their 3 metre carriages - this one being serviced. We have eleven of these carriages. All our rolling stock at Sheffield is serviced regularly and recorded as such. The bogies are interchangeable and we always have a spare just in case. Note the springing, which is two stage i.e. first the carriage and then with passengers! Each wheel can withstand a 1" deflection. The axle weights on a fully loaded 3 metre carriage may well exceed those of your loco!
 

George Coles

Joined: 4-08-09

Topics: 19

Replies: 99

Posted: Mon 19th Feb 2018, 9:22am

I think we have the answer to your original question now. If the axles in your bogies are not able to move horizontally in relation to each other, then you have the equivalent of a four legged chair on an uneven floor, unless, as Peter wrote above, you track is perfectly flat. If you raise one rail on the bends in your layout, then that puts a twist in the track, and a rigid (unsprung) bogie will tend(!!) to derail.

Back at the end of December you tried to post a picture of the offending bogie. Can you try again? If it doesn't work, my offer of 30th December stands.

It may be worth pointing out that the bogie in Mick's picture (above) has the bearings rigidly mounted to the bogie sides, but the sides themselves are not rigidly joined across the bogie, and are free to rock fore and aft, thus allowing the axles to twist relative to each other.
There are lots more points of interest in Mick's pic, but I think the best thing is for you to show us yours.
 

HauteSaoneFrance

Joined: 2-01-14

Topics: 30

Replies: 102

Posted: Mon 19th Feb 2018, 1:06pm

I like the 4 legged chair comparison George! e used to have Coles free on 4 wheels diesel electric crane with a rigid chassis, parts of the yard were uneven so every no and again you would find no drive withe one of the two driving wheels spinning.

My bogies are CMD with rigid axles but the top plate to fix the bogie to the chassis is sprung so allowing the bogie as a whole to tip a little side to side, looks like the Cromar White is similar? I see 17 d miniatures do a bogie with springs to each bearing housing as well as the top fixing plate being sprung,
 
 
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