I live near the CN’s former DMIR Proctor Hill that leads to the Duluth Docks and when trains come down, man, there is basically a blue colud with a train in it. Wouldnt this burn the shoes off the ore cars?
The blue cloud is caused by wear on the brake shoes. I’m sure that carmen check every car before leaving Proctor Yard at the top of the hill to make sure that each car has a good set of shoes.
Eventually, yes. I would guess that the shoes have to be replaced rather frequently on those trains. If they do not, the alternative is a train in the lake.
The further a brake shoe is from the wheel the less effective is the braking effort. On the Metra suburban equipment the brake shoes are set to be only about 1/4 inch or less from the wheels. So as the shoes on the ore trains are worn, the braking effort is reduced (not a desireable condition).
Yup… given time, that is. Most shoes have a composition friction material (used to contain asbestos – not anymore!) which does wear off. If they are under heavy load and heat up enough, they will smoke – and if they are under even heavier load, they will lose a lot of their efficiency (and then the engineer hasn’t much to do but hang on and pray).
That hill of which you speak is a bear, and always has been for loaded trains!
And if the shoes get hot enough, they begin to melt, losing ALL of their efficiency.
That is one reason why runaways happen. If the engineer waits too long to set air, causing the train speed to increase too much, then all the shoes can do is get hot–the force of gravity is too much even for the friction brakes to hold the train against the pull, even in emergency.
That is what happened to that train that ranaway years ago in California and derailed on a curve, crashing into some houses. I had read that even 24 hours after the wreck, some of the train wheels were still too hot to touch.
I seem to recall that certain hills had speed restrictions that, if exceeded, would cause the above mentioned situation, and if the train got over that certain speed, the crews were instructed to place the trian in emergency and immediately jump off.
Once past the “point of no return”, all the train crew can do is either jump or ride it out.
Quite right, Z – there is a very definite maximum power which the friction brakes can handle (and I do mean power, not energy). There were, and are, a number of hills which have speed restrictions. At one time, some railroads allowed higher speeds for trains with operating dynamics, but after a couple of catastrophic runaways the limit is set for the power which the air brakes alone can handle.
Note that this is different from the kind of runaway you get when you don’t set the air enough, or set and release too often, either one resulting in depleting your train’s reservoirs and leaving no brakes.
If im not mistaken, (which i probably am) some of the DMIR trains are run down the hill backwards with the loco’s running in front and backing it down the hill. They also run Dyno 8 i believe.
What I don’t get is why you sometimes see brake shoes along the rails! Is it possible for them to just plain fall off? Do they ever replace them out on the road??
Brake shoes are not replaced on line of road…only in terminals. Brake shoes along the line of road come from a mechanical malfunction and it is possible of one to ‘fall’ off from time to time when their securing mechanism breaks…anything that is made by man is subject to failing over time.
Brakes - any brakes - convert mechanical energy into heat through the function of mechanical resistance which generates heat and wear on the parts involved. Dynamic braking uses electrical resistance instead of mechanical resistance but still generates heat.
That is what happened to that train that ranaway years ago in California and derailed on a curve, crashing into some houses. I had read that even 24 hours after the wreck, some of the train wheels were still too hot to touch.<<
The main reason for the runaway on SP on the Cajon Pass in 1989 that you speak of was mainly due to insufficient Dynamics. Also, the weight of the train was not correct on the crews paper work. The Engr and Condr both talked about the speed they were making up the grade out of Palmdale and thought something was not quite right. They asked for and received a helper, which DID not inform the head end that they only had one of two units working in dynamics.That was the reason for the runaway.
Virlon
saveyour ticket… the P.E. will rise again.
Believe it or not, the shoes on cars are held on with only a simple long pin…it clips through the brake head and a few slots in the steal back of the shoe.
A good carman can change out a set on one side of a truck in under a minute.
Sometimes, the pin fails, and a shoe gets thrown off.
No big deal, every car is inspected when it gets yarded, so the missing shoes get replaced quite quickly.
Ed
Which is a very good reason to not stand too close to the tracks as a train is going by. A brake shoe at 50 mph would sting quite a bit (as would springs, banding, etc).
While I was waiting a BNSF unit coal train to come one day, i found a brake shoe. Are they supposed to look like this?: straight,then up, then over,then down, then over again.
Yes, you are correct as to the cause of the runaway. I was merely pointing out that once the runaway situation had developed, the melting was the reason that putting the train in emergency did not slow the train sufficiently to avoid the wreck.
I am working on the restoration of the 2926 <exAT&SF> and our loco cant move over 25 mph without a string of cars for braking, 500 tons of loco will over come 100 square inchis of brake surface any day…
Gunns
Huh? They are pressure activated - the efficency is based on said pressure, not “how far from the tread” the brake shoe is…
As the brake cylinder travels further out (as is the case if it has to travel further to meet the resistance of the wheel), the cubic inch area that the aux resevoir has to fill increases; and as volume increases, pressure decreases, thus a reduction in braking effort.
Technically yes, but as the volume of the aux reservoir is a lot greater than the volume of the brake cylinder the effect is negligable…
BTW: Does anybody else get a security alert pop-up thingy whan they open this thread?? Something about a certificate whatnot…
If you say so. I guess Metra and the other railroads just keep those carmen that are continually adjusting brakes employeed out of the goodness of their hearts. And Metra’s edicts that cylinder travel not exceed a certain distance was issued just for the fun of it.