BRAKE SHOES

[coborn35]

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?

[CSSHEGEWISCH]

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.

[zardoz]

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).

[jchnhtfd]

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!

[zardoz]

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.

[jchnhtfd]

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.

[coborn35]

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.

[NellsChoo]

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??

[BaltACD]

QUOTE: Originally posted by NellsChoo

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.

[BaltACD]

QUOTE: Originally posted by coborn35

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?

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.

[Anonymous]

>>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.

[edblysard]

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

QUOTE: Originally posted by NellsChoo

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??

[zardoz]

QUOTE: Originally posted by edblysard

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

QUOTE: Originally posted by NellsChoo

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??

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).

[coborn35]

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.

[zardoz]

QUOTE: Originally posted by virlon



>>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.

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.

[Gunns]

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

[Anonymous]

QUOTE: Originally posted by zardoz

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).

Huh? They are pressure activated - the efficency is based on said pressure, not "how far from the tread" the brake shoe is...

[zardoz]

QUOTE: Originally posted by uzurpator

QUOTE: Originally posted by zardoz

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).

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.

[Hugh Jampton]

QUOTE: Originally posted by zardoz

QUOTE: Originally posted by uzurpator

QUOTE: Originally posted by zardoz

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).

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..

[zardoz]

QUOTE: Originally posted by Hugh Jampton

QUOTE: Originally posted by zardoz

QUOTE: Originally posted by uzurpator

QUOTE: Originally posted by zardoz

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).

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.

[georgel]

YES THE SECURITY THING CAME UP ON ME.I'M NOT YELLING I JUST CAN'T TYPE !
TRY TO CONVINCE SOMEONE WHO LIVES ALONG THE TRACKS THAT THAT BLUE SMOKE ISN'T HAZARDUS.

[jchnhtfd]

QUOTE: Originally posted by Hugh Jampton

QUOTE: Originally posted by zardoz

QUOTE: Originally posted by uzurpator

QUOTE: Originally posted by zardoz

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).

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..

To amplify just a little bit -- it is possible for the brake travel to be sufficiently long to affect the braking effort, but only if the brake rigging is WAY out of whack.

And the pop up is someone on this thread has a server which does not provide the proper certificate for a picture... usually not a problem.

[Anonymous]

And under the proper conditions a brake shoe can heat up enough, and thereby transfer enough heat to the wheel, for the wheel to come off the axle! Big problems then. Luckily it doesn't happen often.

[Anonymous]

zardoz - this does not sound right.

Trains are braked by controlling the pressure in the brake line.

[edblysard]

You are confusing train air brake operation with automotive hydraulic brake operation.

With hydraulic brakes, the shoe or pad rest against lightly the drum or disc, so the travel distance for the brake shoe is far less than the distance the piston can travel, which gives you infinite variable pressure, the harder you pu***he pedal, (apply pressure) the more pressure you apply to the shoe, the faster you stop.

With train brakes, you have a fixed distance the piston can travel, and a fixed number of reductions (pressure) you can apply.

The reason for this is because with hydraulic brakes, you are only stopping one vehicle, with train brakes, you are stopping several, and each one acts different...its not the single application of one set of brakes that stops the train, its the cumulative total of all the brakes on all of the cars.

If the pressure on one car was far in excess of the others, you can have a mess real quick...

Next time you get the chance, look hard at the brake rigging diagram plate on a rail car...note it involves brake beams, levers and rods, which translates the piston travel into braking force.

The piston has a limited distance it can travel; I believe it is 6” max.

Because each wheel does not have its own piston, but uses the mechanical rigging to allow one piston per car to apply all the brakes on that car, you have to allow some play in them, because each axel has a brake beam across the car, wheel to wheel, and it has to be able to pivot and self adjust to "seat" against the wheel tread.

If it didn’t, it would not only lock the wheel set and make it slide, but it would lock it in a straight line with the car body, and if you’re in a curve, your wheels and trucks have to be able to pivot on the king pins.

To make up for some of this play, brake arms have a adjuster, which allows you to set the distance from the brake shoe face to the wheel tread on each brake shoe, so all the shoes on a car are the same distance for the tread.

Because there are so many variables involved, empty cars, loaded cars, cushion under frames...you stop a train in steps, not like a auto, where you step on the brake pedal, and get immediate response in the auto slowing, and you can brake by feel and seat of the pants, because you are only stopping one car...where as you have to apply brakes in steps on a train, and allow the momentum to bleed off, then apply another reduction, so forth and so on...one of the engineers here can give you the steps on the train brake valve.

Maybe the best way to explain it is, you apply the brakes on a train not to force it to stop, but instead, you apply the brakes, and allow the weight/friction of the slowing cars to drag the train to a stop.

Ed

[BaltACD]

QUOTE: Originally posted by EFCO

And under the proper conditions a brake shoe can heat up enough, and thereby transfer enough heat to the wheel, for the wheel to come off the axle! Big problems then. Luckily it doesn't happen often.

In modern railroading, with 40 years actual experience in it, I have yet to hear of this be a cause of an incident; that being said in Steam Locomotive days, the tire (containing the flange and the surface that contacts the rail) was shrunk fit on the wheel center of the drivers. Extended use of the locomotive brakes could cause the tire to heat and expand and come off the wheel center and become the cause of a major delay, if not a catastrophic derailment..

It has been known for imporperly mounted wheels to come disengaged from the axle, however.

[Anonymous]

QUOTE: Originally posted by EFCO

And under the proper conditions a brake shoe can heat up enough, and thereby transfer enough heat to the wheel, for the wheel to come off the axle! Big problems then. Luckily it doesn't happen often.

I don't think so.......................

Virlon
save your ticket..... the P.E. will rise again.
I

[jimrice4449]

Back in olden times when I worked the BN train from Pullman Wa***o E Lewiston Idaho we had a REALLY stiff grade getting from the high Palouse country down to the Clearwater River. W/ a fairly heavy train we would sometimes have to stop and let the wheels cool. Now those things were so hot they not only smoked but changed color. They were about the color of a new, brightly blued gun. We never had any wheels fall off though.