Re: Wheels/gaps/turnouts


Roger J Miener <Roger.Miener@...>
 

Mike Brock speaks of the interrelationship between wheels and wing
rails...

An interesting point. However, the code 110 wheel actually doesn't
drop at
all. The reason is that the turnout frog/flange gap dimensions for
track
standard S-3 matches the code 110 wheel.
What follows are links to three photos in the abpr archives. Please
note the credits on each page once it opens. These photos, together
with the text below, may be of assistance to those who have a bit of
trouble visualizing just exactly what is going on as the wheel passes
over the flangeway gap in a frog. Below we will see two views of a
crossing that utilizes railbound manganese frog castings and then we
will finish by looking a photo of a spring frog. I wish I could find
other photos because these particular configurations can be confusing,
but they will have to do for the moment.

So, let's begin.

In the first photo we see a wide view of most of a crossing - not the
whole thing. What you will see here are the shiny paths of wear left
by wheels as they pass through the crossing. Of interest here are the
parallel wear lines left by the flange-root radius portion and the
"false flange" portion of the tread as typically found on worn wheels.
When wheels wear, the pretty coned taper of the tread wears away
rather quickly and the tread eventually assumes a concave or cupped
shape. This wear results in the creation of a shallow and somewhat
broad "false flange" at the outer edge of the wheel tread accompanied
by the regular flange which now sports a worn flange-root radius that
bespeaks a flange that is both thinner and sharper that it was when
new.

Two things about this first photo that may confuse -- First is the use
of manganese inserts in the frogs - you have to mentally scoot things
around to think of how the rails would look if all the frogs were of
bolted rail construction - but then you wouldn't be able to see very
much evidence of the wear left by the false flanges -- Second is that
this crossing is using frogs of a much lower number than that
typically found in turnouts. This latter fact makes it difficult to
see that the wing rail is carrying the wheel across the flangeway gap
until such point as the flange can again ride on the closure rail.
(In other words, as you get closer and closer to a 90 degree
crossing - you get less and less "wing rail action".) So, here's the
1st photo (each of the following URLs will wrap so it's copy and paste
to get the whole thing into the browser window):
http://www.railfan.net/cgi-bin/thumb/abprphoto.cgi?/railpix/ABPR/septe
mber01/09-02-01/Diamond3PaolaKs.jpg

Next up is a detail shot of this same crossing. Here we are looking
at one of the end frogs, and the wear caused by false flanges on the
wheels is *really* evident. Indeed, this wear pattern makes it easier
to see that the outer portion of wheel tread begins to be supported on
the "wing rail portion" of the manganese insert at a point some
distance in advance of the flangeway gap. Just trace the path of a
wheel running from screen lower right to screen upper left. See how
the wear pattern to the left of the frog point begins at a location
prior to the 1/2" point of the frog? No? Well, then, try this --
Draw a horizontal line between the two points of wear - the outer ones
to the left and right of the frog point. Notice how this line crosses
the rails of the frog some distance behind the point of the frog?
Yes? Good! Now you got it.

Also clearly evident in this photo are what are called risers. False
flanges on wheels make it necessary to slowly raise the wheel rather
than allow the false flange to abruptly collide with the backside of a
rail or other part of a turnout or crossing. Do you see that
rectangular part of the casting that extends back toward the viewer
and alongside the running rail on each side of the inner or crotch
portion of the frog? The vertical side of this portion of the casting
is bolted to the running rail. It's the top surface of that "tongue"
that is of interest here. Please notice how it slopes upwardly from
its near end until, as it gets closer to the actual point of the frog,
it is level with the adjacent rail. More importantly, notice how the
wear on the riser's top surface begins *before* the transverse joint
between the casting and the adjacent rail. That gives you a good feel
for how deep false flanges can be. Notice how obvious it is that the
center of the left-hand approaching rail is not as worn as the wear
evident along its two edges - this wear pattern being even more
obvious once the wheels are running on the top surface of the casting
portion. This wear pattern is witness to the prevalence of cupped
worn tread profiles traversing this crossing. It's now time for photo
number 2:
http://www.railfan.net/cgi-bin/thumb/abprphoto.cgi?/railpix/ABPR/septe
mber01/09-02-01/Diamond2PaolaKs.jpg

Finally, we move on to the photo of the spring frog. (We are here to
look for wear patterns and to understand the operation of the frog -
so please ignore the folks shown in the photo who insist that it is
fun to be run over by a train.) First off, notice that once again we
see a riser - here it is located in the crotch of the frog. And once
again we can see wear left on the top surface of the riser by the
false flanges of the wheels passing through on the main road through
the turnout - not to mention the false flange wear (groove!) evident
on the top surface of the sprung wing rail! Since this is a spring
frog, there is no flangeway gap to bedevil wheels passing through the
frog on the main route. Indeed, the wheel sees the frog pretty much
as if it were a solid piece of rail - which, of course, is why spring
frogs were invented in the first place. However, if you mentally
shove the sprung wing rail back by the distance of one flangeway width
from its companion frog point rail, then I think you can clearly see
how that wing rail would support the wheel until the wheel had rolled
not only past the frog point but also rolled past the flangeway gap
beyond.

The deep wear caused by false flanges, evident in this photo,
dramatically demonstrates the actual width of the wheel. Keeping that
width in mind, use your Mark I eyeball to visualize the process of a
wheel traversing the other path through the turnout - i.e., moving
away from you, the viewer, and along the left hand frog point rail -
the wheel using the backside of its flange to nudge the left hand
sprung wing rail over against the springs and thereby gain the wheel's
passage through the frog. Notice that the outer edge of the wheel
tread will first begin riding on the right hand wing rail at least
eight inches in advance of where the wheel passes beyond the 1/2"
point of the frog and thereby ceases to be supported by any portion of
the frog point. From that point (pun intended), it's home free for a
smooth transition to running on the closure rail. Here is Photo 3:
http://www.railfan.net/cgi-bin/thumb/abprphoto.cgi?/railpix/ABPR/septe
mber01/09-04-01/Frog1.jpg

When I began this mini-essay, I suggested that the manganese inserts
in the crossing frogs and the sprung wing rail in the spring frog
might be confusing. Now that I am done, I think that I am convinced
that this potential for confusion is outweighed by the fact that these
particular trackage components clearly show the wear patterns produced
by false flanges and thereby give a vivid visual cue in each photo as
to the width of the wheels.

Also, just for ducks and in each instance, please do attempt some
mental gymnastics with regard to the photos by mentally doubling the
flangeway width while still holding the wheel tread width constant.
To do this you first scoot the wing rails out to twice the flangeway
width shown in the photos - and then - you will also have to slide the
wing rails toward the points of the turnout (away from the point of
the frog) so that the gauge edge of the closure rails will remain
aligned with the gauge edge of the frog point rails. If you are
successful in this exercise, you will see how the wing rails *are not
now able to support* the constant tread width wheel across the
flangeway gap of your now rearranged turnout.

There goes our constant tread width wheel, right off the tip of the
point. I'll let you be the one to visualize what you next will see -
and hear! Oh dear, what to do? Well, for starters, try doubling the
width of the wheel tread. Hmmm. Starting to look like a 110 thou.
width wheel and a 50 thou. width flangeway -- Isn't it?

So, I'll now leave you where Mike Brock left you, together with my
hope that the foregoing will help you to better understand how the
width of a wheel tread interacts with both flangeway width and with
wing rails at frogs.

Roger Miener
at Tacoma WA

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