Dan_Bower%RPI-MTS.Mailnet@MIT-MULTICS.ARPA (09/18/85)
The sections of track you saw being installed last year are called
panels. The length of a panel is commonly 39' because that is the
most common length of rail rolled in the states. 39' was chosen
because a 39' rail handily fits in a 40' gondola. Consequently,
39' panels handily fit on 40' flat cars. To reduce the number of
joints in track, rails of 78', 25m and others have been tried.
This is nothing new. I've seen 60' rails that were rolled in 1902.
However, long rails are gaining new popularity as methods of
handling have improved.
Rails are hot rolled from carbon steel. If the rails were cast,
the resulting crystaline structure would be far too brittle. A
cast rail could not be dependably bent around a curve, and it
would break easily under the impact of a train. Rolling ingots
into blooms, then into rails creates a far more malleable steel
that is still hard enough to withstand a train without deforming.
There is a tradeoff between hardness and malleability. The harder
a rail, the better it will stand up against plastic deformation
(steel deforming like butter, but slower). However, the harder the
steel, the more likely it is to shatter. One way around this is to
heat treat the rail after rolling. This involves reheating and
quenching. The result is a harder but not so brittle steel. Some
mills (USS) advocate hardening just the head, whereas others
(Bethlehem) harden the whole rail. Another tact is to use special
alloys. Molybdenum steel is available from CF&I. This has better
performance than some heat treated rails at a competitive price.
Having no special heat treating step, Moly steel is cheaper to
produce.
So why couldn't you roll rails of a train length? When rolling
steel, you must keep a very consistent temperature throughout. It
would be *very* expensive to maintain rolling temperature for a
1440' rail. Also, after rolling, rail steel must be very carefully
and slowly cooled. This is to let hydrogen escape for within the
rails. Hydrogen interstitials in steel make for very dangerous
flaws in rail. So to roll very long rails, you would have to have
an effective cooling pit as long as the rail.
Thus rails are rolled in standard lengths and then welded
together. Welding is most commonly done by the flash butt method.
This is where you literally put a few thousand volts on one rail,
ground the other and move the ends close enough to draw an arc.
The heat of the arc melts the steel, and the rails are shoved
together. The weld is left to cool and you move to the next weld.
This process can be done with the rail in track, but the best
quality is achieved at a stationary facility.
The fastenings you saw ("staples and pretzels") are most likely
Bethlehem Steel's "Lockspikes" and "Pandrol" clips. The advantage
of this system is that it is resilient (springy, so the fastening
gives a bit when the train goes by in lieu of pulling out of the
tie). It is also such that a rail can be removed without
disturbing the tie. Since rails invariably have different lives
than wood ties, being able to change rails quickly without damaging
the tie is important. With the system Bethlehem sells, the tie
plates are fastened with the cotter-key-like spikes to the tie
such that when the rails are set down, they are in gauge. (4' 8
1/2" in most of the Western world.) The rails are fastened with
the spring clips that look like pretzels to the tie plates, and
not directly to the tie. ("Pandrol" is a trademark of the British
firm that holds the patent. An Englishman named Pandrol invented
them just before WWII. Bethlehem holds the sole US license for
Pandrol clip production. There are at least 2 competing designs,
one American and one German, that have much the same advantages.
Lockspikes are a Bethlehem invention, as far as I know. By the
way, standard overall lengths for spikes range from 5 3/4" to 7
1/2". Remember, the tie itself is no more than 7" thick.)
The "heat sinks" you saw are called rail anchors. Actually, they
have nothing to do with direct heat transfer. They restrain the
force of expansion and contraction due to heat and impact by
gripping the rail on both sides of a tie. The tie is anchored by
the ballast (that's why they call it ballast) and it doesn't move.
(hopefully...) Under really wretched extremes, the rail will pull
apart or buckle anyhow. If properly installed, it takes one heck
of a heat wave or cold snap to do this.
Separate rail anchors are not necessary with Pandrol clips. The
clip holds the rail so tightly that they actually outperform
standard anchors.
By the way, if the rail that was replaced after a year was new
when it when in, it was most likely not sold for scrap. There
would have been a lot of life left in that rail yet. If it was
new, the railroad might have taken it to a shop to be welded or
reconditioned and used elsewhere. (If it wasn't new, then I
wouldn't be surprised that the Seashore gang got 'em. They have
a mainline extension project going on.)