( TEHACHAPI: Two Tracking Updates) by KP Harrier ( with other contributors to the Thread).
There is a discussion of specif styles of switches used ( equilateral and moveable point frogs switches).
The discussion seems to center around why the specific type of switch is used and part of that is concerning the wear patterns produced by the traffic patterns over those switches. Some time ago I was doing some work for a local Memphis manufacturer of railroad switches, and got introduced to their use of hardened switch points. Apparently, that hardening process increased the wearability of the parts hardened with explosives ( types of plastic explosive strips placed around the frogs and detonated, to created the hardened final product.)
It would seem to be an expensive and valid way to create a longer wearing track part, which would equate to a saving for the railroad who owned and maintained those switches.
Is this process too expensive to use currently, or have methods improved enough so that the track can be repaired or replaced more readily, does the hardening enhance the use or detract as too expensive?
The links don’t open for me, but the process sounds interesting. I take it that the expolsion compresses the steel so it becomes more dense. But that raises the question of how much size reduction occurs and whether the products need to be made oversize to compensate for the explosive reduction.
I would also expect that this explosion must be made with precisely shaped charges that perfectly encapsulate the product to be treated. Also, it might be a challenge to detonate the charge at many points simultaneously in order to make the compression uniform.
Generally, that is the process for detonating an atomic bomb.
The first link is a report which is slightly difficult to read - the translation isn’t very smooth. They were also talking about some metallurgy that is way over my head…
The forum software doesn’t want to play nice today.
The original detonation-hardening experiments were made in Russia IIRC, as a sort of spinoff of implosion-charge technology. Detonation nanodiamonds are a kind of cognate field.
I view this process as a form of directional forging, and (when implemented with fascias or overlays) a way to provide physical “close-plating” of hard materials or coatings onto a substrate without high heat or other damage.
I had thought that the ‘hardening’ was not for the frog as a whole, but only the wearing portions – the areas that can’t be properly addressed by, for example, hot-working a high-manganese alloy casting or the like. It has clearly made sense (to me) to provide a proper overlay for high-speed/high-load rails that would preclude all the recognized problems with work-hardened martensite plates inducing stress cracking in railheads, or other highly-stressed areas – and this would involve detonation ‘alloying’ rather than just conducting forgelike hardening… particularly in the current generations of head-hardened rail production.
On a conventional frog, for example, only the area where flange contact needs to be supported could be given a very hard coating – Stellite or Hastelloy, to name a couple – which would otherwise be difficult to bond effectively (particularly over the wide potential temperature range track ‘sees’). The actual cost of preparing the charges, and of the metal and environment prep, and of the actual alloy used for the hard coating, is not particularly great, and I would expect the lifetime gains to be substantial and meaningful even before the labor and admin costs of more frequent servicing are included.
Movable frogs involve some further considerations, but I cannot imagine anything other than good hard coatings for any component of Class 9 track, where any wear that produces line and surface defects will become rapidly accelerating, perhaps even failing catastrophically without substantial early warning. &
“…The original detonation-hardening experiments were made in Russia IIRC, as a sort of spinoff of implosion-charge technology. Detonation nanodiamonds are a kind of cognate field…”
reference this link to ad to what Overmod said: ( admittedly it carries a date of 1968, but it confirms his thoughts as to the Russian Origin(?)…"
Having spent over forty years in the steel industry and wear resistant coating field I think what happens is the explosion rapidly heats the steel surface and quickly quenches it. This causes the carbon in the steel to form carbides which are very hard in the grain boundaries. Localized hardness with good ductility would be the result increasing wear life with no negative side effects from brittleness which go hand in hand with hardness.
(1) Explosive hardening of steel castings has been going on for decades in this country (I don’t neccessarily buy that the Russians invented it, they have a bad habit of “inventing” everything except what our politicians claim to have invented…only your metallurgist knows for sure!)…In the proper hands, c4 is pretty amazing stuff.
(2) Switch7Frog , where be thou?
(3) Crossing Frogs and turnout frog manganese castiings don’t always make it through the explosive hardening process. Many fail and come out with spiderweb cracks. ( kinda looks like broken automotive glass)…many a custom-made crossing frog fails before it’s shipped because of this, causing delays in delivery (and frustrated roadmasters hanging-on with bubblegum/band-aids/belts&suspenders until the new trackwork parts arrive).
(4) Explosive hardened castings have a stamped “EH” or “H” in the top of the frog casting. Many of the Class 1’s pay the premium for explosive hardened steel in main line applications where impact loadings are high; service hardening isn’t worth the risk.
The line between conservative engineering practices and rampant paranoia is a fine one, indeed. A good engineer asks himself/herself repeatedly how a design/process/implementation can bite him/her in the kiester. A not-so-good engineer just hopes it will work after the print is initialed or signed.
[:)] Mudchicken; switch7frg be here today. While leaving “rip track” I was wondering if dated tie plates are still used as replacements on wooden ties ?? Don’t know about frog hardening but have had a fire lit under my tail from time to time. I guess date tie nails are not used since the advent of concrete ties This post is in answer to your item # 2 I found a Dated PRR 1942 tie plate by chance in a ditch at Dayton Ohio in 1970 and a 38 tie nail in the ashes at a burn site a few years back. I would guess you have seen quite a few RR things in your wanderings on the railroad.