More details about "side hardened rail".
The hardening of railway rails only on the head part may not be ever the best way to improve the performances of rails.
Maybe, only the unilateral, superficially, incomplete, or sometimes lack of interest, tackling of problem or research may lead to the only one conclusion that the 'head hardened rails' are an economical, and well-come procedure to prolong the service time of railway rails.
'Head hardened rails' may look as an un-luck compromise between the mechanical engineering, and the building (construction) one. The rail is taken into consideration alike a beam having a rolling surface, - that may be in fact as possible wrong.
A true hardened rail... consists in a rail with a strong base end (side) parts, strong web, and, softer head (360...420 HB), but with harder ends (sides).
This is a very important fact in curved tracks, when the centrifugal force, trends to camber the web and the base of rail, at maximum amplitude when the wheel is at the point (equal distant, inner) in-between two sequent sleepers.
In this point (case), the inside side-end of rail base (which is toward the centre of track) is upward arched (bended), while the exterior one, is downward arched. And,... while, the top of web trends to be much outside (of truck) pushed, than the base of web. Therefore, it archs too.
In this case, a higher strongness of rail head, will not dimminuish this effect, as long as it is stronger and harder. This discrepancy leads to permanent contradiction of oscillations amplitude between structures of web, and, base-sides, than those of the head.
Even if the oscillations are very, very short, however, their recycling leads to the rail fatigue. Therefore it requires to achieve a stronger structure of web and base sides, that oppose to the micro-moments which destroy (fatigue) the rail.
In this case, the lower-lowest structure, quenching, tempering defect, or, martensitic structure, in head of rail, will lead at premature fatigue.
Therefore, the first way to improve the rail service time and quality, especially for curved tracks, is to achieve a stronger web and base side ends, than those of head, but, of course, at a convenable hardness level of head.
Main and important disadvantages of head hardened rails, may be, as case, as follow:
- It results a great discrepancy (of strength and behavior in service) between the head and the rest of rail parts - web and base (foot).
- It worsens the contact between the rail and the tyre of wheels.
- It lingers unavailing and excessive the time of rails lopping (running in), especially in case of usage of second-hand (hardened head) rails in light duty or low traffic routes.
Don't forget it! A longer time of rails lopping... means... a premature wear of wheel tyres..!!
- Bad (worse) contact between rails head and wheels (tyres) leads to a lower adherence.
- In curves of railroads (with "equal-hardness" head rails), - we mean that both the head hardened rails and the untempered ones, have a bad beheaving in service.
More exactly - the interior side of rail head will be prematurely weare (related to the top surface of head).
The rolling surface becomes smaller, but having almost the same hardness as the side roundings of head (where the flange of wheel is pressing in curve tracks) resulting premature wear in wheel rolling surfaces.
In case of exchange the (head hardened) rails of a curved track (to use the interior rail as second-hand instead the exterior one)... the running-in of both of rails... may look as a true disaster... !
It may seem true amazing... how any of research centres pass over of these considerations, and promote longer only this 'head hardening' concept, as the only one, as only the best one.
All these disadvantages may be very good done away by side-hardening of rails
Short description of 'side hardened rails' concept :
A 'side hardened rail' is a railway (railroad) rail, which is stronger hardened on web, on sides of head, and (on upper part of base/foot, or) on base side ends, and less hardened on the rolling surface.
The highest hardness of the tempered steel, may be around the neutral axe (middle part of web) and on base side-ends, and the lowest hardness, may be on head top (rolling surface). (Attention! The hardness of the tempetred steel, not of the untempered one, or of those of rail).
The middle of the below part of base, as well as the inside of head are low, or may be, almost not hardened.
In case of rails having stronger base sides and web, the full troostitic micro-structure may be suitable, at least for further special railways usage, and in case that the bainitic rails is not an economical solution.
'Side hardened rails', may be considered one among of the few cases in technical domain, where, a steel piece in stronger hardened in (the) non-working surfaces, than it is in the working ones.
And, possible, even In case of bainitic microstructure achievement, (especially a lower bainite one), but not only in case of common tempering, - fortunately, because of vignol(e) rail cross shape, - after the last cooling process (after the isothermal quenching),... may be achieved a hardness, almost, due to invers-dependence of the minimal thickness of each rail part (head, web, base).
This fact represents exactly what is required for a high quality rail.
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