Rail

Types of rails

The modern rail is generally of the “Flat-bottom” type; in a cross section, one distinguishes the shoe which are pressed on the cross-piece, the mushroom which constitutes the track, and the heart , net vertical which connects mushroom to the shoe. On the important lines, the standard linear density of the rail is of 60 kg/m.

The double headed rail, whose section is symmetrical, had been designed to make it possible to turn over the worn rail and thus to double its lifespan. This principle was abandoned.

Grooved rails (standard “Broca”) are used for the ways embedded in road roadways, in particular for the industrial facilities and the lines of Tramway.

Pose rails

The installation of the rails is done normally with expansion joints, the rails, of 18 or 36 m length, freely sliding in the fish-plates (parts which ensure the junction of two successive rails). In this case electric continuity must be assured. More and more develops the technique known as of the “long rails” or LRS (long welded rails), in which the coupons of rail of 80 m are welded in workshop in lengths from 320 to 400 meters. These bars are posed on very big lengths, unbounded real, the weldings necessary being realized on the spot. Dilation is forced by the friction of the cross-pieces on the ballast. That supposes joined together certain of the platform and minimum radius stability conditions of curvature. At the end of the LRS are installed apparatuses of dilation, like with the right of some works of art.

The ballast consists of Roche S hard crushed (generally, it acts of eruptive rocks: Granite, Rhyolite, Quarzite…) who must resist the Attrition, which blunts the angles. The thickness of the ballast is function of the load and the intensity of the traffic, 30 cm on traditional line, 40 cm on LGV.

A traditional railway is fixed on Traverse S in Bois resting on a made stone ballast crushed at arrises. The fixing is done thanks to elastic coach screws or fasteners.

The cross-pieces ensure the transmission of the load the ballast, and the maintenance of the spacing and the slope of the rails. The travelage, i.e. the number of cross-pieces to the kilometer is variable, generally of 1666 traverses/km to the SNCF. The cross-pieces can be:

of wood (generally of the Oak, but one uses also hard exotic wood, the such Azobé, of reduced lifespan (20 to 30 years) but easy to implement);
in Steel (noisier, are not used any more in France in new installation);
in Concrete, of important lifespan (50 years), there exists about it of two types: Bibloc, connected by a metal bar, prestressed concrete monobloc. The concrete cross-pieces are called Blochet S.

During their phase of preparation, the cross-pieces out of wooden are soaked with creosote at the time of a passage out of drying oven. The creosote is a hydrocarbon assembly used in the protection of wood.

The railway can also be posed without ballast, directly on a concrete bed. It is the case of the tunnel of Marseilles on LGV the Mediterranean, like in Germany of the line ICE between Frankfurt and Cologne. This process reduces maintenance but is more expensive and does not allow to correct the defects of geometry easily.

The crossings and changes of ways are done in general by trackside equipment which include/understand shunting S, crossings (crossing of two ways without tongue-rails) and of the crossings junctions simple or double, authorizing the crossing of two ways and shunting towards one or two directions. At the time of the vapor there were revolving, valid bridges especially for vehicles of weak footing.

In addition to its functions of bearing and guidance, the rail often has a function of safety: it is used as circuit with the currents of indication, which makes it possible to put at the red a signal automatically when a vehicle shorts-circuit the two rails. Moreover, the rail constitutes the return circuit of the electric current of traction towards the sub-station of food.

Characteristics of the rail

The railway rail is in Acier, with a rate of average Carbone, about 0.6% to 0,8%, but a rate of Manganèse and important Silicium, 0,7% to 1,2% and 0.1% to 0.6% respectively, which make it hard and allow him to support high constraints. The rails being massive metal products, they must be free from Hydrogène. Indeed, the small size of the hydrogen atom enables him to circulate in the end product, until locally creating bubbles likely to cause a spontaneous rupture of the rail.
The rails are hot rolled (temperature of about 1200 degrees) and undergo a Corroyage (reduction of section since the bloom to the finished rail) from at least 7. This Corroyage can however be insufficient for certain applications: the solidification of blooms must then be well maîtrisée.
For these carbon steels one does not use the usual terminology of the Sidérurgie; one spoke about nuances 700,800 or 900A (MPa) until 2002, of nuances such as for example R260 (hardness HBW on the table of bearing) according to European standard EN13674 nowadays.

The manufactured rails have symmetrical profiles. With the installation, they are slightly tilted towards the interior of the way of approximately:

1/20e in France, Belgium, Italy, Spain…
1/30e in Denmark, in Sweden
1/40e in Germany, Central Europe

One speaks thus about " pose with 20th, the 40e".

A very great number of rail sections existed. Most widespread today (50E6 - in the past U50, and 60E1 - in the past UIC 60…) comprise a table (above mushroom) with a radius of 200 to 300 mm, side vacation of ray 12 to 13 mm, and often an intermediate blending radius, for example from 60 to 80 Misters the rails wear, especially in curve, and move away from these theoretical values.

The table of bearing of the wheels is of conical form with a concave connection towards the roll. It is the shape of the wheel which allows the Essieu railway monobloc, by difference of the rays of bearing right-hand side-left, car-to be centered in the way when it is off-set laterally, without action of external bodies. This mechanical control enables him to take the broad curves without using its roll.

The profile of wheel standardized by the International union of the railroads, said “profile UIC”, comprises a part with the 1/40e and a transition curve towards the roll. This profile is also called S1002, according to the designation of that which had been selected among the various profiles tested.

Conicity, i.e. the angle (in radian) with the contact wheel-rail is specific to each couple - profile of wheel/rail section, and varies with wear. It is a function of the side position of the axle in the way, therefore wheel relative with the rail, which can vary typically + 8 mm between butted with the rolls. It is sensitive to the installation of the rail, wear, the spacing.

The equivalent conicity is the value of this function for a given play in the way. For example, in a new state, for a play of +-3 with +-5 mm it is of:

0,16 to 0,24 for the S1002/rail couple with the 1/40e;
0,01 for the S1002/rail couple with the 1/20e.

Being a local value of the function, it is very sensitive to the installation of the rail. Strong conicity characterizes a contact able car-to direct the axle well, but it is likely to return the Bogie and thus the unstable vehicle. One cures it with stiff suspensions. It is about a different compromise for a TGV and a subway.

Surfaces of contact between wheel and rail are about cm2; one calculates them starting from the curves of the profiles, using the theory of Hertz on the resilient contact (1887). the pressures can be very high, about 1000 MégaPascal. The tangent efforts are calculated by the theory of Kalker (1967).

The rails of Tramway are often posed flat, and their wheels are sometimes cylindrical. The turns are so tight on the networks of trams which one does not even seek always to use the nipple effect. One limits wear by the greasing of the rolls and by not charging too the axles.

In France as in a major part of the countries, the spacing of the rails is generally of 1,435 meter (except specific industrial ways or of tourism where the spacing can vary much). To increase the nipple effect one surécarte ways of railroad in the curves, except for the trams which use grooved rails not allowing this gauge clearance under penalty of an abnormal wear of the internal side of the wheels.

Maintenance of the rail

The maintenance of the railway way is concentrated on the ballast and the straightness of alignment of the rails. The latter is checked under load, for example in France with the cars " Mauzin". One can rectify the deviations by stuffing of the ballast, by change of the cross-pieces or the fasteners if they are damaged, or by " Renewal Sees Ballast" (RVB) if the way is considered to be too old.

The maintenance of the rails relates to their internal or external defects. Under the action of the passage of the wheels, the contacts can tire the rail. Internal defects or badly made weldings can generate cracks not emerging which one detects by ultrasounds. External cracks can appear, especially in the curves, where there is relative slip wheel-rail. One detects these defects of surface by sensors with Eddy current, which detect also the rippling.

The average main thing of preventive maintenance as regards ways is the grinding, which makes it possible to eliminate the defects of surface likely to generate cracks, such as for example the rippling or contact fatigue (RCF or rolling contact tires in English). Each grinding removes up to 1 mm thickness of steel and gives again a form appropriate to mushroom.

The monitoring of a railway network by these methods is critical for safety but also for the control of the costs of maintenance.

There exist rails called without maintenance, colaminés hot with a stainless plate which makes it possible the table not to oxidize. The contact on these rails makes it possible to guarantee shunting, when the rails are used in the track circuits.

Origin of the word

The word " rail" is of British origin, and it is only the transposition, at one time quite former to the invention of the railroad, of the French word " règle" itself resulting from Latin " Regula". The " railway" British is a " way of règles". (We find the same root in the words " rectitude" and " rigide")

Illustrated direction

By extension, the rail indicates the whole of the linked activities to the railroads.

By analogy, one indicates by a rail a small heap of Drogue (generally of the Cocaïne) laid out on line on a mirror (or another plane surface), using a razor blade. This provision makes it possible to the consumer to inspire drug directly in the Nez using a small tube.

Railroad
Railway

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