In order to improve and expand the package of services offered to its customers, D.R.Ferroviaria Italia has developed a new production plant for the production of railway switches including all their components.
D.R. Ferroviaria Italia specialises in the design and construction of SPECIAL EXCHANGES IN FIGURE, BIVES, COMMUNICATIONS and SPECIAL DEVIATIONS aimed at optimising the space inside factories and private junctions. A special Technical Office provides consultancy services to companies by developing on cad-cam the diversion devices that best meet the customer’s needs.
In order to guarantee the maximum quality and reliability of the product, every single phase of the production process is subjected to careful checks and final tests.
Supply of railway materials
The flexibility in the production organization and the professionalism of the workers, within a reality of limited dimensions, is able to support the customer’s request with high quality standards in a short time. The company also sells crossbars, interlayers, fastening systems, Vignole rails and Burback anchorage systems and collaborates with important national and international companies including RFI.
What are switches
The switches, or turnouts, are devices that allow a train to pass from one track to another. They consist of a fixed and a mobile part. The rails of the mobile part are called “needles” which rest on those of the fixed part called “contraghi”.
The turnouts can be operated electrically at a distance or by hand on site. In some secondary locations there are turnouts that are manoeuvred remotely by hand using a tie-rod system. New types of “hydrodynamic” switches are also being installed on some lines.
During the construction of a turnout, the “normal” position of the turnout is established. The other position is called “reverse”. As a rule, the “normal” position is the correct track position.
When a turnout is met by a train on the “needles” side, i.e. on the side that allows input in two different directions, it is said that the turnout is taken “at the tip”. In the opposite direction it is said that it is taken “by kick”. The turnouts are said to be arranged either “right” or “left” depending on the position of the needles, i.e. depending on the direction in which the vehicles are entering by looking at the turnout from the tip side.
A train that, encountering a football turnout arranged for the opposite direction, forces the needles, it is said to “heel” the turnout.
TYPES OF TURNOUTS
The turnouts can be simple when they allow entry on another track that originates from the turnout. Simple switches are “right” or “left” depending on whether the diverted branch branches off to the right or left of the main branch of the correct track. They are “symmetrical” when both branches are diverted or involve a reduction in speed. Two simple diversions immediately following each other, so that the needles of the second one are inside the moving part of the first diversion, constitute a “double” diversion.
When two turnouts placed on parallel tracks allow the passage from one track to the other, they are said to form a “communication”. The turnouts of a communication are normally operated simultaneously.
In the case of double communication it can be seen how the two diverted branches of communication cross each other forming a “crossing”. In this case the crossing does not allow trains to pass from one track to the other.
THE “INTERSEZIONE” OR ENGLISH DEVICES
For reasons of space two consecutive turnouts can be joined into a single structure called “English turnout”.
If a crossing is equipped with turnouts allowing trains to pass from one track to another, it is called an “English turnout”.
The English turnout is called “simple” if it allows the passage from one branch to another of a crossing only from one source, otherwise it is called “double”. In the case of the figure above, only vehicles coming from A may switch to D or B respectively, and vehicles coming from D may switch to A or C. Vehicles coming from B can go towards A and those coming from C only towards D.
Deviatoio inglese doppio
(per gentile concessione di Pontelli Enrico)
SPEED OF THE TURNOUTS
The turnouts normally allow the passage in one position at the maximum speed allowed by the line, while in the other position (the one involving a track curve) they must be travelled at reduced speeds of 30, 60 or 100 km/h respectively depending on the radius of curvature (or tangent) of the turnout. The branch that does not involve a speed reduction is called the “correct route” branch, the other “diverted route” branch.
The train that engages the deviating branch of a turnout, travelling through a curve, is subject to a lateral acceleration equal to v2 /R (where ‘v’ is the train speed and ‘R’ the radius of curvature).
Since turnouts are normally flat, i.e. without a cant that compensates for this lateral acceleration, the maximum value of lateral acceleration tolerated (to prevent the train derails or passengers from suffering significant lateral impacts) is 0.65 m/s2.
Therefore the maximum engagement speed of a curve is given by the formula V=2.91 R1/2.
From this formula some standard radii of curvature have been determined for the construction of turnouts.
The switches currently in production in the F.S. have the following characteristics.
TURNOUT IMMOBILIZATION DEVICES – BEADABLE AND INTALLONABLE TURNOUTS
Depending on the needle immobilization device, turnouts are called “hookable” if their heel, in addition to needle displacement, does not normally cause damage, while they are called “intallonabili” if their heel causes the shunting devices of the turnout to break and, if necessary, break or deform the rails of the turnouts themselves.
The “intallonabili” turnouts are placed on the tracks travelled by trains at speeds over 30 km/h. This is because the “beadable” immobilization devices guarantee the immobility of the switch needles are for speeds equal to or lower than 30 km/h.
For a more detailed explanation see the next point.
The needles of the switches can be rigid hinge or elastic hinge. In rigid hinged switches, the mobile part consists only of the end part of the needles which is “hinged” to the rest of the switch. With elastic hinged switches the complete needle, starting from the heart of the switch to the tip, is moved by the operating devices. In this case there is a real “bending” of the rail.
DEVIATOI TALLONABILI, INTALLONABILI, …
As already mentioned above, the turnouts are manoeuvred by hand or electrically (lately some hydraulic turnouts have been “born” in High Speed lines). Once a turnout has been manoeuvred, it must be blocked in this position. The mobile part (needles) of the turnout is immobilised by means of devices (turnout stops) which, in the case of manoeuvring with an electric box, are made inside the box itself.
These switches are normally “hookable”, i.e. they consist of a block made with a spring pin that is inserted in a recess in the rod connected to the switch needles. This spring supports a certain amount of effort, therefore, if a vehicle were to engage the turnout on the kick side in the “false” position (i.e. arranged for the other direction), the pin would lift up allowing the needles to move without normally damaging either the armament (rails, needles, …) or the shunting box. This device is suitable when the switches are engaged by shunting or trains travelling at a maximum speed of 30 km/h.
If the trains engage the top turnout for speeds above “59 km/h”. (60, 100 or more), the vibrations caused by the passage of the needles could exceed the force of the spring of the aforementioned pin, possibly allowing the needles to move with imaginable consequences (derailment of the train). In these cases, the turnouts on the station or line tracks that can be travelled at speeds of over 30 km/h have “intallonabili” shunting devices, i.e. the rod that allows the turnout to be immobilised is blocked in one of the two extreme positions not only by a spring pin but also by a fixed steel pin that is inserted in a hole.
The heeling of such turnouts certainly causes damage to the shunting box (a shunting box costs 4 million lire or more) and possibly the bending or breaking of the turnout needles which could also lead to the diversion of the rolling stock. (The heeling of a turnout is in any case a serious irregularity except in some remote control stations where there are special heeling turnouts with elastic return in the initial position that are normally “heeled” by trains leaving).
To avoid these drastic situations, especially in stations where a lot of manoeuvring movements take place, some turnout boxes are made intallonable at the command, i.e. the fixed steel pin does not always “fall” into the blocking hole but only when the central apparatus controls the movements of trains that engage the turnout at speeds above 30 km/h. In newly built A.C.E.I.’s, the intallonability is controlled for all the movements of trains that use a turnout (even at a speed of 30 km/h). Therefore, for switches taken by “kick” and those to be manoeuvred, the gear stop can still be heeled.
This device is made with an electromagnet in the turnout case which is normally powered and attracts the fixed pin upwards without “falling” into the hole of the needle blocking rod. If the turnout is required to be beadable, the electromagnet is automatically disconnected allowing the pin to fall into the locking hole. In this case, the “white” part of the black/white rectangle is lit on the Q.L. with a fixed light. If the intallonability does not occur due to a fault or remains active (always due to a fault) when not required, this symbol lights up with a flashing light and an alarm signal sounds in the central apparatus cabin.
Also the turnout manoeuvre is controlled from the central apparatus cabin. When the turnout is in the normal position, a fixed white light lights up on the corresponding lever of the manoeuvring desk, if it is in the upside-down position a fixed blue light is lit. When, due to faults, the switch does not assume either position (an obstacle preventing needle operation) or when the control device fails, the white or blue light starts flashing and an alarm bell sounds. Obviously in this situation there is no opening of the signals for the train.
THE OPERATION OF TURNOUTS AND MOBILE HEART TURNOUTS FOR HIGH SPEED LINES
The structure of a turnout allows the vehicles to be directed in one direction or the other, forcing the internal edges of the wheels to run along a given rail. This is achieved by manoeuvring the “moving part” of a turnout. The mobile part of the turnout is made up of rails ending in a “point” called “turnout needles”, which come close to the left or right rail. When the needles are approached to the left rail (see the image below), the turnout allows the vehicle to be inserted on the right branch of the turnout and vice versa.
Nel caso dell’esempio in questione, il bordino della ruota esterna (nel senso della curva) si inserisce e percorre l’ago sinistro del deviatoio (il termine sinistro o destro si riferisce sempre guardando il deviatoio dalla parte della punta) mentre il bordino della ruota interna passa nello spazio esistente fra la rotaia e l’ago destro. L’ago sinistro viene detto, in questo caso, ago “accosto” in quanto tocca la rotaia esterna sinistra, l’ago destro è detto ago “discosto” in quanto non tocca, anzi sta a distanza adeguata, la rotaia destra.
La tolleranza massima ammessa per l’ago accosto è molto piccola: ad un metro dalla punta dell’ago accosto lo spazio massimo tollerabile fra ago e rotaia esterna e di 4 millimetri!!!
Quando, per guasto, ostacoli o simili, non si riesce a raggiungere questo spazio minimo, lo scambio “perde il controllo” ovvero da una segnalazione di guasto in cabina di manovra degli scambi impedendo l’apertura del segnale.
Nel percorrere il deviatoio, il bordino della ruota viene a trovarsi, ad un certo punto, in corrispondenza di una struttura chiamata “cuore del deviatoio” che è separata dagli aghi e pertanto costituisce una interruzione della continuità della rotaia.
In the case of the example in question, the edging of the outer wheel (in the direction of the curve) is inserted and runs along the left needle of the turnout (the term left or right always refers to looking at the turnout from the tip) while the edging of the inner wheel passes through the space between the rail and the right needle. In this case, the left needle is called the needle “pulled in” because it touches the left external rail, the right needle is called the needle “diverted” because it does not touch the right rail, on the contrary it is at a suitable distance.
The maximum tolerance allowed for the needle is very small: one metre from the tip of the needle, the maximum tolerable space between the needle and the external rail is 4 millimetres!
When, due to faults, obstacles or the like, this minimum space cannot be reached, the turnout “loses control”, i.e. by a fault signal in the switching cabin preventing the signal from opening.
When travelling along the turnout, the edge of the wheel is, at a certain point, in correspondence with a structure called the “heart of the turnout” which is separated from the needles and therefore constitutes an interruption in the continuity of the rail.
Per evitare che in tale posizione i bordini della ruota perdano del tutto il contatto con la rotaia comportando l’eventuale deragliamento del veicolo, in corrispondenza del cuore del deviatoio esistono due “controrotaie” (vedi fig. 1).
Il passaggio dei bordini sul cuore e sulla controrotaia comporta un brusco spostamento laterale del veicolo (detto “contraccolpo”) che si trasmette al veicolo stesso e alle rotaie.
Per velocità di percorrenza fino a 200 km/h questo contraccolpo risulta tollerabile ai fini delle sollecitazioni impresse sia all’armamento che ai veicoli stessi, ma a velocità superiori si potrebbero creare problemi di usura in breve termine delle infrastrutture e del materiale rotabile (veicoli) nonché notevoli disagi sia ai viaggiatori che alle merci trasportate.
Per evitare questo è stato creato un “deviatoio nel deviatoio”. La struttura del “cuore” non è più rigida e fissa ma a sua volta è costituita da un “ago” che indirizza il bordino della ruota nella posizione richiesta. In questo caso non è più necessaria l’istallazione della controrotaia.
In order to prevent the wheel flanges from completely losing contact with the rail in this position and causing the vehicle to derail, there are two “counter-rails” at the heart of the turnout (see fig. 1).
The passage of the edgings on the heart and the counterrail leads to an abrupt lateral shifting of the vehicle (called “kickback”) which is transmitted to the vehicle itself and to the rails.
At speeds of up to 200 km/h, this recoil is tolerable for the stress on both the vehicle and its equipment, but at higher speeds it could lead to short-term wear and tear on the infrastructure and rolling stock (vehicles) as well as considerable inconvenience to both passengers and the goods transported.
To avoid this, a “turnout in the turnout” has been created. The structure of the “heart” is no longer rigid and fixed but in turn consists of a “needle” which directs the wheel rim to the required position. In this case the installation of the counter-rail is no longer necessary.
Unlike the “fixed heart” in fig. 2, the mobile heart consists of a flexible device (mobile tip) which is operated in sync with the actual needles of the diverter and which gives continuity to the rolling plane of the wheel eliminating the “unguided space” and therefore the need for the installation of the counterrail.
Finally, also to compensate for lateral acceleration at high speeds, the rails of the turnouts on the A.V. lines are mounted slightly inclined by 1/20 with respect to the vertical axis to reduce the risk of any lateral instability of the vehicles’ bogies.