The E.646 and E.645 locomotives project was started in 1953, with a new model engine that was to be installed on the modified chassis of the already-existing six-axle locomotive E.636. A similar concept for a 4-axle locomotive led to the development of the E.444 high-speed locomotive in the 1960s.
The first prototypes were delivered in October 1958. The first thirty-seven individual locomotives differed only in their livery: twenty built for passenger traffic were painted in grey-green, while seventeen built for goods were painted in auburn. Later, the freight locomotives were reclassed E.645. The total number of locomotives built amounted to 295 units.
Locomotives from each class servedr with FS Trenitalia on push-pull services, and many were been converted in E.645 and assigned to goods services until 2009. They were replaced by E.464 engines on regional services.
Class E.646 did not follow the standard Italian class numbering rules where the last digit indicates the number of motors, as it mounted 12 two by two mechanically coupled 82-333FS type electric motors, each providing 360 kilowatts (480 hp), fed from the 3000 V catenary. These motors were more powerful than those mounted on the predecessor E.636 class and able to improve performance up to 50% with only a 20% increase in weight; this also increased the mass available for adhesion, giving it better hauling ability.
Maximum speed was 140 km/h (87 mph) for the E.646. The E.645 had a different gear ratio — 21/68 instead of 25/64 — which reduced the maximum speed to 120 km/h (75 mph), while increasing tractive effort. The locomotives weighed 110 t (108 long tons; 121 short tons) (E.645: 112).
To reach higher speeds, the motors could be electrically connected in four ways:
|Combination||Motors set-up||Field shunts levels allowed||Maximum current allowed|
|Series||All motors are connected in series||Five||700 A|
|Series-Parallel||Two branches of six motors each||Five||1100 A|
|Parallel||Three branches of four motors each||Three||1650 A|
|Super-Parallel||Four branches of three motors each||Three (none on some 645)||1800 A|
Due to the ability of the DC motors to absorb very high currents at low speeds, a rheostat needed to be connected in series to the traction motors when starting the train, to avoid drawing excessive current. The rheostat was gradually excluded as speed builds up and is also reintroduced when a transition to another is made; like almost every Italian electric locomotive since E.626, rheostatic exclusion was commanded through a controller (formed by a lever mounted on a curved notched support, commonly called respectively maniglione and roncola in Italian) subdivided into several notches, each representing a portion of the rheostat, plus four (one for each combination) special intermediate "end combination" notches.
The driver gradually excluded the rheostat by rotating the lever counterclockwise, paying attention to not exceed the maximum allowed current (in this occurrence, the "maximum current relay", and consequently the "Main Breaker" (IR, Interruttore Rapido) opens), until he reachef the end combination notches, meaning that the rheostat is fully excluded for that combination; at this point, he couls pass to the following combination or insert the field weakening shunts to further increase current. There were 31, 11, 9 and 8 notches on the roncola, each representing a portion of rheostat in the respective combinations.
In the 1960s the E.646 locomotives were updated with the standard 78-wire cable, fire extinguishing system and automatic rheostatic exclusion system (Avviatore Automatico) to permit remote commanding by driving coaches on commuter push-pull passenger services.
Air production was granted by two 1000 l compressors, that filled the main tanks used by the braking system and other components (horn, whistle, contactors etc.).
Main auxiliary services also included the 3000 V motor cooling fans, which were also used as generators to produce current used to recharge the 24 V DC batteries, that fed the low tension devices (lights, relays, solenoid valves, etc.).
Some units sere also been fitted with static converters to feed auxiliary services and recharge batteries.
Like all non-electronic Italian locomotives, E.646 werr technically simple; driving personnel couls often easily fix problems and get the locomotive moving for enough time to end the service or at least free the tracks.
For testing purposes, units E.645.016 and 017 were built with an even shorter gear ratio (20/69), that allowed a maximum speed of 110 km/h. These units were intended to be used for hauling heavy trains on steep lines. This modify was not applied on other E645s, however units 016 and 017 remained on regular service with their gear ratio for many years. Unit 016 was scrapped prematurely, as being involved in Murazze di Vado (see below) accident in 1978, while unit 017 reverted to the usual 21/68 ratio in the first half of the 1990s; however it retained the shorter roncola with considerably less notches than the usual E.645/6 ones.
On April 15, 1978, an accident involved units E.645.016 and E.636.282 in Murazze di Vado (in the province of Bologna). The train hauled by the two locomotives derailed due to damage to the line caused by a landslide, and ended poised over a slope. When the first rescue had already arrived, both locomotives were hit by an ALe 601 railcar on the express service Freccia della Laguna; the coaches fell into the slope, while the locomotives piled up one on top of the other on their sides. The accident caused 32 deaths and 120 wounded. Verona's football club was travelling on this train. They escaped unhurt because at the time of the accident they were having lunch in the restaurant wagon. After the accident, E.645.016 was scrapped.
In Florence Firenze Castello station, on March 23, 1998, unit E.646.009 was hit by EMU ETR 480-34, that was running between Rome and Bergamo, and that passed a signal at 'danger' without stopping (SPAD); the accident caused one dead and 39 wounded. The E.646 was later decommissioned.
First series E.645, with FS Class E.636-like cab
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