The Ferrovie dello Stato Italiane (FS; Italian State Railways) Class 746 (Italian: Gruppo 746) is a class of 2-8-2 'Mikado' steam locomotive. These were the biggest locomotives ever built by the Ferrovie dello Stato, even though not the fastest, which were the Class 691s.
The Class 746 originated from the need of a fast locomotive that, while having similar performance to the 'Pacific' Class 690, could have a lower axle load and therefore wider route availability; this could be achieved by adding another driving axle, and accepting a lower top speed (reverting to a leading Italian bogie). To achieve high performance, it was decided to adopt a symmetric compound engine (a Von Borries design), with the two inside high pressure (HP) cylinders having the motion for their valves derived from the outside Walschaerts valve gear; this was unusual for Italian locomotive practice, where the compound engine had been shelved once the superheating technology had become available in the 1910s.[1][2]
Forty locomotives were ordered to the Ernesto Breda, which produced them in 1922, and then ten more in 1926; Gio. Ansaldo & C. built ten more, fitted with Caprotti valve gear, in the same years. The latter were initially classified as Class 747, but in 1930 they were reclassified as the 746.100-110 subclass.[2]
Operations and modifications
The Class 746 initially operated on the Milan-Bologna-Florence-Rome-Naples main line; after portion of it were electrified, they served on the Milan-Turin and the Milan-Brescia railways. In the 1960s they were operating in Sicily and on the Adriatic coast railway (based at Ancona shed), until their withdrawals, which were concluded by 1967. While fast, powerful and suitable for both fast passenger and goods trains, the Class 746 proved difficult to start and somewhat uneasy when running at or close to its top speed (with both problems originating from its compound engine); also, at higher speeds the low-pressure cylinders contributed relatively little to the locomotive's power output. The locomotives fitted with Caprotti valve gear also turned out to have problems when functioning in reverse.[2][3] Their poor riding qualities and their huge mass (for Italian standards) led some Milanese crews to nickname them "Krassin"[a].[4]
In 1930 all the locomotives were modified with improved draughting. In 1932 four locomotives, two with Walschaerts valve gear (the 746.007 and the 046) and two with Caprotti valve gear (the 746.107 and the 108), were modified with a simple-expansion engine; while results were very encouraging, with the modified locomotives being as performant as the unmodified ones but performing better at higher speeds, the widespread electrification meant that this experiment was not followed up with more conversions.[2][4]
Preservation
Two Class 746 locomotives survive into preservation: the 746.031, a static exhibit in the Museo della Scienza e della Tecnologia "Leonardo da Vinci" in Milano, and the 746.038, long preserved in the FS workshop of Verona and recently moved to Pistoia, to await a possible restoration.
Notes
^The Krassin was a Russian icebreaker famous in Italy for having saved the survivors of the Polar expedition of Umberto Nobile; the implication was that the Class 746 locomotives likewise tended to 'break' the rails.
^ ab"Gr. 746 FS". Märklinfan Club Italia. Retrieved 5 October 2019.
Cornolò, Giovanni (July 2014). "Locomotive a vapore". TuttoTreno (3).
Kalla-Bishop, P. M. (1986). Italian state railways steam locomotives : together with low-voltage direct current and three-phase motive power. Abingdon: Tourret Publishing. ISBN0905878035.
January 07, 2023
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The Ferrovie dello Stato Italiane FS Italian State Railways Class 746 Italian Gruppo 746 is a class of 2 8 2 Mikado steam locomotive These were the biggest locomotives ever built by the Ferrovie dello Stato even though not the fastest which were the Class 691s FS Class 746FS locomotive 746 031 as preservedType and originPower typeSteamBuilderErnesto Breda 50 Gio Ansaldo amp C 10 Build date1923 1927Total produced60SpecificationsConfiguration UIC1 D1 h4vGauge1 435 mm 4 ft 8 1 2 in standard gaugeLeading dia 1 110 mm 43 70 in Driver dia 1 880 mm 74 02 in Trailing dia 1 125 mm 44 29 in Length14 085 mm 46 ft 2 1 2 in Axle load16 2 tonnes 15 9 long tons 17 9 short tons Loco weight98 8 tonnes 97 2 long tons 108 9 short tons Tender weight49 6 tonnes 48 8 long tons 54 7 short tons Total weight149 tonnesFuel typeCoalFuel capacity6 000 kg 13 000 lb Water cap 22 000 litres 4 800 imp gal 5 800 US gal Firebox Firegrate area4 3 m2 46 sq ft Boiler pressure16 kg cm2 1 57 MPa 228 psi Heating surface237 m2 2 550 sq ft Superheater Heating area112 m2 1 210 sq ft CylindersFour compoundHigh pressure cylinder490 mm 680 mm 19 29 in 26 77 in Low pressure cylinder720 mm 680 mm 28 35 in 26 77 in Valve gearWalschaerts CaprottiPerformance figuresMaximum speed100 km h 62 mph Power output1 750 CV 1 290 kW 1 730 hp at 75 km h 47 mph Tractive effort14 000 kgf 137 kN 30 900 lbf Contents 1 Design and construction 2 Operations and modifications 3 Preservation 4 Notes 5 ReferencesDesign and construction EditThe Class 746 originated from the need of a fast locomotive that while having similar performance to the Pacific Class 690 could have a lower axle load and therefore wider route availability this could be achieved by adding another driving axle and accepting a lower top speed reverting to a leading Italian bogie To achieve high performance it was decided to adopt a symmetric compound engine a Von Borries design with the two inside high pressure HP cylinders having the motion for their valves derived from the outside Walschaerts valve gear this was unusual for Italian locomotive practice where the compound engine had been shelved once the superheating technology had become available in the 1910s 1 2 Forty locomotives were ordered to the Ernesto Breda which produced them in 1922 and then ten more in 1926 Gio Ansaldo amp C built ten more fitted with Caprotti valve gear in the same years The latter were initially classified as Class 747 but in 1930 they were reclassified as the 746 100 110 subclass 2 Operations and modifications EditThe Class 746 initially operated on the Milan Bologna Florence Rome Naples main line after portion of it were electrified they served on the Milan Turin and the Milan Brescia railways In the 1960s they were operating in Sicily and on the Adriatic coast railway based at Ancona shed until their withdrawals which were concluded by 1967 While fast powerful and suitable for both fast passenger and goods trains the Class 746 proved difficult to start and somewhat uneasy when running at or close to its top speed with both problems originating from its compound engine also at higher speeds the low pressure cylinders contributed relatively little to the locomotive s power output The locomotives fitted with Caprotti valve gear also turned out to have problems when functioning in reverse 2 3 Their poor riding qualities and their huge mass for Italian standards led some Milanese crews to nickname them Krassin a 4 In 1930 all the locomotives were modified with improved draughting In 1932 four locomotives two with Walschaerts valve gear the 746 007 and the 046 and two with Caprotti valve gear the 746 107 and the 108 were modified with a simple expansion engine while results were very encouraging with the modified locomotives being as performant as the unmodified ones but performing better at higher speeds the widespread electrification meant that this experiment was not followed up with more conversions 2 4 Preservation EditTwo Class 746 locomotives survive into preservation the 746 031 a static exhibit in the Museo della Scienza e della Tecnologia Leonardo da Vinci in Milano and the 746 038 long preserved in the FS workshop of Verona and recently moved to Pistoia to await a possible restoration Notes Edit The Krassin was a Russian icebreaker famous in Italy for having saved the survivors of the Polar expedition of Umberto Nobile the implication was that the Class 746 locomotives likewise tended to break the rails References Edit Wikimedia Commons has media related to FS 746 Cornolo 2014 pp 408 411 a b c d Kalla Bishop 1986 p 75 Cornolo 2014 p 417 a b Gr 746 FS Marklinfan Club Italia Retrieved 5 October 2019 Cornolo Giovanni July 2014 Locomotive a vapore TuttoTreno 3 Kalla Bishop P M 1986 Italian state railways steam locomotives together with low voltage direct current and three phase motive power Abingdon Tourret Publishing ISBN 0905878035 Retrieved from https en wikipedia org w index php title FS Class 746 amp oldid 1126028188 Design and construction, wikipedia, wiki, book, books, library,
