FS Class 746

FS locomotive 746.031 as preserved

Type and origin
Power type	Steam
Builder	Ernesto Breda (50), Gio. Ansaldo & C. (10)
Build date	1923–1927
Total produced	60

Specifications
UIC class	1′D1′ h4v
Gauge	1,435 mm (4 ft 8 ¹⁄₂ in) standard gauge
Leading dia.	1,110 mm (43.70 in)
Driver dia.	1,880 mm (74.02 in)
Trailing dia.	1,125 mm (44.29 in)
Length	14,085 mm (46 ft 2 ¹⁄₂ in)
Axle load	16.2 tonnes (15.9 long tons; 17.9 short tons)
Loco weight	98.8 tonnes (97.2 long tons; 108.9 short tons)
Tender weight	49.6 tonnes (48.8 long tons; 54.7 short tons)
Fuel type	Coal
Fuel capacity	6,000 kg (13,000 lb)
Water cap	22,000 litres (4,800 imp gal; 5,800 US gal)
Firebox: • Firegrate area	4.3 m² (46 sq ft)
Boiler pressure	16 kg/cm² (1.57 MPa; 228 psi)
Heating surface	237 m² (2,550 sq ft)
Superheater:
• Heating area	112 m² (1,210 sq ft)
Cylinders	Four, compound
High-pressure cylinder	490 mm × 680 mm (19.29 in × 26.77 in)
Low-pressure cylinder	720 mm × 680 mm (28.35 in × 26.77 in)
Valve gear	Walschaerts, Caprotti

Performance figures
Maximum speed	100 km/h (62 mph)
Power output	1,750 CV (1,290 kW; 1,730 hp) at 75 km/h (47 mph)
Tractive effort	14,000 kgf (137 kN; 30,900 lbf)

The Ferrovie dello Stato Italiane (FS; Italian State Railways) Class 746 (Italian: Gruppo 746) is a class of 2-8-2 'Mikado' steam locomotive.

Design and construction

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, 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]

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.^[4]^[5]

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.

References

Wikimedia Commons has media related to FS 746.

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. ISBN 0905878035.
"Gr.746 FS". Märklinfan Club Italia. Retrieved 20 May 2016.

Classes of Ferrovie dello Stato locomotives

Steam

Tender locomotives	100 102 103 110^I 110^II 111 112 113 114 116 117 118 119^I 119^II 120 121 122 136 139 140 150 155 158 160 161 162 163 164 170 180 181^I 181^II 182^I 182^II 183 185 186 187 190 193 194 195 196 197 198 200 201 206 207 208 209 211 212 215 216 217 218 219 220 221 222 223 224 255 260 261 262 265 268 269 270 271 272 290 291 292 293 310 320 380 385 388 390 391 394 395 396 397 400 410 420 421 422 423 424 425 450 451 452 453 454 455 460 470 471 472 473 474 475 476 477 478 479 480 482 499^I 499^II 500 510 512 513 530 540^I 540^II 542 543 545 550 552 553 554 555 556 560 600 601 603 604 605 606 607 623 625 626 630 640^I 640^II 645 650 652 653 656 660 666 670 671 672 675 676 677 680 681 682 683^I 683^II 685 686 687 688 690^I 690^II 691 720 728 729 730 731 735 736 737 740 741^I 741^II 743^I 743^II 744 745 746 747^I 747^II 750

Tank locomotives	800^I 800^II 801 802^I 802^II 803^I 803^II 804 805 806 809 810^I 810^II 811 812 813 814 815^I 815^II 815^III 816 817 818 819 820^I 820^II 821^I 821^II 822 823 824 825 826^I 826^II 827 828^I 828^II 828^III 829 830^I 830^II 831 835 842 848 849 850^I 850^II 851 870 871 874^I 874^II 875 876 877 880^I 880^II 881 882 885 893 894 895 896^I 896^II 897 898 899^I 899^II 900 902 904 905 906 910 912 915 940 950 980 981 999

Narrow gauge locomotives	R.201 R.202 R.300 R.301 R.302 R.305 R.306 R.310 R.370 R.401 R.402 R.410 R.440 R.441 R.442 R.443 R.600 P U

Electric

Rechargeable battery	E.421

650 V DC Third rail	E.220 E.320 E.321 E.420 E.620

3,6 kV AC Three-Phase	E.330 E.331 E.332 E.333 E.360 E.380 E.390 E.430 E.431 E.432 E.550 E.551 E.552 E.554

10,6 kV AC Three-Phase	E.470 E.471 E.472 E.570

3 kV DC	E.321 E.322 E.323 E.324 E.326 E.400 E.402A E.402B E.403 E.404 E.405 E.412 E.414 E.424 E.428 E.434 E.444 E.444R E.447 E.453 E.454 E.464 E.621 E.625 E.626 E.632 E.633 E.636 E.645 E.646 E.652 E.655 E.656

25 kV AC	E.491 E.492

Diesel

Light shunters	206 207 208^I 208^II 209 210 211 R.212 213^I 213^II 214 215 216 218^I

Shunters	218^II 225 234 235 236 245 250 255

Heavy shunters	Ne 120 D.141 RD.142 D.143 D.145 D.146 D.147 356 372 Ne 700

Train locomotives	D.341 D.342 D.343 D.345 D.442 D.443 D.445 D.449 D.461

see also Category:Rolling stock of Italy

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