Question

Stripping overburden in the lIllinois coal belt, the Dusty Coal Company uses 270-horsepower track-type tractors (with direct-drive transmissions) and drawn scrapers. The overburden is a very soft loam that weighs 2,800 Ib/yd (loose). Estimated RR factor for the haul road is 300 lb/ton. If the scraper weighs 35,000 lb (empty) and carries 25 loose cubic yards per trip, what is the RR of the loaded unit? What operating gear and speed do you estimate for the loaded machines on level ground? (See Table 14.4.) Table 14.4 Speed and Drawbar Pull (270 hp) (Track-Type Tractor) Drawbar Pull Forwarda Forward Reverse At Rated rpm Maximum at Lug Gear mph km/h mph km/h lb lb 1.6 (2.6) 52,410 (23,790)63,860 (28,990) 2.1 (3-4) 2.1 (3.4) 39,130 (17,760) 47,930(21,760) 2.9(4.7) 2.9 (4.7) 26,870 (12,200) 33,210(15,080) 4 3.7 (6.0) 3.8 (6.1) 19,490 (8,850) 24,360 (11,060) 4.9 (7.9) 4.9 (7.9) 13,840 (6,280)17,580 (7,980) 6.7 (10.8) 6.8 (10.9)8,660 (3,930) 11,360 (5,160) aUsable pull will depend on traction and weight of equipped tractor

RR = Rolling Resistance

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Answer 1

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