Railway maintenance can be a real grind
Railroads are the most economical means of moving heavy payloads long distances overland. But railroads require regular maintenance - but not for just locomotives and rolling stock. The track itself can wear down, warp, shift out of alignment, and suffer all kinds of surface defects, such as corrugations, shelling, galling, and pitting. This is especially true on curves, where track is punished by side forces as locomotives and rolling stock transmit incredibly high stresses to the rails.
The solution to this harsh treatment of the track comes in the form of a specialized, diesel-powered maintenance-of-way locomotive - in effect, a specialized grinding train. This locomotive relies on a series of hydrostatic drives for propulsion and speed control. One such manufacturer of these locomotives is Loram Maintenance of Way, Inc., Hamel, Minn.
Rail grinding renews a rail's surface condition. In fact, Loram considers rail grinding to be the single most effective maintenance practice to control the effects of rolling contact fatigue, restore profile, and maximize value from the rail asset. A benefit of Loram's rail grinders, in particular, is efficient metal removal, which minimizes the required number of grinding passes per mile.
Fewer passes per finished mile
John Simmons, of Oil Air Products, Hamel, Minn.,says each locomotive has two grind cars. "Usually there's an auxiliary car attached, too. Three cars would be the usual number - one for the crew and the other two for grinding." The closed-circuit hydrostatic drive system for each grind car uses three of Denison's P14P Gold Cup axial-piston pumps and eight M7V axial-piston motors. Each pump displaces 14 in.3/revolution and is rated 6000 psi; each motor displaces 7.25 in.3/revolution. Simmons continues, "The overall system is controlled by a sophisticated PLC control system to provide coordination between the rail grinder cars and the drive system."
Jim Walker, application engineer at Denison, adds, "The pumps are controlled by a single customized Denison Venus controller specifically set up for this application. The motors are each controlled by a Denison Jupiter driver card. When grinding, speed is regulated by a closed-loop speed control through the Venus control. A communication link between the drive cars enable equal load sharing. This ensures consistent speed and that each drive car shares the load."
The control accomplishes this through a programmed-in algorithm to maintain the proper speed relationship between pumps and motors throughout the speed range. Explains Simmons, "In the grind mode, maximum speed is 15 km/hr - just under 10 mph. When not grinding, the travel mode is set, and the speed can go to 100 km/hr - just over 60 mph. Speed control is open loop, but load sharing remains in effect."
For more information, call Denison Hydraulics at (937) 644-3915, or visit www.denisonhydraulics.com