1
Widiger Hans, Hoffmann Dieter: Transport system for underground mining. November 27, 1973: US3774547 (8 worldwide citation)

A transport system for underground mining in which the cars, including the tractor and the trailer cars, have a plurality of supporting wheels in the form of flanged rollers provided with concavely curved surfaces which engage a track consisting of a pair of longitudinally extending convexly curved ...


2
Widiger Hans, Hoffmann Dieter: Mine car transportation system. Fraser Malcolm W, December 17, 1974: US3854421 (6 worldwide citation)

A transport system for underground mining in which the cars, including the tractor and the trailer cars, have a plurality of supporting wheels in the form of flanged rollers provided with concavely curved surfaces which engage a track consisting of a pair of longitudinally extending convexly curved ...



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