Substantial metal flaking occurs on many AS/RS stacker cranes, either on the rails or drives wheels treads or on both. Relatively short wheel service lives and metal flakes along the rails are proof of high metal surface wear. The shiny metal particles indicate high surface pressure poorly distributed and excessive lateral wheel migration.
Increasingly higher crane weights and traversing speeds, combined with starting, accelerating and braking action under varying loads, amplify this situation. Because a crane does not tend to drive in a straight line but migrates laterally somewhat across the top of the rail, the stress on the metal surfaces is increased even further.