Rotating Unions for Coil Winders

During flat steel production casted steel is often rolled into its final thickness in mill trains. In order to fabricate the finished product into a size that can easily be transported, the flat rolled strand is wound to coils. These coils are then loaded onto special wagons or trucks and are unrolled from the coil at the end-users' plant. Hydraulic shafts are deployed to wind and unwind the coil. The main function of these hydraulic devices is to grip the coil firmly during rotation. This is the aspect where hydraulic rotating unions are required. Hydraulic oil is forced with high pressure into hydraulic shafts. However, both high loads and permanent pressure are the stress factor for mechanical seals. If pressure is kept idle over a longer period of time (coil installation), oil will be constricted onto the surface of the seals. Restarting the unit will subsequently result in a lack of seal lubrication. The seals are stacked dry on top of each other and interface abrasively with their immediate environment, resulting in a much shorter service life for the rotating union.