Increasing the load capacity of planar ferrofluid bearings by the addition of ferromagnetic material

Ferrofluid pocket bearings are a type of bearing that are able to carry a load using an air pocket encapsulated by a ferrofluid seal. Previously designed ferrofluid bearings show the great potential of the stick-slip-free and low viscous friction bearings, however until now the load capacity is limited. In this article a method is presented to increase the load capacity in a simple and cost effective way by the addition of ferromagnetic material around the magnet. First, a mathematical model of the bearing is presented and is validated by experiments using an axially magnetized ring magnet surrounded by two steel rings. The model is used to optimize the dimensions of the added ferromagnetic material for maximum load capacity. Depending on the fly height, the load capacity has been increased by a factor three to four by the addition of steel rings to the ferrofluid pocket bearing configuration.