Abstract
The novel contribution of this research is insight into the influence of different parameters in the magnet configurations on the load and stiffness of a ferrofluid pressure bearing. It is shown that magnets with a small cross-section magnetized alternatively up and downwards combine a high load capacity and moderate stiffness while being low on material cost and complexity. The configuration where magnets are placed alternatively in left and right direction magnetized inter spaced with iron yields the highest load capacity and stiffness, albeit at the cost of weight and complexity. It is shown that an increase in the number of magnets is beneficial for the stiffness in both magnetization configurations, as is an increase in remanent flux density of the magnet. A metal bottom plate made of iron reduces the necessary height of the magnet in the up-down magnetization configuration. The model was validated using a bearing pad arranged in the up-down configuration. The force-displacement curve of this pad was measured in a load frame, using the APG 513 A ferrofluid from Ferrotec. A load capacity of 1.75 N/cm2 was achieved, this exceeds previous pressure bearing implementations and performs comparable or better than implementations of single seal ferrofluid pocket bearings. These results show that the ferrofluid pressure bearing is a passive alternative in motion systems where the designer otherwise would have needed to use an active bearing.
Highlights
Plain bearings have many benefits, such as compact design, easy of manufacturing, high resistance to shocks, low vibration levels, and low levels of fatigue [1]
It is shown that an increase in the number of magnets is beneficial for the stiffness in both magnetization configurations, as is an increase in remanent flux density of the magnet
Iron is modelled using the B–H curve for soft iron material in the built in COMSOL library, magnets are modelled with a uniform remanent flux density, and the air and ferrofluid are modelled as having a relative permeability equal to one
Summary
Plain bearings have many benefits, such as compact design, easy of manufacturing, high resistance to shocks, low vibration levels, and low levels of fatigue [1]. They are not generally found in precise motion systems as they suffer from stick-slip effects. A major difference between the plain and ferrofluid bearing is that the ferrofluid bearing doesn’t exhibit stick slip effects. Because of this the ferrofluid bearing is an excellent alternative to the bearings commonly used in precise motion systems
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