In this article we will talk about ceramic bearings: electrically insulated and non-magnetic, in more detail we will discover how a ceramic bearing, once again, can prove to be an effective solution. Fully ceramic bearings can be an extremely effective solution in all those situations where it is necessary to protect the bearing from magnetic fields or eddy electric currents.Eddy electric currents can be very dangerous for a bearing made of steel due to the so-called point effect, that is the physical phenomenon for which, in an electrically conductive material, the electric field intensifies in the areas with greater curvature. The increase in the electric field can lead to the formation of an electric discharge or, even, to a real electric current within the contact area between the rolling element and the track. The effect of these discharges on the steel with which the bearings are made can be extremely negative because it causes erosion phenomena which, in a short time, can affect the functionality of the bearing and therefore cause extraordinary maintenance and costly machine downtime.
Eddy currents also have a negative effect on the lubricants used in bearings. In fact, by causing oxidation and deterioration of the chemical characteristics, they further reduce the life of the bearing with an increase in maintenance costs.
The most common situations in which eddy electric currents can occur are the following:
In the axles and traction motors of railway vehicles, in direct or alternating current motors and in electric generators it may happen that the electric currents that circulate or that are generated inside them are not or cannot be effectively contained and, therefore, pass even through the bearings of the motor itself.
In arc welding, the process of joining two metal edges is carried out by creating an electric arc. If there are bearings in the equipment involved in the welding operation, it could happen that electric currents caused by the welding arc pass through them.
Due to a physical principle of electrodynamics, electric currents are generated in a conductor subject to variable magnetic fields. Since the steel used in bearings is a conductor, electric currents can be created in a bearing immersed in a magnetic field.
The solutions adopted so far to obviate the effects of eddy currents on the bearings are basically of two types: electrical insulation outside the bearing or adoption of electrically insulated bearings. Let's see the two solutions in more detail.
The use of ceramic material bearings can represent a valid and more effective alternative to the bearings indicated above.
Two configurations are possible:
In both cases, the electrical insulation is determined by the use of ceramic rolling elements that do not allow the passage of eddy currents between the inner and outer ring of the bearing.
The choice to adopt the hybrid version or the fully ceramic version is linked to functional and economic aspects:
In any case, the ceramic bearing, and in particular the totally ceramic bearing, can represent a winning choice allowing to improve the performance of the machine in which it is inserted and reducing the frequency of maintenance operations with a consequent economic advantage.
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