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Electric motor rotor and stator

When building a traditional electric machine (motor or generator), the idea is to distribute the flux very evenly over both the rotor and stator surfaces where they contact the air gap. This means using either grain-oriented steels and rotating each lamination slightly from the previous one to provide a relatively even flux path, or using a non-grain-oriented steel and having the flux distribute on its own.

Grain-oriented steels are good for lowering magnetizing flux - provided the grain in each lamination is aligned in the same direction. This can also help with reducing stray loss and eddy loss (flux that travels parallel to the shaft and does no useful "work").

Most electrical steels used in stator and rotor construction also have an insulating coating applied; some of these are organic materials and some are inorganic (solvent-based) materials. The choice is typically made based on a combination of temperature gradient and local environmental laws. The inorganic (solvent) materials can generally withstand higher temperatures but are far less eco-friendly in the manufacture of the coating material or in the curing of the coating after it is applied.

Since most coatings are applied after the rolling-to-thickness process, these are usually cold-rolled steels. The use of cold- vs hot-rolled material can also be based on tooth / slot geometry: for very narrow teeth that require "post processing" for a coating, hot rolled is often used because the material will retain its geometry better through the temperatures used to cure the coating.

Skewing is the relationship between a rotor "turn" and a stator "turn". Each manufacturer is different; and different machines (synchronous, induction, Permanent magnet, direct current) approach it differently. For example - it is usually easier to skew the stator laminations of an AC machine, because the insertion of the coils is easier. For a DC machine, skewing of the rotor is preferred for the same reason. The amount of skew is typically one slot pitch ... which means that one end of the machine has the slot centerline aligned with the opposite end's tooth centerline.

Grain orientation only applies to the lamination steels ... not the conductor materials.

Energy efficient bearing is really a misnomer. However, they can be thought of as those that are sized to have relatively low friction coefficients and therefore low thermal losses (so that you don't have to use extra energy to cool the lubricant). In the bigger picture, they would also use a lubricant that is less energy-intensive to produce and / or require less replacement.

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