Explosion-Proof Motor Sweep-Bore Failure Inspection and Analysis
2026-02-12
Sweeping fault refers to a mechanical failure where the stator and rotor of an explosion-proof motor come into contact. This fault represents the extreme state of uneven air gap between the motor's stator and rotor. Diagnosing and analyzing uneven air gaps without actual sweeping contact is relatively challenging. However, when friction has already occurred, the visible fault location and symptoms make analysis comparatively easier.
Stator Eccentricity Issues
Compared to the rotor, the stator remains stationary. The inner circumference of the explosion-proof motor's stator core must be coaxial with the flanges at both ends of the frame, ensuring its centerline aligns with the rotor shaft axis. This alignment guarantees uniform air gap during motor operation. When stator eccentricity occurs, the stator-rotor air gap exhibits maximum and minimum clearances at fixed stator positions, with these points lying on a straight line. When the minimum clearance reaches zero, actual contact occurs between stator and rotor—known as shaft rubbing. This fault manifests as localized friction on the stator and full-circumference shaft rubbing on the corresponding rotor.
Rotor Eccentricity Issues
For explosion-proof motors, the rotor's outer surface must be concentric with the shaft bearing position. When rotor eccentricity occurs, it similarly causes uneven air gaps between the rotor and stator. Given the rotor's rotational nature, the eccentric position is dynamic, making the minimum air gap point also dynamic. When the minimum air gap reaches zero, solid friction occurs between the stator and rotor. The resulting fault manifestation is a full-circumference scratch pattern on the stator and localized damage on the rotor.
Loose Fit Between Frame and End Cover Flange
If neither the stator nor rotor exhibits misalignment, but the frame flange and end cover flange have loose fits, it is easy for one end (or both ends) of the rotor to deviate. In such cases, analyzing extreme failures like bore scraping reveals that friction occurs at the end of the core, typically manifesting as localized damage on the stator and circumferential damage on the rotor. When friction occurs at both ends, the two friction points are distributed diagonally.
Key Control Points
The above three fault manifestations are representative of uneven air gaps. To mitigate such issues, measures should be implemented in component machining processes, fit tolerances, and quality control:
(1) Control of coaxiality between both frame flange ends and the core position during frame machining. Different component manufacturers and motor producers have adjusted machining processes based on equipment conditions to ensure the frame itself meets coaxiality requirements.
(2) Coaxiality requirements between the end cover bearing housing and the flange;
(3) Selection and maintenance of reference points during rotor turning;
(4) Control of radial fit tolerances between: frame and end cover, frame and stator core, end cover and bearing, bearing and shaft, shaft and rotor core.
For most motor manufacturers, uneven air gaps are relatively uncommon. However, some manufacturers with relatively outdated machining processes still exhibit gaps in component processing. Even if no shaft rubbing failures occur, issues like vibration and low-frequency electromagnetic noise caused by uneven air gaps persistently arise. To address this issue, manufacturers may resort to reducing the rotor outer diameter or enlarging the stator bore. However, such solutions inevitably compromise other performance metrics or even lead to non-compliance.
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Nanyang Explosion-Proof is a specialized manufacturer of explosion-proof motors and high-efficiency motors integrating design, production, sales, and service.
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