Edge chip
May affect seating, adhesive coverage or fragment control.
+86 13587171685
Vincent@vanguard-tech.cn
Permanent-Magnet Rotor Quality
Separate cosmetic variation from structural and corrosion risk before a damaged magnet becomes part of a rotating assembly.
Engineering Overview
Sintered NdFeB is hard and brittle. Magnets can chip or crack after impact, clamping or uncontrolled attraction to another part. A damaged coating can expose the substrate to corrosion, while a structural crack may be unacceptable in a rotor that sees centrifugal and thermal loading. The drawing must identify which surfaces are critical for the air gap, bondline, sleeve clearance and corrosion barrier. No single visual defect limit is suitable for every motor.
May affect seating, adhesive coverage or fragment control.
Can compromise the integrity of the rotating component.
May expose NdFeB to its service environment.
Can contaminate the bondline or motor air gap.
Image Gallery
These images show coating damage, magnet interfaces and permanent-magnet assembly contexts. They are examples, not pass/fail reference standards.
Defect Classification
Use separate codes for substrate chip, visible crack, plating or coating lift, corrosion stain, machining mark and contamination. Record location against a drawing datum and note whether the feature crosses a bond face, air-gap face, radial edge or end face. A photograph with scale and lighting reference is more useful than “minor chip” written alone.
Do not hide a defect under adhesive and assume the bond will restore magnet strength. Equally, a magnet that produces the expected field can still have a mechanical crack or a compromised corrosion barrier.
Risk Matrix
| Finding | Possible Consequence | Initial Disposition | Evidence to Capture |
|---|---|---|---|
| Crack through the magnet body | Fragment release under rotation or thermal cycling | Segregate for engineering review; do not install by default | Crack path, length, location and lot |
| Chip on bond face | Changed contact area or adhesive bondline | Compare with approved interface specification | Chip footprint, depth and seat geometry |
| Chip on air-gap edge | Debris, altered clearance or local field variation | Hold until critical-surface criterion is checked | Edge location, size and loose particles |
| Coating peeled to substrate | Corrosion and possible coating propagation | Review coating acceptance and environment | Exposed area, layer condition and corrosion signs |
| Loose magnetic debris | Bond contamination or air-gap damage | Quarantine and clean by approved method | Particle source, count and affected parts |
Inspection Workflow
Check separators, impact evidence and lot labels.
Remove permitted loose contamination without scraping coating.
Use defined lighting, magnification and orientation.
Measure defect dimensions against drawing datums.
Use approved material, coating and rotor criteria.
Check newly exposed edges, debris and seating.
Prevention Plan
| Process Step | Common Mechanism | Control to Consider |
|---|---|---|
| Shipping and kitting | Parts collide in a tray or package | Individual cavities, separators and drop control |
| Machining and finishing | Edge stress or surface flaw | Approved edge geometry and final visual inspection |
| Plating or coating | Local coverage gap or adhesion failure | Coating validation and process monitoring |
| Magnetization | Post-process handling impact | Non-contact or controlled-transfer fixtures |
| Rotor bonding | Clamp point load or magnet snap-in | Guided placement and force-limited tooling |
| Sleeve installation | Interference or debris trapped at interface | Fit review, cleanliness and post-assembly checks |
Engineering Support
A useful acceptance standard separates critical from noncritical surfaces, defines the measurement method and connects the limit to testing. For high-speed rotors, crack and retention review may require structural analysis and overspeed validation. For corrosive duty, coating continuity and environmental qualification matter. Cosmetic appearance alone is not an engineering disposition.
Ningbo Vanguard Technologies supports custom magnets, coatings, rotor assemblies, tooling, inspection planning and failure analysis. We can help make magnet acceptance practical for both prototype builds and repeat production.
FAQ
For motor engineering and procurement teams.
No. Its significance depends on location, depth, loose fragments, bondline geometry, air gap and rotor duty. Use the approved drawing criterion.
Adhesive should not be assumed to restore structural strength. A cracked rotor magnet needs engineering disposition and validation before use.
No. Magnetic testing can identify some field defects, but it does not replace visual and structural inspection for cracks or coating damage.
Guided placement, clamp load and sleeve operations can introduce damage or trap debris after incoming inspection.
Exposed NdFeB may be vulnerable in a humid or aggressive environment. The specific risk depends on coating system and service conditions.
Send your magnet drawing and service conditions for engineering review.
