Product Descriptions
Rare Earth Segment Arc Magnet – Precision Curved Magnets for High‑Torque Motors
When designing a high‑performance permanent magnet rotor, the shape of the magnet directly influences torque ripple, back EMF waveform, and overall efficiency. Our rare earth segment arc magnets are sintered neodymium‑iron‑boron (NdFeB) components engineered with precise arc geometry – optimizing the air gap flux distribution for BLDC, PMSM, and servo motors. These arc segments are manufactured using 100% virgin rare‑earth materials (purity ≥95%, no recycled scrap) in a fully integrated IATF 16949‑certified facility. Available in grades from N35 to N52, as well as high‑temperature series (N38UH up to 180°C, N42EH up to 200°C), our rare earth segment arc magnets deliver high remanence (up to 1.48 T) while maintaining excellent coercivity. Each magnet is precision ground on the inner radius, outer radius, chord, and end faces using CNC rotary grinders, achieving tolerances of ±0.03 mm on all critical dimensions. Standard arc angles include 60°, 72°, 90°, and 120°, with custom angles from 30° to 150° available. Ni‑Cu‑Ni triple plating (13‑18 μm) provides ≥72 hours salt spray resistance; optional epoxy or Parylene coatings offer electrical insulation for high‑voltage systems. Every batch is 100% flux‑tested and supplied with a material certificate and dimensional report.
Why Arc Segments Improve Motor Performance
Reduced Cogging Torque
The curved profile of a rare earth segment arc magnet closely follows the rotor surface, producing a more sinusoidal flux transition as the rotor turns. This significantly lowers cogging torque, resulting in quieter, smoother motor operation.
Higher Torque Density
By concentrating magnetic flux at the air gap, arc segments allow shorter motor lengths or smaller diameters for the same torque output. This is critical for weight‑sensitive applications like drones and electric vehicles.
Consistent Assembly
With tight chord height and radius tolerances, segments from the same lot fit seamlessly on the rotor core. This reduces adhesive gap variation and ensures consistent magnetic balance across poles.
Technical Specifications – Rare Earth Arc Segment Magnets
The table below lists common grades and typical geometric parameters for rare earth segment arc magnets. Custom designs are available based on your rotor drawing.
| Grade | Br (T) | Hcj (kA/m) | BHmax (kJ/m³) | Max Temp (°C) | Typical Applications |
|---|---|---|---|---|---|
| N42SH | 1.30-1.32 | ≥1590 (≥20 kOe) | 318-334 (40-42 MGOe) | 150 | Industrial servos, spindle drives |
| N40UH | 1.25-1.29 | ≥1990 (≥25 kOe) | 302-326 (38-41 MGOe) | 180 | EV traction motors (secondary) |
| N38EH | 1.22-1.26 | ≥2388 (≥30 kOe) | 287-310 (36-39 MGOe) | 200 | High‑performance automotive, hybrid systems |
| N45 (standard) | 1.33-1.37 | ≥955 (≥12 kOe) | 342-358 (43-45 MGOe) | 80 | Fans, pumps, home appliances |
*Standard arc geometry: inner radius 20‑200 mm, outer radius = inner radius + thickness (3‑20 mm), length 10‑200 mm, arc angle 30°‑150°. Custom tooling available.
Magnetic direction
Coating / Plating
High-Precision Manufacturing
With precision grinding and cutting, tolerances of +/-0.05mm can be achieved during the manufacturing process.
Magnetic Grade Parameters
Full‑Process Quality – From Alloy to Finished Arc
Our vertically integrated facility controls every step of rare earth segment arc magnet production. We begin with vacuum induction melting of virgin neodymium, iron, boron, plus dysprosium or terbium for high‑temperature grades. The alloy is jet‑milled to 3‑5 μm powder, then pressed in a segmented die under a magnetic field to achieve radial orientation. Sintering and two‑stage heat treatment optimize the microstructure for maximum coercivity and remanence. Post‑sintering, segments are ground on all critical surfaces using CNC rotary grinders with in‑process gauging. Ni‑Cu‑Ni plating is applied in automated barrel lines with real‑time XRF thickness monitoring. Final inspection includes 100% magnetic flux measurement (Helmholtz coil), full dimensional check (CMM or optical comparator), and coating adhesion testing. Salt‑spray samples are run per ASTM B117. All shipments include material test certificates with traceability to raw material lots. We are IATF 16949 and ISO 9001 certified, meeting automotive and industrial OEM standards.
Packaging & Logistics – Ready for Production Lines
Each arc segment is placed in a dedicated foam pocket within anti‑static trays to prevent edge chipping. Trays are stacked and packed into reinforced export cartons with desiccant. Lead times: standard segments 10‑12 days; custom tooling 15‑20 days after drawing approval. Free samples available for qualified projects. We support just‑in‑time delivery and consignment stock for high‑volume OEMs.
FAQ
Q: What are the two main types of rare earth segment arc magnets, and how do they differ?
A:NdFeB (e.g., N35–N52) offers high remanence (1.2–1.48 T) but low max operating temperature (80–150°C). SmCo (e.g., Sm2Co17) has lower remanence (0.96–1.15 T) but excellent thermal stability (250–350°C) and corrosion resistance. Choose SmCo for high heat or aggressive environments.
Q:Why is radial orientation more difficult for rare earth segment arc magnets than parallel orientation?
A: Radial orientation requires flux lines to curve from the inner to outer arc surface. During pressing, a specialized radial field fixture is needed, which reduces green compact strength. Cracking risk is high. Parallel orientation is simpler and cheaper, though it produces less optimal flux distribution in some motor designs.
Q: How does the arc segment shape affect the risk of irreversible demagnetization in rare earth magnets?
A: Thin inner radius sections (near the ID) experience higher opposing fields from stator currents. For rare earth materials with low Hcj (e.g., N40H), the inner arc tip can demagnetize first. Increasing arc thickness or using a higher Hcj grade (e.g., N40SH) prevents this without changing outer dimensions.
Q: How do you measure the arc angle tolerance of a rare earth segment magnet, and why does it matter?
A: Use a CMM or optical comparator. Typical tolerance: ±0.5° to ±1°. Tighter tolerances increase cost. Arc angle error causes unbalanced magnetic pull and torque ripple in BLDC motors. For matched pairs, sort magnets into bins with ≤0.2° variation to avoid performance scatter.
Q: Can rare earth segment arc magnets be used in high‑speed spindles (>50,000 rpm)?
A: Yes, but eddy current losses become severe due to low resistivity (~1.5 µΩ·m for NdFeB). Use segmented (laminated) magnets or a conductive sleeve with insulation coating. SmCo has slightly higher resistivity (~5 µΩ·m) and lower losses. Above 80 m/s surface speed, consider bonded rare earth or Halbach arrays.