Thermal-stability guide
When should a motor design consider SmCo instead of NdFeB?
Compare the heat-exposure requirement, magnetic working point and component validation—not material names alone.
The short answer
Consider SmCo when the design needs magnetic performance after prolonged heat exposure and the candidate NdFeB grade does not meet the required stability. Make the comparison grade-specific and test-specific; the decision is not a universal replacement rule.
What the published comparison actually measures
Page 26 of Hangda’s company presentation compares 35H SmCo with 38UH NdFeB. The stated method is an initial flux measurement after magnetizing at 20 °C, followed by elevated-temperature exposure and a new flux measurement after cooling.
| Test element | Reported condition |
|---|---|
| Compared materials | 35H SmCo and 38UH NdFeB |
| Initial condition | Magnetize and measure magnetic flux at 20 °C |
| Heat-exposure temperatures | 100 °C, 150 °C and 180 °C |
| Exposure durations | 1–1000 hours |
| Follow-up measurement | Measure flux after cooling |
| Reported quantity | Irreversible magnetic-flux loss relative to the initial measurement |
The displayed curves show the 35H SmCo samples tending towards a more stable loss level after their initial heat exposure, while the 38UH NdFeB samples show further loss over the reported duration. This is a qualitative reading of the published plots, not a newly calculated percentage improvement.
Read the result within its boundaries
After cooling is not the same as while hot. This comparison concerns the magnetic loss remaining after heat exposure. It does not give the motor’s available torque or the magnet’s field during operation at 180 °C.
The grade and test configuration matter. The page names two material grades but does not provide a complete specimen geometry, sample count or statistical study. It should not be extrapolated to all NdFeB grades, every magnetic circuit or all production batches.
Time is part of the requirement. Short peaks, long steady-temperature exposure and repeated thermal cycling are different validation cases. A 1000-hour hold is not a complete service-life qualification.
Turn a comparison into a selection plan
- Define the thermal duty. Identify continuous and peak magnet temperatures, exposure duration and cycling in the intended motor.
- Set an acceptance target. Specify allowable change in flux or field, the measurement location and whether the requirement applies while hot, after cooling, or both.
- Compare candidate grades. Review their magnetic properties at the relevant test temperatures, reverse-field exposure and load line in the chosen geometry.
- Evaluate representative components. Agree sample conditioning, measurement methods and acceptance criteria before making a production material change.
Hangda supports discussion of magnetic performance and thermal stabilization alongside custom magnet geometry and assembly development. Use the published comparison to frame the questions; use your component-validation results to approve the design.
Discuss a thermal-stability requirementSource publications: Company presentation, p. 26 · 2026 brochure, pp. 4–5. Document library.
Engineering questions
What does Hangda’s 35H / 38UH comparison measure?
The company presentation describes magnetization and an initial flux measurement at 20 °C, heat exposure at 100, 150 or 180 °C for 1–1000 hours, and another flux measurement after cooling. The reported comparison concerns irreversible flux loss after exposure.
Can the result be used as a universal SmCo vs NdFeB performance claim?
No. It compares the stated 35H SmCo and 38UH NdFeB samples under the reported conditions. It does not establish the performance of every grade, motor geometry, thermal cycle or reverse-field condition.