Magnetic Circuit Design for PM Motors: Ring Construction Before Magnet Grade

The 29 November 2025 external-OD scans compare nominal Ø36.6 × Ø29.8 × 17 mm, 10-pole specimens: radial N45SH, segmented N50SH and integrated Halbach N45SH. Recorded N/S peaks were 415.74/−423.29 mT, 521.39/−519.46 mT and 629.00/−627.71 mT respectively. Probe standoff and measurement uncertainty were not recorded, and the reports give no pass judgement.

These are historical surface-field traces, not air-gap, back-EMF, torque or bore-field measurements. The N50SH specimen is retained as historical evidence, not a current Mainrich offer. Using N peaks, 629.00/415.74 minus one is about 51%; 629.00/521.39 minus one is about 21%. The segmented peak is about 17% below Halbach when Halbach is the denominator.

Mean absolute N/S peaks give about 50% and 21%. The original radial trace was described as trapezoidal, segmented as square with saddle peaks and Halbach as near sinusoidal. Those descriptions apply to the recorded OD traces only. A motor back-EMF test needs the assembled magnetic circuit and winding.

Compare orientation tooling and magnetization with the mechanical assembly. Segmented construction introduces joints that need bonding and retention qualification; a one-piece route has different tooling and dimensional constraints. Halbach arrangements can concentrate flux toward one side, but no bore scan was supplied for these specimens.

Measure the bore field against the limits of any encoder or electronics fitted there. Use a motor model and matched tests to assess cogging, harmonics, torque and losses; the OD traces cannot rank total motor performance or cost.

Select the grade using the actual hot demagnetization curves, the magnetic circuit working point and the worst opposing field. A suffix is a nominal material class, not a guaranteed motor temperature limit or a chemical recipe. Mainrich’s sintered NdFeB range is N30 to N56, with no AH grades. The top grade depends on the temperature series: N56, N54M, N52H, N52SH, N50UH and N45EH.

Confirm the grade, suffix, geometry and production route for each drawing. This summary does not offer every combination; grades outside it in educational examples are not Mainrich supply offers. The reported N45H magnetic comparison and the separate historical 50H Dy-reduction example have different scopes.

See the GBD evidence and limitations. Finished-part savings require a quotation and qualification of the proposed route.

The radial-ring TDS, Rev A of 31 July 2026, states OD 20 to 75 mm, ID 15 to 68 mm, wall 2 to 7 mm and height 5 to 50 mm, with ±0.05 mm standard dimensional tolerance within the qualified route. These limits are not freely combinable. Confirm the drawing, grade, pole pattern and individual features before quotation.

The separate integrated-Halbach route states ±0.02 mm on critical features, subject to feature and drawing confirmation. For magnet assemblies, also agree shaft concentricity, bonding, retention, measurement after assembly and document scope. Check the current certificate for the actual manufacturing entity, address and activity. Agree PPAP level and required reports for the order; a network relationship does not certify every plant or assembly.

With the seven points below we can come back on construction, grade and temperature class together instead of one item at a time. Our engineering response is within 1 business day, and pricing within 2 business days.