ClassA Motor

Auxiliary material

Insulation Bobbin & Slot Liner

Resin drying → Injection moulding → Inspection

✓ Expert reviewed All content on this page has been reviewed by a senior motor engineer.

Process flow

3 main process steps, with the equipment and instruments used at each step, their main suppliers, and the technical control points.

  1. 1

    Resin drying

    PA66+GF pellets are dried before moulding.

    ⚙ Injection Moulding Machine & DryerAutomated
    International
    ENGEL, ARBURG
    Mainland China
    Haitian International

    Technical control points:

    • ▪Moisture content — 0.1–0.2% (dehumidifying dryer about 80 °C, 2–4 h)Check: Moisture analyser; every lot
    • ▪Regrind ratio — ≤ 25% (within the UL file allowance)Check: Weighing record; every lot
  2. 2

    Injection moulding

    Bobbins (end plates) are moulded, optionally with insert-moulded terminals.

    ⚙ Injection Moulding Machine & DryerAutomated
    International
    ENGEL, ARBURG
    Mainland China
    Haitian International

    Technical control points:

    • ▪Melt and mould temperature — Melt about 280–300 °C; mould about 70–90 °CCheck: Machine monitoring; continuous
    • ▪Short shots and flash — None (flash can cut magnet wire)Check: Visual / camera; 100%
    • ▪Thin-wall thickness — ≥ drawing minimum (insulation creepage and clearance)Check: CMM / micrometer; first article and sampling
    • ▪Weld-line strength — No breakage at weld lines in snap / bend testCheck: Functional test; sampling
  3. 3

    Inspection

    Dimensions, appearance and flammability conformance are checked.

    ⚙ CMM, Roundness & Runout GaugesTest instrumentSemi-automaticManual
    International
    MitutoyoDongguan, HexagonGuangzhou, MarpossShenzhen+1 more →
    Mainland China
    To be added

    Technical control points:

    • ▪Critical dimensions — Slot fit per drawingCheck: Fit gauge; sampling
    • ▪Cracks and burns — NoneCheck: Visual; AQL sampling
    • ▪Flammability — UL 94 V-0 at the minimum wall thicknessCheck: UL yellow card / material lot certificate; every lot

Incoming inspection & approval tests

  • Flammability ratingUL 94 (V-0)
  • Glow-wire GWFI / GWITIEC 60695-2-12 / -13
  • Comparative tracking index (CTI)IEC 60112
  • Ball pressure / heat resistanceIEC 60695-10-2
  • Relative temperature index / thermal classUL 746B, IEC 60216
  • Slot-liner breakdown voltage and tensile strengthIEC 60626

Buyer FAQ

What does the insulation system include?
Slot liners and wedges, end insulators or bobbins, phase separators, lead sleeving, the magnet-wire enamel and the impregnating varnish. They are qualified together as one system for a thermal class (UL 1446 / IEC 61857).
Which bobbin plastic should I use?
PA66 + glass fibre (UL 94 V-0) for class B / F, PBT or PPS for higher temperature or dimensional stability, and LCP for thin-wall, high-temperature parts. Ask for the RTI (relative thermal index) of the grade.
Can I change one insulation material on my own?
Not without checking the certification. Replacing a component of a UL-recognised insulation system may require re-testing or a file update; use only materials already listed in your system or approved alternates.