Compare DMD and DM motor insulation paper

‌Differences Between DMD and DM Insulation Papers in Motors‌ The ‌DMD‌ and ‌DM‌ used in motor insulation papers are ...

‌Differences Between DMD and DM Insulation Papers in Motors‌

The ‌DMD‌ and ‌DM‌ used in motor insulation papers are two common composite insulating materials. Their differences primarily lie in their ‌structure, composition, performance characteristics, and application scenarios‌. The core difference is that ‌DM has a two-layer structure, while DMD has a three-layer structure‌.

Here is a detailed comparison:

Characteristic	DM (Aramid Paper Laminate)	DMD (Polyester Film Aramid Paper Composite)
‌Full Name‌	‌D‌acron/‌M‌ylar (Non-standard, often confused) ‌Correct:‌ Nomex-based bilayer composite paper	‌D‌acron/‌M‌ylar/‌D‌acron ‌Correct:‌ Nomex-Polyester Film-Nomex trilayer composite paper
‌Structure‌	‌Bilayer‌ composite: One layer ‌Nomex®‌ (Aramid paper) + One layer ‌Polyester Film (PET)‌	‌Trilayer‌ composite: One layer ‌Nomex®‌ + One layer ‌Polyester Film (PET)‌ + One layer ‌Nomex®‌
‌Main Components‌	Surface: Nomex® (Aramid fiber) Base: PET (Polyester film)	Both Surfaces: Nomex® (Aramid fiber) Middle Core: PET (Polyester film)
‌Physical Properties‌	* ‌Relatively thinner, softer‌ * Better flexibility * ‌Relatively lower‌ mechanical strength	* ‌Thicker, stiffer‌ * ‌High‌ mechanical strength (especially tensile & tear resistance) * Good rigidity & dimensional stability
‌Electrical Properties‌	* Excellent ‌dielectric strength‌ (Nomex property) * Good electrical insulation	* ‌High dielectric strength‌ (due to Nomex surfaces) * Excellent electrical properties, though slightly lower than pure DM layer at same thickness (PET film core has slightly lower dielectric strength than Nomex paper)
‌Thermal Class‌	‌Typically Class F (155°C)‌ (Nomex is F/H class material)	‌Typically Class B (130°C) or Class F (155°C)‌ (Depends on specific Nomex grade & adhesive. F-class DMD is common.)
‌Thermal Performance‌	* Excellent ‌high-temperature stability‌ (Nomex property) * Low thermal shrinkage	* ‌Exceptional dimensional stability‌ (provided by PET core) * Very low thermal shrinkage * Limited by PET film melting point (~254°C)
‌Chemical Resistance‌	* ‌Excellent solvent, acid & alkali resistance‌ (Nomex property) * Good moisture resistance	* ‌Good solvent, acid & alkali resistance‌ (Nomex surfaces protect) * Good moisture resistance * PET film has slightly lower hydrolysis resistance than Nomex
‌Key Advantages‌	* ‌Exceptional high-temperature performance (F/H class)‌ * ‌Highest electrical strength‌ * ‌Soft, easy to process, excellent flexibility‌ * Superior chemical resistance	* ‌Very high mechanical strength, stiffness, puncture & tear resistance‌ * ‌Outstanding dimensional stability & flatness‌ * Good electrical insulation * Balanced overall performance (thermal, electrical, mechanical)
‌Typical Applications‌	* ‌Slot liners‌ (especially where flexibility & high temp needed) * ‌Phase/coil separation insulation‌ * ‌Layer insulation‌ * Lead insulation * Components needing F/H class heat resistance	* ‌Slot liners‌ (especially where high mechanical strength, slot cut resistance & shape retention are critical) * ‌Backing insulation‌ * ‌End-winding support blocks/ spacers‌ * ‌Insulating parts requiring superior flatness & rigidity‌ * Widely used in small/medium motors, generators, transformers
‌Cost‌	‌Higher‌ (Nomex raw material cost)	‌Moderate‌ (Less Nomex than pure DM; higher than standard paper-based materials)

‌Summary of Key Differences:‌

‌Layer Structure:‌

• ‌DM = Two layers:‌ Nomex paper + PET film.
• ‌DMD = Three layers:‌ Nomex paper + PET film + Nomex paper.

‌Core Performance Differences:‌

• ‌DM emphasizes:‌ ‌High-temperature performance (F/H class), highest electrical strength, flexibility.‌
• ‌DMD emphasizes:‌ ‌Highest mechanical strength (tensile, tear, puncture), superior dimensional stability, flatness, and stiffness.‌

‌Typical Thermal Class:‌

• DM typically achieves ‌Class F (155°C)‌.
• DMD is most commonly ‌Class B (130°C) or Class F (155°C)‌ (depending on materials and adhesive).

‌Selection Guideline:‌

• ‌Need ultimate high-temperature resistance (F/H class) and electrical strength, with high flexibility requirements?‌ -> Choose ‌DM‌.
• ‌Need maximum mechanical strength, rigidity, and dimensional stability to withstand slot stresses and maintain shape, along with good electrical performance and thermal resistance (typically B or F class)?‌ -> Choose ‌DMD‌.
• ‌Need a well-balanced material for general-purpose small/medium motors?‌ -> ‌DMD‌ is extremely popular due to its excellent mechanical properties and good cost-performance ratio.

‌Important Notes:‌

• Naming conventions can sometimes cause confusion (e.g., meaning of “D”). The most reliable approach is to consult the material specification sheet, clearly identifying its structure (Nomex/PET) and thermal class (Class B/F/H).
• Different grades of Nomex paper, PET film, and adhesives exist in the market, leading to variations in specific product performance (e.g., max thermal class, bond strength, long-term thermal aging).
• For critical applications, always refer to the manufacturer’s detailed technical datasheet for selection.

In conclusion, ‌DM‌ is the “specialist” in high-temperature resistance and electrical strength, while ‌DMD‌ is the “versatile workhorse” for mechanical strength and stability. Each excels in its respective areas, and the choice depends on the specific requirements of the motor design and operating environment. For common household motor repairs, DMD is usually the more prevalent choice; but for high-temperature environments (like industrial motors or inverter-driven motors), DM’s thermal advantages become crucial.

(Note: Nomex® is a registered trademark of DuPont for its meta-aramid paper/fiber.)