Armature Design and the Role of Insulation
The armature is the heart of a motor. It consists of:
- A lamination stack of stacked electrical steel sheets that forms the magnetic circuit.
- Copper windings that carry the current.
- The commutator, which reverses the current direction in the windings.
- Insulating parts: these include armature insulation, slot insulation, spacer discs and commutator insulation.
The armature insulation is placed into the slots of the lamination stack and electrically separates the copper wire from the iron core. In addition, it protects against mechanical abrasion during winding, dampens vibrations in operation and ensures dielectric withstand strength even at high speeds.
Materials for Armature Insulation
Material selection depends on the required thermal classes of insulation (IEC 60085) and on mechanical and thermal requirements. Common materials are:
- Pressboard (electrical insulating board): economical, proven for standard motors with low to medium thermal load.
- Polyester films (PET, for example Hostaphan, Mylar): high mechanical strength and good electrical properties, widely used in electric motors.
- Aramid paper (Nomex): temperature and voltage resistant, standard for long-lasting and heavily loaded motors.
- DMD laminates (Dacron/Mylar/Dacron): combination of polyester and nonwoven, suitable for medium temperature classes.
- Polyimide films (Kapton): extremely heat resistant, used in high-performance motors and aerospace applications.
- Mica products (Mikanit, mica tape): excellent dielectric strength for extreme voltages and temperatures.
Combining materials (for example Nomex/PET laminates) enables tailor-made properties.
Manufacturing Processes
Armature insulation is produced as stamped parts, roll sections or kiss-cut elements. The process depends on batch size and requirements:
- Stamping: economical for large series, with high precision.
- Roll slitting: ideal for standardised strips or slot liners.
- Kiss-cut: enables self-adhesive or easily removable insulation elements.
- Laser processing: precise for prototypes and complex geometries.
Dimensional accuracy is typically verified according to DIN ISO 2768 to avoid manufacturing and assembly errors.
Requirements and Testing
Armature insulation must ensure several properties:
- Electrical safety: high dielectric strength, compliance with creepage and clearance distances.
- Thermal resistance: continuous operation depending on the thermal class (Class B 130 °C, F 155 °C, H 180 °C or higher).
- Mechanical stability: resistance to abrasion and pressure during winding.
- Processability: suitability for automated winding processes.
- Long-term stability: resistance to ageing against moisture, oils, varnishes and vibration.
Typical tests include dielectric withstand strength, thermal ageing, dimensional inspection and mechanical load tests.
Fields of Application
- Classic electric motors: DC and universal motors in machine tools, household appliances, pumps.
- Generators: protection of windings under continuous load and high voltages.
- Automotive and e-mobility: hairpin motors, high-voltage drives, electric steering systems.
- Special applications: drives for rail and aerospace, which place the highest thermal and mechanical demands.
GOBA Takeaway
Armature insulation is an indispensable element in motor construction. It protects windings from electrical breakdown, ensures thermal stability and extends machine service life. Depending on the application, the material range extends from simple pressboard to high-performance solutions made of Nomex, Kapton or mica. Precise manufacturing and compliance with DIN ISO 2768 ensure that these insulating parts can be used reliably in series production. For buyers, designers and quality managers this means: the right material selection and clean processing of the armature insulation determine the operational safety of the motor.
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