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The Wrapping Method
The defining characteristic of our polyimide tape wrapped wire is the application method. Unlike enamelling, where multiple coats of varnish are applied and cured in an oven, tape wrapped construction involves spirally wrapping a polyimide film tape around the round copper conductor . The tape is coated on one or both sides with a suitable adhesive—typically fluorinated ethylene propylene (FEP)—which enables heat sealing after wrapping .
The wrapping process is performed on specialized taping machines designed to apply polyimide based films around electrical conductors with precise tension control and overlap . The tape width, wrapping tension, and overlap percentage are carefully controlled to ensure complete coverage and consistent insulation thickness. The overlapping regions of the tape are then heat-sealed at temperatures ranging from approximately 240°C to 350°C, bonding the tape to itself and forming a continuous, void-free insulation sheath .
Single and Double Wrapping Configurations
Our polyimide tape wrapped round copper wire is available in two standard configurations: single wrapping and double wrapping.
Single wrapping consists of one layer of polyimide tape applied in a spiral pattern with controlled overlap. This configuration provides basic dielectric protection and is suitable for applications where insulation thickness constraints favor minimal build.
Double wrapping involves two layers of tape, typically applied in opposite directions. This cross-lapped construction ensures complete coverage with overlapping seams uniformly staggered, providing enhanced dielectric strength and mechanical protection compared to single wrapping.
The choice between single and double wrapping depends on the application’s voltage rating, operating environment, and specific performance requirements.
Heat Sealing: The Critical Step
The heat sealing process is what distinguishes tape wrapped polyimide wire from simple tape covering. After wrapping, the wire passes through a heating zone where the FEP adhesive on the polyimide tape melts and flows. Upon cooling, the FEP solidifies, creating a unified insulation structure where the tape layers are bonded to each other and, to some extent, to the conductor surface .
This heat sealing step addresses a fundamental challenge of film-wrapped constructions: the geometric discontinuity created by the overlap. With sufficient thermal bonding, the melted FEP fills any gaps between overlapping layers, achieving a continuous sheath that resists moisture penetration and maintains dielectric integrity under thermal cycling and mechanical stress . The result is an insulation system that is both waterproof and oil-proof, suitable for the most demanding environments.
Dimensional Specifications
Conductor Diameter Range
Our polyimide tape wrapped round copper wire is manufactured to meet the dimensional requirements of IEC 60317-43:1997, which specifies that the nominal conductor diameters covered by the standard range from 1.600 mm up to and including 5.000 mm . This diameter range encompasses the most common sizes for high-performance motor, generator, and transformer applications requiring class 240 insulation.
The conductor is manufactured from high-purity oxygen-free copper with a minimum copper content of 99.95%, ensuring excellent electrical conductivity. The resistivity at 20°C does not exceed 0.01724 Ω·mm²/m, in accordance with relevant material standards.
Tape Thickness and Insulation Build
The polyimide tape used for wrapping is typically available in thicknesses ranging from 0.025 mm to 0.050 mm (1 to 2 mils). The total insulation build is determined by the tape thickness, the number of layers, and the overlap percentage. For double wrapping configurations, the insulation thickness is approximately the sum of the two tape layers plus the thickness of the adhesive layers.
Standard constructions using 0.025 mm tape with 50% overlap in a single wrapping configuration provide a balance of insulation thickness and conductor space utilization. Double wrapping with the same tape thickness and overlap achieves greater dielectric strength at the cost of increased overall diameter.
Thermal Performance: Class 240 Capability
Temperature Index and Heat Shock
Our polyimide tape wrapped wire is rated for class 240 operation, meaning it has a temperature index of at least 240°C and a heat shock temperature of at least 260°C . This thermal rating is among the highest available for organic insulation materials and significantly exceeds the capabilities of conventional enameled wires.
The temperature index of 240°C means the insulation system can operate continuously at this temperature while maintaining its electrical and mechanical properties over the equipment’s service life. The heat shock temperature of 260°C reflects the insulation’s ability to withstand short-term temperature excursions without cracking, delaminating, or failing .
Regional Differences in Classification
It is worth noting that in some countries, including Canada, Russia, and the United States, the same product is assigned a class 220 rating rather than class 240 . This difference reflects variations in testing methods and classification criteria across regions rather than any fundamental difference in the product itself. The practical performance of the wire is the same regardless of the regional classification.
Implications for Equipment Design
The class 240 thermal capability provides transformer and motor designers with substantial thermal headroom. A motor wound with class 240 insulation can deliver higher power output than an equivalent motor with lower-rated insulation, simply because the higher temperature rating allows greater current density in the conductors. Alternatively, for a given power output, the higher thermal class permits a smaller motor design, reducing material costs and installation space.
Electrical and Mechanical Properties
Dielectric Performance
The dielectric strength of polyimide tape wrapped wire is determined by the tape thickness, number of layers, and the quality of the heat sealing. Polyimide film itself exhibits dielectric strength of approximately 4,500 V/mil for heat sealable grades such as Oasis® 200TRT515 . When applied in a wrapping configuration with proper heat sealing, the insulation system provides breakdown voltage values exceeding 5,000V for double wrapping configurations.
Mechanical Characteristics
Polyimide tape provides excellent mechanical protection. The film has tensile strength of approximately 20 kpsi and elongation at break of approximately 60% . These mechanical properties are retained even after extended thermal aging, ensuring the insulation remains intact under mechanical stress and vibration.
The tape wrapping process itself contributes mechanical benefits. The spiral wrapping creates a structure that is resistant to cut-through and abrasion, protecting the conductor during winding operations and service.
Key Applications
Aerospace and Aviation
Polyimide tape wrapped wire has been the principal insulation choice for aerospace wire and cable for over 30 years . The combination of 240°C temperature rating, low weight, and excellent mechanical durability makes it suitable for the demanding requirements of aircraft, missiles, and satellite applications .
Oil-Immersed Transformers
The heat-sealed polyimide tape construction provides an effective seal against moisture and oil . This makes our polyimide tape wrapped wire suitable for oil-immersed transformer applications where the insulation must withstand continuous exposure to transformer oil while maintaining dielectric integrity at elevated temperatures.
High-Temperature Motors and Generators
Motors and generators operating in high-temperature environments—such as those used in steel mills, foundries, and other heavy industrial processes—benefit from the class 240 thermal capability of polyimide tape wrapped insulation .
Downhole and Submersible Equipment
The moisture seal achieved through the heat sealing process makes polyimide tape wrapped wire suitable for downhole oilfield equipment and submersible pumps . The insulation withstands water immersion and pressure without degradation.
Quality and Standards Compliance
Our polyimide tape wrapped round copper wire is manufactured in compliance with IEC 60317-43:1997 . When referencing this product, the following information should be provided: the standard reference (IEC 60317-43), the conductor diameter, and the grade . For example, a typical designation would be: 60317-43 IEC 3.000 mm grade A2.
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