The production of PTFE insulated products differs fundamentally in extruded wires and taped wires and cables.

Extruded PTFE cores

In extruded PTFE conductors, the PTFE material is continuously applied around the conductor using a paste extrusion process. This is followed by a sintering process in which the material is thermally compacted.

Characteristics

• Homogeneous, closed insulating layer
• Very smooth surface
• High dimensional accuracy and uniform wall thickness
• Good mechanical stability
• Very good electrical properties
• High dielectric strength

Advantages

• Ideal for thin-walled, precise insulation
• Very good reproducibility
• Economical for medium to large production volumes
• Particularly suitable for medical technology, aviation and sensor technology

Typical applications

• Medical cables
• High-frequency cables
• Sensor and measurement cables
• Miniature cables

Taped (tape-wrapped) PTFE cores

Manufacturing process

Here, the conductor is spirally wrapped with a PTFE tape. The wrapping is then also sintered so that the layers bond together.

Characteristics

• Overlapping tape structure
• Very high temperature resistance
• Very flexible
• Higher notch and bending resistance for certain applications

Advantages

• Very well suited for large conductor cross-sections
• High mechanical load capacity
• Suitable for extreme temperature ranges
• More flexible for special constructions

Typical applications

• High-temperature cables
• Energy and furnace technology
• Aerospace
• Applications with high mechanical stress

The most important differences at a glance

The processing of PTFE is generally more complex than with PVC or PE. In particular, it is important to observe the reduction ratio specified by the manufacturers of the PTFE powders. The reduction ratio is the ratio of the cross-sectional area of the preform to the cross-section of the insulation on the conductor. These reduction ratios range from 100 to 4000, depending on the type and manufacturer of the PTFE powder. The maximum achievable run length for a cable results from the volume of the extruder, which is determined by the length and diameter of the cylinder. The volume can be “distributed” over the conductor, always taking into account that the cross-section of the preform must match the cross-section of the insulation on the conductor.

Since the cylinder length of the extruder is predetermined by the design, only the cylinder diameter is a variable parameter on the machine. In our PTFE extruders, both larger and smaller cylinders can be installed, e.g. Ø = 76 mm instead of the usual 64 mm. For a conductor with a diameter of 0.5 mm and an insulation outer diameter of 1.2 mm, the following reduction ratios result (with a recommended reduction ratio of 3000 by the manufacturer):

• Extruder cylinder Ø 64 mm (mandrel rod Ø 16 mm) ratio 1 : 2468
• Extruder cylinder Ø 76 mm (mandrel rod Ø 16 mm) ratio 1 : 4180

Thus, with the large cylinder and the above example product, the value would exceed the manufacturer's recommended reduction ratio. The total length of our cylinders is up to 3000 mm.

It is therefore not possible to install arbitrarily large cylinders in an extruder to obtain greater run lengths, since the cross-sectional area of the insulation must always match the cylinder diameter. Typical achievable run lengths are 2000–6000 m. The line speeds at which the cable is produced depend on the thickness of the insulation. The solvent contained in the PTFE raw material must fully evaporate and sinter out in the sintering tower so that the cable achieves its positive properties after completion. Typical speeds of PTFE core extrusion lines are around 60 m/min. With very thin insulation layers, speeds of 100 m/min are also possible. The limiting factors here are more in physics and chemistry than in machine technology.

A particular characteristic of the quality of a PTFE cable extrusion line is the achieved concentricity, i.e. how far the conductor has shifted from the center of the insulation. The thinner the wall thickness of the insulation, the more difficult it becomes to achieve high concentricity. The thinner the wall, the more noticeable eccentricities become. With a very thin wall thickness, achieving 92% concentricity is difficult. However, our extruders also achieve impressive values here.

Furthermore, it should be noted that the production of PTFE cables is technically very demanding compared to processing "conventional" materials. It is essential that machine operators exercise great care at every single step in the production process.