5 Steps to Designing a Continuous Flexible Cable (Lapp USA)

Designing a continuous flexible copper cable involves carefully selecting materials and construction techniques to ensure that the cable meets the specific performance requirements for its intended applications. This process includes selecting copper strands, insulating the conductor, adding a braided shield, and finishing with an outer jacket. Below is a detailed guide to the design process, followed by a discussion of various applications.

0:00 – Intro to cable design
0:25 – Copper strands
0:47 – Conductor insulation
1:07 – Copper braid shield
1:17 – Jacket materials
1:37 – Applications for continuous flexibility

1. Design of the Copper Strands

The design process begins with choosing the copper strands that will serve as the cable’s conductor. The properties of copper, such as its high electrical conductivity and ductility, make it an ideal choice for flexible cables.

Stranding Process

• Solid Conductor: This is a single solid piece of copper, offering higher strength but limited flexibility.
• Stranded Conductor: Stranded copper is made by twisting multiple thin bare copper wires together to form a single conductor. This design enhances flexibility, making it suitable for applications where the cable needs to bend, flex, or move frequently.
• Stranding Options: The number of strands and the gauge of the wire (AWG – American Wire Gauge) are key design choices. Higher strand counts (e.g., 7, 19, 49, 133, or more) result in more flexible cables. For extreme flexibility, finely stranded copper (higher strand count with smaller gauge) is often chosen.
• Tinning the Strands: For improved corrosion resistance, the copper strands can be coated with a thin layer of tin (tinner copper). This is particularly useful in environments with moisture, chemicals, or where soldering is required.

Design Considerations

• Flexibility: Depending on the application, finer strands increase flexibility and reduce the chances of breakage under repeated bending.
• Conductivity: The diameter of the conductor affects electrical conductivity. Larger conductors carry more current with less resistance, which must be balanced with the need for flexibility.

2. Conductor Insulation

After the copper strands are chosen, the next step is to insulate the conductor. The insulation serves to prevent electrical shorts and protect the conductor from environmental factors like heat, moisture, chemicals, and abrasion.

Materials for Insulation

• PVC (Polyvinyl Chloride): PVC is commonly used for its cost-effectiveness, flexibility, and resistance to oils and chemicals. It can also be flame-retardant.
• XLPE (Cross-Linked Polyethylene): Known for its high temperature resistance and low dielectric constant, XLPE is suitable for high-performance applications.
• TPE (Thermoplastic Elastomer): TPE offers excellent flexibility and toughness. It’s used in cables requiring good performance in harsh environmental conditions.
• Silicone Rubber: Silicone insulation provides excellent heat resistance and flexibility in extreme temperature ranges (-60°C to +180°C).
• PTFE (Polytetrafluoroethylene): PTFE insulation, commonly known as Teflon, is used where superior temperature resistance and chemical resistance are needed.

Design Considerations

• Dielectric Strength: The insulation must be thick enough to provide adequate dielectric strength for the cable’s voltage rating.
• Flexibility and Durability: Insulation materials must be selected to ensure that they do not crack or degrade under repeated bending or exposure to environmental factors.

3. Braided Shield

The braided shield is an essential component for cables used in environments with significant electrical noise, electromagnetic interference (EMI), or radio frequency interference (RFI). The shield provides a layer of protection that prevents external interference from affecting the cable’s performance.

Types of Shielding

• Braided Copper Shield: This consists of thin copper strands woven in a braid around the insulated conductor. It offers good coverage and flexibility while maintaining high conductivity. The braid can be either tinned or bare copper.
• Aluminum Foil Shield: This shield provides 100% coverage but is less flexible compared to a braid. It is often used in combination with braided shields.
• Spiral Shield: Consists of a continuous spiral of copper around the conductor, offering good flexibility but not as much coverage as braided shields.

Design Considerations

• Coverage: Braided shields typically provide coverage between 85% and 95%, balancing flexibility and interference protection.
• Shield Material: Copper is preferred for its conductivity, but aluminum is sometimes used to reduce cost or weight.
• Flexibility: The type of braid pattern and material used can impact the overall flexibility of the cable.

4. Outer Jacket

The outer jacket is the final protective layer of the cable, shielding the internal components from mechanical damage, environmental hazards, and chemical exposure.

Materials for the Outer Jacket

• PVC: Commonly used for its versatility, cost-effectiveness, and ease of extrusion. It is also available in flame-retardant variants.
• TPE: Provides enhanced flexibility and abrasion resistance. It is used in cables subjected to frequent movement.
• Polyurethane (PUR): Known for its superior toughness, wear resistance, and flexibility, PUR is often used in cables that require high abrasion resistance.
• Neoprene: Offers good resistance to oils, chemicals, and UV exposure, making it suitable for outdoor use.
• Nylon: Used as a protective layer to increase abrasion resistance and strength.

Design Considerations

• Abrasion and Tear Resistance: The outer jacket should protect the cable from cuts, abrasions, and impacts.
• Chemical and UV Resistance: In outdoor or industrial environments, the jacket material must resist chemicals, oils, and UV exposure to prevent degradation.
• Flexibility: For cables used in moving or flexing applications, the outer jacket must be flexible enough to allow the cable to bend without cracking.

5. Final Construction

After selecting the individual components, the cable is assembled in layers. The copper strands are first stranded together, followed by insulation, the application of the braided shield, and finally, the extrusion of the outer jacket.

Applications of Flexible Copper Cables

1. Robotics: Flexible copper cables are essential in robotic systems, particularly in articulated arms and machinery that undergo frequent movement. The high flexibility allows for the bending and twisting of the cables without degrading their performance. These cables often have durable outer jackets to resist wear and tear from mechanical motion.
2. Automotive and Transportation: Flexible cables are used in automotive systems for wiring in doors, dashboards, and other moving parts. In electric vehicles (EVs), these cables must handle high voltages and currents while maintaining flexibility to route through confined spaces.
3. Medical Devices: In medical devices, such as imaging equipment and patient monitors, flexible copper cables are used to ensure reliability and ease of movement. They must be insulated with materials that can withstand sterilization processes and exposure to body fluids.
4. Renewable Energy Systems: Solar panels and wind turbines require flexible copper cables to connect moving parts. These cables must be weather-resistant and able to handle fluctuating currents from energy generation.
5. Industrial Automation: Factories often use flexible cables in automated machinery, where the cable’s ability to move and bend with the machinery is critical. These cables must endure high wear and tear while transmitting power and signals without interference.
6. Military and Aerospace: Flexible cables are used in aircraft, spacecraft, and military vehicles, where space and weight are limited, and the cables must endure extreme environmental conditions, including temperature variations, vibrations, and exposure to chemicals.
7. Consumer Electronics: Headphones, charging cables, and other personal electronics rely on flexible copper cables for daily use. The cables need to be lightweight, durable, and capable of enduring constant bending without breaking.
8. Marine Applications: Ships and submarines use flexible cables for onboard systems that must resist corrosion from seawater, extreme pressures, and mechanical stress. These cables are often sheathed with waterproof materials to protect the internal components.
9. Data and Telecommunications: Shielded flexible copper cables are used in data transmission and telecommunications networks to prevent EMI and RFI. They must ensure the integrity of the signal over long distances while providing flexibility for installation.

Conclusion

Designing a continuous flexible copper cable involves careful selection of copper strands, insulation materials, shielding techniques, and outer jacket materials to meet the specific requirements of the application. The process involves balancing factors such as flexibility, durability, conductivity, and protection against environmental factors. Flexible copper cables are used across a wide range of industries, including robotics, automotive, medical, renewable energy, industrial automation, military, aerospace, consumer electronics, marine, and telecommunications. Each application demands specific cable characteristics to ensure optimal performance under varying conditions.

This comprehensive design process ensures that the cables can withstand the mechanical and electrical demands of their applications while maintaining flexibility, durability, and reliability.

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