Enclosures, Cabling & Connectors


In a state of flex: specifying the correct continuous flex cable types

July 2008 Enclosures, Cabling & Connectors

Continuous flex, oil-resistant cables are designed for continuous flexing applications that are found in automated factories. The most common are called robotic or automation cables. Through the use of unique stranding and cabling techniques, and specially blended insulating and jacketing materials, continuous flex cables have reduced downtime on high-speed automated equipment. Continuous flex cables are specifically designed for C-track applications, high speed automated process equipment, continuous flex applications, and automated control applications.

Conductor design

The demands placed on flexible control cables increase dramatically with the speed and sophistication of robots and automated equipment. Continuous flexing, bending, and exposure to destructive solvents and oils can take their toll on flexible control cables.

Cable materials must be resilient so that once the cable completes a flexing cycle, they will immediately return to their original unstressed condition. The copper conductors must be made of finely drawn strands rather than coarse strands. In addition, the cable must be designed so that the individual conductors inside the jacket have freedom to move, preventing harmful stress on the conductors.

Control and power cables operating in high-speed automated equipment, like gantry robots, pick-and-place machines, conveyor systems, assembly systems, and machine tools, are subject to continuous flexing and twisting. While it is possible to use standard control cables in these applications, they will not deliver the long-term performance of cables designed exclusively for this purpose.

Jacketing choices

The number of chemical solvents and oils used throughout the industry is enormous and growing steadily. Each one is potentially harmful to a control cable. Some of these chemicals are potent enough to completely destroy cables. The hostile agent is drawn into the jacketing material, causing it to balloon, soften, and ultimately disintegrate. Alternatively, it may leach a similar chemical from the jacketing material causing it to become brittle. Choosing the appropriate jacket material requires knowledge of its expected operating environment.

Stand PVC is the most used jacketing material. However, it is only suitable in environments with minimal amounts of industrial oils. Special types of PVC have been developed that are resistant to most oils, and can be used freely where these oils are present. Polyurethane jackets have a similar resistance to oils and solvents as special types of PVC, while providing increased abrasion resistance.

What are the options?

There are seven categories of continuous flex cables:

1. Moderate flex cables are designed for use in cable tracks, automated handling equipment and machine components in constant operation. They are often available with a flexible tinned copper braid shield to provide isolation from electrical interference. Special features include a moderate resistance to oils and a minimum bend radius equal to 10 times the cable diameter.

2. High-speed continuous flex cables are designed for continuous flex applications in high-speed automated equipment. They are also available with a flexible tinned copper braid shield to provide isolation from electrical interference. Typical applications are found in industrial robotics, machine tools, automated doors and material handling centres. Special features include: resistance to oils, solvents, water-based coolants, and abrasion; a minimum bend radius of 8 times the cable diameter; non-wicking tape and specially formulated compounds enhancing the cables' flexibility; super fine copper stranding; and UL and CSA recognition.

3. Ultra flexible continuous flex cables are designed for small bend radius application and can be used without restriction in the most modern automated manufacturing systems. The insulation and flame-retardant jacketing materials are mechanically and chemically resistant to harsh environments. They are available with a flexible tinned copper braid to provide isolation from electrical interference and are designed for use, both indoors and outdoors, in wet, dry, and extremely cold conditions. Typical applications are found in machine tools, gantry robots, pick-and-place units, automated handling equipment, conveyor systems and packaging equipment. Special features include: resistance to oils, abrasion, and cold temperatures; a minimum bend radius of five times the cable diameter; non-wicking tape and specially formulated compound enhancing flexibility; extra fine copper stranding; and CE conformance recommendation.

4. High-speed continuous flex data transmission cables are designed for automated production processes requiring increased flex life characteristics and durability. Special assembly techniques and small cable diameters allow installation in confined operating areas. The cables are available with a flexible tinned copper braid shield to provide isolation from electrical interference. The cables are also available with special paired assembly to ensure maximum interference suppression in analogue or digital signal transmissions. Typical applications are found in gantry robots, pick-and-place units, automated handling equipment, conveyor systems and packaging equipment. Special features include: resistance to oils and abrasion; a minimum bend radius of eight to 15 times the cable diameter; non-wicking tape and specially formulated compounds enhancing flexibility; and extra fine copper stranding.

5. Continuous twisting robotic cables are designed for use in applications where combined twisting and bending stresses occur. Special smooth-core insulation and slide wrapping ensure consistent performance even when subjected to long term torsional stress. This unique cable accurately transmits control signals and power supply in automated applications requiring twisting movement. The maximum torsional angle these cables can accommodate is plus or minus 360° per metre. The cables are available with a flexible tinned copper braid shield to provide isolation from electrical interference. Typical applications are found in bottling and packaging equipment, welding robots, grinding and cutting machines, pick-and-place robots, rotary tables, and portable hand tools. Special features include: oil, chemical, and abrasion resistance; a minimum bending radius of 15 times the cable diameter; non-wicking tape and specially formulated compounds enhancing flexibility; fine copper stranding; and CE conformance recommendation.

6. Continuous flex servo cables are designed for automated servo systems. They provide power and signal to a servo motor while withstanding continuous flex cycles. A unique combination of signalling and power cables in one jacket, they provide functional safety, reliability and durability, while reducing weight and saving space. They can be used in all electrical equipment in dry, damp, and wet conditions. Shielding is required to prevent distortion of the precise control and feedback signals created by electromagnetic interference (EMI). Typical applications are found in cable tracks, assembly lines, CNC machines, industrial robots and pick-and-place machines. Special features include: oil, chemical, and abrasion resistance; a minimum bending radius of 12 times the cable diameter; specially formulated compounds enhancing flexibility; and extra fine copper stranding.

7. The single conductor, double-insulated design utilises Class K stranding, thereby providing an extremely tight bend radius and superior flexibility resulting in easier handling and installation in a confined operating area. These cables can be used for internal or external applications without conduit. Typical applications are found in spindle motors, welding robots, cable handling systems and cable tracks requiring flexible power cable and interconnect wire from the power supply to the machine. Special features include: resistance to abrasion, mineral and synthetic oils, and water-based coolants; a minimum bending radius of five times the cable diameter; and Class K stranding.

Conclusion

Cable life can be increased dramatically by specifying the proper cable and the proper jacketing material for each application, installing it correctly, and understanding its requirements. This knowledge will result in lower operating costs, higher reliability, and longer functional cable life. A full electronic cable specification tool can be found on www.lappcable.co.za/cablefinder.html

For more information contact Grant Joyce, Lapp Cable, +27 (0)11 201 3213, grant@lappcable.co.za, www.lappcable.co.za



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