Control cables increasingly have to withstand temperature extremes in applications such as food and beverage machines, industrial ovens, furnaces, foundries, and industrial process equipment. These applications can subject the cable to continuous-use temperatures as low as −50°C and as high as 180°C.
For these environmental conditions, customers have to think about cables with jacket materials other than PVC. A growing class of control cables occupies a middle ground between over-engineered specialty cables and commodity PVC cables. Silicone or cross-linked polyolefin copolymers can take over in thermal environments that would cause PVC cables to fail prematurely. Here’s a closer look at these cables, and in particular, how they balance thermal performance against other desirable cable properties.
Improving the thermal performance of a control cable can be a balancing act. Some of the changes to cable construction that widen the operating temperature range can compromise the cable’s electrical or mechanical properties. Silicone and cross-linked polyolefin cables do a good job striking that balance.
Both materials dramatically widen the continuous use temperature range of control cables. A typical PVC control cable, for instance, can function in a temperature range from −40 to 90°C. While a silicone-based cables work comfortably in a range from −50 to +180°C.
The conductor material is also an important factor. For higher temperatures, a coated conductor is necessary in order to protect the bare copper effectively against corrosion. Tinned copper conductors should be used within a cable with a jacket made of silicone or cross-linked polyolefin.
With the most advanced cable technology, the additional thermal performance will not affect the electrical properties of the cable at all, and any effects on mechanical properties will be minor or even advantageous. Compared to traditional PVC cables, the silicone and cross-linked polyolefin cables will exhibit:
- Equivalent flexibility—though polyolefin cables are slightly stiffer than silicone or PVC cables
- Improved wear resistance (for cross-linked polyolefin)
- Improved chemical resistance
- Equivalent flame performance
- Halogen-free construction
The only downside of cables designed for temperature extremes is that they are more costly than a commodity control cable, usually by 250% or so. However, the silicone and polyolefin cables are typically 65% less than a fluoropolymer specialty cable.
Silicone cables are suitable for applications involving high temperature, high voltage, and a need for flexible wiring. They are also resistant to UV radiation, hydrolysis, oils, chemicals, and plant and animal fats. For these reasons, they are commonly employed in metal processing applications—as well as in the industrial, automotive, and automation industries—because of their superior chemical resistance properties.
The second material alternative, crosslinked polyolefin, is formed from a combination of heat and high pressure—either by irradiating or chemically cross-linking the compound. These cables exhibit important electrical properties that make them ideal for medium- to high-voltage applications. These benefits include:
- Increased thermal strength
- Improved corrosion and abrasion resistance
- Resistance to solvents, detergents and other operating fluids
- Resistance to high temperatures
Alex Terpe is a product manager for the Lapp Group.