Excessive Heat or Frigid Cold

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December 02, 2020

Excessive heat or frigid cold, these custom cable materials will withstand the most extreme temperatures

As those of us in the Midwest begin to bundle up for frigid winter temperatures, others are shedding layers as their summers begin to heat up! No matter where you are in the world, your device may be performing in one or both ends of the extreme temperature spectrum. This article will walk through a few of the key custom cable design considerations for selecting appropriate materials that will ensure reliable performance despite the harsh environment in which it may need to perform.

Conductors

Let us start at the beginning with the conductors! Conductor materials, being the core of the cable, make a big difference on longevity and signal reliability of the cable. When designing for cables in high temperature environments, you may want to consider the following two conductor materials:

  • Nickel-plated
    • Nickle-plated copper is often used in high temperature applications due to its ability to withstand up to 450°C. In addition, the nickel plating offers corrosion and wear resistance.
  • Alloys
    • Alloys are a combination of 2 or more metals. Silver, nickel, copper, beryllium, cadmium, RoHS-compliant chromium are selected for their overall toughness, break strength, and flex-life. Alloys are another great option for high temperature applications.

If the cable is being designed for frigid temperatures, you will want to keep flexibility in mind. A solid conductor will be more rigid and easier to break when put under stress. If flexibility is important for your application, it is recommended that you select a conductor with a high strand count. As a general rule, the higher the strand count, the more flexible the conductor will be.

Tubing

Tubing is one component that has a variety of functions inside of a custom cable. For example, a tube could be used to dissipate heat or to vent pressure or steam. The tube could even be used to carry warm water in order to help protect the cable from getting too cold and failing. Depending on the specific high temp application, your cable design engineer will want to ensure that the tube wall thickness and material is suitable for the high heat exposure and will not break down and potentially expose the conductors.

Tubing could also be used inside of a cable to vacuum liquids, supply air, or other gases. If exposed to cold environments, the tube material and construction will again need to be considered. There are different material options for tubing such as nylon, PVC, and even PTFE. A cable designer will help you choose the best material for your application to ensure the tube will not kink or collapse in the cold environment. Durometer or shore hardness of the material is important because although a low durometer can make the material more flexible, it can also make it much more brittle and more prone to cracking and breaking.

Insulation and Jacketing

When choosing conductor insulation and jacket materials for extreme temperature environments, fluoropolymers tend to be top of mind as they offer a myriad of benefits for both extreme heat and frigid cold. As mentioned with tubing materials, durometer or shore hardness should also be kept in mind with conductor insulation and cable jacket. While fluoropolymers will perform well in the cold, they will be more rigid. A lower durometer material will offer more flexibility but will be more prone to cracking.  Below is a list of a few of the most common fluoropolymer materials to compare the features and benefits of each.

PTFE

  • The most fluorinated of all of the fluoropolymers, resulting in superior performance in terms of resistance to extreme temperatures, chemicals, oils, solvents, cut, crush, and abrasion
  • The main downside to PTFE has been the fact that this material has to be ram extruded, which means there are length restrictions based on how much resin can fit into the chamber. Northwire, however, offers an extrudable PTFE that offers a more consistent wall thickness and no length restrictions!

PFA

  • PFA is the closest to PTFE in terms of superior performance characteristics
  • One trade-off for the high-performance characteristics is the price

FEP

  • The first melt processable fluoropolymer to be released
  • FEP does not have the almost universal chemical resistance featured by PTFE and PFA, but does offer a more cost-effective alternative to PFA where these two characteristics are not as imperative

ETFE

  • Features improved cold flow resistance, higher tensile strengths, and increased abrasion resistance
  • Although not fully fluorinated like the 3 above, ETFE maintains high temperature performance, very good electrical properties, and chemical inertness

Other materials such as Santoprene, TPEs, or Northwire’s BioCompatic also do well in extreme temperatures. Check out the BioCompatic data sheet by clicking here to compare the features and benefits of Northwire’s innovative cable material compared to Santoprene and Silicone. Keep in mind that Northwire has cable design experts available to assist you with material selection specific to your end application.

As we all know, harsh environments can put added stress on devices and the cable connectivity solution. Below are some additional factors to think about when designing for extreme temperatures, which will impact design choices.

Flexibility

  • Will the cable be used in a static application or will it be moving? Cold temperatures can decrease the flexibility of a cable and make it very brittle. If flexibility is important, consider a TPE (thermoplastic elastomer) or a TPU (urethane) as both jacket materials are rugged and perform well in low temperatures.
  • If instead, the cable would be in a static environment, a good question to ask is whether the cable will be supported/contained or free to move in the wind? If the cable is able to move, brittle point is important because the jacket could crack if the cable could come into contact with other objects at sub-zero temperatures. If that is a possibility, be sure to check the cold bend radius of the material being selected.

Temperature Variation

  • Will the temperature stay relatively constant or will it fluctuate from cold to warm to hot and back to cold? If so, what is the cycle time of the fluctuation?

Liquid Exposure

  • Another consideration is whether the cable will be exposed to liquid. Especially if the temperature reaches the freezing point! You will also want to keep the termination to the connector in mind. If exposed to liquid, it may be wise to use an over-mold to help protect the connection points while being flexed and to help protect from any liquid it may encounter. A water-tight connector may be needed as well to prevent water ingress.

Connector Choice

  • Will the cable assembly be installed and frequently handled in freezing temperatures? If so, be sure to select a connector that features a high mating cycle count, so that the connector housing or internal pins do not crack and break when being connected and disconnected.

There are a variety of custom cable materials and added cable component options such as tubing to consider when putting a design together. Cable design experts are available to make recommendations for appropriate material selection based off of the needs of your specific application and the environment in which it needs to perform. Whether you have a napkin sketch or fully identified specifications, Northwire’s cable designers are here to help.

 

Get in touch with a NWI Cable Specialist today to start your Cable Design