← TXL Wire vs GXL Wire | Product Knockout RG213 vs LMR400 | Product Knockout →

Shrinkback on Small Gauge PTFE Wire

Wednesday, January 29, 2020

Wire and cable comes in many sizes, shapes, and configurations: small or large gauge, round or flat, multi- or single conductor, solid or bunched stranding. All types of wire and cable have their own challenges, especially when working with smaller gauges becoming more and more delicate the smaller the wire gets. Shrinkback or breaking of the adhesion, especially PTFE, between the insulation and stranding is one of the issues that may arise when working with smaller wires and cables.

What is PTFE Shrinkback?

PTFE insulation shrinkback occurs when a cable’s insulation pulls away from a termination connector or cable splice. When it pulls back, it increases the insulation clearance or the distance between the end of the insulation and the termination device. Increased insulation clearance leaves part of the conductor exposed, increasing the risk of wire shorts and destroying the protective seal that the insulation and jacketing are designed to provide. This allows dirt and water into the cable and is a damaging factor that can cost a lot of time and money in cable replacements.

What Causes PTFE Insulation Shrinkback?

Shrinkback is a result of mechanical stress and heavy handling after the manufacturing process. Since PTFE is a non-stick material, an adhesive is applied to the conductor during the manufacturing process to keep the insulation in place. Afterwards, that adhesive can remain brittle and break apart from physical stresses. The PTFE insulation will automatically return to its true size when the adhesion is broken and friction isn’t enough to hold it in place around the conductor. It is typically discovered shortly after a piece of small gauge wire has been stripped back and prepared for termination.

How Do We Prevent Shrinkback?

Although it may seem like PTFE shrinkback is unavoidable, there are several steps that you can take to minimize its effects. It has been determined that smaller gauges, 24AWG and smaller, with 7 strands or less are the most common types to display shrinkback. Due to the small size of the stranding, the insulation does not have a lot of material to grip, making the PSI requirements for the jacket adhesion very low. This makes it very important not to over manipulate the wire during processing to prevent the breakdown of the adhesion of the insulation to the stranding. Here are some best practices that Allied uses to reduce the opportunity for shrinkback due to over-handling.

  • - Reels should always use the largest cores possible to eliminate memory, as well as over bending the wire.

  • - Do not over tighten payout reels. Keep tight enough to provide proper tension but not enough to cause drag and stretch wires.

  • - Minimize how often the wires pass around guide pulleys, eyelets, counter wheels, etc.

  • - Use the largest-sized bend radius whenever possible - the smaller and longer the bend, the bigger reduction in adhesion.

  • - Eliminate or minimize pressure on wires as they pass through counters, drive wheels and drive belts.

  • - Reduce the number of passes through capstans or de-reelers (dancers) with small guide wheels.

Following these simple steps is the best way to fight PTFE shrinkback as they will help prevent stretching the insulation and destroying its adhesion to the stranding. Use this knowledge to defend yourself against shrinkback problems in your future wire and cable jobs. Preventing problems like these are the key to finding cable that will last for a long time in your applications. Allied Wire & Cable follows these best practices to mitigate shrinkback as much as possible, however, it’s never a guarantee if it’s ever truly eliminated. Results can vary from reel to reel. 

Find more technical information and wire and cable resources from Allied Wire & Cable.

Filed Under: Allied Encyclopedia

Please login or register to post comments.