Exotic materials yield peak tubing performance.

High performance just wasn't enough for the customers of Glenair, Inc. in Glendale, Calif. The company extrudes convoluted tubing used to protect wiring in aircraft, buses, and trains. This critical application typically uses tubing made from fluoropolymers such as PTFE, EFTE, PFA, and FEP. But customer demands for halogen-free flame resistance, higher heat resistance, greater hoop strength, and lighter weight forced the company to try something new, says Tom Young, manager of composite products.

Glenair found a solution in high-end polyetherketone engineering thermoplastics such as PEEK from Victrex USA Inc., West Chester, Pa., and one other resin that the company would not reveal. As one of a small number of tubing manufacturers that are pioneering use of these exotic resins, Glenair discovered that higher performance can be achieved without higher cost.

LESS IS MORE

With these unusual resins, Glenair extrudes highly flexible tubing in diameters from 0.188 in. up to 2 in. The polymers are halogen free, offering UL 94V-0 flame resistance down to 0.007 in. thickness without the use of additives. In addition, the polyetherketones are said to offer high hoop strength and crush resistance and better chemical resistance than PTFE. While fluoropolymers reportedly need radiation crosslinking to achieve glass-transition temperatures around 200 C, the polyetherketones have Tg's around 260 C without special treatment.

Besides having lower specific gravity than fluoropolymers, the higher performance of polyetherketones allows Glenair to downgauge its tubing from 0.025-0.030 in. to a thickness range of 0.010-0.015 in. Using less material saves both weight and cost. The company can thus sell the new tubing at the same price as the fluoropolymer products, even though the polyetherketone resins are much more expensive. The new tubing may find use in medical applications, Young says.

Glenair uses proprietary die technology to make the helical convoluted tubing. Otherwise, the extrusion equipment is the same as for making fluoropolymer tubing.