Tech Briefs
Radiant heat protection

Federal-Mogul's ReflecTube is a nylon 4,6 convolute currently used in fuel lines, control cables, and wire harnesses.

Traditionally there have been two approaches to thermal protection: insulation of a component that has an internal heat source and protection of a component from an external heat source. The performance criteria are different for each method so different types of protection products are used. For insulation of a component, braided fiberglass sleeving is usually the product of choice. A typical application is the heat-treated, saturated glass braid that is currently used on exhaust gas recirculation (EGR) tubes. The sleeve insulates the EGR tube to contain heat and protect the surrounding components.

The second and fastest-growing approach is to protect components against the external heat source. Because the problem is radiant heat, aluminized reflective products provide the best protection, according to Tammy Ebersole, Automotive Product Manager, Federal-Mogul Systems Protection Group. The aluminized product is placed on the component that requires protection so that the heat is reflected away, reducing surface temperature. Typical applications include battery cables and components adjacent to the exhaust manifolds.

"Thermal protection requirements are becoming more demanding with each new generation of vehicles," said Ebersole. "The combination of increased emissions controls, sophisticated electronics, and additional safety features create a tightly packaged engine compartment."

Crowded engine compartments translate to reduced airflow and the increased likelihood of exposing sensitive components to damaging heat. Protection of these components has become a major concern as engine compartment temperatures continue to rise. Because engine compartments are so tight, routing may bring a component close to a heat source, while at the same time the entire area may be in a high-temperature ambient-air condition. While providing good radiant heat protection, standard reflective products have not been able to survive the heat soaks or high temperature heat spikes. According to Ebersole, "This new thermal scenario created the need for a group of products that could provide radiant heat protection yet survive in a high temperature environment without degradation."

Federal-Mogul developed a new family of products that addresses the problem, including ReflecTube and ReflexWrap. "Both were designed using advanced materials and manufacturing methods that enable them to provide multiple types of thermal protection," said Ebersole.

ReflecTube is a highly reflective nylon 4,6 convolute that can withstand a 170°C (338°F) continuous operating temperature. The flexibility of the product and its ability to be installed after component assembly allows for use in areas with tight space constraints. Current applications include fuel lines, control cables, and wire harnesses.

ReflexWrap is a coated fiberglass product with a laminate of reflective material. The product is designed to withstand a 200°C (392°F) heat soak without degradation in radiant heat protection. The product is constructed as a self-closing wrap with a secondary adhesive seal, ensuring a 360° reflective surface. It is currently used on the brake lines of several production platforms.

Introduction of new products has started to address some of the thermal management issues that engineers face during vehicle design. "As vehicles continue to increase in complexity, the thermal scenarios will continue to change," said Ebersole. "In order to provide the appropriate level of protection, thermal protection products will need to continue to evolve to meet increasing stringent requirements."

Jean L. Broge