Cowles, R., Shives, A., and Rauchholz, D., "Aqueous Heat Reflective Coating for Engine Compartment Isolators," SAE Int. J. Engines 7(3):1610-1617, 2014, doi:10.4271/2014-01-2082.
To satisfy the increased expectations of customers, engineers are challenged to increase fuel economy while also improving noise, vibration, and harshness (NVH) performance. In order to improve fuel economy, engine compartment designs have become more compact with reduced air flow. Elevated temperatures caused by these designs can degrade the durability and acoustic performance of the fibrous acoustic insulator material. A typical method for protecting insulators from elevated temperatures is to apply an aluminum foil patch to the surface. However, foil patches can restrict the insulator's ability to absorb sound and can be difficult to apply to complex part shapes. Foil patches can be perforated to allow the insulator to absorb sound, but there is a cost penalty as well as potential for long term performance degradation due to blocked perforations. Since NVH targets are also increasing, it's important to maximize the benefit of each part. Given these performance challenges, a heat reflective coating (HRC) has been developed as a cost effective alternative to perforated foils. HRC can be easily spray applied directly to the insulator surface and reduces the operating temperature of parts exposed to radiant heat. The thickness of this coating can be controlled to allow the insulator to maintain sound absorption performance. HRC has also been formulated as an aqueous coating to reduce environmental restrictions along with a flame retardant package to meet UL94-V0 requirements. This paper will discuss this new type of heat protection solution for fibrous insulators.