Predicting the compressive properties of rigid urethane foam

Abstract The classic equation 1 in use throughout the urethane industry to predict the compressive properties of rigid foams is (1)\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm compressive property} = K({\rm density})^a . $\end{document} The value of K and a need to be determined experimentally for each foam system at a given temperature. By evaluating the compressive properties of 14 different rigid urethane foams, a was defined as 1.75 for all materials at all test temperatures. General equations for predicting the foam's compressive properties over a temperature range of −65° to 325°F (−54° to 204°C) were then developed. These general equations appear to be reasonably accurate in predicting the compressive properties of any rigid urethane at any temperature up to the foam's softening point. The equations are of the form shown above with K being a function of temperature only. Finally, the K term was defined as a function of temperature. The equations developed for predicting the compressive strength and modulus of the rigid urethane foams are: (2)\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm compressive strength} = (8.09 - 0.0178T){\rm density}^{1.75} $\end{document} for T equal to or greater than 77°F (25°C), and (3)\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm compressive modulus} = (191 - 0.369T){\rm density}^{1.75} $\end{document} for T equal to or greater than −65°F (−54°C), where the compressive strength and modulus are in pounds per square inch and density is pounds per cubic foot. These equations are valid up to the softening point of the foam.