Temperature and mold size effects on density gradients and mechanical properties in a polyurethane foam system

Rigid polyurethane foams can be used as a thermal or vibration insulator and energy absorption material. They are often molded directly in place, where a smooth, thin skin forms between the mold and the cellular structure of the foam. Density gradients and the skin are shown to have an effect on the mechanical properties of the foam; This work will investigate the effects of processing temperature and mold size on the average density, density gradient, compressive modulus, and compressive strength, for a molded free rise, water blown polyurethane foam system. Four processing temperatures are used during foam fabrication: 25°C, 40°C, 65°C, and 85°C. Three aluminum cylinder mold sizes are used with diameters of 29mm, 41mm, and 51mm. The properties are also compared to reference samples with a uniform density of 0.101 g/cc; Results show that processing temperature and mold size have a significant effect on density, density gradients and some mechanical properties

Temperature and Mold Size Effects on Physical and Mechanical Properties of a Polyurethane Foam

Rigid polyurethane foams are used as thermal or vibration insulators and energy absorption material, and are often molded directly in place, where a smooth, thin skin forms between the mold and the cellular structure. Density gradients and the presence of a skin are known to affect the mechanical properties of the foam. We investigate the effect of processing temperature (25, 40, 65, and 85 C) and mold size (aluminum cylinders with diameters of 29, 41, and 51mm) on the average density and density gradients (radial and vertical) of a free-rise, water blown, rigid polyurethane foam system, and measure the effects on compressive modulus of elasticity and collapse stress. In general, both average density and radial density gradients decrease with increasing processing temperature and larger mold sizes. A reduction in average foam density corresponds with decreases in the elastic modulus and compressive strength. These mechanical properties are compared to reference samples extracted from very large batches of foam with a uniform density of 0.10 g/cc, where normalization of the compressive data shows the elastic modulus to exhibit the strongest dependence on processing temperature and mold size

Cell Morphology and Mechanical Properties of Rigid Polyurethane Foam

Polyurethane foam, used as a supporting or insulating material, is sometimes formed in complex molds with significant variations in geometry and size. This work investigates the relationships between cell morphology, density, and mechanical properties in a molded polyurethane material using relatively small cylindrical molds. Understanding these relationships will help mechanical designers to analyze and predict the responses of foam components accurately. Three mold sizes are used to study changes in cell morphology (cell area, cell diameter, aspect ratio, cell angle, cell edge length, cell face thickness, and cell edge thickness), density, and mechanical properties (Young’s modulus and collapse stress) with respect to position within the mold. The density is shown to increase from the top to the bottom of the reference mold but does not change significantly in the small and tall molds. However, the mechanical and cell morphology properties show more changes in the small and tall molds when compared to the reference mold even though there are only small changes in density