Bubble growth in reaction injection molded parts foamed by ultrasonic excitation

Processing of microcellular foam was studied for polyurethane. Assuming tha t the bubble growth is controlled by diffusion, theoretical prediction was carried out numerically to understand the bubble growth mechanism in the ca vity during mold filling. Final bubble sizes were also predicted by conside ring the gelation time and the diffusion boundary. Viscosity change of the mixed polyurethane resin during polymerization reaction was predicted by co nsidering reaction kinetics. The gelation time was determined to terminate the numerical calculation. The diffusion boundary was predicted based on th e number of nucleated bubbles that had been determined both theoretically a nd experimentally. For processing of polyurethane foam by reaction injectio n molding, ultrasonic excitation was applied to the mixture of polyol and i socyanate. The polyol resin was supersaturated with nitrogen gas at an elev ated pressure and ultrasonic excitation was applied to the mixture after im pingement mixing of two components of the selected polyurethane system. Bub ble nucleation was induced by the ultrasonic excitation and the bubbles wer e grown as the gas was supplied to the bubble from the resin.