The effect of mould temperature on properties of flexible PU Foam

Cold-cure flexible polyurethane (PU) foam moulded products are manufactured by mixing a polyol and an isocyanate in a preheated tool. Foam moulded products frequently have defects such as varying density and surface defects. Defects resulting in scrap amount to 2-4% which translates into millions of pounds. Past research to reduce flexible foam moulding scrap and improve quality has focussed on chemical compositions, chemical reactions and materials development. This research set about understanding and improvement through a manufacturing focus to control and improve the foam moulding process. It was suspected that an uneven mould temperature was among the causes of defects in flexible PU foam parts. However, no detailed published work focusing on the effect of mould temperature on high-resilience cold-cure flexible PU foam moulded parts was found. The aim of this research was to analyse and quantify the effect of mould temperature on flexible PU foam surface texture and density. This could then be used to implement either conformal or non-conformal heating channel systems in foam moulding tools. A specially designed mould was built to produce PU foam samples at varying temperatures from 30°C to 80°C. A unique approach using a 3D Laser scanner and a CT scanner was adopted to analyse and quantify the effect of mould temperature on the PU foam samples surface texture and density. It was shown that mould temperature had an effect on foam surface texture and density. The foam density increased as the mould temperature reduced, and foam surface texture was coarse at extreme low and high mould temperatures. Analysis with SEM also showed that mould temperature had an effect on foam density due to its effect on foam cell size. Low mould temperature resulted in small cell size contributing to high foam density. High mould temperature resulted in large cell size contributing to low foam density. Results from this research provide a method of predicting the effect of mould temperature on foam density and surface texture at varying temperatures. Results provide a possible method for customising foam density at various sections by developing a non-conformal heating channel to impose large mould temperature variations. Designers and manufacturers could have multiple density in car seats (such as dual density bucket design seats) if required by controlling mould temperature at various mould sections rather than by changing material composition.