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.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.