Investigation and modelling of release behaviour of polymer moulds for polyurethane foam moulding

In recent years the use of polymers has become increasingly significant in almost all areas of industry. Polyurethanes in particular can be produced in an extremely large range of formulations, and with a wide range of properties. The research carried out here was based on polyurethane foams used within the automotive industry for seating and insulation. One of the biggest problems facing the manufacturers of polyurethane foam is that of releasing a part from its mould without causing damage to either the part or the mould itself. Traditional methods of manufacture involve the use of a steel or aluminium mould, coated with a sacrificial, normally wax-based, release agent in order to allow effective part removal. Various environmental and financial issues are associated with the use of these release agents, and this research, therefore, aimed to provide an alternative to their use. Many companies use moulds manufactured from polymeric materials for short run production, and occasionally it has been observed that in certain cases a PU foam part can be released without using a sacrificial release agent. However, the issue of predicting release of PU foam from a polymer mould is something of a 'black art', and in most cases a company will continue to use a sacrificial release agent in order to prevent any possibility of parts sticking in the mould. The author of this work has shown that the low surface energy of a polymer allows un-aided polyurethane foam release under certain conditions. It has also been shown that, contrary to a large school of thought, the roughness of the substrate had a large effect on the ability of a polymer surface to release. The foam composition was also significant. Crucially it has been shown that, given the input of the surface energy of a polymer substrate, its roughness and the composition of the foam, it is possible to predict whether or not un-aided release should be possible, and a model has been produced in order to allow this prediction for the foams under consideration. This model will provide a company with the ability to identify possible polymeric mould materials, and levels of finishing for these moulds, which have the potential to allow un-aided release of polyurethane parts.