Manufacture of Syntactic Foams: Pre-Mold Processing

Manufacturing processes for syntactic foams made of hollow microspheres and starch were studied. Various manufacturing parameters in relation to the “buoyancy method” were identified and inter-related. An equation based on unit-cell models with the minimum inter-microsphere distance concept for a relation between volume expansion rate of bulk microspheres in aqueous starch and microsphere size was derived and successfully used to predict experimental data. It was demonstrated that the inter-microsphere distance can be calculated numerically for microspheres with known statistical data. The equation relating between volume expansion rate and microsphere size was further extended to accommodate a relation between inter-microsphere distance and microsphere size but with limited accuracy for binders of low starch content. An alternative empirical linear equation for the relation between inter-microsphere distance and microsphere size is proposed for wider applications. A simple method for estimation of syntactic foam density prior to completion of manufacture is suggested. Shrinkage after molding of syntactic foam is discussed in relation with different stages such as slurry, dough and solid. A two-step manufacturing process involving molding and then forming is suggested for syntactic foam dimensional control.