On the fraction of sand grains bounded in molding materials – a new measurement technique

Abstract

We present a method that allows to determine the fraction of unbounded sand grains in a compacted sand-binder system as used in foundry practice. The method uses a dynamic gas permeability measurement technique, which reveals that in foundry sands the permeability is not a constant but depends on the pressure difference driving the flow through it. This effect can be understood on the basis of so-called rattlers, being unbounded sand grains. A model of the effect is developed and evaluated with respect to the volume fraction of unbounded sand grains. The amount of unbounded grains is typically between 1 and 10 volume percent.