Characteristic value that corresponds to the water content of a mold material mixture in molded condition; it is often also referred to as water demand.
However, equal water content in a clay-bonded mold material mixture does not mean equal molding characteristics. The absolute water content for achieving optimum properties of the mold material, is based on a number of factors. These include the properties of the basic mold material (e.g. porosity of the quartz sand grains, water absorption capacity, specific surface area), the type of bentonite, intensity of conditioning, content of bentonite and additives, as well as recirculation condition of used sand (oolitization, dusting). In order to allow for comparison of mold material mixtures of different compositions and for determining optimum absolute water contents for the various molding methods and compaction processes, the concepts of “water demand” and “moisture content” have been introduced.
Today, moisture content is determined using the compaction testing method. The influence the water content has on essential mold material properties is illustrated in Fig. 1. The figure reveals that maximum properties may be achieved with different water contents. Using the example of increasing bentonite content, Fig. 2 illustrates that even with equal moisture content (corresponds to molded condition) different water contents are required (increasing water contents in this particular case).