Basis for the design and solidification of mold contours (see Molding machine).
By performing compaction work, the bulk mold material is brought to higher density. The adhesive forces between the individual mold sand particles, in particular the adhesive forces of the bentonite, and the greater packing density result in the compaction and consolidation of the mold.
The compaction is permanent (plastic), but may also be elastic. In particular with increasing intensity of compaction (high-pressure molding, pulsed compaction), the elastic fraction increases and the so-called elastic recovery may occur. Fig. 1 shows the development of the individual compaction methods.
The compaction process is connected to a decrease in volume and height between the loose and compacted states. With a bulk weight of about 0.8g/cm3, the porosity of bulk sand has an average content of 65% by volume which is reduced to only 35% after compaction. The degree by which a bulk mold sand can be compressed is highly dependent on the moisture content.
In extrusion presses, compression is usually carried out in piston extrusion presses. The pressing pressure is created by the friction of the pressed strand in the press channel as counter pressure to the piston pressure. By changing the press channel diameter and the press pressure and thus the compaction can be regulated.