Mold material for the production of shell molds (Croning molds) and shell cores which can be coated on the basis of cold (cold setting process), warm or hot treatment methods.
Nowadays, the most important treatment process for these sands is hot coating which is practically similar to enamelling.
In this process, quartz sand is heated in a special heating apparatus to temperatures of 120 to 150 °C. Hot sand is mixed up in a core sand mixer together with solid flake-shaped phenolic resin; the resin melts and covers the quartz grains.
This process step is referred to as premixing (premixing time is between 40 and 60 seconds). Then, hexamethylenetetramine solved in water and stearate are added (see calcium stearate). The mixing time of this second step is 60 to 120 seconds. The mold properties after hardening are significantly influenced by the temperature and the additional mixing time.
The hardening process is decelerated by subsequently cooling the mold material to 70 to 80 °C. After removing the still lumped mold material from the mixer, it is pulverized on a vibrating screen where a well pourable mold material is formed which is cooled down to approx. 40 °C.
Cold-setting molding plant
Cold-setting molding line
Organic binder systems
Inorganic binder systems