Coremaking
Cordis is an inorganic binder. Depending on the type of binder, the matrix is assembled from a combination of modified phosphate, silicate and borate groups. Curing of the core in the corebox takes place by removal of water.
Mixing
The moulding sand can be prepared in any commercial mixer. Depending on the core geometry, the rate of addition of Cordis binder to the sand amounts to 2.0 - 3.0 % based on sand. The sand mix is ready to use as soon as it leaves the mixer. If the mix is kept in a sealed container without being exposed to the air, it can still be used after one day of storage. Under normal working conditions, daily cleaning of the core shooter is essential.
Coremaking
The sand mix is shot into a heated corebox to produce cores. Depending on the core geometry, the corebox temperature ranges between 120 - 180 °C. The heat in the corebox should be distributed as uniformly as possible. A peripheral shell of hardened material forms around the outer surface of the core after the sand mix - consisting of sand and water borne binder - enters the corebox. This initial hardening stage is due to a drying process in which moisture - the water solvent - is removed from the core. This is a purely physical hardening process.
Depending on the type of Cordis binder used, a chemical hardening process can then additionally take place. This results in a higher stripping strength than is achieved by straight physical hardening (drying). Depending on the sand used and the type of Cordis binder, cold bending strength levels ranging from 350 - 550 N/cm2 may be achieved at binder addition rates of 1.5 % - 3.0 %. Hardening can be markedly accelerated if the core is gassed with hot air. Such gassing leads to better heating of the moulding sand, and at the same time efficiently purges the water liberated during the drying process in the core. The hardening time of inorganically bonded cores greatly depends on their geometry and that of the coreboxes used. The larger and more compact the core, the more difficult it is to harden. The coreboxes for this process must be constructed to allow a large flow of hot air to be quickly and directly passed through the corebox. These coreboxes should be made of a material that can be heated to approx. 200 °C. Since the rate and degree of hardening is directly related to the passage of hot air, it is important to keep the required air flow at a temperature of 150 °C throughout the entire gassing time.
Core Storage
Inorganically bonded cores should not be stored outdoors or exposed to high humidity conditions for extended periods of time.
Casting and Cooling
Thanks to the inorganic nature of the binder, no residues in the form of condensates develop during the casting operation. Similarly, inorganic binders afford a considerable decrease in casting porosity due to core-related effects. There is no smoke or odour development during the casting operation.