Molding material circulation

Total amount of molding material that is repeatedly available in the foundry after sand conditioning and addition of various components for utilization in the molding bay (Figure).

Throughout molding material circulation, the molding material is subject to distinct changes that have various effects on the molding material system. These changes are characterized by the conditioning behavior of the molding materials and their components. The conditioning behavior is determined by the properties of the raw materials used, such as quartz sand, bonding clay (bentonite) and additives (molding material additive) in interaction with the loads occurring and the technical/technologial parameters of the equipment used for recycling or conditioning of molding material. These interactions and interdependencies characterize the quality of the used molding material introduced into the conditioning station.

And the conditioning behavior has central influence on the efficiency of molding material economy.

Molding material-based changes may be due to the following causes:

Thermal loads
Thermal loads may cause drying of the molding material, significant increase in temperature associated with formation of irreversible wear products with new quality-related properties (such as burn-dead clay, incineration, and coking of the coal dust and/or other lustrous carbon carriers, quartz grain fragmentation) and formation of oolitic shells around the quartz grain.

Mechanical loads
During conditioning and compaction of the molding material they cause reduction of grain size, modification of grain shapes and increase of the proportions of fine particles.

Chemical impacts
The change in anion contents is indicative of such chemical loads and leads to acidification and salification (deactivation) of the circulated material. Pyrolysis products occurring through thermal loads cause coating with bentonite shells.

The properties of the molding materials must be adjusted to the various loads occurring in the process stages to be performed. In doing this, the raw material qualities available, the equipment provided, and the specific characteristics of the production process and the products must be taken into account.

Additional references:

Mold sand testing
Mold material balance
Mold material management
Mold material control
Sand regeneration

  • Figure: Molding material circulation in an iron foundry 
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