Wet tensile strength testing in neutron radiography - cause-property relation studies in bentonite bonded molding sands

• Applicant: Professor Dr. Guntram Jordan
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 268662032

Bentonite bonded molding sand is among the most common mold materials used in founding. One reason for the common acceptance is its reusability. However, the binding quality of used molding sand is reduced to some degree. Therefore, 5% of new mold material is added after each cast. The quality loss of the re-used molding sand is caused by alterations of the clay minerals in the mold material and results in a reduced wet tensile strength among other effects. One consequence of the quality loss is the increased susceptibility to water-related casting flaws such as scabbing. These casting flaws are caused by ruptures which originate from the interaction of increased compressive stress in the hot area facing towards the melt on the one hand and reduced wet tensile strength in the neighboring cooler area on the other hand (the so called condensation zone, in which the moisture from the hot area re-condenses).In spite of the high significance of the condensation zone on the physical properties of the mold material it is still unknown what exactly takes place in the condensation zone while moving through the mold. For instance in the context of rupture, momentary temperatures and water concentrations at the weakest position in the mold material are insufficiently known. Also the dependence of the position and moment of rupture on precedent temperature and water gradients is unknown. A primary aim of the research project, therefore, is to investigate these relations quantitatively. For this purpose, wet tensile strength testing will be conducted in-situ in a neutron radiograph. By these experiments, water concentrations and temperature at the position and moment of rupture as well as the according tensile strengths and the precedent temperature and water gradients can be measured quantitatively. Moreover, the dependence of all these factors on the most important technical mold material parameters such as compactibility and permeability can be investigated.On the basis of the new quantitative data it is possible to analyze which properties in re-used mold material are caused by which mechanisms and processes. Such a scientific quantitative understanding of the cause-property relations by far exceeds the mostly empirical knowledge existing so far. The insights, therefore, can essentially contribute to a development of strategies for an effective improvement of the re-usability of bentonite bonded molding sands.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Wolfgang W. Schmahl