TY - BOOK

T1 - Investigation on the removal of internal sand cores from aluminium castings

AU - Stauder, Bernhard Johannes

N1 - no embargo

PY - 2018

Y1 - 2018

N2 - Casting of metals comprises filling, solidification and cooling of metal melt and causes an intensive heat exchange with the moulding parts. Mechanical loads are introduced by flow, buoyancy and casting shrinkage. Foundry cores, applied to shape internal or undercut contours, consist of a bonded granulate and are characterised by a high free volume. Their physical properties are majorly controlled by the type of granular material and binder, the realised degree of compaction and the thermal exposure, imposing a continuous property change during the casting process. In this thesis, focus was put on the description of cast-in core properties at the end of the casting process, based on thermal conditions of cast aluminium car engine cylinder heads. The predictability of core degradation and the description of their removal behaviour from the castings was investigated based on their thermal history, with particular attention paid on the granular nature of sand cores. Enhancements of foundry-typical mechanical property testing were presented via an improved evaluation of three-point bending tests, resulting in additional parameters allowing to evaluate structural changes of samples. The thermal impact on the mechanical properties was evaluated by standard testing methods over a set of temperature profiles in air and oxygen-reduced environment and summarised via proposed temperature dependent Mohr-Coulomb parameters for several sand core types. Evaluation of the specific fracture energy by wedge splitting tests was applied for the first time on sand core samples. The results exhibited an inverse proportionality of the specific fracture energy with the de-agglomeration rate criterion. This criterion was evaluated from the in-line acquired removed minimum core mass rate during a core removal test and the achieved de-agglomeration degree of the removed core sand. The effect of cast aluminium shrinkage on mechanical damage of cores was demonstrated with core samples of low thermal expansion, high brittleness and a low mechanical property decrease over the temperature. For the prediction of mechanical core removal of different bonded granular material types, the inter-dependency of cast-in cores with the casting must be considered. The herein documented effects, mechanical properties and failure criterion parameters depending on the thermal history constitute an important information to predict mechanical core collapse.

AB - Casting of metals comprises filling, solidification and cooling of metal melt and causes an intensive heat exchange with the moulding parts. Mechanical loads are introduced by flow, buoyancy and casting shrinkage. Foundry cores, applied to shape internal or undercut contours, consist of a bonded granulate and are characterised by a high free volume. Their physical properties are majorly controlled by the type of granular material and binder, the realised degree of compaction and the thermal exposure, imposing a continuous property change during the casting process. In this thesis, focus was put on the description of cast-in core properties at the end of the casting process, based on thermal conditions of cast aluminium car engine cylinder heads. The predictability of core degradation and the description of their removal behaviour from the castings was investigated based on their thermal history, with particular attention paid on the granular nature of sand cores. Enhancements of foundry-typical mechanical property testing were presented via an improved evaluation of three-point bending tests, resulting in additional parameters allowing to evaluate structural changes of samples. The thermal impact on the mechanical properties was evaluated by standard testing methods over a set of temperature profiles in air and oxygen-reduced environment and summarised via proposed temperature dependent Mohr-Coulomb parameters for several sand core types. Evaluation of the specific fracture energy by wedge splitting tests was applied for the first time on sand core samples. The results exhibited an inverse proportionality of the specific fracture energy with the de-agglomeration rate criterion. This criterion was evaluated from the in-line acquired removed minimum core mass rate during a core removal test and the achieved de-agglomeration degree of the removed core sand. The effect of cast aluminium shrinkage on mechanical damage of cores was demonstrated with core samples of low thermal expansion, high brittleness and a low mechanical property decrease over the temperature. For the prediction of mechanical core removal of different bonded granular material types, the inter-dependency of cast-in cores with the casting must be considered. The herein documented effects, mechanical properties and failure criterion parameters depending on the thermal history constitute an important information to predict mechanical core collapse.

KW - Guss

KW - Sandkern

KW - Eigenschaften

KW - Bruchverhalten

KW - Schädigung

KW - casting

KW - sand core

KW - mechanical properties

KW - fracture

KW - damage

M3 - Doctoral Thesis

ER -