## 1 Introduction
### Decoring of Inorganically Bound Sandcores  
Casting technology relies on sand cores to achieve complex, hollow structures with undercuts and cavities [3]. The cores are used individually or are assembled into sand-core packages. They are inserted into the mold. They must be held in position by core holders in the surrounding permanent or sand mold. The sand core stands out of these holding positions after casting and forms a connection to the cavity. This connection is used to extract the sand from the formed cast part, which is the decoring process step. The sand-binder system of the sand core determines which methods can be used to decore it. Sand cores are classified into organically and inorganically bound sand cores [1]. Organic sand-binder systems are based on hydrocarbons and can easily be burnt off. Most of the decoring process is achieved during the casting process due to the heat of the melt. It cracks the sand cores, burns parts of the binder, and allows shaking of the remaining sand out of the openings. The downsides are environmental considerations of the toxic waste and fumes produced during the burnup. Inorganic sand-binder systems use sodium-silicate to harden sand cores. It lacks hydrocarbons and, with it, the downsides of toxicity. However, it cannot be burnt off, and additionally, it hardens even more on the surface, which is in contact with the melt [1]. The decoring of inorganically bound sand cores is their main disadvantage. There are multiple approaches to change the properties, for example, adding additives or changing the ratio of binder to sand [4].  
At the same time, research focuses on understanding the decoring behavior of inorganically bound sand cores [5]. [PERSON] [2] describes the essential parameters to predict the decoring behavior of a sand-binder system and builds a matching theory. According to this theory, the flexural and compressive strength of the sand-binder mixture are the main parameters. Another factor for predicting the decoring behavior is the hydrostatic pressure on the sand core [6]. The cast part shrinks onto the sand core after casting, creating pressure on the sand core. This pressure influences the force needed to fracture the sand core. Starting from an initial fracture area, the decoring proceeds. The Drucker-Prager failure model describes this theory, as shown in Figure 1.  
The failure straight is determined from a three-point bending test and a uniaxial compression test. The cohesion and the internal friction angle phi describe the experimentally calculated failure straight. If the von Mises equivalent stress for a prevailing hydrostatic  
Figure 1: Drucker–Prager model for failure. Adapted with permission from Ref. [2]. 2021, Elsevier.  
pressure is above the failure straight, a fracture occurs in the sand core. The composition of sand and binder defines the parameters of cohesion and phi. If these parameters of a sand-binder system and the hydrostatic pressure state are known, the force needed to fracture can be predicted. The following bullet points summarize our findings:  
* The assumption of a pressure-dependent material model to describe sand-binder systems is valid. It can be seen as essential for an accurate characterization of the mechanical behavior of decoring.
* The decoring behavior of inorganically bound sand-binder systems is significantly influenced by the molding material and the binder system used. The molding material dominates the influence on the decoring behavior.
* Larger binder quantities can lead to higher residual strengths and correspondingly poorer decoring behavior for the same molding material.
* Assuming constant decoring energy, the angle phi and the cohesion of the remaining residual strength after casting are the two main influencing variables for the decoring behavior.