Bestimmung der Härtungskinetik gashärtender Kernherstellungsverfahren zur numerischen Prozesssimulation : durchgeführt am Beispiel eines Polyurethan-Coldbox-Bindersystems

摘要

The manufacture of cast parts by lost moulds is of prominent importance in casting industry. In this field, processes with sand serving as base material take a predominant role. Coherence between the single sand grains may be achieved by different means, with the gas hardening polyurethane-coldbox process being the major route. Today numerical simulation of casting and solidification of metals is widely disseminated in the industry. It's competitive edge in planning of processes and parts' properties is well accepted. While computational simulation is established for the main process step of casting, there is a lack of use in upstream process steps. One of these upstream processes is the production of cores by the polyurethane-coldbox process. In this process parts of the mould or cores, which make up the inner geometry of a cast part, are produced in so called core-boxes. The filling of these core-boxes with a sand-binder mixture is subject to numerical simulation and scientific research today. The second step in PUR-coldbox core production, the hardening of the core by a catalytic agent, amine, is not yet implemented into simulation. This is mainly due to the lack of knowledge of parameters and boundary conditions of the hardening reaction. In the framework of the presented thesis an experimental apparatus has been designed and built to close this blank space. The following problems are solved:- Measurement of the concentration of catalyst in the gassing flow was not feasible in real-time condition so far. The problem was solved by designing and building a gassing apparatus capable of producing a gassing flow of known concentration.- Ultrasound measurement technique was adapted to the highly dynamic hardening process of polyurethane-coldbox binder systems. In order to achieve that goal it is important to know the correlation between the development of sound propagation and mechanical properties in the hardening core. A novel core box for testing sound propagation and mechanical properties was designed and built. Three different sound propagation criteria are identified: The start of the change in speed of sound in the core, the point of inflection and an end in the change of the speed of sound. The experiments show that the criteria t$_{start}$ and t$_{end}$ are well capable of describing the start of hardening and the end of the main hardening reaction.- A second experimental core box was designed and built in order to find the influence of the following parameter on the hardening reaction: - Concentration of the catalyst amine - Flow rate of the air-amine-mixture - Temperature of the air-amine-mixture - Influence of adsorption and desorption of the catalyst on the binder's surface- A third experimental core box serves for measurement of the hardening kinetics in areas in the core secluded from the gas flow.A commercially available polyurethane-coldbox binder system has been tested on the influence of the parameters mentioned above. Now relevant parameters for calibration of numerical simulation models for the hardening of polyurethane cores are available.