Active cooling of resin bonded moulds to reduce the cooling time of heavy-section castings without loss of casting quality

摘要

Foundries are required to produce ever larger structural elements with increasing wall thicknesses of utmost quality. These requirements also increase the solidification times and thus the necessary cooling times of the castings. The solidification and cooling step is therefore decisive for the throughput times of parts and thus has a direct impact on unit prices and capacity. IfG in Diisseldorf was therefore working on a project for the active cooling of cast cold-setting resin bonded moulds by irrigation of the topside of the mould with water. In the context of research, the influence quantities of mould base and mould materials were examined with respect to the motion behaviour of water in mould materials and thermo-physical parameters of dry and moist mould materials were determined. Furthermore, numerous influence quantities such as amount of water, irrigation cycle, temperature range of irrigation and sand/iron ratio were investigated in technical centre experiments regarding the achievable reduction of cooling time of the casting in the mould. Based on the determined base parameters and data, a mathematical model was developed to simulate the processes in the mould during active cooling. It could be proven that the necessary cooling time of casting in the mould can be reduced by up to 30% by active cooling with up to 15% water with respect to the casting weight and depending on the sand/iron ratio. A statistically reliable relationship to the parameterisation of active cooling was established and confirmed by operational trials. Based on the experiment data it was estimated that an amount of water of up to 15% of the casting weight does not cause excessive humidification of the mould material. It was also possible to prove that microstructure and properties were not significantly impaired by active cooling. Even if the active cooling can lead to the increase of residual stress in the top section of the mould, there were no indications that these would lead to distortion or even cracks in the casting. The comparative verification of the emission situation indicated that the emissions of O2, CO, TOC and BTEXN did not increase due to active cooling. Elevated emissions occur in water steam and sulphur combinations, whereby a mildly acidic solution is formed as condensate. Measures for the application of the active cooling are derived from this in practice.