Colloquia

Samenvatting

Sand casting is an old and well established method. However, it is continuously innovated, up to this day. It is a significant part of the metal casting market. Currently, developments in sustainability are set to high priority. Sand casting moulds produce a high volume of (chemical) waste. Regulations become stricter and disposal costs are increasing. Waterglass bound sand moulds are becoming increasingly attractive due to its natural and non-toxic composition plus its very low emissions. Regeneration of mould remains into new foundry sand has become a more prominent strategy to reduce waste, a great challenge for waterglass bound moulds. The strong binder remains must be removed thoroughly, while retaining the sand. Sustainability and financial viability limit regeneration methods, like effective but costly thermal and washing treatments. Wear based regeneration remains as one of the most feasible options, which has the opposite issue of high sand losses. Installations managing these delicate balances are uncommon and difficult to implement. A new installation design was developed and tested for a waterglass type especially developed for regeneration. The installation wears mould remains down to sand by vibration, removing contaminants by fluid bed dust extraction. The main challenge was low mould strength, of which the cause could not be identified with existing quality measurements. Castings made with moulds of 30 N/cm2 flexural strength showed surprisingly good quality for a value this low. It indicates that compression strengths are in fact sufficient. The numerous parameters in the production system relevant and affecting regeneration were identified and evaluated to make the system more defined and find the cause of low strength. Remaining binder film is designated as the root cause, the exact mechanism remains to be validated. The existing quality measurement (ADV-test) is unable to detect this, but it is satisfactory for existing installation types as these were dominated by loose binder film remains in a different form. A thermal treatment of the regeneration sand alone regained an unprecedented full strength, while the ADV-test indicated no change. Regeneration sand quality fluctuated highly and was not homogeneous, depending on the sample rate and size. This issue can occur due to the constant mass flow of sand through the installation in combination with varying properties of the mould remains that go into the installation batch wise. Intensifying and prolonging the wear process inside the installation did not yield to desired improvements, having a reduced effect likely due to water content on the surface and within the binder film.