Use of Sintered Bauxite Sand in Binder Jetting of Casting Cores

In this article, the processing of sintered bauxite sand with a high aluminum oxide content in 3D printing of casting molds and cores with furan resin is investigated regarding the performance achievable with this material system that is tailored for foundry applications. Suitable parameters for processing in a commercial binder jetting system, VX500, were identified. The influence of the binder and catalyst content as well as the coating speed on the properties of 3-point bending strength, surface roughness, and gas permeability is shown and compared with the most used quartz sand system, GS14 RP. Finally, a benchmark geometry to assess the 3D sand printing shape details and a demonstration geometry that is demanding in terms of core removal are produced. The effect of the molding material system on the surface quality of an aluminum casting is quantified. It was found that an increased catalyst content is required to process the bauxite sand in furan 3D printing. Due to its high flowability, this can be added to the sand without any detrimental effects on the coating speed. Indeed, the coating speed could be doubled compared to the silica sand system while the impact of increased catalyst amounts on the resulting emissions needs to be examined. With the bauxite sand, 3-point bending strengths of above 3 MPa and gas permeability of higher than 300 could be achieved with suitable 3D printing process parameters at mean roughness depths R<inf>z</inf> of approximately 170 µm, resulting in a roughness R<inf>z</inf> on the order of 110 µm in the casting. The specific advantages of the bauxite-based ceramic sand, such as low thermal expansion, high sphericity, and proper refractoriness, could be further exploited in 3D-printed cores for advanced ferrous alloys casting applications.