Abstract
The 3D printing of moulds and cores from sand produces waste sand which is disposed of in landfill. Not only is there a financial and environmental cost involved in the disposal of waste sand, the land available for landfill has become increasingly scarce. In addition, the cost of using 100% new sand raises the product price. The importance of this study was to investigate the possibility of recycling furan-bonded silica sand by using dilution (the incorporation of new sand to waste sand).
Both new and used silica sands were precoated with sulphonic acid. Test samples were made from the diluted sand to which new sand was added at the ratios of 20%, 40%, 60% and 80% to the waste sand. The bend strength, friability, flowability and tensile strength were then done on these sand samples.
The results of the tests met the minimum requirements specified by the foundry industry and for the Voxeljet VX1000 printer. The optimum results were achieved with samples made from the waste sand diluted with 60% new sand. At this level of sand mixing, the mechanical properties were as follows, tensile strength of 304.10 N/cm2, bend strength of 637.50 N/cm2, friability of 2.90 and flowability of 25.32o. Compared to other reclamation processes of the 3D printing waste sand investigated in the literature, the sand mixing process applied in this was superior in terms of bend strength, a critical property for suitable sand for the Voxeljet VX1000. The mechanical properties of the waste sand were enhanced, optimising both bend and tensile strengths, while maintaining friability within the specifications. The mixed sand was then tested against mixed sand using mechanically and thermally reclaimed waste sands and found to surpass both in grain fineness and bend strength, while maintaining friability and tensile strength within the specifications. The study found that sand dilution produces good results and is the least expensive reclamation method with the lowest environmental impact because it does not use heat, or mechanical equipment.
This study is original in that it provides accurate mixing proportions of waste sand and new sand during the operation of the Voxeljet VX1000, derived from sand testing experiments and measurements of foundry properties in the laboratory. It also provides a roadmap for 3DP using sand by enhancing efficiency and environmental sustainability, while reducing the cost of sand by recycling.
Keywords: 3D printing, Voxeljet VX1000, waste sand, new sand, recycling, sand mixing