Abstract
Rapid sand casting, also known as binder jetting (BJ), is an additive manufacturing (AM) or three-dimensional (3D) printing technique that directly manufactures sand moulds and cores for foundry applications without the use of patterns. In BJ, a binding liquid is selectively de-posited layer by layer onto a powder bed to bond powder, according to a Computer Aided Design (CAD), to form a 3D part. Pattern making is a vital, but very complex and time-con-suming step in the traditional mould-making process, therefore eliminating this step improves the overall speed of the process and increases flexibility. To date the preferred raw material for rapid sand casting in South Africa is silica sand. This is due to its availability, cost and local supply. However, silica sand is associated with non-negligible disadvantages, including its low refractoriness and high linear thermal expansion coefficient. Chromite sand is generally iden-tified as a suitable refractory material to address the shortcomings of silica sand. The suita-bility of South African chromite sand in rapid sand casting is considered in this investigation. The binder jetting 3D printer used for this project was the Voxeljet VX1000.
Five different commercially available chromite sand samples were purchased from five differ-ent major South African chromite sand suppliers or mines. The methodology of this project was divided into three stages. The first stage involved characterization of the five different chromite sand samples according to American Foundrymen Society standards (AFS). This was to confirm the quality of the sand used and to check if it complied with the specifications required for rapid sand casting. From the results it was discovered that only two samples met AFS specifications.
Stage two was the manufacturing of specimens for tensile, friability and bend testing, using the old traditional moulding method to confirm the sand’s compatibility with the Voxeljet resin and catalyst. The sand additives’ proportions were 4% binder and 0.3% catalyst.
In stage three, the same tensile, friability and bend testing specimens were manufactured using a Voxeljet 3D printer. The results showed that all five chromite sand samples met the strength requirement of 220 N/cm2 required by Voxeljet in which only two out of the five samples met all the requirements for rapid sand casting. This led to the conclusion that South African chromite sand can be considered for rapid sand casting only if it meets all the sand quality requirements.