Abstract
Application of three-dimensional printing (3DP) in sand casting has become well-established in the last three decades. It is regarded as one of the revolutionary technologies at the core of the Fourth Industrial Revolution (4IR) in the additive manufacturing (AM) field. The preferred sand-moulding material in rapid sand-casting applications is silica (quartz) sand as it is the most readily available and cost-effective sand. However, as a refractory material, it has some negative health effects, causing serious illnesses such as chronic obstructive pulmonary disease, lung cancer, sili-cosis and activating latent TB should microscopic quartz fragments enter the respiratory system. It also has some technical limitations that include high thermal linear expansion, and low refrac-toriness and thermal conductivity. It is therefore not suitable for all castings. Other types of refrac-tory sand are available, they are zircon, ceramic, olivine and chromite sand. The last-mentioned is abundantly available in South Africa.
In this study a resin-coated chromite sand for rapid sand casting was manufactured and tested for efficacy. The methodology followed in this study was firstly, to characterize chromite sand in order to determine whether or not a locally sourced chromite sand could be used with the Voxeljet VX1000 3DP process. Secondly, to determine, through in-laboratory testing, the optimal addition of furfuryl alcohol (binder) and sulphonic acid (catalyst) required to produce acceptable sand flow-ability, mechanical strength, friability and ultimately loss on ignition. Thirdly, to use the chromite sand with these now-optimized parameters of binder/acid ratio to print components that meet man-ufacturing standards and specifications using the Voxeljet VX1000 3DP system.
The results of this study showed that chromite sand can be used in the additive manufacturing process using a Voxeljet VX1000 3D printer for rapid sand-casting applications. The optimal ad-dition of catalyst and binder is 0.3 wt% and 4 wt% of the chemically coated sand respectively. This produced a maximum bend strength of 566.25 N/cm2 after heat curing at 110 oC for 2 hours. This study therefore paves the way for the commercialization of chromite sand as a new AM re-fractory raw material in an innovative application that is proudly South African.