Inorganic foundry binders for sustainable sand molding

A good sand mold is an indispensable prerequisite to obtaining a good metal casting. Although sand casting is one of the oldest metal forming technique known to humans, research for alternative molding materials has never stopped, most notably to meet increasing demand for quality, better economics and to meet ever increasing environmental restrictions and regulations. The principal material of sand molds are the sand, binder and different additives depending on the application. Growing worldwide demands for sustainable manufacturing and an increased adoption of additive manufacturing across foundry industry are two underlying motivations for the search of alternative material in this dissertation. Although different organic binders are popularly used in sand molding, there is concern over the volatile organic compounds (VOCs) emitted from thermal breakdown at elevated temperature. Also, the use of 3D printed sand molds is on the rise, which usually employ greater volume of binder than traditional method. It is therefore necessary to use more environmentally friendly binders. In recent times, the interest in inorganic binders have re-emerged due to their environmental friendliness. However, the performance of these need to be properly tested before widespread introduction to foundry practices. Additionally, although silica is the most widely used sand for sand casting, alternatives are sought for various reasons like worker health safety, increased scrutiny for silica sand mining etc. This dissertation is a summary of 4 publications which explored many different sands, binders and additives. Inorganic binders were a focus of these tests while organic binders were also used in some tests to provide a fiducial reference point. The dissertation aims to facilitate the choice of mold materials with a more extensive outlook into their characteristics through a serious of sand, mold and casting quality test. Examples include sand flowability test, mold strength tests, loss on ignition tests, gas emission tests, SEM imaging of fracture surface, 3D scanning of mold and casts for mesh-to-mesh analysis, surface roughness of castings etc. Data from this dissertation will help in part the transition from the use of organic liquid binder to solid inorganic binder, enabling foundries to switch to more sustainable practices. Special emphasis is given to inorganic solid silicate binder, as it has the potential in the sustainability front as well as the simplification of 3D printing of sand molds. Effect of five different additives on solid silicate binder was found out that will aid in further development of the binder. Performance of a heat resistant 3D printed plastic pattern material was explored as well, which can be used with heat hardened inorganic molds.