Hot Box binding systems

ILARDUYA provides a great variety of pre-coated sands matching customer requirements. A pre-coated sand is commonly silica sand lightly coated with phenolic resin and used in foundry cores and moulds manufacturing through shell moulding (Croning process), that consists of putting in contact the pre-coated sand with a hot metal mould so that melted resin creates a sand shell around the mould. The resulting cores have high mechanical strength and casted pieces present outstanding surface properties and top dimensional accuracy.

Pre-coated sand design is closely related to the kind of piece to be casted and the moulding process (dumping or shooting) to be used. Core shape, casting alloy and surface quality requirements in the casted product significantly determine parametres such as sand AFA index or additives incorporation like organic compounds, magnetite, chromite, etc.

Pre-coated sands have unlimited bench life and endless storage time; furthermore, their high fluidity allows filling any mould shape, thus producing low weight hollow cores with less amount of sand.

The Hot Box binding process is a temperature-dependant hardening process that consists in introducing or blowing a damp sand mixture (binder + hardener) into a heated (ca. 220ºC) corebox. Damp sand mixtures can be prepared on site and using any mixer. Hardeners remain inactive at room temperature but once in contact with the hot mould quickly break down releasing acid compounds that start polycondensation reactions. Eventually a third component - a conserver - is added to these mixtures. This third additive reduces core box sticking and increases damp mixture bench life and fluidity.

SANSET resins provide high strength and easy desanding since core pour off without previous mould washing is often possible. The resulting cores feature excellent collapse properties following demoulding and are thus particularly suitable for thin-walled aluminum castings production. A major field of application for this resin is in fittings casting.

RESITAL nitrogen-free phenolic resins present very high bending strength levels even after lengthy core storage periods. Cores made using them are employed in thick-walled grey iron, ductile iron and steel castings for the automotive industry and include transmission, oil galleys, crankcase, body, cylinder, head and gearbox casing cores.

Emissions-reducing phosphate, silicate and borate-based aqueous binding system. At present, this binder is preferred in aluminium foundries due to its excellent collapse properties after casting. Binder addition needs range from 1,5 to 3% depending on the sand quality. The mixture is shot into the hot (120-200ºC) corebox and subsequent curing is enhanced by hot (>150ºC) dry air dewatering.
No odour and gas emissions are detected during core manufacturing or mould filling with the molted metal. Furthermore, the inorganic nature of the binder avoids casting residual condensates. In particular, during core gravity die casting the yield considerably increases due to the absence of cleaning-requiring condensates in metal moulds .