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Hollow castings for commercial and automotive industries - an alternate cost-effective solution

Sasaki, N.

This paper describes a cost effective and patented process known as Convert process to produce hollow castings. This process uses a sand core formed by hot phenolic or cold box resins. It is dipped in patented 'convert' binder (hybrid binder based on silicates and alkali components) and provides good strength at room temperature. After air drying this core can be either used in wax injection tool or, if needed, inserted in the wax pattern. The resulting patterns can be processed in normal shell making and dewaxing. During the preheating operation the organic binder is replaced by an inorganic binder from 'convert' providing sufficient strength during casting: the cores are rapidly heated to 1000 deg C, the organic binder in the core generally burns at 600 deg C, while the convert binder gradually penetrates into the gaps between solid particles by a capillary action thus replacing the organic binder. The convert binder becomes crystallized while producing a hybrid binder from SiO2 and Na2O at temperature up to 1100 deg C. During the post casting cooling and knockout, the convert core disintegrates and is dislodged out of the casting. Standard casting cleaning processes as sand/shot blasting removes the balance of core residue. Lower cost of tooling, core and subsequent removal after casting are main features of this innovative method for commercial and automotive investment castings.