Vacuum-ultrasonic treatment of self-hardening slurry in art casting

Currently, investment casting in monolithic gypsum moulds is promising for the manufacture of art castings from non-ferrous alloys. Capaco-process is most widely used. It consists in the high temperature calcination of mould to remove the model composition and increase strength because of partial sintering of the moulding composition. However, there remains a high probability of occurrence of surface defects on the castings as nodules and wart due to the high adsorption of air bubbles on the surface of cast models. To prevent this, slurry degassing by vibrovacuumation is used, which is carried out in two stages: after mixing and kneading the molding material in the intermediate container and then after pouring the mixture in the casting-box with a model. Vibrovacuum treatment is sufficient to degas the low moulds for small, simple models and is ineffective in the manufacture of complicated thin-profile art castings. The paper presents a method for manufacturing the moulds of self-hardening mixtures for investment casting. It is based on vacuum ultrasonic treatment of slurry. Vacuum-ultrasonic treatment provides the greatest effect of degassing for any size of mould. Also the acoustic streaming provides an outlet of air bubbles from undercuts and “pockets” of complicated thin-profile models that allows to carry out the process in one step after pouring the slurry in the casting-box. For effective degassing of self-hardening slurry a method was developed for calculating the parameters of vacuum-ultrasonic treatment. As a result, it becomes possible to control the process of degassing of self-hardening slurry, which provides high-quality forming for the production of art castings.