Exothermic heating-up of the heads in the lost foam casting

Lost foam casting (LFM) refers to modern casting methods providing high productivity, dimensional and weight accuracy of castings from ferrous and non-ferrous alloys, cost saving of molding materials, exclusion of the use of cores and, as a consequence, coreboxes and equipment for core molding. Alongside with the laws of molding, the processes of formation of the casting itself are very important. Processes of volumetric shrinkage of the casting during crystallization of the metal flooded into the molding box are particularly important since they largely determine the quality of cast sections, metal consumption on heads and pouring gate systems, and thus the process yield and prime cost of the castings. That is why exothermic heating-up of the deadhead metal allowing to reduce metal consumption on heads, and thus to increase the process yield, is a crucial task of the foundry production. In the process of LFM specific conditions appear: mold box evacuation during casting into molds and metal crystallization, formation of reducing atmosphere in them from carbohydrates (products of thermal degradation of polystyrene foam model), endothermic effect from model gasification and the following pyrolysis of its products. All this influences the exothermic reaction behaviour. The research reveals four main factors providing effective work of exothermic mixtures, and also two types of exo-inserted pieces. The research was performed with the use of a synchronous thermal analyser, diffractometers and optic emission spectrometer. Another peculiarity of the process is also in that exo-inserted pieces are put into the head model and metal heating-up occurs not outside the head, but inside it. It is based on the exo-mixture containing aluminium and silicocalcium powder as a reducing agent and iron oxide Fe2O3 as an oxidant. Laboratory and industrial testings of the generated exo-mixture showed the effectiveness of its use in LFM, that allows to reduce metal consumption on heads by up to 25 % in casting carbon steel and ductile iron.