Use of secondary polystyrene as the material component for production of models under LFC

Nowadays the main material for manufacturing the models for lost-foam casting (LFC) is foundry polystyrene of fine fractions of the order of 0.4-0.7 mm. The disadvantage of this material is its relatively high cost, which determines the subsequent relatively high cost of casting by the LFC method. The purpose of this study is to investigate the possibility of replacing recycled polystyrene in the composition of the material for manufacturing the LFC models. The essence of the study is as follows: the secondary polystyrene 0.3-0.5 mm fraction is mixed with cast polystyrene of the T180F grade in the ratios from 10 to 50 % by weight of the mixture. After mixing the mixture is foamed in steam and dried within 15 minutes at the temperature of 30 °C. Then the expanded polystyrene is injected into the molds, after which the filled molds are placed in the autoclave and kept until the polystyrene granules are completely sintered. The finished models are cooled down to the room temperature. Then the blocks of the models are painted, which is done in one layer with a special nonstick coating by dipping into the bath. The painted model blocks are dried in a drying chamber at the temperature of 45-65 °C within 2.5-3.5 hours. It has been determined that with the increase of the share of secondary polystyrene to 50 %, the surface roughness of the model increases sharply (by 45 % compared to the standard), which excludes the possibility of its use over a specified amount. There has also been studied the microstructure and the distribution of tension fields in the castings obtained by this method. The performed analysis has shown no obvious internal defects, such as porosity, shells, non-metallic inclusions, segregation zones and dendritic structures. Thus, the conducted research has demonstrated the possibility of using recycled polystyrene in the composition of the material for the LFC models. The optimal amount is about 40, which ensures high quality castings.