Investigation of casting and pattern parameters in lost pattern casting proccess

viINVESTIGATION OF CASTING AND PATTERN PARAMETERS IN LOSTPATTERN CASTING PROCCESS(Ph.D. Thesis)Necati YALÇINGAZI UNIVERSITYINSTUTE OF SCIENCE AND TECHNOLOGYJuly 2006ABSTRACTThe patterns obtained by injection molding of expandable polystyrene(EPS) beads are used for the production of metal cast parts in the lostfoam process. Bead fusion in the produced part has an important effecton the bead collapse and viscous residue formation during thedegradation of the foam. It has also a significant effect on the tensileand fracture properties of the foam pattern. The bead fusion ofpolystyrene depends on several parameters such as pre-expansiontime, molding time and pressure and pattern density.This thesis comprises of a study of the effect of pre-expansion time,molding time, pressure and pattern density of expandable polystyreneused pattern material in lost foam pattern casting process on beadfusion, mechanical properties, thermal properties and microstructure.Standard tensile samples (ASTM-D638) were prepared from rawexpandable polystyrene subjected to various pre-expansion times (15,30 and 60 s), molding times (20, 30 and 40 s), molding pressures (0,8,0,9, 1,0, 1,1, 1,2 atm) and pattern densities (26,20, 30,70 and 39,07kg/m3).viiThermo gravimetric (TGA) and Differential Scanning Calorimetric (DSC)analysis have been used to define thermal degradation characteristicsof the polystyrene pattern. Tensile test of specimens were achieved dueto mechanical properties. The weight lost and microstructures ofobtained polystyrene pattern were also analyzed to define bead fusion.According to the obtained results; the volume of the bead hasincreased with increasing pre-expansion time of raw granules. It wasobserved that the porosities between beads in polystyrene patterndecreased while values of the bead fusion, the tensile strength andelongation of polystyrene pattern increased with increasing pre-expansion time, pattern density, molding time and molding pressure ofpolystyrene. Although the amount of polystyrene waste has increasedwith increasing pre-expansion time, the temperature at which 50 %weight lost of pre-expanded polystyrene has not changed. The moldingtime has not affected the amount of polystyrene waste, however thedegradation enthalpy increased with increasing pre-expansion andmolding times. Degradation of the raw, pre-expanded and moldedpolystyrene specimens have been taken place at temperatures between350 and 450 0C.Science Code : 710.3.011Key Words : Lost foam casting, full mould, polystyrene,expandable polystyrene, bead fusionPage Number : 123Advisers : Assoc. Prof. Dr. Kadir KOCATEPEProf. Dr. Süleyman TEKEL