화학 균열시험법에 의한 사출성형품의 잔류응력 측정

The Chemical Experiment Crack Measurement of Residual Stresses in Injection Molded Parts

Residual stress in the plastic part is originated from thermal shrinkage and shear stress during injection molding process. Residual stress should be controlled to minimize warpage of part. Chemical Cracking test is one of the methods of measuring residual stress. Cracks developed according to the level of residual stress. In this study chemical Cracking and stress have been investigated to reveal their relationship. Bergen jig have been used to give a strain in the specimen. Specimens have been molded by hot press and annealed to remove residual stresses in specimens. PC and PBT resins were used for specimens. Specimens were fixed in the Bergen jig and immersed into the Solvent to create Cracks in the specimens. Solvents were prepared by using THF (Tetrahydrofuran) and methyl alcohol. Their ratio was 1 to 5 for PC, and used only THF for PBT. As stress increased in the specimen the frequency and density of Cracks in the specimen also increased for PC. The stresses were measured up to around 60 MPa in this experiment. No Cracks were observed in the PBT specimens since it has high chemical resistance.