Weld-line strength of rubber in injection molding: Effect of injection factors and compound characteristics

• Published in: Rubber chemistry and technology Vol. 75; no. 1; pp. 83 - 92
• Main Authors: SEADAN, M, PONGBHAI, P, THAIRAJ, P, WATANA KAMTORNKUL, T
• Format: Journal Article
• Language: English
• Published: Akron, OH American Chemical Society 01.03.2002; Rubber Division
• Subjects: Applied sciences; Carbon black; Chemical engineering; Crack initiation; Crack propagation; Exact sciences and technology; Experiments; Injection molding; Machinery and processing; Moulding and vulcanizing; Polymer industry, paints, wood; Polymers; Rubber; Technology of polymers; Temperature; Tensile strength; Viscosity; Welding; SBR; Surface defect; O ring; Mechanical properties; Injection molding; Curative; Natural rubber; Tensile property; Experimental study; Property processing relationship; Property formulation relationship
• ISSN: 0035-9475; 1943-4804
• DOI: 10.5254/1.3547675

Abstract The effect of injection molding system to weld-line strength in rubber O-rings was studied using a V-shape two-stage REP injection machine. Two types of injection molds were designed and built, a standard dumbbell mold with double gates and a circular cross-section O-ring mold. Several formulations of carbon black filled NR and SBR compounds were used and vulcanization temperature was either 180 or 200 °C throughout. The results show that mold cavity pressure, compound viscosity and compound scorch time are important variables for the weld-line strength of the products. The shot volume change had no direct effect on strength, but mold cavity pressure was an important factor; unfilled shot volume gave low cavity pressure thus lowering the weld-line strength of the O-rings. The compounds having 45 or lower Mooney viscosity, ML(1 + 4)120 °C, had the same weld area strength as that of the other regions of the O-ring, but the high viscosity compounds produced low weld-line strength. Only the compounds with Mooney scorch time shorter than 10 minutes gave low weld-line strength.