Nondestructive determination of curing state of rubbers during vulcanization process

Ülger, Ceren
Aydın, Erdem
Yelbay, Hasan İlker
Kutlu, Ali Erkin
Gür, Cemil Hakan
EPDM (ethylene-propylene-diene monomer) elastomer is one of the most widely used synthetic rubbers in several industries ranging from automotive to heating, ventilation, and air conditioning. Gaskets, bumpers, auto parts, auto brake systems, electrical installation, dust covers, weather stripping and conveyor belts are typical application examples. Quality control is important to ensure the rubber compound products meet the requested mechanical properties. Satisfactory properties can be obtained only by proper compounding and by appropriate vulcanization. Vulcanization is a chemical process that converts natural rubber and other polydiene elastomers into cross-linked polymers which have much improved mechanical properties. The aim of this study is to develop a non-destructive quality control method to determine the curing state, and thus the mechanical properties of elastomers by measuring ultrasonic wave velocity. A series of samples were prepared by curing the EPDM compound at 125oC for different periods ranging from 5 to 90 minutes. The results of the mechanical tests and ultrasonic measurements showed that ultrasonic wave velocity, hardness, and the maximum force increase with increasing curing time, in contrast to the tangent delta values.