Assessment of sulphur content in nitrile rubber through ultrasonic measurement

Ultrasonic testing is a popular non-destructive method for characterising engineering materials and detecting their properties. Diverse quantities of sulphur are incorporated into an uncured rubber compound, which is subsequently cured under specific pressure and heat conditions to attain the desired properties in the final product. The present work represents a quantitative estimation of sulphur content for cured NBR (Nitrile Butadiene Rubber) samples by an ultrasonic approach. The experiments have been conducted using cured NBR samples with varying sulphur content, ranging from 0% to 1.34%. Ultrasonic pulse behaviour at different temperatures (30°C to 160°C) has been observed using an ultrasonic setup which has been developed in-house. A-scan data is obtained at a sampling rate of 80 MHz using an 18 mm diameter broadband transducer with a 1 MHz central frequency. The ultrasonic longitudinal velocity (ULV) of rubber is determined from A-scan data using time-of-flight, and sulphur content has a significant impact on the ULV. At a temperature of 160°C, the ultrasonic longitudinal velocity (ULV) is measured at 1262 m/s for a sample with 0.62% sulphur content, and at 1321 m/s for a sample with 1.34% sulphur content.