Quality assessment of mineral wool insulation plates : Using ultrasonic non-destructive testing

Abstract: In the manufacturing process of mineral wool insulation plates, defects arise, such as unmelted base minerals and uncured binder which gets embedded within the plates. To be able to sort out these defective plates from a manufacturing line, a reliable quality assessment is needed. The aim is to find an ultrasonic non-destructive testing method that can identify the embedded defects. This was achieved through experiments on defective insulation plates using three different ultrasonic non-destructive testing methods that were of interest. These methods were higher harmonics, pulse-echo and through transmission. Of these three, the through transmission method showed the most promising results in finding the defects that were sought after. The through transmission method utilizes two aligned transducers, one acting as a transmitter and one as a receiver. When the defective area passes through the sound beam between the transducers the intensity of the beam drops, indicating that a defect is present. The weakened intensity is due to the signal attenuation, mainly caused by the higher density of the defects compared to the base material in the surrounding insulation plate. The method is well suited for being implemented in a production line since it’s a fast method and, therefore, suited for moving objects. More measurements are needed to establish a reliable reference value to consistently distinguish the defects from the surrounding plate. The method was only evaluated in a small scale experimental environment so further experiments on a larger scale are needed to mimic and evaluate the reliability in the real case scenario of the production lines.