Noise Suppression Spoiler for the Air Ring of a Large Polyethylene Film-Blowing Equipment, 2004 PLACE Conference

This paper presents novel alterations of the design of large polyethylene film-blowing equipment that resulted in significant suppression of the overall sound pressure level (SPL) generated when the machine was operating close to its high output range. SPL suppression obtained was in the order of 27-29 dBA. Analysis showed that the shallow cavity created between the adjustable chimney inner geometry and the fixed chimney of the upper air ring is responsible for a discrete-tone noise around 119 dB. Two positions of the adjustable chimney were found to be responsible for this high single-tone noise. The design alterations responsible for noise suppression include modifications to the lip of the fixed chimney in the form of stream-wise groves (saw-teeth spoiler) and sealing or minimizing the two rows of holes on the side on the adjustable chimney. Noise excitation mechanism and means of alleviation were investigated by acoustic analysis supported by SPL measurements on the full size equipment.