| http://www.w3.org/ns/prov#value | - An improved method of carrying out an extrusion in which an extrusion material in a flowable state is passed through a die under a pressure to impart a desired shape thereto, the improvement comprising a step of resonating the die by an ultrasonic wave at a resonance frequency of 10 kHz to 100 kHz so that the ultrasonic wave has n wavelengths, wherein n is m/2 and m is a positive integer.
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