Polymer melt ultrasonic oscillations

The percussive effect of high intensity vibrations generated in an extruded polymer melt can be influenced by ultrasonic oscillations. The periodic shift in the pressure generated by the action of the screw affects the processed material and the energy transferred to the... 

A survey of extrusion heads for fabrication of profiled plastic items and a study of the rheological performance of melts of polymers in channels when ultrasound was used, was carried out [1]. The construction of a many stream extrusion head for the fabrication of continuous extrusion using ultrasonic oscillations has been produced [2]. 

To produce a high quality surface (10-12), it is necessary to avoid a discontinuous flow of the melt through the profiling channel. A high quality profile with a polished surface is produced with degradation of the polymer surface as a consequence of the effect of the magnetostrictive transducer. The ultrasonic oscillations reduce the toughness of the polymer and the resistance of the wall affect the melt flow at the channel boundary. 

Mathematical description of the process of polymer melting in the extrusion channel is complex when ultrasound is used. The description requires firstly, consideration of the mass flow of the polymer, knowledge of the flow characteristics of the melt, the temperature and pressure of extrusion, sizes of the channel and frequency of ultrasonic oscillations. Secondly, coefficient of swelling of the extrudate, effective viscosity of polymer, pressure of melt, and frequency of oscillations. 

For all the polymers investigated the increase in the flow state of the melt is observed by the use of ultrasonic oscillations. 

When power ultrasound oscillation was introduced to polymer melts, the mobility of the polymer molecules was increased such that, many of the common problems encountered in polymer processing could be resolved. For example, in the case of injection molding, ultrasonic osdllations were applied to improve molecular diffusion across the weld line so as to enhance the weld line strength. 

Ultrasonic welding is used to assemble amorphous and semicrystalline thermoplastic components that have joints that are butt, lap, tongue and groove, and shear. The typical ultrasonic normal vibration in the range of 15-70 kHz and 10-50 pm oscillates two mating components to create the weld. The amplitude of vibration generates the heat required to melt and flow the joint and is thus polymer dependent. Ultrasonic... 

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