On-line Ultrasonic Mould-out Detecting For Plastic Molding Of Polymer

For its superior comprehensive performance, the polymer material has been widely used in various fields. The superiority of the polymer material not only depends on its chemical structure, but also on the polymer products’structure and characteristics formed in molding process and eventually retained in it. Therefore, the detection of the molding process and the material system’s structure and characteristics in the process are very important and critical. The validity and accuracy of the offline detection method and the traditional online testing is low,so it is difficult to apply them to the complex environment in the actual production. Ultrasound,as a kind of machinery wave, can quickly propagates in polymer materials noninvasively and nondestructively.Also ultrasonic velocity and attenuation is closely related to the structure and properties of polymer materials.These unique characteristics make ultrasound potential in the field of on-line and non-contact detection for polymer materials’ molding characteristics. In this article, ultrasonic off-line testing experiment was taken to analyse the effect of different media and different interfaces on ultrasonic online detection. Non-contact and on-line ultrasonic techniques was used to detect Polyurethane’s molding and curing process.The relation between variation of ultrasound signal and variation of Polyurethane’s properties was also discussed.In this paper, virtual instrument technology and the G language,Labview were used to built ultrasonic online detection platform, successfully achieving the collection, preservation, analysis, and processing of the experimental waveform data. The platform includes hardware part and software part. The main function of hardware part is to transmit and receive the ultrasonic signal, complete the conversion between the analog and digital signals, etc.. The software portion includes three modules:ultrasound card driver, signal display, the signal storing, processing and analysis.Ultrasonic offline testing experimental results show that:the ultrasonic attenuation in polymers is more severe than that in small molecule material; ultrasonic attenuation in crystalline polymer materials is larger than that in non-crystalline polymer materials; ultrasound attenuation in polyurethane elastomer is larger than that in amorphous polymer materials. Ultrasonic velocity in small molecule material is the biggest, then that in polymer materials, at last that in polyurethane elastomer. The bigger the hardness of the polyurethane elastomer is, the more severe ultrasonic attenuation is. When the acoustic impedance of the medium is closer to that of Polyurethane elastomer,the ultrasonic transmission into the polyurethane elastomer at the interface is easier.The ultrasonic non-contact and on-line detection for the curing and molding of polyurethane shows that:the ultrasonic non-contact and on-line detection technique is completely feasible. During the entire molding and curing process, ultrasonic velocity first increases and then decreases slowly to a stable value, which is bigger than that at the time of casting; ultrasonic attenuation first increases, then experience a decrease and at last increases to a stable value.