On-line plastic crystallinity measuring method based on pressure sensor and temperature sensor

Abstract

The invention discloses an on-line plastic crystallinity measuring method based on a pressure sensor and a temperature sensor. The on-line measuring method comprises the following steps of: (1) constructing a relation curve of the pressure, specific volume and temperature of plastic, namely a PVT curve; (2) measuring pressure and temperature values of the plastic in a mould in real time by utilizing the pressure sensor and the temperature sensor; (3) calculating the current specific volume v of the plastic according to the PVT curve in combination with the pressure and temperature values measured in real time; (4) calculating the specific volume va when the plastic crystallinity is 0 and the specific volume vc when the plastic crystallinity is 1 according to the PVT curve; (5) calculating the current crystallinity Xc of the plastic. Through the on-line measurement of the crystallinity by using the temperature sensor and the pressure sensor, the invention provides a new universal method for on-line measurement on the plastic crystallinity which is low in price, easy to operate, high in precision and wide in application range, and can be used for solving the difficult problem that the plastic crystal morphology generally only can be measured off-line.

Description

technical field [0001] The invention relates to the field of plastic injection molding, in particular to an online measurement method for plastic crystallinity based on a pressure sensor and a temperature sensor. Background technique [0002] Plastic has the advantages of low density, light weight, good mechanical properties, strong chemical stability, easy processing and low price, and has become a new basic material that keeps pace with steel, cement, and wood. In the fields of electromechanical, instrumentation, chemical industry, automobile, building materials and aerospace, there has been a development trend of "replacing steel with plastic" and "replacing wood with plastic". Injection molding is the most important means of producing high-performance plastic products. During the molding process, the plastic melt experiences different thermal and force histories in the mold cavity, forming complex microscopic crystallization forms. Crystallinity is an important paramet...

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Problems solved by technology

[0003] However, the current measurement methods for the crystallinity of plastics are mainly offline measurement methods, such as differential scanning calorimetry (DSC), small-angle laser light scattering (SALS) and scanning electron microscopy (SEM). These methods can only obtain the final crystallization of plastics. degree, the formation, evolution and structuring process of the crystal form during the molding process cannot be obtained, which has great limitations.

Compared with the off-line measurement method, Zhao Peng et al. realized the on-line measurement of plastic crystallinity in the molding process by using the ultrasonic reflection coefficient on the mold and plastic interface (see Zhao Peng, Fu Jianzhong, He Yong, Chen Zichen. Polymerization for injection molding process On-line measurement method and device for the crystallinity of plastics, the patent application number is 201110214697.9), the method proposed in this invention patent needs to obtain the temperature-density curve of the complete amorphous region of the plastic through quenching, and the accuracy of the curve directly affects the crystallinity measurement results. Moreover, this method needs to use the wavelet transform method to denoise the ultrasonic signal. The quality of the denoising effect also directly affects the measurement results of the crystallinity. Many, the accuracy is difficult to guarantee

In addition, ultrasonic sensors are not widely used in the plastics industry, and the cost of use is high, which limits the application of this method in actual production

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