| Polymer melt viscosity is an important rheological parameter that has an important impact on the quality of the product.Therefore,by measuring the viscosity of the polymer melt during the injection molding process,it is helpful to reveal the rheological behavior of the polymer melt during the injection process.At present,the viscosity of the polymer melt is usually obtained by off-line testing using a rheometer,and the viscosity of the polymer melt measured off-line cannot accurately and accurately characterize the rheological properties of the polymer melt during processing.In this paper,an on-line measurement method for viscosity of polymer melt during injection is proposed,and the reliability of on-line measured melt viscosity is verified.At the same time,combined with the theoretical relationship between melt viscosity and melt pressure drop measured online,it is verified that the apparent viscosity of the melt measured on-line can predict the cavity pressure of the disk mold,and is used for injection by using the on-line measured melt apparent viscosity.Process control provides a theoretical basis for the previous period.This not only provides a more scientific quality control method for injection molding quality control,but also facilitates the upgrading of injection molding equipment and promotes the development of the injection molding industry.In this paper,the physical model of the nozzle of the injection molding machine in the conical flow channel is simplified.The calculation method of the conical flow channel equivalent to the flow path of a certain diameter pipe is proposed.Based on the principle of capillary viscosity measurement,the polymerization is finally realized during the injection process.Online measurement of the melt viscosity of the material.By comparing the rheological curves of on-line measurement with off-line measurement with high-pressure capillary rheometer,and analyzing the error source and uncertainty of on-line measurement of melt viscosity,the reliability of on-line measurement method using injection nozzle is verified.Then,using the apparent viscosity value obtained by the online measurement method,combined with the theoretical relationship between the melt viscosity and the melt pressure drop during the filling process,the melt pressure at the near gate of the cavity is calculated and compared with the actual measured value.In contrast,the accuracy of predicting cavity pressure based on on-line measurement of melt apparent viscosity was verified.The research shows that:(1)In the process of the equivalent flow path of the conical flow channel,the rheological curve and the high pressure capillary flow calculated by the equivalent centerline melt flow velocity equivalent method are compared with the average wall shear strain rate equivalent method.The rheological curves measured by the instrument are closer,which proves the feasibility of the conical flow path to solve the viscosity by the radius equivalent method,which satisfies the need of online viscosity measurement.(2)On-line measurement of melt index of different melt index materials has different degrees of deviation from the measured values of rheometer.By analyzing the influence of melt index on the measurement process,the application of on-line viscosity measurement method on low melt index materials is verified.Sex.(3)By analyzing the measurement error of viscosity of low melt index materials at different temperatures,it is verified that the on-line viscosity measurement method can ensure the stability of measurement results under different temperature conditions.(4)The theoretical value of the near gate melt pressure derived from the on-line measured melt viscosity is similar to that measured by the disc cavity near gate pressure sensor,which verifies that the online viscosity measurement method can be applied to the injection molding process control. |
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