| Plastic film is widely used in various fields,such as industry,agriculture,and daily life.It is an indispensable part of economic development and people's life.At present,the demand for plastic film is gradually increased at home and abroad,the requirements for film's quality become higher at the same time.The parameters that measure the film's quality are mainly tensile strength,tear strength,light transmittance,and thickness uniformity,among which thickness uniformity is one of the most important indicators.In the process of extrusion blown film,the factors affecting the thickness of the film include extrusion material,process parameters and cooling air ring,etc.,in which the cooling effect of air ring on the thickness is one of the greatest impact.Automatic air ring can significantly improve film's output and quality in blown film industry,but the majority blown film factories at home can only rely on imported equipment for production now,so the blown film automatic air ring has become a hot issue in blown film industry.The automatic air ring for extrusion blown film has been taken as the research object in this paper,the flow-field analysis and structure research are carried out.The main work is as follows:(1)Based on the study of the automatic air ring's working principle,the cooling flow-field is modeled by using AutoCAD and ICEM,then the flow field is analyzed by using Fluent.In the aspect of air ring's structure,the influence of upper-orifice and lower-orifice's deflector on flow field is analyzed.In the aspect of process parameters,the influence of air flow and blow up ratio on flow field is analyzed.The static pressure distribution curve of the bubble's surface is used to measure the bubble stability,the surface heat transfer coefficient curve is used to measure the cooling rate.The bubble's stability and cooling rate are used to judge the cooling performance of the automatic air ring.(2)By considering the bubble's stability and cooling rate,the optimum parameters of automatic air ring are determined.The structure parameters of the automatic air ring include the number of the upper air outlet m,the upper-orifice center angle ?,the upper-orifice spacing angle ?,the upper-orifice outlet angle ?,the upper-orifice's air passage width a,the lower-orifice's air passage width b,and the shield baffle opening width d.The static pressure distribution curve and heat transfer coefficient curve of the bubble surface are obtained by setting different structural parameter values to simulate,and the range of structural parameters which could guarantee the best cooling performance of air ring are selected.(3)The control system for automatic air ring is designed after the structural study of automatic air ring.The K300 Capacitance Thickness Sensor made by Kundig is used to measure the thickness of the film.A rotary scanning module is designed to achieve round-trip detection of film's thickness data.The air flow rate is adjusted by the shield baffle which is driven by stepping motors.The LabVIEW software is used to design the host computer interface.The MSP430 microcontroller is used as a control chip and the L298 N is used as a stepper motor driver chip.The program for slave computer is completed in the IAR environment.(4)A simple platform is built for the air distribution verification experiment.The air velocity is measured by air velocity transducer.It is verified that the distribution of air volume is in accordance with the law of normal distribution and the mutual interference of the orifice will become smaller as the orifice spacing increased.The display function of the host computer,serial communication function and the control function of the slave computer are checked in the shield baffle control experiment.The experiment results show that the control system is running well. |
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