Process Analysis And Defect Control On Plastic Pipe Joint With Large Bending Ratio

In the industrial and municipal pipeline systems,the demand for plastic bend pipe elbow is increasing.Union bend elbows,as the key component of the pipeline,have the most complex curving point.Union bend elbows are not only subjected to high levels of stress,but also the most wearable parts of the piping system,usually the unevenly worn.Once broken,it will endanger production and people' s life.Larger bend radius union elbows have such merits compared with the plastic union bend elbows in the practical applications such as reducing the fluid resistance of the pipeline,increasing the flow coefficient,reducing the pressure losses,improving the safety of the pipeline,etc.,so it has a broader application prospects.This paper proposes a new type of plastic bend pipe union elbows injection mold structure of larger radius elbows,carries out the mold structure design and optimization based on numerical simulation,researches the influencing factors and regularities of the injection molding process on the quality of union elbows according to the orthogonal experimental design and obtains a qualified PVC plastic bend union elbow product with a bend radius ratio of 2.67 through the injection molding experimental study.It provides a theoretical basis for improving the quality,dimensional accuracy,and cost reduction of plastic union elbows.In this paper,the author takes the PVC plastic bend pipe elbows as the research objects with a wall thickness of 3mm,the inner radius of 30 mm,and a bending radius of 80 mm and carries out the structural design and optimization of the plastic bend elbows injection molding of the large bend radius ratio.I have established a two-plate one mould for four parts,eight-side core-pulling mechanism,four 90-degree curved cores,and a mold structure that uses a rack and pinion to realize the core-spinning.On this basis,I have adopted the Moldflow numerical simulation software to analyze the filling and cooling process of the four mold structure solutions,obtained the most optimized structural parameters of the optimal pouring system as follows: the diameter of the main channel small end 8mm,taper 3°,diversion channel diameter 8mm,poured diameter of the mouth 3mm.An air vent is provided on the parting surface.The diameter of the cooling circuit is 11 mm.I have obtained the influence of mold structure parameters on the welding mark defects,and the optimized structure have eliminated the welding mark effectively.I was developed The process parameters and molding process experience based on orthogonal experimental test,taking the five key important factors: injection temperature,mold temperature,molding time,pressure holding time and holding pressure to carry out the orthogonal experimental test.The most significant factors influencing the emerging weld marks are the injection temperature and holding pressure time,followed by the mold temperature,holding pressure,and injection molding time have the least effect.The best combination of process parameters for obtaining non-melting marks is: injection temperature 190°C,mold temperature 45°C,injection time 0.8s,holding time 14 s,and holding pressure 90 MPa.An experimental study of the molding process was developed,investigated the effects of injection temperature(160°C,170,180°C,190°C)and mold temperature(30°C,35?,40°C,45°C)on the weld mark and shrinking rate of the product.With the increasing injection temperature,the weld mark at the converging stream gradually decreases,the weld mark at 160°C and 170°C is longer and the eliminate when it comes to 190°C.The contraction rate at the bend elbow connection increases with the increasing injection temperature.After injection temperature reaching 180°C,the effect of temperature on the dimensional shrinkage of the product is not obvious;with the increasing mold temperature,the weld mark decreases,and the shrinkage rate at the connection increases first and then decreases.When the injection temperature is 190°C and the mold temperature is 45°C in the process experiment,a PVC plastic bend elbow fitting with a qualified bending ratio of 2.67 is obtained.