A Study On Factors Influencing Of Molding Shrinkage Rate Of Modified Polypropylene Products For Vehicle

In this paper,the factors that affect the shrinkage of modified polypropylene(PP)materials for vehicle use were systematically studied.Firstly,the test accuracy of shrinkage was examined,and then the effects of injection molding temperature,injection pressure,injection speed,injection molding process,mold size,cooling time on PP shrinkage were scientifically investigated.Additionally,the effect of extrusion process on shrinkage and properties of PP was also studied.Finally,the influence of formula on shrinkage and properties of PP was studied.The experimental consequences show that:(1)The injection rate for unfilled polypropylene was 35-40 mpa,and it was 40 MPa for20% talc filled PP material injection pressure.For the PP/POE system with 20% talc,the parameter was 40 Mpa.(2)The shrinkage descends when the temperature and injection speed is high.The longer the parts are placed after injection,the lower the shrinkage of the material.After being placed after 24 h,the shrinkage of modified PP tends to be stable.Different screw thread combinations,different screw shear strength,different screw speed,material shrinkage and properties of the twin screw extruder vary greatly.The screw 3# presents best physical properties for its shear strength.When the 75 D machine was rotating at a speed of500-550 rpm,the material has the best physical properties.The feeding method of twin screw extruder has little effect on shrinkage and properties of the material.(3)The addition of common additives(Antioxidant,light stabilizer,lubricant,carbon black masterbatch)has little effect on the physical properties of the material,and the shrinkage of the material is about 0.01%.For the same type of PP,the shrinkage of the material decreases with the increasing of melt flow rate.The shrinkage rate of copolymerized PP was lower than that of homopolymerized PP obviously.For the unfilled system,with the increase of LLDPE,the material shrinkage rate decreases rapidly.As HDPE increases,material shrinkage decreases first,then increases,and decreases again.With the increase of TALC content,the shrinkage of the material decreased obviously.In the system of POE toughened PP-TD20,the shrinkage decreased with the increase of POE content.For the PP/POE system which was strengthened by talc,the shrinkage rate of the material decreased with the increasing talc content.The main influencing factors of shrinkage of modified PP for vehicle were systematically studied,the accuracy of shrinkage measurement was improved,and the key factors of shrinkage control were explored.The application of the results of this paper has achieved certain economic benefits.