Experimental study on the influence of pulsatile injection pressure on filling pressure

This article was downloaded by: [Seoul National University]On: 10 April 2015, At: 05:32Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UKPolymer-Plastics Technology and EngineeringPublication details, including instructions for authors and subscription information:/loi/lpte20Experimental Study on the Influence of PulsatileInjection Pressure on Filling Pressure and Filling TimeJin-ping Qu a , Weihua Zhou a , Bin Liu a & Wenzhe Pan aa National Engineering Research Center of Novel Equipment for Polymer Processing, KeyLaboratory of Polymer Processing Engineering, Ministry of Education , South China Universityof T echnology , Guangzhou, P. R. ChinaPublished online: 30 Jun 2007.PLEASE SCROLL DOWN FOR ARTICLEExperimental Study on the Influence of Pulsatile Injection Pressure on Filling Pressure and Filling TimeJin-ping Qu,Weihua Zhou,Bin Liu,and Wenzhe PanNational Engineering Research Center of Novel Equipment for Polymer Processing,Key Laboratory of Polymer Processing Engineering,Ministry of Education,South China University of Technology,Guangzhou,P.R.ChinaThe working principle of a pulsatile injection molding facility is presented.Linear low density polyethylene (LLDPE)disc-samples were made by means of injection molding with pulsatile injection pressure of different pulsatile parameters.Meanwhile,by using the pressure transducers,mold cavity filling pressure changed with real-time was acquired.The results show that,the vibration fre-quency of mold cavity filling pressure is equal to the vibration fre-quency of the ram;the amplitude of mold cavity filling pressure increases with the increase of the vibration amplitude of the ram;the average of mold cavity filling pressure increases and the filling time will be shortened with the increase of the vibration amplitude and/or frequency of the ram.Keywords Filling pressure;Filling tim;Pulsatile injectionpressure;Vibration force field1.INTRODUCTIONThe application of vibration technology in molding of polymer is one of the hot research subjects.Vibration in packing stage via hydraulic device was introduced in early of 1980s [1].Experimental results showed that vibration packing could enhance the quality of injection molded parts [2–4].Vibration force field generated by electromagnetic field in the process of plasticization,injection and packing,implemented dynamical plasticization metering,injection and packing was introduced [5,6].Experimental results showed that the filling pressure will be reduced when the vibration is introduced,the flow of polymer melts became more uniform and the distribution of different components is also more uniform in the parts during the dynamic injec-tion molding [7].Compared with traditional injection molding,pulsatile injection molding has some advantages such as lower injec-tion pressure,lower cavity pressure and shorter cycle of molding,and so on [8,9].The goal of the study is to explore the relationships between the filling pressure =the filling time and vibration parameters in pulsatile injection molding.2.EXPERIMENTAL2.1.EquipmentsTo study the effects of pulsatile injection molding exper-imentally,a facility was developed which applies vibration energy to the polymer melt during molding by vibrating the ram at a certain vibration frequency and =or amplitude.The schematic illustration of pulsatile injection molding facility with a clamp force of 250kN is shown in Fig.1.An experimental mold was made by Guangzhou HUAXINKE Ltd.Co.and was mounted on the pulsatile injection molding facility.The geometry of mold cavity is disc and its diameter is 150mm with a depth of 2mm.Three pressure transducers are set in the mold and located at a distance from the gate along cavity’s radial direction (shown in Fig.2).The data acquisition system is connected with the pressure transducers and monitors the mold cavity pressure.The ram moves downwards at a constant velocity V 0relative to the housing during filling stage in traditional injection molding.In pulsatile injection molding,the vibration device exerts a parallel superimposed vibrating displacement Asin x t on the ram.A and f (f ¼x =2p ,not 2p =x )are the vibration amplitude and vibration frequency respectively.The vibration frequency and amplitude can be adjusted by the control panel.Accordingly,the absolute velocity of the ram during filling stage is:V ¼V 0þA x cos x tð1ÞBy this way,vibration pressure gradient is generated within the flow domains during filling stage and packingAddress correspondence to Jin-ping Qu,National Engineering Research Center of Novel Equipment for Polymer Processing,Key Laboratory of Polymer Processing Engineering,Ministry of Education,South China University of Technology,Guangzhou 510641,P.R.China.E-mail:jpqu@Polymer-Plastics Technology and Engineering ,46:709–712,2007Copyright #Taylor &Francis Group,LLC ISSN:0360-2559print/1525-6111online DOI:10.1080/15583720701271609709D o w n l o a d e d b y [S e o u l N a t i o n a l U n i v e r s i t y ] a t 05:33 10 A p r i l 2015stage.The vibration of the ram drives the vibration of the injection pressure and induces the vibration of polymer melts.Thus,pulsatile injection molding is implemented.2.2.Materials and Technical ParametersThe sample material used in this work is LLDPE (218W 050),made in SAUDI.In experiments,melt temperature was 190 C,mold cool-ant temperature 40 pared with traditional injection,the other two parameters are vibration amplitude and vibration frequency of the ram in pulsatile injection.In our studies,the average volumetric flow rate was constant.The experiments were performed at a range of vibration parameters.3.RESULTS AND DISCUSSION3.1.Effects of Ram Vibration on Mold Cavity Pressure Figure 3depicts the relationships between mold cavity pressure and time of traditional injection molding (novibration applied,i.e.,f ¼0Hz or A ¼0mm).Fig.4depicts the relationships between mold cavity pressure and time of pulsatile injection molding (when f ¼3Hz,A ¼0.1mm).Comparing Figs.3and 4,we can find that the changing trend of mold cavity pressure against time is the same between conventional injection and pulsatile injection.In traditional injection,the fluctuations of mold cavity pressure are tiny and irregular.The variations may be resulted from the pressure variation of hydraulic pump in the injection molding machine during injection molding,or from environment influence on the data acquisition system.In pulsatile injection,except for above men-tioned,mold cavity pressure also have regularfluctuationsFIG.1.Schematic illustration of pulsatile injection moldingfacility.FIG.2.Schematic of location of the mold cavity pressuretransducers.FIG.3.The relationship between cavity pressure and time of traditional injectionmolding.FIG.4.The relationship between cavity pressure and time of pulsatile injection molding.710J.-P.QU ET AL.D o w n l o a d e d b y [S e o u l N a t i o n a l U n i v e r s i t y ] a t 05:33 10 A p r i l 2015during filling stage(at r1¼10mm and r2¼30mm).The frequencies of the latter fluctuations are the same with the vibration frequencies of the ram.Thus it can be seen that the latter fluctuations resulted from the vibration of the ram.3.2.Effects of Vibration Frequency and Amplitudeon Filling PressureThe mold cavity pressure measured by transducer p1was taken as filling pressure in experiments.Although this has difference with actual filling pressure,but it do not obstruct the qualitative studies of the effects of vibration frequency and amplitude on filling pressure.Figure5shows the relationship between filling pressure and time when f varied from0to6Hz at A¼0.10mm dur-ing filling stage.As can be seen from Fig.5,when f¼0Hz, the fluctuations of filling pressure are tiny and irregular; when f¼3Hz,the fluctuation frequency of filling pressureis3Hz;when f¼6Hz,the fluctuation frequency of filling pressure is6Hz.Thus,we can conclude that the fluctuation frequency of mold cavity pressure is the same with the vibration frequency of the ram.As seen in Fig.5,the aver-age filling pressure at f¼6Hz is larger than that at f¼3Hz;the average filling pressure at f¼3Hz is larger than that at f¼0Hz.Thus it can be seen that the average filling pressure increases with the increase of vibration frequency within our research scope.Figure6shows that the relationship between filling pressure and time when A varied from0mm to0.2mm at f¼6Hz during filling stage.As can be seen from Fig.6, the fluctuation of filling pressure at A¼0.20mm is obvi-ously larger than that at A¼0.10mm.So,the fluctuation of filling pressure increases with the increase of vibration amplitude within our research scope.Furthermore,the average filling pressure at A¼0.20mm was larger than that at A¼0.10mm;the average filling pressure at A¼0.10mm was larger than that at A¼0mm.Appar-ently,the average filling pressure increases with the increase of vibration amplitude within our research scope.3.3.Effects of Vibration Frequency and Amplitudeon Filling TimeThe time when mold cavity pressure began to rise at r1¼10mm was taken as the start point of filling time, and the time when mold cavity pressure rapidly rise at r2¼58mm was taken as the end point of filling time in the experiments(shown in Fig.7).However,the actual fill-ing time was the time spent by the flow front region of LLDPE melts moved from the gate to the locationat FIG.5.The relationship between filling pressure and time(A¼0.10mm).FIG.6.The relationship between filling pressure and time(f¼6Hz).FIG.7.Definition of filling time.INFLUENCE OF PULSATILE INJECTION PRESSURE ON FILLING TIME711 Downloadedby[SeoulNationalUniversity]at5:331April215r 3¼58mm.But it do not obstruct the qualitative studies of the effects of f and A on the filling time.Figure 8shows the relationship between filling time and vibration frequency.As can be seen from Fig.8,when f is smaller,filling time decreases sharply with the increase of f ;when f is bigger,filling time decreases slowly with the increase of f .Figure 9shows the relationship between filling time and vibration amplitude.Keeping the vibration frequency constant,filling time decreases quickly with the increase of the vibration amplitude when the vibration amplitudeis smaller and decreases slowly with the vibration ampli-tude when the vibration amplitude is bigger.From above analysis,the filling pressure and the filling time are relative to the vibration frequency and amplitude of the ram within our research scope.These may be caused by reduction of melt viscosity when vibration energy is introduced during the injection molding process.The flow-ability of the polymer melt enhances.So,the filling press-ure decreases and the filling time become shorter.4.CONCLUSIONBy analyzing the experimental results above mentioned,within a range of vibration frequencies and vibration amplitudes,the following conclusions can be drawn:(1)The fluctuation frequency of filling pressure is the same with the vibration frequency of the ram.The fluctuation amplitude of filling pressure increases with the increase of the vibration amplitude.The average filling pressure increases with the increase of the vibration frequency =amplitude.(2)Filling time decreases with the increase of the vibration frequency =amplitude.ACKNOWLEDGEMENTThe authors wish to acknowledge the National Nature Science Foundation of China (Grant 10472034)for the financial support.REFERENCES1.Allan,P.S.;Bevis,M.J.U.S.Patent 4,925,161,1985.2.Wong,C.M.;Chen,C.H.;Isayev,A.I.Flow of thermoplastics in an annular die under parallel oscillations.Polym.Eng.Sci.1990,30(1),1574–1584.3.Ibar,J.P.Melt Viscosity of Plastics Reduction by Vibration During Filling in Injection Molding,ANTEC’97,Toronto,Society of Plastics Engineers,1997.4.Ibar,J.P.Control of polymer properties by melt vibration technology:A review.Polym.Eng.Sci.1998,38(1),1–20.5.Qu,J-P.;Wu,H-W.New technology of dynamic vibration field enhancing polymer injection molding.Plastics 2000,29(6),9–12.6.Qu,J-P.Study of pulsating extrusion characteristic of polymer melt through round-sectioned die.Polymer-plastics Technology and Engineering 2002,41(1),115–132.7.Wu,H.-W.;Qu,J-P.Study on the electromagnetic dynamic plastics injection molding.Polymer Materials Science and Engineering 2000,16(5),165–169.8.Qu, Patent 5,217,302,1993.9.Qu, Patent 5,951,928,1999.FIG.8.The relationship between filling time and vibrationfrequency.FIG.9.The relationship between filling time and vibration amplitude.712J.-P.QU ET AL.D o w n l o a d e d b y [S e o u l N a t i o n a l U n i v e r s i t y ] a t 05:33 10 A p r i l 2015。