AN EXPERIMENTAL INVESTIGATION INTO MELT PUMP PERFORMANCEWalter S. SmithLuke A. MillerTimothy W. WomerXaloy Corporation, Ne...
pump to the melt valve. Figure 2 shows the melt valvecrossection assembly. This was used to vary thedownstream pressure of...
outlet pressure, the pump averaged a 95% of calculatedtheoretical output across all four pump speeds. At a 207bar outlet p...
References1. C. Rauwendaal, Polymer Extrusion, HanserPublishers, NY, 19862. Z. Tadmor and I. Klein, Engineering Principles...
Rate of PP0204060801001201404 7 10 13Pump Speed (RPM)KG/HR138 Bar 207 Bar 276 Bar Theo. RateMelt Temperature of PP10012014...
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An experimental investigation into melt pump performance

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Melt pump performance and efficiencies will vary according to the viscosity of the resin being pumped, and the discharge pressure that the melt pump will need to overcome. Resin melt temperature differences and power requirements of the pump, will vary according to the resin, and conditions that the pump will operate under.

This paper will explore the processing differences in resins on gear pump performance at different pump speeds, at three different discharge pressures. Discharge pressures on the pump will be varied keeping the suction pressure constant, thus increasing the change in pressure across the pump. Melt temperature, and pump efficiency. melt pump motor amperage, and total output, (kg/hr) will then be measured and recorded.

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Transcript of "An experimental investigation into melt pump performance"

  1. 1. AN EXPERIMENTAL INVESTIGATION INTO MELT PUMP PERFORMANCEWalter S. SmithLuke A. MillerTimothy W. WomerXaloy Corporation, New Castle, PAAbstractMelt pump performance and efficiencies will varyaccording to the viscosity of the resin being pumped, andthe discharge pressure that the melt pump will need toovercome. Resin melt temperature differences and powerrequirements of the pump, will vary according to theresin, and conditions that the pump will operate under.This paper will explore the processing differences in (3)resins on gear pump performance at (4) different pumpspeeds, at three different discharge pressures. Dischargepressures on the pump will be varied keeping the suctionpressure constant, thus increasing the change in pressureacross the pump. Melt temperature, and pump efficiency.melt pump motor amperage, and total output, (kg/hr) willthen be measured and recorded.IntroductionMelt pumps are used in extrusion to increase the stabilityof the extruder output, in order to get a more uniformproduct out of a die. Melt Pumps are also used toovercome high die pressures, as in blown film, to isolatethe screw from these high pressures for a more stablescrew output. A good example is a vented, ordevolatilizing, screw application where the head pressureof the extruder cannot be very high as measured at thescrew tip, or the screw will not be able to overcome thehigh head pressure, and the resin will bleed out of the venthole in the barrel. The extruder is typically “slaved”, orcontrolled off the drive of the melt pump; and the extruderwill follow any change in speed made to the gear pumpcontrol.The melt pump that was used in this study had a highvolumetric output compared to the extruder output,causing the data to be taken at lower melt pump speedscompared to an actual production setup in the field.EquipmentThe extruder used for this study was a 90mm (3.5”) x24:1 L/D NRM Extruder with five-barrel water-cooledtemperature zones. It is equipped with a 112 kW (150HP) DC motor. The maximum screw speed is 129 rpm.Figure 1 shows the extruder with (11) melt pressuretransducers located every 2 L/D down the axial length of thebarrel. The standard two-piece extruder configurationconsisted of a separate water-cooled feedblock with aflanged extrusion barrel bolted on the downstream end ofthe feed block. The feed block section then was cooled withwater to prevent any melt bridging due to excessive heatbuildup in the feed port area.A Xaloy EH-35 slide plate Screen Changer was used,which was loaded with a breaker plate and a 20/40/60/20screen pack for each resin trial.The Melt Pump that was used was a Xaloy MHDP –300/200, with a 18.64 kW (25 HP) AC motor, and a GPACmelt pump control system. The volumetric output of themelt pump was 186.1 cc/revolution. The approximaterelation for the volumetric output of a gear pump is asfollows:( ) LqFWPDODQ −×−= 222πWhere: Q= Volumetric OutputFW= Face WidthOD= Outside Diameter of GearPD= Pitch Diameter of GearqL= Leakage FlowThe leakage in the gear pump occurs as follows:1. Backflow over gear lands2. Backflow past sides of gear teeth3. Any material allowed to flow thru bearings4. Backflow past meshing gear teethThe gear pump system was equipped with (3) heat zones,(1) for the pump itself and (2) heat zones for the upstreamand downstream adapters.The upstream adapter connects the screen changer to thegear pump. The downstream adapter connects the gear
  2. 2. pump to the melt valve. Figure 2 shows the melt valvecrossection assembly. This was used to vary thedownstream pressure of the melt pump for each of theresin trials used in this study. Figure 3 shows the entirecomponent configuration downstream of the barrel.A low shear barrier screw with mixer was used for alltesting. This screw was specifically designed as a generalpurpose extrusion screw.A Fluke Data Acquisition System was used to acquire alldata from the process. It will be referred to as NetDAQ.Resins TestedThree virgin resins were used for this study were:• .45 MFR HDPE – Exxon Mobil HD 7845.30• .65 MFR PP – Chevron Phillips Marlex BF03A• 1.5 MFR PS – Dow Styron 685DExperimental ProcedureEach of the three resins were extruded on the same NRM90mm x 24:1 L/D extruder–screen changer–melt pump–melt valve, configuration for three one minute samples atfour different melt pump speeds, at three different meltpump discharge pressures. The suction pressure of themelt pump was set at 69 bar for all trial runs in this study.The discharge pressure of the melt pump was manuallyvaried via the melt valve; to 138 bar, 207 bar, and 276bar. There were a total of thirty-six trial runs in this study.The approximate relation for the volumetric output of agear pump is as follows:For each test, the barrel and screw were completelycleaned. The extruder and downstream components werepre-heated to processing temperature for one hour beforethe testing started. Steady thermal conditions were thenassumed to prevail throughout each of the thirty-six trialruns.Chart 1 shows the processing set temperatures for each ofthe three resins that were processed in this study. Pleasenote that a “hump” type barrel temperature profile wasused in each of the resin trial runs in conjunction with thelow shear barrier screw design. This type barreltemperature profile does enable this barrier screw design toprocess these resins more efficiently.Each test included melt pump speeds of 4, 7, 10, and 13rpm. Melt temperature was checked at each screw rpm usinga hand held IR gun, and a pre-heated melt probe at thedischarge of the melt valve. Three one-minute outputsamples were taken, and averaged at each set melt pumprpm to calculate output rate. The screw speed and meltpump motor amps; inlet and outlet pressures to the meltpump, were all monitored and recorded at one-secondintervals on the NetDAQ.The data were then extracted from the NetDAQ andcompiled with a spreadsheet program.Presentation of Data and ResultsThe results for the .45 MFR HDPE pump trials were asfollows: The melt pump output decreased, as the outletpressure from the pump was increased, by the adjustment ofthe melt valve that was downstream of the melt pump. SeeFigure 4, for the outputs in kg/hr across all four pumpspeeds at the three discharge pressures for HDPE. At a 138bar outlet pressure, the pump averaged a 97.2% ofcalculated theoretical output across all four pump speeds. Ata 207 bar outlet pressure, the melt pump averaged a 94% ofcalculated theoretical output across all four pump speeds. Ata 276 bar outlet pressure, the melt pump averaged 87% ofcalculated theoretical output across all the four pumpspeeds.The discharge HDPE melt temperature was, as expected;greater at higher pump speeds and at higher set outletpressure across all four pump speeds. See Figure 5, for theHDPE melt temperatures at the four pump speeds, and threeset outlet pressures. The average measured HDPE melttemperature for the 138 bar outlet pressure trials was 228°C. The average melt temperature for the 207 bar outletpressure trials was 232°C. The average melt temperature forthe 276 bar outlet pressure trials was 235°C.The pump motor amps were higher at all three outletpressures and pump speeds for the .45 MFR HDPE, than the.65 MFR PP, and the 1.5 MFR PS trials, as shown in Figure10. The calculated pump efficiency was also greater withthe stiffer HDPE resin trials, than the PP and PS resin trials,as shown in Figure 11.The results for the .65 MFR PP pump trials were asfollows: The melt pump output decreased, as the outletpressure from the pump was increased, by the adjustment ofthe melt valve that was downstream of the melt pump. SeeFigure 6, for the outputs in kg/hr across all four pumpspeeds at the three discharge pressures for PP. At a 138 bar
  3. 3. outlet pressure, the pump averaged a 95% of calculatedtheoretical output across all four pump speeds. At a 207bar outlet pressure, the melt pump averaged a 91% ofcalculated theoretical output across all four pump speeds.At a 276 bar outlet pressure, the melt pump averaged 78%of calculated theoretical output across all the four pumpspeeds.The discharge PP melt temperature was, as expected;greater at higher pump speeds and at higher set outletpressure across all four pump speeds. See Figure 7, for thePP melt temperatures at the four pump speeds, and threeset outlet pressures. The average measured PP melttemperature for the 138 bar outlet pressure trials was 232°C. The average melt temperature for the 207 bar outletpressure trials was 234°C. The average melt temperaturefor the 276 bar outlet pressure trials was 235°C.The pump motor amps were on average higher, at outletpressures and pump speeds for the .65 MFR PP, than the1.5 MFR PS trials; but lower than the .45 MFR HDPEresin trials, as shown in Figure 10. The calculated pumpefficiency was also greater with the stiffer PP resin thanthe PS resin trials, but lower than the HDPE trials, asshown in Figure 11.The results for the 1.5 MFR PS pump trials were asfollows: The melt pump output decreased, as the outletpressure from the pump was increased, by the adjustmentof the melt valve that was downstream of the melt pump.See Figure 8, for the outputs in kg/hr across all four pumpspeeds at the three discharge pressures for PS. At a 138bar outlet pressure, the pump averaged a 94% ofcalculated theoretical output across all four pump speeds.At a 207 bar outlet pressure, the melt pump averaged a83% of calculated theoretical output across all four pumpspeeds. At a 276 bar outlet pressure, the melt pumpaveraged 70% of calculated theoretical output across allthe four pump speeds.The discharge PS melt temperature was, as expected;greater at higher pump speeds and at higher set outletpressure across all four pump speeds. See Figure 9, for thePS melt temperatures at the four pump speeds, and threeset outlet pressures. The average measured PS melttemperature for the 138 bar outlet pressure trials was 226°C. The average melt temperature for the 207 bar outletpressure trials was 231°C. The average melt temperaturefor the 276 bar outlet pressure trials was 232°C.The pump motor amps were lower at all three outletpressures and pump speeds for the 1.5 MFR PS, than the.45 MFR HDPE trials and the .65 MFR PP resin trials, asshown in Figure 10. The calculated pump efficiency wasalso lower for the 1.5 MFR PS resin than with the stifferPP and HDPE resin trials, as shown in Figure 11.Discussion of Data and ResultsThe melt pump efficiency depended on both the stiffness ofthe resin and the pressure differential, from the inlet side ofthe pump to the outlet side of the pump. The stiffer theresin, the higher pumping efficiency of the pump wasobserved. The lower the pressure differential from the inletside of the pump to the outlet side of the pump, the higherpumping efficiency of the pump was observed. It can beconcluded that at the higher pressure differentials from inletto the outlet side of the pump, the more “backflow” of resinto the lower pressure inlet side of the pump occurs, resultingin a lower pumping efficiency of the pump. It can also beconcluded that the stiffer the resin, the less pressuresensitive the pump is to a higher pressure differential andthis also resulted higher pump efficiencies.It was also observed that melt pump efficiency was lower atthe lower pump speeds than at the higher pump speeds at thesame pressure differential running the same resin. It can beconcluded that resin pressure flow back towards the inletside of the pump, was greater part of the overall pumpingcapacity at lower pump speeds.It was also observed that the higher the pressure differentialacross the pump, the higher the measured melt temperaturesat the discharge of the melt pump were recorded. The .65MFR PP had the highest measured melt temperatures, thenthe .45 MFR HDPE, and lastly the 1.5 MFR PS.It was also observed that the higher the pump speed, thehigher the measured resin melt temperatures were obtained.Higher melt pump motor amperages were observed for thestiffer resins, and at the higher pressure differentials.Conclusions1. Melts pumps should be properly sized for theextruder and output requirement of the proposedapplication. The pump should not be required torun at excessive speeds resulting in high melttemperatures, resulting in excess downstreamcooling requirements.2. Resin rheological “stiffness”, should be taken intoaccount when designing the clearances on a meltpump system, to assured high pump efficiencies,along with adequate pump lubrication.3. Melt pumps motors should be sized with thehighest pressure differential for the application,along with the resin “stiffness”, in order to insureadequate power availability.
  4. 4. References1. C. Rauwendaal, Polymer Extrusion, HanserPublishers, NY, 19862. Z. Tadmor and I. Klein, Engineering Principlesof Plasticating Extrusion, Reinhold, NY, 1970.3. C. Chung, Extrusion of Polymers, HanserPublishers, NY, 2000.4. F. Henson, Plastics Extrusion Technology,Hanser Publishers, NY, 1997.5. S.Fox, Mechanical Design and ProcessConsiderations for Polymer Gear Pumps inExtrusion, Normag Corporation.KeywordsVolumetric output, melt pump, devolatilizing, NETDAQ Rate of HDPE0204060801001201404 7 10 13Pump Speed (RPM)KG/HR 138 Bar 207 Bar 276 Bar Theo. RateMelt Temperature of HDPE1001201401601802002202402604 7 10 13Pump Speed (RPM)Temperature(°C)138 Bar 207 Bar 276 BarFigure 1-90mm x 24:1 NRM ExtruderFigure 2- Melt ValveFigure 5- HDPE Melt TemperatureFigure 4- HDPE OutputFigure 3- Down StreamEquipmentScreen Changer Melt Pump Melt Valve
  5. 5. Rate of PP0204060801001201404 7 10 13Pump Speed (RPM)KG/HR138 Bar 207 Bar 276 Bar Theo. RateMelt Temperature of PP1001201401601802002202402604 7 10 13Pump Speed (RPM)Temperature(°C)138 Bar 207 Bar 276 BarRate of PS0204060801001201404 7 10 13Pump Speed (RPM)KG/HR138 Bar 207 Bar 276 Bar Theo. RateMelt Temperature of PS1001201401601802002202402604 7 10 13Pump Speed (RPM)Temperature(°C)138 Bar 207 Bar 276 BarAverage Pump Amps Vs.Pressure15.015.516.016.517.017.518.018.519.019.5138 207 276Pressure (Bar)AmpsHDPE PP PSPump Efficiency40%50%60%70%80%90%100%138 207 276Pressure (Bar)(%)HDPE PP PSResin BZ1 BZ2 BZ3 BZ4 BZ5 S/C AD MP AD MVHDPE 190 232 227 221 210 204 204 204 204 204PP 204 232 227 221 216 210 210 210 210 210PS 190 218 213 207 204 204 204 204 204 204Figure 11- Pump EfficiencyFigure 7- PP Melt TemperatureFigure 8- PS OutputFigure 6- PP Output Figure 9- PS Melt TemperatureFigure 10- Motor AmpsChart 1-Processing Temperatures (°C)

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