1、Rotational MoldingAn Introduction to the BasicsPersonal IntroductionR. Dru LawsEmployed with Mity-Lite Engineering throughout and after schoolingBachelors in Mechanical Engineering From BYUMasters in Polymer EngineeringFrom QUB (in Ireland)Engineering Director for Mity Fence SystemsOwner/Founder of

2、RotoScientificExample ProductExample ProductExample ProductExample ProductExample ProductExample ProductPresentation OutlineIntroductionThe MaterialsThe MachinesThe MoldsThe MethodConclusionIntroductionAlso known as rotomolding or rotocastingProcess for manufacturing large, hollow, one-piece plastic

3、 productsBest know for the manufacture of tanks and toys (Little-Tykes)Suitable for small & complex shapesIntroductionHistorical Development1850s:Patent granted for rotomolding principle1910s:Method used for chocolate products1940s:Method used for vinyl plastisols1950s:Invention of PE for the proces

4、s1960s:Rapid expansion in toy industry1970s:Gradual expansion for technical products1990s:Significant improvement in process control (at QUB)Introduction1500 Rotomolders around the worldIntroductionNorth American Market SegmentsIntroduction The ProcessIntroductionStrengthsSmall production runsLarge

5、part capabilityLow tooling costsStress-free” productsShort product development lead timesIntroductionWeaknessesSlow cycle timesLimited material choicesDifficult to automatePoor imageLow technology culturePresentation OutlineIntroductionThe MaterialsThe MachinesThe MoldsThe MethodConclusionThe Materi

6、alsThe MaterialsLow Zero Shear Viscosity is required to aid in the flow of the polymer within moldMFILower MFI resins high strength productsHigher MFI good surface finish and surface detailThe MaterialsParticle shape and size is crucial to the flow characteristics as the mold is rotatingStandard siz

7、e is a 35 mesh powder (500 micron, 0.0197 inches)The MaterialsDry-flow/Bulk-density characteristicsDry-flow is the time it takes 100 grams of resin powder to pass through a funnel of given dimensionsBulk-density is the quantity of undisturbed powder than can fit inside a beaker of specified dimensio

8、nsInversely proportional to each otherThe MaterialsThe MaterialsOther MaterialFoamsPost-processIn-processLiquid reactive polymersMicro-pelletsAdditivesCeramicsPresentation OutlineIntroductionThe MaterialsThe MachinesThe MoldsThe MethodConclusionThe MachinesRock-and-RollClamshellVerticalShuttleCarous

9、elFixedIndependentElectric & Jacket Rock-and-Roll MachinesRock-and-Roll MachinesClamshell MachinesVertical MachinesShuttle MachinesFixed Carousel MachinesIndependent Carousel MachinesElectric MachinesThe MachinesThe “ARM” and “PLATE”Presentation OutlineIntroductionThe MaterialsThe MachinesThe MoldsT

10、he MethodConclusionThe MoldsMaterialsSteelMildStainlessAluminumCastMachinedPlateThe MoldsAnatomyFrame and SpiderTwo or more sections (with draft)Parting line with alignment featuresClamping hardware and pry-pointsVent (breather) tubesTexture and other featuresRelease agentsThe Molds Frame and Spider

11、The Molds - Mold SectionsThe Molds - Parting LineThe Molds - Parting LinesThe Molds - Parting LinesThe Molds - Clamping HardwareThe Molds Pry PointsThe Molds - VentsThe Molds - VentsThe Molds Kiss-OffsThe Molds - ThreadsThe Molds - InsertsPresentation OutlineIntroductionThe MaterialsThe MachinesThe

12、MoldsThe MethodConclusionThe MethodLoadingHeatingCoolingUnloadingThe Method - LoadingA predetermined amount of resin is loaded into the moldThe mold is closed after the flanges have been cleared of resin particlesThe mold is secured shutRotate the mold to ensure no tools have been left on the machin

13、eThe Method - HeatingRotate the mold in a high-temperature environmentThe resin will always sit at the lowest point of the cavity (powder pool)It will slowly coat the mold interior until all the resin has meltedThe resin will then continue to densify as the gap between the particles disappearsRemove

14、 the mold from the oven when the powder has completely melted and densifiedThe Method - CoolingRotate the mold in a room temperature environmentThis allows the layer of resin to cool and solidifyWater can also be used, but care should be exercisedThe Method - UnloadingRemove the clamping system“Pry”

15、 open the moldLift the completed, hollow, one-piece part from the mold.Repeat the cycleThe MethodThe concernHow do you really know when it is time to do the next step?When is the resin melted?When is it cooled?In the early 90s, QUB invented an instrument that revolutionized process comprehension and

16、 controlThe RotologThe Method RotologTemperature sensors (4 type-K Thermocouples)RF TransmitterRF Receiver and Signal ConditionerComputer SoftwareReal time monitoring of the temperaturesThe Method RotologThe Method RotologThe Method Temperature ProfilesThe Method IAT ProfileThe Method IAT ProfileThe

17、 Method IAT ProfileThe Method IAT ProfileThe Method IAT ProfileThe Method IAT ProfileThe Method IAT ProfileWe can thus observe:When powder first sticks to the moldWhen the powder has been consumedWhen optimal melt sintering has occurredWhen solidification is occurringWhen the plastic separates from

18、the moldABCDEThe Method IAT ProfileThe Peak Internal Air Temperature (PIAT) is the key process control parameter and is independent of all other process variables (point C)CThe Method Other important (QUB) developmentsPressurization (Dynamic Venting)Permanent temperature feedback (K-Kontrol)RotoSim computer simulationWorldwide training seminars and consultingPPRC Rotomolding divisionPresentation OutlineIntroductionThe MaterialsThe MachinesThe MoldsThe MethodConclusionConclusionThough in a state of infancy, Rotomolding offers un