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LIM Liquid silicone rubber and solid silicone injection molding
world ofinnovation
LIM AND HTV A material with great potential for many applications
The term"silicone”standsforpolymerswhose chains,incontrasttohydrocarbonpolymers,donot consist of carbon atoms,butinstead of siliconandoxygen atoms(siloxane chains).However,hydrocarboncompounds,inthesimplestcasemethane,orthemethylgroup-CH3)derivedfromit,arebondedtothetwo unocupiedbonds of thesilicon.Thematerialpropertiescanbealteredbybonding themwithothertypes of hydrocarbon,such as ethane,propane,hexane,et..
The combinationofaninorganicchainwithorganicoutermoleculesgivesthesiliconesa uniquerangeof properties not achieved by any other plastic material.
The advantages
_{\mathfrak{D}} Extensive range of applicationfrom-50to +250°C (special types from -110 to +300°\mathsf C)
_{\mathfrak{D}} Highflashpoint and advantageous fire behavior
x Good electrical insulation property
_{\Rightarrow} Excellent resistance to weathering and aging
(3) High dimensional stability even under long-term load (sealing)
》High bio-compatibility, odor and taste neutrality (medical use,baby care,etc.)
Accordinglyextensive anddiversifed arethefeldsof applicationandmanufacturing options.Theyrange from sealing parts,medical components and baby care products up to crystal-clearopticallenses.
Dependingonthechainlengthand/ormolecularweight,thephysicalstatesvaryfromliquidorviscous tosolid.Accordingly,siliconepolymers are divided intoliquid siliconerubber [= short chains) and solid silicone.Byaddingcatalyzers andcross-linking agents,hydrocarbonbridges(cros-linking)betweenthe siloxane chainscanbe produced and thus permanentlyelasticpolymers(silicone rubber).Both liquid and solid silicone can be injection-molded.
PROCESS TECHNOLOGY Mixing, injection, cross-linking
The technology for liquid silicone processing
》In its original state,liquid silicone consists of liquid and transparent siliconein equal quantities.The silicone componentAcontains an additionalplatinumcatalyzer,thesilicone component B a cross-linking agent.Normally fillersforreinforcement,suchassilicic acid or quartz,are added tobothcomponents as well.
> Both material components are delivered in 20-liter or 200-liter metal drums.These are connected witha metering system,and the lids of thedrumsaresubsequentlyreplacedbythe disk pistons of thematerial loading devices coupled with hydraulic or electric feed units. When the pistons advance,they apply pressure to the contents of the drum.Both material components are fed into a static mixer through tube connections simultaneously and in equal quantities.The mixing process starts the additive cross-linking reaction.In the mixer, colorants and/orother additivescanbeblended into the transparent silicone as well.
》From the mixingblock,the activated material blend is conveyed underpressure through a tube connection to the feed zone of the injection molding machine's LSR barrel. The barrel is cooled tobetween20 and 25°C byliquid circuit zones, to slow down the cross-linking process. As soon asasetvolumeof thereactiveblend has been dosed, it is injected into a mold heated up to between 170 and 220°\mathsf C. Accelerated by the heat input,the completion of LSR cross-linking takes no more than a fewseconds.
\gg Control of the dosing and mixing system is synchronized via an interface with the injection molding machine.
LIM MACHINETECHNOLOGY Complete equipment package ex factory
The basic machines for LIM injection molding are the standard machinesfromtheMicroPower,SmartPower andEcoPowerseries. The LIMmachinesfromWITTMANNBATTENFELDare characterized byinjectionunitsspecially adapted tothematerial attributesof liquid silicone and other LSR-specific equipment options.
The LIM equipment package follows a modular concept like the standard machines.It covers a widerangeof injectionvolumes and mold sizes.
The LIM equipment options:
） Injection unit withpneumaticshut-off nozzlefor 2-component liquid silicone processing
(3) Spring-activated checkvalve
(3) Interface for 2-component material blending, dosing andfeeding system
y Cooling circuit drillings in the mold platens
y Vacuum package
\gg Cooling water monitor
_{rm{\scriptsizecent}}rm{\scriptsizemu}_{rm{\scriptsizecent}} Backwash filter
Moreover,anextensiverange ofequipmentpackage optionsis availabletoadaptthemachineindividuallytotherelevant application.
THELIMMACHINEEQUIPMENTPACKAGE Matured by many years of practice
LIM The highlights
》Theinjection unit
Thanks to their open design,allinjection units of the MicroPower,SmartPowerandEcoPowerseriesoffereasy access for cleaning and maintenance.For 2-component liquid silicone processing a liquid-cooled barrel and a liquid-cooledneedleshut-off nozzle areused.
》LIMcheckvalve
A spring-activated diskcheckvalve version,which allows active closing and prevents thelow-viscosity materialfromflowing backduring injection
》Mold-mediainterfaces
MoldsforLIMinjectionmolding require avacuum connectionforoperationinterfacesand/orconnections for electrical mold heating,and optional compressed air and power connections.
》Vacuum,watermonitor,backwashfilter
The vacuum pump ismounted at an easily accessible place onthemachineframe.Parameter andmonitoring settings are entered directlyin the machine's control system.Features such as a cooling watermonitor withbackwash filter(cold runner cooling)can be used as an option.
Differentialpressuremeasurementandfilteradapter for LSR
The WITTMANN BATTENFELD feed pressure measurement is equipped with a filter adapter and pressure sensors.Themeasurementtakesplaceasadifferential pressure measurement and is evaluated in thequality table.The measuredvalues canbe used to check the function ofthe non-return valve and the process parameters,and contaminationofthescreenbyalready cross-linked material can alsobe detected.
》Demolding equipment
Options availablefordemolding theoftenverysoft and unstableLSRpartsareeitherdemolding devices (brushing devices) orpartsremovalrobots with electric orpneumaticdrives.
ALWAYSTHERIGHTMACHINE Micro-, Smart- and EcoPower in LIM trim
TheLSRequipmentpackages areavailablefortheMicroPowerSmartPowerand EcoPowermachine series. Withoutexception,allLMinjectionmoldingmachines canbe combined withallbrandsofmaterialload ing,metering and mixing equipment.
》MicroPower
All-electric micro injection molding machine in clamping force size of 15t
》SmartPower
Servo-hydraulicall-round injectionmolding machineinclamping forcesizesrangingfrom25to400t
》EcoPower
All-electric,high-precisioninjectionmolding machineinclamping force sizesfrom55to550t
》Combimould
Bycombining atleasttwoinjectionunits,themachinesfromallthreeseriescanberealizedasmulticomponentmodels.Thesecanbelaid outforprocessing twotypesof silicone,aswellasforproducing combinations of thermoplastics with2-component silicone.
》Medical
All LIMinjectionmolding machinescanalsobedelivered inaMedicalversionforcleanroomproduc.
tion (see special brochure WITTMANN BATTENFELD “Medical").
(\* theoretical shot volume)
MicroPower LiM High precision for smallest parts
Silicone micro parts are used in large quantities in medicine (e.g. implants and sealing elements for hearing aids) or technical appliances (such as optical parts,membrane,micro plug seals and damping elements). WITTMANN BATTENFELD has developed the LIM version of the MicroPower machines for such purposes.
LIM equipment options for MicroPower machines:
_{\Rightarrow} Liquid medium temperature-controlled injection unit to process liquid silicone
》2-component material loading,mixing and metering system for small volumes in compact,modular design
》Control of the LSRmaterial loading and metering system integrated inthe machine'sB8 controlsystem andvisualized on the control system's screen
y Vacuum package
y Mediainterfaces adapted to the specificmold technology
y Easily convertiblefrom anLSRinto an elastomer unit
All equipment optionsforthe standardMicroPowermachine series are available aswell-seeourspecial"MicroPower"brochure.
LIM SmartPower AND EcoPower Safe production of high-quality medical and electronic parts
Thehighbi-compatibility,radiationresistance andexcellentelectricalpropertiesofliquidsilicone,as well asitshightransparency,openupmanyfeldsof applicationinmedicaltechnology,the productionofbabycarearticlesanditemsfortheelectricalandelectronicindustries,wherethepartsmust generally be produced under clean room conditions.WITTMANN BATTENFELD supplies the appropriate machine models.
(Please see our product brochure“Medical"for details.)
LIM COMBIMOULD Open for every configuration
WITTMANNBATTENFELD injectionmolding machinesfromall machineseries canbetransformed into multi-componentinjectionmoldingcelsbyaddingfurtheraggregatestothestandard injectionunit.Inall aggregateconfigurationseveryaggregatecanbeequippedforliquidsiliconerubberinjectionmolding and combinations of aggregatesforthermoplastics withLIMaggregates arealsopossible.Themainfeld of applicationismounting sealingcomponentsonhousings,etc.bysequentialcombinationof thermoplastics injectionmolding withsiliconeinjectionmolding.Forthispurpose,Combimouldmachines areftted with rotary or sliding tables in the clamping unit.
》V-configuration
Injection from above, also into the mold parting line
- Generous adjustment range
-Slide unit on linear guides
-Simple horizontaladjustment
-V aggregate can be moved back completely for an
-Path measurement for nozzle position incl.display
》S-configuration
Slanted position above horizontal injection unit
-Compact machine design
-Small footprint
-S and H aggregates can move independently
-Separate adjustment formoment-free nozzle contact pressure
-Excellent access to the nozzle
》L-configuration
Injectionfrom thenon-operatorside,alsointo the mold parting line
-Slide unit free on the rear of the fixed platen
-Injection unit supported on linear guides
-Large adjustment path
-Access to the nozzles and the mold from the rearvialarge operatorsafety gate
-Fixed platenfreeforstandardlinearrobot
-Path measurement for nozzle position incl. display in control system
》H-H-configuration
Two parallel horizontal aggregates
-Both aggregates can moveindependently
Good thermalseparationof the aggregates
-Compact design
-Easy barrel change
-Short material testing
SOLID SILICONE INJECTION MOLDING HTV processing
Whensolid siliconeistobeprocessed instead ofliquid silicone,theinjectionunitmustbecombined withsuitableequipmenttofeed andliquefytheHTV,whichisgenerallydelivered intheformofblocks. Thisequipmentmodulenownasafeederdevice,consistsofamaterialchamberandapressurepiston unit tomaketheinsertedmaterialflowableandtometeritintotheplasticizingbarrel.Thefeeding processissynchronizedwiththeinjectionmoldingprocess andrunsautomatically.Thepre-compression of thematerialdisplacesvirtuallyalloftheairfromitandthusfacilitatestheproductionofpartsfree of bubbles and shrink holes.
SOLID SILICONEINJECTION MOLDING Equipment in detail
The HTV equipment options:
Compression-free screw conveyorwith checkvalve adapted to the material Water-cooledplasticizingbarrelwithdiving nozzle Evacuating program combined with a vacuum pump and connection points close to the mold area Feeder in the appropriate size Additional temperature control points for the mold 》 Automation equipment forparts removal 》 Automaticmaterial loaderforthefeeder
Anextensiverangeof additionalequipmentoptionsis availablefor individual adjustment of the machines to specific applications.
UNILOG B8 Control system and process monitoring
The Unilog B8 machine control system is theWITTMANN BATTENFELD solution to simplify theoperation of complexprocesses.To thisend,theintegrated industrialPChas beenequippedwithanenlargedintuitivetouchscreenoperatingterminal.The visualization is theinterface to the new Windows10loToperating system,which offersextensive capacityfor process control.In additiontothepivotablemonitorscreen, anintegratedpanel/manualoperating terminal unit isinstalled in the machine's central console.
Forparametersetting andregulation,monitoring and documentation of the LIM injection molding process, an optional program moduleisavailableto complement the standard machinecontrol system.
Integrationofthecoldrunnerneedleshut-offnozzlecontrol directlyinthe machine control system
Setting of the needle shut-off nozzle canbe effected directly via the machine's control system.
Remote accesstothemixing and metering system Depending on the model of the 2-component mixing and metering system, it can be integrated in the machine's control system. Thismakesitpossibleforthemachine operatorto enterthe process parametersdirectlyintothe control system ofthe injectionmoldingmachine.
》Evacuationprogram
Dueto thehigh viscosity and thehighinjection pressures,molds mustbeproducedwithextremelylowtolerances.Toohigh tolerances cause theformationof burrs and webs.With narrow tolerances,the mold seals very tightlyunderhigh pressure, which is why evacuation is necessary prior to injection.Air pockets would cause burnt spots,surface defects andfilling problems.
General facts and figures about theWITTMANN BATTENFELD machine control system canbefound in the special brochure "Unilog B8 control system".
WITTMANN 4.0 Barrier-free communication
WiththeWittmann4.0communicationstandard,theWITTMANN Group has established a uniform data transfer platform between the injection molding machine and the auxiliaries fromWITTMANN. In case of an appliance change,the corresponding visualizations and settings are loaded automatically via an update function,following the principle of "Plug & Produce".
IntegrationofauxiliariesthroughWittmann4.0
\gg WITTMANNFlowconplusflowcontrollers,Gravimaxblenders andAtondryers
-Direct activation and control of the auxiliaries via the machine's control system
-Joint data storage in the production cell,the machine and,via MES,in the corporate network
》WITTMANNrobotswithR9controlsystem
-Robotcontrol via themachine's monitor -High-speed communicationbetweenthemachineand the robot to synchronize theirmovements ：Importantmovementsofthemachinecanbesetviathe robot's R9 control system
》WITTMANN Tempro plus D temperature controllers
-Temperatures canbe set and controlledvia the machine's control system
-All functions can be operated on the appliance as well as via the machine's control system.
Integrationinto anMESsystem
Theintegration of themachines and completeproduction cells into anMESsystemisthe prerequisiteforaneffcient,transparent production plant according to the Industry 4.0 standard. Depending on customers' requirements, small and medium-sized companies as well as global players are offered a compact MES solutionbased onTEMI+.With the Windows10 loT operating system, selected statusinformationfrom all connected machinescan also be displayed as SmartMonitoring on the control system screen of every machine in the plant.
APPLICATIONTECHNOLOGY Above-standard competence
》Automotive
Parts made of silicone elastomers are used in automobiles in large quantities and many varieties,primarily as cable support sleeves for all cableconduits throughbodyworkpanels, but also as folding bellows and damping elements.
》Household/lifestyle
Thanks to its olfactoryand tasteneutrality LSR is ideal for making consumer goods such as baking dishes and closures for drinking bottles.Due to their variable properties in many areas,e.g.electrically conductive or insulating,highheatresistancewithout loss of stability,silicone elastomerparts are an excellentsolutionforcombinedloadsand functions.
》Medicalcomponents
Siliconeisflexible andbio-compatible,therefore suitablefor many applicationsin medical technology and bio science.The portfolio includes respiratory masks, sealing elements for blood filters, as well as prosthetic components and even artificialhearts.Thankstotheirhigh heat resistance,silicone components can be sterilized.
》Opticalparts
Thanks to their excellent optical attributes and heatresistance,silicones are used inlens production and lighting technology.
》Sealing elements
Siliconerubberissuperiortorubberelastomersduetogoodmechanicalproperties acrossawidetemperaturerange(from -50°\mathsf C to +250°C, special types from -110°C to +300~°\mathsf{C}) .This is an important prerequisiteforlong-termpreservation of the sealing function.
》Baby care
Becauseofitsexcellentflexibilityandbiocompatibility,siliconeisidealfor allkindsof baby pacifiers,teething rings and toys.
》Combimould
A prominent application of anadditivemulticomponent injection molding system is the productionofself-cleaning showerheads, which consistof a thermoplastichousing and an elasticjet area made of LSR.Similar applications are housings with directly overmolded seals.
》LIM ^+ Airmould
Similar to injectionmolding of thermoplastics,the gas injection process can be used for thick-walled silicone parts to compensate shrinkage.It can also be used for targeted formation of hollow spaces to reduce the consumptionofexpensivematerials.
WITTMANNBATTENFELDGmbH WienerNeustadterStrasse81 2542 Kottingbrunn|Austria Tel.: +43 2252 404-0 info@wittmann-group.com www.wittmann-group.com
