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LIM

Liquid silicone rubber and solid silicone

injection molding

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LIM AND HTV

A material with great potential for many applications

The term “silicone” stands for polymers whose chains, in contrast to hydrocarbon polymers, do not consist

of carbon atoms, but instead of silicon and oxygen atoms (siloxane chains). However, hydrocarbon compounds, in the simplest case methane, or the methyl group (-CH3) derived from it, are bonded to the two

unoccupied bonds of the silicon. The material properties can be altered by bonding them with other types

of hydrocarbon, such as ethane, propane, hexane, etc..

The combination of an inorganic chain with organic outer molecules gives the silicones a unique range of

properties not achieved by any other plastic material.

The advantages

» Extensive range of application from –50 to +250 °C (special types from –110 to +300 °C)

» High flashpoint and advantageous fire behavior

» Good electrical insulation property

» Excellent resistance to weathering and aging

» High dimensional stability even under long-term load (sealing)

» High bio-compatibility, odor and taste neutrality (medical use, baby care, etc.)

Accordingly extensive and diversified are the fields of application and manufacturing options. They range

from sealing parts, medical components and baby care products up to crystal-clear optical lenses.

Depending on the chain length and/or molecular weight, the physical states vary from liquid or viscous

to solid. Accordingly, silicone polymers are divided into liquid silicone rubber (= short chains) and solid

silicone. By adding catalyzers and cross-linking agents, hydrocarbon bridges (cross-linking) between the

siloxane chains can be produced and thus permanently elastic polymers (silicone rubber). Both liquid and

solid silicone can be injection-molded.

Photo: Wacker Silicones

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PROCESS TECHNOLOGY

Mixing, injection, cross-linking

The technology for liquid silicone processing

» In its original state, liquid silicone consists of

liquid and transparent silicone in equal

quantities. The silicone component A contains an

additional platinum catalyzer, the silicone

component B a cross-linking agent. Normally

fillers for reinforcement, such as silicic acid or

quartz, are added to both components as well.

» Both material components are delivered in

20-liter or 200-liter metal drums. These are

connected with a metering system, and the lids

of the drums are subsequently replaced by the

disk pistons of the material 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/or other additives can be blended into the

transparent silicone as well.

» From the mixing block, the activated material

blend is conveyed under pressure through a tube

connection to the feed zone of the injection

molding machine’s LSR barrel. The barrel is

cooled to between 20 and 25 °C by liquid circuit

zones, to slow down the cross-linking process. As

soon as a set volume of the reactive blend has

been dosed, it is injected into a mold heated up

to between 170 and 220 °C. Accelerated by the

heat input, the completion of LSR cross-linking

takes no more than a few seconds.

» Control of the dosing and mixing system is

synchronized via an interface with the injection

molding machine.

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The basic machines for LIM injection molding are the standard

machines from the MicroPower, SmartPower and EcoPower series.

The LIM machines from WITTMANN BATTENFELD are characterized

by injection units specially adapted to the material attributes of

liquid silicone and other LSR-specific equipment options.

The LIM equipment package follows a modular concept like the

standard machines. It covers a wide range of injection volumes and

mold sizes.

The LIM equipment options:

» Injection unit with pneumatic shut-off nozzle for

2-component liquid silicone processing

» Spring-activated check valve

» Interface for 2-component material blending,

dosing and feeding system

» Cooling circuit drillings in the mold platens

» Vacuum package

» Cooling water monitor

» Backwash filter

Moreover, an extensive range of equipment package options is

available to adapt the machine individually to the relevant

application.

LIM MACHINE TECHNOLOGY

Complete equipment package ex factory

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THE LIM MACHINE EQUIPMENT PACKAGE

Matured by many years of practice

LIM

The highlights

» The injection unit

Thanks to their open design, all injection units of the

MicroPower, SmartPower and EcoPower series offer easy

access for cleaning and maintenance. For 2-component

liquid silicone processing a liquid-cooled barrel and a

liquid-cooled needle shut-off nozzle are used.

» LIM check valve

A spring-activated disk check valve version, which

allows active closing and prevents the low-viscosity

material from flowing back during injection

» Mold-media interfaces

Molds for LIM injection molding require a vacuum connection for operation interfaces and/or connections

for electrical mold heating, and optional compressed

air and power connections.

» Vacuum, water monitor, backwash filter

The vacuum pump is mounted at an easily accessible

place on the machine frame. Parameter and monitoring settings are entered directly in the machine’s control system. Features such as a cooling water monitor

with backwash filter (cold runner cooling) can be used

as an option.

» Differential pressure measurement and filter adapter

for LSR

The WITTMANN BATTENFELD feed pressure measurement is equipped with a filter adapter and pressure

sensors. The measurement takes place as a differential

pressure measurement and is evaluated in the quality

table. The measured values can be used to check the

function of the non-return valve and the process parameters, and contamination of the screen by already

cross-linked material can also be detected.

» Demolding equipment

Options available for demolding the often very soft

and unstable LSR parts are either demolding devices

(brushing devices) or parts removal robots with electric

or pneumatic drives.

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EcoPower 110

SmartPower 120

MicroPower 15

The LSR equipment packages are available for the MicroPower, SmartPower and EcoPower machine series.

Without exception, all LIM injection molding machines can be combined with all brands of material loading, metering and mixing equipment.

» MicroPower

All-electric micro injection molding machine in clamping force size of 15 t

» SmartPower

Servo-hydraulic all-round injection molding machine in clamping force sizes ranging from 25 to 400 t

» EcoPower

All-electric, high-precision injection molding machine in clamping force sizes from 55 to 550 t

» Combimould

By combining at least two injection units, the machines from all three series can be realized as multicomponent models. These can be laid out for processing two types of silicone, as well as for producing

combinations of thermoplastics with 2-component silicone.

» Medical

All LIM injection molding machines can also be delivered in a Medical version for clean room production (see special brochure WITTMANN BATTENFELD “Medical”).

(* theoretical shot volume)

ALWAYS THE RIGHT MACHINE

Micro-, Smart- and EcoPower in LIM trim

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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:

» 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 LSR material loading and metering system integrated in the machine’s B8 control system and visualized on the

control system’s screen

» Vacuum package

» Media interfaces adapted to the specific mold technology

» Easily convertible from an LSR into an elastomer unit

All equipment options for the standard MicroPower machine series

are available as well – see our special “MicroPower” brochure.

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LIM SmartPower AND EcoPower

Safe production of high-quality medical and electronic parts

The high bio-compatibility, radiation resistance and excellent electrical properties of liquid silicone, as

well as its high transparency, open up many fields of application in medical technology, the production of baby care articles and items for the electrical and electronic industries, where the parts must

generally be produced under clean room conditions. WITTMANN BATTENFELD supplies the appropriate

machine models.

(Please see our product brochure “Medical” for details.)

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LIM COMBIMOULD

Open for every configuration

WITTMANN BATTENFELD injection molding machines from all machine series can be transformed into

multi-component injection molding cells by adding further aggregates to the standard injection unit. In all

aggregate configurations, every aggregate can be equipped for liquid silicone rubber injection molding,

and combinations of aggregates for thermoplastics with LIM aggregates are also possible. The main field of

application is mounting sealing components on housings, etc. by sequential combination of thermoplastics

injection molding with silicone injection molding. For this purpose, Combimould machines are fitted 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 horizontal adjustment

– V aggregate can be moved back completely for an

absolutely free mold space

– Path measurement for nozzle position incl. display

in control system

» L-configuration

Injection from the non-operator side, also into 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

rear via large operator safety gate

– Fixed platen free for standard linear robot

– Path measurement for nozzle position incl.

display in control system

» S-configuration

Slanted position above horizontal injection unit

– Compact machine design

– Small footprint

– S and H aggregates can move independently

– Separate adjustment for moment-free nozzle

contact pressure

– Excellent access to the nozzle

» H-H-configuration

Two parallel horizontal aggregates

– Both aggregates can move independently

– Good thermal separation of the

aggregates

– Compact design

– Easy barrel change

– Short material testing

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SOLID SILICONE INJECTION MOLDING

HTV processing

When solid silicone is to be processed instead of liquid silicone, the injection unit must be combined

with suitable equipment to feed and liquefy the HTV, which is generally delivered in the form of blocks.

This equipment module, known as a feeder device, consists of a material chamber and a pressure piston

unit to make the inserted material flowable and to meter it into the plasticizing barrel. The feeding

process is synchronized with the injection molding process and runs automatically. The pre-compression

of the material displaces virtually all of the air from it and thus facilitates the production of parts free

of bubbles and shrink holes.

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SOLID SILICONE INJECTION MOLDING

Equipment in detail

The HTV equipment options:

» Compression-free screw conveyor with check valve adapted to

the material

» Water-cooled plasticizing barrel with diving 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 for parts removal

» Automatic material loader for the feeder

An extensive range of additional equipment options is available for

individual adjustment of the machines to specific applications.

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UNILOG B8

Control system and process monitoring

The Unilog B8 machine control system is the WITTMANN BATTENFELD solution to simplify the operation of complex processes. To this end, the integrated industrial PC has

been equipped with an enlarged intuitive touch screen operating terminal. The

visualization is the interface to the new Windows® 10 IoT operating system, which

offers extensive capacity for process control. In addition to the pivotable monitor screen,

an integrated panel/manual operating terminal unit is installed in the machine’s

central console.

For parameter setting and regulation, monitoring and documentation of the LIM injection molding process, an optional program

module is available to complement the standard machine control

system.

» Integration of the cold runner needle shut-off nozzle control

directly in the machine control system

Setting of the needle shut-off nozzle can be effected directly via

the machine’s control system.

» Remote access to the mixing 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.

This makes it possible for the machine operator to enter the

process parameters directly into the control system of the

injection molding machine.

» Evacuation program

Due to the high viscosity and the high injection pressures, molds

must be produced with extremely low tolerances. Too high

tolerances cause the formation of burrs and webs. With narrow

tolerances, the mold seals very tightly under high pressure,

which is why evacuation is necessary prior to injection. Air

pockets would cause burnt spots, surface defects and filling

problems.

General facts and figures about the WITTMANN BATTENFELD

machine control system can be found in the special brochure

“Unilog B8 control system”.

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WITTMANN 4.0

Barrier-free communication

With the Wittmann 4.0 communication standard, the WITTMANN

Group has established a uniform data transfer platform between

the injection molding machine and the auxiliaries from WITTMANN.

In case of an appliance change, the corresponding visualizations

and settings are loaded automatically via an update function, following the principle of “Plug & Produce”.

Integration of auxiliaries through Wittmann 4.0

» WITTMANN Flowcon plus flow controllers, Gravimax blenders

and Aton dryers

– 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

» WITTMANN robots with R9 control system

– Robot control via the machine’s monitor

– High-speed communication between the machine and the

robot to synchronize their movements

– Important movements of the machine can be set via the

robot’s R9 control system

» WITTMANN Tempro plus D temperature controllers

– Temperatures can be set and controlled via the machine’s

control system

– All functions can be operated on the appliance as well as via

the machine’s control system.

Integration into an MES system

The integration of the machines and complete production cells

into an MES system is the prerequisite for an efficient, 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 solution based on TEMI+. With the Windows® 10 IoT operating system,

selected status information from all connected machines can also

be displayed as SmartMonitoring on the control system screen of

every machine in the plant.

Wittmann 4.0 system

With Wittmann 4.0, the

machines, robots and auxiliaries are united to become

a single technical organism, which communicates

externally via a specifically

allocated IP address. Such a

“Single point entry” with an

integrated internal firewall

substantially increases cyber

security.

“Single point entry”

via a router into the

Industry 4.0 world

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APPLICATION TECHNOLOGY

Above-standard competence

» Household/lifestyle

Thanks to its olfactory and taste neutrality,

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, high heat resistance without loss

of stability, silicone elastomer parts are an

excellent solution for combined loads and

functions.

» Optical parts

Thanks to their excellent optical attributes

and heat resistance, silicones are used in lens

production and lighting technology.

» Automotive

Parts made of silicone elastomers are used

in automobiles in large quantities and many

varieties, primarily as cable support sleeves

for all cable conduits through bodywork panels, but also as folding bellows and damping

elements.

» Medical components

Silicone is flexible and bio-compatible, therefore suitable for many applications in medical

technology and bio science. The portfolio includes respiratory masks, sealing elements for

blood filters, as well as prosthetic components

and even artificial hearts. Thanks to their high

heat resistance, silicone components can be

sterilized.

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» Baby care

Because of its excellent flexibility and biocompatibility, silicone is ideal for all kinds of

baby pacifiers, teething rings and toys.

» LIM + Airmould®

Similar to injection molding 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

consumption of expensive materials.

» Sealing elements

Silicone rubber is superior to rubber elastomers due to good mechanical properties

across a wide temperature range (from

–50 °C to +250 °C, special types from

–110 °C to +300 °C). This is an important

prerequisite for long-term preservation of the

sealing function. » Combimould

A prominent application of an additive multicomponent injection molding system is the

production of self-cleaning shower heads,

which consist of a thermoplastic housing and

an elastic jet area made of LSR. Similar applications are housings with directly overmolded

seals.

WITTMANN BATTENFELD GmbH

Wiener Neustädter Strasse 81

2542 Kottingbrunn | Austria

Tel.: +43 2252 404-0

info@wittmann-group.com

www.wittmann-group.com

LIM | Article number: BPK0000049 | (English) | 2022/08 | Subject to change. | Printed in Austria.