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8/2/2019 MATS324C6 RTM
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ExtrusionInjection Moulding
Resin Transfer Moulding
John Summerscales
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Extrusion
normally a screw in a barrelpushes a stream of material through a die
to produce a constant cross-section.
confined to use with discontinuous fibreas the action of the screw breaks fibres
not a significant technique in the production of
composite components finds use in compounding (mixing) to provide
pellets for injection moulding.
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Injection Moulding (IM)
closed cavity mould toolplaced at the output end of an extruder
discrete charges of material are delivered,
to "injection mould" components normally thermoplastic matrix, but
o RIM = reaction IM for thermosets
o RRIM = reinforced RIMfor short fibre thermoset composite
o SRIM = Structural RIM
for pre-loaded continuous fibre composites
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Injection Moulding (IM)
Image from
http://www.rutlandplastics.co.uk/
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Injection Moulding (IM)
Images from http://www.rutlandplastics.co.uk/
Close Inject
HoldOpen & Eject
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Injection Moulding (IM)
Image from
http://www.rutlandplastics.co.uk/
1. Guide Pins2. Runner3. Gate4. Sprue Bush
5. Locating Ring6. Mould Cavity7. Ejector Pins8. The Shot9. Sprue
1 2 3 4 5
6
7
8
9
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Case study:injection-moulded beamless
passenger terminalseating component
Knowledge Transfer Partnership with Zoeftig in Bude
- winner of UoP Enterprise Award for KTP of the Year 2009
- images from http://www.zoeftig.com/products.aspx#furniture
http://www.zoeftig.com/products.aspxhttp://www.zoeftig.com/products.aspx8/2/2019 MATS324C6 RTM
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Shear controlled technologies
Wolfson Centre for Materials Processingdeveloped Shear Controlled Technologiesto improve orientation in short fibre composites
o SCOREX: shear controlled orientation in extrusiono SCORIM: sco in injection moulding
Images fromhttp://www.brunel.ac.uk/about/acad/wolfson/cmp/technology
>
http://www.brunel.ac.uk/about/acad/wolfson/cmp/technologyhttp://www.brunel.ac.uk/about/acad/wolfson/cmp/technology8/2/2019 MATS324C6 RTM
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Resin Transfer Moulding
image from http://www.netcomposites.com/education.asp?sequence=59
http://www.netcomposites.com/education.asp?sequence=59http://www.netcomposites.com/education.asp?sequence=598/2/2019 MATS324C6 RTM
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Resin Transfer Moulding (RTM)for most thermoset resins and fabrics two moulded surfaces
inserts, fixing points and lightweight core materialsincorporated at moulding stage.
place dry fibre (preform) in mould cavity
close mould, then inject resin to fill porespace. cure (thermoset) resin, then remove component from mould.
net-shape, so requires only minimal trimming.
superior dimensional tolerances to hand-lay/autoclave products
reduced worker and environmental hazardso Elimination of uncontrolled emissions of VOCs.
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Magnum Venus Plastech
RTM Division schematic
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SRIM .. vs .. RTM
SRIM RTM
Resin polyurethane epoxy or polyester
InjectionPressure (kPa)
10000-40000 100-1000
Mould fill time < 1 min >> 1 min
Mould tool Steel Steel or FRP
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Resin Transfer Moulding (RTM)
most composite manufacturing processinvolve only short range flow of the resinthrough the laminate thickness
RTM involves long-range flow of resinparallel to the laminae, through the porespacebetween the reinforcement fibres
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Resin Transfer Moulding (RTM)
Darcy equation (1856): Q = K.A.P/.L
whereo Q = volumetric flow rate
o K = constant of proportionality (permeability)
oA = cross section normal to the flow direction
oP = pressure differential driving the flow
o = fluid viscosity
o L = length of mould.
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Resin Transfer Moulding (RTM)
Kozeny (1927) - Carman (1937)
Q = .A.m2.P/k..L
whereo is the porosity (1-Vf)
o m is the hydraulic radius,
o k is the Kozeny constant.
not in the
examination
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RTM: fabric compressibility Quinn and Randall
oVf= K1 + K2.P Toll and Mnson
o P = kE(Vfn - Vfo
n)
whereo P = applied pressure
o K1 and K2 are constants
ok = power-law coefficient
o E = through-plane modulus of fabric
o Vf= fibre volume fraction,
o Vfo = limiting fibre volume fraction (P = 0)
o n = power-law exponent.
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RTM: viscosity
initial resin viscosity ~200 mPa.so 1 mPa.s = 1 centipoise.
Becker: upper limit for viscosity = 800 mPa.s
non-injection point (NIP) = 1000 mPa.s
The flow front is effectively stationary ato this viscosity, and
o low pressure used in the process
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RTM: thermoplastics
molten thermoplastic polymers too viscous in-situ polymerisation possible with:
o caprolactam (e.g. DSM) to produce polyamide 6,
laurolactam (e.g. EMS) to produce polyamide 12o cyclic butylene terephthalate oligomers
(e.g. Cyclics) to produce PBT polyester
but generally a high-temperature process.
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RTM: resin delivery
mixing by static mixers in the resin feed line premixed and fed from a pressure pot
o compressed air above resin drives it to mould
two basic approaches:o constant flow rate with variable pressure
(usually via pumps), or
o constant pressure with variable flow rate(pressure pot).
introduce the initial resin at low pressure
/flow rate in order to minimise "fibre wash":
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RTM: flow strategies
uniaxial (slow)
radial
convergent (fast)
o inlet
o vent
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RTM: mould tools with only positive pressure,
the mould edges may leak resin.
reinforcement can be placed over the sealsto provide a path for air to escape
with vacuum, it is important that thetool has vacuum integrity
o no paths for air ingress through the tools itself.
some vacuum systems use peripheralchannel at higher vacuum than the cavity
to clamp the mould halves together.
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RTM: flow problems and solutions
reinforcement pack incompletely fills mouldo => "race tracking
mould deflectiono => "easy flow paths"
both may produce dry spots in the component.
these feature can be used to generate"galleries" which feed the resin to specificpositions in the mould.
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RTM: flow processes/voids
at low pressure,flow primarily in tow by capillary effect
at high pressure,
flow primarily between tows
if flow not balanced
then air can be trapped leading to voids
voids are slowly dissipatedby continued resin flow over their surfaces
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RTM: typical applications
marine propeller
hull of AdvancedComposite Armoured
Vehicle Platform (ACAVP)
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RTM: typical applications
Lotus car bodies Beneteau yachts
British Rail (now First Great Western)High Speed Train cabs
Chelton radomes
Dowty aircraft propellers
jet engine blocker doors
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RTM: process simulation CRIMSON (NIST)
LIMS (Delaware) PAM RTM (ESI-Group)
RTMFLOT (Montreal) discontinued
RTMWorx (NL)o developed from pi-7/SEPRAN (TNO Delft)
RTMworx simulation ofKok en van EngelenDen Haag (NL) bus seat
http://www.polyworx.com/apz/kveng/http://www.polyworx.com/apz/kveng/8/2/2019 MATS324C6 RTM
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RTM: process simulation
other modelling techniques include:o computational fluid dynamics (CFD)
o Pore-Cor
o Pore-Flow
mesh-less methodso smoothed particle hydrodynamics (SPH)
o finite pointset method (FPM)o natural element method (NEM)
o discrete element method (DEM)