Processing of PMCs

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Processing of PMCs

• Varies from simple intensive methods to automated
  methods
• The methods of production will depend on factors
  such as cost, shape of components, number of
  components and required performance

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1. Hand methods

• Hand lay-up
• Mould is treated with a release agent-to prevent
  sticking
• Gel coat layers are placed on the mold- to give
  decorative and protective surface
• Put the reinforcement (woven rovings or chopped
  strand mat)
• The thermosetting resin is mixed with a curing
  agent, and applied with brush or roller on the
  reinforcement
• Curing at room temperature

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Concept of hand lay-up process
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• What are the Advantages and Disadvantages of Hand
  lay-up methods?

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• 2) Spray-up
• Variation of hand lay-up
• Mould is treated with a release agent-to prevent
  sticking
• Gel coat layers are placed on the mold- to give
  decorative and protective surface
• The gun sprays the mixture of chopped fiber,
  resin catalyst on to a mould
• Rolled out to remove entrapped air give a
  smooth surface
• Poor roll out can induce structural weakness by
  leaving air bubbles, dislocation of fibers and
  poor wet out

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Concept of spray-up process
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2. Moulding Methods

• Matched-die moulding (Acuan Terpadan)
• -The composite material is pressed between heated
  matched dies
• -Pressure required depends on the flow
  characteristics of the feed materials
• - The feed materials flows into the contours of
  the mould and cures at high temp.

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Matched die-moulding
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• 2 forms of feed materials
• Sheet moulding compound (SMC)
• Sheet of resin-fiber blend which contains
  additives (curing agent, release agent
  pigments). Clean to be used give good
  consistency in properties
• b) Dough moulding compound (DMC)
• Blends (in dough forms) of all the necessary
  constituents (but only short fibers are used)

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2. Moulding Methods

• b) Forming methods by employing gas pressure
  (Kaedah Tekanan Gas)
• 3 methods
• Vacuum forming/vacuum bagging (Beg vakum)
• Autoclave moulding (Acuan autoclave)
• Pressure bagging (Beg tekanan)

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Vacuum Bagging -1 die is required for this
process - Pressure is obtained atmospheric
1. Used preimpregnated reinforcement/ wet lay- up
materials 2. Flexible sheet is sealed to the
mould 3. Vacuum until air is removed
Bleeder/Breather ply is used to trap air.
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Vacuum bagging kevlar laminate
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• Autoclave Moulding

• Autoclave, tube structure and
• Pressures are supplied in it
• - Mould is placed in autoclave
• Supply gas (N2), and forced the bag into the
  mould
• Able to produce high density, product for
  critical applications such as in the aerospace
  industry

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• Pressure Bagging

• A flexible bag is placed over
• the lay-up on the mould
• - Atmospheric pressure is used for shaping
• - Compressed air forces the lay-up into the mould

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• c) Low pressure, closed mould system
• This method consists of placing the reinforcement
  in a closed mould, then insert the matrix
  materials into the mould
• Example in Resin Transfer Molding (RTM), the low
  viscosity resin is injected into the closed
  mouldusing a low pressure, and cured

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• Resin Transfer Molding (RTM)
• Is commonly used in the aerospace and automotive
  industry.
• The process consists of mixing resin with a
  hardener (or initiator) and injecting the
  combination into a mold which contains dry
  fibers.
• The mix of resin hardener is then injected at a
  low pressure of 5 psi (34.5 kPa) into a mold.
• The resulting part is cured at room temperature
  for several hours.
• Advantages
• Low pressure 5 psi (34.5 kPa)
• Fiber loadings are typically around 50-60
  (Volume)
• Preform architecture can be very complicated

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Typical RTM Process

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Process diagram of the automotive industry
Hand lay-up used For complex and
large Component in small quantity but the process
is slow Match die moulding- expensive but
component can be produced rapidly RTM- small
runs, simmple components, and longer run for more
complex components
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3. Pultrusion/Pultrusi

• Used to manufacture components with continuous
  lengths and constants cross-sectional shape (rod,
  tubes, beam, etc)
• Continuous process, easily automated (production
  rates are high, hence it is vey cost effective),
  variety of shapes are possible
• Starting materials can be in the forms of Prepreg
  or fiber resin

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Schematic Diagram of pultrusion process
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• Methods
• Continuous rovings of the reinforcement are
  impregnated with the resins (passing through a
  bath of resin)
• Then pulled through the heated die (compact
  give shape to the composites)
• Curing takes place in the heated die Oven
• Puller used to pull the whole system with certain
  speed (Pultrusion- pulling action)

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4. Filament Winding/Pelilitan Filamen

• Process to produce a hollow (usually cylindrical)
  shape
• End products pressure vessel, storage tanks, and
  aerospace parts such as helicopter blades.
• Wet winding (fiber resin) dry winding
  (prepreg)

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Schematic diagram of filament winding process
Helical
Circumferential
Polar
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• Methods
• The fibers are passed through the resin bath
• Then continuously wound onto the mandrel
• After number of layers, curing is carried out in
  an oven or room temperature.
• Mandrel is removed

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Some Commercial PMCs

• Fiber reinforced epoxy
• Glass fibers are common reinforcement for PMCs
• Glass fiber reinforces polyesters (GRPs) are
  popular in the market, glass fiber reinforced
  epoxies (GREs) are the second
• GREs- good strength stiffness, strong bonding
  of glass fibers to epoxy

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• GREs are generally employed in low volume high
  technology applications
• Coupling agents are used to improved wetting and
  bonding silanes
• Glass fibers in composites can be degraded by
  water, results in loss of strength
• Water reaches the fibers via defects or by
  diffusion in matrix, then attack the interface

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Effect of different types of Coupling Agents on
the strength of epoxy laminates as a Function of
the Time exposed to Boiling Water
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Theeffect of a silane coupling agent on
interfacial behavior in the presence of water
Hydrolysis of the covalent M-O bond
b) Shear displacement at the polymer-glass
interface
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Some Commercial PMCs

• 2) PEEK matrix composites
• -PEEK thermoplastic (TP) (advantages of TP???)
• PEEK is a relatively costly TP, with good
  mechanical properties
• Used in high performance applications, i.e.
  carbon fiber reinforced PEEK is a competitor for
  carbon reinforced epoxy, Al-Cu Al-Li in the
  aircraft industry

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Some Commercial PMCs

• 3) Rubber Matrix Composites
• Reinforced rubber used in conveyer belt, tyres,
  fire-resistant cable sheathing, etc.
• Common type of reinforcement in rubber is Carbon
  Black (increase stiffness, strength abrasion
  resistance). Carbon can absorb most of UV from
  natural light, hence decrease degredation of
  rubber

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• Another example of particulate reinforcement is
  Aluminium tri-hydroxide, which is flame
  retardent. Can be incorporated up to 70 into the
  rubber insulation of heavy duty electrical cable.
• Hybrid carbon black and continuous reinforcement
  (steel wire) are used in tyre applications