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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• 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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QUIZ-Soalan 2004/2005

• Bincangkan salah satu teknik penghasilan komposit
  polimer yg menggunakan prapreg sebagai bahan
  pemula (teknik kering). Perbincangan harus
  meliputi gambarajah skematik teknik yg dipilih,
  bagaimana teknik ini beroperasi, kebaikan teknik
  kering ini jika dibandingkan dengan teknik basah
  dan produk yang dihasilkan daripada teknik ini.

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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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(No Transcript)
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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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Composite Manufacturing Complexity
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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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The effect 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
  retardant. 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