Pre-preg/moulding compounds Vacuum bag Autoclave Diaphragm moulding Compression moulding. - PowerPoint PPT Presentation

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Pre-preg/moulding compounds Vacuum bag Autoclave Diaphragm moulding Compression moulding.

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use an autoclave: advanced pressure cooker. autoclave is a pressure vessel with pipework to allow a vacuum to be ... economics demands high autoclave loading ... – PowerPoint PPT presentation

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Title: Pre-preg/moulding compounds Vacuum bag Autoclave Diaphragm moulding Compression moulding.


1
Pre-preg/moulding compoundsVacuum
bagAutoclaveDiaphragm moulding Compression
moulding.
  • John Summerscales

2
Pre-preg (usually epoxy matrix)
  • Reinforcement is pre-impregnated
  • with B-staged resin
  • A-stage soluble and fusible
  • B-stage swollen but not dissolved by a
    variety of solvents
  • C-stage rigid, hard, insoluble, infusible
  • safer than liquid resins
  • mixing done by suppliers gt better quality
  • expensive relative to dry reinforcements

3
Pre-preg
  • finite shelf life note use-by date
  • if out-of-date should not be used for
    applicationswhich may result in injury, loss or
    damage.
  • time the roll of the material is out of cold
    storage will reduce its useful life (out-life)
  • normal to allow the material to warm to ambient
    temperature before use as condensation may form
    on cold material 

4
Pre-preg systems
  • cold-cure (not normally prepreg)
  • cure at ambient temperature
  • low temperature systems
  • cure at 60ºC, out-life typically 3 months
  • medium temperature systems
  • cure at 120ºC, out life typically 6 months,
  • high temperature systems
  • cure at 180ºC, out-life typically one year.

5
Pre-preg
  • key considerations include
  • drape formability to complex curvatures
  • tack stickiness
  • debulk every few layers subject the stack to
    vacuum in temporary bag or a vacuum table.

6
Moulding compounds
  • normally unsaturated polyester resin matrix
  • normally short fibre reinforcement
  • normally supplied "just in time" for the
    production of composite componentsusually by
    compression moulding
  • Compounds marketed in three major forms
  • bulk moulding compound (BMC)
  • dough moulding compound (DMC)
  • sheet moulding compound (SMC)

7
Vacuum bag (VB)
  • VB procedures as in lecture C5,but reinforcement
    now pre-impregnated

8
Compressibility of fabrics
  • Quinn and Randall
  • Vf a b vP
  • Toll and Månson
  • P kE(Vfn Vfon)
  • k power-law coefficient
  • E elastic modulus of fibres (normal to plane!)
  • Vf fibre volume fraction
  • Vfo limiting fibre volume fraction, below which
    P0
  • n power-law exponent
  • also Freundlich equation (see C8 webpage)

9
Toll and Månson exponents
  • Fibre kE Vfo n Reference
  • Wool 13 1.45 3 J Schofield, J Textile
    Institute, 1938 3
  • Wool 420 2 3 CM van Wyk, J Textile Institute,
    1946 4
  • Planar 4500 3 5 S Toll et al, ICCM-9, 1993 5
  • spun glass roving 820 8.5 YR Kim et al, Polymer
    Composites, 1991 6
  • fluffy glass roving 260 7 YR Kim et al, Polymer
    Composites, 1991 6
  • straight glass roving 700 15.5 YR Kim et al,
    Polymer Composites, 1991 6
  • graphite roving 500 14.5 YR Kim et al, Polymer
    Composites, 1991 6
  • Mat 115 3.5 R Gauvin Chibani, SPI-43, 1988
    7
  • Mat 100 4.5 JA Quinn and Randall, FRC-4, 1990
    1
  • Weave 500 11 YR Kim et al, Polymer Composites,
    1991
  • Weave 8 7 R Gauvin Chibani, SPI-43, 1988 7
  • Weave 15 9 JA Quinn and Randall, FRC-4, 1990
    1

10
Autoclave
  • only possible to apply1000 mbar pressure with a
    vacuum bag
  • to achieve greater levels of consolidation,use
    an autoclave advanced pressure cooker
  • autoclave is a pressure vessel withpipework to
    allow a vacuum to be maintained in the bagged
    work-piece.
  • temperature control is normally by
  • gas- or electric-heating
  • proportional-integral-derivative (PID) controller

11
Autoclavesfrom http//www.aeroform.co.uk/pics
12
Autoclave temp./pressure cycle
13
Autoclave
  • dwell to get correct resin viscosity
  • cure to achieve optimum properties
  • high capital cost equipment
  • long cycle times
  • economics demands high autoclave loading
  • mould tools designed to permit circulation of
    heated air
  • VB consumables may be a thermal barrier

14
Pressclave
  • pressclave alternative relatively inexpensive
    technology
  • normally a hinged frame with an elastomeric
    membrane so vacuum can be drawn under the
    membranevia perforations in the pressclave base
    and external pressure is applied outside the
    membrane.

15
Diaphragm forming (DF)
  • autoclave technique used solely for thermoplastic
    matrix composites
  • laminate laid up flat between 2 diaphragms
  • superplastic aluminium sheets, or
  • high-temperature polymeric films
  • diaphragms are clamped in a frame
  • the laminate is not clamped
  • laminate is formed over mould tool usingheat,
    vacuum and pressure in the autoclave. 

16
Diaphragm forming (DF)
  • disadvantages
  • diaphragms are normally a disposable item
  • rubber membranes can be used for limited
    production runs
  • considerable literature on(avoiding) wrinkling
    of the reinforcement

17
Compression moulding
  • two matched (usually steel) mould halvesmounted
    in a (normally hydraulic) press
  • movement limited to one axisnormal to the plane
    of the mould

18
Compression moulding
  • unlike VB/autoclave processes,no consolidation
    pressure on vertical surfaces
  • near vertical surfaces subject to wrinkling
  • may be resolved by the use of
  • rubber-block moulding, or
  • hydroforming (pressurised liquid)
  • substituting the male mould half

19
Compression moulding materials
  • Several materials suitable
  • prepreg continuous fibres in epoxy resin
  • prepreg short fibres in polyester resin
  • sheet moulding compound (SMC)
  • dough moulding compound (DMC)
  • bulk moulding compound (BMC)
  • prepreg short fibre in a thermoplastic matrix
  • continuous random orientation filamentglass mat
    thermoplastics (GMT)
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