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Transcript of Auto Clave c
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Advanced Composite
Processes
Dr. S. Nagaraja RaoPrincipal, PG Section,
G.T.T.C, Mysore
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Advanced composite ProcessesCommon feature to all polymeric composite processes:Combining resin, curing agent, reinforcing fiber,
and in some cases a solvent.
Heat and pressure: Shape and "cure" the mixture into a
finished part.
Resin : Hold the fibers together, protect them & transfer
the load to the fibers in composite part.
Curing agent/ hardener: Acts as a catalyst and helpsin curing the resin to a hard plastic.
Reinforcing fiber: Imparts strength and other required
properties
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Major Processes
Processes:
Automated
Manual
Combined
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Basic process types
Formulation:
Mixing of resin, curing agent, and anyother component required
May involve adding the componentsmanually into a small mixing vessel
or
In case of larger processes componentsmay be pumped into a mixing vessel
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repregg ng Resin and curing agent mixture are impregnated into
the reinforcing fiber.
Prepregs main forms:
1. woven fabrics
2. roving
3. unidirectional tape.
Fabrics and tapes -continuous rolls in widths up to
72 inches and lengths up to several hundred feet. Fabric or tape thickness constitutes one ply in the
construction of a multi-ply lay-up.
Impregnated roving is wound onto cores orbobbins
prepreg must be stored in a refrigerator or freezeruntil use
cold storage prevents the chemical reaction fromoccurring prematurely.
Prepreg materials used in advanced compositeindustry- aircraft and aerospace.
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PREPREG MANUFACTURE
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Open Molding processes
part being manufactured is exposed to the
atmosphere.
worker typically handles the part manually
Higher potential for exposure
The resin mixture may be a liquid being
formed onto a reinforcing material
or prepreg material being formed for finalcure.
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Open Molding process
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Closed Molding processes
All or part of the manufacture takes place in a
closed vessel or chamber.
The liquid resin mixture or prepreg material may
be handled or formed manually into the
container for the curing step.
Liquid resin mixtures pumped into the container,
usually a mold of some type, for the curing step.
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Sequential or batchprocesses
Manufacture of a single part at a time, insequence.
This type of process is usually required:
Part being made is small complex in shape
curing phase is critical
finishing work must be minimized
small number of parts
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Continuous processesare typically automated to some degree
and are used to produce larger numbers
of identical parts relatively quickly.
These processes are typified by
pumping of the resin mixture into the
mold, followed by closed curing.
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Resins
The resin systems used to manufacture
advanced composites are of two basictypes: thermosetting and thermoplastic.
Thermosetting resins predominate
today, while thermoplastics have only a
minor role in advanced composites
manufacture.
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Thermosets
Thermoset resins require addition of a curing agentor hardener and impregnation onto a reinforcingmaterial, followed by a curing step to produce acured or finished part. Once cured, the partcannot be changed or reformed, except forfinishing.
Common thermosets :
Epoxies
Polyurethanes
Phenolic and amino resins Bismaleimides (BMI, polyimides)
Polyamides
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EPOXIES Epoxies: Most commonly used in today's PMC industry.
Basic epoxy compounds: reaction product of epichlorohydrin and
bisphenol-A.
Epoxy compounds are also referred to as glycidyl compounds.
Types of epoxy compounds : glycidyl ethers (or diglycidyl ethers),
glycidyl esters, and glycidyl amines.
Several of these compounds are reactive diluents and are sometimesadded to the basic resin to modify performance characteristics.
The epoxy molecule can also be expanded or cross-linked with other
molecules to form a wide variety of resin products, each with distinctperformance characteristics.
These resins range from low-viscosity liquids to high-molecularweight solids. Typically they are high-viscosity liquids.
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Curing agent or hardener:
They control the reaction rate
Determine the performance characteristics of the finishedpart.
These compounds act as catalysts for the reaction
Curing agents :
Aromatic amines.
4,4'-methylene-dianiline (MDA)
4,4'-sulfonyldianiline (DDS).
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Other types of curing
agents&Resins
Aliphatic and cycloaliphatic amines
polyaminoamides
amides
anhydrides.
Note:The choice of curing agent depends on the cure andperformance characteristics desired for the finished part.
Polyurethanes are another group of resins used in advancedcomposite processes.
These compounds are formed by reacting the polyol componentwith an isocyanate compound, typically toluene diisocyanate(TDI);
methylene diisocyanate (MDI) and hexamethylene diisocyanate(HDI) are also widely used.
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RESINS AND CURINGS(CONTD)
Phenolic and amino resins are anothergroup of PMC resins. They are usedextensively in aircraft interiors becaosue
of their exceptional low smoke and heatrelease properties in the event of a fire.
The bismaleimides and polyamides arerelative newcomers to the advancedcomposite industry and are used forhigh temperature applications.
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AUTOCLAVE CURING &
BONDING
Prepreg method adopts both vacuum
bagging & autoclave for consolidation &
curing.
Autoclave
Pressure Temperature (Heat)
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AUTOCLAVE CURING
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AUTOCLAVE CURING &
BONDING
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Advantages
Superior Products
Complex parts can be producedProblems:
Heat loss
ControlCostly
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Filament Winding
Winding Methods
Wet Dry Post Impregnation
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Filament Winding
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Winding Types
Hoop
CircumferentialRadial
Helical
AxialPolar
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Process of Winding
A continuous wire or tape or mat of
fibrous material is dipped in a resin bathand wound on a mandrel in the desired
orientation and desired thickness.
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Resins used
Epoxy --- most common
Polyester --- most commonPhenolic
Silicon
Thermoplastics
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Examples of combination
Graphite for longitudinal stiffness, Fiberglass
to resist hoop direction.
Carbon for strength, Aramid for impact
strength.
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Desirable Factors
Proper control of resin viscosity,
consistency TemperatureTension control
Proper shape of mandrels
Rotational speed of mandrelsPost curing
Ch t i ti f fil t
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Characteristics of filament
wound parts
Voids minimum
FlexibilityJoints between the composite and metal
can be made easily
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Advantages
Varying size
High strength in desired directions
Less material wastage
Forming shapes easy Panels and fittings can be included during winding
Parts with high pressure ratings can be made
Continuous process and thus faster production
Overall production cost is lower
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PULTRUSION
Continuous reinforcement fibers areimpregnated with resin shaped by drawingthrough a die.
Types of die:
Fixed High pressure
Floating Low & Medium pressures
Multiple
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PULTRUSION
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PULTRUSION
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Applications
Building panels
Electrical insulators
Supports & panels for truck trailers
Door support for automobiles Ladder rails
Pressure tanks (Trunk portion)
Aircraft flooring
Rods, Stringers, Stiffness for aircraft and automobileleaf springs (Shock absorbers)
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Advantages (contd.)
Storage tanks
Pipes
Chimney liners Lightening arresters
Springs
Shafts Wind turbine blades