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8/13/2019 Intro to GRP and Hand Laid-Up GRP Moulding-PNS JAUHAR
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15-Feb-14 1Introduction to GRP and Hand Laid-upGRP Moulding
INTRODUCTION TO GRP ANDHAND LAID-UP GRP MOULDING
BY LT CDR M HASAN ADIL PN
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AIM
To apprise the audience about various GRP materials,
methods for the production of hand laid-up GRP
moulding, common defects and quality control of GRP
layup
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SCHEME OF LESSON
Introduction to GRP
Materials
Moulds and Mould Preparation
Preparation of Material for Moulding
The Moulding Operation
Curing of Mouldings
Finishing Operations
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Day 1 & 2
Day 3
Day 4
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SCHEME OF LESSON
Sandwich Structures
Handling/Transportation of finished
Mouldings
Health and Safety
Common Defects and Quality Control
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Day 5
Day 6
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REFERENCES
Defence Standard 02-701 (NES 701) Part 1
Defence Standard 02-701 (NES 701) Part 2
Fiberglass Boat Design and Construction
by Robert J Scott
Open Sources (Internet web sites)
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INTRODUCTION TO GRP
Glass Reinforced Plastic (GRP) or Fiberglass ReinforcedPlastic(FRP) is a two component structural matrix consistingof:
Fiberglass or glass material
Thermosetting Liquid resin
GRP is a truly synergetic material in which combination of twomaterials has superior characteristics than either materialindividually
Resin with relatively poor physical properties and would notperform well as structural material
The glass portion though composed of strong glass filaments,is utilized as fabric and has no structural capabilities except intension
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INTRODUCTION TO GRP
Matrix of glass and resin is similar in principle toreinforced concrete where
Like steel reinforcing bars, glass reinforcement aremain load carrying members
The resin performs a function similar to concrete insupporting and positioning the reinforcement so that itcan perform effectively
Glass material provides the major strength whereas
resin binds the glass reinforcement together anddistributes applied loads uniformly between theindividual glass fibres
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INTRODUCTION TO GRP
Advantages of GRP
Resistance to marine environment (Anti fouling paint
however required)
Light Weight (One half the weight of equivalent steel orwood structures and almost equal in weight to
Aluminum)
High strength to weight ratio. Long exposure to marine
environment has little effects on its properties Seamless Construction
Chemically inert (No threat of galvanic corrosion)
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INTRODUCTION TO GRP
Advantages of GRP
Ability to orient fiber strength
Ability to mold complex shapes
Good against impact loads (such as slamming)
Competitive Cost (In case of serial production)
Ability to mold in colours
Easy Repair Low maintenance
Durability (Prolonged Hull life)
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INTRODUCTION TO GRP
Disadvantages of GRP
Stiffness
Modulus of elasticity 2 x 106PSI as compared to steel with
30 x 106
PSI and Al with 10 x 106
PSI . Modulus ofelasticity can go up to 4-6 x 106 PSI in case of
unidirectional laminates or high strength glass/carbon
composites
GRP in disadvantage in deflection critical application
Relatively lower fatigue strength. Notch toughness to be
evaluated to determine stress concentration problems at
hatch corners, ending of stiffeners, decks etc
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INTRODUCTION TO GRP
Disadvantages of GRP
Low bucklingstrength
Creep
GRP has tendency to creep if subjected to long termloading, though this not a problem with normal boatstructures
Vibration
Low abrasionresistance than metals but better thanwood, thus necessitates use of bumpers or chafingplates in areas where abrasive loads might occur
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INTRODUCTION TO GRP
Disadvantages of GRP
Vulnerability to Fire
Flame spread rate of conventional GRP and Plywood
is same
Fire Retardant resins available though they give out
toxic flames and properties of laminate decrease with
heat
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MATERIALS
GRP consists of:
Layup Resins
Glass material
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LAYUP RESINS
The resins used for hand lay-up GRP fabrication are
all liquids, that can be cured to form tough solids by
the addition of suitable curing agents
Various types of resins are: Polyester Resins
Epoxide Resins
Phenolic Resins
Gelcoat Resins
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LAYUP RESINS
POLYESTER RESINS
Polyester resins are normally used as these areusually:
The most economical Easy to handle
Generally non-dermatitic
The curing of polyester resins is brought about by
the addition of two materials i.e. a curing agent(catalystnormally a peroxide) and anaccelerator (normally a cobalt soap)
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LAYUP RESINS
POLYESTER RESINS
The catalyst promotes a chemical reaction causingcross-linking of molecules in the resin
The accelerator controls the rate of cure of the resin and,
in particular, the usable pot life (gel-time) The amount of catalyst & accelerator used with a given
resin should always be that recommended by the resinmanufacturers
The accelerators and curing agents for Polyester resinsMUST NEVER BE MIXED TOGETHER. Each material isto be mixed separately with the resin, first theaccelerator, second the catalyst. Neglect of thisprecaution can lead to a fire or an explosive reaction
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LAYUP RESINS
PHENOLIC RESINS
Phenolic resins have excellent inherent resistance to firecombined with very low smoke and toxic evolution
The curing of phenolic resins is brought about by the
addition of a catalyst. The amount and type of catalystused is fixed by manufacturers
Gel-coat phenolic resin pastes have been developed togive phenolic laminates smooth pin-hole free surfacefinishes
Phenolic resins should not be used for GRP mouldingsthat are likely to come into contact with foodstuffs,directly or indirectly
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LAYUP RESINS
GEL COAT
A resin applied to the surface of a mould and gelled
before lay-up. The gel-coat becomes an integral part
of the finished moulding, and is usually used toimprove surface finish
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LAYUP RESINS
It is important to note that all the resins (polyester,
epoxide, phenolic) do not develop their full
mechanical properties as soon as they have
hardened. All types require a period of several days
at room temperature for a reasonably full cure, but
the rate of cure can be accelerated by the
application of heat. Again the resin manufacturers
recommendations should be followed
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GLASS REINFORCEMENTS
Glass reinforcements are available in five forms
Chopped Strand Mat (CSM)
Woven Rovings (WR)
Woven Fibre Cloths Combination Cloths
Double-bias Cloth
The composition of the glass should be that known
as E-glass
High strength reinforcements also exist and arediscussed in later part
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GLASS REINFORCEMENTS
Chopped Strand Mat (CSM)
CSM, consisting of randomly dispersed glass fibres about50mm long held together with a suitable binder
Cheapest and most widely used reinforcement
Moderate strength Homogeneous material with equal physical properties in all
directions
Easy to wet
Builds up laminate thickness at rate of 20 piles/inch (If mat
weighs 1 ounces per sq foot) When working with mats, it is important to use the minimum
amount of resin consistent with good wetting of the glass.CSM should comply with BS 3496 for use with polyesterresins
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GLASS REINFORCEMENTS
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CHOPPED STRAND MAT (CSM)
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GLASS REINFORCEMENTS
Woven Roving (WR)
WR consist of glass rovings (bundles of glass fibres)woven into either a plain-weave cloth, for generaluse, or as a predominantly unidirectional cloth forstructures requiring maximum strength in onedirection
Higher strength than mat
Good drapeability and handling characteristics
Builds up laminate thickness rapidly (25 piles/inch)
Good resistance to impact because of continuous anduntwisted strands
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GLASS REINFORCEMENTS
Woven Roving (WR)
Woven rovings for use with polyester resins are to
comply with BS 3749 or NES 166
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GLASS REINFORCEMENTS
Woven Fibre Cloth
Woven fibre cloths are manufactured from spun
yarns and are available in a range of weights and
weaves. Because of their high cost, cloths arenormally used for structures in which a high strength
to weight ratio or where close control of resin to
glass ratio is required
The choice of weave is generally dictated by thestresses which the structure will have to withstand
when in use
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GLASS REINFORCEMENTS
For maximum impact strength
Cloth having a large amount of crimp in the fibres isrequired; this is achieved by using a square-weave clothwoven from heavy yarns
The highest compressive, flexural and tensile strengths Cloths of low-fibre crimp such as satin-weave and
unidirectional cloths
Satin-weave cloths also have the desirable property of
drape which enables them to follow surfaces havingcompound curvature
Woven fabrics are to comply with BS 3396; Parts 13and be made from E-glass
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GLASS REINFORCEMENTS
Combination Cloth
Combination cloth is a mixture of CSM and WR and
is used to improve cost efficiency. However care
must be taken to ensure that the weave of thewoven roving is in the correct direction for the
design requirement and that the inner layers of
glass are completely wetted by the resin
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GLASS REINFORCEMENTS
Double Bias Cloth
Double-bias cloth has the fibres at angles and is
used to lay down reinforcement at various angles in
large mouldings where it would be uneconomical orimpractical to lay the normal 0/90 cloth at an angle
when strength in all directions is required
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GLASS REINFORCEMENTS
Surfacing Tissue
Surfacing tissues are very thin (0.25mm0.44mm)
reinforcing fabrics used to strengthen the gel-coat of
a GRP structure to prevent crazing of the resin andto minimize impact damage. Very thin glass mats
are sometimes used but non-woven synthetic fabrics
are generally preferred. Only a single layer of
surfacing tissue is use
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GLASS REINFORCEMENTS
High Strength Reinforcements
Number of high strength reinforcements availablebut use limited due high cost
Most commonly used such reinforcement is S Glass,KEVLAR and carbon fiber, woven in bi-directional oruni-directional fabric with minimum number of fill orcross fiber
Carbon fiber generally laid up with epoxy resin
Besides being expensive, consideration of highstrength laminate is complicated by relativeperformance. E.g
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STORAGE OF MATERIALS
Glass Reinforcements
Rolls of glass reinforcements to be stored in clean
dry room with humidity less than 70%
Rolls individually wrapped in moisture-proof wraping
Rolls of material should not be stood on end;
suitable racks or shelving should be provided
NOTE: Dampness of glass reinforcements causes anirreversible loss of reinforcing strength
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STORAGE OF MATERIALS
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CORRECT WAY WRONG WAY
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STORAGE OF MATERIALS
GRP Chemicals
Polyester resins and accelerators, epoxide resins,
and phenolic resins should be stored in a cool dry
place, at a temperature no higher than 20C Organic peroxide catalysts present a hazard when
stored in bulk
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SCHEME OF LESSON
MATERIALS
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MOULDS AND MOULDS
PREPARATION
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MOULDS
A variety of materials is suitable for the construction
of moulds for hand-laid GRP
Sheet Metal Moulds
Made from aluminum alloy or mild steel sheet
Sheet metal moulds are suitable for small mouldings
and short production runs
Metal moulds for use with phenolic resins should be
either stainless steel or plated to avoid acid attack
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MOULDS
Sheet Metal Moulds
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MOULDS
Timber Moulds
Moulding surface of the mould is sealed to prevent the
absorption of parting agent and resin into the timber. This
can be achieved, together with a good surface finish, by
applyingseveral coats of furan varnish to the mould
Timber moulds are only used for short production runs
(about 50 per mould)
For the production of large numbers of small items
densified wood is preferred to the more usual timbers
Timber moulds should not be used for the production of
phenolic resin mouldings
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MOULDS
GRP Moulds
GRP moulds are made from a master pattern, orwhen available, an existing item
Polyester moulds should be well cured to ensure thatno free styrene is present that could result in releaseproblems
Plaster and Concrete Moulds
Wax Moulds
Flexible Moulds
Moulds with Undercuts
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MOULD PREPARATION PRIOR
LAY-UP Any moulds which have been stored out-of-doors should
be allowed to acclimatize to the conditions within themould shop before laminating begins
Inspect and Clean/Repair
Apply releasing agent
Wax, polyvinyl alcohol, sodium alginate water solutions,and polymeric resin solutions (Frekote) are preferred. Nosilicone containing release agents should be used whenthe moulding is to be painted/coated or bonded to othermoulding, or when the application calls for acoustictransmission (radomes), as some of the release agent isalways transferred to the moulding
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SCHEME OF LESSON
MATERIALS
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PREPARATION OF
MATERIALS FORMOULDING
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MATERIAL PREPARATION FOR
MOULDINGReinforcements
Reinforcements to be cut as per mould contours
A cutting and marking-out table is essential and shouldbe reserved for this purpose to avoid accidental
contamination of the glass
Cut reinforcement should be laid on clean woodensheets for transport to the mould
Whilst it is desirable to carry out tailoring operations in
the glass reinforcement store, tailoring may be carriedout in the moulding shop provided that the cutting-outtable is isolated from other operations
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MATERIAL PREPARATION FOR
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MATERIAL PREPARATION FOR
MOULDING
Safety Precautions
The accelerators and curing agents for Polyester
resins MUST NEVER BE MIXED TOGETHER. Each
material is to be mixed separately with the resin, firstthe accelerator, second the catalyst. Neglect of this
precaution can lead to a fire or an explosive
reaction
The recommendations with regard to operator safetyand fire risk apply when handling resin will be
discussed at the end
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MATERIAL PREPARATION FOR
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MATERIAL PREPARATION FOR
MOULDING
Moulding Inserts
Timber and metal inserts are used in GRP
mouldings to provide anchoring points for bolts and
screws and as reinforcing or stiffening members Timber inserts should be clean. Any contamination
should be removed with glass paper. Some timber
preservatives may inhibit the cure of the resin. Zinc
naphthenate is acceptable as a timber preservative
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SCHEME OF LESSON
MATERIALS
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MOULDING OPERATION
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MOULDING OPERATION
Moulding Shop
The shop used for the actual moulding operationshould preferably be used for this purpose alone. Noother form of operation should be allowed in the
moulding area (except for cloth cutting, resin mixingif extremely essential)
The shop is to be heated such that the roomtemperature never falls below 15C during
lamination and 10Cduring curing Condensation should be kept to minimum. Draught
free ventilation to remove vapours
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MOULDING OPERATION
Moulding Shop
Air flow velocity over the face of uncured laminates
must not exceed 1metre/sec; greater air-flow
velocity would remove styrene too rapidly andprohibit satisfactory cure
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MOULDING OPERATION
Moulding Tools
Tools are required to ensure thorough impregnation
of the glass and that all air bubbles are worked out
The usual tools are paint brushes, metal, polythene,nylon and lambswool rollers, flat squeegees
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MOULDING OPERATION
Moulding Tools
Paint brushes used for hand lay-up should have
unvarnished handles and bristles (hair, coat). The
varnishes used in brush manufacture and rubbercompounds used for setting some brush bristles are
resin solvent and inhibit resin cure
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MOULDING OPERATION
Laminating Temperatures
Polyester Resin
Laminating should not to be undertaken when theambient temperature is below 15C or above 30C
Epoxide Resins
Manufacturers advice should be sought regardinglaminating temperatures for epoxide systems
Phenolic Resins Laminating should be carried out at a minimum
temperature of 15C
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MOULDING OPERATION
Application of Gel Coat
The first step in fabricating a GRP moulding by hand
lay-up is to apply a gel-coat. The gel-coat may be
applied either by hand or by spray gun Hand application of gel-coat resins should be:
By means of a camel-hair brush or a lambswool roller.
The rate of application should be approximately
450600g/m2 which gives a gel-coat 0.40.5mm thick
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MOULDING OPERATION
Application of Gel Coat
If applied by spray gun
The resin will have to be diluted with styrene (if apolyester) to allow for styrene loss by evaporation
The dilution rate recommended by the resinmanufacturer is not to be exceeded
To achieve even coverage, it may be necessary touse a thixotropic additive or a formulated gel-coatresin. The gel-coat should be lightly pigmented, tothe colour scheme of the finished moulding, to assistcomplete coverage of the mould
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MOULDING OPERATION
Application of Gel Coat
The gel-coat should be inspected as per Part 2 ofNES 701 prior layup
After the gel-coat has been applied to the mould, thesurfacing tissue should be laid in the mould and begently rolled into the gel-coat
The gel-coat should then be allowed to gel (gel timeas specified by manufacturer), before proceedingwith the build up of the laminate. Lay-up of thelaminate should then follow within 12 hours of thegel-coat setting
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MOULDING OPERATION
Lay-up of Laminates
The tailored section of reinforcement should beweighed and to ensure complete wetting out of thereinforcement, a slightly greater weight of mixed
resin than is required to give the specified resinglass ratio should be taken
Apply resin using paint brush on first layer oflaminate
Using a roller or squeegee, the resin should beworked through the reinforcement until the latter isthoroughly wetted and visible air bubbles minimized
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MOULDING OPERATION
Lay-up of Laminates
A second application of resin should now be madefollowed by a second layer of reinforcement and so onuntil the finished thickness of the laminate has been
reached Less and less resin may be required for successive
layers of reinforcement
Over-rolling must be avoided. This is particularly
important when using glass mats as the binder dissolvesin the resin and if the laminate is over-rolled the glassfibres are distributed by the roller so that glass-rich andresin-rich areas are formed in the laminate
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MOULDING OPERATION
Lay-up of Laminates
Edges of adjacent pieces should be butted oroverlapped depending on the application andthickness tolerance
Overlaps should be 5075mm in the case of CSM
For WR the weft selvedge tails should overlap theouter warp roving of the adjacent cloth by their ownlength (20mm)
Overlaps should when possible be staggered to aidproduction of a smooth surface
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MOULDING OPERATION
Lay-up of Laminates
Butts in the reinforcement should be staggered
150mm relative to butts in the underlying ply and
superimposed butts must be separated by at leastsix passing plies
Corners and re-entrant angles in a moulding should
be thoroughly wetted
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MOULDING OPERATION
Lay-up of Laminates
Mouldings over 9mm in thickness must be laid up inseveral stages to avoid excessive exothermic heatduring the initial cure of the resin
Practical maximum layup limit, at compartmenttemperatures of 20C, is approximately four plies of600g/m2 CSM or ten plies of 830g/m2 WR; if thislimit is reached, a period of 12 hours is to elapse
before any further plies are laid When the compartment temperature is higher, the
number of plies laid must be reduced
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MOULDING OPERATION
Lay-up of Laminates
When unbalanced weave-materials are being used, egunidirectional cloths, care must be taken to ensure thatthe cloth warp is laid in the direction of maximum stress
Inspection is essential during each stage of fabrication
For large mouldings, pre-impregnated cloth should beused. The glass cloth is passed to a resin dispenser intowhich resin and catalyst are fed at a controlled rate to
give the required resin:glass ratio. The dispensingequipment is mounted on a gantry and traversed acrossthe mould laying down the impregnated cloth which isthen consolidated using rollers or squeeges
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MOULDING OPERATION
Lay-up of Laminates
If completion of a lamination is delayed for an extendedperiod a peel-ply, usually of terylene, should be lightlyrolled into the surface. This can be peeled-off when
laminating recommences. If a peel-ply cannot be laiddown then, if the elapse period extends for more thanseven days, the surface of the laminate should be wipedwith styrene and left 15 minutes or abraded (care beingtaken to avoid cutting plies of reinforcement) before
additional plies are laid. Lay-up delays of up to sevendays are acceptable without surface preparation of useof peel-ply
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MOULDING OPERATION
Lay-up of Laminates
Phenolic-based adhesives are widely used in
woodworking, consequently no woodworking
operations using phenolic-based adhesive shouldbe allowed in the moulding shop
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SCHEME OF LESSON
MATERIALS
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CURE OF MOULDS
Cure Time in Moulds
After completion of the lay-up, the assembly must beleft until the resin has hardened sufficiently
The cure period varies with the resin used and thedesign specification and/or the resin manufacturersrecommendations
In cases of difficulty in the removal of mouldings, theapplication of compressed air between the mouldingand the mould is usually an effective aid
Phenolic resin mouldings may be heated to4070C whilst still in the mould.
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CURE OF MOULDS
Postcure
Although amoulding is usually strong enough to behandled some twelve hours after the completion ofthe lay-up, the resin will not have hardened
sufficiently for the maximum mechanical propertiesof the laminate to have developed; therefore, a post-cure must be applied to the moulding beforefinishing operations can be carried out
Post cure may include leaving mould at room tempfor specified time or in a heated room for specifiedtime
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CURE OF MOULDS
Postcure
A period of at least 24 hours at room temperature
must be allowed to elapse before any post-cure is
applied
The lower the post-curing temperature, the less
chance of distortion in the moulding
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Temperature 20C 30 C 40 C 80 C 120 C
Post-cure time 30 days 14 days 3 days 7 hours 2 hours
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SCHEME OF LESSON
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FINISHING OPERATIONS
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FINISHING OPERATIONS
The finishing operations carried out on GRPmouldings, are much the same as those used for
other materials, e.g sawing, drilling of holes, riveting,
painting, etc
In all cases, deviations from normal wood or metal
working practice are necessary if the best product is
to be made
Mouldings are to be fully cured before finishingoperations are begun
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FINISHING OPERATIONS
Sawing and Trimming
The direction of cut must always be such as to startat the gel-coat and then proceed into the body of themoulding. This prevents chipping and crazing of the
gel-coat Saw blades must always be sharp and correctly set
After sawing, the cut edge of the moulding shouldbe smoothed with fine emery cloth applied along the
length of the cut edge and never at right angles to itas this latter action causes local delamination andchipping of the gel-coat
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S G O O S
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FINISHING OPERATIONS
Drilling
All holes drilled in GRP should be drilled from the
gel-coat side
Holes more than 6mm diameter require the use ofrigidly supported back-up pieces of hardwood or
plastic to prevent chipping of the back face
Holes in excess of 40mm diameter and non-circular
holes should be cut either by sawing or using anelectrometallic diamond edge routing tool
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FINISHING OPERATIONS
Drilling
If a hand held jig saw of the pattern which cuts as
the saw is drawn into the body of the tool is used,
sawing must be carried out from the back of the
laminate to avoid gel-coat damage
The cut edges of all holes should be sealed with a
coat of room temperature curing epoxide resin or
polyester resin Safety precautions in drilling of GRP are the same
as for sawing (will be discussed in health and safety)
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FINISHING OPERATIONS
Water-Jet Cutting
Water-jet cutting is relatively new and offers fast, lowtemperature, distortion-free, accurate and clean cutting
Abrasive water-jet cutting, in which abrasives are
introduced into the water jet, is especially suited to non-homogeneous materials, such as GRP, that are abrasivein nature and damaging to more conventional cuttingtools
The equipment can have simple XYmovement or haveintricate shape cutting capabilities by the use ofcomputer controlled articulated robots with multiple axescutting ability
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FINISHING OPERATIONS
Water-Jet Cutting
A hydraulically driven intensifier unit pumps filteredand conditioned water, at pressures up to 410 MPaand rates of 4 to 8 L/min
The high pressure fluid is expelled through an orificeto form a jet of water, propelled at speeds up to850m/s
For abrasive water-jet cutting an abrasive material,
eg garnet grit, is introduced into the water streamafter the primary jet is formed. A fine grit may beused to produce a smooth surface finish
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FINISHING OPERATIONS
Water-Jet Cutting
Because composite materials may delaminate in the
area surrounding the initial penetration, the water-jet
is usually activated away from the work piece and
then guided into the desired edge
The technique produces very low dust-level, so
reducing the risk to health and fire hazard. However,
because of the air coupling into a large high-velocityvolume of air/water, noise levels are high and
appropriate ear protection is required
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FINISHING OPERATIONS
Laser Cutting
Focused CO2 laser beams are now being used tocut a wide range of composites and complex cuttingcan be achieved by manipulating the beam by a
five-axes robot In order to cut, a laser must be integrated with the
means to deliver the beam, handle the workpieceand be in an enclosure that ensures the safety of
personnel from the beam and any irritating and/ortoxic gases released by the thermal degradation ofthe resin
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FINISHING OPERATIONS
Laser Cutting
When cutting GRP thermal damage to the matrix
may result due to heat conduction along the fibres.
Also when cutting laminates over 10mm thick
charring may be a problem
Charring is a chemical process of
incomplete combustion of certain solids when
subjected to high heat. The resulting residue matteris called Char.
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FINISHING OPERATIONS
Bolting of Laminates Fasteners must never be pulled up directly on to the
laminate surfaces but should have large diameterwashers or a drilled clamping plate of the fasteningmaterial under both the bolt head and the nut
Where the use of nuts and bolts is not possible andrecourse has to be made to the use of bolts screwed intotapped holes, a metal insert should be included in themoulding. The fastening holes can then be drilled andtapped in the insert
A wire thread insert (Helicoil or Crosswire) in a holetapped in the GRP is only suitable for lightly loadedstructures
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FINISHING OPERATIONS
Bolting of Laminates
Bolt hole spacing should be:
not less than 3 bolt diameters from the edge of the
laminate; from 3.5 to 4.5 bolt diameters apart for structural and
watertight joints;
from 5 to 8 bolt diameters apart for non-structural
applications.
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FINISHING OPERATIONS
Riveting of Laminates Riveting of laminates should be avoided whenever
possible. However, when used, rivets should be of softaluminium and be driven with a washer of the samematerial under both head and point. Rivets greater than
5mmshould be avoided whenever possible Spacing of rivets should be:
not less than 3 rivet diameters from the edge of thelaminate
from 3.5 to 4.5 rivet diameters apart During all riveting operations, GRP mouldings must be
very soundly supported
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FINISHING OPERATIONS
Riveting of Laminates
Explosives and similar riveting systems must not be
used. The proprietary Advel fastener is
recommended as an alternative to riveting for sizes
above 5mm
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SCHEME OF LESSON
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SANDWICH STRUCTURES
SANDWICH STRUCTURES
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SANDWICH STRUCTURES
Sandwich structures consist of lightweight core materialwith a skin of GRP on either side
The purpose of sandwich construction is to increaserigidity of panel by increasing its thickness with relatively
little increase in weight The core materials commonly used are:
Wood
Foamed Plastics
Honeycomb
Microballons
Buoyancy Foam
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SANDWICH STRUCTURES
Alternative core materials, i.e polyetherimide (PEI)and phenolic foams, possessing superior fire
characteristics to those listed above are being
evaluated and may eventually be considered
The basic lay-up technique is used when making
sandwich structures, with some detail modifications
in both mould design and lay-up procedure.
NES 752 may be considered as guideline
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CORE MATERIALS
WOOD
Plywood, Soft Woods and Balsa are typically used
woods as core material
Plywood
Good strength, rigidity and ability to withstand local loads
Commonly used for bulkheads and deep girders
Relatively heavy and should be of exterior grade only
Hard woods are not used since they have tendency toswell and crack the covering laminate and do not bond
well with GRP
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CORE MATERIALS
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CORE MATERIALS
WOOD Soft Woods
Soft woods such as pine used for framing and similarapplication
Can cause swelling problems, however, bond wellwith GRP
Balsa
Balsa wood, weighing b/w 6 to 9 pounds per cubicfoot, is commonly used as light weight core materialfor small boat construction
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CORE MATERIALS
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CORE MATERIALS
WOOD
Balsa
In end grain configuration, with the grain
perpendicular to laminate, the bond strength isrelatively high, upto 1000 PSI due the resin wicking
into elongated cells of balsa
Bond strength can further be increased by use of
vacuum injection, which provides added benefit offilling the gaps between individual balsa blocks to
prevent water migration through core
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CORE MATERIALS
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CORE MATERIALS
WOOD
Due possible rotting, swelling and degradation, the
use of wood cores in areas below the waterline, or
adjacent to tanks is not recommended unless
special precautions are taken
In case of balsa, there has been a controversy over
its use below waterline. Some research however
shows penetration of the end grain balsa of lessthan 1/8 inch after 1000 hours exposure to sea
water
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CORE MATERIALS
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CORE MATERIALS
FOAMED PLASTIC Polystyrene
Not generally recommended since it is attacked bypolyester resin
Polyurethane
A rigid material which will generally not conform to surfacecurvature, however, used in boat building
Polyvinyl Chloride (PVC)
PVC available in thermoplastic form, when heated to 200deg F, softens sufficiently to be draped over curvedsurface. It regains its hardness when returns to room temp
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CORE MATERIALS
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CORE MATERIALS
FOAMED PLASTIC Polyvinyl Chloride (PVC)
Tendency to soften when heated can however causeproblems if ambient temp is too high. Hence use of PVCon surfaces exposed directly to intense sunlight like deck
or in engine room compartment is not recommended A cross linked foam containing both PVC and polyurethane
is available which reduces above mentioned problem, buthas somewhat reduced properties
PVC core material is also softened by polyester resin and
must be either treated with a sealant or used inconjunction with resin having a styrene content below 30%and gel time of less than 30 min for the first layer ofre-inforcement
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CORE MATERIALS
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CORE MATERIALS
FOAMED PLASTIC
Structural grade foams usually have 96 to 128 Kg
per cubic meter density. Lighter foams may be used,
however physical properties diminish rapidly with
decreasing density
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CORE MATERIALS
HONEYCOMB
Honeycomb cores of aluminium, fibergalss laminate,
phenolic, waterproof paper and nylon are available
in various sizes and weights
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CORE MATERIALS
HONEYCOMB They have light weight, good rigidity and poor
resistance to concentrated loads
Highly developed fabrication techniques required to
produce good bonding b/w core and facing.Imperfect bonding will result in water travelthroughout core in case of a leak
In marine construction, honeycomb cores limited to
interior decks, flats and bulkheads where lightweight is essential
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CORE MATERIALS
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CORE MATERIALS
MICROBALLONS Light weight hollow glass or gas-filled phenolic
spheres and polystyrene beads embedded in resinare example of high density, trowelled-in-place core
material presently being used in some boat hullsand deep-submergence vehicles
Use is limited due high cost, used only where highcore strength is required
Alternate may be a core insert of vermiculite andresin (80% resin by weight)
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CORE MATERIALS
BUOYANCY FOAM
Polyurethane or polystyrene foams of about 32 Kg
per cubic meter used for flotation in small boats
Foams may be installed as pre-cured blocks or incase of polyurethane foamed in place
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SCHEME OF LESSON
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SCHEME OF LESSON
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HANDLING/TRANSPORTATION
OF FINISHED MOULDINGS
HANDLING/TRANSPORTATION
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OF FINISHED MOULDINGS
PREPARATION All traces of release agents, fibers, dust etc should be
cleaned/removed
Openings should be blanked in order to prevent ingress offoreign agents likely to be met during transportation or
storage. Care should be taken to ensure that enclosedmouldings are ventilated at all times
When necessary to prevent overstressing during handling andtransportation, temporary stiffening/support devices may beused
Where lifting positions have been provided in design, drawingshowing lifting position, handling technique, equipmentrequired and any other important information for safety likerestriction on angle of lift, should be provided
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OF FINISHED MOULDINGS
LIFTING
When lifting lugs are not provided, moulding should
only be lifted using webbing or rope slings passed
around the mould
Chain or wire rope is permitted if adequate
arrangement to prevent local loads and abrasion is
made
When lifting, care should be taken not to applyshock loads to the lugs or moulding
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OF FINISHED MOULDINGS
TRANSPORTATION
Loads imposed by transportation should be
considered and temporary supports provided if
necessary
Moulding should be secured to avoid its movement
during transportation
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HEALTH AND SAFETY
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HEALTH AND SAFETY
HANDLING RESINS All resins and solutions should be handled and used
in well-ventilated flameproof areas
The warning against the mixing together of undiluted
curing agents and accelerators needs no furtheremphasize because of the fire and explosion risksinvolved
Catalysts, being organic peroxides, present a
hazard when stored in bulk and should be storedseparately, preferably outside the main building in ametal lockable-bin sited in a cool, shady position
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HEALTH AND SAFETY
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HEALTH AND SAFETY
HANDLING RESINS
Operators handling resins should use a suitable
barrier cream. Any resin contamination of the skin
should be cleaned off with a cream formulated for
this purpose, followed by soap and water. Solvents
must never be used to remove resins from the skin
as they remove the natural oils from the skin and
increase the risk of dermatitic troubles. It is also
possible for rubber or PVC protective gloves toabsorb resin and so lead to skin irritation
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HEALTH AND SAFETY
HANDLING RESINS
When handling curing agents and accelerators,
operators should wear suitable protective clothing,
goggles and gloves. Any accidental splashes in the
eye should be immediately thoroughly washed out
with water and then be attended by a doctor
Some people are sensitive to amine curing agents
associated with epoxide resins and readily developdermatitis and should avoid all contact with such
materials
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HEALTH AND SAFETY
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HEALTH AND SAFETY
WASTE DISPOSAL Large spillages of resin or resin solutions must be dealt
with promptly and operators should wear appropriateprotective equipment
Liquid resins should be absorbed on to dry sand orsimilar inert materials for controlled incineration. Rags orpaper used as absorbents constitute a fire risk andshould be disposed of in the same way, as promptly aspossible
In the event of a serious spillage which enters publicdrains or waterways, the Local Water Authority must beinformed immediately (CANT SAY ABOUT PAKISTAN)
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HEALTH AND SAFETY
WASTE DISPOSAL Waste peroxides must be disposed off after
consulting safe procedures from OEM
Empty drums etc contain vapours of the monomer
present in the original resin solution and thereforeentail fire, explosion and noxious vapour risks. Theyshould only be disposed of by methods that followrecognized safe procedures
Disposal of contaminated solvents should only beundertaken after consultation with the relevantAuthorities
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SCHEME OF LESSON
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SCHEME OF LESSON
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COMMON DEFCTS AND
QUALITY CONTROL
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INSPECTION METHODS
CURED LAMINATES
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CURED LAMINATES
VISUAL INSPECTION
Visual inspection to be carried out after removing
parting agent and adequately cleaning laminate
Visual inspection to be carried out using light. Whereaccess is possible, inspect from both sides
Inspection is to be carried out in subdued light,
using an inspection lamp of sufficient intensity to
penetrate the laminate
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INSPECTION METHODS
CURED LAMINATES
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CURED LAMINATES
VISUAL INSPECTION
When inspecting visually, following points should be
specially scrutinized:
surface imperfections and general appearance freedom from air voids entrapped in the laminate.
(The use of unpigmented resin makes visual
inspection much easier)
dimensions
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INSPECTION METHODS
CURED LAMINATES
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CURED LAMINATES
ULTRASONIC INSPECTION
Ultrasonic inspection may be used to measure:
Laminate thickness,
Lack of adhesion 0 compression waves should be used with
frequencies in the range 0.5 to 5MHz. Guidance on
the selection and use of ultrasonic equipment is
given in NES 729 Part 5
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INSPECTION METHODS
CURED LAMINATES
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CURED LAMINATES
TAP TESTS
The coin tap method is a simple test and is based upon
the principle that a laminate will resonate differently
when lightly tapped with a coin should there be any
variations in the laminate underneath the point of testing Method requires training and practice to obtain reliable
result
Mechanical device as a Tapometer (manufactured by
Rolls Royce MatEval Ltd) may be used. It producesmore consistent results, however, training and
experience is required
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INSPECTION METHODS
CURED LAMINATES
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CURED LAMINATES
RADIOGRAPHIC INSPECTION
Radiographic inspection may be used to detect
some types of cracking and gross damage to
reinforcement
Radiography generally unsuitable for the detection
of lack of bonding or delamination
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GEL-COAT DEFECTS
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GEL COAT DEFECTS
Surface Fibre Pattern Star Cracking
Crazing
Pin Holes on Gel-Coat
Cratering and Blistering Wrinkling of Surface
Poor Adhesion
Fish Eyes
Internal Dry Patches Leaching
Distortion or Warping
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GEL-COAT DEFECTS
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G CO C S
SURFACE FIBRE PATTERN
If the gelcoat is thin or the reinforcement is applied
before the gelcoat is sufficiently cured the roving
pattern may print through and be visible in the
gelcoat when the hull is released
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GEL-COAT DEFECTS
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Fault Cause Remedy
Surface Fibre Pattern
Gel-coat not cured
sufficiently before
commencing lay-up
Ensure adequate cure
of gel-coat
Gel-coat too thin
Ensure gel-coat
minimum thickness of
0.3mm
GEL-COAT DEFECTS
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STAR CRACKING
Due to an over thick gelcoat but this time it must have
received an impact from the inside
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GEL-COAT DEFECTS
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Fault Cause Remedy
Star Cracking
Result of an over thick
gel-coatoccurs when
laminate has received areverse impact
Ensure gel-coat no
thicker
than 0.5mm
GEL-COAT DEFECTS
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CRAZINGCrazing usually indicates a gelcoat which is too thick
and has crazed during flexing of the hull
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GEL-COAT DEFECTS
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Fault Cause Remedy
Crazing
Gel-coat too thickUse even thickness gel-
coat
Use a brittle resin orresin containing excess
monomer
Use properly formulatedgel-coat resin
Excessive accelerator in
formulation or curing
temperature too high.
(Sometimes givesorangepeeleffect)
Check resin formulation
Use experimentally
verified mixAvoid high temperatures
GEL-COAT DEFECTS
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PIN HOLES IN GEL-COATSmall air bubbles trapped during the cure show up on
release
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GEL-COAT
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Fault Cause Remedy
Pinholes in Gel-coat
Gel-coat not wetting
release agent on mould
Use non-silicone wax on
mould surface followed by
a PVA release agent
Minute air bubbles in the
surface of the laminate.
Caused by poor mixing of
filler into thixotropic gel-
coat and/or overbrushing of
gel-coat when applied to
mould
Mix resin by mechanical
means. Apply resin
carefully using minimum
brushwork consistent with
uniform resin coverage
Occluded air in the filler
used in resin formulation
Use only fillers which have
been treated for use with
polyester or epoxy resin asappropriate
Dust particles in the parting
agent or the gel-coat
Mould under clean
conditions. Ensure that dust
cannot fall on mould before
application of gel-coat
GEL-COAT DEFECTS
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CRATERING AND BLISTERINGAn indication of delamnation between layers on older
vessels. It is potentially the most serious of problems
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GEL-COAT DEFECTS
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Fault Cause Remedy
Cratering and Blistering
Usually caused by air or
solvent trapped between
gel-coat and laminate
proper. If reinforcementis carefully rolled down
this defect should not
occur
Check resin:glass ratio;
a deficiency of resin
often causes air ubbles.
Check the grade of anyglass mat used. If the
binder is insoluble in the
resin the fibre will not
bed down. Ensure that
parting agent is
thoroughly dry before
applying gel-coat
If parting agent not
thoroughly dry, volatileswill cause lifting of gel-
coat
GEL-COAT DEFECTS
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WRINKLING OF SURFACEThis is caused by the heat released by the following
laminate immediately attacking an under cured thin
gelcoat
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Fault Cause Remedy
Wrinkling of Surface
Too thin a gel-coat
which is under cured.
Often on verticalsurfaces
Prevent drainage of gel-
coat by ensuring
adequate amount of
thixotropic agent informulation
Under cure as a result of
styrene (or other
monomer) evaporation
Ensure that there are no
draughts in vicinity of
the moulding
GEL-COAT DEFECTS
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POOR ADHESIONIt occurs when a gelcoat is left unreinforced for too
long. A weekend is long enough
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GEL-COAT DEFECTS
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FISH EYESFish Eyes are caused by the gelcoat de-wettingfrom
the polished mould surface in spots. Occurs mainly
when silicone based waxes are used. These, in
particular car waxes, should be avoided
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GEL-COAT DEFECTS
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INTERNAL DRY PATCHESAreas where resin has not penetrated
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GEL-COAT DEFECTS
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LEACHINGLeaching a serious fault. Severe weathering can
remove a poor resin from surface of a laminate
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GEL-COAT DEFECTS
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DISTORTION OR WARPING Causes
Differential shrinkage between unreinforced gel-coat
and reinforced laminate
Remedy
Use a reinforced gel-coat
Use thin gel-coat
Use a specially formulated gel-coat resin
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ACCEPTANCE CRITERIA
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GEL-COAT Small areas up to 1200mm2 exhibiting defects
shown on previous slides are acceptable except in
case of radomes and sonar domes
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LAMINATE DEFECTS
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BUBBLES IN BODY OF LAMINATEAir trapped in a laminate is undesirable because its
presence lowers the strength of the part, reduces
radar and acoustic transparency, and in extreme
cases, results in a porous laminate
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LAMINATE DEFECTS
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Fault Cause Remedy
Bubbles in Body of
Laminate
Insufficient resin and/or
incorrect binder on glass
mat
Check resin glass:ratio
being worked. Ensure mat
binder is soluble in resin in
use. Check operator is fully
trained
Damp reinforcement
Check reinforcement
storage conditions. If
recently delivered,
reinforcement may require
drying in a warm room
Excessively short gel-timeor too thick a lay-up leading
to excessive heating or
resin on gelation
Check resin formulation. Do
not lay-up more than 8mm
of laminate at one time
LAMINATE DEFECTS
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RESIN-RICH AND GLASS-RICH AREAS (WASHING)This defect is almost entirely confined to chopped strand mat reinforced
laminates and is caused by excessive working of the material during
fabrication leading to displacement of the glass and consequently to
glass-rich and resin-rich areas. Resin-rich areas in a laminate are
points of weakness and, if excessive, call for rejection of the moulding
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LAMINATE DEFECTS
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Fault Cause Remedy
Resin-rich and
Glass-rich Areas
Generally with mat
laminates, caused by
over-rolling of the
reinforcement afterbinder has dissolved
Check operator is fully
trained. No more rolling
than is necessary to
remove air should becarried out
LAMINATE DEFECTS
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DELAMINATED AREAS WITHIN BODY OFLAMINATE
Internal delaminations are caused by the application of
excessive local force, usually when the moulding is
being removed from the mould, or by localcontamination of the reinforcement. An internal
delamination may also be detected by tapping the
surface of the laminate with a coin. A delaminated area
gives a deadsound whilst a perfect area gives a clearringing sound
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LAMINATE DEFECTS
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DELAMINATED AREAS WITHIN BODY OFLAMINATE
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LAMINATE DEFECTS
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LAMINATE FAULTS AND CAUSES
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Fault Cause Remedy
Delaminated Areas
within Body of Laminate
Localized contamination
of reinforcement
Check storage and
handling of
reinforcement.
Cleanliness is essential.
Occasionally chrome
finishes are misapplied.This is shown by green
patches on
Reinforcement. Reject
Inadequate wetting of
glass. Brushes or rollers
contaminated with wateror solvent
Caused by operator
carelessness
Use of excessive force
in removing mould tool
Minor form of crazed
areas(below)
LAMINATE DEFECTS
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LAMINATE FAULTS AND CAUSES
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Fault Cause Remedy
Crazed Areas
Resin-rich patchesSee Resin-rich and
Glass-rich Areas
Local impact damage.
Excessive localizedforce used in removing
moulding from mould
Treat mouldings with
respect particularly
before post-cure. Use
absolute minimum offorce when stripping
mouldings. Check
release agent
application methods
Tacky Laminate
Surface
Loss of monomer byevaporation
Gel-time too long
Air-inhibited resin
system used
Check resin formulation.
Use resin not prone to
air inhibition
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LAMINATE DEFECTS
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INTERNAL DRY PATCHES (WHITE LAMINATES)White laminates are found when the resin fails to wet
the surface of the reinforcement. As a result the
pattern of the reinforcement may be clearly seen
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LAMINATE DEFECTS
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INTERNAL DRY PATCHES (WHITE LAMINATES)This condition is caused by gross contamination of the
reinforcement, by the use of a finish which is not
compatible with the resin system, or by local exotherm.
The result is an unacceptably weak and possiblyporous laminate. Small areas may be considered for
repair but large areas should always be rejected
(Read NES for more details)
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LAMINATE DEFECTS
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Fault Cause Remedy
Internal Dry Patches
Attempting to
impregnate more than
one layer of glass at a
time
See Resin-rich and
Glass-rich Areas
Use of insufficient resin.
Inadequate
consolidation
Check resin:glass ratio
Incorrect finish on glass
Ensure that glass wets-
out satisfactorily withresin in use
LAMINATE DEFECTS
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Fault Cause Remedy
Undercure
Workshop temperature
too low
No laminating to be
undertaken at
temperatures below
15C
Loss of styrene caused
by draughts
Ensure no draughts or
excessive air flow over
laminate
Presence of inhibitors
e.g unsuitable pigments
Check materials
Check resin formulation
Incorrect resin
formulation, e.g too
little catalyst or
accelerator
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EXTRA SLIDES
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LINKS
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SPUN YARN
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A yarn made by taking a group of short staple fibers,which have been cut from the longer continuous
filament fibers, and then twisting these short staple
fibers together to form a single yarn, which is then
used for weaving or knitting fabrics
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Introduction to GRP and Hand Laid-up
GRP Moulding
By Lt Cdr M Hasan Adil PN
CRIMP
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When warp and weft (fill) yarns interlace infabric they follow a wavy or corrugated path.Crimp percentage is a measure of this wavinessin yarns.
Percentage crimp is defined as the meandifference between the straightened threadlength and the distance between the ends of thethread while in the cloth, expressed as apercentage.
C=(l-p)/p*100%
where, c = crimp, l = uncrimped length and p =crimped length
Warp is the lengthwise or longitudinal thread ina roll, while weft is the transverse thread
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SATIN WEAVE
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A weave in which each weft thread floats over asmany as 12 warps and then under a single warp.
The next weft passes over the same number of
warps, but is woven in by different warps
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NOTCH TOUGHNESS
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Notch toughness is the ability that a material possesses toabsorb energy in the presence of a flaw
A tough material will resist the initiation of a crack at points ofstress concentration. Although, under certain abnormalconditions, the stress may rise locally to such levels that acrack is initiated, a tough material will better resist the
propagation of the crack. The consideration of fracturemechanics principles may be necessary in some instances.Some examples of when notch toughness should be specifiedinclude:
dynamic or impact loading
fatigue loading service temperatures below 25 degrees F.
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CREEP & ABRASION
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Creep In materials science, creep is the tendency of a
solid material to move slowly or deform permanently
under the influence of stresses.
Abrasion
The process of wearing down or rubbing away by
means of friction
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BUCKLING
http://en.wikipedia.org/wiki/Materials_sciencehttp://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Materials_sciencehttp://en.wikipedia.org/wiki/Materials_sciencehttp://en.wikipedia.org/wiki/Materials_science8/13/2019 Intro to GRP and Hand Laid-Up GRP Moulding-PNS JAUHAR
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In practice, buckling is characterized by a suddenfailure of a structural member subjected to
high compressive stress, where the actual
compressive stress at the point of failure is less than
the ultimate compressive stresses that the material iscapable of withstanding.
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TOOTH PITCH
http://en.wikipedia.org/wiki/Stress_(mechanics)http://en.wikipedia.org/wiki/Stress_(mechanics)http://en.wikipedia.org/wiki/Stress_(mechanics)http://en.wikipedia.org/wiki/Stress_(mechanics)8/13/2019 Intro to GRP and Hand Laid-Up GRP Moulding-PNS JAUHAR
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The distance between one tooth tip and the next
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MOULDING OPERATION - PICS
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Application of Honey Wax
MOULDING OPERATION - PICS
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Application of GelCoat
MOULDING OPERATION - PICS
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Application of Surfacing Tissue
MOULDING OPERATION - PICS
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Application of CSM
MOULDING OPERATION - PICS
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Application of Woven Roving
MOULDING OPERATION - PICS
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Application of Woven Roving
MOULDING OPERATION - PICS
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Application of CSM and Dislaminating Cloth
MOULDING OPERATION - PICS
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Sheet Release
MOULDING TOOLS
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GEL-COAT DEFECTS
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SURFACE FIBRE PATTERN Causes
Gel-coat not cured sufficiently before commencing
lay-up
Gel-coat too thin
Remedy
Ensure adequate cure of gel-coat
Ensure gel-coat minimum thickness of 0.3mm
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GEL-COAT DEFECTS
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STAR CRACKING Causes
Result of an over thick gel-coatoccurs when
laminate has received a reverse impact
Remedy
Ensure gel-coat no thicker than 0.5mm
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GEL-COAT DEFECTS
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CRAZING Causes
Gel-coat too thick
Use a brittle resin or resin containing excess monomer
Excessive accelerator in formulation or curing temperaturetoo high (Sometimes gives orangepeeleffect)
Remedy
Use even thickness gel-coat
Use properly formulated gel-coat resin Avoid high temperatures
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GEL-COAT DEFECTS
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PIN HOLES IN GEL-COAT
Causes
Gel-coat not wetting release agent on mould
Minute air bubbles in the surface of the laminate. Caused by poor mixing of fillerinto thixotropic gel-coat and/or overbrushing of gel-coat when applied to mould
Occluded air in the filler used in resin formulation
Dust particles in the parting agent or the gel-coat
Remedy
Use non-silicone wax on mould surface followed by a PVA release agent
Mix resin by mechanical means. Apply resin carefully using minimum brushworkconsistent with uniform resin coverage
Use only fillers which have been treated for use with polyester or epoxy resin asappropriate
Mould under clean conditions. Ensure that dust cannot fall on mould beforeapplication of gel-coat
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GEL-COAT DEFECTS
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CRATERING AND BLISTERING Causes
Usually caused by air or solvent trapped between gel-coat andlaminate proper. If reinforcement is carefully rolled down thisdefect should not occur
If parting agent not thoroughly dry, volatiles will cause lifting ofgel-coat
Remedy
Check resin:glass ratio; a deficiency of resin often causes air
bubbles. Check the grade of any glass mat used. If the binder isinsoluble in the resin the fibre will not bed down. Ensure thatparting agent is thoroughly dry before applying gel-coat
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GEL-COAT DEFECTS
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WRINKLING OF SURFACE Causes
Too thin a gel-coat which is under cured. Often on verticalsurfaces
Under cure as a result of styrene (or other monomer)evaporation
Remedy
Prevent drainage of gel-coat by ensuring adequate amountof thixotropic agent in formulation
Ensure that there are no draughts in vicinity of themoulding
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GENERAL DEFECTS AND
ACCEPTANCE CRITERIA
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GEL-COAT
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Fault Cause Remedy
Surface Fibre Pattern
Gel-coat not cured
sufficiently before
commencing lay-up
Ensure adequate cure of
gel-coat
Gel-coat too thin Ensure gel-coat minimumthickness of 0.3mm
Distortion or Warping
Differential shrinkage
between unreinforced
gel-coat and reinforced
laminate
Use a reinforced gel-coat
Use thin gel-coat
Use a specially formulated
gel-coat resin
Star Cracking
Result of an over thickgel-coatoccurs when
laminate has received a
reverse impact
Ensure gel-coat no thicker
than 0.5mm
MOULDING OPERATION
8/13/2019
Recommended