intro to grp and hand laid-up grp moulding-pns jauhar

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


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


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


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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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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CHOPPED STRAND MAT (CSM)


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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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Woven Roving (WR)

Woven rovings for use with polyester resins are to

comply with BS 3749 or NES 166

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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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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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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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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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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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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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CORRECT WAY WRONG WAY


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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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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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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


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


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


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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

MATERIALS

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A Guide to Methods for Production of

Hand Laid-Up GRP Mouldings 73

FINISHING OPERATIONS


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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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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


up GRP Moulding


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S G O O S


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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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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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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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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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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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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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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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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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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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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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88/187


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

15-Feb-14 88


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SCHEME OF LESSON


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SCHEME OF LESSON

MATERIALS

15-Feb-14



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


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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


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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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GRP Moulding 93

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

15-Feb-14


GRP Moulding 94

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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GRP Moulding 95


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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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GRP Moulding 97

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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GRP Moulding 98

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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GRP Moulding 99

CORE MATERIALS


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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

15-Feb-14


GRP Moulding 100

CORE MATERIALS


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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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GRP Moulding 101


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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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GRP Moulding 103

CORE MATERIALS


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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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GRP Moulding 104

SCHEME OF LESSON


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SCHEME OF LESSON

MATERIALS

15-Feb-14



HANDLING/TRANSPORTATION

OF FINISHED MOULDINGS



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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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GRP Moulding 106



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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

15-Feb-14


GRP Moulding 107



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TRANSPORTATION

Loads imposed by transportation should be

considered and temporary supports provided if

necessary

Moulding should be secured to avoid its movement

during transportation

15-Feb-14


GRP Moulding 108


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110/187

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

15-Feb-14


GRP Moulding 111


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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

15-Feb-14


GRP Moulding 113

HEALTH AND SAFETY


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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

15-Feb-14


GRP Moulding 114

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)

15-Feb-14


GRP Moulding 115

HEALTH AND SAFETY


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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

15-Feb-14


GRP Moulding 116

SCHEME OF LESSON


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SCHEME OF LESSON

MATERIALS

15-Feb-14



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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GRP Moulding 119

INSPECTION METHODS

CURED LAMINATES


120/187

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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GRP Moulding 120

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

15-Feb-14


GRP Moulding 121

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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GRP Moulding 122

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

15-Feb-14


GRP Moulding 123

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

15-Feb-14


GRP Moulding 124

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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GRP Moulding 125

GEL-COAT DEFECTS


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15-Feb-14


GRP Moulding 126

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


127/187

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


128/187

15-Feb-14


GRP Moulding 128

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


129/187

CRAZINGCrazing usually indicates a gelcoat which is too thick

and has crazed during flexing of the hull


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GEL-COAT DEFECTS


130/187

15-Feb-14


GRP Moulding 130

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


131/187

PIN HOLES IN GEL-COATSmall air bubbles trapped during the cure show up on

release


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GEL-COAT DEFECTS


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GEL-COAT

15-Feb-14


GRP Moulding 132

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


133/187

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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15-Feb-14


GRP Moulding 134

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


135/187

WRINKLING OF SURFACEThis is caused by the heat released by the following

laminate immediately attacking an under cured thin

gelcoat


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GEL-COAT DEFECTS


136/187

15-Feb-14


GRP Moulding 136

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


137/187

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


139/187

INTERNAL DRY PATCHESAreas where resin has not penetrated


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GEL-COAT DEFECTS


140/187

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

15-Feb-14


GRP Moulding 141

ACCEPTANCE CRITERIA


142/187

GEL-COAT Small areas up to 1200mm2 exhibiting defects

shown on previous slides are acceptable except in

case of radomes and sonar domes

15-Feb-14


GRP Moulding 142


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LAMINATE DEFECTS


144/187

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

15-Feb-14


GRP Moulding 144

LAMINATE DEFECTS


145/187

15-Feb-14


GRP Moulding 145

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


146/187

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

15-Feb-14


GRP Moulding 146

LAMINATE DEFECTS


147/187

15-Feb-14


GRP Moulding 147

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


148/187

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

15-Feb-14


GRP Moulding 148

LAMINATE DEFECTS


149/187

DELAMINATED AREAS WITHIN BODY OFLAMINATE

15-Feb-14


GRP Moulding 149

LAMINATE DEFECTS


150/187

LAMINATE FAULTS AND CAUSES

15-Feb-14


GRP Moulding 150

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


151/187

LAMINATE FAULTS AND CAUSES

15-Feb-14


GRP Moulding 151

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


152/187

LAMINATE DEFECTS


153/187

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

15-Feb-14


GRP Moulding 153

LAMINATE DEFECTS


154/187

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)

15-Feb-14


GRP Moulding 154

LAMINATE DEFECTS


155/187

15-Feb-14


GRP Moulding 155

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


156/187

15-Feb-14


GRP Moulding 156

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


157/187

EXTRA SLIDES


158/187

LINKS


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SPUN YARN


159/187

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

15-Feb-14 159


GRP Moulding

By Lt Cdr M Hasan Adil PN

CRIMP


160/187

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

15-Feb-14


GRP Moulding 160

SATIN WEAVE
http://en.wikipedia.org/wiki/File:Warp_and_weft.jpg


161/187

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

15-Feb-14


GRP Moulding 161

NOTCH TOUGHNESS


162/187

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.

15-Feb-14


GRP Moulding 162

CREEP & ABRASION


163/187

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

15-Feb-14


GRP Moulding 163

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_science


164/187

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.

15-Feb-14


GRP Moulding 164

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)


165/187

The distance between one tooth tip and the next


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MOULDING OPERATION - PICS


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Application of Honey Wax



167/187


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Application of GelCoat



168/187


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Application of Surfacing Tissue



169/187


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Application of CSM



170/187


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Application of Woven Roving



171/187


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Application of Woven Roving



172/187


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Application of CSM and Dislaminating Cloth



173/187


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Sheet Release

MOULDING TOOLS


174/187


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GEL-COAT DEFECTS


175/187

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

15-Feb-14


GRP Moulding 175

GEL-COAT DEFECTS


176/187

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

15-Feb-14


GRP Moulding 176

GEL-COAT DEFECTS


177/187

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

15-Feb-14


GRP Moulding 177

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

intro to grp and hand laid-up grp moulding-pns jauhar

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