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UNIT

III

MANUFACTURING OF ADVANCED

COMPOSITES


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CONTENTSMANUFACTURINGOFCOMPOSITES

Preparation of moulding compounds

Prepregs

Hand lay up methodAutoclave method

Filament winding method

Compression moulding

Reaction Injection moulding


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PREPARATIONOFMOULDINGCOMPOUNDS

High polymer material is mixed with 4 to 10

ingredients each of which discharges a useful

function during moulding or impart some usefulproperty to the finished artifact


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TYPESOFMOULDINGCOMPOUNDING

INGREDIENTS

1.Resin

2.Plasticizer

3.Fillers 4.Lubricants

5.Catalyst Or Accelerators

6.Stabilizers 7.Colouring Materials


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TYPESOFMOULDINGCOMPOUNDINGINGREDIENTS-

1.RESIN

It is a binder which holds different constituents together

Resin in the most specific use of the term is ahydrocarbon secretion of many plants, particularlyconiferous trees.

Resins are valued for their chemical properties andassociated uses, such as the production of varnishes,adhesives and food glazing agents


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1.RESIN

Synthetic resins are viscous liquids that are

capable of hardening permanently.

Otherwise, chemically they are very different from

the various resinous compounds secreted by

plants


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1.RESIN-EXAMPLES

Acrylate Resin

Acrylic

Acrylic Resin

Polyethylene

Phenolic, Phenolic Resin

Phenoplast

Epoxy Glue

Epoxy Resin

Melamine Resin

Polyvinyl Resin

Vinyl Polymer

Vinyl Resin


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1.RESIN

Some are thermosetting plastics in which the term

"resin" is loosely applied to the reactant or product,

or both. "Resin" may be applied to one of two

monomers in a copolymer (the other being called a

"hardener", as in epoxy resins).

For those thermosetting plastics which require only

one monomer, the monomer compound is the

"resin.


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1.RESIN


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TYPESOFMOULDINGCOMPOUNDINGINGREDIENTS

2.PLASTICIZERS

Plasticizers are materials that are added to resinsto increase their plasticity and flexibility

They neutralise the part of the intermolecular forces

of attraction between macromolecules of resins

They impart a greater freedom of movementbetween the polymeric macro molecules of resin

there by increasing the flexibility and plasticity of

the compound material.


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2.PLASTICIZERS

Phthalate esters areplasticizers used in polyvinyl chloride(PVC) to soften the hard PVC by

lubricating the areas between

polymer strands so that it can be

used in consumer products like

inflatable pools and food packaging.

Almost 90% of the market for plasticizer is for PVC, giving this

material improved flexibility and durability.

Plasticizers work by embedding themselves between the chains of

polymers, spacing them apart (increasing the "free volume"), and

thus significantly lowering the glass transition temperature for the

plastic and making it softer.


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2.PLASTICIZERS

Plasticizers evaporate and tend to concentrate in

an enclosed space; the "new car smell" is caused

mostly by plasticizers evaporating from the car

interior.


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3.FILLERS

Fillers are added to give the final plastic better

hardness , tensile strength , finish and workability.

Advantages :

Reduces cost

Reduces shrinkage

Reduces brittleness

Examples :

Carborundum,Quartz,Mica to provide extra hardness

Barium salts to make plastic impervious to X-rays

Addition of asbestos provides heat and corrosion

resistance .


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4.LUBRICANTS

Added to make moulding of plastic easier.

To impart a flawless , glossy finish to the products .

Prevents plastic material from sticking to the

fabricating equipment. Eg: Waxes , Oils , soaps etc


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5.CATALYSTSORACCELERATORS

Are added only in case of thermosetting plastics.

Accelerates the polymerization of fusible resin

during moulding operation into crosslinked infusibleform .

Eg: Hydrogen peroxide

Acetyle sulphuric acidBenzoyl peroxide


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6. STABILIZERS

Improve thermal stability during processing

Eg :

Vinyl chloride

UV light stabilizers are used frequently in plastics,

including cosmetics and films.

The primary function is to protect the substancefrom the long-term degradation effects from light,

most frequently ultraviolet light.


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7.COLOURINGMATERIAL

Used in high polymer artifacts

Eg: Organic dystuffs

Opaque inorganic pigments


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Carbon fiber epoxy

rein prepreg


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PREPREGS

Prepreg is the industry term for high quality

reinforced fibers , which are preimpregnated with aresin system and partially cured to B-stage.

B-stage is an intermediate cure stage of a thermosetting

resin that lies between the completely uncured stageand a completely cured stage.

Ready to mold or cure material in sheet form which

may be tow , tape , cloth or mat impregnated withresin.


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ADVANTAGES

Consistent quality and consistent resin to

reinforcement ratio

Few rejections

Less variance in mechanical properties .

Finest quality material.

Reduce the handling damage to dry fibers. Increased curing pressure reduces voids and

improves fiber wetting


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PREPREGS

A prepreg consists of a reinforcement material

preimpregnated with a resin matrix in controlled

quantities.

The resin is partially cured to a B-stage, and in this

form is supplied to the fabricator, who lays up the

finished part and completes the cure with heat and

pressure.

The required heat and pressure will vary with the

resin system and the intended application.


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PREPREGS


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METHODSOFPRODUCINGPREPREG

1.Solvent Solution Pre-impregnation Process orSolution Coating

2.Hot Melt Pre Impregnation Procedure.

Solution coating saturates the reinforcement with resindissolved in carrier solvent.

Hot melt coating uses heat and pressure to impregnatethe fibers with resin.

The prepreg is typically laid against the paper orpolyethylene film separator called interleaf so that thepreperg dont stick on to itself and is wound around acore.


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1.SOLVENT SOLUTION PRE-IMPREGNATION

PROCESS

Woven fabric or fiber yarn is passed through a resin

rich solution .

Prepreg is then dried to remove the solvent

Excess resin is then removed via doctor blade ormetering rolls

Then the product is staged to the cold stable

prepreg form (B-Stage )


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1.SOLVENT SOLUTION PRE-IMPREGNATION PROCESS


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HOT MELT PREIMPREGNATION PROCEDURE

It replaces solvent method because of

environmental concerns and a need to exert bettercontrol over the amount of resin on the fiber .

Issues with Solvent method :

Stringent Air emission control regulations and liabilities .

High cost of maintaining solution ovens .


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In this process woven fabric or fiber yarn is passed

over a series of rollers .

The molten polymeric resin wets the fibers and then

the resin impregnated sheet of fibers is compacted

over a sheet of release paper and subsequently

wrapped on rolls for storage .


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At the hot melting machine , the fibers go through a

metered comb to maintain their parallel integrity for evenspreading , and are laid on a release film containing a

controlled amount of resin .

Another role of release film , either dry or film coated , ispositioned above the fibers.

The fibers sandwiched between the films are pulled along

the tape line with pull rollers as pressure is applied fromsets of heated compaction rolls metered to the prepreg

thickness


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The compaction ensures that the fibers are evenly spreadapart and wet out .

Once through the heated compaction area , the sandwichtypically passes through cooling rolls before the carrierpaper is removed.

Great care is taken to control the temperature

Trimming is done at both sides of the prepreg to exact

width is down just before rewinding

At the end of the tapeline , windup rolls remove one layerof carrier film and reroll it for disposal.


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PREPREGCLASSIFICATION

1.Bleed System

2.No Bleed or Net Resin Content System


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BLEEDSYSTEM

The bleed system Prepregs are those, which

contain excess matrix that is bled off during the

cure cycle by the use ofBLEEDER PILES.

Bleeder piles are the layers of fiber glass cloth or other

highly absorbent material


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NOBLEEDSYSTEM

Curing of prepreg takes place underheat and

pressure

Bleeder piles are generally not required for no

bleeding system

P


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DISADVANTAGESOF PREPREGS

Shelf Life Since the epoxy is in a B-stage, it is required to be

stored either refrigerated or frozen prior to use.

Additionally, the overall shelf life can be low.


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DISADVANTAGESOF PREPREGS

Cost Prohibitive

When manufacturing composites through a process

such as vacuum infusion, the raw fiber and resin are

combined on site.

However, when using prepregs, the raw material mustfirst be prepregged. This is most often done off-site at a

specialized company that focuses on prepregs. This

added step in the manufacturing chain can add

increased cost, and in some instances close to double

the material cost.


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3.HAND LAYUP METHOD


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WET/HANDLAYUPMETHOD

Hand Lay-Up is well suited for low volume

production of product.

This method can be used for both corrosion barrier

and the structural portion.


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WET/HANDLAYUPMETHOD


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WET/HANDLAYUPMETHOD

A mold must be used for hand lay-up parts unless

the composite is to be joined directly to another

structure.

The mold can be as simple as a flat sheet or have

infinite curves and edges.

For some shapes, molds must be joined in

sections so they can be taken apart for part

removal after curing.


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WET/HANDLAYUPMETHOD

Reinforcement fibers can be cut and laid in the

mold.

It is up to the designer to organize the type, amount and

direction of the fibers being used.

Resin must then be catalyzed and added to thefibers.

A brush or roller can be used to impregnate the

fibers with the resin.

The lay-up technician is responsible for controlling theamount of resin and the quality of saturation.


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MATERIALSUSEDFORHANDLAYUP

Resins:

Any, e.g. epoxy, polyester, vinylester,

phenolic.

Fibres:

Any, although heavy aramid fabrics can

be hard to wet-out by hand.


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HAND LAYUPMETHOD ADVANTAGES

Advantages:

i) Widely used for many years.

ii) Simple principles to teach.

iii) Low cost tooling, if room-temperature cure resins

are used.

iv) Wide choice of suppliers and material types.

v) Higher fibre contents, and longer fibers than with

spray lay-up.

Hand Lay Up Method


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Figure 15.4 Hand lay-up : (1) mold is treated with mold release agent; (2) thin gel coat

(resin) is applied, to the outside surface of molding; (3) when gel coat has partially

set, layers of resin and fiber are applied, the fiber is in the form of mat or cloth;

each layer is rolled to impregnate the fiber with resin and remove air; (4) part is

cured; (5) fully hardened part is removed from mold.

Hand Lay-Up Method


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HAND LAY-UP METHOD


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HANDLAYUP METHOD - DISADVANTAGES

Resin mixing, laminate resin contents, and laminate

quality are very Dependent On The Skills of laminators.

Low resin content laminates cannot usually be achieved

without the incorporation of excessive quantities of

voids.

ii) Health and safety considerations of resins. The lower

molecular weights of hand lay-up resins generally

means that they have the potential to be more harmful

than higher molecular weight products. The lowerviscosity of the resins also means that they have an

increased tendency to penetrate clothing etc.


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HANDLAYUP METHOD - DISADVANTAGES

iii) Resins need to be low in viscosity to be

workable by hand. This generally compromises

their mechanical/thermal properties due to the need

for high diluents levels.


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TYPICAL APPLICATIONS

Standard wind-turbine blades

Production boats,

Architectural moldings


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PRODUCTS MADEBY HAND LAY-UP

Generally large in size but low in productionquantity - not economical for high production

Applications:

Boat hulls

Swimming pools Large container tanks

Movie and stage props

Other formed sheets

The largest molding ever made was ship hulls forthe British Royal Navy: 85 m (280 ft) long


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FILAMENTWINDINGPROCESS


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Filament winding is automated processes for

creating parts of simple geometry wherein

continuous resin impregnated fibres are wound

over a rotating male tool called mandrel.

Filament winding process


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FILAMENT WINDING

Resin impregnated continuous fibers are wrapped around arotating mandrel that has the internal shape of the desired

FRP product; the resin is then cured and the mandrel

removed.

The fiber rovings are pulled through a resin bathimmediately before being wound in a helical pattern onto

the mandrel.

The operation is repeated to form additional layers, each

having a criss-cross pattern with the previous, until thedesired part thickness has been obtained.


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Figure 15.8 Filament winding.

Filament Winding


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TYPESOF FILAMENTWINDINGPROCESS

(i) The Polar Or Planer Method

(ii) The High Helical Pattern Winding.


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THEPOLARORPLANERMETHOD

A winding in which the filament path passes tangentto the polar opening at one end of the chamber andtangent to the opposite side of the polar opening atthe other end.

The polar or planer method of winding utilizes afixed mandrel and a shuttle that revolves aroundthe longitudinal axis of the part to form longitudinalwinding patterns.

This type of winding is used if the longitudinal fibresare required with angle less than 25 to the mandrelaxis.


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THEPOLARORPLANERMETHOD

HELICAL WINDING PROCESS


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HELICALWINDING PROCESS

A winding in which the filament or band advances

along a helical path, not necessarily at a constant

angle except in the case of a cylindrical article.Inthe high helical pattern winding, the mandrel rotates

while the shuttle transverses back and forth. Both

the mandrel rotation and shuttle movement are in

the horizontal plane. By controlling the mandrel

rotation and shuttle speed, the fibre angle can be

controlled.

.


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HELICALWINDINGPROCESS

Angles of 25-85 to the mandrel rotation axis are

possible


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After completion of the winding, the filament wound

structure is cured at room temperature or in an

oven.

The mandrel is removed after the curing. The

mandrel, which determines accurate internal

geometry for the component, is generally the only

major tool.


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Low cost mandrel materials such as cardboard orwood can be used for winding low cost routine

parts. For critical parts requiring close tolerances,

expensive mandrels designed for long term use

may be required.

For high temperature cure 315C (600F), graphite

mandrels with low thermal expansion may be

advantageous. However, attention should be paidfor potential difficulties for mandrel removal.


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TYPESOFMANDRELS

Mandrels are eitherREMOVABLE or NON-REMOVABLE.

Removable mandrels are classified according to

the removal techniques as:

Entirely removed.

Collapsible.

Breakable or soluble.


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THESELECTIONOFMANDREL

1. Part size and complexity

2. Size of openings

3. Resin system and its curing

4. The number of components to be

fabricated.


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THEREQUIREMENTSFORAMANDREL

It must be stiff and strong enough to support

its own weight and the weight of the applied

composite while resisting the fibre tension

pressure from winding and curing.

It must be dimensionally stable and should

have thermal coefficient of expansion greater

than the transverse coefficient of thecomposite structure.


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MATERIALSUSEDFORCONSTRUCTIONOF

MANDREL.

Low melting temperature alloys used for smalldiameter applications.

Sand, soluble plaster and eutectic salts used for

irregular shapes.

Inflatable material used in applications where

sometimes the mandrel remains a part of the structure.

Segmented metal used for high production rates, and

where the mandrel can be withdrawn through a small

hole in the part.


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This process utilises large tonnage presses whereinthe part is cured between two matched steel dies

under pressure and high temperature. The moving

platen is heated either by steam or electricity to

promote thermal curing.


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Curing of the part is affected by the followingfactors:

Size of platen, which determines the length and width of

the part, which can be cured.

Total tonnage of the press, which determines the

pressure to be exerted on the projected surface area of

the part.


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After placing the laminate to be cured called the'charge' in the core of the mold, the cavity is then

closed at a rate of usually 4-12 mm/sec.

In most cases the mold is heated to 150C (302F),which causes the charge viscosity to be reduced.

With increasing mold pressure as the mold is

closed, the charge flows towards the cavityextremities, forcing air out of the cavity.


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The molding pressure based on projected part arearanges from 0.7 to 9 MPa (100 to 1200 psi).

Higher molding pressure causes sink marks, while

lower pressure cause scumming of the mold andporosity.


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The curing time is usually between 25sec to 3 minutes depending on several

factors including

resin-initiator-inhibitor reactivity

part thickness

component complexity

mold temperature.


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ADVANTAGEOFTHECOMPRESSIONMOLDING

The primary advantage of the compression moldingis its ability of producing large number of parts with

little dimensional variations

A wide variety of shapes, sizes and complexity can

be produced by compression molding.


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DRAWBACKS

High tooling cost

Need for large heated presses.

Thus, this method is not practical for low volume

production.

TYPES OF COMPRESSION MOULDING


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TYPES OF COMPRESSION MOULDING

PROCESSES

1.Sheet Moulding Compound. (SMC)

2.Bulk Moulding Compound. (BMC)

3.Wet system Compression Moulding.

4.Reinforced Thermoplastic Sheet Compression

Moulding.


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Sheet moulding compound (SMC) or sheet

moulding composite is a ready to mould fibre-

reinforced polyester material primarily used in

compression moulding.

The sheet is provided in rolls weighing up to

1000 kg.
http://en.wikipedia.org/wiki/Polyesterhttp://en.wikipedia.org/wiki/Compression_mouldinghttp://en.wikipedia.org/wiki/Compression_mouldinghttp://en.wikipedia.org/wiki/Compression_mouldinghttp://en.wikipedia.org/wiki/Compression_mouldinghttp://en.wikipedia.org/wiki/Polyester


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SHEET MOULDING COMPOUND(SMC)

It refers to both material and process for producingglass fiber reinforced polyester resin items .

SMC is a totally integrated compound in sheet form

that incorporates all reinforcements resin , chemicalthickness , fillers , mould release agents and other

ingredients .

Also includes pigments and shrink control agents


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SHEET MOULDING COMPOUND(SMC


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A SMC processing machine produces molding

compound in sheet form.

The glass fibre is added to a resin mixture that is

carried onto a plastic carrier film.

After partial cure, the carrier films are removed.

The sheet molding material is cut into lengths and

placed onto matched metal dies under heat and

pressure


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ADVANTAGESOF SMC MOLDINGPROCESS

High volume production.

Excellent part reproducibility.

Minimum material scrap.

Excellent design flexibility.

Parts consolidation.


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BMC is a combination of chopped glass strands and Resin

in the form of a bulk pre-preg.

BMC is suitable for either compression or injection

molding.

Injection molding of BMC is used to produce complex

components such as electrical equipment, car

components, housings for electrical appliances and tools,

in large industrial volumes.
http://composites.owenscorning.com/glossary.htmlhttp://owenscorning.com/composites/glossary.htmlhttp://owenscorning.com/composites/glossary.htmlhttp://owenscorning.com/composites/glossary.htmlhttp://owenscorning.com/composites/glossary.htmlhttp://composites.owenscorning.com/glossary.html


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BULKMOULDINGCOMPOUND


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Unlike SMC, it is not necessary to include amaturation stage. Consequently, BMC pre-preg

formulations contain higher filler contents.

The chopped glass strands vary in lengthdepending on the level of performance required.

Reinforcement content generally ranges between

15 and 20 percent; however, it may reach 25

percent for the highest performance. BMC uses a lower reinforcement content than SMC

and permits higher filler loadings with lower costs.

BULKMOULDINGCOMPOUND
http://owenscorning.com/composites/glossary.htmlhttp://owenscorning.com/composites/glossary.html


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APPLICATIONSOFBULKMOLDINGCOMPOUND

Pump housing

A/C components

Circuit Breakers

Computer components

Power Tools

Gear cases

Electrical insulators

WETSYSTEMCOMPRESSIONMOULDING


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Matrix ( Liquid Resin ) is pumped to dryreinforcement in press mounted and heated

matched metal moulds

Hydraulic pressure forces the liquid resin to flowthrough the reinforcement and hold the material in

place until cure is completed at the cure

temperature of 120C to 180C

WETSYSTEMCOMPRESSIONMOULDING


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The equipment used for WCM is same as the BMC.

Matrix material is thermosetting polyester vinylester

and epoxy , resins filled with inert materials such as

clay , calcium carbonate and alumina , catalyst andpigment to form a complete liquid system which

require only the addition of heat for curing

Reinforcement is chopped strand mats andcontinuous strand mats

REINFORCED THERMOPLASTIC SHEET


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REINFORCEDTHERMOPLASTICSHEET

COMPRESSIONMOULDING

Utilizes precombined sheet of thermoplastic resinand glass fiber reinforcement

These sheets are cut into blanks which are

preheated to a specified temperature and loded into

matched metal compression mould. Under pressure , heat softened blanks flow and fill

the mould.

The mould is maintained at a temperature which

causes the sheet to solidify and allows demouldingof the part



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Matrix :

Thermoplastic Resin , Polypropylene ,

thermoplastic polyester , polycarbonate and

nylon.

Reinfrocement :

Continous glass fiber mats


COMPRESSIONMOULDING


COMPRESSION MOULDING


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ADVANTAGES

Maximum design flexibility

Low capital cost

Tooling cost is low

Minimum material scrap

High volume production

COMPRESSIONMOULDING



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DISADVANTAGES

DISADVANTAGES

Operater skill dependent

Lower impact resistance

Only one molded surface is obtained

Longer curig times required


COMPRESSIONMOULDING


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APLICATION

Helmets

Automotive bumper

Radiator supports

Battery trays


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INJECTIONMOULDING

INJECTION MOULDING


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Injection molding is a manufacturing process forproducing parts from both thermoplastic and

thermosettingplastic materials.

INJECTIONMOULDING
http://en.wikipedia.org/wiki/Manufacturinghttp://en.wikipedia.org/wiki/Thermoplastichttp://en.wikipedia.org/wiki/Thermosettinghttp://en.wikipedia.org/wiki/Plastichttp://en.wikipedia.org/wiki/Plastichttp://en.wikipedia.org/wiki/Thermosettinghttp://en.wikipedia.org/wiki/Thermoplastichttp://en.wikipedia.org/wiki/Manufacturing


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Material is fed into a heated barrel,

mixed, and forced into a mold cavitywhere it cools and hardens to theconfiguration of the cavity.

INJECTIONMOULDING

INJECTION MOULDING


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INJECTIONMOULDING


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CLAMPING - the moving and

fixed platens of the injection

moulding machine holds the

mould tool together under

pressure.

INJECTION - the molten plastic

that has been melted from pellet

form in the barrel of the moulding

machine is injected under

pressure into the mould.

DWELLING - after the molten

plastic has been injected into the

mould pressure is applied toensure all cavities are filled.

COOLING - the plastic parts are

then allowed to solidify in the

mould.
http://www.rutlandplastics.co.uk/moulding_machine.shtmlhttp://www.rutlandplastics.co.uk/moulding_machine.shtmlhttp://www.rutlandplastics.co.uk/mould_tool.shtmlhttp://www.rutlandplastics.co.uk/moulding_machine.shtmlhttp://www.rutlandplastics.co.uk/moulding_machine.shtmlhttp://www.rutlandplastics.co.uk/mould_tool.shtmlhttp://www.rutlandplastics.co.uk/mould_tool.shtmlhttp://www.rutlandplastics.co.uk/moulding_machine.shtmlhttp://www.rutlandplastics.co.uk/moulding_machine.shtmlhttp://www.rutlandplastics.co.uk/mould_tool.shtmlhttp://www.rutlandplastics.co.uk/moulding_machine.shtmlhttp://www.rutlandplastics.co.uk/moulding_machine.shtml


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OPENING - the moving platen moves away from the fixed platen separating

the mould tool.

EJECTION - rods, a plate or air blast then aids ejection of the completed

plastic moulding from the injection mould tool.

The length of time from closing the mould to ejecting the finished plastic

moulding is the cycle
http://www.rutlandplastics.co.uk/mould_tool.shtmlhttp://www.rutlandplastics.co.uk/mould_tool.shtmlhttp://www.rutlandplastics.co.uk/mould_tool.shtmlhttp://www.rutlandplastics.co.uk/mould_tool.shtmlhttp://www.rutlandplastics.co.uk/mould_tool.shtmlhttp://www.rutlandplastics.co.uk/mould_tool.shtmlhttp://www.rutlandplastics.co.uk/mould_tool.shtml


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PROCESS CHARACTERISTICS

Utilizes a ram or screw-type plunger to force molten

plastic material into a mold cavity .

Produces a solid or open-ended shape that hasconformed to the contour of the mold.

It is ideal for producing high volumes of the same

object

I


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wire spools, packaging, bottle caps, automotive dashboards,

pocket combs,

, one-piece chairs and small tables,

storage containers,

mechanical parts (including gears),

and most other plastic products available today.

Injection molding is the most common method of

part manufacturing..[4].

INJECTIONMOULDING
http://en.wikipedia.org/wiki/Packaginghttp://en.wikipedia.org/wiki/Injection_moldinghttp://en.wikipedia.org/wiki/Injection_moldinghttp://en.wikipedia.org/wiki/Packaging


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ADVANTAGESOFINJECTIONMOLDING

high production rates

repeatable high tolerances

the ability to use a wide range of materials

low labor cost

minimal scrap losses

little need to finish parts after molding


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DISADVANTAGES

expensive equipment investment

potentially high running costs

the need to design moldable parts.

REACTIONINJECTIONMOLDING


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It is similar to injection moulding except thermosetting

polymers which requires a curing reaction to occur

within the mold.

The RIM Process involves a chemical reaction between

the two liquid components. Initially, the liquids are held

in separate, temperature-controlled feed tanks. The

chemicals are fed through supply lines to metering units

that precisely meter both chemicals, at high pressure, to

a mixhead device.

Reaction injection molding


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RIM parts are created through a process thatbegins when two liquid reactants - an Isocyanate

component and a Polyol resin mixture - are held in

separate tanks at an elevated temperature with

agitators.

These liquids are fed through supply lines at high

pressure to the mixhead.


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When the injection begins, valves open in themixhead and the liquids enter a chamber in the

mixhead at high pressures (usually between 1,500

and 3,000 psi) and high speeds.

Here they are mixed by high-velocityimpingement.

From the mix chamber, the mixed liquid flows into

the mold at atmospheric pressure and undergoes

an exothermic chemical reaction, forming a polymerin the mold.


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Reaction time is usually expressed in seconds. Forextremely large parts the reaction time can be

extended to allow for proper filling of the mold.


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ADVANTAGES

strong, flexible, lightweight parts which can easilybe painted.

The bi-component mixture injected into the mold

has a much lower viscosity than moltenthermoplastic polymers, therefore large, light-

weight, and thin-walled items can be successfully

RIM processed.

This thinner mixture also requires less clamping

forces, which leads to smaller equipment and

ultimately lowercapital expenditures.
http://en.wikipedia.org/wiki/Capital_expenditurehttp://en.wikipedia.org/wiki/Capital_expenditure


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The disadvantages are slow cycle times, comparedto injection molding, and expensive raw materials.

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