Material Technology

1 J3022 Material Technology 1

CHAPTER 6 : PLASTIC

6.0 Plastic

Plastic : An organic polymer material (with carbon and hydrogen

base) with the ability to flow into a desired shape when

heat and pressure are applied to it and retain the shape

when they are withdrawn

Polymer : A material consisting of long molecular chains or

networks of low-weight elements to form a single

compound

Thermoplastic Thermosetting Plastic Polycarbonate Phenol formaldehyde

Polysulfone Epoxy

Fluorocarbon Polyester

Nylon Amino Resin

Acetal Phenol formaldehyde

Acrylonitrile-Butadiene-Styrene Alkyds

Cellulosic

Polyethylene

Polystyrene

Polypropylene

Polyvinyl Chloride

Acrylic

6.1 The History of Plastic

1. Regnault (1835)

a France chemical scientist

introduce a chemical material called vinyl chloride monomer

transformed in white powder (polyvinyl chloride - PVC)

but not popular because of not enough raw materials at that

moment


2. Alexander Parkes (1855)

origin from Birmingham, England

won a bronze medal at the 1862 Great International Exhibition

in London

produced a hard but flexible transparent material, which he

called Parkesine from an organic material derived from

cellulose

claimed that this new material could do anything rubber was

capable of, but at a lower price

Parkesine soon lost its luster due to the high cost of the raw

materials needed in its production

3. John Wesley Hyatt (1866)

an American, finally came upon the solution with celluloid

produced billiard balls using celluloid as a substitute for

4. Leo Hendrik Baekeland (1907)

a Belgian-born American living in New York state

developed a liquid resin that he named Bakelite

6.2 Properties of Plastic

1. The general properties :

i. light ii. processable

iii. durable iv. resist corrosion v. colour stay

vi. translucent vii. transparent

viii. good electric insulator ix. good thermal insulator x. wear resistance

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6.3 Polimer 1. Polymer

a chemical substance made up of a lot of mer or repeating units or

molecules to form a long flexible chain

a material consisting of long molecular chains or networks of low-

weight elements to form a single compound

2. Polymerization

a process of linking the monomers together to form a polymer

a chemical reaction in which high-molecular-mass molecules are

formed from monomers

3. Monomer : a single molecule or a small molecule that may become

chemically bonded to other monomers to form a polymer.

4. Homopolymer : polymeric materials which consist of polymer

chains made up of single repeating units.

5. Copolymer : consist of polymer chains made up of two or more

chemically different repeating units which can be in different

sequences.

Linear polymer M – M – M – M

Alternating copolymer M – O – M – O – M – O

Random copolymer O – M – O – O – M – O – M

Block copolymer M – M – M – O – O – O – M

6. Amorphous (non-crystalline)

a substance having no specific space lattice, the molecules being

distributed at random

a structure not having the long range repetitive pattern of atoms

arrangement

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6.4 Polymer Structure

It is a long linkage structure.

The chains of molecules bonded by a weak force and flexible

causes the carbon bondage to move and rotating in the chains.

Polymer exists in two structures : amorphous (non-crystalline)

and semi-crystalline.

6.4.1 Amorphous Structure (non-crystalline)

At a high temperature, the polymer became a viscous liquid

where the chains moved and glide into one another in tangled

state.

The chains arrangement are randomize and not in certain

geometry pattern.

When the temperatures are reduced, the flexibility of molecule

properties is blocked and it is similar to the glassy state.

6.4.2 Semi-Crystalline Structure

With slow cooling, the molecules will have the certain structure.

Causing the molecule to packed together and increased the

forces between them, with higher strength, rigid and brittle.

The polymer formed with 90% in crystalline chains and the

remain in amorphous state.


6.5 Types of Polymer Chains

There are 4 types of molecule chains by polymerization process as

shown in the figure below :

i. Linear chain polymers

a. in the form of a long molecular chains

ii. Branched chain polymers

b. the linear chain with a series of branched

iii. Cross-linked chain polymers

c. with short links which connected the closer chains together

iv. Network chain polymers

d. molecular structure in 3 dimension networks

6.6 Polymerization Processes

1. Polymerization : a chemical reaction in which high-molecular-mass

molecules are formed from monomers.

2. Two types of polymerization process :

a. Addition Polymerization

chain reaction involves the straight-forward addition of

monomers of the same kind or of different kinds

it is occurs between molecules or monomers contains carbon

bonding when temperature, pressure and certain catalyst are

given

examples :

i. Polyester are formed from ethylene polymerization

ii. Polyvinyl Chloride (PVC)


b. Condensation Polymerization

step reaction involves between two monomers with the

elimination of a simple by product, such as water, hydrogen

chloride, etc

it is occurs when two monomer substances react together to

produce polymer and small molecules (usually water) will be

expelled

6.7 Differences between Thermoplastic and Thermosetting

The plastic are divided into 2 large groups :

a. Thermoplastics

- group of plastics that can be softened every time they are heated

- with no curing (chemical change) takes place during the

moulding operations

- they then can be reshaped

- e.g. Polyethylene, Nylon, PVC (Polyvinyl Chloride)

b. Thermosetting plastics

- group of plastics that only can be heated and formed only once

- undergo chemical change (curing) during moulding

- can never again be softened by heating

- e.g. Epoxy, Polyesters

6.8 Thermoplastic

Thermoplastic materials belong to the linear and branched

chain polymers that are obtained by addition or condensation

polymerization of monomers.

They can be softened, hardened or resoftened repeatedly by

application of heat.

Thermoplastics are solids at room temperature , melted or

softened by heating, placed into a mold and then cooled to give

the desired shape.


The monomer linear chains structure of thermoplastics :

M – M – M – M – M – M

M – M – M – M – M – M

M – M – M – M – M – M M is molecule or monomer

When heated, the chains will move separately and took place to a new

position and maintain to that position after the heat and pressure

removed.

The additives of thermoplastics :

1. Filler

i. wood flour, calcium carbonate, glass fiber, asbestos,

aluminium powder, mica granules

ii. to improve the impact strength and reduce shrinkage

during moulding

2. Plasticizers

i. to make plastics softer and more flexible

ii. to improve flow properties

iii. to reduce rigidity and brittleness

3. Lubricants

i. substance that reduces friction when applied as a surface

coating to moving parts to fix the processing and

flowability

4. Colourants

i. subdivided into dyestuffs, organic and inorganic pigments

ii. pigments more able to resist the temperature and lights

5. Antioxidants

i. prevent oxidation, the polymer reacting with oxygen

ii. oxidation can cause loss of impact strength, elongation,

surface cracks and discolouration

iii. antioxidants help prevent thermal oxidation reactions

when plastics are processed at high temperatures and

light-assisted oxidation when plastics are exposed to UV

light

iv. stabilizers


6.8.1 Properties of Thermoplastics

can be softened and hardened repeatedly by applying the

appropriate thermal and pressure

can be attached/ jointed using heat and pressure

not liquidify but flow at appropriate pressure and heat for injection

moulding

when blowed, acts like glasses, can be shape as bottles and round

by using pressure or vacuum technique

are linear chain polymers form by a long carbon chains through

covalent bonding


Thermoplastic Types Properties Application

1.Polyethylene /PE

a.melting temperature : 110C - 137C b. LDPE

low in crystalline

low in density c. HDPE

high in crystalline – chains are able to pack closer together

high in strength d. translucent e. costly f. tougher in room and lower temperature

g. good flexibility upto 73C h. corrosion resistance i. good insulator properties

i. textiles ii. loudspeaker cones

iii. recording tapes iv. photographic films v. containers

vi. electrical insulators vii. chemical tubes

viii. kitchen appliances

2. Polystyrene / PS

a. melting temperature : 150C - 243C b. odourless c. relatively brittle unless modified d. rigid e. processable but tends to be brittle f. good dimensional stability g. good insulating properties h. low-mold shrinkage i. easy processed j. low cost

i. automobile interior parts ii. kitchen appliances

iii. appliances housings iv. housewares v. lens

vi. battery housings vii. radios

3. Polyvinyl Chloride / PVC

a. melting point : 204C b. less elastic and flexible c. high in strength and brittle d. good solvents resistance e. higher chlorine contents : chemical and heat resistance, tougher and harder f. good electric current resistance g. stable and moisture resistance i. heat resistance j. low in cost because cheaper and processable

i. furnitures ii. shoes

iii. electrical wire insulations iv. floor mats v. housewares

vi. pipes vii. window frames

4. Polymethyl Methacrylate / PMMA/ Perspex/ Acrylic

a. melting point : 160C b. rigid c. cannot be opaque d. transparent e. impact resistance better than glass f. good chemical resistance g. good moisture resistance h. environment resistance i. electrical resistance

i. glazing for aircrafts and boats

ii. advertising signs iii. safety shields iv. protective goggles v. lenses

vi. automotive lenses vii. wind shields

viii. laboratory appliances


5.Polypropylene/PP

a. melting temperature : 165C - 177C

b. heat resistance upto 120C without deformation c. strong but flexible d. good chemical, moisture and heat resistance e. low density f. strong bonding g. dimensional stability

i. kitchen appliances ii. packaging

iii. laboratory wares iv. bottles v. electrical appliance parts

vi. television cabinets vii. insulators or wiring coats

6.Polyamides / PA/ Nylon

a. melting point

- Nylon 6, 6 : 250 - 266C

- Nylon 6 : 216 - 225C b. good resistance to most common

solvents c. strong, tough and flexible d. absorb moisture acts as a plasticizer e. low in stiffness, strength and hardness f. tend to fray easily g. have little resilience to shock loads h. high in heat-deflection temperatures i. good chemical resistance j. low melt viscosity k. easy processability

i. gears ii. valves

iii. bearings iv. cams v. surgical equipments

vi. fibers for textiles vii. fishing lines

viii. climbing ropes

7.Acetals

a. excellent long-term load-carrying properties

b. dimensional stability c. high regularity d. high strength e. high heat-deflection temperature f. low friction coefficients g. good processability h. good solvent resistance i. low moisture absorption j. wear resistance k. excellent fatigue resistance l. flammable m. stiff n. creep resistance o. moisture resistance

i. water pump impellers ii. electric kettle bodies

iii. housings for domestic appliances

iv. plumbing fittings v. bearings

vi. cams vii. gears

viii. door-lock components ix. zippers x. seat belts

xi. rollers xii. valves

8.Acrylonitrile-Butadiene-Styrene / ABS

a. high dimensional stability b. remains tough c. impact resistance d. abrasive resistance e. chemical resistance f. good tensile-strength properties g. good ductility properties h. electrical resistance i. flammable

i. moulding television and radio set cabinets

ii. telephone housings iii. bags iv. crash helmets v. pipes and fittings

vi. computer housings and covers


9.Cellulosic / Cellulose Acetate

a. rigid, strong and tough b. low resistance of weather, thermal and

chemical c. good insulator d. excellent water absorbent e. soften in boiling water f. dangerously flammable

i. automotive accessories ii. pipes and tubes

iii. telephone sets iv. tooth brushes v. spectacle frames

vi. screwdrivers and other small tools handles

vii. toys viii. table tennis balls

ix. ball pens

10.Polycarbonates / PC

a. good impact strength b. resist to a variety of chemicals c. resist to petroleum products and

most solvents d. good heat resistance e. good dimensional stability f. good electrical insulation properties g. good optical properties h. extremely tough i. higher scratch resistance j. good creep resistance

i. helmets ii. optic lenses

iii. bulletproof window glass iv. bottles v. food processing tools

vi. electrical insulators vii. safety shields

viii. medical appliances

11.Polysulfones / PSU

a. heat and chemical resistance b. transparent c. tough d. high tensile strength e. rigid f. heat-resistance g. low tendency to creep

i. steam iron components ii. coffee mixtures

iii. hot water contennas iv. sterilize medical

instruments v. microwave containers

vi. television components vii. airplane cabin interiors

12. Fluorocarbons / Polytetrafluoroethylene (PTFE)

a. heat resistance b. chemical attack resistance c. weather and electrical resistance d. non-stickiness e. good electrical insulator f. lowest coefficient of friction

i. lining for chemical equipment

ii. non-stick coating for cooking utensils

iii. electric insulators for wires and cables

iv. bearings v. gaskets


6.9 Thermosetting Plastic

Thermosetting materials belong to the three-dimensional cross-

linked or network polymers.

Once they have been set and hardened, they cannot be remelted

and returned to their original state (cannot be recycled or reused)

The three-dimensional cross-linked structure :

M – M – M – M – M

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M – M – M – M – M

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M – M – M – M – M

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M – M – M – M – M

Stronger material and insoluble to the solvents because

impossible for the solvents to enter and breaks the chains.

6.9.1 General Properties of Thermosets

melted material when the first time heated and then settled or

preserved into hard and rigid shape at that temperature

after the first formation, no changes will happen eventhough

heat and pressure applied

usually harder, stronger and more brittle than thermoplastic


Thermosetting Plastic Types Properties Application

1.Phenol Formaldehyde / PF/ Phenolic

a. good electrical resistance b. heat insulating properties c. good oil and grease resistance

d. stable upto 150C e. high hardness and strength f. good heat and water resistance g. can be coloured h. low in cost

i. heat resistance upto 500F j. soluble for chemical and weak acid k. stable shape l. low moisture absorbent and

beneficial for design accuracy m. brittle but rigid

i. telephones ii. plastic components in

automotives iii. electrical insulator

components iv. laminating some types

of plywoods and particleboards

v. bottle caps vi. house appliances

vii. steerings

2.Epoxy / EP

a. good chemical resistance b. strong, firm and good stickiness to

glass and metal c. wear and impact resistance

accordingly to material and mould used

d. good mechanical and electrical properties

e. dimensional stability f. thermal resistance

i. casting materials ii. mouldings

iii. protection to electric conductor parts

iv. paint additives v. stickers

vi. lamination materials production

vii. printing works viii. tanks

ix. shafts

3.Polyester

a. heat resistance (weather) b. acid or salt solubility resistance c. strong and hard depends to material

used d. coating works through electricity

e. heating temperature less than 500F

i. plastic components in automobile

ii. helmets iii. chairs iv. fans v. house pumps

vi. fuses vii. bottle caps

4.Amino Resins (Ureas and Melamines)

a. highly rigid at the ends of the molecule

b. scratch resistance c. as polishing layer or coating d. glossy resistance e. resist liquid, gasoline, oil and other

detergents

f. thermal resistance between 60F -

180F g. hardly damage or softer h. stronger i. electrical properties

i. Urea : cover switches, buttons, electrical appliances

ii. Melamine : door knob, machine equipments and as adhesive for plywood industry and the wood particleboard as bonding

iii. Amino (Melamine and Urea) : surface coating for papers and fabrics or frames


5.Alkyds a. excellent electrical insulation b. good impact force resistance c. dimensional stability d. unaffected by water and most

organic solvents

i. electric and electronic components


6.10 The Advantages Of Plastics

1. Excellent electrical insulation properties.

2. Good insulation properties.

3. Certain plastics has good chemical resistance.

4. Good resistance to shock and vibration.

5. Transparent and translucent.

6. Easily coloured.

7. Easily assembled or jointed.

8. Repairing the self lubricating.

9. Good wear and scratch resistance.

6.11 The Disadvantages Of Plastics

1. Measurement dimension changed by humidity and high thermal

extension.

2. Low temperature duration for operation (150 - 600F).

3. Brittle at low temperature.

4. Softer and less elastic than metal.

5. Certain plastics are easily affected by ultra-violet.

6. Creeps occurs at any temperature.

7. Easily burnt.

6.12 Factors For Plastics Usages

1. Processable and assembleability compared to metals

e.g. plastic moulding production

- do not need any finishing or tidying process

2. Plastics materials are cheaper than metals

e.g. nylon replacing zinc

3. Plastic properties

e.g. insulation, self lubrication, etc

4. Plastic-metal composites can be produced to achieve better properties

e.g. plastic-metal reinforcement are good electrical conductors,

lightness and easily produced

5. Multiple functions in the same time

e.g. housing or covers, insulators and self lubricating bearing


6.13 Plastic Manufacturing Process

In plastic products manufacturing process, varies of machines used

depends upon the shape products and types of resins used.

Such as :

1. Injection Moulding Process

2. Extrusion Moulding Process

3. Blow Moulding Process

4. Transfer Moulding Process

5. Compression Moulding Process

6. Rotational Moulding Process

7. Thermoforming Process

9. Calendaring Process

10.Casting Process

Injection Moulding Process

1. The basic concept of injection moulding machine is a heat-softened

thermoplastic material is forced by a screw-drive cylinder into a

relatively cool mould cavity that gives the plastic the desired shape.

2. The mould usually made from tool steels or beryllium cuprum and

can be multiple cavities so that more than one component can be

injected in every cycle of process.

3. It was the fastest process and widely used.

4. Figure 5 shows the typical components of injection moulding

machine.


5. Work principles :

i. the raw material (resins or pellets) are inserted into the

hopper

ii. under gravity manipulating, the resins enter the injection

channel which surrounded by heater

iii. certain temperature applied depends upon types of material

used, usually around 75C - 95C for smaller products and

120C - 260C for larger products

iv. when the resins becomes softer, it will be injected using

weither the reciprocating-screw or torpedo plunger

v. the softened plastics will be enter directly to the nozzle and

enters the mould cavity

vi. to ensure the mould was fully injected, pressure between

35MPa to 40 MPa are used

vii. the product will be solidify in the mould cavity under water

cooling cycle through the mould

viii. after that, the injector will be pulled back, the mould then

opened and the products will be retrieved from the mould

ix. the connecting opener will retrieved the product where the

ejector pins will ejected the product from the mould


6. The advantages :

i. the injector mould usage are faster than pressure mould (torpedo

plunger)

ii. mould cost are lower because of the simplicity

iii. various shape, intricate or thinner products can be produced

iv. high quality parts can be produced at a high production rate

v. the process has relatively low labour costs

vi. good surface finishes can be produced on the moulded part

vii. the process can be highly automated.

7. The disadvantages:

i. sink = caused by moulding temperature or the pressure are higher

ii. flashing = caused by unfitted mould

iii. bubble = caused by cold mould or the pressure are too low

iv. uncompleted moulding = the material did not enter the mould fully,

example : small gates

v. weld line = caused by cold mould, low moulding temperature and

time for injection are too fast

vi. not economical for small production

vii. certain mould only for certain product

viii. high cost of machine means that a large volume of parts must be

made to pay for the machine

ix. the process must be closely controlled to produce a quality

products.

Extrusion Moulding Process

1. A process that supplies a continuous stream of thermoplastic

material/ products with equally cross-section where it is directly

produced through a shaping tool or to some other subsequent

shaping process (dies) placed directly on the end of the extrusion

machine.



i. the pellets or resins are inserted into the hopper

ii. the material then fed into the heated cylinder by rotating screw

iii. when the material become softer, it will be forced continuously

by the rotating the screw ram

iv. the products or outcomes are formed into continuous shape

v. after the product exiting from the die, it will be cooled by air (air-

blast system), water (water-bath system) or become cold by

interact will cold roll surface where then it will be solidifies while

rolling

vi. extruded products such as pipe, rod, etc, extrude this way

because it can be curved or bended after extruded with hot water

by sinking it in it

3. The advantages :

i. continuous extrusion

ii. accurate measurement

iii. good finishing

iv. economical for mass production

4. The disadvantages :

i. the dies are easily wear out

ii. need to be closely controlled

iii. thermosetting materials are not suitable because it solidifies

quickly


Blow Moulding Process

1. It is suited for the manufacture of bottles and other simple hollow

shaped parts, from a preformed plastic tube.

2. It is a process producing thermoplastic products using injection or

extrusion method where the material are softened will be injected or

extruded into the mould and then blowed with air.

3. It is a cylinder or tube of heated plastic called a parison is placed

between the moulds. The mould is closed to pinch off the ends of the

cylinder and compressed air is blown in, forcing the plastic against

the walls of the mould.

4. Work principles for extrusion blow moulding method :

i. the resins or pellets are inserted into the hopper

ii. with gravity manipulating, the materials enter the injection or

extrusion chamber or cylinder which surrounded with heater

iii. when the materials become softened (plasticizers), it will be

injected or extruded using screw rotator or torpedo plunger

iv. the hot and softened material called parison

v. the materials will be flow straight to the nozzle and enter the

mould cavity

vi. top of the parison will be cutted off using a blade

vii. the air then blowed into the parison through a cavity at the top

of the mould

viii. the plastic will be cooled, then solidified in the mould under

water cooling system cycling in the channels in the mould

ix. after that the mould will opened and the product will be

retrieved

x. the connecting opener will retrieved the products using ejector

pin to eject the product out from the mould


5. Work principles for stretch blow moulding method :

i. the plastic is first moulded into a "preform" using the injection

molded process

ii. these preforms are produced with the necks of the bottles,

including threads (the "finish") on one end

iii. these preforms are packaged, and fed later (after cooling) into an

blow molding machine

iv. in this process, the preforms are heated (typically using infrared

heaters) above their glass transition temperature, then blown

using high pressure air into bottles using metal blow moulds

v. usually the perform is stretched with a core rod as part of the

process

vi. the stretching of some polymers, such as PET (polyethylene

terephthalate) results in strain hardening of the resin, allowing

the bottles to resist deforming under the pressures formed by

carbonated beverages

6. The advantages :

i. it does not need the finishing or tidying

ii. various of products, intricate or thinner can be produce


i. not economical for small production

ii. certain mould only for certain product

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Transfer Moulding Process

1. It is a process where the moulding compound is first softened by heat

in a transfer chamber and then is forced under high pressure into one

or more mould cavities for final curing.

2. In this process, the resin is not fed directly into the mould cavity but

into a chamber outside the mould cavities. When the mould is closed,

a plunger forces the plastic resin from the outside chamber through a

system of runners and gates into the mould cavities.

3. It is also used for moulding thermosetting plastics such as the

phenolics, ureas, melamines and alkyds.

4. The plastic material flowing process into the mould causing the heat

transferred equally and quickens the chemical reaction for cross

linking or curing.


i. the resins were placed in a chamber (preclosed mould) outside

the mould cavity forming a preformed plastic shape

ii. then heated at certain temperature where it will be plasticize

iii. when it softened, it then forced into the mould cavity (closed

mould) as hot melt plastic material by a plunger through a

system of runners and gates

iv. then let it cooled to solidified

v. after the plastic has cured, the plunger is removed and the mould

cavity then opened

vi. the parts is then ejected by ejector pin and removed the plastic

parts from the mould

6. The advantages :

i. the solidifies timing for transfer moulding are faster than

compression moulding

ii. the inserting timer are shorter because of the usage of bigger

preformed material which can be heatened quickly

iii. this process is suitable to form parts that need small metal

insertened because the plastic material entering the mould cavity

in stages without using higher pressure


iv. intricate shape and with variation of bigger cutting can be

produced

v. no flash is formed during moulding and the moulded part requires

less finishing

vi. many parts can be made at the same time by using a runner system


i. losing material in flowing channel

ii. mould cost are higher than compression moulding mould

Compression Moulding Process

1. It is a process where two parts mould combined together under one

compression and then formed a cavity accordingly to the component

shape.

2. In the process, before the combined, the resin (thermosets) may be

preheated, is loaded into a hot lower part of the mould containing

one or more cavities. The upper part of the mould is forced down on

the resin and then applied pressure and heat melts the resin and

forces the liquefied plastic into filling the cavities forming the needed

component.


3. Many thermosetting resins such as the phenol formaldehyde, urea

formaldehyde and melamine formaldehyde resins are formed into

solid parts by the compression moulding process.

4. The formation is prepared under certain pressure by using upper part

of the mould. This is similar to forging process for metal and facing

flashing problem where in need for trimming or cutting process.


i. the materials inserted into the mould as preformed powdered

shape because of heat and pressure

ii. the preheated material is loaded into a hot mould containing the

cavity

iii. the upper part of the mould is forced down on the plastic resin,

pressure and heat are then applied, forces the liquified plastic to

fill the cavity

iv. continued heating is required to complete the cross-linking of

the thermosetting resin

v. then the part is ejected from the mould

6. The advantages :

i. mould costs are low

ii. short flow of material reduces wear and abrasion on moulds

iii. production of large parts is more feasible

iv. more compact moulds are possible

v. expelled gases from the curing reaction (cross-linking process) are

able to escape during the moulding process



i. complicated part configurations are difficult to make with this

process

ii. inserts may be difficult to hold to close tolerances

iii. flash must be trimmed from molded parts

Rotational Moulding Process

1. It is a process to forming big hollow component in small or average

quantities where a thin metal mould consists of two separated parts

and designed to rotating in two axis which 90 to each other.


i. loading a measured quantity of polymer (usually in powder form)

into the mould

ii. the mould then heated in an oven whilst it rotates, until all the

polymer has melted and adhered to the mold wall

iii. by that homogeneous layer with similarity/ accuracy thickness

will be formed accordingly to the mould shape

iv. the material/ product are cooled while the machine rotated

before removed it from the mould by bringing the mould to the

cooling station where water are sprayed to the mould

v. the mould then brought to the last station where the product will

be removed from the mould

3. This process only limited for materials that has low melting

temperature in small quantities and protype production such as :

a) Polyethylene

b) Polypropylene

c) Polyvinyl Chloride


Thermoforming Process

1. It is a process when a heated plastic sheet is forced into the contours

of a mould by heat and pressure or vacuum.

2. Mechanical pressure may be used with mating dies or a vacuum may

used to pull the heated sheet into an open die. Air pressure may also

be used to force a heated sheet into an open die.

3. There are several categories of thermoforming, including vacuum

forming, pressure forming, twin-sheet forming, drape forming, free

blowing, and simple sheet bending.

4. Work principles for vacuum forming method :

i. the plastic sheet/ material was placed in between the opened

mould and the heating coils by clamping it to the moveable

clamper

ii. then the sheet was brought closer to the coils to softened it,

usually placed on top of the machine

iii. when the sheet are softened enough, the clamper with sheet back

to its place and in the same time the mould which usually placed

below the clamper moving up towards the softened sheet

iv. the air between the sheet and the mould then are gasped out or

vacuumed causing the sheet to fit tightly to the mould which the

air holes can be seen in the opened mould

v. then air are blowed to separated the forming sheet and mould and

in the same time cooled the product

vi. the mould then moved downward to its original place and the

formation that occurs from the sheet are the product that need to

be trimmed or cut off

5. The advantage :

i. low in mould cost because it can be formed using plaster,

thermosetting plastic, wood or aluminium

6. The disadvantage :

i. hollowed or opened space components cannot be produced

because of the different pressure when the forming process

occurs.

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7. Materials that can be used :

a) Polystyrene

b) Acrylonitrile-Butadiene-Styrene (ABS)

c) Polyvinyl Chloride

d) Polypropylene

e) Polyethylene

8. Applications :

used to formed plastic sheets for certain shape such as :

- food packaging

- yogurt package

- motorcycle fairing

- vehicles bumper


Casting Process

1. It is a process by the use of a liquid or powder material that is shaped

without the application of significant pressure.

2. Casting is a manufacturing process by which a liquid material such as

a suspension of minerals as used in plastic is introduced into a mould,

allowed to solidify within the mould, and then ejected or broken out

to make a fabricated part.

3. For thermoplastics, liquid monomer is poured into the mould and,

with heat, allowed to polymerize in place to a solid mass.

4. For thermosets, they are poured into a heated mold wherein the

cross-linking reaction completes the conversion to a solid.

5. Casting is used for making parts of complex shape that would be

difficult or uneconomical to make by other methods, such as cutting

from solid material.

6. Encapsulation and potting are terms for casting processes in which a

unit or assembly is encased or impregnated, respectively, with a

liquid plastic which is subsequently hardened by fusion or chemical

reaction.

Calendaring Process

1. It is a process to produced sheets or films by passing the soft or half

gel thermoplastic materials through a number of pairs of heated

rollers which the heat and pressure are applied to the materials and

the rolls in combination are called calendars.

2. Usually this process applied in stages of rolling before final products

with certain thickness achieved.

3. Materials used : PVC and copolymers that contains Vinyl Chloride.

4. The thickness of products between 0.05 – 0.7mm and with width

upto 1m.

http://www.answers.com/topic/mineral

http://www.answers.com/topic/monomer

http://www.answers.com/topic/polymerize

http://www.answers.com/topic/hardened-2



i. polymer powders, adhesives and other additives were mix in

normal condition

ii. stirred in closed heated mixture

iii. the softened or half gel materials from the mixture then

masticated between two heated rolls that squeeze it out into a

film or sheet

iv. the heated sheet or film then trimmed and then passes around

one or more additional rolls (calendars) before being stripped off

as a continuous film

6. The calendres contains with 3 to 4 rollers made of hardened steel,

steel covered with fiber or cast irons.

7. The calendering rollers has polished surface and the cylinders have

drilled holes to channeled heated liquid, oil or water.

http://www.answers.com/topic/squeeze

Material Technology

Engineering

chemical material

organic polymer material

polymer chains

o random copolymer o

new material

organic material

j3022 material technology

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