me 2201 unit 5 plastics ppt

8/10/2019 ME 2201 Unit 5 Plastics PPT

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PLASTIC COMPONENT MANUFACTURE

-plastics are organic solids or resins-they generally contain O, C, H, N & other elements

-these organic compounds are called polymers

-polymers are divided into

1.Plastics 2.Fibres 3. Elastomers (rubber)

-plastic can be made to flow by heat or pressure

-plastic components are manufactured by single operation

and not in steps (as in the case of metals)

-they are light weight & suitable to manufacture variety of

products including automobile parts, aircraft components


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TYPES OF PLASTICS;

Thermoplastics Thermosetting plastics

-can be repeatedly softened -not possible

by heating & hardened by cooling

-formed by addition polymerization -formed by condensation

polymerization

-can be re-moulded -not possible

-low molecular weight -high molecular weight

-products: automobile parts, elec.& -photo films, insulation tape,

telephone parts hoses etc.


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EXAMPLES OF

THERMOPLASTICS THERMOSETTING PLASTICS

-cellulosic -epoxy resins

-nylons -amino resins-polyethylene resins -phenolics

-polystyrene -silicons

-polypropylene

-polycarbonate

-acrylic resin

-vinyl plastics


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Properties of Plastics

-less brittle than glass

-light weight, & yet possess good strength & rigidity

-have dielectric properties & hence suitable for electrical components

-possess good toughness

-mass production is easier than metals

-good deformability, heat resistance


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FORMING & SHAPING OF PLASTICS

(characteristics of forming & shaping of plastics)

1.Blow moulding :

Used to produce hollow thin walled products( containers); production rate is

high

2.Casting :

Use to produce simple & intricate shapes with suitable moulds : low production

rate.

3.Compression mould :

Similar to die-forging ; medium production rate

4.Extrusion:

Used to produce long, uniform solid or hollow sections at high production rates


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FORMING & SHAPING OF PLASTICS

(characteristics of forming & shaping of plastics)

5.Injection moulding :

Used to produce complex shapes ; high production rate : costly tooling

6.Rotational moulding :

Used for large hollow shapes ; low tooling cost; low production rate

7.Thermoforming :

Used to produce deep cavities; low tooling cost; medium production rate

8.Transfer moulding :

Used to produce more complex parts; high production rate


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Plastic Pellets (raw material )


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INJECTION MOULDING

- It is a process in which polymer is heated to highly plastic state & forced to

flow under high pressure into mould cavity where it solidifies by cooling.

-It is widely used for moulding thermoplastic components

-Injection moulding machines have high production capacity

-This method is suitable for making parts with complex threads,

intricate shapes, thin walled parts etc.

-Some of the products are:

cups, containers, tool handles, toys, knobs, plumbing fittings, elec. &

communication components

-Limitation of this process :

reliable temp. control & non-corrosive dies


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Screw type Injection Moulding


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Plunger type

Screw type Injection moulding


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Screw Type Plunger Type


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Working principle of Screw type Injection Moulding


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Injection moulded products


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BLOW MOULDING

-It is used to create hollow enclosed components

-There are two basic types of blow moulding process:

1. Extrusion Blow Moulding

2. Injection Blow Moulding

-most widely used materials for blow moulding :

-low density polyethylene (LDPE)-high density polyethylene (HDPE)

-polypropylene (PP)

-polyvinyl chloride (PVC)

-polyethylene terephtalate (PET)

-this method is widely used for manufacture of PET bottles

& other disposable containers


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Blow moulding

Blow moulded products


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Injection blow moulding


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Injection blow moulding:

-in this type, the starting parison is injection moulded

-injection mould is opened & parison is transferred to

the blow mould

-soft polymer inflated to conform to the blow mould

-blow mould is opened & product is removed-compared to extrusion blow mould, this process is slow

& hence less widely used

-suitable for plastic bottles, jars, containers

-this process uses thermoplastics

-thin walled hollow products are possible

-wall thickness of product can be increased byincreasing the parison tube wall thickness


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Extrusion blow mold


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EXTRUSION BLOW MOULDING:

-the steps involved are:

-extrusion of parison

-parison is inched at top & sealed at bottom

-the two halves of mould are brought together

-parison tube is inflated so that it takes the shape of mould cavity.

-mould is opened & product is removed

-this process is generally automated

- and has very high production rate


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ROTATIONAL MOULDING

( this process is similar to centrifugal casting)

-Uses gravity inside a rotating mould to achieve a hollow form

-Also called Roto-moulding

-Generally used for thermoplastic polymers

-Thermosetting & elastomers are also used

-Steps involved :

-Required amount of polymer powder is loaded in the molud

-Mould is heated & simultaneously rotated

-The powder impinges on the internal surface of mould

-A layer of uniform thickness is formed

-The mould is cooled & the plastic solidifies

-Mould is opened & product is removed


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Rotational moulding Machine


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Rotational Moulding Process


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Roto-molded products

EXTRUSION


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EXTRUSION

-It is a compression process, where the material is forced to flow thro a die

orifice to provide long, continuous product whose cross sectional shape is

determined by the shape of orifice

-in this process, the feed stock is pellet or powder

-It is heated, melted & forced to flow thro the die opening by means of rotating

screw conveyor.

The screw conveyor has three sections:

-Feed section: here the feed is moved from the hopper & preheated

-Compression section : here the polymer is transformed into liquid

consistency & compressed

-Metering section : the melt is homogenized & pumped

thro the die opening


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Extrusion moldingExtrusion moulded products

Complex shapes with constant cross sections can be extruded

-Wire & cable coating for insulation is an important polymer extrusion

process

-Typical products: plastic rods, pipes, channels, window frames etc.


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Blown Film Extrusion Process


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Blown film extrusion products


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THERMOFORMING

-it is a process in which a flat thermoplastic sheet is heated

& deformed into the desired shape-this process is widely used in packaging of consumer products,

bathtubs, internal lining of refrigerators

Three categories of Thermoforming

1. Vacuum Thermoforming:

-in this process, vacuum is used to draw preheatedsheet into a mould cavity.

2. Pressure Thermoforming :

-in this process, thee sheet is pressurized from above

into the mould cavity.

3. Mechanical Thermoforming:

-in this process, matching positive & negative molds arebrought together against heated sheet & forced

to form the shape.


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Thermoforming Process

Thermoformed Products


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Vacuum Thermoforming Process:

Process steps:

1.flatplastic sheet is softened by heating

2.It is placed over the concave mould cavity

3.Vacuum draws the sheet into the cavity

4.The plastic hardens on contact with cold mould cavity

5.The product is removed from mould & trimmed


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-In this process, top & bottom moulds are used

-pressure is applied from the top mould

-better dimensional control is possible

-costlier than the other two methods


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COMPRESSION MOULDING

-It is a process in which the preheated moulding material is placed in a

heated mould cavity & compressed

-This process employs thermosetting resins to make different products

-Large & intricate parts can be moulded

-It is a high volume, high pressure method & suitable for molulding complex,

high strength fibre-glass reinforcements

-widely used for thermosetting plastics

-Used for manufacturing rubber tyres

-Compression moulding process can be either manual,

semiautomatic or fully automatic


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Compression molded products


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TRANSFER MOULDING

-In this process, thermosetting resin is heated in a separate chamber & then the

softened polymer is forced into a heated mould, where curing occurs.

-Transfer moulding is capable of moulding more irregular shapes that that of

compression moulding

Two types of transfer moulding :

1. Pot Transfer Moulding:

- in this type, the charge is injected from a pot thro a vertical channel into the

cavity

2. Plunger Transfer Moulding:

-in this type, the charge is injected by means of plunger from a heated well,

thro lateral channels into the mould cavity


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Transfer Moulding Process


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Transfer molded products

Plunger transfer

Pot transfer


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Manufacturing process for :

Thermo-plastic plastics & Thermo-setting plastics

1.Injection moulding 1.Blown film moulding

2.Blow moulding 2.Compression moulding

3.Rotational moulding 3.Transfer moulding

4.Extrusion moulding

5.Thermoforming


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-Various methods of bonding (continued..)

5.Induction welding : An inert metal is placed in between the parts &

-magnetic field is passed.

-The high frequency (450 KHz) causes

to heat the metal & plastic parts fuse together.

6.Dielectric welding : Used in packaging process. High voltage & frequencies

-produce dielectric heating & fuse the plastic

7.Hot-platen welding : Parts are softened by heated tool & pressed.-fluorocarbon is used to avoid sticking of tool with parts.

-used for large, irregularly shaped parts.

me 2201 unit 5 plastics ppt

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