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Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering 1 Chapter Three Materials, Metals and Alloys 3-1 - Metals and Alloys Metals are polycrystalline bodies consisting of a great number of fine crystals. Pure metals possess low strength and do not have the required properties. So, alloys are produced by melting or sintering two or more metals or metals and a non-metal, together. Alloys may consist of two more components. Metals and alloys are further classified into two major kind namely ferrous metals and non-ferrous metals. (a) Ferrous metals are those which have the iron as their main constituent, such as pig iron, cast iron, wrought iron and steels. (b) Non-ferrous metals are those which have a metal other than iron as their main constituent, such as copper, aluminum, brass, bronze, tin, silver zinc, invar etc. 3-2- Classification of Carbon and Low-Alloy Steels Steels can be classified by a variety of different systems depending on: 1. The composition, such as carbon, low-alloy or stainless steel. 2. The manufacturing methods, such as open hearth, basic oxygen process, or electric furnace methods. 3. The finishing method, such as hot rolling or cold rolling. 4. The product form, such as bar plate, sheet, strip, tubing or structural shape 5. The de-oxidation practice, such as killed, semi-killed, capped or rimmed steel. 6. The microstructure, such as ferritic, pearlitic and martensitic. 7. The required strength level, as specified in ASTM standards.

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Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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Chapter Three

Materials, Metals and Alloys

3-1 - Metals and Alloys

Metals are polycrystalline bodies consisting of a great number of fine crystals. Pure

metals possess low strength and do not have the required properties. So, alloys are

produced by melting or sintering two or more metals or metals and a non-metal,

together. Alloys may consist of two more components. Metals and alloys are

further classified into two major kind namely ferrous metals and non-ferrous

metals.

(a) Ferrous metals are those which have the iron as their main constituent, such as

pig iron, cast iron, wrought iron and steels.

(b) Non-ferrous metals are those which have a metal other than iron as their main

constituent, such as copper, aluminum, brass, bronze, tin, silver zinc, invar etc.

3-2- Classification of Carbon and Low-Alloy Steels

Steels can be classified by a variety of different systems depending on:

1. The composition, such as carbon, low-alloy or stainless steel.

2. The manufacturing methods, such as open hearth, basic oxygen process, or

electric furnace methods.

3. The finishing method, such as hot rolling or cold rolling.

4. The product form, such as bar plate, sheet, strip, tubing or structural shape

5. The de-oxidation practice, such as killed, semi-killed, capped or rimmed

steel.

6. The microstructure, such as ferritic, pearlitic and martensitic.

7. The required strength level, as specified in ASTM standards.

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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8. The heat treatment, such as annealing, quenching and tempering, and thermo

mechanical processing.

9. Quality descriptors, such as forging quality and commercial quality.

3- 3- Classification by carbon content wt % 1. Dead soft (0.05 – 0.15)

Wires, rivets, chain, sheet, strip, welded pipe

2. Mild (0.10 – 0.30)

Rolled plate, structural shapes, gears, forgings

3. Medium Carbon (0.30 – 0.60)

Connecting rods, crane hooks, shafts, axles, gears, rotors, rails

4. High Carbon (0.6 – 1.0) , hardness of 450 to 600 BHN

Screw drivers, saws, drills, dies, hammers, punches, chisels.

5. Ultrahigh Carbon (1.0 – 1.4)

Special applications such as making railway, springs, mandrels, taps, balls,

pins, tools, and thread metal dies.

3-4- Classification by alloy content Manganese steels

Silicon‐manganese steels

Chromium steels

Chromium‐nickel (stainless) steels

Tungsten‐chromium‐vanadium (tool) steels

etc.

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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Fig.3-1 Effect of carbon on properties of steel

Fig.3-2 Properties of steels as influenced by carbon content

3-5-- Classification of cast irons

Found in 5 common varieties depending on the form of carbon in the

microstructure.

3-5-1-Grey iron (carbon presents as free flaky graphite). Grey cast iron is grey in

color which is due to the carbon being principally in the form of graphite (C in free

form in iron). It contains:

C Si Mn P S Fe

2.5 - 3.8%. 1.1 - 2.8 % 0.4 - 1.0% less than

0.15%

less than

0.1%

Remaining

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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Properties and characteristics: 1. It possesses lowest melting of ferrous alloys.

2. It possesses high vibration damping capacity.

3. It has high resistance to wear.

4. It possesses high fluidity and can be easily cast into complex shapes and thin

sections.

Application

Gas or water pipes for underground purposes.

Manhole cover, machine bed.

3-5-2- White iron (carbon present as iron carbide compound) For low-silicon cast

irons (containing less than 1.0 wt% Si) and rapid cooling rates, most of the carbon

exists as cementite instead of graphite. A fracture surface of this alloy has a white

appearance, and thus it is termed white cast iron.

An optical photomicrograph showing the microstructure of white iron is presented.

Thick sections may have only a surface layer of white iron that was ‘‘chilled’’

during the casting process; gray iron forms at interior regions, which cool more

slowly. As a consequence of large amounts of the cementite phase, white iron is

extremely hard but also very brittle, to the point of being virtually unmachinable.

Its use is limited to applications that necessitate a very hard and wear-resistant

surface and without a high degree of ductility—for example, as rollers in rolling

mills, rolls crushing jaw, crusher plates. Generally, white iron is used as an

intermediary in the production of yet another cast iron, malleable iron. The

chemical composition of white cast iron is given as:

C Si Mn P S Fe

3.2 - 3.6% 0.4 - 1.1 % 0.1 - 0.4% less than 0.3%

less than 0.2%

Remaining

Properties and characteristics Extremely hard, have very little commercial uses.

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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It has a high tensile strength and a low compressive strength .

Possesses excellent abrasive wear resistance.

Since it is extremely hard, therefore it is very difficult to machine.

Application

Grinding media ball.

Raw material for malleable iron.

3-5-3- Ductile cast iron

When small quantities of magnesium or cerium is added to cast iron, then graphite

content is converted into nodular or spherical form and it is well dispersed

throughout the material. Compositions of ductile cast iron are as follows:

C Si Mg Ni Mn Fe

3.2 – 4.2 % 1.0 - 4.0 % 0.1 - 0.8% 0.0 - 3.5% 0.5 - 0.1% Remaining

3-5-4 - Malleable cast iron

Heating white iron at temperatures between 800 and 900 c˚for a prolonged time

period and in a neutral atmosphere (to prevent oxidation) causes a decomposition

of the cementite, forming graphite, which exists in the form of clusters or rosettes

surrounded by a ferrite or pearlite matrix, depending on cooling rate.

The ordinary cast iron is very hard and brittle. Malleable cast iron is unsuitable for

articles which are thin, light and subjected to shock. It can be flattened under

pressure by forging and rolling. It is an alloy in which all combined carbon

changed to free form by suitable heat treatment. Graphite originally present in iron

in the form of flakes which is the source of weakness and brittleness.

The tensile strength of this cast iron is usually higher than that of grey cast iron. It

has excellent machining quality and is used for making machine parts for which the

steel forging and in which the metal should have a fair degree of machining

accuracy.

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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Properties

1. Malleable cast iron is like steel than cast iron.

2. It is costly than grey cast iron and cheaper than softer steel.

Applications

Malleable cast iron is generally used to form automobile parts.

Table (3-1 ) a comparison between grey, white, and steroidal cast iron

IC = internal combustion engine

3-6- Stainless Steels

The stainless steels are highly resistant to corrosion (rusting) in a variety of

environments, especially the ambient atmosphere. Their predominant (major)

alloying element is chromium; a concentration of at least 11 wt% Cr is required.

Corrosion resistance may also be enhanced by nickel and molybdenum additions.

The five types of stainless steel are:

1-Ferritic, 2-Martensitic, 3-Austenitic, 4-Duplex 5-Precipitation Hardening.

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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3-6-1- Martensitic stainless steels are similar to low alloy or carbon steels, having

a structure similar to the ferritic steels. However, due the addition of carbon, they

can be hardened and strengthened by heat treatment, in a similar way to carbon

steels. The main alloying element is chromium, typically 12 - 15%, molybdenum

(0.2-1%), no nickel, except for two grades, and their structures are "body-centered

tetragonal" (bct). They are classed as a “hard" ferro-magnetic group .In the

annealed condition, they have tensile yield strengths of about 275 Mpa and so

they are usually machined, cold formed, or cold worked in this condition. The

strength obtained by heat treatment depends on the carbon content of the alloy.

Increasing the carbon content increases the strength and hardness potential but

decreases ductility and toughness. Corrosion resistance is lower than the common

austenitic grades. Cold Working not recommended - Suitable only for minor

deformation. Severe deformation will result in cracking. Some applications

include: Valve Parts, Pump Shafts, Automatic Screw Machined Parts, Motor Shafts

, Washing Machine Components, Bolts and Nuts, Studs, and Gears.

3-6-2-Ferritic stainless steels has properties similar to mild steel but with the better

corrosion resistance. The most common of these steels are 12% and 17%

chromium containing steels, with 12% used mostly in structural applications and

17% in house wares, boilers, washing machines and indoor architecture.

Currently such steels are rated in the lower range of corrosion resistance for

reinforcement. It is composed of the α ferrite (BCC) phase.

3-6-3-The austenitic stainless steels are the most widely used type of stainless

steel make up over 70 % of total stainless steel production. It has FCC structure,

and it is the most corrosion resistant because of the high chromium contents and

also the nickel additions at least 7%, which makes the steel structure fully

austenitic and gives it ductility.

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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The most widely used austenite steel is the 304, also known as 18/8 for its

composition of 18% chromium and 8 % nickel. The range of applications of

austenitic stainless steel includes house wares, containers, industrial piping and

vessels, architectural facades and constructional structures. its application has a

large scale of service temperature, non-magnetic properties and good weldability.

Notes: Austenitic and ferritic stainless steels are hardened and strengthened by

cold work because they are not heat treatable.

Both martensitic and ferritic stainless steels are magnetic; the austenitic stainless

is not.

3-6-4 -Austenitic-Ferritic (Duplex) have a mixed microstructure of austenite and

ferrite, the aim usually being to produce a 50/50 mix, although in commercial

alloys the ratio may be 40/60. Duplex stainless steels have roughly twice the

strength compared to austenitic stainless steels and also improved resistance to

localized corrosion, particularly pitting, crevice corrosion and stress corrosion

cracking. Duplex stainless steels are characterized by high chromium (19–32%)

and molybdenum (up to 5%) and lower nickel contents than austenitic stainless

steels. The properties of duplex stainless steels are achieved with overall lower

alloy content than similar-performing super-austenitic grades, making their use

cost-effective for many applications. Duplex grades are characterized into groups

based on their alloy content and corrosion resistance. Duplex steels are mostly used

in petrochemical-, paper - pulp machinery, and shipbuilding industries.

3- 6-5- Precipitation-hardenable (PH) stainless steels are hardenable by "ageing

treatments" and so have some similarities to the martensitic types, although the

metallurgical mechanism for hardening is different and are capable of strengths of

up to 1700 Mpa. They generally have a martensitic structure and so are usually

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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ferro-magnetic. It has corrosion resistance comparable to austenitic varieties.The

most common alloy is uses about 17% chromium and 4% nickel.

The "PH" types have good ductility and toughness, depending on the heat-treated

condition. Their corrosion resistance is comparable to the (304) austenitic. They

can be welded more readily than "conventional" martensitic types and have been

developed and used more widely in the US than in the UK for example in

aerospace applications.

Fig 3- 3- factors affects on stainless steel selection.

3-7 - Non-ferrous metals are those which have a metal other than iron as their main

constituent, such as copper, aluminum, brass, bronze, tin, silver zinc, invar etc.

3-7-1- Aluminum and its alloys

Aluminum and its alloys are characterized by a relatively low density (2.7 g/cm3

as

compared to 7.9 g/cm3 for steel), high electrical and thermal conductivities, and

a resistance to corrosion in some common environments, including the ambient

atmosphere. Many of these alloys are easily formed by virtue of high ductility; this

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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is evidenced by the thin aluminum foil sheet into which the relatively pure material

may be rolled. Since aluminum has an FCC crystal structure, its ductility is

retained even at very low temperatures. The chief limitation of aluminum is its low

melting temperature 660°C , which restricts the maximum temperature at which it

can be used.

The mechanical strength of aluminum may be enhanced by cold work and by

alloying; however, both processes tend to diminish res istance to corrosion.

Principal alloying elements include copper, magnesium, silicon, manganese, and

zinc.

Non heat- treatable alloys consist of a single phase, for which an increase in

strength is achieved by solid solution strengthening.

Others are rendered heat treatable (capable of being precipitation hardened) as a

result of alloying. In several of these alloys precipitation hardening is due to the

precipitation of two elements other than aluminum, to form an intermetallic

compound such as MgZn2 .

Principal advantages

Light weight (D=2.7 g/cc, compared to 7.9 g/cc for steel.)

High electrical and thermal conductivity

Corrosion resistant.

Easy to form due to high ductility (FCC structure)

Mechanical properties improved by cold working, alloying, and heat

treatment

Easy to recycle

Principal disadvantage – Low melting point (660 °C).

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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3-7-2- Copper and its alloys

Copper and copper-based alloys, possessing a desirable combination of physical

properties, have been utilized in quite a variety of applications since antiquity.

Unalloyed copper is so soft and ductile that it is difficult to machine; also, it has an

almost unlimited capacity to be cold worked. Furthermore, it is highly resistant to

corrosion in diverse environments including the ambient atmosphere, seawater, and

some industrial chemicals. The mechanical and corrosion-resistance properties of

copper may be improved by alloying.

Most copper alloys cannot be hardened or strengthened by heat-treating

procedures; consequently, cold working and/or solid-solution alloying must be

utilized to improve these mechanical properties.

The most common copper alloys are the brasses ( copper with zinc) alloys. Brasses

alloys are of two types one of brass which is relatively soft, ductile, and easily cold

worked. The other type having higher zinc content alloys are generally hot worked.

Some of the common uses for brass alloys include costume jewelry, gilding metal,

cartridge casings, automotive radiators, musical instruments, electronic packaging,

and coins.

The bronzes are alloys of copper and several other elements, including tin,

aluminum, silicon, and nickel. These alloys are somewhat stronger than the

brasses, and have a high degree of corrosion resistance.

Characteristics

High electrical and thermal conductivity

Very good corrosion resistant

Principal advantages

Pure copper has poor strength and very high ductility (FCC structure),

giving unlimited workability but poor machinability.

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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Mechanical properties improved by cold working and alloying (most Cu

alloys are non heat treatable).

Applications : electric wire, rivets, screening, gaskets, nails, Bearings, bushings,

piston rings, pipe fittings, and gears

3-7-3- Magnesium and its alloys Perhaps the most outstanding characteristic of magnesium is its density, 1.7 g/cm3,

which is the lowest of all the structural metals; therefore, its alloys are used where

light weight is an important consideration (e.g., in aircraft components).

Magnesium has an HCP crystal structure, is relatively soft, and has a low elastic

modulus: 45 GPa. At room temperature magnesium and its alloys are difficult to

deform; in fact, only small degrees of cold work may be imposed without

annealing. Consequently, most fabrication is by casting or hot working at

temperatures between 200 and 350°C. Magnesium, like aluminum, has a

moderately low melting temperature 651°C. Chemically, magnesium alloys are

relatively unstable and especially susceptible to corrosion in marine environments.

On the other hand, corrosion or oxidation resistance is reasonably good in the

normal atmosphere; it is believed that this behavior is due to impurities. Fine

magnesium powder ignites easily when heated in air; consequently, care should be

exercised when handling it in this state.

For many applications, magnesium alloys have replaced engineering plastics that

have comparable densities in as much as the magnesium materials are stiffer, more

recyclable, and less costly to produce. For example, magnesium is now employed

in a variety of hand-held devices (e.g., chain saws, power tools, hedge clippers), in

automobiles (e.g., steering wheels and columns, seat frames, transmission cases),

and in audio-video-computer-communications equipment (e.g., laptop computers,

camcorders, TV sets, cellular telephones).

Extremely light weight (D 1. 7 g/cc).

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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Pure Mg is soft, but having a HCP structure, cold workability is limited.

Most fabrication is done by casting or hot working.

Principal disadvantages

Low melting temperature 651°C)

Poor corrosion resistant in marine environment, relatively good in normal

atmosphere.

Relatively unstable, fine powder ignites easily.

3-7-4- Titanium and its alloys

Titanium and its alloys are relatively new engineering materials that possess an

extraordinary combination of properties. The pure metal has a relatively low

density (4.5 g/cm3), a high melting point 1668°C and an elastic modulus of 107

GPa. Titanium alloys are extremely strong; room temperature tensile strengths as

high as 1400 MPa are attainable, yielding remarkable specific strengths.

Furthermore, the alloys are highly ductile and easily forged and machined. The

major limitation of titanium is its chemical reactivity with other materials at

elevated temperatures. This property has necessitated the development of

nonconventional refining, melting, and casting techniques; consequently, titanium

alloys are quite expensive. In spite of this high temperature reactivity, the corrosion

resistance of titanium alloys at normal temperatures is unusually high; they are

virtually immune to air, marine, and a variety of industrial environments.

They are commonly utilized in airplane structures, space vehicles, surgical

implants, and in the petroleum and chemical industries.

Principal advantages

Relatively low density ( D=4.3 g/ cc), high melting point ( 1668°C, high

elastic modulus (E=107 GPa)

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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Titanium alloys are extremely strong (~1400 MPa), and have remarkable

specific strength

Highly ductile and easily forged and machined.

Very good corrosion resistant

Principal disadvantages

Chemical reactivity at high temperatures, causing costly non‐conventional

production technique to be developed.

3-8 - Polymers

Polymers, derived from the Greek terms for “many parts,” are large molecules comprised

of many repeat units that have been chemically bonded into long chains.

The Structure of Polymers (plastics)

Polymers are created by the chemical bonding of many identical units . These polymers

are specifically made of small units bonded into long chains. Carbon makes up the

backbone of the molecule and hydrogen atoms are bonded along the carbon backbone.

Polymers that contain primarily carbon and hydrogen are classified as organic polymers.

Polypropylene and polystyrene are examples of these.

Even though the basic makeup of many polymers is carbon and hydrogen, other elements

can also be involved. Oxygen, chlorine, fluorine, nitrogen, silicon, phosphorous and

sulfur are other elements that are found in the molecular makeup of polymers. Polyvinyl

chloride (PVC) contains chlorine. Nylon contains nitrogen. Teflon contains fluorine.

Polyester and polycarbonates contain oxygen. There are also some polymers that, instead

of having a carbon backbone, have a silicon or phosphorous backbone and these are

considered inorganic polymers. Silk, cotton, and wool are examples of natural polymers.

Polymer classification:

Elastomer Thermoset/ thermosetting

Thermoplastic : crystalline , and amorphous.

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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There are three basic type of polymer packing: chain, branch, and network as shown in Figure below:

As the name implies, thermosetting plastics or thermosets are set, cured, or

hardened into a permanent shape. The curing, which usually occurs rapidly under

heat or ultraviolet (UV) light leads to an irreversible cross-linking of the polymer.

Thermoplastics differ from thermosetting materials in that they do not set or cure

under heat. When heated, thermoplastics merely soften to a mobile, flowable state

where they can be shaped into useful objects. Upon cooling, thermoplastics harden

and hold their shape. Thermoplastics can be repeatedly softened by heat and

shaped.

1- Thermoplastics :

Fig (3-5 (a) Chains in polymers like polypropylene form spaghetti-like tangles with no regular repeating pattern—that structure is amorphous or ‘glassy’. (b) Some polymers have the ability to form regions in which the chains line up and register, giving crystalline patches. The sketch shows a partly crystalline polymer structure. (c) Elastomers have occasional cross-links between chains, but these are far apart, allowing the chains

between them to stretch. (d) Heavily cross-linked polymers like epoxy inhibit chain sliding.

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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Thermoplastics soften and melt when heated and harden when cooled. Because of

this behavior, these resins can be injection molded, extruded or formed via other

molding techniques. This behavior also allows production scrap - runners and

trimmings, for instance - to be reground and reused, but some degradation or loss

of mechanical properties can occur during subsequent re-melting. Thermoplastics

are further classified by their crystallinity, or the degree of order within the

polymer’s overall structure. As a crystalline resin cools from the melt, polymer

chains fold or align into highly ordered crystalline structures.

Thermoplastics can be classified as amorphous or semi crystalline plastics.

Most polymers are either completely amorphous or have an amorphous component

even if they are crystalline. Amorphous polymers are hard, rigid glasses below a

sharply defined temperature, which is known as the glass transition temperature.

Above the glass transition temperature the amorphous polymer becomes soft and

flexible and can be shaped. Mechanical properties show profound changes near the

glass transition temperature. Many polymers are not completely amorphous but are

semi-crystalline. Crystalline polymers have melting points that are above their

glass transition temperature.

The degree of crystallinity and the morphology of the crystalline phase have an

important effect on mechanical properties and depend upon both the polymer and

the processing technique. Crystalline plastics will become less rigid above their

glass transition temperature but will not flow until the temperature is above the

crystalline melting point. At ambient temperatures crystalline / semi-crystalline

plastics have greater rigidity, hardness, density, lubricity, creep resistance, and

solvent resistance than amorphous plastics.

Generally, the higher a polymer’s glass transition temperature, the better it will

perform at elevated temperatures. As a rule, transparent plastics — those used in

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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headlight lenses and lighting fixtures, for example — are amorphous rather than

crystalline. The most common transparent thermoplastics include polycarbonate,

polystyrene, and (poly methyl) methacrylate.

2- Thermosets / thermosetting:

Unlike thermoplastics, thermosets form cross links, inter-connections between

neighboring polymer molecules that limit chain movement. This network of

polymer chains tends to degrade, rather than soften, when exposed to excessive

heat. Until recently, thermosets could not be remelted and reused after initial

curing. Today’s most-recent advances in recycling have provided new methods for

remelting and reusing thermoset materials.

3- Elastomer

Elastomer plastics are usually the chain, branch, or even network type. The

polymer chains are very loosely intertwined. As a result, the elastomers are pliable

and stretchy. Another name for elastomer is rubber. An example of this type of

polymer would be silicon rubber.

The properties of polymers/ plastics:

Plastics do not usually conduct electricity due to its importance in preventing

electric hazards in electrical and electronics equipment.

1- Plastics may be transparent is practical in package foods because we can see

the food condition.

2- Plastics are safe and hygienic, for example hospital and food industry use

many different kind of plastics.

3- Plastics are lightweight and this is important, for example in car

manufacturing because the cars spent less fuel and this is good for the owner

and environment. (If we burn less petrol we produce less CO2)

4- Plastics are tough and durable.

Chapter three Selection of Materials and processes Dr.May George Amin Fourth class - 2013-2014 Dep. of Production Eng. And Metallurgy industrial Engineering

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5- Plastics are good insulators; we use plastic to insulate our houses, for food

and drinks containers, to protect fragile objects, etc.

6- Plastic is a flexible material, it is very important to the manufacturing

industry, we can make practically whatever form we want.

7- Plastic is very resistant to chemicals.

8- Plastic is cost-effective and convenient (useful).

Polymer Forming Techniques

Compression & Transfer molding

Injection molding

Extrusion

Blow molding

Casting