CHAPTER CHAPTER NAME

1. Plastics

History

Composition

Polymerization process

Composition

Properties of plastics

Common plastics & uses

Different manufacturing processes for Plastics:

• Injection Moulding.

• Compression Moulding.

• Blow Moulding.

• Compression Moulding.

• Plastics Extrusion.

• Thermoforming.

• Slush Moulding.

• Transfer moulding.

• Calendaring.

Gate type

Design Rules For Plastic Parts:

• Maximum wall thickness

• Corners

• Draft

• Ribs

• Bosses

• Undercuts

• Threads

TYPICAL NOMINAL THICKNESS FOR VARIOUS

CLASSES OF THERMOPLASTICS

DEFECTS of PLASTICS

Welding Techniques

Hot gas welding

Heat seal

Freehand welding

Speed tip welding

Extrusion welding

Contact welding

Hot plate welding

High frequency welding

Injection welding

Ultrasonic welding

Friction welding

Spin welding

Laser welding

Transparent Laser Plastic Welding

Solvent welding

Welding rod

PLASTICS • Growing demand in the automotive sector

Plastics In Automotive Markets Today

Abbreviations

PLASTICS:

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids

that are mouldable. Plastics are typically organic polymers of high molecular mass, but they

often contain other substances. They are usually synthetic, most commonly derived from

petrochemicals, but many are partially natural.

History

Early plastics were bio-derived materials such as egg and blood proteins, which are

organic polymers. Treated cattle horns were used as windows for lanterns in the Middle

Ages. Materials that mimicked the properties of horns were developed by treating milk-

proteins (casein) with lye. In the 1800s the development of plastics accelerated with Charles

Goodyear's discovery of vulcanization as a route to thermoset materials derived from natural

rubber. Many storied materials were reported as industrial chemistry was developed in the

1800s. In the early 1900s, Bakelite, the first fully synthetic thermoset was reported by

Belgian chemist Leo Baekeland. After the First World War, improvements in chemical

technology led to an explosion in new forms of plastics. Among the earliest examples in the

wave of new polymers were polystyrene (PS) and polyvinyl chloride (PVC). The

development of plastics has come from the use of natural plastic materials (e.g., chewing

gum, shellac) to the use of chemically modified natural materials (e.g., rubber,

nitrocellulose, collagen, galalite) and finally to completely synthetic molecules

(e.g., bakelite, epoxy, polyvinyl chloride).

Bakelite

The first so called plastic based on a synthetic polymer was made

from phenol and formaldehyde, with the first viable and cheap synthesis methods invented in

1907, by Leo Hendrik Baekeland, a Belgian-born American living in New York state.

Baekeland was looking for an insulating shellac to coat wires in electric motors and

generators. He found that combining phenol (C6H5OH) and formaldehyde (HCOH) formed a

sticky mass and later found that the material could be mixed with wood flour, asbestos, or

slate dust to create strong and fire resistant "composite" materials. The new material tended

to foam during synthesis, requiring that Baekeland build pressure vessels to force out the

bubbles and provide a smooth, uniform product, as he announced in 1909, in a meeting of the

American Chemical Society.[12]

Bakelite was originally used for electrical and mechanical

parts, coming into widespread use in consumer goods and jewelry in the 1920s. Bakelite was

a purely synthetic material, not derived from living matter. It was also an early thermosetting

plastic.

ASTM: American Standard Test Methods; is a scientific organisation defining standards on

physical and mechanical testing of materials to obtain objective characteristics used for

comparison purposes and for design of articles. The standards are partly used to formulate

ISO (International Standards Organisation) ones.

Composition

Most plastics contain organic polymers. The vast majority of these polymers are

based on chains of carbon atoms alone or with oxygen, sulphur, or nitrogen as well. The

backbone is that part of the chain on the main "path" linking a large number of repeat units

together. To customize the properties of a plastic, different molecular groups "hang" from the

backbone (usually they are "hung" as part of the monomers before linking monomers

together to form the polymer chain). The structure of these "side chains" influence the

properties of the polymer. This fine tuning of the properties of the polymer by repeating unit's

molecular structure has allowed plastics to become an indispensable part of the twenty-first

century world.

Additives

Additives: these are in general low molecular weight chemicals added to plastics and

rubbers to improve certain characteristics such as ultraviolet absorbers, antioxidants and heat

stabilisers, lubricants, plasticisers, flame retardants, cross-linking and blowing agents,

pigments and dyes. Impact modifiers are polymeric materials added to improve the impact

resistance of e.g. PVC, PP, PBT, PA. A separate class of additives are the fillers such as

talcum, wood flour, and reinforcing agents like glass and carbon fibres.

Alloys: strictly speaking, alloys refer to metals and do not exist in plastics. The term is used

interchangeably with blends for mixtures of two or more polymers. Examples are alloys or

blends of polycarbonate (PC) with ABS or with polybutylene terephthalate (PBT).

Blend" an intimate mixture of two or more polymers to obtain the good properties of each,

for example semi-crystalline polypropylene (PP) mixed with 10 to 30% rubbery EPDM

results in a blend with good heat resistance and extraordinary impact resistance. Also the mix

of polycarbonate (PC) with ABS terpolymer results in a blend with the good heat resistance

of the PC part and the low temperature impact resistance of the ABS. Instead of the term

blend, trade literature and producers also use alloy. Blends are made passing the components

in powder or pellet form in a dry blender followed by a heated twin screw extruder to obtain

an intimate blend.

Polymerization process Plastics are one group of polymers that are built from relatively simple units called

monomers (or mers) through a chemical polymerization process. This process is illustrated

below. Processing polymers into end products mainly involves physical phase change such as

melting and solidification (for Thermoplastics) or a chemical reaction (for Thermosets).

Structure of polymers The basic structure of a polymer molecule can be visualized as

a long chain of repeating units, with additional chemical groups forming pendant branches

along the primary "backbone" of the molecule. Although the term plastics has been used

loosely as a synonym for polymer and resin, plastics generally represent polymeric

compounds that are formulated with plasticizers, stabilizers, fillers, and other additives for

purposes of processability and performance. Other polymeric systems include rubbers, fibers,

adhesives, and surface coatings. A variety of processes have been employed to produce the

final plastic parts,

Polymer family, the formation of plastics, and the polymerization process

Classification

Plastics are usually classified by their chemical structure of the polymer's backbone

and side chains. Some important groups in these classifications are

the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Plastics can also

be classified by the chemical process used in their synthesis, such as condensation, poly-

addition, and cross-linking.

There are two types of plastics: thermoplastics and thermosetting polymers.

Thermoplastics are the plastics that do not undergo chemical change in their composition

when heated and can be molded again and again.

Thermoplastics

A Thermoplastic, also known as a thermosoftening plastic, is a polymer that

becomes pliable or moldable above a specific temperature, and returns to a solid state upon

cooling. Most thermoplastics have a high molecular weight, whose chains associate

through intermolecular forces; this property allows thermoplastics to be remolded because the

intermolecular interactions spontaneously reform upon cooling. In this way, thermoplastics

differ from thermosetting polymers, which form irreversible chemical bonds during the

curing process; thermoset bonds break down upon melting and do not reform upon cooling.

Thermoplastic materials can be formed into desired shapes under heat and pressure and

become solids on cooling.

• If they are subjected to the same conditions of heat and pressure, they can be reprocessed

into new shapes.

Thermoplastics based on their crystallization are classified into

Amorphous Thermoplastics

• Some thermoplastics donot crystallise on heating and are termed as amorphous plastics

Used in applications where clarity is important.

• They are frequently used in applications where Clarity is important and are subjected

to stress cracking and less chemically resistant.

• Ex: PMMA, PS and PC.

Semi crystalline Thermoplastics.

Thermoplastics which crystallises to some extent are known as Semi crystalline

Thermoplastics..

• They are resistent to Solvents and other Chemicals.

• Ex:PE,PBT, PP and PET.

Examples include polyethylene, polypropylene, polystyrene, polyvinyl-chloride,

and polytetrafluoroethylene (PTFE). Common thermoplastics range from 20,000 to

500,000 amu, while thermosets are assumed to have infinite molecular weight. These chains

are made up of many repeating molecular units, known as repeat units, derived

from monomers; each polymer chain will have several thousand repeating units.

THERMOSETTING PLASTIC

A thermosetting plastic, also known as a thermoset, is polymer material that

irreversibly cures. The cure may be done through heat (generally above 200 °C (392 °F)),

through a chemical reaction (two-partepoxy, for example), or irradiation such as electron

beam processing.

Thermoset materials are usually liquid or malleable prior to curing and designed to

be molded into their final form, or used as adhesives. Others are solids like that of the

molding compound used insemiconductors and integrated circuits (IC). Once hardened a

thermoset resin cannot be reheated and melted back to a liquid form.

According to IUPAC recommendation: A thermosetting polymer is a prepolymer in a

soft solid or viscous state that changes irreversibly into an infusible, insoluble polymer

network by curing. Curing can be induced by the action of heat or suitable radiation, or both.

A cured thermosetting polymer is called a thermoset.

Thermosets can melt and take shape once; after they have solidified, they stay solid.

In the thermosetting process, a chemical reaction occurs that is irreversible. The vulcanization

of rubber is a thermosetting process. Before heating with sulphur, the polyisoprene is a tacky,

slightly runny material, but after vulcanization the product is rigid and non-tacky.

TABLE 1. Effects of additives, fillers, and reinforcements on polymer properties

Additive / Filler / Reinforcement

Common materials Effects on polymer properties

Reinforcing fibers Baron, carbon, fibrous

minerals,

glass, Kevlar

Increases tensile

strength.

Increases flexural

modulus.

Increases heat-

deflection

temperature (HDT).

Resists shrinkage and

warpage.

Conductive fillers Aluminum powders,

carbon

fiber, graphite

Improves electrical

and

thermal conductivity.

Coupling agents Silanes, titanates Improves interface

bonding between polymer

matrix and the

fibers.

Flame retardants Chlorine, bromine,

phosphorous,

metallic salts

Reduces the

occurrence and

spread of combustion.

Extender fillers Calcium carbonate,

silica, clay

Reduces material

cost.

Plasticizers Monomeric liquids,

lowmolecular-

weight materials

Improves melt flow

properties.

Enhances flexibility.

Colorants (pigments and

dyes)

Metal oxides,

chromates, carbon

blacks

Provides

colorfastness.

Protects from

thermal and UV

degradation (with carbon

blacks).

Blowing agents Gas, azo compounds,

hydrazine

derivatives

Generates a cellular

form to obtain a low-

density material.

Other classifications

Other classifications are based on qualities that are relevant for manufacturing

or product design. Examples of such classes are the thermoplastic and

thermoset, elastomer, structural, biodegradable, and electrically conductive. Plastics can also

be classified by various physical properties, such as density, tensile strength, glass transition

temperature, and resistance to various chemical products.

Biodegradable plastic

Biodegradable plastics break down (degrade) upon exposure to sunlight (e.g., ultra-

violet radiation), water or dampness, bacteria, enzymes, wind abrasion, and in some

instances, rodent, pest, or insect attack are also included as forms

of biodegradation or environmental degradation. Some modes of degradation require that the

plastic be exposed at the surface, whereas other modes will only be effective if certain

conditions exist in landfill or composting systems. Starch powder has been mixed with plastic

as a filler to allow it to degrade more easily, but it still does not lead to complete breakdown

of the plastic. Some researchers have actually genetically engineered bacteria that synthesize

a completely biodegradable plastic, but this material, such as Biopol, is expensive at present.

The German chemical company BASF makes Ecoflex, a fully biodegradable polyester for

food packaging applications.

Natural vs synthetic

Main article: Bioplastic

Most plastics are produced from petrochemicals. Motivated by the finiteness of

petrochemical reserves and possibility of global warming, bioplastics are being developed.

Bioplastics are made substantially from renewable plant materials such as cellulose and

starch.

In comparison to the global consumption of all flexible packaging, estimated at 12.3

million tonnes/year, estimates put global production capacity at 327,000 tonnes/year for

related bio-derived materials.

Amorphous: used for polymers lacking crystalline structures like acrylics (PMMA),

polystyrene (PS), polycarbonate (PC) and polyvinylchloride (PVC). Amorphous plastics are

usually hard, glassy and transparent in appearance and exhibit a wide melting or softening

temperature range.

PMMA

PS

PC

Crystalline: Many plastics are semi-crystalline, which means that some 30 to 70% of

crystallites are present in the structure surrounded by an amorphous polymer. These polymers

are non transparent because they exist in two distinct phases. Examples are polypropylene

(PP), polyacetal (POM), polyamides (PA), polybutylene terephtalate (PBT) and they exhibit a

rather sharp softening or melting temperature.

PE

PP

Crystalline vs amorphous

Some plastics are partially crystalline and partially amorphous in molecular structure,

giving them both a melting point (the temperature at which the attractive intermolecular

forces are overcome) and one or more glass transitions (temperatures above which the extent

of localized molecular flexibility is substantially increased). The so-called semi-

crystalline plastics include polyethylene, polypropylene, poly (vinyl chloride), polyamides

(nylons), polyesters and some polyurethanes. Many plastics are completely amorphous, such

as polystyrene and its copolymers, poly (methyl methacrylate), and all thermosets.

Molded plastic food replicas on display outside a restaurant in Japan

The properties of amorphous and crystalline polymers: General properties

Soften over a wide range of temperatures

Distinct and sharp melting point

Lower specific gravity

Higher specific gravity due to better

packing

Lower tensile strength and tensile Higher tensile strength and tensile

modulus

modulus

Higher ductility and impact strength

Lower ductility and impact strength

Lower creep resistance

Higher creep resistance

Tend to be transparent

Tend to be translucent or opaque

Higher dimensional stability

Lower dimensional stability

Lower fatigue resistance

Higher fatigue resistance

Bond well using adhesives and solvents

Difficult to bond using adhesives and

solvents

Lower chemical resistance and resistance

to stress cracking

Higher chemical resistance and resistance

to stress cracking

Structural applications only (not for

bearing and wear)

Good for bearing and wear, as well as for

structural applications

Effects of Fillers/Reinforcements – Functions

Traditionally, fillers were considered as additives, which, due to their unfavorable

geometrical features, surface area or surface chemical composition, could only moderately

increase the modulus of the polymer, while strength (tensile, f lexural) remained unchanged

or even decreased. Their major contribution was in lowering the cost of materials by

replacing the more expensive polymer; other possible economic advantages were faster

molding cycles as a result of increased thermal conductivity and fewer rejected parts due to

warpage. Depending on the type of filler, other polymer properties could be affected; for

example, melt viscosity could be significantly increased through the incorporation of fibrous

materials. On the other hand, mould shrinkage and thermal expansion would be reduced, a

common effect of most inorganic fillers.

The term reinforcing filler has been coined to describe discontinuous additives, the

form, shape, and/or surface chemistry of which have been suitably modified with the

objective of improving the mechanical properties of the polymer, particularly strength.

Inorganic reinforcing fillers are stiffer than the matrix and deform less, causing an overall

reduction in the matrix strain, especially in the vicinity of the particle as a result of the

particle/matrix interface. As shown in Figure 1-3, the fiber ―pinches‖ the polymer in its

vicinity, reducing strain and increasing stiffness . Reinforcing fillers are characterized by

relatively high aspect ratio, α, defined as the ratio of length to diameter for a fiber, or the ratio

of diameter to thickness for platelets and f lakes. For spheres, which have minimal

reinforcing capacity, the aspect ratio is unity. A useful parameter for characterizing the

effectiveness of a filler is the ratio of its surface area, A, to its volume, V, which needs to be

as high as possible for effective reinforcement.

In developing reinforcing fillers, the aims of process or material modifications are

to increase the aspect ratio of the particles and to improve their compatibility and interfacial

adhesion with the chemically dissimilar polymer matrix. Such modifications may enhance

and optimize not only the primary function of the filler (in this case its use as a mechanical

property modifier), but may also introduce or enhance additional functions. New functions

A cylindrical reinforcing fiber in a polymer matrix: a) in the undeformed state; b) under a

tensile load (reprinted with permission of Oxford University

Surface area-to-volume ratio, A/V, of a cylindrical particle plotted versus aspect ratio, a = l/d (reprinted with

permission of Oxford University

fillers, thus broadening their range of applications, are illustrated by the examples below.

As described by Heinold ,the first generation of fillers soon after the commercialization of

polypropylene included talc platelets and asbestos fibers for their beneficial effects on

stiffness and heat resistance. The search for a replacement for asbestos due to health issues

led to calcium carbonate particles and mica f lakes as the second-generation fillers. Mica was

found to be more effective than talc for increasing stiffness and heat resistance, while calcium

carbonate proved to be less effective in increasing stiffness, but increased the impact

resistance of PP homopolymers. Surface modification of mica with coupling agents to

enhance adhesion and stearate modification of calcium carbonate to assist dispersion were

found to enhance these functions and introduced other benefits such as improved

processability, a means of imparting color, and reduced long term heat ageing. Other fillers

imparted entirely different functions. For example, barium sulfate enhances sound absorption,

wollastonite enhances scratch resistance, solid glass spheres add dimensional stability and

increase hardness, hollow glass spheres lower density, and combinations of glass fibers with

particulate fillers provide unique properties that cannot be attained with single fillers. An

additional example of a family of fillers imparting distinct new properties is given by the

pearlescent pigments produced by platelet core-shell technologies .

These comprise platelets of mica, silica, alumina or glass substrates coated with films of

oxide nanoparticles, e.g. TiO2, Fe2O3, Fe3O4, Cr2O3 . In addition to conventional

decorative applications, new functional applications such as solar heat re f lection, laser

marking of plastics, and electrical conductivity are possible through selection of the

appropriate substrate/coating combinations.

Properties of plastics

The properties of plastics are defined chiefly by the organic chemistry of the polymer

such as hardness, density, and resistance to heat, organic solvents, oxidation, and ionizing

radiation. In particular, most plastics will melt upon heating to a few hundred

degrees celsius. While plastics can be made electrically conductive, with the conductivity of

up to 80 kS/cm in stretch-orientedpolyacetylene, they are still no match for most metals

like copper which have conductivities of several hundreds kS/cm.

PROPERTIES OF PLASTICS

In order to make proper designs with any material, including plastics, it is necessary

to know certain physical, chemical, electrical and mechanical properties of the material. The

following are the terms that are important in specifying the properties of a plastic.

Mechanical Properties

Plastics have the characteristics of both a viscous liquid and a spring-like elastomer,

traits known as a viscoelasticity. These characteristics are responsible for many of the

characteristic material properties displayed by plastics. Under mild loading conditions, such

as short-term loading with low deflection and small loads at room temperature, plastics

usually react like springs, returning to their original shape after the load is removed. Under

long-term heavy loads or elevated temperatures many plastics deform and flow similar to

high viscous liquids, although still solid.

Creep is the deformation that occurs over time when a material is subjected to

constant stress at constant temperature. This is the result of the viscoelastic behavior of

plastics.

Stress relaxation is another viscoelastic phenomenon. It is defined as a gradual

decrease in stress at constant temperature.

Recovery is the degree to which a plastic returns to its original shape after a load is

removed.

Specific gravity is the ratio of the weight of any volume to the weight of an equal

volume of some other substance taken as the standard at a stated temperature. For plastics,

the standard is water.

Water absorption is the ratio of the weight of water absorbed by a material to the

weight of the dry material. Many plastics are hygroscopic, meaning that over time they

absorb water.

Tensile strength at break is a measure of the stress required to deform a material

prior to breakage. It is calculated by dividing the maximum load applied to the material

before its breaking point by the original cross-sectional area of the test piece.

Tensile modulus (modulus of elasticity) is the slope of the line that represents the

elastic portion of the stress-strain graph.

Elongation at break is the increase in the length of a tension specimen, usually

expressed as a percentage of the original length of the specimen.

Compressive strength is the maximum compressive stress a material is capable of

sustaining. For materials that do not fail by a shattering fracture, the value depends on the

maximum allowed distortion.

Flexural strength is the strength of a material in bending expressed as the tensile

stress of the outermost fibers of a bent test sample at the instant of failure.

Flexural modulus is the ratio, within the elastic limit, of stress to the corresponding

strain.

Izod Impact is one of the most common ASTM tests for testing the impact strength

of plastic materials. It gives data to compare the relative ability of materials to resist brittle

fracture as the service temperature decreases.

For finding hardness, Rockwell Number is the net increase in depth of impression as

the load on a penetrator is increased from a fixed minimum load to a high load and then

returned to a minimum load.

Coefficient of thermal expansion is the change in unit length or volume resulting

from a unit change in temperature. Commonly used unit is 10-6

cm/cm/C.

Thermal conductivity is the ability of a material to conduct heat; a physical constant

for the quantity of heat that passes through a unit cube of a material in a unit of time when the

difference in temperature of two faces is 1C.

Heat Deflection temperature (HDT) test is one in which a bar of the polymer is

heated uniformly in a closed chamber while a load of 66psi or 264psi is placed at the center

of the horizontal bar. The HDT is the temperature at which a deflection of 0.25mm is noted at

the center. The HDT indicated how much mass the object must be constructed of to maintain

the desired form. It also provides a measure of the rigidity of the polymer under a load as

well as temperature.

limiting oxygen index is a measure of the minimum oxygen level required to support

combustion of the polymer.

Absorption. Polymers have a potential to absorb various corrodents the come to

contact with, particularly organic liquids. This can result in swelling, cracking and

penetration to the substrate of the component.

Toxicity

Due to their insolubility in water and relative chemical inertness, pure plastics

generally have low toxicity. Some plastic products contain a variety of additives, some of

which can be toxic. For example, plasticizers like adipates and phthalates are often added to

brittle plastics like polyvinyl chloride to make them pliable enough for use in food

packaging, toys, and many other items. Traces of these compounds can leach out of the

product. Owing to concerns over the effects of such leachates, the European Union has

restricted the use of DEHP (di-2-ethylhexyl phthalate) and other phthalates in some

applications. Some compounds leaching from polystyrene food containers have been

proposed to interfere with hormone functions and are suspected human carcinogens.

Whereas the finished plastic may be non-toxic, the monomers used in the manufacture of the

parent polymers may be toxic. In some cases, small amounts of those chemicals can remain

trapped in the product unless suitable processing is employed. For example, the World Health

Organization's International Agency for Research on Cancer (IARC) has recognized

that vinyl chloride, the precursor to PVC, as a human carcinogen.

Environmental issues

Plastics are durable and degrade very slowly; the chemical bonds that make plastic so

durable make it equally resistant to natural processes of degradation. Since the 1950s, one

billion tons of plastic have been discarded and may persist for hundreds or even thousands of

years. Perhaps the biggest environmental threat from plastic comes from nurdles, which are

the raw material from which all plastics are made. They are tiny pre-plastic pellets that kill

large numbers of fish and birds that mistake them for food.

Prior to the ban on the use of CFCs in extrusion of polystyrene (and general use, except in

life-critical fire suppression systems; see Montreal Protocol), the production of polystyrene

contributed to the depletion of the ozone layer; however, non-CFCs are currently used in the

extrusion process.

Incineration of plastics

Plastics can be converted into a fuel since they are usually hydrocarbon-based and can

be broken down into liquid hydrocarbon. One kilogram of waste plastic produces a liter of

hydrocarbon. In some cases, burning plastic can release toxic fumes. Burning the plastic

polyvinyl chloride (PVC) may create dioxin.

Recycling

Thermoplastics can be remelted and reused, and thermoset plastics can be ground up

and used as filler, although the purity of the material tends to degrade with each reuse cycle.

There are methods by which plastics can be broken back down to a feedstock state.

The greatest challenge to the recycling of plastics is the difficulty of automating the

sorting of plastic wastes, making it labor intensive. Typically, workers sort the plastic by

looking at the resin identification code, although common containers like soda bottles can be

sorted from memory. Typically, the caps for PETE bottles are made from a different kind of

plastic which is not recyclable, which presents additional problems to the automated sorting

process. Other recyclable materials such as metals are easier to process mechanically.

However, new processes of mechanical sorting are being developed to increase capacity and

efficiency of plastic recycling.

While containers are usually made from a single type and color of plastic, making

them relatively easy to be sorted, a consumer product like a cellular phone may have many

small parts consisting of over a dozen different types and colors of plastics. In such cases, the

resources it would take to separate the plastics far exceed their value and the item is

discarded. However, developments are taking place in the field of active disassembly, which

may result in more consumer product components being re-used or recycled. Recycling

certain types of plastics can be unprofitable, as well. For example, polystyrene is rarely

recycled because it is usually not cost effective. These unrecycled wastes are typically

disposed of in landfills, incinerated or used to produce electricity at waste-to-energy plants.

A first success in recycling of plastics is Vinyloop, a recycling process and an

approach of the industry to separate PVC from other materials through a process of

dissolution, filtration and separation of contaminations. A solvent is used in a closed loop to

elute PVC from the waste. This makes it possible to recycle composite structure PVC waste

which normally is being incinerated or put in a landfill. Vinyloop-based recycled PVC's

primary energy demand is 46 percent lower than conventional produced PVC. The global

warming potential is 39 percent lower. This is why the use of recycled material leads to a

significant better ecological footprint.

In 1988, to assist recycling of disposable items, the Plastic Bottle Institute of

the Society of the Plastics Industry devised a now-familiar scheme to mark plastic bottles by

plastic type. A plastic container using this scheme is marked with a triangle of three "chasing

arrows", which encloses a number giving the plastic type:

Plastics type marks: the resin identification code[31]

1. PET (PETE), polyethylene terephthalate

2. HDPE, high-density polyethylene

3. PVC, polyvinyl chloride

4. LDPE, low-density polyethylene,

5. PP, polypropylene

6. PS, polystyrene

7. Other types of plastics (see list, below)

Common plastics and uses

Due to their relatively low cost, ease of manufacture, versatility, and imperviousness

to water, plastics are used in an enormous and expanding range of products, from paper clips

to spaceships. They have already displaced many traditional materials, such

as wood, stone, horn and bone, leather, paper, metal, glass, and ceramic, in most of their

former uses.

A chair made with a polypropylene seat

ABS (Acrylonitrile-Butadiene-Styrene)

Typical Applications

Automotive (instrument and interior trim panels, glove compartment doors, wheel covers,

mirror housings, etc.)

Refrigerators, small appliance housings and power tools applications (hair dryers,

blenders, food processors, lawnmowers, etc.)

Telephone housings, typewriter housings, typewriter keys

Recreational vehicles such as golf carts and jet skis.

PA 6 (Polyamide 6, Nylon 6, or

Polycaprolactam)

Applications

Used in many structural applications because of its good mechanical strength and rigidity. It

is

used in bearings because of its good wear resistance.

PA 12 (Polyamide 12 or Nylon 12)

Typical Applications

Gear wheels for water meters and business machines

Cable ties

Cams

Slides

Bearings

PA 66 (Polyamide 66, Nylon 66, or Poly

(hexamethylene adipamide))

Applications

Competes with PA 6 for most applications. PA 66 is heavily used in the following:

The automotive industry

Appliance housings

Where impact resistance and strength are required

PBT (Polybutylene Terephthalates)

Typical Applications

Household appliances (e.g., food processor blades, vacuum cleaner parts, fans, hair dryer

housings, coffee makers)

Electronics (e.g., switches, motor housings, fuse cases, key caps for computer keyboards,

connectors, fiber optic buffer tubing)

Automotive (e.g., grilles, body panels, wheel covers, and components for doors and

windows)

PC (Polycarbonate)

Typical Applications

Electronic and business equipment (e.g., computer parts, connectors)

Appliances (e.g., food processors, refrigerator drawers)

Transportation (e.g., head lights, tail lights, instrument panels)

PC|ABS (Polycarbonate-Acrylonitrile-

Butadiene-Styrene Blend)

Typical Applications

Computer and business machine housings

Electrical applications

Cellular phones

Lawn and garden equipment

Automotive components (instrument panels, interior trim, and wheel covers)

PC|PBT (Polycarbonate |

Polybutyleneterephthalate Blend)

Typical Applications

Gear cases and automotive (bumpers)

Applications that require chemical and corrosion resistance, high heat resistance, high

impact strength over wide temperature ranges, and high dimensional stability

PE-HD (High Density Polyethylene)

Typical Applications

Major use is in blow-molding (packaging) applications such as:

Containers in refrigeration units

Storage vessels

Household goods (kitchenware)

Seal caps

Bases for PET bottles

PEI (Polyetherimide)

Typical Applications

Automotive (engine components: temperature sensors, fuel and air handling devices

Electrical/electronics (connector materials, printed circuit boards, circuit chip carriers,

explosion proof boxes)

Packaging applications

Aircraft (interior materials)

Medical (surgical staplers, tool housings, non-implant devices)

PE-LD (Low Density Polyethylene)

Typical Applications

Closures

Bowls

Bins

Pipe couplings

PET (Polyethylene Terephthalate)

Typical Applications

Automotive (structural components such as mirror backs, and grille supports, electrical

parts such as head lamp reflectors and alternator housings)

Electrical applications (motor housings, electrical connectors, relays, and switches,

microwave oven interiors)

Industrial applications (furniture chair arms, pump housings, hand tools)

PETG (Glycol-modified PET; Copolyesters)

Typical Applications

PETGs offer a desirable combination of properties such as clarity, toughness, and stiffness.

Applications include:

Medical devices (test tubes and bottles)

Toys

Displays

Lighting fixtures

Face shields

Refrigerator crisper pans

PMMA (Polymethyl Methacrylate)

Typical Applications

Automotive (signal light devices, instrument panels)

Medical (blood cuvettes)

Industrial (video discs, lighting diffusers, display shelving)

Consumer (drinking tumblers, stationery accessories)

POM (Polyacetal or Polyoxymethylene)

Applications

Acetals have a low coefficient of friction and good dimensional stability. This makes it ideal

for

use in gears and bearings. Due to its high temperature resistance, it is used in plumbing (valve

and pump housings) and lawn equipment.

PP (Polypropylene)

Typical Applications

Automotive (mostly mineral-filled PP is used: dashboard components, ductwork, fans,

and some under-hood components)

Appliances (doorliners for dishwashers, ductwork for dryers, wash racks and lids for

clothes washers, refrigerator liners)

Consumer products (lawn/garden furniture, components of lawn mowers, sprinklers)

PPE|PPO (Polypropylene Ether Blends)

Typical Applications

Household appliances (dishwasher, washing machine)

Electrical applications, such as control housings, fiber-optic connectors

PS (Polystyrene)

Typical Applications

Packaging

Housewares (tableware, trays)

Electrical (transparent housings, light diffusers, insulating film)

PVC (Polyvinyl Chloride)

Typical Applications

Water distribution piping

Home plumbing

House siding

Business machine housings

Electronics packaging

Medical apparatus

Packaging for foodstuffs

SAN (Styrene Acrylonitrile)

Typical Applications

Electrical (receptacles, mixer bowls, housings, etc. for kitchen appliances, refrigerator

fittings, chassis for television sets, cassette boxes)

Automotive (head lamp bodies, reflectors, glove compartments, instrument panel covers)

Household appliances (tableware, cutlery, beakers)

Cosmetic packs

Polyester (PES) – Fibers, textiles.

High-density polyethylene (HDPE) – Detergent bottles, milk jugs, and molded plastic

cases.

Polyvinylidene chloride (PVDC) (Saran) – Food packaging.

Low-density polyethylene (LDPE) – Outdoor furniture, siding, floor tiles, shower

curtains, clamshell packaging.

High impact polystyrene (HIPS) -: Refrigerator liners, food packaging, vending cups.

Polyurethanes (PU) – Cushioning foams, thermal insulation foams, surface coatings,

printing rollers (Currently 6th or 7th most commonly used plastic material, for instance

the most commonly used plastic in cars).

Special purpose plastics

Melamine formaldehyde (MF) – One of the aminoplasts, and used as a multi-colorable

alternative to phenolics, for instance in moldings (e.g., break-resistance alternatives to

ceramic cups, plates and bowls for children) and the decorated top surface layer of the

paper laminates (e.g., Formica).

Plastarch material – Biodegradable and heat resistant, thermoplastic composed

of modified corn starch.

Phenolics (PF) or (phenol formaldehydes) – High modulus, relatively heat resistant, and

excellent fire resistant polymer. Used for insulating parts in electrical fixtures, paper

laminated products (e.g., Formica), thermally insulation foams. It is a thermosetting

plastic, with the familiar trade name Bakelite, that can be molded by heat and pressure

when mixed with a filler-like wood flour or can be cast in its unfilled liquid form or cast

as foam (e.g., Oasis). Problems include the probability of moldings naturally being dark

colors (red, green, brown), and as thermoset it is difficult to recycle.

Polyetheretherketone (PEEK) – Strong, chemical- and heat-resistant

thermoplastic, biocompatibility allows for use in medical implant applications, aerospace

moldings. One of the most expensive commercial polymers.

Polyetherimide (PEI) (Ultem) – A high temperature, chemically stable polymer that does

not crystallize.

Polylactic acid (PLA) – A biodegradable, thermoplastic found converted into a variety of

aliphatic polyesters derived from lactic acid which in turn can be made by fermentation

of various agricultural products such as corn starch, once made from dairy products.

Polymethyl methacrylate (PMMA) – Contact lenses (of the original "hard" variety),

glazing (best known in this form by its various trade names around the world; e.g.,

Perspex, Oroglas, Plexiglas), aglets, fluorescent light diffusers, rear light covers for

vehicles. It forms the basis of artistic and commercial acrylic paints when suspended in

water with the use of other agents.

Polytetrafluoroethylene (PTFE) – Heat-resistant, low-friction coatings, used in things like

non-stick surfaces for frying pans, plumber's tape and water slides. It is more commonly

known as Teflon.

Urea-formaldehyde (UF) – One of the aminoplasts and used as a multi-colorable

alternative to phenolics. Used as a wood adhesive (for plywood, chipboard, hardboard)

and electrical switch housings.

Etymology

The word plastic is derived from the Greek πλαστικός (plastikos) meaning capable of being

shaped or molded, from πλαστός (plastos) meaning molded. It refers to their malleability,

orplasticity during manufacture, that allows them to be cast, pressed, or extruded into a

variety of shapes—such as films, fibers, plates, tubes, bottles, boxes, and much more.

The common word plastic should not be confused with the technical adjective plastic, which

is applied to any material which undergoes a permanent change of shape (plastic

deformation) when strained beyond a certain point. Aluminum which is stamped or forged,

for instance, exhibits plasticity in this sense, but is not plastic in the common sense; in

contrast, in their finished forms, some plastics will break before deforming and therefore are

not plastic in the technical sense.

Different manufacturing processes for Plastics: • Injection Moulding.

• Compression Moulding.

• Blow Moulding.

• Compression Moulding.

• Plastics Extrusion.

• Thermoforming.

• Slush Moulding.

• Transfer moulding.

• Calendaring.

Injection Moulding

Injection moulding is a manufacturing process for producing parts from

both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel,

mixed, and forced into a mould cavity where it cools and hardens to the configuration of the

cavity. After a product is designed, usually by an industrial designer or an engineer, moulds

are made by a mouldmaker (or toolmaker) from metal, usually either steel or aluminum, and

precision-machined to form the features of the desired part. Injection moulding is widely used

for manufacturing a variety of parts, from the smallest component to entire body

panels of cars.

Injection Moulding: Mould Construction and Part Design : Mold

Mold or die are the common terms used to describe the tooling used to produce

plastic parts in molding. Since molds have been expensive to manufacture, they were usually

only used in mass production where thousands of parts were being produced. Typical molds

are constructed from hardened steel, pre-hardened steel, aluminum, and/or beryllium-

copper alloy. The choice of material to build a mold from is primarily one of economics; in

general, steel molds cost more to construct, but their longer lifespan will offset the higher

initial cost over a higher number of parts made before wearing out. Pre-hardened steel molds

are less wear-resistant and are used for lower volume requirements or larger components. The

typical steel hardness is 38–45 on the Rockwell-C scale. Hardened steel molds are heat

treated after machining. These are by far the superior in terms of wear resistance and lifespan.

Typical hardness ranges between 50 and 60 Rockwell-C (HRC). Aluminum molds can cost

substantially less, and, when designed and machined with modern computerized equipment,

can be economical for molding tens or even hundreds of thousands of parts. Beryllium copper

is used in areas of the mold that require fast heat removal or areas that see the most shear heat

generated. The molds can be manufactured either by CNC machining or by using electrical

discharge machining processes.

Injection molding die with side pulls

"A" side of die for 25% glass-filled acetal with 2 side pulls.

Close up of removable insert in "A" side.

"B" side of die with side pull actuators.

Insert removed from die.

Mold design

Standard two plates tooling – core and cavity are inserts in a mold base – "family mold" of

five different parts:

The mold consists of two primary components, the injection mold (A plate) and the

ejector mold (B plate). Plastic resin enters the mold through a sprue in the injection mold; the

sprue bushing is to seal tightly against the nozzle of the injection barrel of the molding

machine and to allow molten plastic to flow from the barrel into the mold, also known as

the cavity. The sprue bushing directs the molten plastic to the cavity images through channels

that are machined into the faces of the A and B plates. These channels allow plastic to run

along them, so they are referred to as runners. The molten plastic flows through

the runner and enters one or more specialized gates and into the cavity geometry to form the

desired part.

Sprue, runner and gates in actual injection molding product

The amount of resin required to fill the sprue, runner and cavities of a mold is a shot.

Trapped air in the mold can escape through air vents that are ground into the parting line of

the mold. If the trapped air is not allowed to escape, it is compressed by the pressure of the

incoming material and is squeezed into the corners of the cavity, where it prevents filling and

causes other defects as well. The air can become so compressed that it ignites and burns the

surrounding plastic material. To allow for removal of the molded part from the mold, the

mold features must not overhang one another in the direction that the mold opens, unless

parts of the mold are designed to move from between such overhangs when the mold opens

(utilizing components called Lifters).

Sides of the part that appear parallel with the direction of draw (The axis of the cored

position (hole) or insert is parallel to the up and down movement of the mold as it opens and

closes) are typically angled slightly (with draft) to ease release of the part from the mold.

Insufficient draft can cause deformation or damage. The draft required for mold release is

primarily dependent on the depth of the cavity: the deeper the cavity, the more draft

necessary. Shrinkage must also be taken into account when determining the draft required. If

the skin is too thin, then the molded part will tend to shrink onto the cores that form them

while cooling, and cling to those cores or part may warp, twist, blister or crack when the

cavity is pulled away. The mold is usually designed so that the molded part reliably remains

on the ejector (B) side of the mold when it opens, and draws the runner and the sprue out of

the (A) side along with the parts. The part then falls freely when ejected from the (B) side.

Tunnel gates, also known as submarine or mold gates, are located below the parting line or

mold surface. An opening is machined into the surface of the mold on the parting line. The

molded part is cut (by the mold) from the runner system on ejection from the mold. Ejector

pins, also known as knockout pins, are circular pins placed in either half of the mold (usually

the ejector half), which push the finished molded product, or runner system out of a mold.

The standard method of cooling is passing a coolant (usually water) through a series of

holes drilled through the mold plates and connected by hoses to form a continuous pathway.

The coolant absorbs heat from the mold (which has absorbed heat from the hot plastic) and

keeps the mold at a proper temperature to solidify the plastic at the most efficient rate.

To ease maintenance and venting, cavities and cores are divided into pieces,

called inserts, and sub-assemblies, also called inserts, blocks, orchase blocks. By substituting

interchangeable inserts, one mold may make several variations of the same part.

More complex parts are formed using more complex molds. These may have sections called

slides, that move into a cavity perpendicular to the draw direction, to form overhanging part

features. When the mold is opened, the slides are pulled away from the plastic part by using

stationary ―angle pins‖ on the stationary mold half. These pins enter a slot in the slides and

cause the slides to move backward when the moving half of the mold opens. The part is then

ejected and the mold closes. The closing action of the mold causes the slides to move forward

along the angle pins.

Some molds allow previously molded parts to be reinserted to allow a new plastic

layer to form around the first part. This is often referred to as overmolding. This system can

allow for production of one-piece tires and wheels.

Two-shot or multi-shot molds are designed to "overmold" within a single molding

cycle and must be processed on specialized injection molding machines with two or more

injection units. This process is actually an injection molding process performed twice. In the

first step, the base color material is molded into a basic shape, which contains spaces for the

second shot. Then the second material, a different color, is injection-molded into those

spaces. Pushbuttons and keys, for instance, made by this process have markings that cannot

wear off, and remain legible with heavy use.

A mold can produce several copies of the same parts in a single "shot". The number of

"impressions" in the mold of that part is often incorrectly referred to as cavitation. A tool

with one impression will often be called a single impression(cavity) mold. A mold with 2 or

more cavities of the same parts will likely be referred to as multiple impression (cavity)

mold. Some extremely high production volume molds (like those for bottle caps) can have

over 128 cavities.

In some cases multiple cavity tooling will mold a series of different parts in the same

tool. Some toolmakers call these molds family molds as all the parts are related. Examples

include plastic model kits.

Terminology:

Cavity: This is the half of the mould that forms the outer surfaces of the part. It is

characterized by the negative impression of the part carved into the cavity block.

Core: This is the half of the mould that forms the backside of a part. In general, the core

material rises up from the core block and almost fills in the back of the cavity. The resulting

space between the core and cavity is the wall thickness of the part that will be moulded.

Parting line: This is the interface where two parts of the mould, such core and cavity or slide

and mold, come together. This term refers both to the interface and the resulting witness line

that is molded into the part.

Shutoff: This is a place where two parts of the mold shut against each other and prevent

plastic from passing through. Technically speaking, the main parting line interface is a

shutoff, but the term is seldom used in this instance. Usually, the term applies to a situation

where one part of the mold closes against another to form a slot or hole, or it is sometimes

used to refer to the interface where a slide shuts against a core or cavity. Sometimes, the

shutoff surfaces are parallel to the direction that the mold opens. When this happens, draft has

to be added to avoid grinding the parts of the mold against each other. This type of shutoff is

sometimes referred to as a sliding shutoff or a slide-by. An example of this will be seen on

the vent mold.

Undercut: An overhanging feature on the part that would prevent it from being removed

from the mold.

Process characteristics

Utilizes a ram or screw-type plunger to force molten plastic material into a mould cavity

Produces a solid or open-ended shape that has conformed to the contour of the mould

Uses thermoplastic or thermoset materials

The process usually begins with a conventional production mould. These tools can be

multi-cavity and produce millions of parts

A parting line, sprue, gate marks, and ejector pin marks are usually present. None of

these features are typically desired. They are the results of the parting of the mould for

ejection of the formed part

Applications

Injection molding is used to create many things such as wire spools, packaging, bottle

caps, automotive dashboards, pocket combs, some musical instruments (and parts of them),

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. It is ideal for producing high volumes of the same object. Some

advantages of injection molding are high production rates, repeatable high tolerances, the

ability to use a wide range of materials, low labor cost, minimal scrap losses, and little need

to finish parts after molding. Some disadvantages of this process are expensive equipment

investment, potentially high running costs, and the need to design moldable parts.

Lifter:

Lifter Action in an injection mold provides for the molding of undercuts. The

undercut can be internal or external on the part. Typical parts are battery compartment covers

on cell phones and calculators. The Lifter also aids the ejection process.

Typical components in a lifter mold include Lifter, which forms the undercut and possibly

the adjacent geometry and is attached to a blade, rod, arm etc.

T-Coupling

U-Coupling

There are many different configurations of lifters made by manufacturers. Exploring

Catalogs and websites can generate many ideas. Unique lifters are common, and can aid in

the ease of creating a design suitable for the undercut of a given part.

Lifter angles typically do not exceed 28 degrees from the vertical, as exceeding 28 degrees

causes a concern for wear. Conversely, if the angle is on the small side (1-5 degrees), the

travel required (if using ejection to move the lifter) to release the part is a concern.

(undercut distance=(2x+35))

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Slider:

Slide Action requires several mechanical components to enable the molding of

complex part geometry. Slides are usually used for exterior action, and typically pull a core

located on the "B" side of the mould.

Slide Action moulds typically contain the following components:

Angle Pin (also referred to as: Cam, or Horn Pin)

The function of the Angle Pin is to move (drive) the Slide attached to the "B" side of

the mould. Angles are typically 5-28 degrees from the vertical. The angle and length of the

pin is determined by the amount of travel is required for the "Side-Pull" of the part.

Slide

The slide can be a steel that forms a portion of the part, or it can retain core pin or other

shape of core steel. The slide usually rests upon a wear plate and retained via a gibing

system. There typically is a wear plate attached to the slide that enables the heel block to

push the slide in for final locking before injection.

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L-Gibs (or Gibbing)

L-Gibs are used to contain the slide, and ensure that the slide moves in an accurately

and smoothly without any significant misalignment of the slide to the other cavity forming

steels. L-Gibs and wear plates are usually Lamina Bronze. Grease grooves are added to aid

in preventing wear.

Wear Plate

The wear plate provides a surface that will resist wear when the slide moves over it,

during the life of the mold.

Slide Retainer

The Slide Retainer holds the slide in the fully open position to ensure that the slide

does not move until it is supposed to (otherwise, damage will result to the mold). There are

many types of slide retainer mechanisms, some are standard components. A Ball-detent can

be used as a retainer.

Slide Lock

Slide Locks are required to "Lock" the slide in place for injection. The lock takes ALL

the pressure off the Angle Pin during injection (the angle pin does not touch the slide during

injection). The angle of the lock is typically 2-4 degrees greater (from the vertical) than the

Angle Pin.

Gate type

As important as selecting the optimal gate size and location is the choice of the type of

gate. Gate types can be divided between manually and automatically trimmed gates.

Manually trimmed gates

Manually trimmed gates are those that require an operator to separate parts from

runners during a secondary operation. The reasons for using manually trimmed gates

are:

The gate is too bulky to be sheared from the part as the tool is opened.

Some shear-sensitive materials (e.g., PVC) should not be exposed to the high shear rates

inherent to the design of automatically trimmed gates.

Simultaneous flow distribution across a wide front to achieve specific orientation of

fibers of molecules often precludes automatic gate trimming.

Gate types trimmed from the cavity manually include:

Sprue gate

Edge gate

Tab gate

Overlap gate

Fan gate

Film gate

Diaphragm gate

External ring

Spoke or multipoint gate

Automatically trimmed gates

Automatically trimmed gates incorporate features in the tool to break or shear the

gate as the molding tool is opened to eject the part. Automatically trimmed gates

should be used to:

Avoid gate removal as a secondary operation.

Maintain consistent cycle times for all shots.

Minimize gate scars.

Gate types trimmed from the cavity automatically include:

Pin gate

Submarine (tunnel) gates

Hot runner gates

Valve gates

Sprue gate

Recommended for single cavity molds or for parts requiring symmetrical filling.

This type of gate is suitable for thick sections because holding pressure is more effective. A

short sprue is favored, enabling rapid mold filling and low-pressure losses. A cold slug well

should be included opposite the gate. The disadvantage of using this type of gate is the gate

mark left on the part surface after the runner (or sprue) is trimmed off. Freeze-off is

controlled by the part thickness rather than determined the gate thickness. Typically, the part

shrinkage near the sprue gate will be low; shrinkage in the sprue gate will be high. This

results in high tensile stresses near the gate.

Dimensions

The starting sprue diameter is controlled by the machine nozzle. The sprue

diameter here must be about 0.5 mm larger than the nozzle exit diameter. Standard sprue

bushings have a taper of 2.4 degrees, opening toward the part. Therefore, the sprue length

will control the diameter of the gate where it meets the part; the diameter should be at least

1.5 mm larger than or approximately twice the thickness of the part at that point. The junction

of sprue and part should be radiused to prevent stress cracking

A smaller taper angle (a minimum of one degree) risks not releasing the sprue from

the sprue bushing on ejection. A larger taper wastes material and extends cooling time.

Non-standard sprue tapers will be more expensive, with little gain.

Sprue gate

Edge gate

The edge or side gate is suitable for medium and thick sections and can be used on

multicavity two plate tools. The gate is located on the parting line and the part fills from the

side, top or bottom.

Dimensions

The typical gate size is 80% to 100% of the part thickness up to 3.5 mm and 1.0 to 12 mm

wide. The gate land should be no more than 1.0 mm in length, with 0.5 mm being the

optimum.

Edge gate

Tab gate

A tab gate is typically employed for flat and thin parts, to reduce the shear stress in the

cavity. The high shear stress generated around the gate is confined to the auxiliary tab, which

is trimmed off after molding. A tab gate is often used for molding P.

Dimensions

The minimum tab width is 6 mm. The minimum tab thickness is 75% of the depth of the

cavity.

Tab gate

Overlap gate

An overlap gate is similar to an edge gate, except the gate overlaps the wall or surfaces. This

type of gate is typically used to eliminate jetting.

Dimensions

The typical gate size is 10% to 80% of the part thickness and 1.0 to 12 mm wide. The gate

land should be no more than 1.0 mm in length, with 0.5 mm being the optimum.

Overlap gate

Fan gate

A fan gate is a wide edge gate with variable thickness. This type is often used for thick-

sectioned moldings and enables slow injection without freeze-off, which is favored for low

stress moldings or where warpage and dimensional stability are main concerns. The gate

should taper in both width and thickness, to maintain a constant cross sectional area. This will

ensure that:

The melt velocity will be constant.

The entire width is being used for the flow.

The pressure is the same across the entire width.

Dimensions

As with other manually trimmed gates, the maximum thickness should be no more than 80%

of the part thickness. The gate width varies typically from 6 mm up to 25% of the cavity

length.

Film or flash gate

A film or flash gate consists of a straight runner and a gate land across either the entire length

or a portion of the cavity. It is used for long flat thin walled parts and provides even filling.

Shrinkage will be more uniform which is important especially for fiber reinforced

thermoplastics and where warpage must be kept to a minimum.

Dimensions

The gate size is small, typically 0.25mm to 0.5mm thick. The land area (gate length) must

also be kept small, approximately 0.5 to 1.0 mm long.

Film or flash gate.

Diaphragm gate

A diaphragm gate is often used for gating cylindrical or round parts that have an open inside

diameter. It is used for single cavity molds that have a small to medium internal diameter. It

is used when concentricity is important and the presence of a weld line is not acceptable.

Dimensions

Typical gate thickness is 0.25 to 1.5 mm.

Internal ring gate.

External ring gate

This gate is used for cylindrical or round parts in a multicavity mould or when a diaphragm

gate is not practical. Material enters the external ring from one side forming a weld line on

the opposite side of the runner this weld line is not typically transferred to the part.

Dimensions

Typical gate thickness is 0.25 to 1.5 mm.

External ring gate.

Spoke gate or multipoint gate

This kind of gate is used for cylindrical parts and offers easy de-gating and material savings.

Disadvantages are the possibility of weld lines and the fact that perfect roundness is unlikely.

Dimensions

Typical gate size ranges from 0.8 to 5 mm diameter.

Multi-point gate.

Pin gates

Pin gates are only feasible with a 3-plate tool because it must be ejected separately from the

part in the opposite direction The gate must be weak enough to break off without damaging

the part. This type of gate is most suitable for use with thin sections. The design is

particularly useful when multiple gates per part are needed to assure symmetric filling or

where long flow paths must be reduced to assure packing to all areas of the part.

Dimensions

Gate diameters for unreinforced thermoplastics range from 0.8 up to 6 mm. Smaller gates

may induce high shear and thus thermal degradation. Reinforced thermoplastics require

slightly larger gates > 1 mm The maximal land length should be 1 mm. Advised gate

dimensions can be found in the table below.

Pin gates.

Dimensions of gates (* wall thickness larger than 5 mm should be avoided).

Submarine (tunnel) gates

A submarine gate is used in two-plate mold construction. An angled, tapered tunnel is

machined from the end of the runner to the cavity, just below the parting line. As the parts

and runners are ejected, the gate is sheared at the part. The tunnel can be located either in the

moving mould half or in the fixed half. A sub-gate is often located into the side of an ejector

pin on the non-visible side of the part when appearance is important. To degate, the tunnel

requires a good taper and must be free to bend.

Dimensions

Typical gate sizes 0.8 mm to 1.5 mm, for glass reinforced materials sizes could be larger.

Tunnel gate.

A variation of the tunnel gate design is the curved tunnel gate where the tunnel is machined

in the movable mold half. This is not suitable for reinforced materials.

Curved tunnel gate.

Hot runner gates

Hot runner gates are also known as sprueless gating. The nozzle of a runnerless mold is

extended forward to the part and the material is injected through a pinpoint gate. The face of

the nozzle is part of the cavity surface; this can cause appearance problems (matt appearance

and rippled surface). The nozzle diameter should therefore be kept as small as possible. Most

suitable for thin walled parts with short cycle times, this avoid freezing of the nozzle.

Hot runner gates.

Valve gates

The valve gate adds a valve rod to the hot runner gate. The valve can be activated to close the

gate just before the material near the gate freezes. This allows a larger gate diameter and

smoothes over the gate scar. Since the valve rod controls the packing cycle, better control of

the packing cycle is maintained with more consistent quality.

Valve gate.

COMPRESSION MOLDING

• Compression molding is the simplest method used for the production of elastomeric

materials. The term comes from the fact that the mold cavity compresses the material as it

closes, forming the part. Material is placed directly into the cavity then closed , put under

pressure (compressed) forcing the material to conform exactly to the cavity. The cure occurs

as the pressure and heat cause the thermoset material to crosslink.

• Materials that are typically manufactured :

Polyester fiberglass resin systems , Poly(pphenylene sulfide) (PPS), and many grades of

PEEK.

Products: FRP Nuts, Spacers, Step Blocks, Insulating Sheets,etc

Blow molding (also known as blow moulding or blow forming) is a manufacturing

process by which hollow plastic parts are formed. In general, there are three main types of

blow molding: extrusion blow molding, injection blow molding, and stretch blow molding.

The blow molding process begins with melting down the plastic and forming it into a parison

or preform. The parison is a tube-like piece of plastic with a hole in one end in which

compressed air can pass through.

The parison is then clamped into a mold and air is pumped into it. The air pressure

then pushes the plastic out to match the mold. Once the plastic has cooled and hardened the

mold opens up and the part is ejected.

Advantages:

High Production rate; Complex shapes can be obtained with uniform thickness;

Little scrap is generated.

Disadvantages:

Few material options; High tooling and equipment costs; Poor surface finish.

Limited to hollow shapes with thin wall and low degree of asymmetry.

Blow Molding Products:

_Applications: Bottles, containers, ducting.

_Materials used for blow moulding:

Low Density Polyethylene (LDPE)

High Density Polyethylene (HDPE)

Polyethylene Terephtalate (PET)

Polypropylene (PP)

Polyvinyl Chloride (PVC)

Plastics extrusion is a high volume manufacturing process in which

raw plastic material is melted and formed into a continuous profile. Extrusion produces items

such as pipe/tubing, weather stripping, fence, deck railing, window frames, plastic films,

themoplastic coatings, and wire insulation.

Plastic extrusion moulding is a process of producing a continuous work piece by forcing

molten plastic through a shaped die. As the hot material exits the die the material is carried

along a conveyor, cooled, and cut to the desired length

_Extrusion produces items such as pipe/tubing, weather stripping, window frames, adhesive

tape and wire insulation.

Plastics Extrusion Products:

_Typical plastic materials that are used in extrusion include but are not limited to:

Polyethylene, polypropylene, acetal, acrylic, nylon(polyamides), polystyrene,

acrylonitrile butadiene styrene (ABS) and polycarbonate.

Thermoforming:

_Thermoforming is a manufacturing process where a plastic sheet is heated to a pliable

forming temperature, formed to a specific shape in a mold, and trimmed to create a usable

product.

_ A variety of thermoplastic materials can be thermoformed such as Acrylic (PMMA),

Acrylonitrile Butadiene Styrene (ABS), Cellulose Acetate, Low Density Polyethylene

(LDPE), High Density Polyethylene (HDPE), Polypropylene (PP), Polystyrene (PS),

Polyvinyl Chloride (PVC) etc

_Depending upon the different methods of forcing the thermoplastic sheet to

conform to the mold, the thermoforming include the following:

1. Vacuum Forming.

2. Pressure forming.

3. Mechanical forming.

Vacuum Thermoforming:

A vacuum is formed between the mold cavity and the thermoplastic sheet. The vacuum

pressure (typically 14 psi) forces the sheet to conform to the mold and form the part shape.

_Pressure Thermoforming:

The air pressure (typically 50 psi, but up to 100 psi) is applied on the back side of the sheet to

help force it onto the mold. This additional force allows the forming of thicker sheets and

creating finer details, textures, undercuts, and sharp corners.

Mechanical Thermoforming:

The thermoplastic sheet is mechanically forced into or around the mold by direct

contact. Typically, a core plug will push the sheet into the mold cavity and force it into the

desired shape.

_Advantages: Can produce very large parts; High production rate; Low cost

_Disadvantages: Limited shape complexity; Limited to thin walled parts; Scrap cannot be

recycled; Trimming is required.

_Applications: Packaging, open containers, panels, cups, signs

Rotational Moulding:

A pre-determined amount of powdered or liquid thermoplastic or thermoset is poured

into the mould . Mould is closed, heated and rotated in two different axis planes until contents

have fused to inner walls of mould. The mould is cooled then opened and part is removed.

• Advantages: Low mould cost. Parts obtained are isotropic in nature. Large hollow parts can

be obtained in one piece.

• Disadvantages: Limited to Hollow parts. Production rate is slow.

• Most commonly used materials are Polyethylene, Polypropylene, Polyvinyl chloride,

Nylon, Polycarbonate.

• Applications:Products that can be manufactured using rotational moulding include storage

tanks, bins and refuse containers, airplane parts, doll parts, road cones, footballs, helmets and

rowing boats. Playground slides and roofs are also generally rotomolded.

Slush Molding:

In slush moulding, a closed mold rotates around one or more axes.

• The powder fuses onto the hot mold surface and sinters together.

• After cooling, the result is a three-dimensional skin that exhibits very even wall thicknesses

– regardless of the design complexity of the part.

• Advantages: Low mold costs. Economical for small Production runs.

• Disadvantages: Limited to hollow parts and limited choice of materials can be used.

Production rates is very low.

Applications: Automotive pieces , PVC masks, Industrial Boots, Toys, Dolls

Transfer Molding:

In this process, a thermosetting charge (preform) loaded into a chamber immediately

ahead of the mold cavity, where heated; pressure is then applied to force the softened

polymer to flow into the heated mold where curing occurs.

Transfer moulding is of 2 types

(1) Pot Transfer moulding

(2) Plunger transfer moulding.

Advantages:

Good Dimensional Accuracy: Rapid production rates; Complicated parts can be produced.

Disadvantages:

Moulds are expensive; High material loss; In sprue and runners.

Applications:

Some products are utensil handles, electric appliance parts, electronic component, and

connectors.

Calendering:

• The plastic material is hot rolled through a series of rollers to get a desired thickness of

continuous flat plastic sheet.

• Advantages: Low cost and sheets obtained are isotropic.

• Disadvantages: Limited to sheet materials; Very thin films not possible.

Pot Transfer moulding

Plunger Transfer

moulding

Design Rules For Plastic Parts:

• Maximum wall thickness

• Corners

• Draft

• Ribs

• Bosses

• Undercuts

• Threads

Wall Thickness

If there was only one rule for the injection moulding process it would have to be "maintain

uniform wall thickness".

10% increase in the wall thickness provides appx. 33% increase in the stiffness. But

increasing wall thickness also add to part weight, cycle time and material cost.

Changing the wall thickness after mold design will be too expensive.

Normal range of wall thickness

The vast majority of injection molded parts wall thickness range from 0.8 mm to 4.8 mm!

Nominal wall thickness should not exceed 4.0 mm.

Walls thicker than 4.0 mm will result in increased cycle times (due to the longer time

required for cooling), will increase the likelihood of voids and significantly decrease the

physical properties of the part.

A wall thickness variation of ±25% is acceptable in a part made with a thermoplastic having a

shrinkage rate of less than 0.01 mm/mm. If the shrinkage rate exceeds 0.01 mm/mm, then a

thickness variation of ±15% is permissible

Maximum wall thickness:

• Decrease the maximum wall thickness of a part to shorten the cycle

time (injection time and cooling time specifically) and reduce the part

volume

Incorrect Correct

Part designed with thick wall . Part designed with thin wall

Uniform wall thickness will ensure uniform cooling and reduce defects

• Incorrect- Non uniform wall Correct- Uniform wall thickness

thickness (t1 ≠ t2) (t1 = t2)

Corners :

•Round corners to reduce stress concentrations and fracture

•Inner radius should be at least the thickness of the walls

Incorrect- Sharp corners Correct- Filleted corners.

Draft :

Apply a draft angle of 1°- 2°to all walls parallel t o the parting direction to facilitate removing

the part from the mold.

Incorrect- No Draft angle Correct- With Draft angle.

Ribs :

Ribs provide a means to economically augment stiffness and strength in moulded parts

without increasing overall wall thickness.

•Locating and captivation components of an assembly

•Providing alignment in mating parts

•Acting as stops or guides for mechanisms Consideration for Rib Design: Thickness Height

Location Quantity Moldability

•Add ribs for structural support, rather than increasing the wall thickness

Incorrect- Thick wall of thickness t Correct- Thin walled ribs of thickness t

•Orient ribs perpendicular to the axis about which bending may occur.

Incorrect- Rib direction under load F Correct- Rib direction under load F

•Thickness of ribs should be 50-60% of the walls to which they are attached

•Height of ribs should be less than three times the wall thickness

•Round the corners at the point of attachment

•Apply a draft angle of at least 0.25.

If using multiple ribs, space them unevenly or orient them to prevent resonance amplification

from the impact energy

•Avoid boxy shapes that concentrate impact forces on rigid edges and corners

•Use rounded shapes to spread impact forces over larger areas.

•Wall thickness of bosses should be no more than 60% of the main wall thickness.

•Radius at the base should be at least 25% of the main wall thickness

•Should be supported by ribs that connect to adjacent walls or by gussets at the base.

Incorrect- Isolated boss Correct- Bosses with ribs

Correct- Bosses with gussets

•If a boss must be placed near a corner, it should be isolated using ribs

Incorrect- Ribbed Boss in corner Correct- Ribbed Boss in corner

Undercuts :

• Minimize the number of external undercuts

• External undercuts require side-cores which add to the tooling cost.

• Some simple external undercuts can be molded by relocating the parting line

Simple External Cut Mould cannot separate

New parting line allows undercut

Redesigning a feature can remove an external undercut

Part with hinge Hinge requires side-core

Redesigned hinge New hinge can be molded

•Minimize the number of internal undercuts •Internal undercuts often require internal core

lifters which add to the tooling cost

•Designing an opening in the side of a part can allow a side-core to form an internal undercut.

Internal undercut accessible from the side

Redesigning a part can remove an internal undercut

Part with internal undercut Mold cannot separate

Part redesigned with slot New part can be molded

•Minimize number of side-action directions

Additional side-action directions will limit the number of possible cavities in the mold

Threads

•If possible, features with external threads should be oriented perpendicular to the parting

direction.

•Threaded features that are parallel to the parting direction will require an unscrewing device,

which greatly adds to the tooling cost

TYPICAL NOMINAL THICKNESS FOR VARIOUS

CLASSES OF THERMOPLASTICS

Thermoplastic Resin Family Typical Thickness Ranges (mm)

ABS,Acrylonitrile-Butadiene-Styrene 1.143-3.556

Acetal 0.762-3.048

Acrylic 0.635-3.81

Liquid Crystal Polymer 0.2032-3.048

Long-Fiber Reinforced Plastics 1.905-25.4

Modified Polyphenylene Ether 1.143-3.556

Nylon 0.254-2.921

Polyarylate 1.143-3.81

Polycarbonate 1.016-3.81

Polyester 0.635-3.175

Polyester Elastomer 0.635-3.175

Polyethylene 0.762-5.08

Polyphenylene Sulfide 0.508-4.572

Polypropylene 0.635-3.81

Polystyrene 0.889-3.81

Polysulfone 1.27-3.81

Polyurethane 2.032-19.05

PVC,Polyvinyl Chloride 1.016-3.81

SAN, Styrene-Acrylonitrile 0.889-3.81

DEFECTS of PLASTICS

Many flaws and defects can be avoided by using good part and tool design

techniques. As a part designer it is a very good Idea to be aware of your options in tooling

and to consider those while designing your part. For example, have potential gate locations in

mind. Try to guess where knitlines will occur and how different gate locations will affect

them. How easy will it be to trim the gate? The more parts you study, the better you will get

at predicting flow. Be sure to communicate your intentions to the tool designer and get his

feedback to influence your future designs.

Avoiding thick sections can add up to huge savings over the lifetime of a tool. Thick sections

increase the cycle time of each shot, narrow the processing window, require overpacking, and

cause reject parts.

BLUSH

DEFINITION: Dull discolored or whitish

area on the surface of the part, usually at

the gate.

CAUSE: Shear stress between polymer

molecules during injection. The gate may

be too small or injection speed too fast.

LOCATION: Usually at the gate. May

also occur where there is a sudden change

in part thickness.

CURE: Adjust injection speed and if

BLUSH

necessary adjust gate dimensions. An

independent water circuit in the mold that

allows pinpoint temperature control at the

gate can also help.

BURN

DEFINITION: Discoloration usually

black, brown or dark yellow/brown

depending upon severity. Feels rough and

crunchy. Frequently accompanied by

short shot in burn area.

CAUSE: Usually indicates a need for

more venting or heat buildup in tool.

When air is trapped in the tool and cannot

escape, the extreme pressure causes the

air to ignite, burning the edge of the part.

LOCATION: Most often seen in deep,

blind ribs where a lot of air can be forced

into a small space.

CURE: Add more parting line vents near

burn or vent pins in deep ribs. Vent pins

are just ejector pins that fit a little loose.

They may also have a flat ground down

one side to let the air escape.

BURN

COLD FLOW

DEFINITION: Wavy or streaked

appearance on part surface. Looks like a

fingerprint or small waves like you would

see on the surface of water.

CAUSE: Low melt temperature, low

injection speed or low injection pressure.

LOCATION: Hard to fill or last to fill

areas.

COLD FLOW

COLD SLUG

DEFINITION: Cold piece of plastic that

has been forced into the part along with

the melt.

CAUSE: 1.Plastic from last shot left in

nozzle solidifies between shots. The tool

designer usually is able to allow for a

"cold slug well" in the runner to catch this

piece. 2.Cold slug effects can also occur

at the end of a long runner.

LOCATION: If allowed to enter the part

it can travel anywhere.

CURE: Add a cold slug well at each

intersection in the runner. Addition of a

shortened ejector pin on the runner very

close to the gate may divert the cold slug.

For direct sprue gating try to make a

feature in the part to catch the slug or use

a heated nozzle.

COLD SLUG

CONTAMINATION

DEFINITION: Foreign particles

embedded in the part.

CAUSE: 1.Burned material in the press

barrel. 2.Contaminated regrind. 3.Grease

or particles that have not been cleaned

from the mold.

LOCATION: Anywhere.

CONTAMINATION

DELAMINATION

DEFINITION: Separation of plastic

surface layer giving a flaking or onion

skin effect.

CAUSE: 1.Contaminated resin. May be

caused by incomplete machine purging,

unclean material handling equipment or

impure regrind.

LOCATION: Anywhere.

DELAMINATION or PEELING

DISCOLORATION

DEFINITION: Deviation from the

original intended color of the material as

compared to the manufacturers color chip.

CAUSE: 1.Contaminated resin.

2.Overheated resin. 3.Incorrect regrind

ratio. 4.Incorrect color mixing or

blending.

LOCATION: Entire part.

DISCOLORATION

DRAG

DEFINITION: Fine, straight lines scraped

in the line of draw.

CAUSE: Depends upon location. 1.Cavity

side happens during mold opening and is

usually from insufficient draft for the

texture used or from overpacking. 2.Core

side drag happens during ejection and is

usually from inadequate draft, rough core,

or overpacking.

LOCATION: May be in opening

direction or side action direction. Cavity,

core, slide, or lifter.

CURE: Solve overpacking problem.

Cavity side drag, tone down the texture

by stoning then bead blast. Core side

drag, polish core, add draft.

DRAG

FLASH

DEFINITION: Excess plastic squeezing

out perpendicular to the part at parting

line.

CAUSE: 1.Plastic injection force

exceeding the clamping pressure of the

press. (Overpacking.) 2.May happen at

first shots while mold is being dialed in.

3.Poorly constructed or worn out mold.

LOCATION: Along any parting line.

CURE: Run the mold in a bigger press.

Relieve areas of the parting surfaces that

FLASH

are not immediately adjacent to the part.

Leave 0.500 in. of shutoff land around the

part.

GLOSS

DEFINITION: Smooth shiny areas on the

part surface.

CAUSE: 1.Underpacking 2.See section

on plateout below.

LOCATION: Hard to fill areas.

GLOSS

JETTING

DEFINITION: Squiggly line in part

pointing to gate. Looks like a worm in the

part.

CAUSE: 1.Incorrect gate placement or

size. The gate is positioned in such a

manner as to aim the plastic straight into

an open area. The plastic launches out

into the open like a piece of "silly string"

and then stacks up in squiggles.

LOCATION: Near gate.

CURE: Aim the gate at an obstacle that

interrupts the flow. Use different gate

style or larger gate.

JETTING

KNITLINE

DEFINITION: A line where the molten

polymer flow fronts meet in the mold.

Incomplete adhesion occurs along the

knitline and causes a weak point in the

plastic part.

CAUSE: Cold fronts meeting in the tool

where molten plastic fronts meet.

LOCATION: Cold fronts meeting in the

tool where plastic flows around obstacles

or over raised areas in the metal. It is

guaranteed that you will have a knitline as

the plastic flows around any opening in

the part. Recessed text or Icons can also

cause small cosmetic knits.

CURE: Frequently it is possible to place

the gate in such a manner as to push the

knit lines into obscure areas. If this is not

possible use "flow directors" on the non-

cosmetic side of the part to push the

knitline into a corner, crease, or shadow

to hide it. Flow directors are usually just

shallow raised areas in the plastic that are

cut into the tool with a large ball end mill.

Sometimes it is possible to add a "sump"

that the cold material flows out into. This

sump is then clipped off.

KNITLINE

BAD GATE TRIM

DEFINITION: Either too much or too

little plastic where the gate has been

trimmed off.

CAUSE: 1.location of the gate on a

concave or convex part surface can make

it difficult to accurately trim the gate.

2.Another cause can be inadequately

trained or uncoordinated people doing the

trimming.

LOCATION: Gate.

CURE: Place the gate on a straight edge if

possible. A good trim job takes good

eye/hand coordination. Use of a gate

trimming fixture can work well for high

volume gate trimming. Use self degating

techniques where possible such as tunnel

gates or banana gates. Of course gating to

a noncosmetic area is always preferred,

but not always feasible.

BAD GATE TRIM

MISMATCH

DEFINITION: The cavity side of the tool

does not fall in perfect registry with the

core side resulting in a step at parting

line. It may look like flash if it is slight. If

it is smooth as your finger runs across one

way and feels sharp the other way it is

mismatch. If you can feel it both ways it

is flash.

CAUSE: 1.Uneven pressure in the mold

cavity can push the cavity one direction

and the core the other. This usually

happens in very asymmetrical parts or

parts with a parting surface that slopes

only one way. 2.Moldmaker did not

properly position the cavity relative to the

core. 3.In older tools mismatch may occur

as locking faces wear.

LOCATION: At parting lines.

CURE: Straight locks at parting line. The

best are those made by Progressive

Components.

MISMATCH

PIN PUSH

DEFINITION: Circular or semicircular

white stress rings on the side of the part

opposite an ejector pin. May even be

raised circular bumps. In serious cases

pins may push right through the part!

CAUSE: 1.Overpacking. 2.Sticking on

the core. 3.Inadequate ejection.

LOCATION: On the cosmetic side of the

part opposite an ejector pin.

CURE: Solve overpacking problem.

Polish core or increase draft on core. Add

more ejector pins. More small pins are

better than a few big ones.

PIN PUSH

PLATEOUT

DEFINITION: A change of mold texture

over time that is not due to wear.

CAUSE: 1.Buildup of chemical residue

from out gassing. 2.Buildup of mold

release.

LOCATION: Anywhere

CURE: Have the mold cleaned.

PLATEOUT

PULLING

DEFINITION: Deformed, twisted and

smeared plastic in the part usually on, or

adjacent to steep vertical faces.

CAUSE: 1.Cavity side: A portion of the

part sticking to the cavity on tool opening.

Listen to the mold as it opens to see if you

can hear it pop free. 2. Core side: Uneven

part ejection is not pushing the part out

straight. The part gets skewed as it ejects,

the resulting damage is called pulling.

LOCATION: Anywhere in part.

CURE: Cavity side pulling, add undercuts

or texture on core side so part pulls

cleanly from the cavity. Core side pulling,

add ejection. More small pins are better

than a few big ones.

PULLING

SHORT SHOT

DEFINITION: Missing plastic or features

that are not fully formed. Missing corners

or features have a smooth, rounded

appearance.

CAUSE: Under packing, low injection

pressure, trapped gas.

LOCATION: Areas of the part farthest

from the gate, thin areas or delicate

features. Generally the last part of the

mold to fill.

CURE: Make sure the tool is adequately

vented and push more plastic in.

SHORT SHOT

SINKS

DEFINITION: Depressions or dimples in

the part that are usually adjacent to thick

areas. In clear parts, bubbles can be seen

in thick areas. These bubbles can be the

precursors of shrink.

CAUSE: As the plastic cools it shrinks. If

there is an area that is proportionally

thicker than the rest of the part, then the

plastic will shrink more in the thick spot

causing it to collapse inward.

LOCATION: 1. Wall perpendicular to

ribs or bosses that don't conform to the

66% rule. 2. Inconsistent wall thickness.

i.e. Thick areas adjacent to thin areas.

CURE: Maintain constant wall thickness

by coring out. If you must have thick

areas lead gradually into them. Follow the

66% rule for wall thickness. Keep it down

to 60% or less if you can.

Frequently the solution to sink is to pack

the part out tighter. Over packing can then

cause other problems. The best solution is

to avoid it in the first place with good part

design.

Other problems that can be caused by

SINK

VOID or DEEP SINK

sink include part warpage, twisting,

stress, and part breakage.

For more info visit the ribs and

bosses section of this website.

BUBBLE

SPLAY

DEFINITION: Silver or whitish streaks

CAUSE: 1.Moisture in material.

2.Overheated material.

LOCATION: Anywhere. Most

predominant near gate.

SPLAY

WARP

DEFINITION: The failure to maintain

flatness of a plastic part that was intended

to be flat. Distortion from the intended

shape of the plastic part.

CAUSE: 1.The underlying cause of most

part warpage is the shape of the part

itself. The pattern, shape, and thickness of

ribs on the part as they undergo shrinkage

have the greatest effect upon warpage.

These effects can be controlled to some

degree by differential cooling of the mold

(a different temp on the cavity than on the

core). 2. Over packing can induce warp.

LOCATION: Present to some degree in

most Injection molded parts but most

easily detected on large flat parts.

CURE: Alas there is no cure for this one,

only control. Differential mold cooling

can get you parts that are flatter. A

WARP

cooling fixture that the part is placed into

immediately after ejection can also

straighten the part. However these effects

are usually temporary and upon being

subjected to elevated temps or time parts

will return to their natural shape. Your

best bet is to follow the 66% rule and

minimize rib height. Flat parts are more

susceptible to warpage than curved parts.

Note: On long thin flat parts the gate is

best placed between 60-70% down the

part length to minimize warp.

Welding Techniques

A number of techniques are used for welding plastics.

Hot gas welding

Hot gas welding, also known as hot air welding, is a plastic welding technique using

heat. A specially designed heat gun, called a hot air welder, produces a jet of hot air that

softens both the parts to be joined and a plastic filler rod, all of which must be of the same or

a very similar plastic. Welding PVC to acrylic is an exception to this rule.

Hot air/gas welding is a common fabrication technique for manufacturing smaller

items such as chemical tanks, water tanks, heat exchangers, and plumbing fittings.

In the case of webs and films a filler rod may not be used. Two sheets of plastic are

heated via a hot gas (or a heating element) and then rolled together. This is a quick welding

process and can be performed continuously.

Heat seal

A variety of heat sealers are available to join thermoplastic materials such as plastic

films: Hot bar sealer, Impulse sealer, etc.

Freehand welding

With freehand welding, the jet of hot air (or inert gas) from the welder is played on

the weld area and the tip of the weld rod at the same time. As the rod softens, it is pushed into

the joint and fuses to the parts. This process is slower than most others, but it can be used in

almost any situation.

Speed tip welding

With speed welding, the plastic welder, similar to a soldering iron in appearance and

wattage, is fitted with a feed tube for the plastic weld rod. The speed tip heats the rod and the

substrate, while at the same time it presses the molten weld rod into position.

A bead of softened plastic is laid into the joint, and the parts and weld rod fuse. With

some types of plastic such as polypropylene, the melted welding rod must be "mixed" with

the semi-melted base material being fabricated or repaired. These welding techniques have

been perfected over time and have been utilised for over 50 years by professional plastic

fabricators and repairers internationally. Speed tip welding method is a much faster welding

technique and with practice can be used in tight corners. A version of the speed tip "gun" is

essentially a soldering iron with a broad, flat tip that can be used to melt the weld joint and

filler materiel to create a bond.

Extrusion welding

Extrusion welding allows the application of bigger welds in a single weld pass. It is

the preferred technique for joining material over 6 mm thick. Welding rod is drawn into a

miniature hand held plastic extruder, plasticized, and forced out of the extruder against the

parts being joined, which are softened with a jet of hot air to allow bonding to take place.

Contact welding

This is the same as spot welding except that heat is supplied with conduction of the

pincher tips instead of electrical conduction. Two plastic parts are brought together where

heated tips pinch them, melting and joining the parts in the process.

Hot plate welding

Related to contact welding, this technique is used to weld larger parts, or parts that

have a complex weld joint geometry. The two parts to be welded are placed in the tooling

attached to the two opposing platens of a press. A hot plate, with a shape that matches the

weld joint geometry of the parts to be welded, is moved in position between the two parts.

The two opposing platens move the parts into contact with the hot plate until the heat softens

the interfaces to the melting point of the plastic. When this condition is achieved the hot plate

is removed, and the parts are pressed together and held until the weld joint cools and re-

solidifies to create a permanent bond.

The most common form of this welding is butt heat fusion welding which welds two

circular tubes end to end.

High frequency welding

Certain plastics with chemical dipoles, such as PVC, polyamides (PA)

and acetates can be heated with high frequency electromagnetic waves. High frequency

welding uses this property to soften the plastics for joining. The heating can be localized, and

the process can be continuous. Also known as Dielectric Sealing, R.F. (Radio Frequency)

Heat Sealing.

In a ferromagnetic work piece, plastics can be induction-welded by formulating them

with metallic or ferromagnetic compounds, called susceptors. These susceptors absorb

electromagnetic energy from an induction coil, become hot, and lose their heat energy to the

surrounding material by thermal conduction.

Radio frequency welding is a very mature technology that has been around since the

1940s. Two pieces of material are placed on a table press that applies pressure to both surface

areas. Dies are used to direct the welding process. When the press comes together, high

frequency waves (usually 27.12 MHz) are passed through the small area between the die and

the table where the weld takes place. This high frequency (radio frequency) field causes the

molecules in certain materials to move and get hot, and the combination of this heat under

pressure causes the weld to take the shape of the die. RF welding is fast. This type of welding

is used to connect polymer films used in a variety of industries where a strong consistent

leak-proof seal is required. In the fabrics industry, RF is most often used to weld PVC

andpolyurethane (PU) coated fabrics. This is a very consistent method of welding.

The most common materials used in RF welding are PVC and polyurethane. It is also

possible to weld other polymers such as nylon, PET, EVA and some ABS plastics.

Injection welding

Injection welding is similar/identical to extrusion welding, except, using certain tips

on the handheld welder, one can insert the tip into plastic defect holes of various sizes and

patch them from the inside out. The advantage is that no access is needed to the rear of the

defect hole. The alternative is a patch, except that the patch can not be sanded flush with the

original surrounding plastic to the same thickness. PE and PP are most suitable for this type

of process. The Drader injection weld is an example of such tool.

Ultrasonic welding

In ultrasonic welding, high frequency (15 kHz to 40 kHz) low amplitude vibration is

used to create heat by way of friction between the materials to be joined. The interface of the

two parts is specially designed to concentrate the energy for the maximum weld strength.

Ultrasonic can be used on almost all plastic material. It is the fastest heat sealing technology

available.

Friction welding

In friction welding, the two parts to be assembled are rubbed together at a lower

frequency (typically 100–300 Hz) and higher amplitude (typically 1 to 2 mm (0.039 to 0.079

in)) than ultrasonic welding. The friction caused by the motion combined with the clamping

pressure between the two parts creates the heat which begins to melt the contact areas

between the two parts. At this point, the plasticized materials begin to form layers that

intertwine with one another, which therefore results in a strong weld. At the completion of

the vibration motion, the parts remain held together until the weld joint cools and the melted

plastic re-solidifies. The friction movement can be linear or orbital, and the joint design of the

two parts has to allow this movement.

Spin welding

Spin welding is a particular form of frictional welding. With this process, one round

piece is held stationary, while a mating one is rotated at high velocity while lightly against

the stationary piece. The rotatated piece is then pressed firmly against the fixed piece. This is

a common way of producing low- and medium-duty plastic wheels, e.g., for toys, shopping

carts, recycling bins, etc.

Laser welding

This technique requires one part to be transmissive to a laser beam and either the

other part absorptive or a coating at the interface to be absorptive to the beam. The two parts

are put under pressure while the laser beam moves along the joining line. The beam passes

through the first part and is absorbed by the other one or the coating to generate enough heat

to soften the interface creating a permanent weld.

Semiconductor diode lasers are typically used in plastic welding. Wavelengths in the

range of 808 nm to 980 nm can be used to join various plastic material combinations. Power

levels from less than 1W to 100W are needed depending on the materials, thickness and

desired process speed.[1]

Diode laser systems have the following advantages in joining of plastic materials:

Cleaner than adhesive bonding

No micro-nozzles to get clogged

No liquid or fumes to affect surface finish

No consumables

Higher throughput

Can access work-piece in challenging geometry

High level of process control

Requirements for high strength joints include:

Adequate transmission through upper layer

Absorption by lower layer

Material compatibility – wetting

Good joint design – clamping pressure, joint area

Lower power density

A sample list of materials that can be joined include:

Polypropylene

Polycarbonate

Acrylic

Nylon

ABS

For a more in depth list of materials as well as weldable material combinations, please

refer to the Laser Plastic Welding Material Compatibility Chart

Specific applications include sealing / welding / joining of: catheter bags, medical

containers, automobile remote control keys, heart pacemaker casings, syringe tamper evident

joints, headlight or tail-light assemblies, pump housings, and cellular phone parts.

Transparent Laser Plastic Welding

New fiber laser technology allows for the output of higher laser wavelengths, with the

best results typically around 2,000nm, significantly higher than the average 808nm to

1064nm diode laser used for traditional laser plastic welding. Because these higher

wavelengths are more readily absorbed by thermoplastics than the infra-red radiation of

traditional plastic welding, it is possible to weld two clear polymers without any colorants or

absorbing additives. Common Applications will mostly fall in the medical industry for

devices like catheters and microfluidic devices. The heavy use of transparent plastics,

especially flexible polymers like TPU, TPE and PVC, in the medical device industry makes

transparent laser welding a natural fit. Also, the process requires no laser absorbing additives

or colorants making testing and meeting biocompatibility requirements significantly easier.

Solvent welding

In solvent welding, a solvent is applied which can temporarily dissolve the polymer at

room temperature. When this occurs, the polymer chains are free to move in the liquid and

can mingle with other similarly dissolved chains in the other component. Given sufficient

time, the solvent will permeate through the polymer and out into the environment, so that the

chains lose their mobility. This leaves a solid mass of entangled polymer chains which

constitutes a solvent weld.

This technique is commonly used for connecting PVC and ABS pipe, as in household

plumbing. The "gluing" together of plastic (polycarbonate, polystyrene or ABS) models is

also a solvent welding process.

Dichloromethane (methylene chloride), which is obtainable in paint stripper, can

solvent weld polycarbonate and polymethylmethacrylate. Dichloromethane chemically welds

certain plastics; for example, it is used to seal the casing of electric meters. It is also a

component - along with tetrahydrofuran - of the solvent used to weld plumbing.

Plastic Welding supplies

Welding rod

A plastic welding rod, also known as a thermoplastic welding rod, is a rod with

circular or triangular cross-section used to bind two pieces of plastic together. They are

available in a wide range of colors to match the base material's color.

An important aspect of plastic welding rod design and manufacture is the porosity of

the material. A high porosity will lead to air bubbles (known as voids) in the rods, which

decrease the quality of the welding. The highest quality of plastic welding rods are therefore

those with zero porosity, which are called voidless.

OS

PLASTICS • Growing demand in the automotive sector

Different types of polymer are used in over 1000 parts of all shapes and sizes, from all

plastics ,dashboards and fuel tanks to radiator.

By volume, from bumper to bumper, cars today contain more plastics than traditional

materials. Yet, thanks to their light weight, they account for on average only 9.3 per cent (or

105kg) of the total weight.

MATERIALS USED IN EUROPEAN AUTOMOBILE PRODUCTION 1998

Bumpers -PP, ABS, PC 10.0

Seats- PUR, PP, PVC, ABS, PA 13.0

Dashboard- PP, ABS, PA, PC, PE 15.0

Fuel systems -PE, POM, PA, PP 7.0

Body (including body panels)- PP, PPE, UP 6.0

Under the bonnet components -PA, PP, PBT 9.0

Interior trim- PP, ABS, PET, POM, PVC 20.0

Electrical components- PP, PE, PBT, PA, PVC 7.0

Exterior trim- ABS, PA, PBT, ASA, PP 4.0

Lighting- PP, PC, ABS, PMMA, UP 5.0

Upholstery- PVC, PUR, PP, PE 8.0

Other reservoirs- PP, PE, PA 1.0

Plastics In Automotive Markets Today

Plastics encompass a wide variety of functional polymeric compounds that exhibit a

vast range of desirable properties. They are durable, strong and lightweight. They can be

made transparent, translucent or opaque; soft, flexible or hard in almost any shape, size or

color. They can be heat-, chemical- and corrosion resistant.

They are excellent thermal and electrical insulators and also can be made electrically

and thermally conductive. Because of plastics‘ versatility, they are extremely cost-effective in

a wide variety of commercial applications including a broad range of uses in the

transportation market. The use of both thermosets and thermoplastics in passenger vehicles

has grown from about 30 kilograms per vehicle in 1970 to about 150 kilograms today. A

midsize automobile manufactured in North America is about 10-12 percent plastics by

weight. The material volume is much higher. Because plastics are versatile and lightweight,

they make up approximately 50 percent of the material volume of new cars.

The Need for Fuel Efficiency and Reduction in Green House Gases

Leading experts say that the easiest and least expensive way to reduce the energy

consumption and emissions of a vehicle is to reduce the weight of the vehicle. To achieve

lightweight architectures, without compromising on rigidity, automakers have been

researching the replacement of steel with plastics, composites, foams, aluminum and

magnesium. The recycling and recovery of end-of-life vehicles, which involves recovery

targets of 85%, are driving the auto industry to adopt lightweight materials technology to

meet these recovery targets. Weight reduction also offers a potentially cost-effective means to

reduce fuel consumption and greenhouse gases from the transportation sector. It has been

estimated that for every 10% reduction in the weight of the total vehicle, fuel economy

improves by 5-7%. Thus for every kilogram of vehicle weight reduction, there is the potential

to reduce carbon dioxide emissions by 20 kg.

Common Themes and Top Priorities

At the Technology Integration Workshop, six important themes were repeatedly cited as

central to the challenge of enhancing future automotive safety using plastics.

1. Improve Characterization and Predictive Modeling of Plastics – Continuous improvement

in predictive modeling of the crash performance of plastic components is vital to

strengthening the position of plastics as a preferred automotive material. Automotive

designers also require extensive materials characterization data for new plastics as they

become available. Obtaining reliable, validated constitutive data may require a coordinated,

industry-wide effort.

2. Develop Material Classifications, Test Standards, and Performance Specifications – To

encourage design engineers and original equipment manufacturers (OEMs) to choose plastics

over competing materials, designers must be confident in the materials‘ ability to achieve

required performance in the application. Because plastics are less familiar than metals to most

design engineers, the plastics industry must benchmark performance and create material

classifications to characterize their products. Afterward, OEM material performance

specifications and test methods must be updated and expanded to reflect the unique properties

and capabilities of these new materials.

3. Enhance Crash Performance with Improved Energy Management – Managing the impact

energy created during a crash and protecting occupants from absorbing too much of this

energy is a fundamental part of vehicle safety. Advanced plastic components and systems in

the interior, body and exterior, and powertrain systems are sought to allow automakers to

manage crash energy in creative, more effective ways.

4. Uncover Plastic Opportunities under Evolving Active and Passive Safety Standards and

Light weighting Regulations – Understanding technology needs for meeting evolving safety

standards and light weighting regulations addressing both crash worthiness and crash

avoidance is a necessary foundation for planning future plastics research. The industry must

better define plastics performance requirements of new safety standards and use with new

integrated components, alternative fuel vehicles, powertrain options, and transportation

infrastructure. Once these issues are determined, new opportunities for optimizing safety and

light weighting with plastics should be identified.

5. Accommodate Changing Demographics to Older Population – As the population of older

drivers increases, improved counter measures and crash performance systems will be needed

to keep these passengers safe. Many older drivers have lower biomechanical tolerances and

require special safety features to avoid injury. With targeted research, highly versatile plastics

may enable important advances in safety features that are needed to protect the 65-and-older

population.

6. Make Automotive Safety with Plastics Affordable – Optimizing material selection for

automotive safety components will require that plastics become more affordable, both as a

material and as they enable efficiency gains throughout the vehicle manufacturing and

assembly process. At the same time, the perception among automotive customers must be

changed to appreciate the value of safety features enabled by plastics to increase their

willingness to select those features.

Plain steel

PLASTICS • Drivers for the 21st century

Thanks to plastics, the cars we dream of today are quickly being developed – offering

high performance, cleaner driving and advanced safety and convenience features.

As we enter an era of mass customisation, where products will increasingly be

tailored to meet individual requirements, diversity will become the new rule. Cars will come

in all shapes and sizes, metamorphosing into new ‗part-carpart- truck‘ combinations. Plastics‘

versatility and flexibility will support the trend in the automotive industry to build very

different cars based on the same chassis and a core set of components, thus reducing research

and development time and the retail price. Plastics-based composite materials will

substantially reduce the weight of the future car and, as a result, less energy will be required

to propel it. In fact, the 100kg of plastics that have been added to the average car have already

displaced 200 to 300kg of other materials. Thanks to lightweight plastics, driving 50

kilometres on one litre of fuel will soon be possible and the commercialisation of electric cars

that need just 40kW instead of the 120kW a conventional-size vehicle requires today, could

be only a few years away.

As we move into the next century, cars will be fitted with hybrid engines that draw

their energy from a combination of sources including fuel, plastics-based solar panels,

batteries and fuel cells – which generate electricity catalytically from hydrogen – thus further

reducing emissions of CO2.In 20 years time, cars may even drive themselves, using satellite

based Global Positioning Systems (GPS) to take their passengers safely to the nearest hotel

on a cross country trip. New plastics are increasingly being tailored to meet the needs of the

electronic car of the future. Looking forward to the 21st century, plastics in automotive

applications will continue to contribute significantly to the drive towards building better,

safer and cleaner cars. The plastics industry will continue to work closely with the

automotive industry to meet this challenge by developing technologies and products to turn

transport dreams into a reality.

14.2%DEFECTS MANUAL

ENGINEERING FEATURES

Retainer

Snap

Clips

Bolts

Washer

Welding points

Steel vs. Plastics: The Competition for Light-Vehicle Fuel Tanks

As weight and cost savings drive changes in performance criteria for automotive materials,

original equipment manufacturers (OEMs) are taking a harder look at the historically terne-

coated steel used for gas tanks. This article compares steel and plastic for gas tank uses

according to performance attributes and a competitive analysis. Legislation issues and

current OEM activity are included.

INTRODUCTION

Historically, terne-coated steel (an 8% tin-lead coating) has been the mainstay for

automotive gas tanks; however, several issues are changing the performance criteria that must

be met and, thus, threaten the application of steel products. The drivers for a material change

are legislation, increased required part life to ten years/241,350 kilometers, permeability,

weight, packaging, safety, and cost. In this article, the performance attributes of the plastic

and steel alternatives are reviewed from an original equipment manufacturer (OEM)

perspective in the critical areas of manufacturability, cost, design, weight, safety, corrosion,

and recyclability.

A comparative analysis of the various plastic and steel alternatives indicates that steel

remains a cost-effective material that meets all of the required performance criteria. A more

specific cost comparison of the new plastic tanks (i.e., multilayer or barrier coated) with the

new steel tanks is still required. Many of the drivers such as lead reduction, clean fuels,

permeability, and weight are a direct result of legislative and regulatory pressures

PLASTIC FUEL TANKS

Since the mid-1980s, automakers have been displacing coated-steel fuel tanks with

plastic ones. During the 1993 model year, approximately 2.7-3 million cars and trucks built in

North America used nonmetallic tanks. This represents 22-25% of the market, compared to

16% in 1990. By comparison, the European market uses 70-90% plastic tanks, and the

Japanese market uses 5% plastic tanks4 (Figure 1).

Although plastic-tank applications have experienced some reversals as a result of the

stricter permeation standards, some experts believe their usage will gain momentum by the

end of the decade as new plastics technology is converted to commercially feasible

operations. The Delphi VII report by theUniversity of Michigan indicates that experts predict

plastic tanks will capture 28% of the North American market by the end of 1996 and up to

50% of the market by 2000.5 However, this projection needs to be tempered with the higher

manufacturing cost and recyclability issues of the multilayer plastic tanks that will be

required to meet the stricter permeation standards.

This projection is considered as the worst-case scenario for steel if the industry fails to

provide the OEMs with a cost-effective steel alternative that meets all of the performance

criteria. Table I indicates the production volume of vehicles built in North America;6 Table II

shows the estimated number of plastic gas tank units (according to Delphi VII projections)

and their impact on steel shipments.

As of 1993, the steel industry lost the opportunity to ship about 34,473 tonnes of steel

as a result of plastics gains in gas-tank applications. In the worst-case scenario, continued

acceptance of plastic gas tanks will increase steel's loss to 71,667 tonnes in 2000—an

additional 43,544 tonnes. This means that annual shipment of 125,191 tonnes of steel will be

reduced by better than a third to a total of about 81,646 tonnes per year.

PLASTICS TECHNOLOGY

High-density polyethylene (HDPE) has been the resin of choice for plastic gas tanks,

and production capacity has been on the increase. Kautex of Canada built a new plant in

Avilla, Indiana, to meet anticipated increases in demand for plastic automotive fuel tanks.

Production was scheduled for 400,000 tanks in 1994 and eventually will be boosted to

between 600,000 and 700,000 units per year.7 These plastic tanks are currently being used

on Chrysler's Jeep Cherokee and T300 trucks.

Belgium-based Solvay is the exclusive supplier of plastic fuel tanks to General

Motors' Saturn Division. Solvay has also expanded their Canadian subsidiary in Blenheim,

Ontario, and installed two new blow-molding machines to make HDPE tanks for

the Chrysler's LH series and Viper sports car. Chrysler expects to sell 300,000 LH vehicles,

all with HDPE tanks that offer more volume capacity than steel tanks. Monolayer-HDPE

tanks offer long-term structural integrity but will not meet future permeation

requirements. Chrysler started to switch in 1995 to multilayered HDPE to meet the more

stringent SHED test.

The emergence of new technologies has enabled the increase of plastic gas tanks.

These new technologies can be grouped into either multilayer or barrier types.

Multilayer Technology

Some manufacturers see multilayer tank technology as the answer to stricter emission

standards. Ford uses six-layer fuel tanks made of HDPE and, at one point, considered a $110

million investment in machinery and equipment to produce the tanks (which would have been

the first commercial use of coextruded tanks). However, Ford decided to increase steel-tank

stamping capacity at Dearborn; the Explorer and the new F-150 truck(PN96) gas tanks have

been switched back from plastic to zinc-nickel coated steel.

Kautex is supplying Ford's facility in Milan, Michigan, with this six-layer technology.

The tanks are designed to meet California's stricter evaporative fuel standards and consist of

an inner layer of HDPE joined by an adhesive layer and barrier layer of polyamide or

ethylene-vinyl alcohol copolymer. An additional adhesive layer is joined by a layer of

"regrind" and an outer layer of HDPE.

Walbro Automotive Corporation began commercial production of multilayer plastic

fuel tanks for 1995 models. Annual production of these multilayer tanks is expected to reach

500,000 units by 1998. Their tank uses a barrier layer of ethylene-vinyl alcohol (EVOH) that

is sandwiched between two layers of HDPE.

Barrier Technology

Air Products and Chemicals of Allentown, Pennsylvania, has commercialized a

fluorine-based barrier technology that enables plastic fuel tank manufacturers to meet more

stringent emissions standards. The SHED tests completed in 1992 on Airoguard plastic tanks

produced by Kautex of Canada indicated hydrocarbon permeation rates as low as 0.1 g/24

h—significantly lower than rates for tanks using previously available barrier technology. The

performance of the Airoguard tanks compares with multilayer extrusion tanks while

maintaining the long-term structural integrity of monolayer tanks.10

Solvay Automotive of Troy, Michigan, has developed technology to keep HDPE tank

emissions down to 0.2 g/24 h or less, even with methanol-containing fuels.11

Using

technology called Solvay-optimized fluorination, Solvay equals or exceeds the permeation

performance of coextrusion with EVOH barrier resin. Solvay continues to add multilayer

capacity to meet Chrysler's requirements.

Aero Tec Laboratories of Ramsey, New Jersey, has developed a semiflexible safety

fuel tank made from an undisclosed olefin compound of polymers and antidiffusion-barrier

additives.12

The tank can be used for race cars and military vehicles as well as general

automotive aftermarkets.

STEEL FUEL TANKS

North American auto manufacturers are currently supplied with tanks comprising a steel

substrate coated with either terne or zinc-nickel. In all, about 125,191 tonnes of steel

substrate per year are applied to gas tanks.Stainless steel tanks have been tested, and although

effective in flexible fuels, they are difficult to form without severe breakage occurring during

stamping. Also, stainless steel is expensive, with an estimated cost ratio to terne steel

exceeding 5:1.The electrocoated zinc-nickel product is painted on both sides with an

aluminum-rich epoxy. Industry accelerated tests on the corrosion of painted zinc-nickel

confirm that it will meet a ten-year life in current fuels and flex-fuels and resist external

corrosion.Testing the characteristics of painted galvanneal (zinc-iron alloy coated steel) have

found it effective for resisting corrosion on both the inside and outside surfaces of the

tank. General Motors has a product undergoing testing.

Hot-dipped tin has also been found to be effective for resisting all fuels, but it does

require a paint coating for exterior protection from road-induced corrosion. This product

welds faster than painted terne and has a better potential for good solderability than painted

galvanneal and zinc-nickel coated steel substrates, permitting the attachment of fuel filler

tubes and other lines.

PERFORMANCE ATTRIBUTES: PLASTIC VERSUS STEEL

Manufacturability

Terne plate holds a materials cost advantage over HDPE: $0.66-0.79/kg vs. $0.86-

1.08/kg.13

The cost of the material is not the only driver; consideration includes the net cost

of the fabricated tank and its reliability within the total fuel system of the vehicle, including

the tank, filler tube, level control, baffles, the housing reservoir for the sending unit, and other

assorted tubing, fittings, and seals from the tank to the engine. All of these components must

function properly with the various fuel types and for the life of the car. Unforeseen corrosion

can easily contaminate the fuel delivery system and cause costly repairs.

Manufacturing costs for either tank material seem conflicting, depending on the

source. Nevertheless, due to the invested capital of OEMs on stamping, welding, and

assembly equipment for metal tanks, their cost structure indicates a lower cost per piece on

steel tanks versus plastic ones, with the latter usually being outsourced (except for

some Ford models).

Plastic tanks are formed by blowing a thick continuous tube of HDPE within a mold

that determines the final shape of the virtually seamless part, which could include the filler

neck. The blowing molds are cast from aluminum and cost considerably less than machined

steel dies used to stamp steel tanks. In general, four or more molds are integrated into one

rotary style blow-molding machine to achieve the desired productivity (i.e., one station blows

while the other one cools). Typically, the OEMs outsource the plastic tanks to various

suppliers who bid for the business. The plastic tank manufacturer also has to either chlorinate

or fluorinate the plastic to retard permeation, and both processes can be highly toxic if

mishandled. This represents additional OSHA requirements, which add to the cost of the

tank.

Design Features and Weight

Plastic tanks have the ability to meet packaging constraints with complex shapes, and

design engineers have greater flexibility in the car design and styling without having to worry

about fitting the gas tank. The plastic tank could virtually be made to fit whatever cavities are

left by the design. Other attachments to and within the plastic tank require gasketed

mechanical joints. However, plastic swells with constant exposure to organic liquids and

vapor, thus making the joints very critical in the event of repairing the tank hardware.

The average gas tank for a compact automobile (e.g., Nissan Altima) can boast weight

savings of up to 30% versus a similar steel tank.14

However, Cadillac claims that although

their plastic tanks allow design flexibility with increased safety, they do not achieve any

weight savings over steel tanks.15

These two examples seem to contradict the general view

that plastic's weight advantage increases with the size of the tank. On the other hand, the new

permeability requirement is expected to diminish the weight advantage of plastics.

Safety

One critical part of the performance criteria of the tank is its ability to meet crash

requirements. Generally, plastic tanks are considered safer in crashes because they are

seamless and, thus, not prone to failures in the vulnerable seam areas. They are not a source

of sparks. Also, plastic tanks deform and have some ability to rebound back to shape. When

steel tanks absorb energy and deform, the pressure within the tank increases as the volume

decreases. This makes them vulnerable at welded or clamped areas where failure can

potentially occur.

The thermal properties of the chosen material are also an issue, especially due to the

proliferation of injector fuel delivery systems, where a portion of the unused fuel delivered by

the gas pump is returned to the gas tank at "engine-hot" temperatures. At the same time, the

tank must withstand extreme temperatures in North America from -40°C to 79°C in-tank

temperatures. The 79°C temperature not only exceeds the boiling point of the alcohol fuels,

but also creates sagging problems for plastic (especially under the weight of a filled tank)

while the extreme cold introduces potential cracking problems. As a result, OEMs resort to

heavier gauge plastic, negating at least some of the weight advantage, and must also use

support brackets and special shields against the heat of local sources like an inferior or

perforated muffler or tailpipe. High ambient temperatures underneath the car remain a

consideration.

Plastic acts as an insulator to retard heat transfer to the fuel when compared to a steel

tank. In the case of an under-car fire, plastic tanks will retard the rise in fuel temperature, but

they will soften, sag, and eventually release the fuel. A steel tank does not sag in a fire;

however, the fuel temperature may rise rapidly, perhaps resulting in over pressurization and

release of fuel through a mechanical fitting. The American Iron and Steel

Institutereports16

that a series of more than 75 tests undertaken by the National Fire

Prevention Research Foundation and Factory Mutual Research Corporation indicated that

plastic containers storing flammable or combustible liquids in general purpose warehouses

fail abruptly when exposed to a small fire. This failure results in a rapidly developing spill

fire that overpowers conventional sprinkler systems. The same tests conducted with

flammable and combustible liquids stored in steel containers resulted in no spill fire, no

excessive temperatures, no content involvement, and no significant loss of visibility due to

smoke. The fires involving the steel containers extinguished themselves. These findings have

led to a return to steel containers from plastics for safety and fire insurance cost reasons. It is

not known if tests have been conducted by OEMs to compare the performance of steel and

plastic tanks in under-car fire situations.

Corrosion

Corrosion is a well-known concern on both the inside and outside surfaces of tanks.

The outside surfaces and supporting structure are exposed to road chemicals, salt, mud, and

gravel. The corrosion issue is critical with zinc-coated products that replace terne plate

because of their sacrificial nature, which puts an even higher demand on the quality of the

barrier film for both inside and outside surfaces. In contrast, the HDPE gas tanks are inert to

the corrosive environments inside and outside the tank.

Recyclability

The Resource Conservation and Recovery Act discourages the use of materials that

cannot be recycled and might end up in landfills.17

As a result, automotive-design engineers

must not only meet customer, design, styling, cost, weight, and regulatory needs but also

environmental criteria. All materials suppliers must show that their product is not only lighter

and cost effective but also recyclable. In this respect, plastics must work the hardest to show

that they are recyclable and have the ability to be recovered in vehicle disassembly in a cost-

effective manner. To accomplish these objectives, automotive designers must develop

prototypes that can be disassembled easily into the various material groups that have a

recycling infrastructure.

Despite progress in recycling, the proliferation of plastics in automotive applications faces

some hurdles.

The absence of a plastics recycling infrastructure. The infrastructure for recovering

and recycling the ferrous content of cars is well established—70-80% of a typical

passenger car is recoverable steel and iron.

The molding process for plastic fuel tanks. As is the case for other ap-plications, this

process results in roughly 30% of plastic material ending as industrial waste.18

The necessary sorting of the various plastics types since mixing types can ruin the

batch. This is not a problem with steel—the scrap industry recycles 10.8 million

tonnes per year of shredded automotive iron and steel, which is used to make new

steel products.19

The lack of technology that dismantlers can use to quickly collect various plastics.

The current infrastructure of automobile dismantlers, shredders, and scrap-metal

processors is steel dominated and relies on magnetic separation and inexpensive

shredding equipment for efficient and low-cost processing. In the case of terne gas

tanks, the units are removed from the car, flattened, baled, and sent either to special

operators that can reclaim the lead or to the steel mill.

Cost. Recycled plastics are not cost competitive with virgin plastics.

While the recycling of HDPE gas tanks is easier to tackle in terms of dismantling and

avoiding type mixing, these tanks will not meet the new evaporative emissions standards. The

barrier-type and multilayer tanks that will meet such standards can pose a bigger challenge to

recycle in a cost-effective manner.

Table 1.1 Abbreviations

Symbol Plastic or composite

ABS

Acrylonitrile butadiene styrene copolymer

APK

Aliphatic polyketone

ASA

Acrylonitrile styrene acrylate copolymer

BMC

Bulk moulding compound

BMI

Bismaleimide

DMC

Dough moulding compound

EP

Epoxide (epoxy)

EPP

Expanded polypropylene

EPS

Expanded polystyrene

ETFE

Tetrafluoroethylene copolymer

EVOH

Ethylene vinyl alcohol

GFR

G lass fibre reinforced

GMT

G lass mat thermoplastic

HCPP

Highly crystalline polypropylene

HDPE

High density polyethylene

HIPS

High impact polystyrene

LCP

Liquid crystal polyester or liquid crystal polymer

MF

Melamine formaldehyde resin

MPF

Melamine phenol formaldehyde moulding compound

PA

Polyamide (nylon)

PA-GF

Glass fibre reinforced polyamide

PAEK

Polyarylether ketone

PAl

Polyamide-imide

PAA

Polyarylamide

PAS

Polyarylsulphone

PAT

P olya rylterep htha late (polyarylate)

PBT

Polybutylene terephthalate

PC

Polycarbonate

PCTFE

P olyc hi orotri flu orethyle ne

PDAP

Poly (diallyl phthalate)

PE

Polyethylene

PEK

Polyetherketone

PEEK

Polyetheretherketone

PEI

Polyetherimide

PEN

Polyethylene naphthalate

PEOX

Poly (ethylene oxide)

PES

Polyether sulphone

PET

Polyethylene terephthalate

PF

Phenol formaldehyde (phenolic)

PI

Polyimide

PMMA

Poly (methyl methacrylate) (acrylic)

PMMI

Poly (methyl methacrylate imide)

PMP

Poly (methylpentene)

POM

Polyoxymethylene

PP

Polypropylene

PPA

Polyphthalamide Vinyl ester resin

PP-E

Expanded polypropylene

PPF

Polyphenylene ether

PPO

Polyphenylene oxide (=PPE)

PPS

Polyphenylene sulphide

PS

Polystyrene

PSU

Polysulphone

PTFE

P olyeth ra fl uo roet hyle ne

PU

Polyurethane

PUR

Polyurethane

PVB

Polyvinyl butyrate

PVC

Polyvinyl chloride

PVDC

Polyvinylidene chloride

PVDF

Polyvinylidene fluoride

PVF

Polyvinyl fluoride

R-RIM PUR

Reinforced reaction injected moulded polyurethane

SAN SMA

Styrene acrylonitrile copolymer

SMC

Styrene maleic anhydride

S-RIM PUR

Sheet moulding compound

TPE-A

Structural reaction injection moulded polyurethane

TPE-E

Thermoplastic polyamide elastomer

TPE-O

Thermoplastic polyester elastomer

TPE-U

Thermoplastic polyolefin elastomer

UF

Thermoplastic polyurethane

UP

Urea formaldehyde

VP Unsaturated polyester resin