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Acknowledgments

This document was produced in collaboration with the Education Liaison Group andother leI staff on Teeside, who assisted with the technical details and provided support.for printing and the teachers involved. Out of print Ifll and ESPI booklets provided aframework of information which was built upon by the working party. The coverphotographs were supplied by leI.

Members of the Working PartyDon Raspin - Education Liaison, ICIKeith Waugh - Development Officer, Design and Technology, Cleveland L.E.A.Polly Brettle - Advisory Teacher, Design and Technology, Cleveland L.E.A.Paul Bennington -Head of Technology, Ormesby School, ClevelandDavid Barrass - Head of Technology, Hartlepool Sixth Form College, Cleveland

EditorAlan Stan cliffe

Polymer Industry Education CentreDepartment of ChemistryUniversity of YorkHeslingtonYorkY015DD

Telephone (0904) 432523

© Jointly held by ICI and the University of York

Published 1994ISBN: 185342700 4

The copyright holders waive the copyright on the material which follows to the extentthat teachers may reproduce this material for use with their pupils in the establishmentfor which the material was purchased, but for all other purposes permission to reproduceany of this material in any form must be obtained from leI orthe University of York.The material may not be duplicated for lending, hire or sale.

CONTENTS

PageIntroduction

SECTION1 SCHOOLBASEDPROCESSES1.1 WORKSHOP PRACTICE 1

1.1.1 Storage 11.1.2 Protective masking 11.1.3 Static electricity 1

1.2 SAFETY WITH ACRYLIC 21.2.1 Handling and machining 21.2.2 Flammability 21.2.3 Pressure shaping 2

1.3 FABRICATIONPROCESSES 31.3.1 Safety 31.3.2 Perspex acrylic sheet 31.3.3 Marking out 31.3.4 Edge treatment 31.3.5 Cutting straight lines 41.3.6 Cementing 51.3.7 Machining 7

1.4 SIMPLE THERMOFORMING TECHNIQUES 81.4.1 Effect of moisture 81.4.2 Oven heating 81.4.3 Single curvature forming 91.4.4 Double curvature forming 1 1

1.5 VACUUM FORMING 1 31.5.1 Equipment 1 31.5.2 Moulds 1 41.5.3 Heating times 1 51.5.4 Cooling times 1 6

1.6 FLUID BED COATING 1 7

SECTION2 INDUSTRIALBASED PROCESSES2.1 PROCESSINGMETHODS 1 8

2.1.1 Extrusion 1 82.1.2 Balloon blowing 1 92.1.3 Calendering 202.1.4 Injection moulding 2 12.1.5 Thermoforming by pressure 222.1.6 Thermoforming by vacuum 232.1.7 Biaxial stretching of film 242.1.8 Glass Reinforced Plastics Lay-up and Moulding 252.1.9 Plastic laminates 272.1.10 Compression moulding 282.1.11 Rotational moulding 292.1.12 Extrusion blow moulding 302.1.13 Injection stretch blow moulding 3 12.1.14 Dip moulding 332.1.15 Structural foam moulding 34

1

APPENDICESAppendix 1 Properties and applications - Thermoplastics 3 5Appendix 2 Properties and applications - Thermosets 3 6Appendix 3 Physical properties of some thermoplastics 3 7Appendix 4 Chemical resistance of some thermoplastics 3 8Appendix 5 Summary of main industrial processes 39Appendix 6 Equipment and materials suppliers 40Appendix 7 Other resources 4 1

Trade names and abbreviations associated with different materials areincluded in the tables listed above.

11

Introduction

This booklet has been produced in response to enquiries from teachers ofDesign and Technology seeking information on working practices in industryand schools relating to thermoplastics. It is not an exhaustive reference guidebut does provide an introduction to basic techniques suitable for schools and themore common processes found in industry.

The booklet is intended as a resource for the teacher but could also be used as asource of information for students engaged in Design and Technology projectwork for National Curriculum Key Stage 4 and for 16+ courses. Some of thepractical working methods outlined will also be relevant to Design andTechnology projects at Key Stage 3 of the National Curriculum. Teachersinvolved with the Scottish Curriculum for Technical Education, particularlywith the 11-18yrs age group, will find the information relevant.

Section one considers storage and safety procedures to be observed in schoolsand colleges in respect of plastics materials. It then goes on to outline somepractical processes which can be undertaken using equipment normally foundin school/college Design and Technology departments.

Practical workshop processes have been outlined using acrylic as a samplematerial since this is one of the most commonly used in schools. However,most of the techniques described will be suitable for other thermoplastic sheetmaterials (e.g. polystyrene, PVC, ABS) providing consideration is given todifferences in softening temperatures and appropriate categories of adhesives.Some techniques previously used in schools are now restricted as a result ofregulations relating to Control of Substances Hazardous to Health (COSHH)and are not included in this document.

It is common for all acrylic materials to be incorrectly described as Perspex.In fact Perspex is an ICI trade name for their own acrylic products. Whenreferring to the material in general terms the correct title is Acrylic .

.~ection two describes some of the more common industrial processes currentlyIn use.

Appendices 1 to 5 provide extensive tables of properties, applications andprocesses which will be useful for both teachers and older students studying atsixth form and FE levels. Appendix 6 lists equipment and material suppliers;appendix 7 lists locations of other resources.

iii

SECTION 1

SCHOOL BASED PROCESSES

1~1 ACRYLIC: WORKSHOP PRACTICE

1.1.1 Storage

Acrylic and other thermoplastic sheet is best stored on its edge in storage rackshaving a backboard at a slight angle to the vertical (an A-Frame). Theprotective masking is left in position and the material should not be allowed tobow.

Such storage provides adequate support and permits sheets to be withdrawnwithout danger of damage. Horizontal storage is not recommended as sheets aredifficult to withdraw, and any dirt, swarf or grit trapped between them maydamage their surfaces.

Store rooms should be well ventilated, cool and dry. The masking on extrudedacrylic sheet helps to protect against moisture absorption but cannot eliminate it.For this reason, acrylic should be stored in a dry area.

1.1.2 Protective masking

The paper/adhesive masking system used for many years on acrylic is beingreplaced. ICI Acrylics has introduced a polyethylene film masking with apressure-sensitive adhesive backing for the protection of cast 'Perspex' sheets.Sheets masked with a pressure-sensitive adhesive polyethylene film (PSPE) offerthe end user several advantages. The film will not fall off, is more stable toclimatic variations and can be cut or machined in place.

PSPE masking can be kept in place for local bending applications provided heatersare not in direct contact with the film, but PSPE masking cannot be otherwisethermoformed. The masking must be removed prior to heating the acrylic forthermoforming, normalising or annealing.

The surface of sheet masked with PSPE will not now need to be washed prior tocementing or thermoforming. However, for all surface decoration requirements,it is recommended that after removing the masking the surface of the sheet berinsed with clean water (to remove particles of dust and neutralise any residualstatic charge) and dried with a soft dry cloth.

Whenever possible the protective masking should be left attached to acrylic to avoidsurface damage. It is also useful for marking out shapes before machining.

1.1.3 Static electricity

To eliminate static on a finished article, use Acrylic Anti-static Cleaner or otherapproved products. However, if cementing, screen printing or spray painting,only use warm soapy water, rinse well and dry.

1.2 SAFETY WITH ACRYLIC

1.2.1 Handling and machining

Acrylic is a hard material. Sharp edges could cause cuts, and flying chips coulddamage eyes.

Recommended practice

• Sharp corners and edges should always be removed (see page 3) before handlingwith bare hands.

• Goggles should always be worn when machining it, as protection againstflying swarf particles.

• When it is being machined, the material should be held firmly and cutting tools,particularly drills (given a negative rake), should be sharpened correctly.

• The manufacturer's recommendations should be followed when coolants areused during machining operations.

• The area should be well ventilated with extraction of both fumes and dust.

1.2.2 Flam mabi Iity

When acrylic is heated, it softens and can be shaped readily. At normal shapingtemperatures of 140 to 170°C, acrylic does not evolve any noticeable amount ofvapour. However, it is dangerous to subject acrylic to flames or prolonged heatingbecause it creates highly flammable and irritant fumes. The flash ignitiontemperature of acrylic is 280°C.

Recommended practiceCare should be taken when thermoforming acrylic and teachers should refer toexisting Health & Safety Regulations.

1.2.3 Pressure shaping

Heated acrylic is often thermoformed by air pressure without a complete mould,either by free blowing or by the use of a skeleton mould. It is possible for theacrylic to burst during forming by air pressure. The possible causes are:

• Excessive air pressure• A faul t in the blank• Damage to the surface of the blank• Contamination of the blank with foreign matter

Safety shields should be provided when acrylic is being blown, to protect theoperator from fragments of acrylic in the event of a burst thermoform. This is notnecessary if a complete mould is being used. Blanks for thermoforming should behandled and stored carefully so as to avoid damage or contaminating the surface.Whenever possible, the protective paper should not be removed until just before theblank is placed in the oven.

2

1.3 ACRYLIC: FABRICATION PROCESSES

1.3.1 Safety

Normal codes of practice must be observed in the workshop. The followingdocuments offer further guidance:

• COSSH*: Guidance for schools (from HMSO)• Risk Assessment for Technology in Secondary Schools (from CLEAPSS)• Topics in Safety (from ASE)• Safeguards in the School Laboratory (from ASE)• Be Safe! - Some Aspects of Safety in School Science and Technology (ASE)• Make It Safe (from NAAIDT)• Managing Health and Safety in Design and Technology Workshops

(from NAAIDT)Addresses for the above documents are listed in appendix 7

Appropriate protective clothing must be worn at all times(e.g. gloves/aprons/dust masks etc.)

1.3.2 Perspex acrylic sheet

Perspex acrylic sheet is produced in two common standard forms. These are castPerspex and extruded Perspextx. Extruded Perspex tx is particularly suitable forvacuum forming whereas cast Perspex is more suited to fabrication processes.

1.3.3 Marking out

The use of fine line permanent markers, chinagraph pencils, scribers andmasking tape is recommended with normal marking out procedures.

1.3.4 Edge treatment

SandingSanding discs and finishing machines can be used with care for trimming andsmoothing very rough edges, but avoid overheating. Goggles and dust masksshould always be worn when abrading any plastics materials.

Abrasive paperA fine grade 'wet or dry' abrasive paper will produce a smooth surface suitable forpolishing.

PolishingThe machined surfaces of acrylic may be brought to a high surface gloss by carefulbuffing or hand polishing with 'Perspex' polishes or conventional metal polishes.Usually an intermediate smoothing operation is required to avoid extendedpolishing times.

* COSSH - Control of Substances Hazardous to Health

3

1.3.5 Cutting straight lines

Scribe-breaking

Acrylic up to 4.0 mm thick may be cut in a straight line by deeply scoring onesurface with a sharp metal scribing knife, clamping the sheet with the scribedline uppermost and aligned with the edge of a bench, and breaking the sheet bypressing steadily downwards on the free part.

A suitable blade is the Stanley Knife Scriber blade No. 5194.

IF CUTTING LONGLENGTHS. CLAMP THESTRAIGHT EDGE DURINGBREAKING. PRESSSTEADILY DOWNWARDS.

Scribe breaking acrylic

Hand sawing

When cutting irregular shapes, acrylic may be cut using a hacksaw or fretsawprovided they are sharp and have fine teeth. Coarse tooth saws and heavypressures will cause chipping.

Preferably clamp the acrylic close to the line of the cut when hand sawing toprevent cracking of the sheet.

Power sawing

Band saws and fretsaws can be used in production work but always ensure thatthe pitch of the teeth is less than the thickness of the material being cut. Materialshould not be forced through the saw. Strips of sellotape over the line of cut willhelp to dissipate heat produced by friction from the saw blade and prevent the sawcut from 'welding up' behind the blade.

4

1.3.6 Cementing

Acrylic can be cemented to acrylic with 'Tensol' cements. 'Tensol' cements canalso be used to cement acrylic to some non-acrylic materials.

'Tensol' adhesivesThe most useful 'Tensol' adhesives for joining acrylic are 'Tensol' Cement 12 - asolvent based adhesive and 'Tensol' Cement 70 - a polymerising adhesive. 'Tensol'Cement 12 is supplied ready for use. Care should be taken not to shake or drop thebottle, which might cause air bubbles in the liquid. (Ideally, 'Tensol' Cement 12should be stored in a refrigerator with other similar chemical materials).

'Tensol' Cement 70 is a two part adhesive, prepared by mixing twenty parts ofComponent A to one part of Component B. The mixture should be stirredthoroughly and left to stand for a few minutes until any air bubbles havedispersed. The mixture must be used within 20 minutes of mixing. Roomtemperature must be above 15°C.

'Tensol' Cement 70 (A + B) should be stored in a cool dark place. At very lowtemperatures, crystals of component B may appear in the mixture. It is importantthat any crystals be dissolved before use. The film of 'Tensol' is normally appliedto one surface only. If there is a glossy surface and one which has been machined,the cement should be applied to the machined surface.

When using 'Tensol' cement 70, always ensure excess cement is applied as thecement will shrink 20% during reaction. Only apply light pressure.

ApplicationEnsure all surfaces to be glued are perfectly clean and grease free. Assemble thejoint when the cement has been in contact with the surface for about 30 seconds. Ifleft for a longer period a skin will form over the cement which can prevent thejoint from being bonded successfully.

CareCurrent safety procedures should be followed at all times. Use 'Tensol' and othersolvent cements in a well ventilated room, ideally equiped with appropriate fumeextraction facilities, and away from sources of ignition.

Other adhesivesThere are a range of adhesives available for joining plastics materials. Some havea permanent rubbery quality for use with flexible plastics and in joining plastics toother materials. There are also hot melt adhesives available which rely on heat tomelt a plastics pellet or film to produce a join. Some adhesives rely on evaporationof a solvent while others involve the mixing of two liquids or pastes which thencure by chemical reaction.

There are a range of commercial liquid solvent cements available for use withthermoplastics. Some solvent cements will work on several plastics (e.g. acrylic,ABS, butyrate, styrene) while others will only work on one particular plasticmaterial. Reference should be made to manufacturers instructions andguidelines. Special dispensers and applicators are also available.

Various Bostik, Epoxy Resin (Araldite) and Cyanoacrylate (Super Glues)preparations are suitable for joining plastics but their use is subject to safetylegislation and current local authority regulations and practice.

5

Suggestions for cementing techniques

WIRE PACKITO ASSISTCAPILLARYACTION:REMOVE BEFOREGEL STAGE.

MASKING REMOVEDAT GEL STAGE.

ANGLE JOINT.

USEPLENTY OF CEMENT.

REINFORCINGFILLET.

Note - When using solvent cement to join two dissimilar plastics, the hardermaterial should have its joint surface softened by applying a light coat of solventprior to bringing the two surfaces together.

6

1.3.7 Machining

The machining characteristics of acrylic sheet (cast or extruded) are similar tothose of brass or hard aluminium, but there is one very important difference. Thisis that acrylic will start to deform if it is heated to temperatures in excess of 80°C.Therefore the heat generated by the cutting tool must be kept to a minimum. Thiswill minimise any stress being produced in the machined area and reduce thepossibility of causing any alteration to the machining characteristics of thematerial. Where possible, acrylic should always be machined with thepolyethylene masking film left in place.

NB. Acrylic is a notch sensitive (brittle) material and care must be taken to ensurethat no notched areas are introduced during machining. Sharp cutting tools willhelp to avoid this.

Cutting tools

These must be kept sharp not only to produce a good surface finish but to minimisethe amount of heat generated.

Dri II ing

Standard twist drills up to 5 mm are quite suitable for drilling acrylic, as also aremany of the drills specially developed for plastics such as step drills and conedrills. It is recommended that standard twist drills above 5 mm be sharpenedwith a negative rake to prevent 'grabbing' during the drilling process.

Always clamp the acrylic sheet firmly against a piece of wood or other softmaterial before drilling and never use a centre punch to mark the position of thehole, as this will crack the acrylic. Typical drilling speeds are shown in the tablebelow:

Dr ill ApproximateDiameter Drill Speed

(m m) (rev/min)

1.5 70005.0 180012.0 900

Turning

Acrylic can be turned to engineering tolerances on metal-working lathes andmany of the techniques used for metal can be applied. Tool bits made from high-speed steel are preferable. Speeds and feeds are similar to those for brass.

Milling

Care must be taken when milling acrylic because cutter rotation is usually slowerthan for other machining operations. The feed and depth of cut should be matchedto the cutter.

7

1.4 SIMPLE THERMOFORMING TECHNIQUES

When acrylic cast sheet is heated to 150-170°C it becomes rubber-like and can bestretched into complicated shapes. After cooling to 90°C, or below, the acrylic willretain the shape imposed on it. If re-heating takes place the acrylic will return toits original flat sheet form. Cast acrylic sheet should not be heated totemperatures above 170°C as this will produce highly flammable, irritant fumes.

When extruded acrylic sheet is heated to 140-150°C it behaves in a soft and rubber-like way. In this state it can be thermoformed in a similar manner to acrylic castsheet. When the material is heated to 170-200°C it behaves in a thermoplasticmanner and can be thermoformed into complex shapes using very little pressure.It is this characteristic which makes Perspex tx an excellent vacuum formingmaterial.

1.4.1 Effect of moisture

Extruded acrylic sheet materials will absorb moisture when exposed to a humidatmosphere. Absorbed moisture can seriously affect the thermoformingperformance of acrylics and causes blisters of about 2-3 mm diameter to appearduring heating. If this occurs the sheet can be dried out by 'heat soaking' at atemperature of 85-95°C for 24 hours (with the protective masking removed fromboth sides). When cool, the 'dried' sheet should be protected against any furthermoisture absorption by wrapping in polyethylene film.

1.4.2 Oven heating

Heating is normally done in a small oven. Ideally an air circulated oven should beused.

Heating times in an air oven for Perspex tx

Thickness Heatlnc Timesmm At 150°C At 160°C At 170°C

min min min2 1 6 12 8

2.5 1 7 1 3 83 1 9 14 94 22 1 6 115 25 18 126 28 21 14

It is most important not to exceed these times because of material elongation invertical ovens or shelf marking where the material is heated horizontally.

8

1.4.3 Single curvature thermoformingThis means that, in general, the heated sheet is not stretched but allowed to bendor fold along a single axis.

Drape formingFor items with a shallow single curvature, the heated acrylic sheet is placed in aconcave mould and allowed to settle under its own weight until it rests on thesurface of the mould. For convex moulds - light pressure will be needed until thesheet is cool. Both methods are illustrated in the diagrams below.

For convex moulds -some pressure will beneeded until sheet is cool.

CLOTH FORMER.

Simple drape forming

Making a tube from acrylic sheetA suitable length of polyvinyl chloride (PVC) tube (e.g. plastic drain pipe) can beused as a mould to form a tube from flat acrylic sheet. The plastic pipe is cutlongitudinally down one central axis to create two halves. These are then heldtogether along one edge by use of a tape/cloth style hinge. One edge dimension ofthe acrylic sheet should be cut to match the internal circumference of the PVCtube when closed.The two halves of the PVC tube mould are laid open and the heated flexible acrylicsheet placed in position over them, taking care to match the correct edge of theacrylic with the curved circumference profile of the mould. The mould is thenclosed allowing the acrylic sheet to take on the shape of the internal curvature.The closed mould can be held in a simple jig as shown below until the acrylic coolsdown.

Forming a cylindrical tube from acrylic sheet

9

Simple scrolling for letters or curvesSimple jigs can be made to form scrolled curve shapes similar to wrought ironwork. Strips of acrylic are cut to size, heated and formed around the jigs whenflexible. An example of a simple arrangement is illustrated below.

Acrylic strip formed into a scroll shape on a simple jig

Local bendingAngled bends along straight lines can be obtained by heating the acrylic locally onboth sides using a strip heater. Simple jigs can be constructed to hold the acrylic inposition during the cooling period as illustrated below.

'Perspex' heatedlocally alongline of bend

Acrylic shapes held in a simple jig while cooling

1 0

1.4.4 Double curvature thermoforming

This requires force to be applied to the sheet by using either air pressure, vacuum,a press with a male and female mould, or a combination of these techniques. Theacrylic sheet has to be firmly clamped before stretching or shaping takes place.This should be done quickly to avoid undue loss of temperature after heating,which could cause excessively strained shapings. Toggle clamps are the mostconvenient for this process. It is advisable to heat the clamping frame to 60-70°Cbefore positioning the acrylic sheet.

Toggle clamp

Free-blowingIn this process heated acrylic sheet is shaped by use of direct air pressure orvacuum without the use of a mould. The outer edges of the acrylic sheet are heldby a clamping ring and the heated sheet is then subjected to pressure or vacuum tocreate a natural bubble shape. The pressure or vacuum is set and the setting ismaintained throughout the cooling period. Pressures of up to 10 N/cm2 aresufficient for most school work. A simple arrangement is illustrated below.

Controlled heIght

Heated 'Perspex'

tnrnrnrnq lines Compressed air

Free blowing an acrylic bubble shape

1 1

Simple press forming (plug and yoke)A simple male and female mould (plug and yoke) which can be constructed fromMedium Density Fibre Board (MDF) is illustrated below. The heated acrylic sheetis sandwiched between the plug and yoke of the mould which are then forcedtogether under pressure causing the acrylic to take on the shape of the mould. Byplacing the mould on the table of a pillar drill, the drill press can be used to applythe required force.

Dowel location pins

Constructed ~from M.D.F.

Simple plug and yoke arrangement

1 2

1.5 VACUUM FORMING

A variety of related techniques are included in the description vacuum forming.Their common feature is the shaping of a hot sheet of thermoplastic material byremoving the air from one side of the sheet and thus, in effect, 'sucking' it into orover a mould.Perspex tx is ideally suited to the technique of vacuum forming on machineswhich are designed for this purpose.Perspex tx can be formed with the clear protective masking in place on the uppersurface of the sheet if required but any imperfections in the masking film such ascuts, holes and blisters may leave slight impressions on the surface of the sheet.

1.5.1 Equipment

Machines used for commercial production are designed so that they will operatewith the minimum of attention and for some specialised applications they havebeen designed to function completely automatically. Such complexity is notneeded for school applications, and is indeed undesirable. Simple and relativelyinexpensive machines suitable for school use are now available frommanufacturers (see Appendix 6).

A simple vacuum forming machine consists of 4 main parts:

A heaterA vacuum boxA clamping system for the thermoplastics sheetA vacuum system

The clamping system must hold the sheet firmly in place to form a vacuum tightseal with the box. A frame made from small-section angle iron, and held downwith quick-acting clamps is usually used for the clamping system.The vacuum system must remove the air quickly from the vacuum box - this ismore important than achieving a high vacuum.

Mould

Thermoplasticsheet

"Oampingframe---4~Clamp

Rubber seal

Perforatedmould support

A typical vacuum former arrangement

With a simple vacuum forming machine as described above articles can beformed using female or male moulds.

1 3

Working sequence:

Heat applied to makethe plastic pliable

Vacuum release valveopened to withdraw air

Thermoplastic clampedabove the mould

Soft Thermoplasticsucked into mould

Vacuum formed sheetallowed to cool

Vacuum release valveclosed when plastic set

Plastic mouldingremoved from former Repeat the cycle

1.5.2 MouldsMoulds for vacuum forming are simple to construct. Although for commercialproduction aluminium moulds are frequently used, wood, plaster, mediumdensityfibre board (MDF), and papier mache are suitable, and even clay has beenused, but a mould must be designed carefully.Vents must be provided to ensure the rapid evacuation of all the air trappedbetween the mould and the material being formed. The vents may convenientlytake the form of a series of small holes, about Irnm in diameter where they emergefrom the working surface, drilled in the lowest part of the mould and in any localdepressions or cavities within the mould area. These small holes should becounter bored to about 6 mm in diameter for the greater part of their length (fromthe back of the mould to within about 3 mm of the mould face), and connect withthe holes in the mould support.

~. ;I ~ /: :: .Air passages Bottom of mould rebated or resting

on thin 'spacers' to allow air passage

Typical mould features

It is important to allow some degree of taper on the vertical faces of a mould inorder to allow for shrinkage of the material as it sets and to enable the moulding tobe removed from the mould. Recommended tapers are 0.50 to 10 for female mouldsand 2-100 for male moulds, depending on the depth of draw (i.e. the distance fromthe plane of the clamping frame to the deepest part of the mould) and on thematerial being used.

All internal and external corners of moulds should be radiused (rounded) and thesurface made as smooth as possible, to reduce the risk of imperfections beingtransmitted through the thickness of the sheet. Marks on moulds can spoil theappearance of the finished article, particularly when clear sheet is used. Goodseparation can be achieved by use of a release agent such as talcum powder.

1 4

The distribution of material thickness in articles which are vacuum formeddiffers according to whether a male or female mould has been used. This isillustrated in the diagrams below:

Thickness at: a - 1.02 mm-. b b - 1.02 mm., I •••

\~ Ic - 0.65 mmd - 0.50 mme - 0.50 mm

.1 If f - 0.65 mm

Typical material thickness distribution from a female mould

Thickness at: a - 1.27 mmb • 0.65 mm.,

fl IV r c - 0.25 mm

1 f \ d - 0.40 mme - 0.50 mmf - 1.27 mm

cl dl g - 1.27 mm

Typical material thickness distribution from a male mould

1.5.3 Heating times

Heating times will depend on individual circumstances. In average conditions atime of 20 seconds per millimetre of thickness can be used as a guide for clearsheet; for opals 10% longer should be allowed.

Comparison of the vacuum forming performancesof extruded and cast acrylic sheet

Heating Approximate Perspex tx Standard Perspextime surface (extruded) (cast)

(seconds) temperature (OC) 3 mm Clear 3 mm Clear

100 210 Maximum heating timet Surface degradationdefinition

90 200 Good definition Surface degradation

80 185 Good definition Maximum definition obtainablewith standard Perspex

70 170 Good definition Fall-off in definition

60 160 Slight fall-off in definition Continued fall-off in definition

50 140 Continued fall-off Too cold

40 120 Definition equal to that Too coldof standard Perspex at80 seconds

These results were achieved on a laboratory vacuum forming machine with alower rate of heating than the average quoted earlier.

1 5

1.5.4 Cooling times

The cooling time for extruded acrylic sheet is more critical than its heating time.The exact time is dependent on mould temperature, sheet thickness, ambienttemperature and type of forced air cooling (if employed).

Cooling times can be expected to be fairly short, i.e. less than 60 seconds for 3 mmthick sheet under average conditions. Extended cooling will allow the material toshrink back on to the mould to a point where the forming will crack from a weakspot or notch sensitive area. If not cooled for long enough, the forming will distort.Ideal conditions must be found by trial and error.

It is preferable to remove thermoformings from the mould while they are still hot(surface temperature 95°C) as this procedure eliminates most of the locked-instress which can cause stress-cracking to develop in service. Always wearprotective gloves when doing this.

1 6

1.6 FLUID BED COATING

Fabricated metal articles can be covered with a thermoplastics coating (egpolyethylene) by use ofa fluidised bed of powder.

The construction of a fluidised bed is illustrated below. Air at low pressure ispassed through the porous base of a container into which the thermoplasticspowder has been placed. Care should be taken to use a sufficient quantity ofthermoplastic material in order to achieve steady fluidisation without 'boiling' ofthe powder.

The metal article to be coated is first cleaned of oil and grease, and then heated inan oven, before being plunged in to the fluidised bed. Some powder will fuse andstick to the hot metal; the coated article is then removed from the bed and returnedto the oven to completely fuse the coating.

The temperature to which the article needs to be heated before coating will dependon the thermal capacity of the article. A thin wire construction, for example, willrequire a higher temperature than will a solid rod of steel. When low densitypolyethylene is used for the coating, a temperature of about 180°C is suitable formost articles. Temperatures above this may result in degradation of the polymer,producing harmful fumes.

--1------ Fluidised bed

Porous base

Air in

Typical fluidised bed arrangement

1 7

SECTION 2

INDUSTRIAL BASED PROCESSES

2.1 PROCESSING METHODS

2.1.1 Extrusion

Products• drain pipe and guttering• window frames and curtain rails• roofing sheet• plastic hose• wire insulation• flat sheet can also be made by extrusion.

Containers and bottles can be produced from extruded tube by a blowing process.

ProcessExtrusion is a method of moulding thermoplastic material into continuous lengths ofprofiles. These may be solid or hollow. Pipe and tube are examples of the latter.

In extrusion, a thermoplastic in the form of granules is fed from a hopper into anextrusion machine. The material is softened under the action of heat and pressureand then extruded to the required form (e.g. window frame profiles) from a die fixed tothe nozzle of the machine. This method can be used to produce all types of polyvinylchloride (PVC), polyethylene (PE) and polypropylene (PP) thermoplastic pipe and tube.

Various shapes and sizes of extrusion can be produced using different dies. Twoexam ples are shown below:

tube/pipe

Two typical extrusion shapes

Large screw forces heated plasticalong the chamber and

through the die

Hopper containingplastics granules

extrusion/

Cooled chamber

base

Spool for flexible extrusions interchangeable electric motorsteel die

A typical extruder arrangement

1 8

2.1.2 Balloon blowing

Products• dustbin liners and carrier bags• more luxurious uses where attractive tinting or surface finish is involved

Polythene films will, after suitable treatment, take printing inks and this allowsinformation about a polythene-wrapped product to be printed on the pack.

ProcessIn balloon blowing, a plastic melt is extruded and then a different die and air blowerare used to produce a balloon of plastic which can be nipped or pressed into a doublefilm called layflat tubing. This can be made into bags by cutting the material intolengths and heat sealing one end. A gusseting device is sometimes used to fold atriangular section along the sides of the layflat tubing so that when it is made intobags the gusset can open to increase the volume inside the bag.

Balloon extrusion is very rapid and the film produced can range in thickness from2 mm to 0.1 mm.

wind-upgusseting device

_ guide board

plastic balloon

layflat tubing with gussets

layflat tubing without gussets

compressed air supply

Typical balloon extrusion system

The air ring at the base of the balloon serves to cool the molten plastics material

1 9

2.1.3 Calendering

Products• protective sheet• shower curtains• stretch wrap film

ProcessSuitable thermoplastic compositions are passed through heated metal rollers withprogressively smaller gaps to produce continuous film and precision thin sheet. Thismethod is used to produce polyvinyl chloride (PVC) flexible film in widths of up to 4metres, and thin PVC and polystyrene (PS) rigid foils for use in thermoformingprocesses or making sheet material. Embossing techniques can also be incorporatedinto the rolling process.

Hopper

ExtruderCompressor

Wind up

Cooling jets ofcompressed air

A typical calender system

20

2.1.4 Injection moulding

Products• buckets and washing up bowls• agricultural produce boxes - high density polyethylene (HDPE) and

polypropylene (PP)• growing pots - polystyrene (PS)• TV and hi-fi cabinets - high impact polystyrene• telephones and gear wheels

ProcessInjection moulding is probably the most widely used process for makingthermoplastic items in large numbers. However, it is not economic for making smallnumbers of a particular moulding because of the initial set-up costs and expenseinvolved in producing the moulds for the machine. With injection moulding,thermoplastic material (in granular form) is fed from a hopper into the heated barrelof the machine. The barrel contains a revolving screw which carries the granulesalong to where they are softened to a liquid state. The molten thermoplastic is thenforced under high pressure through a small nozzle into a split mould where thematerial rapidly solidifies, taking on the shape of the mould. When the material isset, the mould is opened and the moulding ejected. Sophisticated complex moulds canbe pre-heated by built in systems to assist material flow prior to cooling.

Injection moulding is suitable for moulding all thermoplastics and a wide variety ofdomestic and agricultural items are produced by this method.

HopperThermoplastic pellets

o000000

Mould

o

Controlso 0

A typical injection moulding machine

21

2.1.5 Thermoforming by pressure

Products- thin -walled growing trays and seed boxes-Tight-weight disposable trays- corrugated polyvinyl chloride (PVC) sheet for growing frames

ProcessThe process of thermoforming consists of heating a thermoplastic foil or sheet(usually polystyrene or PVC) until it is soft, then placing it over a former or mouldonto which it is pressed mechanically into shape. The sheet takes on the shape of theformer or mould and on cooling sets to the shape. The cooled shape is then removedand excess material trimmed off. This is a fairly simple process for speed in massproduction where precision is not too critical.

\,-_~rI

MouldingMould

The pressure thermoforming process

22

2.1.6 Thermoforming by vacuum

Products• yoghurt pots and vending machine cups• point-of-sale display• fridge linings• equipment housings

ProcessIn this process, plastic sheet is heated until it is soft and then sucked into a mould orformer by withdrawing air from the mould cavity, thus creating a vacuum. To assistthe forming process, the mould table is sometimes raised, pressing the mould lightlyinto the softened plastic sheet just before activating the vacuum. Moulds and formerscan be male or female for this process.

Slide to p!ace heater.. . Heater over thermoplastic sheet

"'-------111-:omoT06 0000olOo0ID00OO"OOIDm ;fJ

EvacuationTank Vacuum Pump

A vacuum forming machine arrangement

23

Vent holes

2.1.7 Biaxial stretching of film

Product• polypropylene (PP) and polyester (PE) films

ProcessBiaxial stretching is the process of stretching semi-molten film in two directions(normally on two axis at 90° to each other) as it leaves the heated die of an extruder.

~ ~ ~ ~ ~ ~ ~.... .... .... .... .... .... ....

~ ~ ~ ~ ~ ~ ~ ~ ••.... " . ., ........~....~,HOT,~....~....•• ~ ~ ~ ~ ••~....~"FILM'~....~....,, .... "" ,,~ ~ ~ ~ ~ ~ ~.... .... .... .... .... .... ....~ ~ ~ ~ ~ ~ ~.... .... .... .... .... .... ....

~ ~

Biaxially stretching polymer film

In the case of polypropylene and polyester films, crystallisation occurs on stretching,increasing the mechanical strength of the material and decreasing the water vapourpermeability. One production method for biaxially stretched polyester film isillustrated below.

extrusion

chilling of extrudate

stretching across

width using heat

setting of film using heat

coiled film

A typical production system for biaxially stretched film

The molten plastic is extruded through the slit of a metal die, producing a hot moltenribbon of film. The hot ribbon then drops on to a chilled metal roller to solidify it andpull it away from the die. The cooled ribon of film then passes through an oven whereit is reheated and stretched first along its length and then across its width (biaxialstretching). The film is then held in the stretched condition and allowed to cool (set)before being wound into large rolls for despatch to the customer.

24

2.1.8 Glass Reinforced Plastics (GRP) Lay-up and Moulding

Products

• canoes• boat and car bodies• chemical plant• architectural claddings

Process (GRP lay-up)The lay-up technique for Glass Reinforced Plastics (GRP) involves a comparativelysimple profile mould of metal, wood or plaster and the following processes:

1. Liquid polyester resin, mixed with a catalyst (or hardener), is applied to themould to form a pre-gelled coat.

2. Glass fibre in mat or woven fabric form is laid on the first gelcoat and liquidpolyester resin/catalyst mix is sprayed on until the fibre layer is saturated.

3. When the resin mix has hardened, the moulding is removed from the mould.Curing (setting) can take place in the cold or can be speeded up by heating.

Glassfibra

I PregeJled\~... I /resin coat['t:::~.J1--....Moulding

Lay-up technique for GRP

Glass Fibres __Catalysed Resin __

Accelerated Resin _

DETAIL OF SPRAYGUN GRPLAY-UP TECHNIQUE

fibre glass rovings

Spraygun

--.Roller for compacting GRP

Separate spraygun nozzles

Pressurised resin tankof male mould

Catalysed resin

Mobile trolley

Automatic fibre dispenser and resin spraygun

25

Process (GRP moulding)Two other technique used with Glass Reinforced Plastics (GRP) are the rubber-bagand matched-die moulding methods in which pressure is applied to the top surface ofthe moulding during processing. Various compositions of polyesterresin/catalyst/glass fibre are used to produce mouldings in both these pressurisedprocesses. By heating, comparatively fast hardening of the resin is possible. The twomethods are illustrated below.

Air-tight seal/

inflated with

air

Uncured GRP layup

Pressure bag method of moulding GRP

Pad regulatingmoulding thickness

\

Dowel Pins tolocate male and

female mould halves1

Mould Cavity inwhich GRP is placed

Matched mould method for GRP

26

2.1.9 Plastic laminates

Products• decorative work top surfaces

ProcessDecorative thermosetting plastic laminates have become commonly known as'Formica', 'Warerite', 'Arborite', etc. but these are just trade names belonging toproducts of individual companies. The dark underside of the laminate consists oflayers of brown paper impregnated with a thermosetting resin, phenol-formaldehyde(PF). The outer surface of the laminate consists of a decorative paper bonded to theunderlayer of phenol-formaldehyde resin. This decorative paper is covered with athin paper skin impregnated with melamine-formaldehyde resin (MF) and bonded tothe underlayers using heat and pressure in a hydraulic press.

The process of producing thermosetting decorative laminate is illustrated below.

hot air

paper impregnated paper

I

a) Paper impregnation

MF ( --------- _thin overlay paperresin impregnated -- decorative printed paper

========::::1 _ heavy white underlay paper

resin i::'egnated ( J -- brown base papers

b) Impregnated paper assembly

cut impregnated

paper assembly

stripping plates from laminate~~~~--..:rrr:--..=== decorative laminate

pressing

c} Pressing and finishing

Thermosetting decorative laminate making

The paper sheets are impregnated with a liquid thermosetting resin. These sheetsare then dried, laid up in a loose stack and pressed between specially surfaced metalsheets in a multi-platen press under conditions of high pressure and temperature(1000 N/cm2and 150°C). Under these conditions, the resin flows between the sheetsand cures (hardens) to give the final laminate.

27

2.1.10 Compression moulding

Products• 'hard' electrical plugs and sockets• fuse boxes• lamp holders• saucepan handles• insulators

ProcessCompression moulding is used mainly to process thermosetting plastics. The correctamount of plastics material, usually in powder form, is measured into a two partmatched die mould. The mould is closed under pressure and heated, causing thematerial to soften and flow into the shape of the mould before setting hard. Mouldingpowders for use in compression moulding are made up from various blends of resinswith cellulose and mineral fillers. The traditional thermosetting resins are urea-formaldehyde (UF), melamine-formaldehyde (MF) and phenol-formaldehyde (PF).

The press for compression mouldinghas a central ram which applies forcehydraulically to a heated mould.

~- __ +---:...' THERMOSETTINGPOWDER INTHE MOULD

PRESS

HYDRAULICPUMP

ELECTRICMOTOR

A typical compression moulding system

28

2.1.11 Rotational moulding

Products• litter bins and dustbins• storage tanks (water, etc.)• traffic bollards

ProcessRotational moulding is used to make large hollow articles (e.g. containers) usually inlow density polyethylene (LDPE). The LDPE material in powder form is fed into ahollow sheet metal mould in the shape of the item to be produced. The mould is thenheated whilst rotating about two axes so that the plastic melts and flows to form a skinover the inner surface of the mould. The mould is then cooled, opened and the hollowmoulding removed. For open-top tanks (e.g. water cisterns) simple large hollowmouldings may be cut in half to provide two such products. For closed tanks (e.g.liquid fertiliser spray equipment) pipe inlets and valves can be fitted after moulding.

Remove moulding~

Rotator arm ~

Mould filled with thermoplastic powder(PVC/polythene) then heated by gas flame

whilst rotating

Mould with molten plastic adhering to all

inside surfaces is taken from gas flameand cooled by water jet whilst rotating

Rotational moulding

29

2.1.12 Extrusion blow moulding

Products• bottles• drums• car fuel tanks• heater ducting

ProcessA length of hot plastic tube is first produced by extrusion and then lowered into anopen two part hollow mould of the final product shape. The mould is then closed andsealed so that the tube can be inflated, to take on the internal shape of the mould,using compressed air. When cool, the mould is opened and the product removed.Precision hollow mouldings can be produced by this method. The cycle for blowmoulding a bottle shape is illustrated below.

knife

extruder

~:~ screw turns all <h. time tomake a continuous hot plastics parison ortube.

Plastics bottles of all shapesand sizes can be made inthis way.

When the length of tube is correct. it issurrounded by the mould and cut oHwith a knife attached to the machine.

With the moulding removed. the mould isnow ready for another cycl •.

air blower

Blow moulding sequence of operations

30

2.1.13 Injection stretch blow moulding

Products• fizzy drink bottles - carbonated soft drinks (C.S.D.)• jars and non carbonated bottles• toiletries and cosmetics containers

The average 'fizzy drink' bottle contains a liquid pressurised to 14 atmospheres bycarbon dioxide. Polyethylene terephthalate (PET) has a sufficiently low permeabilityto prevent carbon dioxide seeping through it and this makes it a suitable plasticsmaterial for fizzy drink bottles. The strength of PET can be improved by the process ofbiorientation during production of the container (bottle) in a similar manner toprinciple ofbiaxial stretching of polymer film (see p24). This produces containerswith improved stacking strength and resistance to stress-cracking, which will alsowithstand the pressure of normal gaseous drinks. The design of fizzy drink bottlesalso makes maximum use of designs for pressurized containers in that they arecurved on as many areas as possible, including the base. Most bases are now of thepetaloid design (see diagram on adjacent page).

Process

The method of blow moulding bottles for gaseous contents is mostly a two part processin order to incorporate the biorientation of the material mentioned above. The firststage is to produce a hollow cylinder, domed at one end, by injection moulding. Thisshape is known as a 'parison'. The parison is then removed from the injectionmoulder, re-heated to make sure it is pliable enough and transferred to a bottle mouldfor the second stage of blow moulding in to the final shape. The second stage causesthe material to be stretched (oriented) in two directions at right angles to each .other(axial along the length of the cylinder and diametral across its diameter) thus givingthe required strength properties.

Stage 1

mould clamping and opening mechanism plastic moulding pallets

mould

Injection moulding to produce parisons

Parison ready for blow moulding

31

Stage 2

Mould openwith PET parison in positionready for blow moulding into

bottle shape

Mould closedwith blown bottle completed

ready for removal

The pets/aid design of most pop bottle bases

32

2.1.14 Dip moulding

Products• protective gloves• balloons• handle grips

ProcessTemperature controlled mandrels of the product shape are dipped into a bath ofplastic paste or fluidised powder. The paste/powder softens and forms a skin aroundthe mandrel shape which when cool can be peeled off. Alternatively, products of othermaterials (e.g. metals) can be dipped and the plastic material then forms a fixeddurable coating on the outer surface of the product.

Coated mandrelafter dipping

Glove mandrelto be dipped

Producing rubber gloves by dip moulding

33

2.1.15 Structural polyurethane (PU) foam moulding

Products• computer housings• tool handles• casings/cabinets• furniture shells• decorative simulated wood effects for wall panelling

ProcessA two part pre-mix of polyurethane foam is poured rapidly into a split cavity mould.The chemical reaction of the mix causes the foam to expand rapidly and take on thecavity form of the mould. The foam sets within a few minutes to produce strong,lightweight mouldings. A development of this process is used to make integrallyskinned PU foams; a combination of a foam interior with a hard solid skin or surfacewhich can be finished with lacquers.

Two part mixinto mould

Split cavity:-...~---- mould

Mix expands intoshape of mould

Compression moulding process

34

APPENDICES

Appendix 1

THERMO PROPERTIES APPLICATIONSPLASTICS

ACRYLICS Rigid. glass-clear. glossy. extremely weather Signs. lenses. inspection windows. taillightPMMA resistant. excellent for vacuum forming. casting lenses. synthetic fibres. lighting diffusers. leafletPerspex and fabricattng dispensers. hi-f dust covers

Acrylonitrile Butadiene Rigid opague, glossy/textured. tough. colourful. Telephone handsets. rigid luggage. domesticStyrene excellent for injection moulding and appliance housings (food mixers). margarine

ABS thermoforming tubs. car facia panelsCyclolac

Cellulosics Rigid. transparent. tough (even at low Spectacle frames. toothbrushes: tool handles.CA. CAB. CAP. CN temperatures. low electrostatic pick up. easily transparent wrapping. metaltzed parts (reflectors

Cellophane injection moulded. relatively low coat etc) pen barrels. typewriter keysEthylene Vinyl Acetate Flexible (rubbery). transparent. glossy. excellent Teats. inflatable toys. handle grips. flexible tubing.

EVA low temperature flexibility (-70°C). good chemical record turntable mats. ice cube trays. beer tubing.resistance. high friction coefficient vacuum cleaner hose. freezer doors

Fluoroplastics Semi rigid. translucent. exceptional anti stick/low Non-stick coatings. gaskets. packings. bearings.PlFE. FEP friction characteristics. superior chemical high and low temperature electrical and medical

Teflon resistance. impervious to fungi or bacteria. high applicationstemperature stability (260°C). low temperaturetoughness (-160°C)

Nylons Rigid. translucent. tough. hard wearing. fatigue Gear wheels. bushings. zips. pressure tubing.PA (Polyamides) and creep resistant. resistant to fuels. oils. fats synthetic fibres. bearings (particularly for foodMaranyl. Zytel and most solvents. steam steriltzable processing machinery). curtain runners.

carburettor partsPolyacetals Rigid. translucent. very tough. spring-like Business m/c parts. small pressure vessels.

POM qualities. good stress relaxation resistance. good aerosol valves. coil formers. clock and watch parts.Delinn, Kemetal friction and wear and electrical properties nuclear engtneering componentsPolycarbonate Rigid. transparent. outstanding impact Crash helmet visors. riot shields. vandal-proof

PC resistance (to -150°C) and weather resistance. glazing. baby feeding bottles. safety helmets.Lexan, Makrolon good dimensional stability. very good dielectric greenhouse double glazing. miners' phones and

properties battery cases. film/slide casettesPolyesters Rigid. clear. extremely tough. good creep and Carbonated drink bottles. business m/c parts.

(Thermoplastic) fatigue resistance. wide range temperature synthetic fibres. parts for 1V tuners andPETP. PBTP. (PETj resistance (-40° to 200°C) transformers. fire alarm parts. coffee makers andMelinex. Terqlene, toasters

DacronPolybutylene Semi rigid. translucent. tough. chemical and heat Boil-in-bag food packaging films. industrial pipes.

PB resistant. good barrier properties. environmental high temperature tubing (500 psi @ 85°C). centraland mechanical stress crack resistant. good heating systemselectrical insulation

Polyethylene (HIgh Semi rigid. translucent. very tough. high impact Chemical drums. jerricans, carboys. qualityDensity) resistance. weatherproof. excellent chemical kitchen ware. collanders, bins. toys. picnic ware.

HDPE. HMWPE resistance. low water absorption. non-toxic. easy household and hospital ware. cable insulationRfgidex processtng bv most methods. low cost

Polyethylene (Low Flexible. translucent/waxy. durable. weatherproof. Squeeze bottles. toys. wrapping films. utilityDensity) good low temperature toughness (to -60°C). easy kitchen ware. carrier bags. high frequency

LDPE. LLDPE to process by most methods. low cost. excellent insulation. garment bags. chemical tank liningsAlkathene chemical resistance

Polypropylene Semi rigid. translucent (Integral hinge property). Sterilizable laboratory and hospital ware.PP.OPP excellent chemical resistance. extremely tough. containers and snap fit closures ropes. moulded

Propathene exceptional fatigue resistance. steam steriltzable. hinges. packaging film. car accelerator pedals.high surface gloss/texture heater ducting. door handles. washing m/c parts.

suitcases. electric kettles. children's platesPolystyrene (General Brittle/hard. metallic transparent/opague, Toys and novelties rigid packaging. refrigerator

Purpose) glossy. low cost. unsuitable for outdoor use. trays and boxes. cosmetic packs and costumeGPPS excellent X-ray resistance. free from odour and jewellery. lighting diffusers

taste. easy processingPolystyrene (HIgh Hard/rigid. opague/translucent. satin surface Yoghurt pots. refrigerator linings. vending cups.

impact) finish. impact strength up to 7 x GPPS. other kitchen and bathroom cabinets. toilet seats andHIPS properties similar tanks. closures. instrument control knobs. radio

and 1V cabinetsPolysulphone (family) Outstanding oxidative stability at high High/low temperature. high technology. e.g.

PES. PEEK. temperature (-200°C to +300°C) microwave grills. chemotherapy devices.Udel, Victrex transparent/opaque. rigid/flexible. high cost. electro/cryo surgical tools. radornes, fuel cells.

specialised processtna aerospace batteries. nuclear reactor componentsPolyphenylene Oxide Rigid. opague, glossy. outstanding dimensional Business m/c and 1V housings. automotive

PPO stability (particularly under stress at high instrument casings. coffee pot and washingNoryl temperature and humidity conditions). difficult to machine parts (where high temperature and

process (blended to ease injection mouldtngl moisture critical) replacement for die castingsStyrene-Acrylonitrile Rigid. transparent. tough. resistant to oils and Drinking tumblers. ht-fl covers. lenses. water jugs

San greases. resistant to stress cracking and crazing. and toothbrush handles. kitchen and picnic waregood processability

Polyvinyl Chlorlde Rigid/flexible. clear/opague, durable. Drainpipes and guttering and roofing sheets.PBC weatherproof. non flammable. good impact cable and wire insulation. floortng/hoseptpe,

strength. excellent electrical insulation stationery covers. fashion footwear. "cling film"properties. limited low temperature performance "imitation leather" fabrics

Polymethylpentene Rigid. clear. tough. lightweight (density 0.83 Laboratory ware. syringes. lamp covers (goodPMP gm/em 3). chemical resistant. additives required heat resistance) radar and microwaveTPX for outdoor use applications. encapsulation. printed circuit

boards. microwaveable. food packa~n~Polyurethane Flexible. clear. elastic. wear resistant Impermeable Soles and heels for sports shoes. football boots.

(thermoplastic) hammer heads. seals. gaskets. Ovrtngs, rollers.PUR(PU) skate board wheels. synthetic leather fabrics.

silent running gears and sprockets for officemachines

35

Appendix 2

THERMOSETS PROPERTIES APPLICATIONSPhenolics Brittle, opaque, excellent electrical Ashtrays, fuseboxes,

PF and heat resistance, outstanding lampholders, bottle closures,Bakelite resistance to deformation under saucepan handles, toilet seats,

load, low cost thrust washersEpoxies Rigid, clear, very tough, chemical Adhesives, coatings, embedding,

EP resistant, excellent adhesion potting, electrical components,Ara/dite properties, high resistance to chemical pump components,

cracking, low curing shrinkage cardiac pacemakersPolyurethanes Elastic abrasion and chemical Printing and industrial rollers,

(cast resistant, impervious to gases, can solid tyres, die pads, wheels, shoeelastomers) be produced in wide range of heels (particularly suited to low

PUR hardnesses quantity production runs) carbumpers

Polyesters Rigid, clear/opaque, tough, Boat hulls, building panels, car(unsaturated) chemical resistant, fire resistant, bodies, lorry cabs, tanks andSMC, DMC, GRP high strength, low creep, good ducting, compressor housings,

(when electrical properties and low also embedding and coatingsreinforced) temperature impact resistance, low

costAlkyds Rigid, opaque, tough, heat resistant, Automotive distributor caps,

NVC excellent arc and tracking circuit breakers, switch gear,resistance, excellent long term coloured appliance housingsdimensional stability, fungusresistant, good colour stability

Allylics Hard, transparent, exceptional Optical coatings, face shields,DAP, DAIP, ADC abrasion resistance and electrical sealants for metal castings,

insulation properties (even under critical long-term highhumid conditions), outstanding reliability electricalcombination of mechanical/ applications (e.g. radomes)chemical properties

Polyamidesl Rigid, opaque, high strength, Aerospace components,Aramids exceptional thermal and electrical reinforcing fibres, high

PI properties (up to 480°C), excellent temperature resistant foamsKev/ar dry bearing properties when filled chemical filters, arc welding

with PTFE, excellent resistance to torchesionizing radiation, high cost

Aminos Rigid, opaque, tough, very hard and Decorative laminates, clock(Melaminesl scratch resistant, self cases, lighting fixtures,

Ureas) extinguishing, free from taste and dinnerware, heavy dutyMF, UF odour, wide colour range electrical equipment, also

adhesives, bonding andlaminating resins, and surfacecoatings

Furan Rigid, opaque, high strength at Chemical plant (competitive withelevated temperatures, excellent stainless steel), laboratorychemical resistance, self floors, foundry cases andextinguishing, low smoke moulds, specialised insulatingemission, resistant to carbon foamdisulphide

Vinyl Esters Rigid, translucent, good corrosion Chemical tanks, ducts, piping,resistance, low viscosity process equipment (particularly

in corrosive chemicalenvironments)

36

Appendix 3

THERMOPLASTICS PHYSICAL PROPERTIESTensile Impact Linear

Modulus Strength Coefficient Maximum use DensityN/mm2 kJ/m2 of Expansion Temp °C g/cm3

per °C x 106

AcrylicsPMMA 2.9-3.3 1.5-3.0 60-90 70-80 1.18

Perspex, OroglasAcrylonitrile Butadiene

Styrene 1,8-2.9 14-55 65-90 75-95 1.04-1.07ASS

Cyclolac, Lustran, NovodurCellulosics

CA, CAB, CAP, CN 0.5-4.0 2.0-60 80-180 45-70 1.15-1.35Cellophane, Dexel

Ethylene Vinyl Acetate 0.05-0.2 no break 160-200 55-65 0.926-0.950EVA

Fluoropla sticsPTFE,FEB 0.35-0.7 13-no break 120 205-280 1.17

Tef/on, KvnerNylons

PA (Polyamides) 2.0-3.4 4.0-5.0 70 80-110 1.13Maranyl, ZytelPolyacetals

FUJI 3.4 5.5-12 110 80 1.41Delrin, Kematal

PolycarbonateFe 2.4 15-80 70 130 1.20

Lexan, MakrolonPolyesters (Thermoplastic)

PETP, PBTP (PET) 2.5 1.5-3.5 65 70 1.36Melinar

Polybutylene 0.24 no break 130 N/A 0.91PB

Polyethylene(High Density) 0.60-1.3 3.0-nobreak 100 80 0.944-0.965

HDPE, HMWPERialdex

Polyethylene(Low Density) 0.2-0.4 no break 100-220 65 0.917-0.930

LDPE, LLDPENo vex

PolypropylenePP,OPP 0.95-1.30 5-20 70-95 80 0.902

Propathene, Hostalen PP, AJ)J)rylPolystyrene (General

Purpose) 2.3-3.35 2.0-2.5 80 65-85 1.05GPPS

Polystyrene (High Impact) 2.2-2.7 10-20 80 60-80 1.03-1.06HIPS

Polysulphone (family)PES,PEEK 2.1-2.4 60-no break 20-65 160 1.13-1.17

Udel, VictrexPolyphenylene Sulphide

PPS 0.5 <2.5 50 240 1.30Ryton, SUJ)ec

Polyphenylene OxidePPO 2.1-2.5 20-25 60-70 110 1.06

Norvl, Pre vexSty re ne- Ac ry I on i tri I e

SAN 3.4-3.9 2.5-3.0 75 85 1.07Lustran A, Luran, TyrilPolyvinyl Chloride

PVC 2.6 2.0-45 80 60 1.38Hostalit

37

Appendix 4

THERMOPLASTICS RESISTANCE TO CHEMICALSDilute Dilute Oils and Aliphatic Aromatic

Hydro- Hydro- HalogenatedAcids Alkalis Greases Hydro- Alcohols

carbons carbons carbons

AcrylicsPMMA vg vg vg m p p vg

Perspex, Drog/asAcrylonitrile Butadiene

Styrene vg vg vg m p p p/vABS

Cyelolae, Lustran, NovodurCellulosics

CA, CAB, CAP, CN m p vg vg p p pCellophane, Dexel

Ethylene Vinyl Acetate vg vg 9 vg P P vgEVA

FluoroplasticsPTFE,FEB vg vg vg vg vg p/v vg

Teflon, KynarNylons

PA (Polyamides) p 9 vg vg vg g/v pMaranyl, Zyte!Polyacetals

FG\1 p vg g/v vg 9 I V P vgDelrin, Kematal

PolycarbonateFe 9 9 vg m P p N/A

Lexan, Makr%nPolyesters (Thermoplastic)

PETP, PBTP (PET) vg m vg vg p p vgMelinar

Polybutylene vg vg N/A N/A P P N/AA3

Polyethylene(High Density) vg vg m I v p m I v m I v vg

HOPE, HMWPERigidex

Polyethylene(Low Density) vg vg m I v p P P vg

LOPE, LLOPENo vex

PolypropylenePP,OPP vg vg m I v p P P vg

Propathene, Hostalen PP, ApprylPolystyrene (General

Purpose) g/v vg m I v vg P p m I vGJPSPolystyrene (High Impact) m vg m vg p p p/v

HIPSPolysulphone (family)

PES, PEEK vg vg vg m I v p P vgUdel, Vietrex

Polyphenylene SulphidePPS vg vg vg vg vg vg N/A

Ryton, SupeePolyphenylene Oxide

PPO vg vg vg m p p m/vNoryl, Pre vex

Styren e-Acry 10 n i tri IeSAN vg vg vg m p p m I v

Lustran A, Luran, TyrilPolyvinyl Chloride

PVC vg vg g/v vg p m I v g/vHostalit

v - Variable vg - Very Good 9 - Good m - Moderate p - Poor

38

Appendix 5

SUMMARY OF MAIN INDUSTRIAL PROCESSES

PROCESS COMMON APPLICATION DESCRIPTIONMATERIALS

Bottles A hot thermoplastic tube is inflated byBLOW LOPE Drums compressed air into a cooled, split-cavity

MOULDING PET Car fuel tanks mould to produce a precision hollowPVC Heater ducting moulding.

INJECTION Nylon Buckets Molten plastic is injected under highABS/PS Telephones and Gears pressure into a cooled, split mould to

MOULDING HDPE/PP, TV & Hi-fi cabinets produce a high precision moulding.

Litter binsThermoplastic powder is tumbled, heated

ROTATIONAL LOPE and cooled in a split, hollow mould to

MOULDING PVCStorage tanks produce simple shaped, hollow

Traffic bollards mouldingsNylon Drain pipe/Guttering Molten thermoplastic is extruded under

HDPE/PP HoselWire insulation high pressure through a shaped die toEXTRUSION L1)PE Roofing sheet produce a continuous precision section

PVC Window frame

COMPRESSIONFuse boxeslInsulators Thermosetting plastic powder is

Epoxy Lamp holders compressed and heated in a matched die-MOULDING Phenolics Saucepan handles set to mould a precision product

Yoghurt pots Thermoplastic sheet is heated and forcedVACUUM Acrylic Vending cups under vacuum into contact with a cooled

FORMING PS Fridge linings+housings form-mould to produce simple shapedPoint of sale display mouldings

DIP L1)PEProtective gloves Temperature controlled mandrels are

Balloons dipped into a bath of plastic paste orMOULDING PVC Handle grips fluidised powder to produce a peelable

skin (or durable coating)Protective sheet Hot thermoplastic is passed through a

L1)PE Shower curtains series of temperature controlled rollsCALENDERING PVC Stretch wrap film with progressively smaller gaps to

PS produce continuous, precision thin sheet(also embossed if required)

GAP Epoxy Boats/Car bodies Layers of glass fibre matt are laid-up andPolyester Chemical plant wetted with a thermosetting resin into a

LAMINATING resin Architectural claddings simple mould form to produce large,strong structural mouldings

STRUCTURAL FOAM PSComputer housings A two-part premix is introduced into a

Tool handles Casings split cavity mould where it expands toMOULDING (PU) PU Simulated wood effect produce strong, lightweight mouldings

Dustbin bags An extruded plastic melt is passedBAUOON L1)PE Carrier bags through a die and air blown into a long

BLOWING HOPE Luxury applications with balloon of plastic film. This is pressed intoattractive finishes double film, cut and heat sealed at one

end to make bags.

AcrylicGrowing trays A thermoplastic foil or sheet is heated

THERMOFORMING Seed boxes until soft and then mechanically pressed

BY PRESSURE ABS/PVC Disposable trays into a former or mould to produce thePS Corrugated PVC sheet product shape.

BIAXIAL PP/PS Polypropylene film Semi-molten film is stretched along twoPolyester Polyester film axes at 90° to one another to increase the

STRETCHED FILM mechanical strength.

PLASTIC PF/MFDecorative work top Brown paper sheets are impregnated

surfaces with resin and laid up in a multi-platenLAMINATE resins (e.g. Formica) press. Pressure and heat are then applied

to produce the final laminate.

PET - Polyethylene terephthalatePF - Phenol-formaldehydeABS - Acrylonitrile butadiene styrene

PP - Polypropylene PU - PolyurethaneMF - Melamine-formaldehyde PS - PolystyreneLOPE/HOPE - Low/High density polyethylene

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Appendlxs

EQUIPMENT AND MATERIAL SUPPLIES

EquipmentBrochures/catalogues of equipment for schools plastics work can be obtained from thefollowing:

C R Clarke & Company (UK) LtdUnit 3Betws Industrial ParkFoundry RoadAmmanfordDyfedSA182LS

Formech Vacuum Forming Machines72 West End RoadHigh WycombeBucksHPl12QQ

MaterialOne of the major problems which face schools is obtaining supplies of plasticsmaterials in appropriate quantities and sizes, at a reasonable cost. The followingoffer various packs of materials to meet school budgets:

EMA Model Supplies Ltd58-60 The CentreFelthamMiddlesexTW13 4BH

Trylon LtdThrift StreetWollastonNorthantsNN97QJ

K&M, Unit24Lion ParkHolbrook Ind. EstateNew Street, HalfwaySheffieldS195GH

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OTHER RESOURCES

Appendix 7

ICI, in conjunction with the Technology in Context project, has produced a resource fordealing with needs and opportunities in the context of using plastics. It consists ofteachers notes and student activity sheets housed in a ring binder and includes a videocassette. From:

SCSST76 Portland PlaceLondonWIN 4AA

The Polymer Industry Education Centre (PIEC) can supply a list of resources aboutplastics, activity packs, fact sheets, information booklets, posters, slides and videoswhich can be obtained from a variety of industrial and other sources. The list isavailable free from:

Polymer Industry Education CentreDepartment of ChemistryUniversity of YorkHeslingtonYorkYOI 5DD

Recommended further reading:

"Design and Plastics" by Mike Hall (ISBN 0-340-40528-7)

National Association of Advisors and Inspectors for Design andTechnology

Consortium of Local Education Authorities for the Provision of ScienceServices

Association for Science Education

Safety publications:

NAAIDT Publications16 Kingsway GardensChandler's FordHampshireS051FE

CLEAPSS School Science ServiceBruneI UniversityUxbridgeUB83PH

ASEPublications SectionCollege LaneHatfieldHertfordshi reALI09AA

HMSOPublications Centre(Telephone Orders)

NAAIDT

CLEAPSS

ASE

41

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