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Acknowledgments
This document was produced in collaboration with the Education Liaison Group and
other 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 a
framework of information which was built upon by the working party. The cover
photographs were supplied by leI.
Members
of
the
Working
Party
Don Raspin - Education Liaison, ICI
Keith 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, Cleveland
David Barrass - Head of Technology, Hartlepool Sixth Form College, Cleveland
Editor
Alan Stan cliffe
Polymer Industry Education Centre
Department of Chemistry
University of York
Heslington
York
Y015DD
Telephone (0904) 432523
©
Jointly held by ICI and the University of York
Published 1994
ISBN: 185342700 4
The copyright holders waive the copyright on the material which follows to the extent
that teachers may reproduce this material for use with their pupils in the establishment
for which the material was purchased, but for all other purposes permission to reproduce
any 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
Page
Introduction
SECTION1 SCHOOLBASEDPROCESSES
1.1 WORKSHOP PRACTICE
1.1.1 Storage
1.1.2 Protective masking
1.1.3 Static electricity
1
1
1
1
1.2 SAFETY WITH ACRYLIC
1.2.1 Handling and machining
1.2.2 Flammability
1.2.3 Pressure shaping
2
2
2
2
1.3 FABRICATIONPROCESSES
1.3.1 Safety
1.3.2 Perspex acrylic sheet
1.3.3 Marking out
1.3.4 Edge treatment
1.3.5 Cutting straight lines
1.3.6 Cementing
1.3.7 Machining
3
3
3
3
3
4
5
7
1.4 SIMPLE THERMOFORMING TECHNIQUES
1.4.1 Effect of moisture
1.4.2 Oven heating
1.4.3 Single curvature forming
1.4.4 Double curvature forming
8
8
8
9
11
1.5 VACUUM FORMING
1.5.1 Equipment
1.5.2 Moulds
1.5.3 Heating times
1.5.4 Cooling times
13
13
14
15
16
1.6 FLUID BED COATING
17
SECTION2 INDUSTRIALBASED PROCESSES
2.1 PROCESSINGMETHODS
2.1.1 Extrusion
2.1.2 Balloon blowing
2.1.3 Calendering
2.1.4 Injection moulding
2.1.5 Thermoforming by pressure
2.1.6 Thermoforming by vacuum
2.1.7 Biaxial stretching of film
2.1.8 Glass Reinforced Plastics Lay-up and Moulding
2.1.9 Plastic laminates
2.1.10 Compression moulding
2.1.11 Rotational moulding
2.1.12 Extrusion blow moulding
2.1.13 Injection stretch blow moulding
2.1.14 Dip moulding
2.1.15 Structural foam moulding
18
18
19
20
21
22
23
24
25
27
28
29
30
31
33
34
1
APPENDICES
Appendix 1 Properties and applications - Thermoplastics
Appendix 2 Properties and applications - Thermosets
Appendix 3 Physical properties of some thermoplastics
Appendix 4 Chemical resistance of some thermoplastics
Appendix 5 Summary of main industrial processes
Appendix 6 Equipment and materials suppliers
Appendix 7 Other resources
35
36
37
38
39
40
41
Trade names and abbreviations associated with different materials are
included in the tables listed above.
11
Introduction
This booklet has been produced in response to enquiries from teachers of
Design and Technology seeking information on working practices in industry
and schools relating to thermoplastics. It is not an exhaustive reference guide
but does provide an introduction to basic techniques suitable for schools and the
more common processes found in industry.
The booklet is intended as a resource for the teacher but could also be used as a
source of information for students engaged in Design and Technology project
work for National Curriculum Key Stage 4 and for 16+ courses. Some of the
practical working methods outlined will also be relevant to Design and
Technology projects at Key Stage 3 of the National Curriculum. Teachers
involved with the Scottish Curriculum for Technical Education, particularly
with the 11-18yrs age group, will find the information relevant.
Section one considers storage and safety procedures to be observed in schools
and colleges in respect of plastics materials. It then goes on to outline some
practical processes which can be undertaken using equipment normally found
in school/college Design and Technology departments.
Practical workshop processes have been outlined using acrylic as a sample
material since this is one of the most commonly used in schools. However,
most of the techniques described will be suitable for other thermoplastic sheet
materials (e.g. polystyrene, PVC, ABS) providing consideration is given to
differences in softening temperatures and appropriate categories of adhesives.
Some techniques previously used in schools are now restricted as a result of
regulations 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. When
referring to the material in general terms the correct title is Acrylic .
.~ection two describes some of the more common industrial
In use.
processes currently
Appendices 1 to 5 provide extensive tables of properties, applications and
processes which will be useful for both teachers and older students studying at
sixth 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 racks
having a backboard at a slight angle to the vertical (an A-Frame). The
protective masking is left in position and the material should not be allowed to
bow.
Such storage provides adequate support and permits sheets to be withdrawn
without danger of damage. Horizontal storage is not recommended as sheets are
difficult to withdraw, and any dirt, swarf or grit trapped between them may
damage their surfaces.
Store rooms should be well ventilated, cool and dry. The masking on extruded
acrylic 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 being
replaced. ICI Acrylics has introduced a polyethylene film masking with a
pressure-sensitive adhesive backing for the protection of cast 'Perspex' sheets.
Sheets masked with a pressure-sensitive adhesive polyethylene film (PSPE) offer
the end user several advantages. The film will not fall off, is more stable to
climatic variations and can be cut or machined in place.
PSPE masking can be kept in place for local bending applications provided heaters
are not in direct contact with the film, but PSPE masking cannot be otherwise
thermoformed. The masking must be removed prior to heating the acrylic for
thermoforming, normalising or annealing.
The surface of sheet masked with PSPE will not now need to be washed prior to
cementing or thermoforming. However, for all surface decoration requirements,
it is recommended that after removing the masking the surface of the sheet be
rinsed with clean water (to remove particles of dust and neutralise any residual
static charge) and dried with a soft dry cloth.
Whenever possible the protective masking should be left attached to acrylic to avoid
surface 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 other
approved 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
Acrylic is a hard material.
damage eyes.
Recommended
machining
Sharp edges could cause cuts, and flying chips could
practice
• Sharp corners and edges should always be removed (see page 3) before handling
with bare hands.
• Goggles should always be worn when machining it, as protection against
flying 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 are
used 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 shaping
temperatures of 140 to 170°C, acrylic does not evolve any noticeable amount of
vapour. However, it is dangerous to subject acrylic to flames or prolonged heating
because it creates highly flammable and irritant fumes. The flash ignition
temperature of acrylic is 280°C.
Recommended
practice
Care should be taken when thermoforming acrylic and teachers should refer to
existing 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 the
acrylic 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 the
operator from fragments of acrylic in the event of a burst thermoform. This is not
necessary if a complete mould is being used. Blanks for thermoforming should be
handled and stored carefully so as to avoid damage or contaminating the surface.
Whenever possible, the protective paper should not be removed until just before the
blank is placed in the oven.
2
1.3 ACRYLIC:
1.3.1
FABRICATION
PROCESSES
Safety
Normal codes of practice must be observed in the workshop. The following
documents 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 cast
Perspex and extruded Perspextx. Extruded Perspex tx is particularly suitable for
vacuum 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 and
masking tape is recommended with normal marking out procedures.
1.3.4
Edge
treatment
Sanding
Sanding discs and finishing machines can be used with care for trimming and
smoothing very rough edges, but avoid overheating. Goggles and dust masks
should always be worn when abrading any plastics materials.
Abrasive
paper
A fine grade 'wet or dry' abrasive paper will produce a smooth surface suitable for
polishing.
Polishing
The machined surfaces of acrylic may be brought to a high surface gloss by careful
buffing or hand polishing with 'Perspex' polishes or conventional metal polishes.
Usually an intermediate smoothing operation is required to avoid extended
polishing 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 one
surface with a sharp metal scribing knife, clamping the sheet with the scribed
line uppermost and aligned with the edge of a bench, and breaking the sheet by
pressing steadily downwards on the free part.
A suitable blade is the Stanley Knife Scriber blade No. 5194.
IF CUTTING LONG
LENGTHS. CLAMP THE
STRAIGHT EDGE DURING
BREAKING. PRESS
STEADILY DOWNWARDS.
Scribe
breaking
acrylic
Hand sawing
When cutting irregular shapes, acrylic may be cut using a hacksaw or fretsaw
provided they are sharp and have fine teeth. Coarse tooth saws and heavy
pressures will cause chipping.
Preferably clamp the acrylic close to the line of the cut when hand sawing to
prevent cracking of the sheet.
Power
sawing
Band saws and fretsaws can be used in production work but always ensure that
the pitch of the teeth is less than the thickness of the material being cut. Material
should not be forced through the saw. Strips of sellotape over the line of cut will
help to dissipate heat produced by friction from the saw blade and prevent the saw
cut from 'welding up' behind the blade.
4
1.3.6
Cementing
Acrylic can be cemented to acrylic with 'Tensol' cements. 'Tensol' cements can
also be used to cement acrylic to some non-acrylic materials.
'Tensol'
adhesives
The most useful 'Tensol' adhesives for joining acrylic are 'Tensol' Cement 12 - a
solvent 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 the
bottle, which might cause air bubbles in the liquid. (Ideally, 'Tensol' Cement 12
should be stored in a refrigerator with other similar chemical materials).
'Tensol' Cement 70 is a two part adhesive, prepared by mixing twenty parts of
Component A to one part of Component B. The mixture should be stirred
thoroughly and left to stand for a few minutes until any air bubbles have
dispersed. The mixture must be used within 20 minutes of mixing. Room
temperature must be above 15°C.
'Tensol' Cement 70 (A + B) should be stored in a cool dark place. At very low
temperatures, crystals of component B may appear in the mixture. It is important
that any crystals be dissolved before use. The film of 'Ten sol' is normally applied
to 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 the
cement will shrink 20% during reaction. Only apply light pressure.
Application
Ensure all surfaces to be glued are perfectly clean and grease free. Assemble the
joint when the cement has been in contact with the surface for about 30 seconds. If
left for a longer period a skin will form over the cement which can prevent the
joint from being bonded successfully.
Care
Current safety procedures should be followed at all times. Use 'Tensol' and other
solvent cements in a well ventilated room, ideally equiped with appropriate fume
extraction facilities, and away from sources of ignition.
Other
adhesives
There are a range of adhesives available for joining plastics materials. Some have
a permanent rubbery quality for use with flexible plastics and in joining plastics to
other materials. There are also hot melt adhesives available which rely on heat to
melt a plastics pellet or film to produce a join. Some adhesives rely on evaporation
of a solvent while others involve the mixing of two liquids or pastes which then
cure by chemical reaction.
There are a range of commercial liquid solvent cements available for use with
thermoplastics. Some solvent cements will work on several plastics (e.g. acrylic,
ABS, butyrate, styrene) while others will only work on one particular plastic
material. Reference should be made to manufacturers instructions and
guidelines. 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 safety
legislation and current local authority regulations and practice.
5
Suggestions
for
cementing
techniques
WIRE PACKI
TO ASSISTCAPILLARY
ACTION:
REMOVE BEFORE
GEL STAGE.
MASKING REMOVED
AT GEL STAGE.
ANGLE JOINT.
USE PLENTY OF CEMENT.
REINFORCING
FILLET.
Note - When using solvent cement to join two dissimilar plastics, the harder
material should have its joint surface softened by applying a light coat of solvent
prior to bringing the two surfaces together.
6
1.3.7
Machining
The machining characteristics of acrylic sheet (cast or extruded) are similar to
those of brass or hard aluminium, but there is one very important difference. This
is 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. This
will minimise any stress being produced in the machined area and reduce the
possibility of causing any alteration to the machining characteristics of the
material. Where possible, acrylic should always be machined with the
polyethylene masking film left in place.
NB. Acrylic is a notch sensitive (brittle) material and care must be taken to ensure
that no notched areas are introduced during machining. Sharp cutting tools will
help to avoid this.
Cutting
tools
These must be kept sharp not only to produce a good surface finish but to minimise
the amount of heat generated.
Dri II ing
Standard twist drills up to 5 mm are quite suitable for drilling acrylic, as also are
many of the drills specially developed for plastics such as step drills and cone
drills. It is recommended that standard twist drills above 5 mm be sharpened
with a negative rake to prevent 'grabbing' during the drilling process.
Always clamp the acrylic sheet firmly against a piece of wood or other soft
material before drilling and never use a centre punch to mark the position of the
hole, as this will crack the acrylic. Typical drilling speeds are shown in the table
below:
Dr ill
Diameter
(m m)
Approximate
Drill
Speed
(rev/min)
1 .5
7000
5.0
1800
12.0
900
Turning
Acrylic can be turned to engineering tolerances on metal-working lathes and
many of the techniques used for metal can be applied. Tool bits made from highspeed 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 slower
than for other machining operations. The feed and depth of cut should be matched
to the cutter.
7
1.4 SIMPLE THERMOFORMING
TECHNIQUES
When acrylic cast sheet is heated to 150-170°C it becomes rubber-like and can be
stretched into complicated shapes. After cooling to 90°C, or below, the acrylic will
retain the shape imposed on it. If re-heating takes place the acrylic will return to
its original flat sheet form. Cast acrylic sheet should not be heated to
temperatures 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 rubberlike way. In this state it can be thermoformed in a similar manner to acrylic cast
sheet. When the material is heated to 170-200°C it behaves in a thermoplastic
manner and can be thermoformed into complex shapes using very little pressure.
It is this characteristic which makes Perspex tx an excellent vacuum forming
material.
1.4.1
Effect
of
moisture
Extruded acrylic sheet materials will absorb moisture when exposed to a humid
atmosphere. Absorbed moisture can seriously affect the thermoforming
performance of acrylics and causes blisters of about 2-3 mm diameter to appear
during heating. If this occurs the sheet can be dried out by 'heat soaking' at a
temperature of 85-95°C for 24 hours (with the protective masking removed from
both sides). When cool, the 'dried' sheet should be protected against any further
moisture 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 be
used.
Heating
times
Thickness
mm
2
2.5
3
4
5
6
in
an
air
oven
Heatlnc
At
150°C At
Perspex
tx
Times
160°C At
min
12
13
14
16
18
21
min
16
17
19
22
25
28
for
170°C
min
8
8
9
11
12
14
It is most important not to exceed these times because of material elongation in
vertical ovens or shelf marking where the material is heated horizontally.
8
1.4.3
Single
curvature
thermoforming
This means that, in general, the heated sheet is not stretched but allowed to bend
or fold along a single axis.
Drape
forming
For items with a shallow single curvature, the heated acrylic sheet is placed in a
concave mould and allowed to settle under its own weight until it rests on the
surface of the mould. For convex moulds - light pressure will be needed until the
sheet is cool. Both methods are illustrated in the diagrams below.
For convex moulds some pressure will be
needed until sheet is cool.
CLOTH FORMER.
Simple
Making
a tube
from
acrylic
drape
forming
sheet
A suitable length of polyvinyl chloride (PVC) tube (e.g. plastic drain pipe) can be
used as a mould to form a tube from flat acrylic sheet. The plastic pipe is cut
longitudinally down one central axis to create two halves. These are then held
together along one edge by use of a tape/cloth style hinge. One edge dimension of
the acrylic sheet should be cut to match the internal circumference of the PVC
tube when closed.
The two halves of the PVC tube mould are laid open and the heated flexible acrylic
sheet placed in position over them, taking care to match the correct edge of the
acrylic with the curved circumference profile of the mould. The mould is then
closed 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 cools
down.
Forming
a
cylindrical
tube
9
from
acrylic
sheet
Simple
scrolling
for
letters
or
curves
Simple jigs can be made to form scrolled curve shapes similar to wrought iron
work. Strips of acrylic are cut to size, heated and formed around the jigs when
flexible. An example of a simple arrangement is illustrated below.
Acrylic
Local
strip
formed
into
a scroll
shape
on a simple
jig
bending
Angled bends along straight lines can be obtained by heating the acrylic locally on
both sides using a strip heater. Simple jigs can be constructed to hold the acrylic in
position during the cooling period as illustrated below.
'Perspex' heated
locally along
line of bend
Acrylic
shapes
held
in a simple
10
jig
while
cooling
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. The
acrylic 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 most
convenient for this process. It is advisable to heat the clamping frame to 60-70°C
before positioning the acrylic sheet.
Toggle
clamp
Free-blowing
In this process heated acrylic sheet is shaped by use of direct air pressure or
vacuum without the use of a mould. The outer edges of the acrylic sheet are held
by a clamping ring and the heated sheet is then subjected to pressure or vacuum to
create a natural bubble shape. The pressure or vacuum is set and the setting is
maintained throughout the cooling period. Pressures of up to 10 N/cm2 are
sufficient for most school work. A simple arrangement is illustrated below.
Controlled
heIght
Heated 'Perspex'
tnrnrnrnq
lines
Free
Compressed
blowing
air
an acrylic
11
bubble
shape
Simple
press
forming
(plug
and
yoke)
A simple male and female mould (plug and yoke) which can be constructed from
Medium Density Fibre Board (MDF) is illustrated below. The heated acrylic sheet
is sandwiched between the plug and yoke of the mould which are then forced
together under pressure causing the acrylic to take on the shape of the mould. By
placing the mould on the table of a pillar drill, the drill press can be used to apply
the required force.
Dowel location pins
Constructed ~
from M.D.F.
Simple
plug and yoke arrangement
12
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 by
removing the air from one side of the sheet and thus, in effect, 'sucking' it into or
over a mould.
Perspex tx is ideally suited to the technique of vacuum forming on machines
which are designed for this purpose.
Perspex tx can be formed with the clear protective masking in place on the upper
surface of the sheet if required but any imperfections in the masking film such as
cuts, 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 operate
with the minimum of attention and for some specialised applications they have
been designed to function completely automatically. Such complexity is not
needed for school applications, and is indeed undesirable. Simple and relatively
inexpensive machines suitable for school use are now available from
manufacturers (see Appendix 6).
A simple vacuum forming machine consists of 4 main parts:
A
A
A
A
heater
vacuum box
clamping system for the thermoplastics
vacuum system
sheet
The clamping system must hold the sheet firmly in place to form a vacuum tight
seal with the box. A frame made from small-section angle iron, and held down
with quick-acting clamps is usually used for the clamping system.
The vacuum system must remove the air quickly from the vacuum box - this is
more important than achieving a high vacuum.
Thermoplastic
sheet
"
Rubber seal
Oamping
frame---4~Clamp
Mould
Perforated
mould support
A typical
vacuum
former
arrangement
With a simple vacuum forming machine as described above articles can be
formed using female or male moulds.
13
Working
sequence:
Thermoplastic clamped
above the mould
Heat applied to make
the plastic pliable
Soft Thermoplastic
sucked into mould
Vacuum formed sheet
allowed to cool
Plastic moulding
removed from former
1.5.2
Vacuum release valve
opened to withdraw air
Vacuum release valve
closed when plastic set
Repeat the cycle
Moulds
Moulds for vacuum forming are simple to construct. Although for commercial
production aluminium moulds are frequently used, wood, plaster, medium
densityfibre board (MDF), and papier mache are suitable, and even clay has been
used, but a mould must be designed carefully.
Vents must be provided to ensure the rapid evacuation of all the air trapped
between the mould and the material being formed. The vents may conveniently
take the form of a series of small holes, about Irnm in diameter where they emerge
from the working surface, drilled in the lowest part of the mould and in any local
depressions or cavities within the mould area. These small holes should be
counter bored to about 6 mm in diameter for the greater part of their length (from
the back of the mould to within about 3 mm of the mould face), and connect with
the holes in the mould support.
~.
;I
~
/:
Air passages
Typical
:: .
Bottom of mould rebated or resting
on thin 'spacers' to allow air passage
mould
features
It is important to allow some degree of taper on the vertical faces of a mould in
order to allow for shrinkage of the material as it sets and to enable the moulding to
be removed from the mould. Recommended tapers are 0.50 to 10 for female moulds
and 2-100 for male moulds, depending on the depth of draw (i.e. the distance from
the plane of the clamping frame to the deepest part of the mould) and on the
material being used.
All internal and external corners of moulds should be radiused (rounded) and the
surface made as smooth as possible, to reduce the risk of imperfections being
transmitted through the thickness of the sheet. Marks on moulds can spoil the
appearance of the finished article, particularly when clear sheet is used. Good
separation can be achieved by use of a release agent such as talcum powder.
14
The distribution of material thickness in articles which are vacuum formed
differs according to whether a male or female mould has been used. This is
illustrated in the diagrams below:
.,-.
b
I
\~
.1
Typical
material
.,
1f
cl
material
Heating
I
r
\
Thickness
a
a
b
c
d
e
f
g
at:
-
1.02
1.02
0.65
0.50
0.50
0.65
mm
mm
mm
mm
mm
mm
mould
female
•
-
1.27
0.65
0.25
0.40
0.50
1.27
1.27
mm
mm
mm
mm
mm
mm
mm
a male
from
distribution
thickness
a
b
c
d
e
f
at:
from
distribution
thickness
IV
dl
Typical
1.5.3
fl
If
•••
Thickness
mould
times
Heating times will depend on individual circumstances. In average conditions a
time of 20 seconds per millimetre of thickness can be used as a guide for clear
sheet; for opals 10% longer should be allowed.
Comparison
of the vacuum
forming
of extruded
and cast acrylic
Heating
time
(seconds)
Approximate
surface
temperature (OC)
100
210
90
Perspex tx
(extruded)
3 mm Clear
performances
sheet
Standard Perspex
(cast)
3 mm Clear
Surface degradation
200
Maximum heating timet
definition
Good definition
80
185
Good definition
Maximum definition obtainable
with standard Perspex
70
170
Good definition
Fall-off
60
160
Slight fall-off
50
140
Continued
40
120
Definition equal to that
of standard Perspex at
80 seconds
in definition
fall-off
Surface degradation
in definition
Continued
fall-off in definition
Too cold
Too cold
These results were achieved on a laboratory vacuum forming machine with a
lower rate of heating than the average quoted earlier.
15
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, ambient
temperature 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 mm
thick sheet under average conditions. Extended cooling will allow the material to
shrink back on to the mould to a point where the forming will crack from a weak
spot 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-in
stress which can cause stress-cracking to develop in service. Always wear
protective gloves when doing this.
16
1.6 FLUID BED COATING
Fabricated metal articles can be covered with a thermoplastics
polyethylene) by use ofa fluidised bed of powder.
coating (eg
The construction of a fluidised bed is illustrated below. Air at low pressure is
passed through the porous base of a container into which the thermoplastics
powder has been placed. Care should be taken to use a sufficient quantity of
thermoplastic material in order to achieve steady fluidisation without 'boiling' of
the powder.
The metal article to be coated is first cleaned of oil and grease, and then heated in
an oven, before being plunged in to the fluidised bed. Some powder will fuse and
stick to the hot metal; the coated article is then removed from the bed and returned
to the oven to completely fuse the coating.
The temperature to which the article needs to be heated before coating will depend
on the thermal capacity of the article. A thin wire construction, for example, will
require a higher temperature than will a solid rod of steel. When low density
polyethylene is used for the coating, a temperature of about 180°C is suitable for
most articles. Temperatures above this may result in degradation of the polymer,
producing harmful fumes.
--1------
Fluidised bed
Porous base
Air in
Typical
fluidised
17
bed arrangement
SECTION
INDUSTRIAL
2
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.
Process
Extrusion is a method of moulding thermoplastic material into continuous lengths of
profiles. 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 an
extrusion machine. The material is softened under the action of heat and pressure
and then extruded to the required form (e.g. window frame profiles) from a die fixed to
the nozzle of the machine. This method can be used to produce all types of polyvinyl
chloride (PVC), polyethylene (PE) and polypropylene (PP) thermoplastic pipe and tube.
Various shapes and sizes of extrusion can be produced using different dies. Two
exam ples are shown below:
tube/pipe
Two
typical
extrusion
shapes
Large screw forces heated plastic
along the chamber and
through the die
extrusion
Hopper containing
plastics granules
/
Cooled chamber
base
interchangeable
steel die
Spool for flexible extrusions
A
typical
extruder
18
arrangement
electric motor
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 allows
information about a polythene-wrapped product to be printed on the pack.
Process
In balloon blowing, a plastic melt is extruded and then a different die and air blower
are used to produce a balloon of plastic which can be nipped or pressed into a double
film called layflat tubing. This can be made into bags by cutting the material into
lengths and heat sealing one end. A gusseting device is sometimes used to fold a
triangular section along the sides of the layflat tubing so that when it is made into
bags the gusset can open to increase the volume inside the bag.
Balloon extrusion is very rapid and the film produced can range in thickness from
2 mm to 0.1 mm.
gusseting device
wind-up
_
guide board
layflat tubing with gussets
layflat tubing without gussets
plastic balloon
compressed air supply
Typical
balloon
extrusion
system
The air ring at the base of the balloon serves to cool the molten plastics material
19
2.1.3
Calendering
Products
• protective sheet
• shower curtains
• stretch wrap film
Process
Suitable thermoplastic compositions are passed through heated metal rollers with
progressively smaller gaps to produce continuous film and precision thin sheet. This
method is used to produce polyvinyl chloride (PVC) flexible film in widths of up to 4
metres, and thin PVC and polystyrene (PS) rigid foils for use in thermoforming
processes or making sheet material. Embossing techniques can also be incorporated
into the rolling process.
Hopper
Extruder
Compressor
Wind up
Cooling jets of
compressed
air
A typical
calender
20
system
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
Process
Injection moulding is probably the most widely used process for making
thermoplastic items in large numbers. However, it is not economic for making small
numbers of a particular moulding because of the initial set-up costs and expense
involved in producing the moulds for the machine. With injection moulding,
thermoplastic material (in granular form) is fed from a hopper into the heated barrel
of the machine. The barrel contains a revolving screw which carries the granules
along to where they are softened to a liquid state. The molten thermoplastic is then
forced under high pressure through a small nozzle into a split mould where the
material rapidly solidifies, taking on the shape of the mould. When the material is
set, the mould is opened and the moulding ejected. Sophisticated complex moulds can
be 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 of
domestic and agricultural items are produced by this method.
Hopper
Thermoplastic
pellets
Mould
o
o
000000
Controls
A
typical
injection
21
o
0
moulding
machine
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
Process
The 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 mould
onto which it is pressed mechanically into shape. The sheet takes on the shape of the
former or mould and on cooling sets to the shape. The cooled shape is then removed
and excess material trimmed off. This is a fairly simple process for speed in mass
production where precision is not too critical.
\,-_~r
I
Moulding
Mould
The
pressure
thermoforming
22
process
2.1.6
by
Thermoforming
vacuum
Products
• yoghurt pots and vending machine cups
• point-of-sale display
• fridge linings
• equipment housings
Process
In this process, plastic sheet is heated until it is soft and then sucked into a mould or
former by withdrawing air from the mould cavity, thus creating a vacuum. To assist
the forming process, the mould table is sometimes raised, pressing the mould lightly
into the softened plastic sheet just before activating the vacuum. Moulds and formers
can be male or female for this process.
Slide to p!ace heater
..
.
Heater
;fJ
over thermoplastic sheet
omoT06 000 0 olOo0ID00OO"OOIDm
"'-------111-:
Vent holes
Evacuation
Vacuum Pump
Tank
A
vacuum
forming
machine
23
arrangement
2.1.7
Biaxial
Product
stretching
of
film
• polypropylene (PP) and polyester (PE) films
Process
Biaxial 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 vapour
permeability. One production method for biaxially stretched polyester film is
illustrated below.
extrusion
chilling of extrudate
setting of film using heat
stretching
across
width 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 molten
ribbon of film. The hot ribbon then drops on to a chilled metal roller to solidify it and
pull it away from the die. The cooled ribon of film then passes through an oven where
it is reheated and stretched first along its length and then across its width (biaxial
stretching). 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 comparatively
simple profile mould of metal, wood or plaster and the following processes:
1.
Liquid polyester resin, mixed with a catalyst (or hardener), is applied to the
mould to form a pre-gelled coat.
2.
Glass fibre in mat or woven fabric form is laid on the first gelcoat and liquid
polyester 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.
Glass
fibra
\~... I
I
PregeJled
['t:::~.J1--....
Lay-up
/resin
coat
technique
for
Glass Fibres __
Catalysed Resin __
Moulding
GRP
DETAIL OF SPRAYGUN GRP
LAY-UP TECHNIQUE
Accelerated Resin _
Spraygun
--.
Separate spraygun nozzles
Roller for compacting GRP
fibre glass rovings
Pressurised resin tank
of male mould
Catalysed resin
Mobile trolley
Automatic
fibre
dispenser
25
and
resin
spraygun
Process
(GRP
moulding)
Two other technique used with Glass Reinforced Plastics (GRP) are the rubber-bag
and matched-die moulding methods in which pressure is applied to the top surface of
the moulding during processing. Various compositions of polyester
resin/catalyst/glass fibre are used to produce mouldings in both these pressurised
processes. By heating, comparatively fast hardening of the resin is possible. The two
methods are illustrated below.
Air-tight
seal
/
inflated with
air
Uncured GRP layup
Pressure
bag
method
of moulding
GRP
Dowel Pins to
Pad regulating
moulding thickness
locate male and
female mould halves
1
\
Mould Cavity in
which GRP is placed
Matched
mould
method
26
for GRP
2.1.9
Plastic
laminates
Products
• decorative work top surfaces
Process
Decorative thermosetting plastic laminates have become commonly known as
'Formica', 'Warerite', 'Arborite', etc. but these are just trade names belonging to
products of individual companies. The dark underside of the laminate consists of
layers of brown paper impregnated with a thermosetting resin, phenol-formaldehyde
(PF). The outer surface of the laminate consists of a decorative paper bonded to the
underlayer of phenol-formaldehyde resin. This decorative paper is covered with a
thin paper skin impregnated with melamine-formaldehyde resin (MF) and bonded to
the 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
( --------resin impregnated
_thin
--
resin i::'egnated
J--
========::::1 _
(
overlay paper
decorative printed paper
heavy white underlay paper
brown base papers
b) Impregnated paper assembly
~~~~--..:rrr:--..===
stripping plates from laminate
cut impregnated
paper assembly
decorative laminate
pressing
c} Pressing and finishing
Thermosetting
decorative
laminate
making
The paper sheets are impregnated with a liquid thermosetting resin. These sheets
are then dried, laid up in a loose stack and pressed between specially surfaced metal
sheets 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 sheets
and 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
Process
Compression moulding is used mainly to process thermosetting plastics. The correct
amount of plastics material, usually in powder form, is measured into a two part
matched die mould. The mould is closed under pressure and heated, causing the
material to soften and flow into the shape of the mould before setting hard. Moulding
powders for use in compression moulding are made up from various blends of resins
with cellulose and mineral fillers. The traditional thermosetting resins are ureaformaldehyde (UF), melamine-formaldehyde (MF) and phenol-formaldehyde (PF).
The press for compression moulding
has a central ram which applies force
hydraulically to a heated mould.
~-
__
+---:...'
THERMOSETTING
POWDER IN
THE MOULD
PRESS
HYDRAULIC
ELECTRIC
MOTOR
PUMP
A
typical
compression
28
moulding
system
2.1.11
Rotational
moulding
Products
• litter bins and dustbins
• storage tanks (water, etc.)
• traffic bollards
Process
Rotational moulding is used to make large hollow articles (e.g. containers) usually in
low density polyethylene (LDPE). The LDPE material in powder form is fed into a
hollow sheet metal mould in the shape of the item to be produced. The mould is then
heated whilst rotating about two axes so that the plastic melts and flows to form a skin
over the inner surface of the mould. The mould is then cooled, opened and the hollow
moulding removed. For open-top tanks (e.g. water cisterns) simple large hollow
mouldings 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.
Rotator arm
~
Remove moulding
~
Mould with molten plastic adhering to all
Mould filled with thermoplastic powder
(PVC/polythene) then heated by gas flame
whilst rotating
inside surfaces is taken from gas flame
and cooled by water jet whilst rotating
moulding
Rotational
29
2.1.12
Extrusion
blow
moulding
Products
• bottles
• drums
• car fuel tanks
• heater ducting
Process
A length of hot plastic tube is first produced by extrusion and then lowered into an
open two part hollow mould of the final product shape. The mould is then closed and
sealed 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 blow
moulding a bottle shape is illustrated below.
extruder
knife
Plastics bottles of all shapes
and sizes can be made in
this way.
~:~
screw
make a continuous
tube.
turns all <h. time to
hot plastics parison or
When the length of tube is correct. it is
surrounded by the mould and cut oH
with a knife attached to the machine.
With the moulding removed. the mould is
now ready for another cycl •.
air blower
Blow
moulding
sequence
30
of
operations
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 by
carbon dioxide. Polyethylene terephthalate (PET) has a sufficiently low permeability
to prevent carbon dioxide seeping through it and this makes it a suitable plastics
material for fizzy drink bottles. The strength of PET can be improved by the process of
biorientation during production of the container (bottle) in a similar manner to
principle of biaxial stretching of polymer film (see p24). This produces containers
with improved stacking strength and resistance to stress-cracking, which will also
withstand the pressure of normal gaseous drinks. The design of fizzy drink bottles
also makes maximum use of designs for pressurized containers in that they are
curved on as many areas as possible, including the base. Most bases are now of the
petaloid design (see diagram on adjacent page).
Process
The method of blow moulding bottles for gaseous contents is mostly a two part process
in order to incorporate the biorientation of the material mentioned above. The first
stage is to produce a hollow cylinder, domed at one end, by injection moulding. This
shape is known as a 'parison'. The parison is then removed from the injection
moulder, re-heated to make sure it is pliable enough and transferred to a bottle mould
for the second stage of blow moulding in to the final shape. The second stage causes
the 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 giving
the required strength properties.
Stage
1
mould clamping
and opening mechanism
plastic moulding
pallets
mould
Injection
Parison
moulding
ready
to
for
31
produce
blow
parisons
moulding
Stage 2
Mould open
with PET parison
in position
ready for blow moulding
into
bottle
shape
The pets/aid
design
with
Mould closed
blown bottle
completed
ready for removal
of most pop bottle
32
bases
2.1.14
Dip
moulding
Products
• protective gloves
• balloons
• handle grips
Process
Temperature controlled mandrels of the product shape are dipped into a bath of
plastic paste or fluidised powder. The paste/powder softens and forms a skin around
the mandrel shape which when cool can be peeled off. Alternatively, products of other
materials (e.g. metals) can be dipped and the plastic material then forms a fixed
durable coating on the outer surface of the product.
Coated mandrel
after dipping
Glove mandrel
to be dipped
Producing
rubber
gloves
33
by dip moulding
2.1.15
Structural
polyurethane
(PU)
foam
moulding
Products
• computer housings
• tool handles
• casings/cabinets
• furniture shells
• decorative simulated wood effects for wall panelling
Process
A 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 the
cavity 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 integrally
skinned PU foams; a combination of a foam interior with a hard solid skin or surface
which can be finished with lacquers.
Two part mix
into mould
:-...~----
Mix expands into
shape of mould
Compression
moulding
34
process
Split cavity
mould
APPENDICES
Appendix 1
THERMO
PLASTICS
ACRYLICS
PMMA
Perspex
Acrylonitrile Butadiene
Styrene
ABS
APPLICATIONS
PROPERTIES
Rigid. glass-clear. glossy. extremely weather
resistant. excellent for vacuum forming. casting
and fabricattng
Rigid opague, glossy/textured. tough. colourful.
excellent for injection moulding and
thermoforming
Signs. lenses. inspection windows. taillight
lenses. synthetic fibres. lighting diffusers. leaflet
dispensers. hi-f dust covers
Telephone handsets. rigid luggage. domestic
appliance housings (food mixers). margarine
tubs. car facia panels
Rigid. transparent. tough (even at low
temperatures. low electrostatic pick up. easily
injection moulded. relatively low coat
Flexible (rubbery). transparent. glossy. excellent
low temperature flexibility (-70°C). good chemical
resistance. high friction coefficient
Semi rigid. translucent. exceptional anti stick/low
friction characteristics. superior chemical
resistance. impervious to fungi or bacteria. high
temperature stability (260°C). low temperature
toughness (-160°C)
Rigid. translucent. tough. hard wearing. fatigue
and creep resistant. resistant to fuels. oils. fats
and most solvents. steam steriltzable
Spectacle frames. toothbrushes: tool handles.
transparent wrapping. metaltzed parts (reflectors
etc) pen barrels. typewriter keys
Teats. inflatable toys. handle grips. flexible tubing.
record turntable mats. ice cube trays. beer tubing.
vacuum cleaner hose. freezer doors
Non-stick coatings. gaskets. packings. bearings.
high and low temperature electrical and medical
applications
Cyclolac
Cellulosics
CA. CAB. CAP. CN
Cellophane
Ethylene Vinyl Acetate
EVA
Fluoroplastics
PlFE. FEP
Teflon
Nylons
PA (Polyamides)
Maranyl.
Zytel
Polyacetals
POM
Delinn,
Kemetal
Polycarbonate
PC
Lexan,
Makrolon
Polyesters
(Thermoplastic)
PETP. PBTP. (PETj
Rigid. translucent. very tough. spring-like
qualities. good stress relaxation resistance. good
friction and wear and electrical properties
Rigid. transparent. outstanding impact
resistance (to -150°C) and weather resistance.
good dimensional stability. very good dielectric
properties
Rigid. clear. extremely tough. good creep and
fatigue resistance. wide range temperature
resistance (-40° to 200°C)
Melinex. Terqlene,
Dacron
Polybutylene
PB
Polyethylene (HIgh
Density)
HDPE. HMWPE
Rfgidex
Polyethylene (Low
Density)
LDPE. LLDPE
Alkathene
Polypropylene
PP.OPP
Propathene
Polystyrene (General
Purpose)
GPPS
Polystyrene (HIgh
impact)
HIPS
Polysulphone (family)
PES. PEEK.
Udel, Victrex
Polyphenylene
PPO
Oxide
Noryl
Styrene-Acrylonitrile
San
Polyvinyl Chlorlde
PBC
Polymethylpentene
PMP
TPX
Polyurethane
(thermoplastic)
PUR(PU)
Semi rigid. translucent. tough. chemical and heat
resistant. good barrier properties. environmental
and mechanical stress crack resistant. good
electrical insulation
Semi rigid. translucent. very tough. high impact
resistance. weatherproof. excellent chemical
resistance. low water absorption. non-toxic. easy
processtng bv most methods. low cost
Flexible. translucent/waxy. durable. weatherproof.
good low temperature toughness (to -60°C). easy
to process by most methods. low cost. excellent
chemical resistance
Semi rigid. translucent (Integral hinge property).
excellent chemical resistance. extremely tough.
exceptional fatigue resistance. steam steriltzable.
high surface gloss/texture
Brittle/hard. metallic transparent/opague,
glossy. low cost. unsuitable for outdoor use.
excellent X-ray resistance. free from odour and
taste. easy processing
Hard/rigid. opague/translucent.
satin surface
finish. impact strength up to 7 x GPPS. other
properties similar
Outstanding oxidative stability at high
temperature (-200°C to +300°C)
transparent/opaque.
rigid/flexible. high cost.
specialised processtna
Rigid. opague, glossy. outstanding dimensional
stability (particularly under stress at high
temperature and humidity conditions). difficult to
process (blended to ease injection mouldtngl
Rigid. transparent. tough. resistant to oils and
greases. resistant to stress cracking and crazing.
good processability
Rigid/flexible. clear/opague, durable.
weatherproof. non flammable. good impact
strength. excellent electrical insulation
properties. limited low temperature performance
Rigid. clear. tough. lightweight (density 0.83
gm/em 3). chemical resistant. additives required
for outdoor use
Flexible. clear. elastic. wear resistant Impermeable
35
Gear wheels. bushings. zips. pressure tubing.
synthetic fibres. bearings (particularly for food
processing machinery). curtain runners.
carburettor parts
Business m/c parts. small pressure vessels.
aerosol valves. coil formers. clock and watch parts.
nuclear engtneering components
Crash helmet visors. riot shields. vandal-proof
glazing. baby feeding bottles. safety helmets.
greenhouse double glazing. miners' phones and
battery cases. film/slide casettes
Carbonated drink bottles. business m/c parts.
synthetic fibres. parts for 1V tuners and
transformers. fire alarm parts. coffee makers and
toasters
Boil-in-bag food packaging films. industrial pipes.
high temperature tubing (500 psi @ 85°C). central
heating systems
Chemical drums. jerricans, carboys. quality
kitchen ware. collanders, bins. toys. picnic ware.
household and hospital ware. cable insulation
Squeeze bottles. toys. wrapping films. utility
kitchen ware. carrier bags. high frequency
insulation. garment bags. chemical tank linings
Sterilizable laboratory and hospital ware.
containers and snap fit closures ropes. moulded
hinges. packaging film. car accelerator pedals.
heater ducting. door handles. washing m/c parts.
suitcases. electric kettles. children's plates
Toys and novelties rigid packaging. refrigerator
trays and boxes. cosmetic packs and costume
jewellery. ligh ting diffusers
Yoghurt pots. refrigerator linings. vending cups.
kitchen and bathroom cabinets. toilet seats and
tanks. closures. instrument control knobs. radio
and 1V cabinets
High/low temperature. high technology. e.g.
microwave grills. chemotherapy devices.
electro/cryo surgical tools. radornes, fuel cells.
aerospace batteries. nuclear reactor components
Business m/c and 1V housings. automotive
instrument casings. coffee pot and washing
machine parts (where high temperature and
moisture critical) replacement for die castings
Drinking tumblers. ht-fl covers. lenses. water jugs
and toothbrush handles. kitchen and picnic ware
Drainpipes and guttering and roofing sheets.
cable and wire insulation. floortng/hoseptpe,
stationery covers. fashion footwear. "cling film"
"imitation leather" fabrics
Laboratory ware. syringes. lamp covers (good
heat resistance) radar and microwave
applications. encapsulation. printed circuit
boards. microwaveable. food packa~n~
Soles and heels for sports shoes. football boots.
hammer heads. seals. gaskets. Ovrtngs, rollers.
skate board wheels. synthetic leather fabrics.
silent running gears and sprockets for office
machines
Appendix 2
THERMOSETS
Phenolics
PF
Bakelite
Epoxies
EP
Ara/dite
Polyurethanes
(cast
elastomers)
PUR
Polyesters
(unsaturated)
SMC, DMC, GRP
(when
reinforced)
Alkyds
NVC
Allylics
DAP, DAIP, ADC
Polyamidesl
Aramids
PI
Kev/ar
Aminos
(Melaminesl
Ureas)
MF, UF
Furan
Vinyl
Esters
PROPERTIES
Brittle, opaque, excellent electrical
and heat resistance, outstanding
resistance to deformation under
load, low cost
Rigid, clear, very tough, chemical
resistant, excellent adhesion
properties, high resistance to
cracking, low curing shrinkage
Elastic abrasion and chemical
resistant, impervious to gases, can
be produced in wide range of
hardnesses
Rigid, clear/opaque, tough,
chemical resistant, fire resistant,
high strength, low creep, good
electrical properties and low
temperature impact resistance, low
cost
Rigid, opaque, tough, heat resistant,
excellent arc and tracking
resistance, excellent long term
dimensional stability, fungus
resistant, good colour stability
Hard, transparent, exceptional
abrasion resistance and electrical
insulation properties (even under
humid conditions), outstanding
combination of mechanical/
chemical properties
Rigid, opaque, high strength,
exceptional thermal and electrical
properties (up to 480°C), excellent
dry bearing properties when filled
with PTFE, excellent resistance to
ionizing radiation, high cost
Rigid, opaque, tough, very hard and
scratch resistant, self
extinguishing, free from taste and
odour, wide colour range
Rigid, opaque, high strength at
elevated temperatures, excellent
chemical resistance, self
extinguishing, low smoke
emission, resistant to carbon
disulphide
Rigid, translucent, good corrosion
resistance, low viscosity
36
APPLICATIONS
Ashtrays, fuseboxes,
lampholders, bottle closures,
saucepan handles, toilet seats,
thrust washers
Adhesives, coatings, embedding,
potting, electrical components,
chemical pump components,
cardiac pacemakers
Printing and industrial rollers,
solid tyres, die pads, wheels, shoe
heels (particularly suited to low
quantity production runs) car
bumpers
Boat hulls, building panels, car
bodies, lorry cabs, tanks and
ducting, compressor housings,
also embedding and coatings
Automotive distributor caps,
circuit breakers, switch gear,
coloured appliance housings
Optical coatings, face shields,
sealants for metal castings,
critical long-term high
reliability electrical
applications (e.g. radomes)
Aerospace components,
reinforcing fibres, high
temperature resistant foams
chemical filters, arc welding
torches
Decorative laminates, clock
cases, lighting fixtures,
dinnerware, heavy duty
electrical equipment, also
adhesives, bonding and
laminating resins, and surface
coatings
Chemical plant (competitive with
stainless steel), laboratory
floors, foundry cases and
moulds, specialised insulating
foam
Chemical tanks, ducts, piping,
process equipment (particularly
in corrosive chemical
environments)
Appendix 3
PHYSICAL
THERMOPLASTICS
Acrylics
PMMA
Perspex, Oroglas
Butadiene
Acrylonitrile
Styrene
ASS
Cyclolac, Lustran, Novodur
Cellulosics
CA, CAB, CAP, CN
Cellophane, Dexel
Acetate
Vinyl
Ethylene
EVA
Fluoropla
stics
PTFE,FEB
Tef/on, Kvner
Nylons
PA (Polyamides)
Maranyl, Zytel
Polyacetals
FUJI
Delrin, Kematal
Polycarbonate
Fe
Lexan, Makrolon
(Thermoplastic)
Polyesters
PETP, PBTP (PET)
Melinar
Polybutylene
PB
Polyethylene
Density)
(High
HDPE, HMWPE
Rialdex
Polyethylene
Density)
(Low
LDPE, LLDPE
No vex
Polypropylene
PP,OPP
Propathene, Hostalen PP, AJ)J)ryl
(General
Polystyrene
Purpose)
GPPS
(High
Impact)
Polystyrene
HIPS
(family)
Polysulphone
PES,PEEK
Udel, Victrex
Sulphide
Polyphenylene
PPS
Ryton, SUJ)ec
Oxide
Polyphenylene
PPO
Norvl, Pre vex
Sty re ne- Ac ry I on i tri I e
SAN
Lustran A, Luran, Tyril
Chloride
Polyvinyl
PVC
Hostalit
PROPERTIES
Linear
Coefficient
of Expansion
per °C x 106
Maximum use
Temp °C
Density
g/cm3
1.5-3.0
60-90
70-80
1.18
1,8-2.9
14-55
65-90
75-95
1.04-1.07
0.5-4.0
2.0-60
80-180
45-70
1.15-1.35
0.05-0.2
no break
160-200
55-65
0.926-0.950
0.35-0.7
13-no break
120
205-280
1.17
2.0-3.4
4.0-5.0
70
80-110
1.13
3.4
5.5-12
110
80
1.41
2.4
15-80
70
130
1.20
2.5
1.5-3.5
65
70
1.36
0.24
no break
130
N/A
0.91
0.60-1.3
3.0-nobreak
100
80
0.944-0.965
0.2-0.4
no break
100-220
65
0.917-0.930
0.95-1.30
5-20
70-95
80
0.902
2.3-3.35
2.0-2.5
80
65-85
1.05
2.2-2.7
10-20
80
60-80
1.03-1.06
2.1-2.4
60-no break
20-65
160
1.13-1.17
0.5
<2.5
50
240
1.30
2.1-2.5
20-25
60-70
110
1.06
3.4-3.9
2.5-3.0
75
85
1.07
2.6
2.0-45
80
60
1.38
Tensile
Modulus
N/mm2
Impact
Strength
kJ/m2
2.9-3.3
37
Appendix 4
THERMOPLASTICS
Acrylics
PMMA
Perspex, Drog/as
Acrylonitrile
Butadiene
Styrene
ABS
Cyelolae, Lustran, Novodur
Cellulosics
CA, CAB, CAP, CN
Cellophane, Dexel
Ethylene
Vinyl
Acetate
EVA
Fluoroplastics
PTFE,FEB
Teflon, Kynar
Nylons
PA (Polyamides)
Maranyl, Zyte!
Polyacetals
FG\1
Delrin, Kematal
Polycarbonate
Fe
Lexan, Makr%n
(Thermoplastic)
Polyesters
PETP, PBTP (PET)
Melinar
Polybutylene
A3
Polyethylene
(High
Density)
HOPE, HMWPE
Rigidex
Polyethylene
(Low
Density)
LOPE, LLOPE
No vex
Polypropylene
PP,OPP
Propathene, Hostalen PP, Appryl
(General
Polystyrene
Purpose)
GJPS
(High
Impact)
Polystyrene
HIPS
(family)
Polysulphone
PES, PEEK
Udel, Vietrex
Sulphide
Polyphenylene
PPS
Ryton, Supee
Polyphenylene
Oxide
PPO
Noryl, Pre vex
Styren e-Acry
10 n i tri Ie
SAN
Lustran A, Luran, Tyril
Chloride
Polyvinyl
PVC
Hostalit
v - Variable
RESISTANCE
TO CHEMICALS
Dilute
Acids
Dilute
Alkalis
Oils and
Greases
Aliphatic
Hydrocarbons
Aromatic
Hydrocarbons
Halogenated
Hydrocarbons
Alcohols
vg
vg
vg
m
p
p
vg
vg
vg
vg
m
p
p
p/v
m
p
vg
vg
p
p
p
vg
vg
9
vg
P
P
vg
vg
vg
vg
vg
vg
p/v
vg
p
9
vg
vg
vg
g/v
p
p
vg
g/v
vg
9I
P
vg
9
9
vg
m
P
p
N/A
vg
m
vg
vg
p
p
vg
vg
vg
N/A
N/A
P
P
N/A
vg
vg
m Iv
p
m Iv
m Iv
vg
vg
vg
m Iv
p
P
P
vg
vg
vg
m Iv
p
P
P
vg
g/v
vg
m Iv
vg
P
p
m Iv
m
vg
m
vg
p
p
p/v
vg
vg
vg
m Iv
p
P
vg
vg
vg
vg
vg
vg
vg
N/A
vg
vg
vg
m
p
p
m/v
vg
vg
vg
m
p
p
m Iv
vg
vg
vg
p
m Iv
g/v
vg - Very Good
g/v
9 - Good
38
m - Moderate
V
p - Poor
Appendix 5
SUMMARY
PROCESS
OF MAIN INDUSTRIAL
COMMON
MATERIALS
APPLICATION
BLOW
MOULDING
LOPE
PET
PVC
INJECTION
MOULDING
Nylon
ABS/PS
HDPE/PP,
Bottles
Drums
Car fuel tanks
Heater ducting
Buckets
Telephones and Gears
TV & Hi-fi cabinets
ROTATIONAL
MOULDING
LOPE
PVC
Litter bins
Storage tanks
Traffic bollards
EXTRUSION
Nylon
HDPE/PP
L1)PE
PVC
Drain pipe/Guttering
HoselWire insulation
Roofing sheet
Window frame
COMPRESSION
MOULDING
Epoxy
Phenolics
VACUUM
FORMING
Acrylic
PS
DIP
MOULDING
L1)PE
PVC
CALENDERING
L1)PE
PVC
PS
GAP
LAMINATING
Epoxy
Polyester
resin
STRUCTURAL FOAM
MOULDING (PU)
PS
PU
BAUOON
BLOWING
L1)PE
HOPE
THERMOFORMING
BY PRESSURE
BIAXIAL
STRETCHED FILM
PLASTIC
LAMINATE
Fuse boxeslInsulators
Lamp holders
Saucepan handles
Yoghurt pots
Vending cups
Fridge linings+housings
Point of sale display
Protective gloves
Balloons
Handle grips
Protective sheet
Shower curtains
Stretch wrap film
Boats/Car bodies
Chemical plant
Architectural claddings
Computer housings
Casings
Tool handles
Simulated wood effect
Dustbin bags
Carrier bags
Luxury applications with
attractive finishes
PP/PS
Polyester
Growing trays
Seed boxes
Disposable trays
Corrugated PVC sheet
Polypropylene film
Polyester film
PF/MF
resins
Decorative work top
surfaces
(e.g. Formica)
Acrylic
ABS/PVC
PS
PET - Polyethylene terephthalate
PF - Phenol-formaldehyde
ABS - Acrylonitrile butadiene styrene
PROCESSES
DESCRIPTION
A hot thermoplastic tube is inflated by
compressed air into a cooled, split-cavity
mould to produce a precision hollow
moulding.
Molten plastic is injected under high
pressure into a cooled, split mould to
produce a high precision moulding.
Thermoplastic powder is tumbled, heated
and cooled in a split, hollow mould to
produce simple shaped, hollow
mouldings
Molten thermoplastic is extruded under
high pressure through a shaped die to
produce a continuous precision section
Thermosetting plastic powder is
compressed and heated in a matched dieset to mould a precision product
Thermoplastic sheet is heated and forced
under vacuum into contact with a cooled
form-mould to produce simple shaped
mouldings
Temperature controlled mandrels are
dipped into a bath of plastic paste or
fluidised powder to produce a peelable
skin (or durable coating)
Hot thermoplastic is passed through a
series of temperature controlled rolls
with progressively smaller gaps to
produce continuous, precision thin sheet
(also embossed if required)
Layers of glass fibre matt are laid-up and
wetted with a thermosetting resin into a
simple mould form to produce large,
strong structural mouldings
A two-part premix is introduced into a
split cavity mould where it expands to
produce strong, lightweight mouldings
An extruded plastic melt is passed
through a die and air blown into a long
balloon of plastic film. This is pressed into
double film, cut and heat sealed at one
end to make bags.
A thermoplastic foil or sheet is heated
until soft and then mechanically pressed
into a former or mould to produce the
product shape.
Semi-molten film is stretched along two
axes at 90° to one another to increase the
mechanical strength.
Brown paper sheets are impregnated
with resin and laid up in a multi-platen
press. Pressure and heat are then applied
to produce the final laminate.
PP - Polypropylene
PU - Polyurethane
MF - Melamine-formaldehyde
PS - Polystyrene
LOPE/HOPE - Low/High density polyethylene
39
Appendlxs
EQUIPMENT
AND MATERIAL
SUPPLIES
Equipment
Brochures/catalogues
following:
of equipment
for schools plastics work can be obtained from the
C R Clarke & Company (UK) Ltd
Unit 3
Betws Industrial Park
Foundry Road
Ammanford
Dyfed
SA182LS
Formech Vacuum Forming
72 West End Road
High Wycombe
Bucks
HPl12QQ
Machines
Material
One of the major problems which face schools is obtaining supplies of plastics
materials in appropriate quantities and sizes, at a reasonable cost. The following
offer various packs of materials to meet school budgets:
EMA Model Supplies Ltd
58-60 The Centre
Feltham
Middlesex
TW13 4BH
Trylon Ltd
Thrift Street
Wollaston
Northants
NN97QJ
40
K&M, Unit24
Lion Park
Holbrook Ind. Estate
New Street, Halfway
Sheffield
S195GH
Appendix 7
OTHER RESOURCES
ICI, in conjunction with the Technology in Context project, has produced a resource for
dealing with needs and opportunities in the context of using plastics. It consists of
teachers notes and student activity sheets housed in a ring binder and includes a video
cassette. From:
SCSST
76 Portland Place
London
WIN 4AA
The Polymer Industry Education Centre (PIEC) can supply a list of resources about
plastics, activity packs, fact sheets, information booklets, posters, slides and videos
which can be obtained from a variety of industrial and other sources. The list is
available free from:
Polymer Industry Education Centre
Department of Chemistry
University of York
Heslington
York
YOI 5DD
Recommended
further
reading:
"Design and Plastics" by Mike Hall (ISBN 0-340-40528-7)
Safety
publications:
NAAIDT Publications
16 Kingsway Gardens
Chandler's Ford
Hampshire
S051FE
Tel: 0703 254440
CLEAPSS School Science Service
BruneI University
Uxbridge
UB83PH
Tel: 0895 251496
ASE
Publications Section
College Lane
Hatfield
Hertfordshi re
ALI09AA
Tel: 0707 267411
HMSO
Publications Centre
(Telephone Orders)
Tel: 01 873 9090
NAAIDT
National Association of Advisors and Inspectors for Design and
Technology
CLEAPSS
Consortium of Local Education Authorities for the Provision of Science
Services
ASE
Association for Science Education
41