71
Manufacturing Industries Division
The design, development and manufacture of a
new and unique tennis racket
R C Haines, M E Curtis, F M Mullaney and G Ramsden
Dunlop Sports Company Limited, Horbury, Wakefield, West Yorkshire
This paper describes how a revolutionary new process was devised for producing top quality tennis rackets from carbonjbre reinforced
thermoplastic by a specially developed injection moulding process. The product and process were evolved following an initial study by a
multi-discipline team in January 1578 which led to a fully engineered manufacturing process starring production in November 1980.
The new racket undercuts the price of competitors’ carbonjbre composite rackets in a market Sector of growing importance, and the
hdded value’ of the product is significantly higher than that for conventional wooden rackets currently manufactured by the Company.
When other comparisons are made with wooden racket manufacture, the new product and process show adGantages in nearly every
aspect of production eficiency.
The new racket and process which are prolected by three patents, won a Design Council Award in 1981 and was the winner of the
Willis Faber Manufacturing EfSectivenes.7 Award organized by the Institution of Mechanical Engineers in May 1582.
1 THE MARKET AND COMPETITIVE ACTIVITY
The United Kingdom has been a manufacturer and
exporter of sports equipment for many years and tennis
rackets have featured in this significantly. The world
boom in tennis since the late 1960s has brought many
non-traditional manufacturers into the business and
rackets based on metal as well as on wood became
established. Due to the relatively low technology and
high labour content of such rackets, manufacture has
moved increasingly to low labour cost areas of the
world, particularly to Taiwan. The UK racket industry
is under ever increasing competitive pressure in this
market sector-a problem common to other areas of
UK manufacturing industry.
Since the early 1970s rackets based on composite
materials (e.g. glass fibre and/or carbon fibre reinforced
plastics) have been introduced particularly in the USA
where the influence of West Coast aerospace technology
has been applied to a variety of products. Such rackets,
although expensive, have found demand where players
are prepared to go ‘up-market’ to obtain advantages in
weight, balance and general playing qualities together
with durability. While composite rackets made in the
USA have been primarily based on carbon fibre, racket
manufacture based mainly on glass fibre has been established in Japan and again, low labour cost Taiwan is
rapidly developing a significant carbon fibre and glass
fibre composite racket industry to supplement established wood and metal racket manufacture.
Market research indicates that though the total world
racket market is relatively static at some sixteen million
units per year, demand for wood and metal rackets is
declining while that for composite types is increasing
rapidly (Fig. 1). It appears that the composite may well
become established at some future date as the most
common type.
Dunlop Sports Company, a wooden racket manufacturer of over fifty years standing, was hard pressed to
This paper was originally submitted as an entry to the 1982 Willis Faber competition. The M S was receiced on I March 1982 and was accepted for publication
o n 7 February 1983.
41:X3 @ IMechE May 1983
10
121
M
8
4i
M
2
I
1
1980
1981
1982
1983
1984
1985
Fig. 1 World market: tennis racket types
Wood
Composite
Metal
Total market
1980
55 per cent
30 per cent
15 per cent
15 million
1985
50 per cent
40 per cent
10 per cent
16 million
meet the demand for wooden rackets in the boom years
of the early 1970s, but some seven years later its
business was being so seriously eroded that it had to
review its position. The Company decided that if it was
to protect its worldwide racket business then it must be
represented in the growing composite sector.
From analysis of competitors’ composite rackets and
internally made experimental versions certain problem
areas were identified :
1. Composite rackets have to be substantially handmade so that potential UK manufacturers would
indeed find it difficult to compete with low labour
cost areas of the world.
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R C HAINES, M E CURTIS, F M MULLANEY A N D G RAMSDFN
Due to hand assembly, the rackets often exhibited
variable strength unless they were ‘over-engineered’.
lJsing expensive carbon fibre, this would increase
costs considerably.
Significant manufacturing time was associated with
the moulding operation due to the fact that thermosetting resins conventionally used have to be subject
t o ‘cure’ times of several minutes duration.
It is necessary to illustrate the above. The term ‘composite material’ is generally understood to refer to fibres
of glass, carbon or other filamentary material coated
with a thermosetting resin (based usually on polyester,
epoxide or phenolic) which are assembled in appropriate geometrical form and then moulded under heat and
pressure to produce the desired product. The product,
being a tennis racket, must conform to the size and
shape dictated by convention. The problem is that composite materials have specific gravities of approaching
twice that of laminated wood and so the only way in
which the requirements can be met is by producing
hollow mouldings or at least mouldings with low
density cores.* Herein lies the necessity for complex
hand building. The desired result is usually achieved by
assembling the uncured composite materials onto some
form of inflatable or expandable mandrel which needs
careful hand fabrication and insertion into a mould,
The process is both slow and costly. The moulding
process itself is normally of several minutes duration
and considerable surface finishing is subsequently
necessary. Stringing holes have to be drilled-in by a
separate operation and generally the process does not
lend itself to high volume production (1).
The requirement was clear. A new composite racket
and manufacturing process were required which would
offer :
(a)
(b)
(c)
(d)
a low labour cost manufacturing route,
high product strength and uniformity,
high production rate,
hopefully, a perceived consumer product advantage.
2 PRODUCT DESIGN AND PROCESS
DEVELOPMENT
A multi-discipline design team from a newly established
R & D Group was brought together consisting of a
plastics technologist, a physicist and design and production engineers. A two-day study session was
arranged in which all aspects of design and manufacture
of composite rackets were considered with no
restrictions being placed on methods or materials.
While their significance was only subsequently realized,
certain important principles were established and were
recorded amongst notes made at the meeting. These
were :
1. To reduce labour costs to a minimum, a plastics
injection moulding proces was desirable.
2. Considerations of specific gravity of composite
materials dictated that the racket structure must be
hollow (as noted previously).
3. It was necessary to specify precisely the dimensions
and appropriate strength and stiffness of a simple test
specimen which would reflect the required properties
*
Nore mctal racketa are baaed on d r m n tube or hollow extruded sections
of a racket. Laboratory trials could then be made on
proposed materials, sections etc.
Having established the above criteria the following
investigations were conducted :
1. A thermoplastic moulding compound based on
nylon with short carbon fibre reinforcement was
identified, and it became apparent that this offered
the highest strength and stiffness of any injection
moulding material. It was very costly, however at
over &16/kg for a 30 per cent loading of carbon fibre
and so would have to be used very efficiently.
2 The prospects of producing hollow injection mouldings were considered. No technology was available
for achieving this, so thought was directed at ways in
which this might be undertaken. The possibilities of
moulding the reinforced plastic around a removable
core was contemplated and in particular the use of a
core which might be subsequently dissolved out (i.e.
a soluble core) was considered. A proposal was made
to use a core of low melting point metal which had a
melting point below that of the melting point of the
reinforced thermoplastics material itself. But how
could the hot plastic material be injected without the
core melting in the first place? The idea was shelved
while other schemes for using removable cores were
investigated.
3. How was the specification of a test specimen, on
which the identification of an appropriate construction depended, to be established? The geometry of a
tennis racket is complex and defies accurate mathematical analysis, but it was realized that nontraditional rackets of appropriate stiffness and
strength were made from aluminium extrusions bent
into a key-hole shape in which the elliptical head was
completed by a separate ‘throat-piece’ of metal or
plastic. A 6 in length of the aluminium extrusion
could be taken, measured for weight, stiffness and
strength and these values used as criteria for a test
specimen of similar length and of a section to be
decided.
While the above investigations were proceeding practical work led to a surpriiing and important discovery.
It was found that a hollow injection moulding could in
fact be made by moulding plastic material around a low
melting point metal alloy, the plastic material being
injected at a temperature well above the melting point
of the metal alloy. This was found to be possible if:
1 . Very high injection speeds were used.
2. A temperature differential of about 130°C existed
between the melting points of plastic and metal
respectively.
It appeared that, providing there was a certain
minimum volume of metal to act as the core, the capacity of the metal to absorb the heat of the injected plastic
was such that the plastic solidified before the metal
started to melt. Here then was the basis of a new
moulding technique.
It was now decided that, to minimize production
costs, the racket stringing holes should be moulded-in
to avoid the drilling process necessary with wooden,
metal and conventional composite rackets. This was
important because hole-edges could be accurately
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73
THE DESIGN, D E V E L O P M E N T AND MANUFACTURE OF A N E W AND UNIQUE TENNIS RACKET
formed to avoid the sharp edges (and so early string
failure) sometimes found on wooden rackets and also to
avoid the use of plastic insulating grommets essential
with metal and composite constructions.
A 6 in long test-piece of cross-section appropriate to
the head of the proposed racket was designed. Wall
thickness of the hollow moulding was determined in
conjunction with the specific gravity of the reinforced
thermoplastic to give appropriate weight. It will be
appreciated that two moulds have to be made-one for
the metal alloy and one for the final plastic moulding.
The metal component when made must be accurately
placed inside the injection mould and located centrally
during the plastic injection phase so that uniform wall
thickness is obtaincd.
In order that the stringing holes can be moulded-in, it
will be appreciated that retractable ‘pins’ are necessary
which pass completely through the moulding at the
injection stage and are subsequently withdrawn to allow
removal of the moulding. To allow this, holes are
required in the metal alloy ‘core’ (these are in turn produced by retractable pins when the core itself is made).
Another important discovery was then made after
examining sample mouldings made using retractable
pins. If, in fact, the retractable pins used in the injection
moulding process are made smaller in diameter than the
holes in the core then plastic material, when injected,
passes down between the pin and the hole in the casting
as well as sheathing the casting. When the metal alloy is
melted out, the plastic material remains to form a
hollow pillar around the string hole position, which
passes across the hollow interior of the moulding. It was
immediately appreciated that this hollow pillar formation would enable much thinner wall sections t o be used
than would otherwise be the case, because the high
stresses imparted by each string on the frame structure
(usually of the order of 60 lb) would be distributed by
the pillar across the frame section. This would enable a
lighter frame to be produced than would otherwise be
the case. This feature was recognized to be patentable
and the first of three patents was taken out on the
product and process (2).
Appropriate wall and pillar sections were established
and it was verified from the test-piece that satisfactory
strength and stiffness would be obtained in a racket
head made to similar dimensions. Suitable drawings
Grommets used in core
location pin holes
V
Hollow pillars
ailow strings
to pass through
I
I
I
Solid pillan
(optional)
Groove for
strings
Section A - A
Fig. 3 Section through moulded frame
were prepared (Figs. 2 and 3). The wall thickness was
established at 2.5 mm and here fortune took a hand. It
was later established, when sections of racket frame
were analysed at Cranfield Institute of Technology, that
the wall thickness chosen produced optimum fibre
alignment in a nylon matrix, thus maximizing strength
and stiffness in the hoop direction (Fig. 4).
From information gained in test-piece analysis a
prototype racket was designed, and two simple moulds
produced for the metal core and final moulding. The
String hole pins
(retractable)
Fuiible core
I
Metal mould
Section A ~A
Fig. 2 Section through mould tool
Fig. 4 X-ray photograph of section through racket showing
fibre alignment [Cranfield Institute of Technology]
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74
R C HAINES, M E CURTIS, F M MULLANEY A N D G RAMSDEN
Fig. 5 Core partially sheathed in carbon fibre reinforced
nylon showing how material flows from single injection point
Fig. 6 Section through hollow moulded racket showing reinforcing pillars around string holes
racket proved to be very strong and met all the requirements of weight and strength, but it was designed from
an engineering viewpoint and its appearance did not
meet with the approval of the marketing department.
Pre-production moulds were then designed after the
approval of a wooden mock-up and this was the basis
of the final production tooling.
A partly moulded racket and a sectioned one are
shown in Figs. 5 and 6 made using the production
tooling.
Having established a viable method of racket frame
manufacture, another problem required solution.
Players have individual preferences regarding racket
weight, balance and grip size. The problem was that
injection moulded frames are identical in every way and
there was no easy facility for suiting individual requirements.
It was then decided to use rigid polyurethane foam as
an internal filling for the hollow structure and for
forming handles of different sizes onto the shaft of the
racket moulding in a second moulding operation.
Choice of a low density foam for the internal filling and
a medium density foam for the handle would allow
frame weight and balance to be varied at will by changing the relative amounts of each foam. Additionally, the
medium density foam was allowed to expand through
holes moulded in the base of the shaft of the frame to
form a handle which was integrally moulded to the
frame structure (Figs. 7 and 8). The use of polyurethane
foam in this way produced good vibration dampening
properties and allowed a variety of rackets to be made
from standard mouldings. The manner in which this
was done was the subject of a second patent application
(3)-
3 ENGINEERING ASPECTS
Machinery and equipment for producing the racket in
large quantities was the subject of special investigation.
The basic necessities were:
(a)
(b)
(c)
(d)
(e)
a means of injection moulding the racket frame,
a means of making castings at high rate,
suitable moulds and tooling for the above,
a method of melting out the cores,
equipment for accurately dispensing polyurethane
foam.
Figures 9-1 4 show the equipment and tooling
referred to below.
The injection moulding machine chosen was a substantially standard 300 ton clamp 16 oz reciprocating
screw machine, the governing factor being the platen
size which had to accommodate a moulding 27 in long.
The necessary 10 oz shot was well within the capability
of the machine-an
important factor in view of the
complexity of the moulding.
The casting process led to special problems due to the
fact that the eutectic tin/bismuth alloy used was not
normally the subject of high production requirements. It
was decided to adapt a commercially available lowpressure die casting machine for the purpose. Such
machines consist essentially of a crucible which can be
pressurized by air to raise a column of molten metal to
a mould situated above the crucible. The machines are
normally used for aluminium casting and the high specific gravity of the tin/bismuth alloy (8.5 compared with
2.7) introduced certain problems regarding metal flow.
De-moulding of the casting, which had only limited
strength, was also a problem if fast cycle times were
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THE DESIGN, DEVELOPMENT AND MANUFACTURE OF A N E W AND UNIQUE TENNIS RACKET
75
MOULDED PLASTIC GRIP FERRULE
HOLES IN FRAMEAUOW
FOAM TO PASS THROUGH
AND FORM HANDLE
I
- \
\
LOW DENSITY
P.U. FOAM IN HEAD
AND SHAFTS
P.U. FOAM IN
HANDLE END OF FRAME
AND ALSO UNDER GRIP
HANDLE AVAILABLE IN
VARIOUS SIZES
Fig. 7 Section through handle
FRAME SECTION BASED ON
HOLLOW RECTANGLE FOR
OPTIMUM UTlLlSATlON OF
MATERIAL PROPERTIES TO
ACHIEVE DESIRED STRENGTH
AND STIFFNESS
HARD WEARING EPOXY PAINT,
SILK SCREEN PRINTED
COSMETICS, AN0 ACID
CATALYSED LACQUER FINISH
INDIVIDUALPILLARS MOULDED
AROUND EACH STRING HOLE
TO GIVE ADDED STRENGTH
AND EASE OF STRINGING
D HEAD
ECTION
DENSITY
'S DAMPE
AND IMPARTS BALANCE
ALL SHARP EDGES
REMOVED
Fig. 8 Section through head
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R C HAINES, M E CURTIS, F M MULLANEY A N D G RAMSDEN
76
Fig. 9 Diecasting the core for the racket frame from low
melting point metal alloy
used. By developing an automatic ejection system and
carefully controlling the temperature of the mould good
castings could eventually be obtained in a cycle time of
2.5 minutes.
Fig. 11 General view of the manufacturing area: the injection moulding machine is in the upper part with die
casting machine immediately behind; the melt-out
conveyors and oven are on the right hand side
4 MOULDS AND TOOLING
The moulds for producing the casting and the injection
moulded frame are substantially the same in general
design as each is required to produce a racket shape
with moulded-in holes in the looped area.
In order that maximum advantage could be taken of
the mechanized processes, it was desirable that the
necessary moving mould parts were automatically actuated. The pins forming the holes in both the casting and
the final moulding were arranged to move in and out
with mould closing and opening. While this is standard
injection moulding practice, the actual moulds were
(a)
(b)
(c)
Fig. 12 Melt-out conveyor and oven showing moulded
rackets on conveyor moving to the oven
Fig. 10 A composite photograph showing the three stages of
racket moulding:
(a) Examination of mould
(b) Metal core fitted into position for the moulding
operation
(c) Mould open after injection to show core
sheathed in carbon fibre nylon material
Fig. 13 Quality control apparatus for checking frame
stiffness
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THF DESIGN. DEVELOPMENI‘ AND MANUFACTURE OF A NEW A N D LJNIQUE TENNIS RACKET
Fig. 14 Handle moulding: polyurethane foam is metered
into moulds clamped around the handle position; a
racket with the handle moulded on is shown separately
highly complex with eight separate sliding blocks
making up the total of sixty-four holes required in each
casting and moulding. In the case of the moulding, it
was important that the core be accurately located so
that uniform wall thickness would be obtained. This
was arranged by the use of four manually operated
retractable locating pins in the elliptical head area of
the racket together with spigots at either end of the
shaft (the top one being situated at the junction of the
twin shafts). All removable parts were fitted with electrical interlocking devices to prevent mould damage
should retraction not take place.
Development work on the moulding process was
required to ensure accurate core centralization which
was improved by the use of spigots incorporated in the
casting. This was the subject of a third patent (4).
The number and position of the injection ports
required special experimentation particularly as these
afFected the number and position of the ‘weld’ lines in
the racket head resulting from material flow from different directions. The speed of mould filling was found to
be critical: if it was too slow the casting melted locally,
if it was too fast bad welds were obtained due to air
entrapment. Eventually a 3 second injection resulting in
a 1.5 minute cycle time was established as giving good
results.
The analysis of the mouldings by Cranfield Institute
of Technology referred to previously indicated that weld
positions were difficult to identify. It would appear that
the very complex flow path created by the pillarstructure causes swirling in the reinforced plastic such
that simple butt-jointing of flow does not occur and
I7
hence there is no reduction of strength at these positions.
Subsequent melt-out of the metal cores was arranged
by conveyorizing the moulding assembly through air
heated ovens at 180”C, the mouldings being held in
holsters in a tilted position so that the metal would run
out from all parts of the frame on melting. This was
assisted by introducing a vibrating action to the frames
in the last one-third of the oven. The molten metal falls
into a tray at the base of the oven where it is collected
for re-cycling.
The melt-out process has been subject to continuous
development and a new method has recently been introduced in which melt-out is carried out in hot oil. This
has the following advantages:
1. More uniform heating prevents distortion of the
moulding.
2. The moulding is annealed and so areas of mouldedin stress are relieved.
3. Lcss metal residuc rcmains inside the mouldings.
4. The method is quicker and uses less electrical energy.
The injection of foam polyurethane to the inside of
the racket frame and to the handle area is carried out
by standard polyurethane dispensing machines capable
of dispensing controlled shot weights so that the final
weight and balance of the rackets can be chosen at will.
The isocyanate and resin components are continuously
circulated in the head of the machinc for consistency.
The capital cost of all the production tooling and
machinery amounted to &160000 (1 979 prices).
5 PRODUCTION EXPERIENCE AND
PRODUCT QUALITY
Volume manufacture started in November 1980 and to
date (February 1982) over 40000 rackets have been
produced on single shift working. The planned capacity
(three shift) is some 120 000 rackets per year.
Some initial difficulty was experienced in ensuring
that the core was accurately centralized and special
ultrasonic thickncss gauges were obtained so that wall
thickness could be accurately monitored. Refinement of
the factors affecting core location overcame these problems.
It was considered that metal oxidation might produce
losses which would add significantly to cost particularly
in view of the high metal cost. However, experience
showed this amounted to less than 1.0 per cent and was
easily accommodated in process costs.
Generally, the process has been found to run
extremely well on a day-in day-out basis with rigorous
quality checks on raw material and finished products
being applied. Excellent strength and uniformity have
been obtained and, comparing with a wooden racket
which by its very nature is a variable product, a
strength advantage of a factor of 3 could be ascribed to
the injection moulded frame.
Comparing it with ‘conventional’ composite frames of
various types and makes, the injection moulded frame is
found to be at least as strong as many, and stronger
than most. This is undoubtedly a reflection on the very
strong structure of internal bracing because otherwise,
short fibre thermoplastic structures would not be
expected to be as strong as continuous filament/thermosetting types.
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78
R C HAINES, M E CURTIS, F M MULLANEY AND G RAMSDEN
6 ECONOMICS OF MANUFACTURE
7 MARKETING AND MARKET ACCEPTANCE
Comparison of the cost effectiveness of the injection
moulded racket is highlighted by comparison of manufacturers’ indicated trade prices (source International
Sport and Leisure Exhibition, National Exhibition
Centre, October 1981). At that time the injection
moulded racket (now called the Dunlop Max 150G) was
E32.05 while competitors’ products were noted to vary
between E l 0 and E58 in excess of this figure.
The actual cost of any racket based on carbon fibre is
greater than one based on wood due to a factor of
around 30: 1 in basic material costs. However, from a
financial view point it is advantageous to produce and
sell products with high added-value” and low cost of
conversion from basic material to finished product and
it is here where the injection moulded racket (IMR)
scores. Comparison of the added value for the IMR
with that for a conventional top quality wooden racket
is as follows, taking wood at an index of 100:
The Dunlop Max 150G was launched at press conferences held in London in November 1980. Excellent
press coverage followed both in the engineering and
technical press and also in the specialist sports press
(56).
The racket and its manufacturing process were featured in BBC’s ‘Tomorrow’s World’ in January 1981
and also in broadcasts on industrial news in the BBC
World Service. It was given a Design Council Award in
1981.
Player acceptance has been excellent and the good
playing qualities were exhibited early in the development with the prototype rackets. These qualities are
undoubtedly due to the very satisfactory combination of
weights, balance, stiffness and strength afforded by the
unique construction and the special properties provided
by the use of carbon fibres in a nylon matrix not previously used in sports equipment. It would appear that
the high stiffness of carbon fibre is tempered by the
comparative elasticity of the nylon to give a
‘sympathetic feel’ to the player on ball contact.
One particular point was noted. Players could very
readily change to the new racket even when previously
used to rackets of varying materials and constructions.
Such adaptability is often not possible with a new
racket and it does demonstrate that the new racket
exhibits ‘easy playability’ and is in fact a ‘player’s
racket’.
The racket was used successfully in international
tournaments in 1981.
Added value (index)
Wood
100
IMR
140
In terms of marginal manufacturing cost, calculated
now and in five years time, during which period the cost
of carbon fibre is expected to fall by around 25 per cent
due to the large volume increase in manufacture, the
following comparison is obtained:
Marginal manufacturing
cost 1982 (index)
Marginal manufacturing
cost 1987 (index)
Wood
100
IMR
180
100
160
It will be noted that the cost differential will decrease
significantly.
Further comparisons with wooden racket manufacture are also warranted in view of the Company’s
current commitment to wooden racket manufacture.
Comparisons have been made on the basis of actual
differences or by taking a wooden racket to have an
index of 100 for comparison purposes as follows :
1. Number of separate
manufacturing stages
(actual)
2. Elapsed time for
manufacture (actual),
weeks
3. Value of work in progress
(index)
4. Manufacturing area
required (index)
5. Number of operatives
per 1000 frames per
week (actual)
6. Energy requirement
(index)
Wood
28
10
IMR
11
The new racket and its method of manufacture enable
an industry under pressure from both cost and changing
technology to compete strongly in a world market
sector of increasing importance. With good patent protection the Company should be able to increase its
market share even above the estimates made and, with
the good financial returns calculated, the product and
process promise a sound means of first stabilizing and
then expanding the racket business of the Company.
4
ACKNOWLEDGEMENT
100
70
100
83
22
17t
100
50
It will be seen that the advantage is always with the
injection moulded frame.
* Addcd value = selling price less cost of materialsand bought-in services.
7 This figure reduces significantly as production increases above loo0 units per
week.
9 CONCLUSION
Acknowledgement is made to Mr F. W. Popplewell formerly of Carlton Sports Company (a Ounlop Sports
Company Subsidiary) for his important contribution to
the work described in this paper.
REFERENCES
Leonard, T. What you get in a graphite racket. Tennis, Sept. 1980.
UK Patent Application GB 2 015 886 A
UK Patent Application GB 2 056 864 A
UK Patent Application GB 2 056 863 A
Knight, R. Injection moulding: it’s a whole new ball game. Eureka,
Dec. 1980.
6 Engineering Materials and Design, Jan. 1981.
1
2
3
4
5
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THE DESIGN, DEVELOPMENT AND MANUFACTURE OF A NEW A N D UNIQUE TENNIS RACKET
79
Materials used in manufacture
APPENDIX
Manufacturing equipment
Custing Machine
A. W. Plume Limited,
‘S N’ Economatic low pressure die-casting machine.
Injection moulding machine
R. H. Windsor Limited,
SP30/300 Model.
Die-casting und injection moulds
Designed and manufactured internally.
Pol yurethune dispensing machine
Engineering Services (Urethanes) Limited,
Cannon C7 polyurethane dispensing machine.
Metal Alloy
Eutectic Fusible Alloy No. 17,
Fry’s Metals Limited,
Mining and Chemical Products Limited
Reinjorced thermoplastic
30 per cent carbon fibre in nylon 6.6 (heat stabilized),
Ref. RC 1006.
LNP Plastics Limited.
Polyurethane muteviais
Lankro Chemicals Limited,
Baxenden Chemical Company Limited.
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