Insight into Reverie & autoclaved
composites
By
Simon Farren
Presented at US Distributor Sector 111
11th April 2009
History of Reverie
Founded in May of 2000 by Simon Farren, previously on the
management team for engineering the Lotus 340R into a
production reality.
Created to offer affordable autoclaved composites to clients.
We design and manufacture a range of quality parts for track
days and professional race team consumers for distribution via
worldwide dealers emphasizing Lotus enhancing products.
What is Carbon Fiber?
• Carbon fiber is a synthetic thread (poly-acrylo-nitrile, rayon or pitch)
heated in an argon atmosphere where carbonization occurs.
• Carbonization temperatures can be altered to produce different
strengths and modulus of the carbon fiber.
• The very fine carbon threads are left as long fibers along the roll
length (UD fiber) with strength in that axis only or woven together
to form a fabric cloth resulting multi-directional strength.
• Carbon fiber can be left dry or pre-impregnated with a thermoset
resin to make it pre-preg.
• The cured resin gives the finished part its molded shape, stiffness,
rigidity and protection of the stressed fibers.
History Of Carbon Fiber
• First developed in 1958 by Dr. Roger Bacon in Cleveland, Ohio,
fibers were manufactured by heating strands of Rayon until they
carbonized. This process was inefficient. The resulting fibers
contained approximately 20% carbon, which resulted in less
strength and stiffness properties.
• Early in the 1960’s, a process was developed using poly-acrylonitrile, as a raw material. This produced a carbon fiber, containing
55% carbon, compared to 93-95% today.
• Early in 1969, Carr Reinforcements in
England first wove a carbon fiber fabric.
Why Composites?
• Carbon fiber is typically 3 X stronger than steel yet 4 X lighter.
• It’s 7 X stronger than 6061 alloy and 2 X stronger than tensile
modulus, with similar weight.
• Tensile modulus (stiffness) ranges from 230 GPa to 441 GPa and
tensile strengths range from 3.5 GPa to 5.9 GPa.
• The ultimate strength and the breaking strength are the same for
carbon fiber. Steel yields prior to reaching it’s ultimate strength.
• There is no yield to carbon fiber, so parts can be repaired with
lamination to the same shape easily.
• Kevlar has a yield strength 7 X higher than steel and about 4 X
lighter than steel. Bullet proof vests are manufactured with it.
Uses Of Composites
• Carbon fiber’s weight, stiffness and strength
benefits make it widely used in boat building,
aerospace, motorsport and sporting goods.
• Other fibers like Kevlar, Dyneema and fiberglass
can be used independently or incorporated
into laminates.
• Resin systems are selected to give the required toughness,
temperature range & protect the stressed fibers from damage.
• Modulus & strengths of fibers, thickness and direction of fibers can
be varied to give the properties required for the part.
Autoclave Processing Pre-Pregs
We process thermoset epoxy pre-pregs using one of two
pressurized & temperature computer controlled autoclaves, which
are used by Formula One teams.
The use of elevated pressure in the autoclave facilitates a high fiber
volume fraction and low void content for maximum strength.
Autoclave Processing Pre-Pregs
The UD pre-preg fiber or woven cloth is hand cut or done by
machine into the shapes and orientation required for each ply of
the component, which form the kit of parts.
Autoclave Processing Pre-Pregs
A mold tool, either male or female, is required to obtain a good
surface finish on one side. Both a male and female compression
tool is needed for a dual molded surface.
First the tool has a release agent
applied to it’s surface to avoid sticking.
Autoclave Processing Pre-Pregs
Each section of a ply is hand placed into the female mold or over
the male mold in the orientations required by the drawing.
Autoclave Processing Pre-Pregs
Some components require the molds to be multi-pieced and
overlapping joints in the pre-preg are often required.
Autoclave Processing Pre-Pregs
Once lay-up is complete, a layer of thin release film (approx 15
microns) is applied over the surface of the pre-preg, where the
vacuum bag may make contact. This allows the breather layer or
bag to release from the cured composite surfaces.
Autoclave Processing Pre-Pregs
A polyester breather fabric layer is then applied to the outside of
the mold and where possible across the component surface. The
purpose of this fabric is to allow a full vacuum path over the
complete mold and component area.
Autoclave Processing Pre-Pregs
Vacuum bags are applied. They can be a single sheet sealed with
tacky tape against the mold’s outer perimeter on a male or female
tool or a tubular envelope bag sealed at both ends to vacuum the
complete perimeter of the mold tool. Any internal tubular bags or
molded latex bladders can be left out of one or both ends of the
tubular bag. A vacuum breach fitting goes through the bag surface
to allow air to be removed.
Autoclave Processing Pre-Pregs
The air is slowly sucked out by a very powerful vacuum pump down
to 5 Torr. The pre-preg resin matrix layers are forced together onto
the mold surface at nearly one atmosphere (14.7 psi approx). As
the air is removed the vacuum bag is carefully manipulated to
ensure it does not stretch too tightly over features.
Autoclave Processing Pre-Pregs
The component is under full vacuum, any internal tubes or bladders
open to atmosphere will be exerting 14.7 psi pressure internally.
The mold is now ready for its thermo set process either in an oven
to cure at 14.7 psi or in an autoclave to cure at up to 100 psi. The
greater the pressure the lower the void content and the higher the
strength and greater surface finish.
Autoclave Processing Pre-Pregs
Once in the autoclave, the vacuum bag is connected to a vacuum
line; a steel wire reinforced line which will not collapse under
pressure. Once the autoclave reaches 14.7 psi, the vacuum circuit
can be externally vented to atmosphere or left connected to
remove volatiles. Most of our component pre-pregs cycle at
temperature for 90 minutes at 120°c or 248°f.
The pressure used depends on the quality of the mold, if the
component is monolithic or
features a core material such
as foam or honeycomb.
Autoclave Processing Pre-Pregs
Once the cure has finished, the mold and component are left to
cool. The bagging film is removed and the mold unbolted, if multisectioned. The component is carefully released with plastic
wedges. The component is now ready to be trimmed to size,
secondary bonded and polished or sanded for paint.
Product Design @ Reverie
Identifying a market niche for a new product, either from
customers, dealer feedback, demand or via our own research.
Each product design is optimized for strength/weight and shaped
within constraints of packaging and aerodynamic performance.
Materials selected by experience, or where required by
mathematical analysis using either hand calculations or
computerized FEA.
Passionate about improvements
Product Design @ Reverie
Products are designed on CAD where packaging requirements and
draft angles can be checked and amended before machining.
Products are prototyped and tested at low cost to prove design
performance; these results are factored into future design
enhancements.
Design to Production @ Reverie
Male patterns from foam or clay are either handmade or CNC
machined from CAD data out of aluminium block or solid epoxy
tooling slabs, which are bonded together to form the cubic block.
Design to Production @ Reverie
Once a male pattern is available, any split lines required for
undercuts can be defined by removable weir walls at 90˚ to the
surface featuring dowel location holes to ensure alignment.
A mold tool can then be hand laid from the pattern with weirs in
carbon fiber and autoclave cured .
For low volume projects, sometimes a high temperature GRP hand
laminated tool is produced.
Tools can also be machined direct from alloy.
A layup drawing is then produced
for the laminating shop.
Reverie In High End Motorsport
WRC
WSB
FIA GT
AMLS
Why Choose a Reverie Part?
• Established reputation for high quality.
• Exceptional design and product testing.
• Autoclaved manufacturing ensuring
high fiber to resin ratio and very low voids.
• Manufacturing controlled on-site.
• Use the highest quality Cytec pre-preg materials.
• Excellent customer service, technical data and help.
• Chosen by some of the best engine builders and race teams.
• Passionate about continuous and constant improvements and
enhancements.