From: jon evans
Carbon fibre 101
This section is intended to give you an introduction to
carbon fibres, to help you understand how to get the
best out of them. If you are a complete novice, this
might all be news but hopefully there is something here
for people who are a bit more knowledgeable too.
Carbon fibre… the latest thing! The new wonder material.
People often think that carbon fibres are the latest thing in modern materials
but carbon fibres have been made for a very long time. The very first electric
light bulbs had carbon fibre filaments and the way they were initially made is
not so far off how industrial carbon fibres are made today. Bamboo fibres
were heated to very high temperatures in a controlled atmosphere. These
fibres did not have the high strength of modern fibres and things have
improved a bit in 133 years. In the 1950s, high strength fibres were produced
from Rayon precursors which combined with epoxy resins that were
commercially produced from the late 1940s gave the first insights into this
remarkable material.
Modern fibres are produced from other high carbon precursors. Advances in
production have mostly focussed on improving the fibre quality and
consistency, production rate and energy use through things like heating the
raw materials directly using microwaves. Carbon is a miracle material and the
precursor is not massively expensive, so the only thing that is stopping it
being used to make nearly everything is cost. The cost is closely linked to
energy prices and like all commodities, demand.
Carbon fibre production is not on the scale of some materials like steel or
aluminium so single big projects that use carbon can directly impact on
wholesale carbon fibre prices. When the Airbus A380 project started up they
used so much carbon fibre that it altered carbon fibre prices in Europe.
Demand stimulates investment in production, which in turn drives the
wholesale price down. As carbon becomes more affordable it suddenly makes
commercial sense for designers to specify it in their products which again
increases demand and drives prices up again. In some cases carbon fibre is
used because it is the only material with the strength to weight ratio to do the
job but in other circumstances the high strength to weight can mean that
reducing weight whilst keeping strength can result in lower operating costs or
performance improvements that outweigh the high material and
manufacturing costs. The current pressure on carbon fibre production is
production of wind turbine blades. The light weight, high strength and massive
stiffness of carbon fibre compared to other materials make it very attractive as
a material for making wind turbine blades. The market is growing more
quickly than the factories can increase production of carbon fibre. Not only is it
a relatively straightforward material to mould into complex shapes like
aerofoils but it’s very light weight means that in a wind turbine it can start to
make useful power at much lower wind speeds than sails made of heavier
materials. This means that the output of a wind turbine with carbon composite
turbine blades can produce more power than one fitted with heavier turbine
blades over its lifetime, which outweighs the materials cost.
There are three main groups of carbon. These groups are 'high strength',
'intermediate modulus' and 'high modulus'. Some people also talk about very
stiff fibres as ultra high modulus but these are really in the high modulus
group. High strength fibres make up 99% of carbon fibre production and is the
type of fibre used to make nearly any off the shelf fabric. It is very strong and
very stiff compared to other materials. At
the other end of the scale are high modulus
or high stiffness fibres. These fibres really
don't want to change their shape and as a
result stay the same shape pretty much, no
matter how much you load them until they
break or more typically shatter. This is not surprising when you think about
other high modulus materials like ceramics. Sometimes stiffness is the most
important thing though and if you want stiffness, high modulus carbon is the
material for the job but it achieves this at the expense of ultimate strength. As
a result high strength (industrial) carbon is stronger than high modulus
carbon, hence the name. The third group is my personal favourite, You would
imagine it is stiffer than High Strength carbon and perhaps a bit stronger than
high modulus but these fibres are by far the strongest fibres and with the
exception of carbon nanotubes which have now become available are the
strongest fibres on the planet. They are also stiffer than high strength fibres,
which is why they are the fibre of choice for the most demanding applications
such as the wings of fighter aircraft such as the Eurofighter.
How is carbon fibre actually made?
Carbon fibres are made by taking a high carbon precursor, stretching or
spinning it and then heating it in an induction furnace to burn away the
impurities until the remaining material is nearly pure carbon in a process
called pyrolisation. The precursor is usually polyacrylanitrile (PAN) or pitch (a
product of oil distillation). Carbon itself, at high temperatures, can easily
combine with oxygen in the air to make carbon monoxide or carbon dioxide,
so the atmosphere inside the furnace needs to be controlled. The resulting
fibres are very thin and can be added to other similar fibres to make up a
bundle of fibres that is collectively called tow. This would be known as
industrial carbon fibre or standard modulus carbon fibre.
An example of an industrial carbon fibre you can buy from me is Zoltec Panex
33. Nearly all carbon produced is industrial carbon. It is then made into tow or
varying thicknesses. The thickness of the tow is described by saying how
many thousands of fibres makes up the tow. 12K tow is made up of 12000
fibres and is 12 times fatter than 1K tow. Tow is the first point at which carbon
can be realistically used to make things through processes like filament
winding and pultrusion, although most of it is made into various weaves of
cloth, structural bonded fabrics or knits.
For some fibres the initial pyrolisation is just the beginning. If you look at the
industrial fibre, it is not a smooth cylinder of carbon but viewed under a
microscope has a rough fissured surface. As you move towards the centre the
carbon has less irregularities/fissures and as a result it is denser. The fibre
can be processed to remove the lower density outer parts of the fibre to
produce a thinner more perfect fibre. This means that a lot of the original fibre
is lost and as a result the cost per volume is magnitudes higher.
The picture below shows an electron micrograph of intermediate modulus
fibres. They have a smoother surface than industrial grades. They are
stronger and stiffer. This means that you need less fibre to have the same
strength. Less fibre means less resin, so the overall weight of something
made with Hexel IM7 or IM9 have the potential to be much lighter than
something made of industrial high strength carbon.
Further processing can produce very stiff fibres from the inner cores of the
fibres. These high modulus fibres by their nature have the lowest yield per Kg
of PAN, use the most energy and time processing to make. As a result they
are rare and used sparingly. Even when you see something claiming to be
‘high modulus’ it may not be what it seems. Firstly it is common practice to
just add a bit of strategic higher modulus fibre here and there but brand it high
modulus, secondly intermediate modulus carbon fibre is also often described
as high modulus because it is higher modulus than industrial high strength
carbon and there is no numerical cut off that says a when an intermediate
modulus carbon becomes a high modulus carbon.
The exact make-up of the precursor, temperature cycles during pyrolisation,
surface treatments etc are specific to each company, which is why there is
such enormous variation in fibre performance. Moreover the quality control
process or even the physical specifications vary enormously from
manufacturer to manufacturer. Some use actual batch data, some produce
some specifically in labs. Generally aerospace grade fibres have the highest
quality control process with quite a bit of paperwork to identify batches and
certify them within the stated parameters.
A general trend is that when carbon fibre becomes processed to become
stiffer, the ultimate tensile strength gets lower. This means that very high
modulus fibres are more brittle and also not as strong as standard modulus or
industrial carbon but they can be several times stiffer.
It would seem you can’t have your cake and eat it… Or can you?
Industrial carbon is already a miracle material in terms of its strength, stiffness
and weight compared to other high tech materials. In many cases additional
processing to make fibres with more stiffness is not a problem as carbon is so
strong, a carbon that is not as strong still makes something plenty strong
enough but there are a range of speciality fibres that buck the trend, These
are characterised by the Hexel intermediate modulus fibres. They are much
stiffer than standard industrial carbon fibres and immensely strong. Although
some manufacturers might describe it as High Modulus, these intermediate
modulus fibres are actually the strongest fibres available, even stronger than
high strength fibres. The reason that intermediate modulus fibres are
important is because they unlock some of the best strength: weight
composites available today.
Fatigue and stress cycles.
Different materials respond in different ways to forces being applied to them In
all practical terms if a steel structure is not caused to flex past a certain point it
will last indefinitely. If it is taken past this point, the crystalline structure is
changed by a process called work hardening. If you repeatedly bend a spoon
or something like a metal coat hanger, it suddenly looses all its strength and
just lets go. Other materials like aluminium lose strength and work harden with
the slightest stress or strain. Even time hardens aluminium and it becomes
weaker. This often means that structures, particularly lightweight structures,
often have a specified working life or are made with a higher factor of safety to
give them a more reasonable working life.
Although aluminium and its alloys is an extreme example of a material that
loses strength easily, most materials lose their strength as they have forces
cycled through them. There are some exceptions though, bamboo and wood
have the same strength after millions of cycles. With carbon fibres it was
initially thought that they too were immune to flexing and retained their
strength no matter how many times they are cycled. It has been found that
higher modulus fibres are prone to failing and appear to lose some of their
strength with time. It is still generally accepted that industrial grades and
intermediate speciality fibres are able to keep most if not all of their strength
with repeated stress cycles over time, which means that composite carbon
fibre materials may be limited only by the resin that forms its matrix.
Anisotropy.
Carbon is unusual in that it is anisotropic. This means that its strength and
modulus is directional. You get 100% of it along the fibre but pretty much
nothing at 90 degrees to the fibre. This means that you often need to design
the component to work with carbon fibres rather than just copy a metal part
where the metal part often takes advantage of the isotropy of metal. If a force
is just going through a structure in one direction, carbon can be many many
times lighter than a metal component for the same strength but the more
complex the forces being applied, the more fibres need to be added at
different orientations, which makes it heavier. The truth is though that you are
unlikely to ever get a fabric woven with the fibres going exactly where you
want them, so making something out of tow and adding fibres only where you
need them will result in the lightest structure you will be able to make,
regardless of the technology available to you. It always helps though to think
about how the forces might move through your structure and make the fibres
line up with those forces, keeping the fibres as straight and flat as possible.
Effect of component weight with varying % resin.
The main thing to consider here is that the physical properties of the matrix
and the fibre are very different. One way to think about it is to pretend that the
fibres are steel rods and the matrix is latex rubber. If you had a big block of
rubber with one steel rod in it, the characteristic of the block is pretty much the
same as the latex rubber. If the block is nearly completely steel bar, with a bit
of latex, the properties of the block would be pretty much the same as the
steel. Bearing in mind the resin is there to transmit forces between fibres and
not a lot else, having more resin than you need just makes things heavier.
Carbon fibre is typically 1.8g/cm3 and epoxy resin is typically 1.1 – 1.3 g/cm3,
so lets look at some examples about how much a standard bit of carbon might
weigh if we are good or bad at controlling resin content.
If you think about a typical 60%:40% carbon-epoxy unidirectional composite
with a physical volume of 1cm3 It would have 1.08g of carbon and of 0.47g
resin, so a total weight of 1.55g.
Now imagine the same amount of carbon but with the theoretical minimum
amount of resin, 0.19g, for a total weight of 1.27g. This is a significant weight
saving for a no reduction in strength. It would be impossible achieve such a
low resin content but unless methods are used to control resin contents, the
percentage of resin can typically be as high as 70% even if the resin is not
cold or in the early stages of gelling.
In wet lay up of carbon using epoxy additional devices need to be considered
to control the resin content and push fibres together.
At 30%:70% carbon to resin, using the same amount of carbon as in the first
example 1.65g of resin would be used to give a total weight of 2.73g for the
same strength. This is twice the weight compared to the theoretical minimum.
For a large item this represents kgs of additional matrix that is not adding any
additional strength as a side effect of this, the overall composite starts to
behave less like the carbon and more like the matrix. This is why when you
look at the data sheets for the fibres there is a tensile strength and modulus
for the fibre and different values for the typical composite.
Unlike knits and structural fabrics, woven cloth passes under and over other
fibres as a result there are much bigger gaps due to surface irregularities that
need to be filled with resin. If pressure is not applied the fibres are not likely to
lie particularly flat too so the amount of additional resin can quickly get out of
hand.
If you are going to the trouble of using high performance fibres you also need
to go to the trouble of controlling the resin content.
Resin for Carbon fibre.
Carbon fibres provide the strength of a composite but the thing that holds the
fibres in place is resin. There are a massive range of modern adhesives but
one group of thermosetting plastics outperform the others by a significant
margin. In order to get the full potential from your fibre, even if it is basic
standard modulus carbon, you will need to use epoxy resin. As a matrix it
develops a much higher density of cross links than other types of resin and
that makes it about 5 times more tenacious than the next best performing
resins Vinylesters. Polyester resins are poor and if you want to use carbon
with polyester, it will fail well before the fibre. You may as well use glass
reinforcement. One of the adhesives that is right out for use as a matrix for
carbon fibres is cyanoacrylate or super-glue style glues. These resins have a
very low bulk modulus and shockingly poor shear strength. The force that the
matrix needs to deal with in a composite is shear. Cyanoacrylate is not
suitable for use with carbon fibres.
Pre-preg
One way to optimise the wetting out of the fabric with the resin is to infuse the
carbon with resin at the factory. This can then be rolled out to get an optimal
resin/carbon ratio. Fabric sold in this way with the resin already in the fabric is
called prepreg or pre-preg, which is short for pre-impregnated. This means
that the resin needs to only set when you want it to, rather than cure at room
temperature, An ambient cure resin such as those sold in yacht chandleries
for boat repair would not work because it would set before it left the factory.
Instead the resins are designed to have an elevated temperature to initiate the
chemical reaction. The impregnated carbon fibre is kept in a freezer until it is
required and can remain workable for days at normal temperatures. This
means that large complicated structures can be made before the mould is
heated in an oven. Once cured at temperature and under pressure of some
sort, the finished item is post cured which means cycling the temperature to
120º or more for a period of hours to relieve internal stresses caused when
the resin cured.
This approach is rarely possible for home users for several reasons: If you are
buying this type of fibre and it is prepreg it is difficult to find any second hand
that is usable. Buying dry fibre is bad enough but if the resin is duff you are
throwing away money. If you are trying to buy it new, it is unlikely you will be
prepared to buy 500Kg at a time… your partner is never happy to come home
to find her fish fingers thawing on the side so you can store a spool of pre
preg tow (or the whole contents of her chest freezer so you can get a part roll
in). High temperature cures and high temperature post cures are much harder
to achieve, Your domestic oven just isn’t accurate enough.
Invariably you will be using ambient cure resin. This sets off at normal room
temperatures and the modern bodger section will go through some tricks to
get the results you want.
Ambient cure epoxy resins.
Ambient cure epoxy resins come in lots of different formulae. When we talk
about granulated sugar it is made of sucrose, The term describes the
chemical, in the same way that table salt tells us it is sodium chloride. With
epoxies, you are talking about a group of materials. They all do a similar sort
of job but have quite different formulations and chemistry. The variables the
chemists mess about with are to do with the viscosity and cure time. Apart
from that the resins can be further modified by the chemists or the user by
adding various things.
If we look at some basic resins they may be general purpose or formulated for
sticking things onto wood, they might be laminating resins, they might be
infusion resins or they might be adhesives.
General purpose/sticking things to wood types of resin have been developed
because epoxy resin is a useful material in the marine industry and leisure
boating. As a carbon fibre enthusiast, this may well be your most economical
route to get epoxy resin, Go to any boat yard with some clean pots and you
will find someone with some big tubs of epoxy. These resins work well with
carbon and have a slight softness to them that makes them less brittle and
unlikely to delaminate through shock or impact.
Laminating resins are quite a bit runnier than general purpose resins and can
have quite slow setting times, high working times before they set. As they are
runny they wet out the fibre well and can be pushed around with a spreader
easily. These resins benefit from post curing at about 70º C.
Infusion resin is a specialist resin that is very runny. It is used by laying out
the fibre and then drawing the resin through the fibre under vacuum. Like the
laminating resin, its properties improve with post curing.
Adhesives as very much like general purpose resin but they have additional
fillers added to make them quite thick and buttery. The main additive to do this
is called silica Gel, which does not add any strength to the epoxy but it does
make it thicker and less likely to slump. This thick consistency makes this type
of epoxy hard to use with carbon because it does not wet the fibre out very
well. You can make any epoxy resin thicker and less likely to slump by adding
silica gel. The maximum is generally considered to be 1% by weight. It is best
added to the resin component in a sealed container and placed somewhere
warm for a few days. This enables the colloidal silica to wet out properly and
impart its properties. If you vacuum your resin prior to using it, to degas it, you
will be able to achieve the same effects much more quickly.
Apart from fillers to make resin thicker, you don’t have so many options on
making it runnier. Some people add solvents like acetone to make the resin
runny but you will need to get a fair bit of heat on to evaporate the solvent
otherwise you will end up with pockets of acetone in the epoxy. This can
make the resin micro-porous and is not recommended.
All epoxy resins tend to be a bit more viscous than polyester or vinylester, so
sometimes to wet out a fabric quickly, it sometimes helps to apply a bit of
heat. If you have an air bubble you can get the hair dyer on it to apply a bit of
local heat. This will make the resin much runnier and can sometimes mean
that resin that is gelling can be made runny enough to wet out a fibre.
Generally It helps to use a diffuser on your hair dryer, as the air jet can be
quite strong and you don’t want to be blowing a pot of epoxy onto the Wilton
carpet. If the hair dryer belongs to your wife or girlfriend (or in the interest of
equal opportunities your husband of boyfriend) wrap the bits you are likely to
hold with cling film or insulation tape. Epoxy gets everywhere and if you
attempt to clean it off with solvent you are likely to damage painted or plastic
things. Equally it is often a good plan to wrap your mobile phone with cling film
too before you start to avoid impulse answering that covers it in glue.
Although cling film has very few uses in terms of being a release agent (as
most of you will have tried at some point), it is helpful in protecting things.
Bear in mind that a hair dryer or convection heater is about the limit. Ambient
cure epoxy resins will not want to be doing much more than 100o C and in
heating it, you will roughly double the reaction speed for every 10 o C
temperature rise. This will mean that the resin will react more quickly and
could add its own heat through the exothermic reaction of the resin and the
hardener.
Controlling the speed of cure of epoxy resins.
It is probably a good time to explain how epoxy resins work. With Polyester
and Vinylester resins, the monomers are mixed with volatiles and an
accelerator. The accelerator is usually added by the vendor prior to sale. The
user adds catalyst as required. If more catalyst is used the reaction will be
faster and if the catalyst is reduced the reaction is slower. In addition to this if
the temperature is varied, the rate of reaction follows the same 10 degree rule
of doubling.
Polyester and vinylester resins do not have anywhere near the shear strength
or number of cross links that epoxy resins do. Acrylics such as cyanocacrylate
are really not a good plan for composites because they have notoriously poor
shear strength, the very force they will be subjected to in a composite. If you
were using Panex 33, there may be times when a vinylester would be useful
such as a large infusion process but on the whole epoxy is the way forward
and for the Hexel fibres I have, it is the only realistic matrix to consider.
With epoxy resins there is a resin and a hardener. Generally the resin lasts for
years, even though the shelf life may be stated as minimal but the hardener
has a definite shelf life and is often the more expensive component.
Harderners and ratios for hardeners are specific to the resin and generally
hardeners are not interchangeable between brands or sometimes resins from
the same manufacturer. Unlike resins that use catalysts, the resin hardener is
a complimentary chemical and there is an exact amount of it required to set
the resin properly. Too much or too little hardener for the amount of resin will
result in a less effective resin. This may not seem too serious for the most part
but if you are using IM9, which is one of the strongest commercially available
carbon fibres, you will already be at the top end of the performance range of
ambient cure resins and you will want to get it as spot on as you can. For that
reason I would suggest using mini scales such as those shown in the picture.
Be aware that these scales are often used by drug dealers, so if you are
telling the staff in Maplin that you need the scales with 0.1g increments
because “you are expecting a 25kg delivery of resin this afternoon” expect to
be arrested shortly afterwards.
Measuring accurately by weight is important but mixing it thoroughly is
important too. When you are sure it is mixed well, it can be a good plan to
pulse it in a vacuum chamber. This takes the gas you have just mixed in back
out and also makes it quite cold. Once you have mixed the resin you can add
microfibres or other additives, although in the case of colloidal silica it often
helps to have added it to the resin some time before. Once you have you
resin ready to go get it spread out. A shallow flat container is better than a
smaller deeper one. This will give you more working time. As soon as you
have mixed your resin, it will start to react. If the temperature is too high and
the container has a lot of resin in it, the resin can get very hot indeed and
even catch on fire. For this reason you should not use glass or polystyrene
containers. Do not under any circumstances attempt to alter the cure time by
changing the hardener to resin ratio. This is one of the best ways to start a fire
or end up with a resin that never sets.
Here is a picture of a home made degasser. It is basically a fibreglass pot
moulded in a plastic mixing bowl from a pound shop with a big chunk of
Perspex I took out of a skip. The seal is a large O ring. For my main line of
resin processing, I have a much bigger box but this was really handy for
smaller quantities and being able to look at the resin as you apply the vacuum
really helps. The fittings are like those on washing machine valves and the
hoses are washing machine hoses. These work well in vacuum and are cheap
and easy to get hold of. I use these fittings on lots of my projects from the
biggest to the smallest. The degasser is really useful for getting air out of resin
and making sure that things you have added are wetted out properly.
Select the speed of the resin system when you buy it. Some epoxies such as
Araldite rapid, which sets in a couple of minutes, does have its place in
tacking things in place but generally you would want to get the slowest resin
system you can get your hands on. It is easier to apply a bit of heat using a
lamp or hairdryer than it is to try and cool a faster setting resin. Working with
tow in particular can be slow work and this often requires good lighting. In the
case where incandescent lighting is being used, be aware that the dark
carbon will absorb infrared off the light and get a lot warmer than lighter
surfaces.
Storage of the resin in cold places can result in crystals forming, These will go
if you gently heat the resin. Hardeners need to be in air tight containers and
last longer if kept out of sunlight.
When the resin cures there is also some interaction with atmospheric
contaminants and although there is not air inhibition like there is with polyester
or vinylester, the surface of the resin is often coated in amines that will act as
a non-stick barrier to further laminations. If the resin has cured enough to go
hard, unless you have used a peel ply, you will have to remove the amines.
These can be hard to sand off because they clog up sand paper like a wax
but they can be washed off with hot soapy water or a suitable solvent.
Post curing resin.
Resins take a long while to complete their cross linking and in doing so, there
can be some internal stresses set up. There is very little shrinkage in epoxy
resin but all the same the mechanical characteristics of the resin can
generally be improved by post curing. With hot set resins the post cure
temperatures are in the order of 120oC and these need to be cycled to quite
specific times. Part of the reason for this is because there is quite a big
change in temperature from the cure temperature to normal operating
temperature and there is obviously differential expansion of the resin and the
fibre. With ambient cure resins the temperature is much more modest, in the
region of 70oC, which can be achieved using a heater and some bubble wrap
or even some clear plastic on a hot day. Post curing ambient cure resins is
achieved in a couple of hours at this sort of temperature.
Cleaning brushes.
Unlike polyester resin, where a quick and regular swoosh in acetone can
mean your brush lasts for ages, you have a couple of options with epoxy. You
either:
1 Use a stick or spreader to apply it and wipe it clean with a rag or tissue
before it sets
2 Use disposable brushes
3 Clean your brushes using what I would describe as the homeopathic
approach. Homeopathy works on a number of dilutions and if you use
acetone in particular, if you wash out a brush in virgin acetone, it may
still go rock hard. In fact you may well see solid bits of cured resin in
the bottom of the container some time later. By having several
numbered pots containing your solvent, you swoosh your brush in the
first and quickly dry it in a tissue and repeat in each container. You will
need at least 4. As the remaining amount of resin is diluted so much in
each subsequent container, there is a good chance on pot 5 that the
brush will be pretty clean… If you are not sure, you can always put it in
a Tupperware pot in the fridge as this will slow down the rate of cure
anyway.
On the solvent front, lots of people use acetone. Avoid using nail varnish
remover as this often has all sorts of oils added. Acetone is not the best
solvent for epoxy. Xylene is the solvent you really want. You can get it in litres
or gallons from companies like Dacrylate. If you do buy from them, the solvent
you want is called R5. Xylene is also a big component in more traditional
cellulose paint solvent, although many of these solvents are hard to get hold
of now that they are moving on to water based paints for vehicle refinishing.
Cleaning you hands using solvent is a really bad plan. Epoxy resins are pretty
toxic and using solvents often enables the epoxy resin to be tracked through
your skin. It might be a better plan to use a barrier cream with gloves and
wash your hands with soap and water. Even cleaning up things with acetone
or xylene will give gloves a hard time and will often go through them, so it is
often better to use tweezers or forceps with cotton based kitchen roll and
solvent. If you get epoxy on your hands and want to get it off, it can be better
to just use a bit of kitchen roll and no solvent.
All of this will mean that you will often end up with a fair bit of contaminated
tissue with resin on it and some with resin and solvent, particularly if you have
used tissue and solvent to clean off excess on your project. I tend to keep a
plastic carrier bag or two near where I am working as it is easy to get bits of
tissue with resin on it all over the place.
On the health and safety front, people are aware of the issues with polyester
resins. Generally your eyes are watering with the styrene (which actually gets
absorbed in the water lubricating your eyes) to the point where ventilation is
self evident. Epoxies on the other hand are not so smelly, a slight almond
aroma perhaps but there are still volatile toxins, particularly if you are doing
the hair dryer trick. They can really hurt you though. I have taken out my liver
on a couple of occasions applying gallons of resin working in boat hulls
without a respirator. This often results in very dark urine and should be
avoided. On-going exposure can also result in sensitivity to epoxy that is often
expressed as a rash on the wrist where the shirt cuff ends. Sensitivity, once
acquired is permanent. Some epoxy resins are more toxic than others.
A final note to those of you with hair. I don’t want to brag but I have loads of
hair and there is a tendency to unwittingly touch your hair when you have glue
on your gloves. Sometimes it is impractical to wear a hat (and you do get
funny looks laminating with your bowler on) so application of a bit of
Brylcreem or similar hair oil means that you don’t end up pulling chinks of your
head out at the end of the day. It will just comb out. Another option if you have
hair or long hair is to get a shower cap and perforate it liberally to avoid
sweating, It must be said a bit of Brylcreem is all together much more rakish
than a puce shower cap.
I hope you have found this instalment interesting. It is all original, rather than
being knocked off from the web, so if you see glaring errors or feel that there
is a need for more detail on one aspect or another, do let me know.
The next instalment is about low tech ways of getting high tech results and is
called the Star Ward Bodger.
All the best with your projects
Jon Evans
From: jon evans
It was always my intention to build up a modest clientele to pass on my surplus carbon fibre
to, without involving ebay and as such I am writing to you directly to let you know what I have
available so you can get your tow at the best possible rates.
I have also been writing some articles about carbon fibre and about some of the interesting
ways people have been using it that I will be sending out over the next few months to give
people ideas about how to make super light carbon reinforcement, cheap and easy ways of
controlling resin content and generally how to get aerospace results without a million pound
budget. I have attached an introduction to carbon fibre, which I hope will contain some
information you will find interesting. Sadly I am still too busy to be setting up a website for it all
but I am still committed to enabling people like yourself access good quality materials in small
quantities.
Obviously I recognise that although you have bought some carbon from me, you don’t
necessarily want to have loads of emails from me. This is a personal email, so there is not an
automatic link to unsubscribe, but you can drop me a quick response to say you are feeling
harassed by being contacted and I won’t contact you again.
As always I am making materials available that I use myself. I currently have 4 types of
reinforcement fibre available and I have summarised these in a table below.
Manufacturer
Fibre name
Type
Fibre size
Tensile
strength
(MPa)
Modulus (GPa)
Zoltec
Panex 33
High Strength
carbon
48K
3800
228
Hexel
IM7
Intermediate
modulus
carbon
12K
5670
276
Hexel
IM9
Intermediate
modulus
carbon
12K
6140
304
Tejin Industries
Twaron
2200
High modulus
para aramid
6K
3176
108
In a nutshell the Zoltec fibre, is a high strength fibre being offered at a low cost in 100g
spools. It has 10X the cross sectional area of IM9 so you get a lot of carbon for your money. It
has physical characteristics in-line with 99% of all carbon produced. You can split the tow to
make thinner bundles as it is not twisted/
The IM7 and IM9 are speciality fibres that are considerably stronger than high strength fibres
and also considerably stiffer too. As a balance of strength and stiffness, these fibres are some
of the highest performing fibres available. IM7 is an aerospace quality fibre and spreads well
to make very light coverings (35gsm unidirectional) as it has a very light size. IM9 is made to
an industrial standard but was until relatively recently one of the strongest commercially
available fibres.
Twaron 2200 is a fibre that is very similar to Kevlar 149, which was developed to make the
new generation ballistics vest. A very light weight fibre, with excellent abrasion, shock,
electrical and heat resistance. One of the handy things about para aramids is that they are
lighter, stronger and less prone to fatigue than glass fibres but completely transparent to radio
waves and microwaves, unlike carbon, which opaque to these signals. If you want abrasion
resistance or strength in areas near your radio receiver aerial, this could well be the material
you want. Specification sheets are available for any of the fibres.
Prices are as follows:
Zoltec Panex 33 100g spool
£8.00
Hexel IM9 12K
20M
£4.90
50M
£9.00
100M
£17.00
320m
£35
Hexel IM712K
20M
£4.90
50M
£9.00
100M
£17.00
380m
£35
Twaron 2200 100M
£6.50
Add-ons
I have called these ‘add-ons’ as they are zero profit items for me. If you buy any of the above
fibres you can add these items. It will be £2.70 to post these items because they are bulky. I
am not keen to sell them as items on their own.
Micro-fibres (cotton) (50g)
£3.50
Micro-light filler (10g)
£3.50
Laminating resin (130g net) choice of hardener speeds
£5.50
Peel ply (Per Metre Square)
£3.00
Cotton micro-fibres are generally used with epoxy resin to make a structural bonding paste
(bog) especially for bonding wood using epoxy fillet joints but it can be added to other resins
to make a structural material.
Microlight filler is a very low density additive to make a super light filling paste that is easy to
sand. It would also be useful for low weight low strength items.
Epoxy laminating resin. This is a 130g pack of resin that has 4 hardener speeds from extra
fast to extra slow. A great general purpose ambient cure resin, which is less toxic than WEST
or SP resins. I made this available primarily for the rolls of £35 intermediate modulus fibre and
100g spools of Panex 33.
Postage is always at cost. Tow up to 100M is £0.85 anything over that and less than 750g in
weight is £2.70. The Zoltec Panex 33 100g spools are £2.70 but you could get other materials
sent as well. All my stuff is sent first class and usually on the same day. You will always get
an email to confirm dispatch.
Payment by paypal or direct bank transfer.
If you place an order by 18th August you will get an additional 10M spool of IM9 free of
charge.
As always I am available to answer carbon fibre related questions via email and will send
pictures of products or data sheets as required.
Kind regards
From: jon evans