Hi,
I’m new to this forum and this is my first thread. My question is
We heat the Carbon fabric to 100°C before use, Why is it required? When i asked , people said carbon absorbs moisture. Is it true?
I do Closed die Moulding of GFRP, What i observe is , after curing the part (Glass Polyimide), the cured part get stuck with the Female mould.
Does GFRP explans at heigh temperature. The Max xuring temperature is 300[COLOR=black][FONT=Arial]°C.[/FONT][/COLOR]
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[COLOR=black][FONT=Arial]Thanks in advance[/FONT][/COLOR]
[COLOR=black][FONT=Arial]Regards,[/FONT][/COLOR]
[COLOR=black][FONT=Arial]M Vignesh[/FONT][/COLOR]
yes, glass expands and contracts more than CF. I’ve never heated CF to get rid of moisture, but on aramids it seems a bigger problem.
The max curing temp is quite high, what kind of resin do you use? And what kind of release?
With Glass i use Polyimide, Cure temp of 300[COLOR=black][FONT=Arial]°C[/FONT][/COLOR]
[COLOR=black][FONT=Arial]I use FREKOTE - 770 NC. Some times part get stuck with Female. Any better suggestions from you for Release agent for 300[COLOR=black][FONT=Arial]°C.[/FONT][/COLOR][/FONT][/COLOR]
Carbon fiber doesn’t absorb moisture, but the sizing applied to it can be affected. I had heard of some part manufacturers heating their carbon fabric before infusing them to create a better bond between the fiber and resin (they validated the practice by producing higher interlaminar shear strength data). I’m not sure if a 100C heat treatment would burn off the fiber sizing, but if the sizing could be removed it could lead to higher strength bonds between the resin and fiber.
1: all fabric, especially nylon will absorb moisture. It is very common to heat to 100-150c for a few hours under vacuum to boil off the moisture. it’s the nature of the beast. Tow retention, and sizing absorbtion is the cause. Again, depending on your resins, it can absorb moisture. ALWAYS dry your thermoplastics under heat and vacuum.
2: Is the mold shaped weird, that you have negative draft angles? What is your mold made from?
3: Removing sizing (~350c to start) WILL NOT HELP BONDING!!! Sizing is what helps bond the resin to the fiber!!!
Actually, the sizing is applied to carbon mainly for processing/handling (i.e. so it won’t fuzz up and turn into black cotton-candy). Sizing on carbon does need to be compatible with whatever resin system you are using, but the main source of fiber-resin bonding is due to the surface treatment the fiber goes through before the size is applied (either a highly acidic or highly basic treatment to apply bonding sites on the fiber). Some sizings will provide increased bonding performance over unsized fiber, so “unsized fiber gives the best bonding” isn’t a hard-fast rule.
Of course, size on glass fiber (silane-based is most common) is the coupling agent between the fiber and resin so thinking it is the same for carbon fibers is a common thought.
@tgundberg,
What i understand is Sizing is very important in glass fabrics and not necessarily in carbon fabric.
Question: What is this acidic or basic treatment? What makes it to enhance the function of reacting surface? Is it applied specifically for the sizing to adhere to the surface? @riff42
If i dry the carbon fabric at 100 degrees, What is the ideal during of heating? If i heat more will it affect the strength of the component?
tgundberg & riff42,
DO please check for other post from me.
Don’t get me wrong, sizing on carbon fiber is still important. In many cases it can improve bonding to the fiber, it’s just not as important as the surface treatment.
As far as what the treatments are, I can’t really say (considered “trade secrets”), but if you do some searching, I think you can find some of the basic chemicals used. Basically, the surface treatment etches the fiber surface, which is generally the area of higher crystallinity, and produces functional groups on the fiber surface. I believe this is similar to a plasma etch that needs to be done on UHMWPE fibers such as Dyneema or Spectra in order to allow resin bonding to the fiber (similar effect at least).
The sizing is applied after the surface treatment, and allows for better handling and resin wetting than unsized fiber. There is a more complex interation between the treatment, size, and resin, but that is what I remember off-hand.
As for your original question, I have been thinking about it and the heating may help soften the sizing and allow better wetting of the fiber (definitely won’t burn it off at those temperatures) which may be why you can get better ILSS values. The builder who told me they did this made some pretty large structures and had been for quite some time, so its hard to agrue with their methods.
depending on your size/thickness, at 100c, it should only be around 30-60min, under vacuum. if you are just placing the dry fabric into the oven, maybe 60-90min. Always keep your fabric sealed in a bag obviously
