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Author: Subject: Bending fibreglass
Davegtst

posted on 14/9/11 at 05:04 PM Reply With Quote
Bending fibreglass

Is it possible to bend it into a slightly different shape? I bought a NACA duct to fit on my nosecone but the nosecone has a very slight curve to it whereas the duct is flat. If i heated it up with a hot air gun would it bend at all. It only needs to bend about 5mm.
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smart51

posted on 14/9/11 at 05:11 PM Reply With Quote
Fibreglass bends under its own weight and can stay warped. You have to be careful about how you store GRP body panels if you want them to still fit your car some months later. I'd guess you could heat it up and bend it and some of the bend would be retained.

It makes me wonder about GRP monocoque cars. Do they banana with age?






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HowardB

posted on 14/9/11 at 05:14 PM Reply With Quote
as glass fibre is a thermoset, then deforming it with heat will be almost impossible. It may be possible to stress it into place, but in this instance filler may well be your friend,...

:-)





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britishtrident

posted on 14/9/11 at 06:04 PM Reply With Quote
No ...........
When it is fresh out the mould GRP ( and still "green" ie. not fully cured) " will bend very slowly to take up shape some extent but once fully cured the shape can't be changed. The rate curing process is rapid at first but gradually slows down.

As an example if stored out the water newly moulded boat hulls have to very carefully supported for the first 6 months or so as they can distort.

Heating will only speed up the curing reaction.

[Edited on 14/9/11 by britishtrident]

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avagolen

posted on 14/9/11 at 06:38 PM Reply With Quote
Hi Guys,

I am going against the flow here.

I was told some time ago that warming fibreglass with a hot air gun will make it go plyable.

I tried it and it does. Changed the shape of my fury boot floor by quite a lot and
it has retained the new shape well. No cracks.

Len.


[Edited on 14/9/11 by avagolen]





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iank

posted on 14/9/11 at 07:15 PM Reply With Quote
You can, but for best results you need moderate heat for a long time (hours) and weights applied carefully to allow it to bend in the direction you want. Plenty of droopy fibreglass bonnets if you look around Stoneleigh due to the heat of the headers. I've seen 4 inches of twist taken out of a beach buggy, but it needed a 'tent' and a space heater for a couple of days as you need to go slowly if you don't want to wreck the gel-coat.

There are some videos on youtube demonstrating a heat gun doing the job on a small strip.





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ashg

posted on 14/9/11 at 08:17 PM Reply With Quote
my bonnet had a kink in it from being wrapped up, warmed it up with a hairdryer and was able to get the kink out very successfully. just use a hair dryer not a heat gun.





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Neville Jones

posted on 15/9/11 at 10:31 AM Reply With Quote
A property of the poly resins is referred to as the Tg point, or glass transition point. This is the point on the temp scale where it changes from a stiff and solid glass like substance, to a pliable soft cheese type substance.

Heat the (cured)resin above the Tg, and it WILL bend, then cool it and it will stay bent.

Most poly's are in the 45c~60c range, some of the more expensive polys are near to 80c, if given proper post cure.

Epoxies are similar, but generally have much higher Tg's.

So, YES, you CAN bend the item, or have a good try. The structural shape will have as much influence as the change point of the resin.

Cheers,
Nev.

Been playing with poly resins for over 50 years!

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40inches

posted on 15/9/11 at 02:59 PM Reply With Quote
The doors from GT40 kits are known to distort when not stored on the body section, the part of the door that forms part of the roof
sticks up. The fix for this is to warm the curved part of the door whilst applying weight to the top, then letting it cool with the wieght in place, works a treat, apparently.






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Mave

posted on 15/9/11 at 05:22 PM Reply With Quote
Yes, Neville is giving the comprehensive and correct answer. Get it above Tg, and you might be able to deform it, CAREFULLY. Try to get the temperature even over the surface and through the thickness (in other words, give it some time while heating; don't use a short hot blast only)

Marcel

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Confused but excited.

posted on 15/9/11 at 05:34 PM Reply With Quote
Nev's right again.
I left my newly aquired Westie bonnet in the back of the espace on a sunny day and it sagged like a b@st@rd.
Gutted and total panic or what?
Thanks to the wisdom of the forum it is now OK.





Tell them about the bent treacle edges!

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