Institutional knowledge

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Legendontour
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Institutional knowledge

Postby Legendontour » Sat Jul 18, 2020 5:55 pm

I’m after some knowledge that I think Nic Lottering published a few years ago, but he’s not currently active on the forum and I’m buggered if I can find it through the search function.

How many layers of fibreglass cloth gives a fixed wall thickness? ie I’ve rolled a 38 mm tube of 135gsm with 5 layers and it’s a bit thin for the nose cone I’ve got off Blake.

As an aside, where do people buy Araldite LY3600 from. I bought my first 1kg from CG composites in Brisbane, but they’ve stopped selling composites material and my local retailer on the Sunshine Coast sells Compset Universal System. I’m not remotely pushing boundaries, but my first 1kg Araldite 3600 has been exceptional.


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Re: Institutional knowledge

Postby kopius » Sun Jul 19, 2020 9:07 pm

There are obviously a few variables, but a ballpark is ~700gsm per mm.

There is a company in SA (need to look it up) that is doing araldyte, but freight is expensive. Give me a call during the week and I can chat to you about other resin options.

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Re: Institutional knowledge

Postby drew » Mon Jul 20, 2020 2:15 pm

Legendontour wrote:How many layers of fibreglass cloth gives a fixed wall thickness? ie I’ve rolled a 38 mm tube of 135gsm with 5 layers and it’s a bit thin for the nose cone I’ve got off Blake.


This question is dependent on the gsm of the cloth you use. I use 200gsm carbon fibre 2x2 twill for my airframe layups and I get ~0.37mm of thickness per layer.

https://forum.ausrocketry.com/viewtopic.php?f=10&t=5886

Legendontour wrote:As an aside, where do people buy Araldite LY3600 from.


I get mine from Kirkside products out here in WA.

https://www.kirkside.com.au/product/k3600-epoxy-laminating-resin/

I've also seen it advertised as Renlam 3600 system and the OEM appears to be Huntsman.
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Re: Institutional knowledge

Postby Kryten » Tue Jul 21, 2020 1:25 pm

Laminate thickness depends on the type of reinforcement AND the amount of resin.
I found this table of guidelines for fibreglass in my files (information provided by FMS):

Laminate thickness table.jpeg
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Re: Institutional knowledge

Postby drew » Tue Jul 21, 2020 3:23 pm

Kryten wrote:Laminate thickness depends on the type of reinforcement AND the amount of resin.


Correct. And the "ballpark" ratio we work towards in the hobby is 1:1, right? And maybe a little less if your layup is under vacuum?

I'm not an expert but from my understanding anything above a 1:1 ratio will both add mass and decrease strength. Truly the worst of both worlds! :lol:
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Re: Institutional knowledge

Postby OverTheTop » Tue Jul 21, 2020 3:27 pm

Correct. And the "ballpark" ratio we work towards in the hobby is 1:1, right? And maybe a little less if your layup is under vacuum?

I'm not an expert but from my understanding anything above a 1:1 ratio will both add mass and decrease strength. Truly the worst of both worlds!


All correct statements from my understanding. I too work to the 1:1 ratio. I think there are some fabrics that deserve a little more for maximum mechanical properties, but not a significant amount IIRC.
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Re: Institutional knowledge

Postby Jim-K » Thu Jul 30, 2020 1:17 am

Your aim should be to maximise the fibre fraction (the bit doing the work) whilst minimising the porosity (ensuring the fibres are stuck together).
Also, make sure you know whether people are talking about weight fractions or volume fractions. The ratios will be different for the same laminate.

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Re: Institutional knowledge

Postby DiscountBatman » Tue Aug 11, 2020 10:59 am

Meury Enterprises here in VIC are selling 4kg K3600 kits for about what I was getting it for in WA:
https://www.meury.com.au/
Might cost you a bit less in shipping coming from the east. No online ordering though, so you'll have to call them up.

I'm using 300gsm 2x2 twill glass and I'm getting about 0.3-0.4mm per layer, but like others have said it depends on the compression between layers etc. Carbon will have thicker layers for the same gsm as its less dense.

Nice little paper that shows the typical volume fraction for woven and unidirectional fibers (Table 5.2, pg. 4).
https://studylib.net/doc/5891342/typica ... -fractions

Using 1:1 fiber weight to resin weight will get you a volume fraction of around 30% with glass, which is what I get when running the numbers on my own layups. Best case scenario you might be able to get to 50%, but that's likely with woven rovings and vac bagging.

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Re: Institutional knowledge

Postby Legendontour » Tue Aug 11, 2020 11:16 am

Thanks for that info. I’ll give Meury a call.


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