Good practices for best structural properties w/o autoclave (???)

[LSfan70s]

What is a good technique to obtain the best structural properties of a flat CF panel?
Since I am not using an Autoclave I was thinking about using two big thick panels of glass as a press mold to obtain similar results of an Autoclave and add some weight to them.
Would this work?
Does someone have a better idea?

 

[wes616]

Atmospheric pressure works pretty good.

Wes C.
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[blakmax]

The main function of the autoclave pressure is to control the void content. Positive pressure reduces the size of the voids caused by volatiles released during the cure cycle. Vacuum exacertbates this problem, while positive pressure reduces the void size. Similar results can be achieved in a press mould.

Regards

Blakmax

 

[Compositepro]

Vacuum Assisted Resin Transfer Molding (VARTM)can be done between two glass plates. Vacuum can apply up to 15 psi of compaction pressure (10 psi is more realistic). To get 15 psi of pressure from dead weight requires 32 feet of water or 4 feet of solid steel.

 

[berkshire]

If you pull a vacuum on your glass plates, by sealing the perimeter and pumping, you will get a lot more effective pressure. You have to put a lot of dead weight on a panel to equal 13 to 14 pounds per square inch.
B.E.

 

[wes616]

Assuming you are using an out-of-autoclave prepreg, for a flat panel, use a vacuum bag and a caul plate. You'll be just fine.

Wes C.
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No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.

 

[GregoireMC]

As said before, if you just want to add dead weight on top of your vacuum bag you will have to put a lot.

On a foot square flat panel you have to add around 5700 lbs to match 3 bar (44 psi) of autoclave overpressure.
If you have a press (or even better a hot press)it can be done.

I did panel with a hot press, without vacuum, in a frame; the quality was good (it could have been better under vacuum I think...).


GregoireMC

 

[LSfan70s]

Wow! So there's no inexpensive way to get good structural results? I also thought vaccum bagging was enough for that.
I also was thinking about building some sort of frame over the mold flat panels (steel panels instead of glass) to avoide the flat panel to bend on the not pressed areas, and press them with a 8 ton long ram jack, but to match those 3 bar you are talking about I guess I will need more than 1 jack.
Thanks everyone for the good information.
If anyone has any other suggestion or idea please go ahead.

 

[SWComposites]

"So there's no inexpensive way to get good structural results? I also thought vacuum bagging was enough for that."

Yes, vacuum bagging can work quite well and produce perfectly acceptable parts. Depends on what materials you are using, and depending on your definition of "good".

What specific material(s) (fiber, resin) are you using? Wet layup, prepreg, resin infusion, or ??? material form?

What are you fabricating? and what properties do you need?

 

[LSfan70s]

Here si we are working into:

Materials we are using: Carbon Fiber 5.7 oz/sq yd,.012" Thick, 3K, 2x2 Twill Weave and CF unidirectional 9.0 oz/sq yd, 12K, .014" thick. We had some from fibreglast and US composites, and probably will be buying more from them. Not using prepregs, and baccum bagging ressin infusion with a 60min epoxy:

http://www.fibreglast.com/product/2060_Epoxy_Hardener_2060/Epoxy_Resins,

and aluminum honeycomb we found localy.

So basically we are building our own aluminum honeycomb flat panels to build a mid size race care chassis, something like this:

http://dpcars.net/dp1v8/dp1017.jpg

And that's why I'm looking for info on getting good structural properties on flat panels.

 

[LSfan70s]

Here si we are working into:

Materials we are using: Carbon Fiber 5.7 oz/sq yd,.012" Thick, 3K, 2x2 Twill Weave and CF unidirectional 9.0 oz/sq yd, 12K, .014" thick. We had some from fibreglast and US composites, and probably will be buying more from them. Not using prepregs, and baccum bagging ressin infusion with a 60min epoxy:

http://www.fibreglast.com/product/2060_Epoxy_Hardener_2060/Epoxy_Resins,

and aluminum honeycomb we found localy.

So basically we are building our own aluminum honeycomb flat panels to build a mid size race care chassis, something like this:

And that's why I'm looking for info on getting good structural properties on flat panels.

 

[LSfan70s]

 

[GregoireMC]

Do you have testing equipment to test the quality of the composite?

Are you using the wet-layup technique or vacuum infusing?