When do you need an Autoclave?

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In my experience with composites, Just the vacuum pump was able to create resin to fibre ratios that were too resin starved. Why would we need autoclaves to reduce the resin to fibre ratios even further when 1 bar pressurer does the trick?
 
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arj1

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In addition to vacuum/pressure control, doesn't the autoclave have temperature control for high(er) temp curing and cooling of the process?
That could be just an oven.
I think the real answer to the OP's question is "when the system supplier demands for it". I know it sounds facetious, but in reality it is how it works - if the manufacturer says "2 bar, 200C for 7 hours, 5 minutes and 21 seconds", then that would be it.
Why would they require it? I think that is to ensure that the resin permeates into the fabric and stays there, plus extracting the excess resin as well. I think the likes of @wsimpso1 would be able to provide a more detailed explanation.
 

wsimpso1

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..n my experience with composites, Just the vacuum pump was able to create resin to fibre ratios that were too resin starved. Why would we need autoclaves to reduce the resin to fibre ratios even further when 1 bar pressurer does the trick?
Lots of reasons to use an autoclave.

Wether you realize it or not, you sort of answered your own question. If your slightly resin starved laminate were compacted under 5 atmospheres instead of 1, it might not have been resin starved.

Also, most prepregs are supplied with enough resin to give low void laminates when compacted at some specified pressure. If they say this is for 75" Hg and you can only get 12", it will come up with voids and mis-lamination. If you want to do vacuum bagging with ambient air pressure, you need prepregs designed for that pressure - which means more resin - more weight in the finished part and probably a much lower Tg on the finished part too..

Then, with many prepregs and many resins, they specify a pressure and temperature vs time schedule to ensure compaction and cure. Good curing autoclaves have programmable controllers to manage the schedule for good parts.

If you are doing ambient pressure bagging and your parts are resin starved, you either need more resin in your wet out or change something in the stack to draw less resin from the part.

Billski
 
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cvairwerks

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When you build big parts....Lots of our parts are cured in autoclaves due to both physical size and tooling weight. Only way to control tings well enough to be sure that the part meets engineering spec. Not fun to have a composite part come from together at Mach air speeds.
 
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