Autoclave curing

[joepacrad]

I am using carbon prepreg & glass in an aluminum mold with a Nomex honeycomb core. Standard is vacuum bagged & autoclave cured at 20PSI. Would higher pressure and venting vacuum do me any good?

 

[berkshire]

There was a thread on this subject in this forum some years ago.

There is a danger, if the vacuum is vented at too low a pressure of air backing up into the layup.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[SWComposites]

"Would higher pressure and venting vacuum do me any good? "
> define what you mean by "good". What is your current problem with the parts?

 

[RPstress]

20 psi is quite low. The usual autoclave cure for sandwich is 35–50 psi. If your core is very light (e.g., 2 lb per cu ft Nomex) it might need a lower pressure. If it's not precured the state of the backing (bag side) skin might be a bit questionable with just 20 psi. On the other hand you'll get less edge crushing with 20 psi. If aesthetics aren't a major concern a bit of edge crushing does no harm, but nice sharp ramp edges do look 'professional,' so some people like them to please customers that little bit extra.

 

[joepacrad]

Thanks for the response.I am using 3/8" thick 2Lb. Nomex core and do require nice sharp edges. This particular part is lightweight only .030" thick skins. The issue is voids on the edges in some places and resin rich in others.

 

[berkshire]

How are you bleeding the part, are you using vertical bleed, or perimeter bleed?
If an area is consistently resin rich, can you add more bleeder ply in that area?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[SWComposites]

what is the part configuration?
what is the core configuration? ramped? angle? square edge?
where exactly are the voids occuring? edge of what?
where exactly is the resin rich area(s)?
how are you detecting/measuring voids? resin rich area?