Re: Resin volume placed on foam


Frankenbird Vern
 

 Both are used..slight vacuum and pressure are applied using pre-pregs. It's called porosity in the industry lingo. The layups are guiding the mechanic by laser light. They don't have time to mark shit with tape or other.. there are also cutting programs.. Gerber machines are the popular one. So 40 or 50 techs are all working in the Oopma Loompa fashion in a freezing cold room. They also do the peel ply layup as part of the schedule before bag and vacuum.  

 The autoclave cure programming is based on the type of resin (how fast it reaches a rubbery condition from a runny thin viscosity) and the ply schedule (numbers of) and type and shape of core, and if film adhesive is used (almost always is used now). Some plys are also bonding (such as electrical) for lightning strike..imbedded in those carbon fiber pre-preg is thin copper mesh. Use the wrong program and the autoclave will for sure create junk parts. All that previous work is lost effort..and a ton of money tossed out as well. 

 I don't know about spacecraft composites (Charlie does..he worked in that world for years) but aluminum mesh was the standard many years ago in aircraft.  The inherent problems of galvanic corrosion using aluminum mesh for strike path made the copper mesh preferred, and because airplanes in general are considered a reusable machine, they (hopefully) live many decades. Rockets and missiles are (until recently) good for one trip..and weight is SUPER critical to even make the mission possible. Copper is heavier and more expensive but delams are not good in any load bearing structure. 

If your rich you don't care if the airplane costs 30 grand more..better it not break or go POOF! in a lightning strike.  

  In some processes we also used pre autoclave ovens...where vacuum only was used. Possibly, in the home shop environment, this process is usable (no foams...so other than layup only parts, now your into buying core and cutting that messy crap..better to just buy flat panels already cured, just do the edge fill and insert potting yourself). The advantage of the pre-preg is 100% you know the resin is saturated. BUT..it is a PAIN to deal with. Clean room and working with gloved hands ALL the time..and freezers...gotta have them to keep the temp low until it is time to "shake n bake'. Humidity too..you have to control all parts of the work environment.    

 The bottom line is; you are correct that all of this background is only superficially related to what is reasonably possible in the home shop environment, Rob. It is correct that bleeder that is "thirsty" will draw your layup dry.  

 Even if I had the money to build what is required to do these same processes, I doubt my neighbors would appreciate it if they knew I had something like this next door.

   

 Years ago my desk was about 50 paces from this same Autoclave when I was on Contract as R&D Manufacturing Engineering on the Beech Premier program in Plant 3.

 

 It go Boom!!!  Thanks be to God no deaths..but serious injury was still the result. 

 Most of the Starship major parts were cured in this same Autoclave. This one is considered a baby now...think about how big the Airbus and Spirit/Boeing Autoclaves are!! 

Vern


From: main@Q-List.groups.io <main@Q-List.groups.io> on behalf of Rob de Bie <robdebie@...>
Sent: Monday, March 29, 2021 3:30 PM
To: main@Q-List.groups.io <main@Q-List.groups.io>
Subject: Re: [Q-List] Resin volume placed on foam
 
I really like this as a thought experiment. And I see some parallels with autoclave processes. In an
autoclave you can apply pressure without the vacuum turned on. Therefore this is sort of similar to
what you propose. I haven't figured out yet whether this leads to different amount of resin flowing
into the bleeder - but my gut feeling says it will have a considerable effect.

And now that I'm thinking about it, a typical autoclave pressure *could* make the resin absorb small
air bubbles. At least that's what I see in resin casting, using polyurethane resin. In that process
one can take one of two very different routes: vacuum casting or pressure casting. In former you
'pull out' the air bubbles, in the latter the pressure makes the resin absorb the air bubbles. Until
tonight I hadn't seen the parallel. But it has nothing to with building a Q1 or Q2 :-)

Rob

On 27 Mar 2021 21:40, Bruce Crain wrote:
> Just a thought.  Would it help to vacuum bag parts and then put sand or lead on top of the outside
> bagging material to use weight to press the resin and glass together tighter into the weave?  It
> would be messy and you would have to keep the mold from creeping but what does the group think and
> does any one have any experience to share about that?  Just thinking outside the box.
> Bruce Crain
>
> ---------- Original Message ----------
> From: "Stuart Grant" <smgrant@...>
> To: main@Q-List.groups.io
> Subject: Re: [Q-List] Resin volume placed on foam
> Date: Sat, 27 Mar 2021 07:18:37 -0700
>
> Here is a link to a YouTube video where Cozy Girrl Randi explains about how Cozy Girrls make
> composite parts, including mixing epoxy, mixing micro, using gloves, low pressure vacuum bagging,
> peel ply, sanding etc. The video was recorded at Sun-N-Fun 2019 and the beginning has a lot of noise
> from the air show but Randi has great tips. https://youtu.be/fmuDOWTr_3c <https://youtu.be/fmuDOWTr_3c>
> If the link doesn't work search YouTube for
>
>
>           Cozy Girrrl's LoVac Composite Tools & Tricks
>
>
>
>





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