For anyone reading this thread that might be having similar issues I think I might have figured out some of the factors going into my above issue and hypothesize a combination of three things interacting (disclaimer this is merely my hazarding a few guesses after a lot trial and error, followed by brainstorming, help from Hanaldo and Chris Rogers, and finally at long last getting a perfect 4'x8' infusion yesterday...)
1) The sealing tape I was using made it a lot more work than it should have been to get a good seal, and using the Airtech Airtech VAC RIC (Resin Infusion Connector) in the center of the part going to the omega flow channel combined to result in my having a very small difficult to perceive leak at the center of my part which was being spread throughout my part for the entire infusion. The infusion I got right I sealed between the connector and the bag from the inside, cut a clean hole in the bag, and also then once putting the tubing into the connector also sealed from the outside of the bag... Seems like there should be a better design out there that is lower profile, but unless a layup absolutely demands it seems like it's better to have all lines come in from the side since it's easier to seal and much easier to detect leaks..
2) The resin on my last two parts didn't make it all the way to the MTI vacuum infusion lines which doubled the volume of any gases that were in the part, and the resin absolutely needs to completely reach the MTI lines so as to reduce the volume of the bubbles back to approximately atmospheric pressure (which causes any small bubbles to fully rise to the top of the surface and be left in the enkafusion, as opposed to the part) BEFORE the resin has begun to thicken.
Cheers,
Dave

Thanks Hanaldo,
I think you're right in terms of my issues being an air leak (or maybe even more than one extremely very very small phantom air leak..).
Doing this project in Hawai'i has me generally working around 29 degrees C already (with the epoxy starting out around 24 degrees C from the mixer to help a little with pot life), and I can definitely reduce the distance between infusion lines (especially once I am hopefully able to graduate to more complicated projects I planned to already be doing..). Adding a thin woven fabric between layers would also be easy enough to do, although the quadaxial is a similar situation to the epoxy in that I purchased a lot in advance due to pricing/shipping/lack of local availability.. At the end of the day I will change whatever has to be changed to achieve success though...

Sometimes a couple pictures are worth a thousand words, same location of the same piece with the bad looking picture being the top and the good looking picture being the bottom...

Quadaxial is really the same as two layers of biaxial with one layer rotated it just saves you some time. But essentially means you are infusing 8 layers of a relatively heavy uni, which can be tricky, but certainly not impossible. Could you use a lighter weight quad, and throw in a couple of layers of a woven fabric in between the quad layers in order to aid resin flow?

I just think you're really going to struggle with your current resin over the distance you're trying to do. Your automated mixer is a great help for sure in terms of having enough pot-life, but it isn't going to help the resin wet-out the fibres properly. Are you able to warm the resin at all, or perhaps warm the layup? Even warming it to 30-40 degrees will have a dramatic effect on resin viscosity, and then the automated mixer can help with getting enough pot life.

Dry spots on top with the tool surface wet out is odd. Generally the flow mesh allows flow over the top, and then the resin has to penetrate down to the surface, so if your surface is wet out then it would stand to reason that the resin had to flow through the top to get there. Not impossible, as infusion can sometimes do strange things, but certainly an interesting symptom. Are you sure they are dry spots rather than areas of delamination from pulling the peel only off? If so, my money is on an air leak messing with things. Or, potentially - the Strechlon choking resin flow on the top, while the perforated core provides sufficient flow channels to the surface. But this makes less sense than an air leak.


There's nothing wrong with how you've perforated the core as long as you have enough perforations, but if your surface is wet out then this sounds fine. 

Infusion is a great process with loads of versatility, but it punishes errors and is unforgiving with material selection. You will certainly be able to get a decent result with what you're doing though, it will just take some effort getting it all working together well enough.

Tearing my hair out looking for a leak is exactly where I've been at for awhile now...
Your advice on using an infusion specific resin is spot on, but I'm going to jump on all the other details of your advice first in the hopes that if I get everything else right I can make use of the 30+ gallons of resin I already have and delay more hazmat shipping orders if at all possible.
(I have been degassing the epoxy in unmixed state and then metering out with a Michael Engineering Super E epoxy mixer with a static mixer as needed to the resin feed line bucket, so as to avoid excess exotherm or introduction of bubbles during the mixing process).
I perforated all the divinycell (by hand using finishing nails hammered into a piece of wood that I predrilled with narrower drill bit on a grid pattern, since I hadn't realized I was going to need perforated core at the time I bought it/availability in Hawai'i... I would be concerned with the holes becoming too small under vacuum since nails were pushed through vs drilling/cutting perforations except that my bottom skin has barely any, if any, dry spots but the top still has some dry spots even on my best attempts so far..).
What I've been infusing is actually quadaxial basalt as opposed to biaxial (weight 680 grams/sq. meter ie 19.9 oz./sq. yard with fiber orientation 0 degrees, 90 degrees, +45 degrees, -45 degrees and made with 13 micron roving), I'll try to get a good picture this evening in terms of the dry spots. Everything I've been making to date has been generally salvageable for non-critical applications a cabinet in a boat before I get things dialed in enough to do transom extensions and interior bulkheads but I'm running out of functional practice pieces so your advice comes at exactly the right time :-)
I can't say enough how much you've given me renewed hope dealing with resin infusions... :-)
David

Few issues stand out to me there, the Strechlon being one of them. However, there's sort of a perfect storm of not entirely suitable materials going on that is likely the bigger issue. 

For one, 600cps resin is not ideal. That is a hand laminating viscosity resin, which is thin enough to potentially work ok with infusion - but the other materials will expand on that issue as well.

4x8 is just about too big an area to successfully infuse with a 600cps resin. It is probably doable, but it is very much on the max of what I would attempt - especially when using biaxial reinforcement, and Divinycell. Is the Divinycell drilled and scored for infusion, or just standard foam core? If it is just standard, this won't work. You need perforations roughly every 2" to let the resin flow through to the surface. Then, biaxials are naturally a bit tougher to infuse. They compact very tightly together, not providing many channels of flow for resin. They can be infused fine, if your resin is low enough viscosity to penetrate. 2 layers is not a big issue, you would probably get good wet out with the 600cps resin if your area was smaller and the core was suitable for infusion.

Strechlon is also not really suitable for infusion. On flat sheets, this is mainly due to the effect Rich mentioned earlier where the Strechlon can actually stretch into and seal off the flow channels created by the flow media, exasperating your flow issues. 

As for your sealing issues, the Strechlon wont be helping here either. Not only is it quite prone to porosity and punctures, but it doesn't stick well to the sealant tape, so you may well have a perfect bag that is still leaking through the perimeter between the bag and the tape. Your sealant tape may also be an issue - I suspect that if it isn't genuine Airtech AT200Y, then it will be an equivalent to. This stuff is not great, as it is quite firm and relatively low tack, which again exasperates the issues of sealing to the bagging film or even the tool. 

My first two suggestions to try would be a regular bagging film rather than a high elongation film, as well as a proper infusion resin. And if your core isn't infusion ready, either perforate it yourself or buy it drilled and scored. Those would be the primary suspects. After that, I would try a different sealant tape too. Your stuff will likely work ok, but it is much less forgiving, which can cause these situations where you tear your hair out looking for a leak that just won't present itself.

Tony,
I am in the US but given how little Strechalon 200 weighs I would be willing to ship you some carefully folded in a USPS international box in exchange for talking through some of my vacuum infusion project problems with me.

(Lets just say the learning curve has been MUCH steeper than I expected.. Switching from Strechalon 200 to Stretchalon 800 seems to have helped, with my hypothesis being pinhole leaks, but I'm still having a hell of a time tracking down leaks for infusions of 600cps epoxy on simple flat 4x8 sheets of divinycell with each side having 2 layers of quadaxial basalt, standard polyester peel ply, enka fusion flow media with any cut parts covered with masking tape to protect from causing pin holes, using omega flow channel and MTI vacuum hose with yellow gum tape. When I think everything is good enough to infuse (~15 millibar),  I STILL have additional issues being not completely saturated in certain areas but a lot of the time I have a hard time getting under 30 millibar (using a robinair 2 stage 6 cfm vacuum pump..) so it seems obviously leak related but I'm not actually finding the leaks...).
Dave

Stretchy film is nice sometimes for wet-bagging secondary bonding, repairs or something but the key is not to make it stretch!  Getting a good neat well-fit bag with standard film is good practice and you learn how to do it and then its not an issue.  I did some truly ugly stuff with stretchy bag early in my vacuum bag learning curve - until I learned the things people have already described.    

Only other place high elongation bag is nice is with autoclave stuff where it adds a little backup because it won't break as easily if bridged - still something to be avoided.  There are some really nice stretchy tube bags that are awesome for inside tubular parts.  Just reduces the chance of expensive failures!

If you always cover up the edges of the flow media, the bag doesn't seem to be that tough. I never had to do that and didn't have problems at all. And I used the "standard" heavy flow media quite a lot.
I use a pa/pe/pa type bagging film.