Im a strong advocate for MTI hose. The first infusion I ever did was with a 2 to 3 inch resin break and MTI hose with great results. Simply lock down the inlet hose the moment all the peel ply is saturated and leave the pump running. As long as the bag successfully drop tests prior to the infusion, you’ll end up with a good result. We never de-gas the resin, and we use the pro-set epoxy infusion resin system exclusively.

What I believe I see in these photos is the result of an air leak, but I also don’t see a resin break which is extremely important.

I'm on Hanaldo's site here. To get reliable and reproducible results with vacuum infusion your bag needs to be perfectly airtight. And then you do not need the pump to apply pressure on the laminate, pressure remains the same during curing.
With a decent size resin break you won't pull air out the system either. And when switching the pump off, you don't get into problems with the resin off-gazing volatiles.
And i know plenty of professionals working in the industry for years who turn off the pump once infused...

Just to clarify the thing on keeping the pump pulling on the bag through the cure - it's like a syringe applying suction even if there is no clear air path.  The laminate stays under pressure even if no air is flowing - and it takes up any slack if you have leak or vapor issues. 

Also, you should avoid sucking resin into your catch pot - with a proper resin brake and holding back your flow media you should have no need to suck resin in - especially with small epoxy parts.  Just fill the part, dial back the vac and clamp the feed.  

I'm sure it can be done - to shut off the pump as soon as the part fills - and maybe I'll try it someday to satisfy the curiosity.  But I can't see any benefit beyond power saving - and the risks of ruining a part are huge.  Literally nobody - tech reps, infusion consultants, bosses, peers - nobody I have ever discussed this with has shut off the pump before the resin has gelled - totally unheard-of in the professional composites world.  This forum seems to be the only place this has come up.

But as Hanaldo suggest, if you have a leak - all bets are off - even a tiny leak can overshadow all the other technical tweaks that make for better infusions.

There's no need to leave the pump running after an infusion, it can't do anything anymore. Even if you did have a leak or moisture issues, the pump can no longer remove that air without removing resin with it. Then once the resin starts to gel, it can't remove anything at all. 


My gut tells me that you have a leak, which is why you had a different result between those pieces - the flow direction change was coincidental. What is your mould made from, it looks like timber? How certain are you that this is 100% air tight?

Leaving the pump running and the outlet open is probably only going to draw resin away from the part and potentially leave the 'A' side looking starved of resin

To ensure that the whole part is sufficiently wetted-out, you need to ensure that things have infused fully so a resin break can be very useful, especially on small-ish parts and leaving the inlet side open for 30 secs to a minute after closing-off the vacuum side should help

Were ambient temperatures at or around 20 degrees during the cure, as the residue left by the stack removal on the 'B' side can be brittle and white-looking where things have cured in colder conditions? I'm also guessing that your slow hardener might require around 48 hours, at least, to fully cure at a reasonable temperature, so you'd need to be wary of de-moulding too early also

From what you've mentioned regarding air bubbles visible and looseness in the bag, it sounds more like evidence of a leak more than any issue with trapped air and I'm not certain if boiling gas is an issue with epoxies? If not doing so already, it's always worth going around all of the perimeter just before allowing in the resin to flow and pressing the bagging tape down firmly once again to ensure that nothing's slightly loosened when pulling the bag down initially

Sometimes a slight leak might occur after closing things off and this can just affect the 'B' side without affecting the surface quality, if you're lucky. Again, might be worth pressing everything down again just in case the introduction of the resin has served to make anything loosen slightly

Even when infusing fairly small parts, I have not seen any benefit in using a de-gassing chamber, as applying a little control to the speed of infusion and ensuring proper wet-out should allow for sufficient de-gassing during the infusion process itself but it might allow you to rule out this area of concern. I know that some people swear by using them, but mine's gathering dust as it really didn't make any noticeably difference and just slowed the process down. Even with quite lengthy degassing, you're still likely to see some air in the infusing resin. 

 

Thanks for the advice, I'll give that a go over the weekend.

My pump is not variable and I don't have a regulator so will probably use an AC manifold gauge and open the hot side slightly to reduce some of the vac.
I also knocked up a quick ghetto degass chamber using a pot, a polycarb sheet and some adhesive rubber door seal...

We're in business! 

Yeah - I have no idea where the idea of turning off the pump came from.  To me that just sounds crazy! 

I don't know any situation where anybody I know/worked for/have talked to has ever turned the pump off after an infusion fills.  Totally asking for trouble if you ask me.  If you were doing that I'd try it again and leave the pump on, just dial the vacuum level back a bit.  

My three big suggestions for all epoxy infusions are:

1 - pull as much vacuum as you can on the dry stack and let it sit (preferably in a warm room for several hours) before you shoot the resin.  
2 - reduce the vacuum from as much as possible to around 20" of mercury right before you clamp off the resin inlet hose.
3 - leave the pump on until the whole thing is cured - and post cure with the vacuum still on if you're going to do that.