Breach unit seal

Talk Composites - The Forum for Advanced Composites

Back

Breach unit seal

Author	Message
MarkMK	MarkMK posted 10 Years Ago HOT Topic Details
Group: Forum Members Posts: 338, Visits: 2K	Have run my first few parts using OOA material (EC's own) and, whilst I've got the last couple to come out with only minor pinholing I'm still aiming for a pinhole-free finish as I don't have the facility to finish with clearcoat, although smaller parts I can coat with epoxy and flat. I'm pretty consistent with getting fully sealed bags with infusion now without need to chase leaks, but finding envelope bagging parts more problematic when, in theory, there should be less to go amiss, so to speak. I'm concerned that my problems may be arising at the breach unit, although I've carefully installed the hosetails using PTFE tape and I'm careful to make sure the through- bag element is screwed down tightly whilst avoiding wrinkles in the bag. I use the larger diameter barb connectors to get a tight fit on the silicone hose too.Cure cycle is a consistent 100° for 8 hours with temps monitored on the parts with thermocouples and an external thermometer. My question is: would any minor leak occuring in this area affect the final part finish if the bag itself was airtight, seeing as it is 'downstream'. Pump is left on during cure with no audible indication from it that there's any air ingress when running, but when left for a few hours during drop tests I've heard a slight tone change for a few seconds when opening the breach unit ball valve. I'm even starting to question the quality of the valve itself. I've also considered curing without the pump, but is a pinhole-free finish realistic to expect even with a totally sealed bag and are there volatiles in the material that really need to be evacuated during cure? Thanks Mark
	Reply Like 4
scottracing	scottracing posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 460, Visits: 5.2K	any air leak will affect the quality of the part, you should always do a leak down test prior to curing to check that there isn't any leaks anywhere in the bag or vac system. One question i do have is regarding your temps and cure cycle, how are you getting to your 100°C? what is your ramp rate as simply sticking the part in the oven at 100 may not allow the resin to flow slowly and allow an effective cure. Pinhole free is very difficult even with autoclave prepregs, in F1 most stuff unless its polished ali tooling will require some secondary finishing work.
	Reply Like 3
ChrisR	ChrisR posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 363, Visits: 3K	I've never been 100% convinced with the ball valve connectors so I went with these Not had a problem with leaks from the breach unit (been using them for 4odd years)
	Reply Like 4
MarkMK	MarkMK posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 338, Visits: 2K	Ah, are they the units from Vac Innovations Chris? Quick connects would certainly make life a little simpler I've been placing the parts into the oven which is already up to temperature and they tend to take 45mins or so to come up to temperature themselves. EC say that there is no need to stick to a slow and controlled ramp with their material, I believe. I have the oven capability to do this, however but guess I need to satisfy myself that everything's totally leak free during cure first If the breach unit could be a possible source of the issue, I'll pay close attention to it next time and also run a few tests on a simple vacuum bagged piece to hopefully establish if it is sealing correctly
	Reply Like 4
Hanaldo	Hanaldo posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	scottracing (15/09/2015) any air leak will affect the quality of the part, you should always do a leak down test prior to curing to check that there isn't any leaks anywhere in the bag or vac system. One question i do have is regarding your temps and cure cycle, how are you getting to your 100°C? what is your ramp rate as simply sticking the part in the oven at 100 may not allow the resin to flow slowly and allow an effective cure. Pinhole free is very difficult even with autoclave prepregs, in F1 most stuff unless its polished ali tooling will require some secondary finishing work. The Easypreg is pretty easy to use, I normally get pinhole free results just sticking it in the oven at 100. Mark, when I first started using Easypreg I found the main culprit for pinholes was me handling the material too much. Repositioning the fabric in the mould or just handling it too much in general caused quite a few pinholes. Just thought I'd mention that.
	Reply Like 5
ChrisR	ChrisR posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 363, Visits: 3K	yes they are
	Reply Like 3
MarkMK	MarkMK posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 338, Visits: 2K	Thanks for confirming Chris Thanks for that Hanaldo, I also recall Paul from EC saying that working the surface layer too much, in particular, can cause pinholing so I'll be mindful of that. I was laying-up a new mould today with quite a few curves to negotiate and found myself having to re-position a few times, so might not get the best finish, but hopefully a bit of finessing of the cutting template will help make the next part much better. Good to know that the promise of pinhole free parts isn't just a myth, so I'll keep at it.
	Reply Like 5