Leaks during or after resin infusion 1

[SB86]

Hey all,

I have been running into a problem for the last few months and I am in need of some advice from the forum.

I am working in a production environment where we are using resin infusion. We are leak checking our parts for at least half an hour (with the actual requirement being 0"hg in 5min). The operators will do their leak check and measure no leaks during their leak check however during infusion they are somehow getting air into their parts. Sometimes we have discovered that there was a leak in the bag and other times we can't find a leak at all. Sometimes instead of leaking during the infusion the part will randomly begin to show streaks of air while it is sitting in the clean room waiting for cure.

All of this happens after we have leak checked the parts. We are getting at least 27"Hg at all times. What is confusing me the most is that this does not happen all the time and it never happens at the same spot while infusing. These parts have been infused, sat in the clean room for 6 hours with no leaks or air, and when we come in the next morning there will be air right through the part.

I have been thinking about the possibility of micro fractures in the composite tooling or possibly something to do with the resin/hardener mixture as it is heating up.

Any help or tips on this situation would be much appreciated!!

Thanks.

 

[Compositepro]

There are a lot of missing details. It appears that you place your vacuum bag in contact with your part. While it is very nice to be able to see the infusion process, this is not a good practice because a pinhole leak in the thin bagging film will ruin your part.

It sounds like you are using a two part room temperature cure resin. If you get any significant exotherm it is quite likely that the rise in temperature could increase the vapor pressure of the resin to above ambient pressure and the resin "boils". If you continue to apply vaccum to outlet port after infusion is complete you can be boiling the resin. Same applies if you have resin leakage into the breather.

 

[SB86]

Hey there,

Thanks for you reply.

We are using the following on top of the part: a layer of peel ply, the infusion pad (edge injection), a layer of infusion mesh, and then the vacuum bag. We can't actually see the part itself but you can see the air in the resin that sits on the top of the part.

If anyone responding to this needs any more information I can provide most (not all) of the details.

Thanks.

 

[SB86]

Oh, and yes we are using a two part room cure resin.

 

[Compositepro]

It is also possible with the infusion mesh that you can infuse too quickly. The resin can flow though the mesh and fill the vacuum line before the part is fully infused. The remaining air is trapped in the part and will tend to rise to the top with time.

 

[Hojo1122]

99% of the time when you get a leak in the bag its usually not the bag but the sealant tape. Best thing to do is to look closely at your sealant tape from the side view, you will see little gaps where there overlaps and its not sticking well. Also make sure that where your sealant stick there is no release agent. the sealant should be difficult to remove after, this is very important. Also do a good 20 minute degass. and a 0 hg drop at 15 mins vac check is a good time, its long enough to see any small drop. 5 minute vac checks are not acurate for tiny leaks. watch for any small peel ply strands, as just one will cause a leak that is not detectable but will bring air in to your part. Also make sure you are using infusion resin. Make sure your vac line is not touching your infusion mesh or laminate, have it connected by peelply only. You do this you should have no problem