Hi guys,
I’m new to resin infusion, I finally made a sealed mould and did a drop test before infusing.
I did a 3h drop test in which it held vacuum pressure.
The ambient temp was between 25-30 degrees Celsius.

The resin was de gassed
I started infusion by slowly loosening the hose clamp on the resin side while the pump was running.
Once I got full wetout, I clamped the vacuum side, and about 30s later I clamped the resin side.

everything looked fine for 2 minutes, then I started noticing the bubbles within the flow media, these bubbles started forming in different areas of the part.

Then I noticed some areas of the bag were very loose, e.g the area where the vac hose connects to the bag.

I’m not sure what’s causing this but it’s the second time it’s happened to me!

Would appreciate some help

Thanks

attached are pics

It can sometimes happen that a leak occurs after the part has infused, even where vacuum was securely held prior to and during infusion. Sometimes the effect of resin running through the part can loosen some part of the perimeter tape and it can become more prone to happening where the bag is quite tightly held

Looking at your picture, it does look like your pleats were quite small and, perhaps, there was some excessive strain around these areas, even though the part looks quite small

I'd recommend using slightly bigger pleats and trying to position the bag so that there's the minimum of strain on them whilst pulling down the vacuum. A bag with plenty of slack will produce less strain on the perimeter tape and it's also worth going around the entire perimeter and pressing things down firmly juts prior to infusion, even if it appears that full vacuum is achieved, just for added certainty

Make sure also that you wipe the areas where the tape is placed to make sure that there's not a build-up of release agent there that might make the tape a bit less sticky when applied. Observe the part for a few minutes after infusion and try to press the tape down quickly if you notice any 'creep' of air occurring, which might help stop the whole part being compromised

Careful prep of the bag should, hopefully, limit the occurrence of such issues, but it can sometimes happen quite inexplicably. On a flat-ish mould, with very clean flange areas, it should be quite rare, though

As said, sometimes when infusing, the bag loosens slightly and it can be enough to unseal a small puncture, or cause the bag to move over something sharp and puncture.  The bubbles give it away quite clearly.

Sometimes if its one tiny leak you will see a "Christmas tree" like pattern of bubbles as the air tracks across and you can follow it back to the leak and plug it with some gum tape. 

I would make extra special care to ensure your working table is 100% perfectly clean with no possible sharp points and also the sides and back of your moulds.  Even the tiniest poking out strand of GRP can pop the bag. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Double bagging is not a good replacement for solving the problem in the first place.  I lay down some breather underneath some bagging film on my work table so I've got a soft surface free of anything that can puncture.  Mines taped down but if you use the table for other things, you can use the lay flat tube nature of the film to make a soft "blanket" for the table top.  Keep it perfectly clean and you can rule out the surface from causing issues.  Sometimes breather on the back of the mould can help but sometimes the excess resin soaks into it making it a pain to remove.  Also some sharp points will press through the breather when under vacuum anyway. So getting the back of the mould smooth is important as well. 

If you are getting good leak tests then your basic bagging is fine, its just the finer details tripping you up somewhere and it is better/more efficient to fix them than try double bagging. - remember anything that has punctured one layer of film may be sticking out enough to puncture the next layer!

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Another thing to try, if not doing so already, is to place a small 'doughnut' of bagging tape around the top of the silicone connectors prior to bagging-up

As you're working around the perimeter, just place the bag over the doughnut on top of the connector and lightly stick down so that there's a little slack between it and the perimeter edge. I say this as, assuming that your envelope bagging was done carefully (and on such a small part is should have been easy enough to ensure a good seal all the way around), it might just be the areas around one or both of the connectors that have caused leaks? This might have been more likely on your initial part, in particular, given the small-ish size and the apparent strain on the bag

The doughnut of tape won't seal things on it's own and you'd still need to apply tape above the bag and around the inlet/outlet pipe as usual, but it does help to reduce the likelihood of the bag being excessively wrinkled when you insert the pipes, especially if you place a finger and thumb over the connector when inserting them though the hole in the bag. Cut the pipes at an angle also, to make inserting them easier. 

I have found that doing this has proved a very reliable way of discounting this element of the bagging process from probable leak sources. I also double back the tape on itself when creating pleats, rather than just fold over a little bit of tape at the top and this also gives a touch more certainty that the tape is thick enough to press down well and create a good seal at the base of each pleat.  

I still encounter the issue you've highlighted from time to time and in most instances it's really difficult to find a logical reason for it happening after the part has infused. As Warren said, be mindful to keep things as clean and tidy as possible when bagging and look out for stray fibres. Create bags with plenty of slack to pull down without straining too much, as a tight bag with little to spare will always be more prone to leaking from the edges and, sometimes, make them more prone to puncture by the edges of the flow media (although I think that this is quite rare in most cases). I tend to wipe around the perimeter with a cloth and a little mould cleaner prior to applying the tape and this helps to ensure that you've got a clean surface to stick to without traces of release agent. Only wipe where the tape will be stuck down, though. 

Be aware of temperature as well, as colder conditions can make the bagging tape less sticky and more likely to leak unexpectedly so definitely worth going around the perimeter several times to ensure that nothings come a little unstuck. 

Once I got full wetout, I clamped the vacuum side, and about 30s later I clamped the resin side."

I usually clamp my resin side when infusion is close to complete and let the vacuum continue to debulk the layup before sealing the vacuum side.  I hope you are able to resolve your issue, let us know.

Tony Stuart