Resin Infusion Failure Question/Mystery

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#1

Hey guys,
Today I infused a small part and I had a failure during the infusion. I enveloped bagged my mould and did a 30 min drop test holding @ 29 mmhg with no loss. I used the MTI hose around the whole part.

The thing is, the infusion went perfectly, but as soon as I clamped the resin feed line, it looked as though an air bubble formed right at the point of where the resin feeds onto the mould although there weren’t my bubbles in the resin since I degassed it. Then the bag loss pressure but my gauge still read 29 mmhg. How is this possible? I checked and its not a faulty gauge. How can the bag lose pressure but still be under vacuum?

Any help would be greatly appreciated.

#2

Where were you measuring your vacuum from?

#3

When you have a strong pump and the MTI hose is surfaced with resin it can be that you can see 29inHG at you catch pot (I guess you mounted the gauge there).
If you then have a leak it can happen that air gets into the bag but will not be evacuated.
In very few cases it can happen that the bag becomes untight when the vacuum gets loss. There is never vacuum in a bag after infusion because the resin is pushed into the fabrics with ambient pressure.
The differnce between MTI and Spiral in this case is that with a spiral you would have sucked the air through the part and would have been able to keep vacuum, and with MTI hose the air stays where it is.
In both cases you will have a part with failure.

#4

Exactly what I was thinking ^

If you aren’t measuring vacuum at the part (completely independent of the rest of the vacuum setup) then you don’t really have any idea what vacuum you’ve got in the bag.

#5

Do you have any pictures or a quick diagram of how you set this up? this is something I’ve always thought about. I don’t use the MTI hose but will pinch off the feed line a little before the infusion reaches the vacuum port cause I noticed near the feed line the bag gets a little loose (as stated above with the resin coming in with atmosphere pressure). Pinching it off early I feel pulls the resin from around the feed line (where its resin rich) to finish off the part. My vac gauge is on my catch pot. I also read an article about “double bagging” due to this issue but never tried that either.

#6

Hey guys sorry for the late response. But yes, Im measuring the vacuum from the catch pot so I guess I don’t really know what the vac is on the part.

So I think I get what you guys are saying. Just to make sure, I did have a leak in the bag? But wouldn’t that mean after doing a drop test and unclamping the vac line to the catch I would have heard the bag being sucked down again? Because it didnt suck back down when i reopened the line to the catch pot which in the pot i had 29 mmhg. What should I do to prevent this in the near future? Also, I thought the MTI hose was supposed to pull the air and leave the resin where it is. Or did I have to much air. Sorry think I’m confusing myself.

Thanks a bunch

AJHR. Here’s a pic of the setup I did on a successful infusion, but I did It the same way as this failure.

#7

The MTI hose can not such air through the resin, that is physicaly not possible. But you should seal the connection between MTI hose and vacuum hose.
If you di not have a digital vacuum gauge you will not find small leaks. The Greisinger GDH 200-14 is a very good invest. Alternative you can double bag, even at such small parts the costs are not much.

#8

O yea sorry about that. Forgot to mention that in the one that failed, I did seal the side between the MTI hose and vacuum hose. Sorry for the inexperienced question. I thought the MTI hose pulls the trapped air through the hose but not the resin?

So the only way to prevent this is through double bagging or putting a gauge at the part and seeing if there is truly a vacuum leak?

Thanks

#9

It is correct that the MTI hose only allows air to pass. But if you are with a small car in a parking garage and a big SUV is blocking the exit it is not impossible for you to get out of the garage, even if you are able to exit because of your size.
With the resin it it little different, but to keep it simple you can look at it from this point.
For a perfect infusion it is always nessesary that your system it 100%tight.
You can read the MTI and double bag thread. Than you will understand everything.

#10

It’s very possible that you developed a leak AFTER the infusion started. It happens, especially with envelope bagging where you’ve got twice as much surface area to puncture. Often the bag can hold for hours and then all of a sudden it will let go.

AJHR, double bagging will not do anything for the issue you are describing. Double bagging exerts no more compaction than a single bag, you could have 100 bags and it wouldn’t do anything. All double bagging does is increase your vacuum integrity, which is critical for infusion.

#11

In this image why is the vacuum line to mti hose not sealed off with vacuum tape? Isnt the yellow tape suppose to seal off the vacuum at the mti hose. Also have u tried the mti valve it is simplified and AMAZING how it works. I would also consider loosing the catch pot when using the mti hose.

#12

just a thought because I had this problem when I did my first vacuum bag. the tip of your resin line I see that there is not much breather cloth, to keep the edges of the tube from tearing the bag and it could be a small tear/ leak that you cannot see or hear, due to the vacuum it will get real tight around that area and it will compact still and show on the gauge but will slowly start loosing vac.

#13

I use the connectors below for the feed line when infusing and have always had good results.
Chris
Carbon fibre works ltd

http://www.easycomposites.co.uk/products/vacuum-bagging/resin-infusion-silicone-connector.aspx

#14

First off, in your picture it doesnt look like your MTI hose is sealed where youre solid outlet tube connects- it looks like its simply shoved in vs air tight, could that be the problem DD?

Some errors/goofs i have made…
How much resin is left in you pot? maybe you moved the inlet tube when you were clamping it down which introduced some bubbles. Also that style clamp is TERRIBLE. its requires so much strength to completely seal the tube off which always caused me to fumble and move my inlet tube (occasionally introducing air whent he pot was low) I only use that style clamp to regulate the flow. folding the tube in half and taping it shut with electrical tape or a clamp works the best IMO.

Are you using resin or epoxy? I’ve had that issue before and I get skeptical shutting the inlet (Mentally i think the outlet draws out the resin for some reason) so towards the end of my pot life i slow down the feed rate till my pot cures around the inlet tube.

Lastly- the dumbest mistake which was the root of 99% of my issues for past year… Apparently I was not using bagging film. I was using Nylon release film instead of bagging, and since its so thin my resin flow would end up piercing the bag usually too late when i noticed…

hope this can be of use to you