Vacuum drop for infusion

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#1

Ive been trying to get a 100% leak less bag for infusion but I just can’t seem to get rid of a tiny tiny leak somewhere in the system.

I currently have my mold bagged and vacuumed down to just about 29" from what I can see on the vaccum gauge which is on my resin trap. I have a valve inbetween my resin trap and vacuum pump. Now with the pump turned off and the valve closed my vacuum seems drops about 1" in an hour or so.

I have an accutrak VPE but I cant find a leak anywhere. Ive checkd all around the bag, the resin trap, my hoses, all my connections but I cant find anything even with the sensitivity turned to the highest.

Any suggestions? I havent infused the part yet.

#2

Have you checked all of the theaded fittings?

#3

1" per hour is completely acceptable.
But place another vacuum gauge on the resin feed line to get a real reading of what the lay-up will see during infusion.

#4

1"/hr is very good! The leak can be anywhere and anything. The shutoff valve, or the bag has a hole even…and a very small one. but that rate is wicked.

#5

So I left the pump turned off, valves closed and left it till the next day.
24 hours later, my bag was at about 15". Im guessing that this is probably as good as can seal the bag.

I vacuumed it back down to 29", held it there for 30mins or so and infused. Part came out great with no voids etc.

Is it even possible to have a system with absolutely no leaks that will just stay at full vacuum??

#6

Yes it is possible, at least to where I haven’t noticed a leak over 3 days of curing. I’ve done it many times but I was infusing flat plates and sealing the bag was very simple.

#7

Technically no, it is impossible.

#8

what was the part? lets have some pics then as its come out good! :slight_smile:

#9

The parts were flat plates that were machined into tensile test coupons. Took some practice but I can now reliably seal plane parts without a problem. The trouble now is that pesky 3rd dimension which is why I’ve been trying to get a leak detector :smiley:

I’ll upload some pics but they’re pretty boring. Just flat pieces of cf, nothing as neat as the cool shapes and figures you guys make.

#10

+1000 correct!!!

#11

Some sources of leaks:

-non return valve in the pump (use a seperate valve)
-the vacuum meter !!! (I once tried to test with a leaking meter. Before I found that out…)
-seams or mould porosity
-fibers under tackytape (can be traced easily usually)
-wooden flanges with epoxy on them. (too little epoxy, cracks, seams, etc)
-resin traps

What you can do is install a vac-view 628 from Airtech in your vacuum line. This at least shows if the leak is in the vacuum part of the setup (non-critical) or is in the bag (possibly critical)