Several questions regarding vacuum bagging & post curing

General Composites Discussions Composites Talk
#1

Sorry for the numerous questions (I did do a search, honest), but here goes;

  1. Does the cost of vacuum bagging & post curing materials (inc. pump, air compressor, heating elements etc…) outweigh its advantages for a small business/workshop setup compared to wet lay up and room temp curing? Or can it be answered by asking ‘how good do you want the parts to turn out?’

  2. When doing vacuum bagging, how do you stop the bottom of the bag from getting sucked up into the valve?

  3. If you go the post cure route with vacuum bagging, do you have to keep the vacuum pump on the whole time during the heat cycle, or is it sufficient to remove all the air and then just heat it up with no further pump suction?

  4. Can more than 1 part be vacuum bagged at a time?

  5. Can peel ply or that perforated plastic be used more than once? I hate the thought of throwing lots of plastic away and having it just sit in a landfill not being biodegradable.

  6. Are there any re-usable vacuum bags? Again, making reference to helping the environment.

Once again, sorry for asking all those but I couldn’t think of a better/more friendly place to ask them. This forum is a dream!

Many thanks,

Kyle.

#2

Just had a thought - I ?think? I’ve misunderstood part of what I said;

Been going on about post curing, but mentioning a heat cycle while vacuum bagging. A post cure happens AFTER the part has cured, correct? If this is the case, is the post cure needed if the part is cured in heat to begin with?

#3

Yes, you definitely need a vacuum pump etc if you wish to make good quality composite parts. And a leak detector is a must in my opinion, will save you so much time trying to track down leaks.

If you are using a thru the bag type breach unit you need to place some breather fabric under it. If you are just using a tube into the bag you’ll need to wrap the end of the tube in breather fabric.

Yes, it is best to keep your parts under vacuum whilst post curing, as long as your bag is not leaking you will not need to keep the pump running.

Yes, dependant on your vacuum pump setup, fittings etc.

You’ll never be able to reuse the peel ply but I guess you could reuse the perforated release film, though it would not be an ideal thing to do.

Yes there are reusable vacuum bags available. For small parts I have been using vacuum storage bags from Dunelm Mill, £1.99 for 2. I can usually get 10 to 20 parts out of one bag before the bags start to leak and even then I could continue to use them it’s just that I would have to leave the vacuum pump running in order to maintain a full vacuum.

#4

1: YES. Vacuum vacuum vacuum! No one is going to want bad, or heavy parts. Unless it’s for cosmetic only reason, people still won’t want something overly heavy.
2:Wrapping the tube in peelply/breather/anything. Same for the through-bag connectors. Make sure you have enough to catch excess resin
3: depends on the resin. check with the manufacturer. Some say unsupported is fine, some require it under vacuum on the mold. If you are keeping the part on the mold after infusion, SOMETIMES you can just throw it in the oven and post-cure. Sometimes you have to rebag, so the distro media nd peelply doesn’t bond to the part!!!
4: yeah, just have a manifold, or tubes running from one to the other.
5: if there is resin stuck to it, toss it. release films can sometimes be reused, even perforated. bags sometimes can depending what you do. You can reuse a vac bag to debulk prepreg until it rips. Thermoplastics don’t have resin flowing, so sometimes you can reuse a bag. In the end, any hole in the bag will cause problems. More you reuse it, the worse it gets. Peelply/breather…no way. toss it.
6: Many kinds of reusable. Mostly silicone bags. Do a search and you will find a few. I can’t think of any right now besides Torr. They are expensive, and sometimes VERY hard to work with. But, can last 10-50 times.

#5

Excellent. Thanks very much marc and riff!