Advice on vacuum bagging please.

Firstly this is not boat building related but I know how good you guys are with composites so forgive me encroaching on your forums.

I am building a small carbon / kevlar kite buggy and would like some advice on the laminating method.

I have done a lot of research on the topic and am intrigued by the possibility of vacuum bagging.

I understand that there are great benefits to vacuum bagging particularly the fact that it will give me a good even pressure on my lay up.

Is it possible for me to put together an effective vacuum bag set up using an industrial vacuum cleaner as the pump?

How crucial is a vacuum gauge?

When sealing the vacuum bag around the mold what is the best way of ensuring a seal? Would mastic and duct tape do the job?

I have read of some people using cling film instead of peel ply. Presumably this will not let exes resin out, but will it still work to give a good finish and stop the bag from sticking to the laminate?

Any advice or comments welcome

Thanks

 

Maybe but unlikely you'll get good results. Most vacuum pumps used in vac bagging and infusion are required to pull a near perfect vacuum and for extended periods of time. Your industrial vacuum cleaner will likely pull 1/3 of the vacuum required and isn't likely designed to run for hours on end either. You'd be better off with an old refrigerator pump which will get you the higher levels of vacuum you require with the ability to run almost forever (more quietly and cheaper too).

When working with composites it's important to control the vacuum placed on a layup for consistant results. Having a way to know how much vacuum you're pulling is essential in getting good results and not wasting expensive materials.

Mastic tape, they type used to seal RV windows works well. It's 1/2 to 3/4 inch wide and 1/16 to 1/8 inch thick often referred to as "Gorilla Snot". You can get a 25' roll for under $10. I've tried all kinds of alternatives and none work as well as mastic tape.

Some people use cling films as a "poor mans peelply" with good results. It's always a good idea to test your materials before laying out expensive parts and risking poor results with untried materials. Normally the release film is perforated to allow excess resin to be caught in the breather material. If you can't get the excess out the part will come out resin rich (in some areas) and be heavier than designed. You'll likely have to pull untreated peelply from the laminate before the resin cures or it may become a permanent part of the layup.

You might want to do some research on "resin infusion" and "vacuum assisted resin transfer" for your project. There's plenty written here and elsewhere (some good vids on youtube).

This picture shows pretty much my setup.

 

ok, thanks very much. i will look into getting a refrigerator pump although i think i will do a trial run with the vac cleaner first. on your advice will also get some mastic tape.
It looks like you have quite an impressive set up.

 

You will be wasting your time with the vac cleaner,they don't achieve enough vacuum and the lack of airflow through the motor is likely to lead to its failure from overheating.Have a look on ebay for the real thing as it will lead to less cost than scraping a badly consolidated laminate.
As for cling film,are you aware of the difference between release film and peel ply?This post may appear disparaging but I would rather not see time and effort expended if the possibility of a successful outcome is not assured.

 

yes i am aware of the difference between release film and peel ply. i was just asking quite how necessary it is as others claim good results by using cling film.
I can see that advice here is that i am likely to write off a load of expensive materials if i don’t invest in a decent set up. I will be honest I expected this sort of response. Thanks.

 

Cling film over peel ply should be fine,it has worked for me when no other release film was available.You could look at the cost of a decent vacuum pump as a hire fee if you sold it on at the end of the project.The thing is they are just too useful to part with.

 

The industrial vacuum is better than nothing for sure, but you'd be surprised at how little actual vacuum is pulled on one. It's more of a volume issue than a pressure one. Give it a show and tell us how it works if it's free to you.

As far as sealing I use "tacky tape" which is very similar to what's been mentioned above. It has a bond that's refered to a "tenacious" and they're not kidding. Will cost a bit more than the above, but it's really designed for autoclaves and 350deg cycles. I'll try to get the exact tape number tomorrow if I can remember.

Cling film makes sense though I've not had the chance to give it a try. Glad you brought it up.

Probably a good idea to try out a small test panel first and see what you get.

Best of luck and do let us know how it turn out. First hand information is always welcome.

 

I think this link would be helpful.. cheers! http://composite.about.com/od/aboutcompositesplastics/l/aa000109.htm

 

Using an industrial vacuum cleaner is no bad idea at all. When in my company we decided to do our own offset printing, we purchased an expensive serious reproduction camera with a 50x60 cm glass plate and an integrated vacuum installation to press the film against the glass. After many years of service an electrical problem developed, so we opened the cover for the first time and... discovered a cheap small vacuum cleaner inside.

With only 25% vacuum there is a force of 2,5 N on every square cm, so on a 10x10 cm area there is already 250 N or 25 kgs to press the laminate together. The advantage is that your 25% vacuum is almost instantly there when you need it, where a vacuum pump needs several minutes. Also, you don't have to worry about small leaks, which makes sealing easier. In fact you need a small leak in the suction tube so the motor doesn't overheat.

 

Ok thanks CDK. I knew that I would never get a perfect vacuum but was hoping that what I could get using the vac cleaner would be better than nothing, or at least better than not using one. I will do be doing a test piece fairly soon and if anybody is interested will keep you informed.

 

Vaccume bagging is definately going in the right direction, using a static bag like capran is old school. Pva bag is much better no problems with releasing off the part and bag lines can almost be totally eliminated. Vaccume can be done also if money is an issue with your air compressor also. But to rent a pump is the way to go and around a min of 28lbs /sq in of vaccume if you have no other assistance with eliminating vaccume loss such as a surgical tubing trough. The bleeder used in the picture above is for infusion not so much for vaccume bagging. Using simple 1" white pvc piping cut in half and waxed with snow seal ( just wipe it on and leave it on) will also work as a bleeder also but u will need to make a catch jar in your mold. Old canning jars with paper cups in the jars for resin, fed from a 1/4" to 1/2" drilled and tapped hole with pipe through the lid of the canning jar and u feed the vaccume through the jar. This also can use more than one jar, if the part is as large as a kayak mold. pictures of the part would help greatly in helping with the best way to bag this part. Oh yes you will also need nylon paddles to move the resin under the bag, these are ussally hand made.