Vacuum Bag

King,

Vacuum bagging is a method of using air pressure differences to clamp parts together. That's the simple part.

Having the vacuum suck the resin into the project is called infusion, and that's a whole lot more complicated. Do NOT try this unless you have experience with vacuum bagging. If you mess this up you have lost the entire cost of materials inside the bag. There are lots of ways to mess it up.

I've done a lot of vacuum bagging, none so far on boats. Getting even clamping takes practice and a bit of research. The way I think of it is like wrapping an odd-shaped gift. With your glass, you can cut the pieces to shape and adjust things in advance. With the bag you need to use bigger pieces, and those pieces need to fit.

Some vacuum films stretch a lot and that helps, but even so you should pay attention to corners both inside and outside, and places where the vacuum line goes. I usually use cheap film (in some cases visquine) which means I need to plan that a lot more.

If you're just using a vacuum bag, then uneven clamping means some parts of the project may be delaminated. If you're using infusion it means you can have a huge pocket of unwanted resin with no fiber in it, and with absolutely no purpose.

Another thing, vacuum infusion generally uses a really thin resin because you want it to flow through the fiber evenly with as few bubbles as possible. The infusion resins are often different chemical compositions than regular resins.

Finally, there's a difference in equipment. A vacuum bag can be used with extremely low-tech gear. I've used a shop vac as a vacuum source, some vacuum cleaner hose or even PVC for the vacuum line, some old blankets to even out the pressure and plain old visquine for bagging film.

Infusion, you need to have a hard vacuum. No worse than 25 inhg, preferably 29, and it needs to be maintained until the resin sets.

Everyone I've talked to about infusion says to start with small pieces and work your way up, and to count on a few total failures. Each piece is different in terms of what you can get away with, and practice makes you more able to judge what you need to do to make it work. I've started collecting equipment but still haven't done an infusion project. The first one will probably be a rudder.

 

Use common sense,example the worst thing is a "tight bag" and one does not have uneven clamping unless somehow a couple toy pumps are plumbed in or extreme leakage.

which is the second rule,have enough pump capicity to quickly draw down the bag if need be,I have seen these Idiots with the ac compressor turned into a pump and the mess they created, once the material is mixed you are on the clock.

which is my third rule,have decent wall clocks so you always know where you are at.

I do not know how one gets resin puddles? BUT stop and learn how to do it right.

Rule four,if using ester resins get a gel timer and do a workup on the bench that is common sense.

When wetbagging large sections by myself I would set the gel time for @ 3 1/2 Hours

Infusion I never let the pressure drop below 28 HG that is asking for trouble.

Do small test panels if it is a new resin system and laminate you are using.

Vacuum cleaners draw typically 108 inches of water while a good vacuum pump draws @ 33 feet of water. Not that you are using that for clamping or wetbagging.

Always try to use the proper material,You save money only to do it over with these "Shortcuts".

 

War Whoop,

I'm trying to point out that there's a huge difference between vacuum bagging and infusion. Vacuum bagging, anything that creates any sort of clamping force counts as vacuum bagging, but infusion is much more specific.

Uneven clamping: If the bag seals right to the epoxy at some point, the pressure in one area might be different than the pressure in the other. I've seen this using wood, not really with glass. In the method I used, we did the layup, put down a barrier sheet to keep the bagging gear from becoming part of the project, then put a breather layer down, then vacuum "supply" lines, then more breather on top of the lines, then sealed the bag. If there is insufficient breather to take care of leakage then you have uneven clamping. If your pump is low volume, a tiny leak can make uneven clamping.

I agree with the high capacity pump, but also know where that pump overheats. Some pumps seem to have a high capacity but not much duty cycle. Keep in mind you need to keep a hard vacuum for most of the cure period, which can be hours. If you're going to get serious about it, use a vacuum reservoir just like a compressor's air tank.

If you're doing an infusion and your bag is forming a fillet over your project (high point to high point, not enough bag to go down all the way down to the surface) you get a puddle of resin in there that does nothing good.

 

We all know there is a difference, I have my own Infusion system.

I have never had a single problem Gluing/Corebonding and HOW is a bag going to become part of the work?? you may well have made a real adhesive breakthrough here.

A space!!!!! what on earth are you using for a bag sheet steel?? at 28 HG there is not much "Bridging" even with the poorest bag setup.

I use large pumps in fact one is for sale in the material section, they run until I turn them off as I will not take a chance on a questionable pump.

You need experience in a Professional shop.

 

Oh Ok, I thought it was a freeze dried mammoth next to a window.

Thanks.

(Now back to our normal program..)

-jim lee

 

@War Whoop,

If you look at post #6 of this thread, you'll see that the OP did NOT know the difference between vacuum bagging and infusion, and was asking for information on how to vacuum bag. That pretty much means he's an amateur, and from the rest of his posts he's got one project to do, not setting up for business.

I'm not trying to sound like a professional, and not trying to tell you about what sounds like part of your business. I'm an amateur, meaning I've done some vacuum bagging in my garage and in other people's garages. I've talked to professionals to learn how to go about this, and I'm familiar with the problems that I had when trying to figure out what the professionals were saying. I would bet that when you say what you say, what the OP understands is quite a bit different than what you're thinking when you say it.

With all that said, I will step out of this thread and let you tell this guy how to set up a shop and build a million boats.

 

I answered in post #10