vacuum pump size

I have vacuumed bagged hulls as large as 100' and what I can tell you is that in order to enfuse a hull of the size your talking about you need a pump that has both high volume and high vacuum. [Read Expensive] You need the high volume to draw down the bag and you need the high vacuum to cause the resin to flow. I purchased a rebuilt 24 SCFM / 29 HG pump for about $2600.00 and I don't believe that pump alone would have done what your trying to do. You might want to consider vacuum bagging a wet pre-preg lamination but then you also have the added expense of additional bagging materials which can also be considerable. Forget using visqueen or any of the other short cuts you often hear of people trying. Best of luck with whatever you decide. I think it's an excellent building method if you can pull it off.

 

Hi Pjitty,
You need to get a pump that can run continously. A chinese 25m3/hr single stage oil vane pump will cost about $1200AUD so is not expensive. This will pull down to 2 millibar. Adequate for your task. You may need to pull the bag down intially with a dust collector or vacuum cleaner but once down it will cope with the process. You will also need a large resin trap. Big enough to hold a standard 9 litre bucket. It needs to have a clear top so you can see the resin level in the bucket. This is because as a beginner you will inevitably get resin through to the pump which is a very bad day. If you can see the bucket you can turn the taps off on the trap then change the bucket, then put the vacuum back on. The pump has to run continously otherwise the bag will decompress, even if you have a "perfect" bag the dissolved gases in the resin will decompress the bag enough to get a poor result.

Peter

 

Peter,

"The pump has to run continuously, otherwise the bag will decompress, even if you have a "perfect" bag the dissolved gases in the resin will decompress the bag enough to get a poor result."

That explains everything, because I thought I was still getting out gassing even after thoroughly warming the cold marine ply. Logic indicated I could turn off the pump on a composite test panel I was vacuum bagging with a vacuum cleaner after laying up by hand. A resin trap was not necessary for this procedure.

The cured panel was OK, but not the quality I expected. A timer for the vacuum cleaner might work to prevent overheating. I wonder if a vacuum pump powered by flowing tap water exists?

Cue http://en.wikipedia.org/wiki/Vacuum_pump

Pericles

 

My pump does't have to run continiously. See my previous post. I can set the vacuum switch to kick off at 29" and back in when vacuum falls to 27". It'll cycle itself off and on as required requiring no intervention from me. The resin I used has a very long curing time +8 hrs so I could just set it and forget it, come back 24 hrs later and demould.

 

Hi Rick,
For infusion it is very important for the bag to hold constant volume. If you turn the pump off and on the bag volume changes. It gets bigger as the pressure decreases, which means that something must be entering the bag to increase its volume. This means you have leaks or the resin is outgassing. 27"Hg is 90% vacuum, 29"hg is 97% vacuum. At 90% vac outgassing is unlikely so you have leaks. This means your bag volume is cycling with a 7% volume difference, I would not recommend this as a robust system. Personally I run my infusions at 99.8% vacuum or 29.9"Hg continously. This maintains a constant bag volume, evaporates any water in the job and bebulks/consolidates the laminate stack to the same thickness everytime.

If your happy with your results thats OK, but you will get variability and occassional problems with this system.
Peter

 

Vacuum Setup Demo

Kelsall Catamarans has been using Resin Infusion as a standard for 7 years. He will be here in the U.S. for a workshop in Florida. If you are interested in seeing the RI system in use there is still time to enroll for the workshop. Here is the link

http://www.multihulldynamics.com/news_article.asp?articleID=139

Pat Ross

 

May I make a distinction. Vacuum is vacuum, for this you need a pump that is able to pull that vacuum. Capacity is not important, it just takes longer to get that vacuum. I consider a small pump for my big infusion jobs (40'hull) as an extra safety fuse. My small pump will not overcome leaks in the bag while a big pump can hide them, that is to say till you open the resin valve. A perfect bag does the trick, not the size of the pump.

 

Using a shop-vac to pull the bag down initially works very well. Sealing up the hole for it once the bag is loosely sucked down is not difficult, a few strips of flash tape work fine.

If the bag is perfect, a remarkably small pump can do the job. It's amazing how few bags are perfect. A big pump shouldn't encourage you to be sloppy, but it will help to hide any inadvertent errors you might make in taping the bag up.

I don't think I'd ever want to use a single pump for anything of significant size. Most of the bagged parts I've done (largely prepreg), I used two pumps, even for stuff only a couple of square metres in area. You never knew when someone would run one of the pumps with no oil, or when one would break a belt, etc. The second pump also helped compensate for any pinholes that formed in the bag.

 

Small ejector pump

A small ejector pump did nicely suck over 30 kg of resin in 40 minutes. The Ejector made vacuum typically 65 -70 % with or without sagging.

 

We build vacuum pumps for the composote industry, and we use any pump of choice (6 m3/h to 150 m3/h), switched with a vacuum switch. (We use a RT121 from Danfoss for that). This vacuum switch is adjustable (by hand, no fancy electronics) for any desired vacuum level, and also an adjustable hysteresis, which can be between 3 and 100 mbar. (we normally set it at 8-10 mbar).

Big advantage is:
-reduced cost (no pump running 24/7)
-audible warning for leaks. When the pump switches on more often, it is time to take a look.
-adjustable vacuum.

----
There is nothing wrong with using a vacuum cleaner for getting the bag down. Just put the hose under the bag, suck most of the air out, then close the last part of the bag. But remember a vacuum cleaner is dependant on moving air for cooling. No moving air, no cooling...

----
About resin infusion media: I am surprised to hear about sunscreen material. I am sure it works, but at least here it is way more expensive then the infusion media we sell...

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About bags: Be carefull with Polyethylene bags. Usually there is a fair amount of recycled material in it, which tends to make the bag porous. Chasing leaks becomes an interesting job then... This seems to vary from batch to batch.
There are multilayer bags, like the L500 from Airtech, which are made of PE film, sandwiched between nylon film (or the other way round, I forgot). However, they make for durable, leak fee bags, and quite economical.

----
Water-driven venturi style pumps: Yes, they exist, I used them in the old days at school in chemical class, however, lot of water, low air flow. (quite high vacuum however). IF you get hold of them, opt for running them in a closed loop with an electrical pump. (or try and explain the African people that you are using potable water just for generating a vacuum...)

 

Andrew, Can you describe where the 30% shade cloth is situated in the layers of the laminate? Is it like a peel ply that peels off after the resin is cured? If it peels off, as I suspect, what kind of finished surface are you left with?

Thanks

Barry

 

You need some sort of separation layer between your laminate and your infusion mesh. Usually this is a perforated film. (more perforation = better)

Peelply also has the name of acting as a release layer, but unless you use a release coated peelply, removing the infusion mesh (which holds resin afterwards, and thus pretty strong and non-cooperating) and the peelply at once is a hell of a job.
Usually peelply is only used at places where it also performs another function: That of leaving a course surface, ready to accept further laminate, glue or anything else.

So basicly:

-laminate
-peelply (optional)
-perforated film
-infusion mesh
-runner system
-vacuum film

 

Herman, thanks for your reply. So, I can eliminate the peel ply by using a perforated film? And if the perforated film and presumably also the infusion mesh contain resin when the resin has setup does that resin come off with the film and mesh or does it remain as part of the composite? If it remains it seems it would be useless added weight.

I did see some kind of demo on one of the websites or forums that showed all this, but I can no longer find it.

Regards

Barry

 

I'm waiting for samples of "Soric" bulker/flow media.

http://www.lantor.nl/index.php/id_structuur/10599/soric.html

Interesting concept for a flow media that remains as part of the layup as a bulker. I know a little off topic for peelply/films but still part of the equation.

You can eliminate the perf film if you want a rough surface (texture) to your finished panel. The flow media and peel ply will bring any cured resin with it when you peel it back from the panel. Some builders leave their peelply on a panel while they're working it to protect the surfaces. Makes it a little harder to get off later after resin fully cures and if you do this you should use treated peelply only or you might not get it off! Don't ask me how I know this!

I've got a bunch of links to vids somewhere. Try Youtube or Google "Resin Infusion".

 

I've got a large 5 HP 3-phase power water cooled vacuum pump that is no use to me if you are interested. It is the TCP-50 model

http://www.anver.com/document/vacuum components/vacuum generators/pumps-tcp.htm

email me at donzi22classic@yahoo.com if interested.