Vacuum Pump Suggestions

I'm shopping for a new vacuum pump.

I have experience with wet layup and smale panels on a 4 x 8 mold board with a small pump.

I'll be starting some bigger projects --- bigger vacuum pump and I figure more forgiving on the leakage.

Perhaps in the future I'll move into resin infusion.
Is it worth it for me to buy a pump capable of resin infusion now? or cross that bridge when it get to it. ??

The resin infusion certainly appeals. Much of the work being done by the vacuum pump. Yes -- I know there are many caveats. I've seen it done, but have never done it.

My shopping guide for vacuum pumps is the Grainger catalog and that is probably where I'll buy the pump.

Suggestions??

Thanks in advance for your help.

James Mills

 

Pumps, if respected, last nearly forever.

I rebuilt a 50-something-year-old Welch two-stage rotary last year. It was the unit's first overhaul, ever. A vane spring had broken and some seals had seized from someone (not me) running it with no oil. Other than that it was in nearly perfect shape. I don't think I've ever used a vac pump younger than myself.

The moral of the story.... if you're going to make the investment, get the best you see yourself needing in the near future. It'll last forever anyway, if you take good care of it.

About that "more forgiving on the leakage", though.... higher flow pumps might be a bit more forgiving, yes, but you usually sacrifice a fair bit of pressure by trying to let a bigger pump compensate for a bad bag. If you want to move to infusion, you must learn to bag with no leaks- and I mean no leaks.

 

I picked up a Robinair 15500 5 CFM off of e-Bay. They're selling now for about $180. Should be capable enough to do some larger scale infusions down the road.

 

if you want to play resin infusion, have a look at the Diab web site, we are using their products in China and no worries, sealing the job correctly is the biggest pain, the vacuum pump is sized to the surface area concerned, so think before you waste money on a tiny pump, it will take days to pull down if it is too small.

i first did this with SP products in Sydney Harbour in the 80's, i still use the same pump, so yes they do last forever if looked after.

 

Hi All,

I'm on the same path as James here... so if it's ok James I have some Q's too ? Seems silly to start a parallel thread on this.

I have 5 vein pumps, 1/4 hp 230V. I assume these are ok for vacuum bagging ? I've read up on them before and they have been said to live forever. The label on them also says continuous rated.

I have made a few vacuum connectors, tested, they seal well in the plastic, garden hose connectors with thread, going through a penny washer and screws into a polyethylene disk I've tapped thread into. Nothing sticks or glues to polyetylene.

Two vacuum resin traps. I'll go look for some more connectors tomorrow. The resin supply pipes are going to be thicker than the vavuum ones.

 

Geezzzz... seems everyone is on holiday (or someting).

If you vacuum bag without peel ply, does the plastic smoothen the finished surface any ? I have a few simple and small pieces to vacuum bag, but I don't know what to expect (yet). Any comment on it appreciated.

 

Thanks for the advice.

Anyone hear of or have experience with Voit vacuum pumps.??

Fannie, I've only done flat panels on a mold board. No peel ply. Lay down the laminate, place the core on top and then suck it down. After cure, flip it over, lay it down again on wet laminate, and suck it down. If you have wet laminate against the bag, any place you have wrinkles in the bag, you'll get that look in your part. I've seen that on boats I've worked on.

My understanding about peel ply is that one of its purposes is to suck out any excess resin in the laminate. If you put too much vacuum on the bag, you'll press too much resin into the peel ply and get a too dry laminate. If you make a mistake and accidentially suck it down too hard, that's it, the resin is on the wrong side of the peel ply.

Good luck.

James Mills

 

In a vacuum bagging technique the purpose of the peel ply is to allow for the separation of your composite stack (core, reinforcement & resin) and your breather material and bag. It is a semi-permeable material, usually nylon or polyethelyne, without binders, that will easily (in most cases) allow you to peel the expendible materials (breather & bag) from your layup. In some materials it will also help, to a small degree, distribute you resin around your layup. Peel ply differs from release film in that it leaves a textured surface that has to be finished. Release film is more like your vacuum bag but with evenly distributed holes to allow resin to migrate from your layup stack to your breather material.

I have seen methods like James describes but only on small parts. If you're suggesting laying up a composite panel w/o peel ply or a release film then you might run into problems with inconsistant vacuum, puddles of resin rich areas and other areas that are resin starved. You will get a shiny surface only if you use no breather. There are some methods that use a breather type material (core mat) that are incorporated in the process into the composite part. Without the breather you'll have a hard time getting an even distribution of vacuum especially if the part is large.

I would recommend getting some cheap materials, blue foam, regular glass cloth and some cheap epoxy and trying the various release films, peel ply's and breather materials available to you. I've had good success with materials bought at the local fabric store. Nylon liner (used on the inside of jackets & dresses) as peel ply and some parachute nylon from the army surplus store. I've also used fiberglass filter material (type used in furnace filters) as breather. Once you get to infusion you'll be looking for flow media. I've gotten a lot of samples from mfgrs and retailers free for the asking. Just tell them you're learning and experimenting with the process and material and they're usually wiling to oblige with free samples or cheap roll-ends.

 

No such thing as too much vacuum. It is possible to bleed your layup too much. Especially on vertical surfaces, but that also involves poor resin choice. Ive found that higher CPS epoxies (600cps +) make for better asthetics when bagging. For that matter, really dont like 600 cps for bagging either.

Best thing you can do is weigh your cloth and use the equivalent amount of resin (theres a lot more to this, but its a good starting point). Guessing can leave you dry, or, really over saturated. Being carefull not to trap air between plys is key, once air is trapped, its really hard to get it to travel anywhere once vacuum is applied. You would think vacuum/pressure would get it moving, but, most of the time it "locks" it in place while your resin is moving elsewhere.

Another way to control bleed is to use perforated release film with various hole diameters depending on how much resin you want to bleed.

 

Fanie,

I've only done vacuum bagging on the cheap. Formica topped mold table, plastic sheathing from the hardware store, bubble wrap for bleeder, and some padding to keep sharp edges of the part from puncturing the bag. Made some nice lightweight polypro' honeycomb and Nomex honeycomb panels that replaced some plywood in a Nomex cored 27' racing catamaran. It was fun and I learned a lot. It made me want to go further with it. The boat turned out well and it is great fun to sail.

Following are quotes from a MAS Epoxies hand out from an IBEX seminar:

"Planning a vacuum bagged repair is the key to success. Time and money may be quickly wasted if an unplanned vacuum repair is executed improperly. Resulting laminates may be dry and airy looking and suffer from low compression fatigue resistance. Over vacuumed (consolidated) laminates are dry because all the resin has been sucked/squeezed out of the laminate (again that great sucking sound , and its not jobs going to Mexico). "

""Caution must be taken not to over consolidate the laminate (i.e. too much vacuum). If this occurs needed resin will be squeezed out through the peel-ply and perforated release ply. This lost resin will not be able to find its way back into the laminate"

"The remaining resin must be monitored in a thin film (I use whatever is left on the laminating table). Using a cotton ball simply dab the cotton ball onto the wet resin film. When the film pulls out lots of fiber from the cotton ball the laminate has set."

"Once the resin has set the needle valve may be fully closed and bag chased for leaks (vacuum levels will likely be in excess of 29" of Hg depending on your pump set up). This final consolidation will squeeze down any remaining micro bubbles with out driving resin out of the laminate (just like tightening a vice)."

The sheet recommends 12" - 14" of Hg prior to the laminate setting.

All the book learning in the world is no substitute for hands on experience.

I was fortunate to have some boat builders experienced in vacuum bagging to help me with the learning curve.

Good luck !!!!

James Mills

 

As I also have it is there are no such thing as too much vacuum. I also understand that you want just enough resin in the material to wet it out, anything more just adds weight and does not contribute to the part's strength.

I know there are glass parts made that has a mold and it gets pressed by pressure instead of vacuum to get as dense a panel as possible, many times more pressure than vacuum bagging. I suspect PCB's (printed circuit board) are made this way. If I can get my boat's hull like that in ie a 3mm - 4mm thickness, I will be a very happy person. The proper amount of resin to glass weight when you vacuum bag, I've read, should be around 60%.

An article I read recently showed the layups, then peel ply, then some absorbent material that would absorb excess resin and lastly of course the plastic bag.

Then after vacuum was drawed on the piece, and leaks sealed (if any) the resin is mixed (while everything still under full vacuum. The taps are then opened and the resin is sucked through the layups. This guy had multiple resin supply buckets and multiple vacuum points going to his resin traps. This allow faster wet-out time and better control of certain areas as you can open or close the supply or the vacuum at various points.

Once the whole layup was wetted through, the resin inlets are sealed and the piece was left under full vacuum until the resin cured, 24 hours in his case.

The pumps then goes off, peel the plastic bag, and peel the peel ply with the absorbent off. This seemed quite thick in some places, but what was left over was the wetted out layup with minimum resin, now cured of course.

The job did look very good.

 

That would be resin infusion. Only no absorbant material is needed for excess resin. You control the resin content by cutting off the resin flow at a pre-determined point. Some people prefer to use flow medium on top of the peel ply, its not really needed, but it does speed up the infusion process. I use it.

 

Hi JRL,
Is resin infusion different from vacuum bagging then ? I was under the impression it's the same thing...

 

Here's a few things I wrote when I was teaching myself infusion.

http://www.compositeforum.werksberg.com/showthread.php?t=2588

http://www.cruisersforum.com/forums/f55/two-new-obsessions-8759.html

infusion stuff is a little farther down in the thread

and

http://www.compositeforum.werksberg.com/showthread.php?t=2285

Here's a good primer from Gurit, definitely worth a read.

http://www.gurit.com/core/core_picker/download.asp?id=141

 

Different, definitely. Similar processes with similar results.

Vac bagging you hand spread the resin. Infusion the resin is pulled through the laminate stack by vacuum.