RE: Vacuum Bagging Techniques

RE: Vacuum Bagging Techniques
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RE: Vacuum Bagging Techniques - 11/23/2004 5:47:09 PM

HenrikJohansson

Posts: 40
Joined: 8/29/2003
From: Vaxjo, SWEDEN
Status: offline

Magne,
The peel ply only need to be used in areas of the lay-up there you will be gluing in the firewall etc to improve the bounding between the parts.
Of course you could use peel ply in the whole lay-up but that would be some very expensive grams to save. The perforated film goes in all other areas.

Brian,
When I make my parts I pull aprox -850Mbar (using breather on the entire lay-up ) of vacuum and the layup goes in the cure oven at 50C, immediately when I’m done laying up the cloth.
I’m not really sure why I’m getting all those pinholes, but it’s certainly not because I don’t have enough vacuum nor the epoxy being to thick.

I was guessing that the problem was that the epoxy got too thin and too much of it went in the absorber, making the layup too dry?

(in reply to buttuh)

Post #: 26

RE: Vacuum Bagging Techniques - 2/16/2005 11:48:30 PM

TGDF

Posts: 133
Joined: 9/27/2004
From: Hoffman Estates, IL, USA
Status: offline

quote:

ORIGINAL: Mike James

I should've used quotation marks, as in ...

The peel-ply is the "perforated release film". I know they're two different products, but we're only using the peel-ply. Actually, Aircraft Spruce's name for it is "Nylon Release Ply". It reminds me of parachute material.

VVvvvvveeeeeeeeerrrrrrrrrrrrryyy interesting.

I bought some perforated release film (Stock #V-20A) and some peel ply (blue with release Stock #V-18AV) from Aerospace Composite Prods. I bought the peel ply because the description was vague, they were listed right next to one and other, and I was unsure what the difference between the two was. That was almost a month ago. I'm just getting ready to try some bagging and after reading the above post, I pulled out the two packages (which until now I had only glanced at) and sure enough, one is a perforated plastic film (which I expected from the description) and the other is regular peel ply cloth, except that the weave is almost microscopic compared to the other peel ply I've got. The threads are so fine that when it first came and I took a quick look, even in full daylight I thought it was a non perforated release film. (Please don't assume from this that ACP's description was vague or lacking. I may have must misread or misunderstood.)

This bagging stuff gets more and more interesting. So many generalities. So few particulars. Makes for so many possibilities. Boggles the mind.

My question, which should be answered soon with an actual part, is, if you bag a foam wing with balsa, then glass it:

1. Do they vacuum bag the surface glass?
2. What kind of finish does the final layup (bagged or not) have?

_____________________________

-Terry
www.TerrenceFoley.com

(in reply to Mike James)

Post #: 27

RE: Vacuum Bagging Techniques - 2/16/2005 11:51:59 PM

TGDF

Posts: 133
Joined: 9/27/2004
From: Hoffman Estates, IL, USA
Status: offline

quote:

ORIGINAL: HenrikJohansson

(Big Snip)

I was guessing that the problem was that the epoxy got too thin and too much of it went in the absorber, making the layup too dry?

H-

Exactly what kind of parts have you been fabricating?
Glassed foam or glass in a mold of some sort?
I'm dying to know more of your experience.

_____________________________

-Terry
www.TerrenceFoley.com

(in reply to HenrikJohansson)

Post #: 28

RE: Vacuum Bagging Techniques - 2/17/2005 5:45:43 AM

TT2

Posts: 648
Joined: 3/19/2002
From: Osborn, MO, USA
Status: offline

quote:

My question, which should be answered soon with an actual part, is, if you bag a foam wing with balsa, then glass it:

1. Do they vacuum bag the surface glass?
2. What kind of finish does the final layup (bagged or not) have?

1. Generally speaking, no. The surface glass is typically very light (0.7 oz-ish) glass that's either applied with epoxy (heavy) or polyurethane (water-based or solvent-based depending on your preferences). Then the surface is sanded, filled with more epoxy / polyurethane, sanded, filled, until the weave is completely filled.

That being said, it might be possible to apply most of the glass at the same time as the balsa and save yourself some work. This would involve using 0.010 or 0.014 Mylar sheets to serve as 'carriers' for the lightweight glass. Essentially you would be creating a wing much like the way 'traditional', non-molded HLG (hand launch glider) wings are created with an extra layer of balsa between the glass and the foam. The mylars would be cut about 1/8" oversize of the wing core and then waxed. The light glass would be layed out on the mylars, trimmed slightly oversized, wet out with epoxy, then trimmed flush with the mylar's edges. Then the 'stack' would be created:
- Mylar
- Glass / epoxy
- balsa
- epoxy (or polyurethane glue)
- foam core
- epoxy (or polyurethane glue)
- balsa
- Glass / epoxy
- Mylar

Adjust the mylars to ensure that they are in the proper positon and then vacuum bag. The mylars could even be painted with primer before laying on the glass and save an additional step.

I've bagged loads of HLG wings (glass/carbon/foam/carbon/glass) but have never tried the method above. I'm sure that some of the pylon racer guys have tried something like this before moving on to fully molded wings, so maybe one of them will chime in.

This is a broad generalization and there are many process 'tweaks' to bagging wings like this...without the balsa. I don't see why it wouldn't work with the balsa. There would be a bit of secondary glassing around the LE, hingelines, etc., but I believe that it could still save you some time. I've done the polyurethane-ing, sanding, repeat-until-hell-freezes-over, and while it produces nice results, I have found it to be very time consuming.

2. The glass would show a little bit of the weave but the weave would disappear after one coat of primer / sanding. If the mylars had been primed before bagging the wings would be ready for the sanding / painting.

-Tom

< Message edited by TT2 -- 2/17/2005 5:52:02 AM >

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As complexity approaches infinity, mean time before failure approaches zero...

(in reply to TGDF)

Post #: 29

RE: Vacuum Bagging Techniques - 2/17/2005 8:21:30 AM

TGDF

Posts: 133
Joined: 9/27/2004
From: Hoffman Estates, IL, USA
Status: offline

quote:

ORIGINAL: TT2

(Big Snip)

If the mylars had been primed before bagging the wings would be ready for the sanding / painting.

-Tom

Thank you. That was helpful. I think I'm on the right track.

In a day or so I'm going to try to make a cylindrical fuse by bagging some glass around a plug. I'm trying for light weight so I'm going to use a ply of uni glass between 2 ply of bid glass. For strength I was hoping to put another similar layer on the outside with a layer of thin packaging foam in the middle. Unfortunately, the foam I had in mind, which looks like it would be perfect, turns out to be polyethylene which the epoxy might not stick to strongly. I've been thinking of using that real flexible, one sided corrugated cardboard instead. I was thinking of using a glass sphere paste on the wavy side of the cardboard to keep the vacuum from crushing it totally. Wish I could find a flexible sheet of foam about an eighth of an inch thick. As its pretty much a test, I might use the foam anyway. The plug is four inches in diameter so I could try balsa sheet but I'm afraid it might be too springy and be a fight.

(sigh) No matter how systematized your system is, the devil is always hiding in the details.

_____________________________

-Terry
www.TerrenceFoley.com

(in reply to TT2)

Post #: 30

RE: Vacuum Bagging Techniques - 2/17/2005 12:56:20 PM

Magne

Posts: 333
Joined: 3/7/2004
From: Moss, NORWAY
Status: offline

quote:

The plug is four inches in diameter so I could try balsa sheet but I'm afraid it might be too springy and be a fight.

Wet (soak) the balsa with water and string it up on the plug to dry for a day or two. It will then retain it's shape.
Magne

(in reply to TGDF)

Post #: 31

RE: Vacuum Bagging Techniques - 2/17/2005 3:42:12 PM

TGDF

Posts: 133
Joined: 9/27/2004
From: Hoffman Estates, IL, USA
Status: offline

quote:

ORIGINAL: Magne

Wet (soak) the balsa with water and string it up on the plug to dry for a day or two. It will then retain it's shape.
Magne

Yeah, I've heard of that. Glue, sand, wet, form..... (Grin, sheepish) What I should have said more honestly is I'm too lazy to go to the trouble. I want a LensCrafters Fuse. I want it layed up and bagged in about an hour. In my defense, it probably would be better to finish the whole structure before one side of the sandwich cures. Probably a small difference as its common to make up additional, symmetrical sides a sandwich in separate cures. MMmmmmmmmm, now that I think of it, it is common to lay up the second side of a wing after the first side cures in a non symmetrical layup. I guess I have no defense after all. (Doesn't that flex or warp the wing?)

(Are LensCrafters nationwide? Whatever. For the benefit of the rest of the world, LensCrafters is a chain of 1 hour eyeglass stores in the Chicago area. Their slogan is that they have your glasses ready in about an hour. Yuck, yuck. I made a funny.)

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-Terry
www.TerrenceFoley.com

(in reply to Magne)

Post #: 32

RE: Vacuum Bagging Techniques - 4/2/2005 8:29:08 PM

TGDF

Posts: 133
Joined: 9/27/2004
From: Hoffman Estates, IL, USA
Status: offline

quote:

ORIGINAL: TT2

(Snip)

That being said, it might be possible to apply most of the glass at the same time as the balsa and save yourself some work. This would involve using 0.010 or 0.014 Mylar sheets to serve as 'carriers' for the lightweight glass. Essentially you would be creating a wing much like the way 'traditional', non-molded HLG (hand launch glider) wings are created with an extra layer of balsa between the glass and the foam. The mylars would be cut about 1/8" oversize of the wing core and then waxed. The light glass would be layed out on the mylars, trimmed slightly oversized, wet out with epoxy, then trimmed flush with the mylar's edges. Then the 'stack' would be created:
- Mylar
- Glass / epoxy
- balsa
- epoxy (or polyurethane glue)
- foam core
- epoxy (or polyurethane glue)
- balsa
- Glass / epoxy
- Mylar

Adjust the mylars to ensure that they are in the proper positon and then vacuum bag. The mylars could even be painted with primer before laying on the glass and save an additional step.

I've bagged loads of HLG wings (glass/carbon/foam/carbon/glass) but have never tried the method above. I'm sure that some of the pylon racer guys have tried something like this before moving on to fully molded wings, so maybe one of them will chime in.

(Snip)

-Tom

Wouldn't the mylar peel off? I ordered some acetate as a release film. What they sent me was their acetate substitute which as far as I can determine is mylar. It generally comes off as easy as dacron peel ply. It is a frosted film rather than clear so it sometimes requires a bit of persuasion to release. And, sort of unbelievably, the epoxy actually picks up the frosted finish of the film!! I knew that epoxy duplicated the mold surface, but the frosted character of that film must be in the 10thousandths to millionths of an inch ballpark. It gives a really silky feel to the finish. Like the finest peel ply finish you can imagine.

_____________________________

-Terry
www.TerrenceFoley.com

(in reply to TT2)

Post #: 33

RE: Vacuum Bagging Techniques - 4/3/2005 5:45:22 AM

crook

Posts: 73
Joined: 1/1/2005
From: Bellflower, CA, USA
Status: offline

even more then that is how you make your bag, and where you place vacuum ports, and not bleeding to much of the resin. First these hobby parts are more for cosmetics then they are structural, soon resin content on the higher side (50-60%) is preferable. Also when vacuum bagging a part or mold make sure your bag is big enuff and what i mean by that is , well just make it huge at first. We say "never have a bag to big" this well provide you excess bag to work out tight areas of vacuumed bag, so you do not bridge bags in certain areas...mainly corner, deep pockets and places like that.where all the all bubbles go to and stay there because bag wasnt firmly pressed in that area, just like an air pocket, or considered a VOID. You need to really inspect and work your bag to make sure theres is no bridging mainly on any surface that will be showing. Just dont turn on vacuum , watch it suck down , check for leaks and think its all good, you may get away with it once , but thal'll probably be it. also your vacuum ports it where the air is being sucked out of your bag, right?..so your resin is going to tend to travel that way. we have seen plenty of hoses get filled before solid, the next morning we came into work....solid stiff $200 hoses in the trash..opps.. just something to think about also when baggin up your parts or tool or whatever application you are doing.......well thats my 2 cents!!

quote:

ORIGINAL: BFoote

Pinholes are caused usually by air bubbles. Air bubbles you say? Its in a vacuum.... Well not really. If you want excellent vacuumed parts you have to have a very good vacuum AT ALLLLLL parts of the vacuumed part, not just at the gauge on the pump! Using breather cloth to give air a route to the vacuum is important. Number of pinholes is lessened to almost nothing the better the vacuum that you have. Ok that was a horrid gramatical sentance. Anyways, if your vacuum is anything lower than say 24 in Hg your work will not be as good. Also, make sure your epoxy is THIN. Reason vacuum works so well is that it moves the resin like a squeege but with more pressure than you can do in a traditional wet layup.

Cheers
Brian

(in reply to BFoote)

Post #: 34

RE: Vacuum Bagging Techniques - 4/3/2005 6:55:12 PM

TT2

Posts: 648
Joined: 3/19/2002
From: Osborn, MO, USA
Status: offline

TGDF wrote:

quote:

Wouldn't the mylar peel off?

It better! Of course the smoother the mylar the easier it will release. I have prepainted the mylars for HLGs with great success...the paint transfers beautifully from the waxed mylars to the glass...but that's another topic that has been covered pretty well recently.

You can use strips of peel ply inside the bag to serve as a 'resin break' between the vacuum hose and breather. This will prevent resin from being sucked into the hose even under full vacuum. In severe cases (or when using VARTM) you can also use a resin trap. These can be easily made for a few bucks (as opposed to the $$$$ for the larger commercial ones)...I use a big glass jar with an aluminum plate lid sealed with tacky tape. A vacuum gauge and two brass barbed bulkhead fittings thru the lid. When the jar gets full of resin I just pitch it and grab another one.

-Tom

_____________________________

As complexity approaches infinity, mean time before failure approaches zero...

(in reply to crook)

Post #: 35

RE: Vacuum Bagging Techniques - 4/3/2005 8:20:55 PM

TGDF

Posts: 133
Joined: 9/27/2004
From: Hoffman Estates, IL, USA
Status: offline

quote:

ORIGINAL: TT2

TGDF wrote:

quote:

Wouldn't the mylar peel off?

It better! Of course the smoother the mylar the easier it will release. I have prepainted the mylars for HLGs with great success...the paint transfers beautifully from the waxed mylars to the glass...but that's another topic that has been covered pretty well recently.

You can use strips of peel ply inside the bag to serve as a 'resin break' between the vacuum hose and breather. This will prevent resin from being sucked into the hose even under full vacuum. In severe cases (or when using VARTM) you can also use a resin trap. These can be easily made for a few bucks (as opposed to the $$$$ for the larger commercial ones)...I use a big glass jar with an aluminum plate lid sealed with tacky tape. A vacuum gauge and two brass barbed bulkhead fittings thru the lid. When the jar gets full of resin I just pitch it and grab another one.

-Tom

Sorry, sorry. I re-read where you said to wax the mylar. Now I see you meant painting the inside of the mylar.

That looks like it would work well. In fact I'm going to try something similar using a thin flexible foam rather than balsa. I want to cut out the time you have to spend cutting, gluing and sanding small sheets into larger ones and then waiting for the shaped wet balsa to dry. I don't think the extra strength and surface hardness comes at all from the stiffness of the balsa. I'll bet dollars to donuts that it comes from the properties of the sandwich itself. The square of the separation of the layers thing. A 1/16 or 3/32 thick sheet of anything is not much, but its a whole lot more (infinitely more?? (sigh) that's a stupid highschool question) than the square of zero thickness.

I think if the balsa is stiffer than foam, the sandwich will be stiffer, but the difference will be small compared to the effort and time saved. If end grain balsa means the grain runs from surface to surface rather than lineally along the surface, the only thing that would be stronger than that is one of the synthetic honeycomb materials. But I think a thin sandwich of just about anything (shirt cardboard even) would end the complaints of how fragile and dentable the surface of a foam wing is with just one layer of 1oz glass.

Your resin trap sounds like my home made stuff. I've never bagged anything so juicy that I got resin in the hose. But I do reuse my peel ply and mylar on non critical areas. A dollar saved is tax free income!! Use that stuff till it falls apart!! My breather is paper towels and old sox. Bags by Hefty!

Also, per 3M, ordinary 3M Scotch Magic Tape is made of acetate! Adhesive backed release film, in other words!

_____________________________

-Terry
www.TerrenceFoley.com

(in reply to TT2)

Post #: 36

RE: Vacuum Bagging Techniques - 4/28/2005 1:00:27 AM

mithrandir

Posts: 680
Joined: 7/16/2003
From: adelanto, CA, USA
Status: offline

Simple... wax the molds as usual.... then... spray primer into the mold, let the primer kick for 12 to 24 hours and then lay up your part... with or without vacuum.... the pinholes come from the epoxy wanting to "Bead-Up" like water does on a freshly waxed car...but the cloth weave doesn't alllow it to bead... just a pin hole pattern that forms between the individual tows of cloth...

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Post #: 37

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