What do you think of this???

General Composites Discussions Composites Talk
#1

I recently purchased some 4" wide fiberglass tape (according to the specs the stuff is similar to 10oz cloth) from Fiberglast with the intent of using it in lieu of manually cutting several 12 foot long 4" wide strips from a roll of style 7781 eGlass. To test the thickness of 1 and 2 layers of the aformentioned glass tape I prepared two test samples on a flat piece of glass. Test stack #1 was: peel ply, one layer 10oz tape, peel ply and test stack #2 was: peel ply, two layers of 10oz tape, peel ply. I used peel ply on both sides becuase I wanted to squeegy out the excess resin and get a realistic idea of the final thickness of the cured laminate. I used vinylester resin catlyzed at 1% for both samples… 24hrs later I peeled the test laminates off off the glass table and removed the peel ply and to my surprise I was able tear the 1 layer laminate about as easily as tearing a strip of cardboard box… yikes! And I can tear as easily in both the 90 and the 0 axis… The two layer laminate tears too but is a bit tougher. So my question is: Is this normal? I know for certain that I cannot tear a layer of my 7781 eGlass… at all. Do you think I purchased some inferior fiberglass tape? The application isnt structural but I do want it to be tough and tearing a layer by hand as easy as cardboard isnt my idea of tough…

Thoughts comments appreciated.

James

#2

Style 7781 is a 8H fabric while your tape is a plain weave fabric. 8H are less prone to “zippering” along the weave pattern than plain weaves. With an H8 you have yarns crossing the perpendicular yarns that are not crimped which make them more difficult to tear. This is one of the reasons that H8 woven fabrics are used in more demanding applications. They still can zipper though along the weave pattern.

The best way to eliminate zippering is to put a layer of fabric at +/-45 to the 0/90 layer. This will make a tougher laminate.

#3

We use BGF 7781 as our main backing in most carbon applications, we stock both versions, certified for aircraft use and non-certified. I stick to it because of what Wyo mentioned above, I find it really easy to work with. I have never tested the 10oz plain weave style like you have, often when we use it is as backing on the mould and 8 layers thick +/- 45 on each layer.

We do have to build a composite shell tomorrow, I may try this to and let you know if I have the same results if that helps at all.

#4

Thanks for the replies… SLS, I look forward to the results of your test tomorrow. On a side note: Does anyone sell an 8H fabric tape (ideally 45 bias) that is comparable to the 7781 cloth?

#5

I have never seen it. You also will not find fabric tape that is bias woven. You can make it your self though. Get a large woven sleeve and split it down the middle. That is how bias wovens are made. They are very prone to distortion and difficult to handle. It’s much cheaper to just cut it from fabric.

#6

1 layer of a 10oz cloth is pretty flimsy so Im not surprised you can easily tear it.

As someone else mentioned I dont think you will really find fabric tape other than for plain weave or uni.

On another note, fiberglast is very very expensive for almost everything they carry. Even with thei 20% off everything deals they run, (one is going on today) their prices are still higher than most other suppliers.

If you are looking to try out different types of fiberglass, my recommendation for a cheap supplier would be Thayercraft.com They sell various types of fiberglass in bundles as small as 10yds, everything from .5oz cloth to 50oz cloth

#7

Thanks for the heads up on the suppliers dusty! I’ve decided to purchase some straight line tape that you place on the fabric and then cut down the middle of the tape to keep the edges from fraying… I’m thinking this will be just the stuff to help me not only cut long 4" wide strips of my 7781 cloth on a 45 bias but also keep the long strips from stretching or otherwise deforming until I can tack the cloth in place with a light mist of spray adhesive… then I hope to remove the tape without distorting the cloth… repeat for a 2nd layer … then lay my bagging materials and infuse.

This particular project is to add a couple of layers of 7781 cloth to the leading edges of a composite aircraft to make the leading edges more durable (the rough leading edges have been shaped to the correct profile by first sanding/shaping approx 1/8" to 3/16" thick resin/micro balloons as a lightweight filler). I want to infuse the two layers of cloth to avoid a bunch of sanding later on down the road which would surely be the result of trying to add the laminates via wet layup…

I plan on bodyworking, priming, sanding & preping the entire wing surface for paint once I complete the leading edge laminates.

Question: Would using peforated release film under my flow media leave a more desirable surface (leading edges) for priming/prepping for paint or would using the red stripe peel ply with its slightly textrued surface be better (give the primer more texture to bite into)? In other words, which method would require the least amount of sanding prior to and after priming to get the surface ready for paint??

#8

Perforated release film is not for infusion. In one of your paragraphs you said to infuse the two layers together. If you’re using vacuum resin infusion, don’t use perforated release film. Use peel ply.

Perforated release film is for wet layup vacuum bagging only

#9

Jbocek, are you familiar with Mylar transfer method? With the this process you take at .014" Mylar, wax it, prime/paint it, and do the layup on to the Mylar. Then you transfer the Mylars to the wing core and put the whole thing in a vacuum bag. Once cured you peel off the Mylar. The paint then transfers to the part and very little finish work is necessary. The Mylar creates a nice glossy finish. This is a great way to do the skins on flying surfaces for low production work.

#10

Perf film style P, P1, P16 and MP22 are perfectly suitable for infusion. A thick infusion mesh can hardly be removed from the laminate without it. (unless you are using Compoflex material).

Also prepregs use perf film.

Peelply is nice, but the name is a bit distracting: you can peel it off, but peeling it with a number of other consumables can be a real pain.
Perf film is normally referred to as “release film” and guess why…

#11

I stand corrected and learned something Herman. Thank you.

Can you please explain what P, P1, P16, and MP22 are and where to get them?

Thank you.

#12

Thankss for all the great ideas guys! I’m new at this and your great tips & ideas are exacly why I love this site!

WYOWINDWORKS: No I’m not familiar with the mylar transfer method but it sounds like a very useful tool to add to my bag of tricks!

Herman: So is it perfectly acceptable for my stack to look something like this?: one layer 4" wide x 20’ (approx) 7781 eGlass strip cut on a 45 bias and lightly tacked to the my leading edge with spray adhesive, then a layer of either peel ply or release film, then flow media or compoflex RF150, then bag and infuse?

My leading edges are currently sanded/shaped from a lightweight mixture of vinylester resin/micro balloons that is approx 1/16" to 3/16" thick - this fill wraps back approx 2-3" on top and 2-3" on the bottom leading edge of the wing. The reason I want to infuse the 7781 cloth is because I feel the resin/micro balloons might not be durable enough (fairly soft material that is easily nicked/damaged) to hold up over the years. The cloth I feel will give a nice durable outer skin to the resin/micro balloons on the leading edge that is resistant to chiping. I thought of adding two layers but the I’m already adding .015" per layer and two is going to add too much material to my LE thus changing the airfoil shape more than I’m comfortable with and creating more body work to blend the laminates to the rest of the wing.

A few follow on questions:

  1. Is it acceptable to infuse only one layer of 9oz 7781 eGlass?
  2. Do you think one layer of 9oz 7781 eGlass cloth on a 45 bias will provide the nice durable skin that I’m looking for?
  3. Which method (peel ply or release film) would produce a surface requiring the least amount of prep sanding before priming.

NOTE: I thought of doing a wet layup with peel ply (run a sqeegy over the peel ply to try and get the resin content as uniform as possible but I’ve spent so much time sanding the leading edges to get to the proper shape I dont want to create more work for myself by having to re-sand the LE like crazy to get back to the nice straight leading edges that I currently have nicely shaped from the resin/micro balloons.)

I look forward to your respons(es)…

#13

Hi Jbocek,

A simpler method of lamination will do you better than infusion in the specific case you are talking about.

If you do infusion, it will be very difficult for you to eliminate the mark-off of resin distribution medium (RDM) from your single ply after its cured. It will most certainly need smoothening with micro/primer. I’ll suggest the following:

  1. Prepare two 30-40 micron polyethylene sheets full length of the layup about 8 inches wide. Prepare a release bag around 20-30% larger than the size of the polyethylene sheet. Prepare a perforated release film of the same length of polyethylene sheet. Prepare a breather sheet of the approx 1/2" smaller than the polyethylene sheet.
  2. Lay down and tape one sheet on a flat clean surface.
  3. Lay your ±45 tape on that.
  4. Mix epoxy/hardener (lets say 10% more than weight of the cloth).
  5. Pour it in the middle of the glass along the length of the tape. It should be one middle pour not in two rows.
  6. Cover the stack with the remaining Polyethylene sheet and leave it like that for 2-3minutes.
  7. Use a squeegee on top of the entire stack to spread the epoxy evenly toward the outside of the glass.
  8. Use a colored marker to mark off the strip of material that you want to actually use outside of the PE stack and cut it off as a single stack.
  9. Peel off one layer of PE and place the exposed layer of the glass epoxy on the part, use squeegee to remove bubbles and peel off the bottom layer of PE AFTER you have removed the bubbles.
  10. Place the perforated film on top of the just made layup.
  11. Place the breather on the perforated film.
  12. Place the vacuum bag on the breather and pull vacuum.
  13. Leave it to cure. (Warm blanket).
  14. Peel off the vacuum stack and the release film.

This should give you a nice surface that you can now sand off with around 120-200 grit and then coat it with your primer.

However, if you’re going to use infusion, you can use the same perforated release film above your dry layup. Infusion will work but will most certainly give you a terrible mark-off that will be a pain to work-off.

All the best.
N

#14

Thanks Nash! I like your suggestions!

  1. Where can I purchase PE sheets?
  2. Will the PE sheets peel off of the resin saturated cloth easily without lifting the cloth from the part? Remember the is a leading edge of a wing so the laminate is wraped around in the shape of a “D” when viewed from the side.
  3. Is it necessary to wax or otherwise coat the PE sheet with release agent so it doesnt stick?
  4. What brand/type of breather do you recommend?
  5. Re pulling a vacuum on the part: I’m thinking one vac line in the center of the wingspan connnected to a “T” with spiral wrap the span of the part (only on one side of the laminate)… does this sound acceptable?

Sorry for all the questions… I just want to do this right the first time!

#15

Oh… and by “terrible mark off” you mean the resin that accumulates under the vac line and makes a ridge that is necessary to sand? Or do you mean the resin will make an uneven line under the peel ply/release film as it moves toward the vac line in the resin brake?

#16

Thanks Nash! I like your suggestions!

  1. Where can I purchase PE sheets?

Any hardware store will have polyethylene sheets. Go to your local home-depot, they should have it.

  1. Will the PE sheets peel off of the resin saturated cloth easily without lifting the cloth from the part? Remember the is a leading edge of a wing so the laminate is wraped around in the shape of a “D” when viewed from the side.

Sure. Just put it between fingers and twist it a bit, you’ll see one edge come off.

3. Is it necessary to wax or otherwise coat the PE sheet with release agent so it doesnt stick?

No, and don’t do anything like that, it’ll be difficult to cut with a pair of sharp scissors.

4. What brand/type of breather do you recommend?
Any breather will work. These are non knitted white felt like things that are also used in construction to remove moisture. You can find a roll at a local hardware store. Or if you want luxury stuff go to Airtech. The purpose of the breather is to absorb excess resin. The membrane with holes (bleeder) is something like WL3700 or WL3900 with perforations from Airtech. Ask your composites supply guy. Don’t try to go cheap here as the quality of imprint you’ll get on the LE will greatly depend on this and how well you bag your LE.

  1. Re pulling a vacuum on the part: I’m thinking one vac line in the center of the wingspan connnected to a “T” with spiral wrap the span of the part (only on one side of the laminate)… does this sound acceptable?

Don’t keep the T on any area that has the layup. Keep it on a hard area and pull light vacuum like 75-80% of ambient pressure.

Sorry for all the questions… I just want to do this right the first time!

If you don’t ask you’ll never know…

#17

Two more follow on questions:

  1. I’m glad you mentioned pulling a “light” vacuum as I would have thought pulling a deep vac to compress the laminate would have been better. Is the reason for this to lighly compress without drying out the laminate?

  2. Re the vac line: Would one vac port at the wing tip or wing root work since pulling only a light vac or should I run spiral wrap along one entire edge of the laminate (each wing will be done separately - approx 12 foot span per side - the laminate is approx 4 inches wide)? If I can get away with only a single vac port at the root for example I think there would produce a cleaner result (less chance for resin to pool under the spiral wrap and then be require removal after cured via sanding)

Thx!

#18

Two more follow on questions:

  1. I’m glad you mentioned pulling a “light” vacuum as I would have thought pulling a deep vac to compress the laminate would have been better. Is the reason for this to lighly compress without drying out the laminate?

Light vacuum: Two reasons. 1. When applying vacuum you should always be at a vacuum less than the vapor pressure of the epoxy. 80% is a safe bet. But if you’re unsure, check with the resin manufacturer. 2. This is actually a vacuum bagged hand-layup, and you’re using the outer skin of the wing as a mold. Well, you don’t want to deform the skin when pulling vacuum, so there’s no need to overdo the vacuum.

  1. Re the vac line: Would one vac port at the wing tip or wing root work since pulling only a light vac or should I run spiral wrap along one entire edge of the laminate (each wing will be done separately - approx 12 foot span per side - the laminate is approx 4 inches wide)? If I can get away with only a single vac port at the root for example I think there would produce a cleaner result (less chance for resin to pool under the spiral wrap and then be require removal after cured via sanding)

I’ll prefer to not use a spiral wrap to vacuum. I’d use the vacuum port between the vacuum bag and the breather. The breather’s main purpose in life is to allow the vacuum to spread evenly under the bag. Try to not use anything hard where the layup is, so you’ll not have a mark-off. I’ll put the vacuum port on a beaver tail at the root. The beaver tail is actually a piece of breather doubled up and kept in the vacuum bag where you can also attach the vacuum port. That gives the laminate a very good transfer of vacuum and no hard point. Check this out on internet. I’m sure someone will have a longer explanation.

All the best,
N

#19

Thank you for the “hand holding” … I appreciate you walking me through this! One last thing: My intent was to use VE infusion resin (when I was planning to infuse) vs epoxy because (a.) the aircraft is constructed with VE resin and (b.) VE resin has a higher TG with room temp cure.

Is it okay to use the VE infusion resin (low viscosity, longer gel time) for the hand layup/vac bag laminate? My regular VE resin would gel WAY before I could prepare the laminate per the steps you’ve outlined and get it bagged before it starts to gel. The VE infusion resin that I have on hand has a 45min to 1hr gel time.

Lastly, laying after removing the excess resin via the two layers of PE sheet (with a squeegee) will there still be enough resin in the cloth to ensure a air bubble free laminate after bagging? (using your method of placing the saturated laminate on the dry wing LE that has been sanded to shape with 80 grit sand paper).

#20

You’re welcome.

Obviously a low viscosity resin will not be a good idea for what you want to achieve. You need a regular VE resin, or you can take your infusion resin and add some cabosil to it, just enough to get the rhealogy that you need. I’ll go back and get a hand layup resin that will gel in around 20-30 mins. Using the method I’ve described ,which incidently is not mine, 15 minutes is plenty to get everything in place. You need to have everything well planned and kept in an organized manner. You can also attach the vacuum bag on the top surface (so that it doesn’t get resin drops on it) and folded upwards while you do your layup. Why don’t you practice it on a small curved part to practice, like say fix a broken surfboard edge. You’ll figure out what works for you and what not.

80 grit is great for any resin. It will give a deep grip to the resin. I’d avoid a infusion resin for this if I were you.