Tips on Working with Vinylester Resin

Discussion in 'Composites' started by wsimpso1, Dec 13, 2019.

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  1. Dec 13, 2019 #1

    wsimpso1

    wsimpso1

    wsimpso1

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    Here I am, all experienced with epoxy and having built a bunch of my composite airplane, and I am having no end of a bad time building a few things with Vinylester Resin where I see the need for it.

    Anybody have experience with Vinyester and have any tips on working with this stuff?

    I am using Derakane 411-350 resin and MEKP catalyst. Bad choices? If better exists, please point me to material and folks who sell it.

    Just to detail my bad time with it, here are the most difficult things so far:

    This stuff really wants to grab my nitrile gloves, scissors, and rubber squeegees. I have learned to not touch the stuff if I can help it, but to use a brush for everything I can in terms of placing and smoothing tapes and new plies. Are there other types of gloves and squeegee materials to work with to use this stuff?

    This stuff does not seem to stay down on underlying surfaces, it tends to lift off if left alone. How do we get it to stay put on surfaces? Maybe a bit of cabosil in the resin?

    Applying tapes to a surface, either to build a layer or attach two parts together, can be a real pain. I am using polyethylene film and it curls up and off the tapes, so the film does not work as a carrier to get a nice tape where I want it. What does work as a carrier film for taping and tabbing with this stuff, and where do you get it? Is there an alternate technique for tabbing and taping? Is there a reasonable substitute for visqueen that works with vinylester?

    I have found that I can make molds or forms from polystyrene foam if I completely cover the form in two layers of packing tape. Doing just a simple wet layup works OK - the foam does not collapse, but I have trouble getting the wet laminations to stay put. Try this with a vacuum bag, and some modest collapse of foam still occurs. I am thinking of applying a full cover of slightly wet micro-epoxy over the entire form, then covering that with packing tape, but I am certain some styrene will get into the foam and cause some distortion. Any tips on making molds and forms of styrene foams so they do not collapse. Or is PU foam the only way to make this work?

    For my header tank, I was planning to make it on a male mold. I figure that I would build the outside body and lid each in three bag cycles plus other operations:
    • Peel ply against form, two BID, peel ply and vacuum bag;
    • Free part from mold, put it back on, pull peel ply from outer layer, then apply Divinycel over most of the surfaces, phenolic plate at each of the connections (fuel lines, gage, level switches, sump drain), and vacuum bag these cores in place;
    • Clean up the outside and then vacuum bag over the outside with two BID;
    • Pull from male mold, clean up the inside, and tab in the baffles/structure;
    • Apply a seal coat to the inside to catch any leak paths;
    • Transfer flanges and bond on a lid.
    Does this even sound like it will work with vinyester?

    After being the composite guy, I am humbled by how much fuss vinylester resin is giving me...

    Bill
     
  2. Dec 13, 2019 #2

    BJC

    BJC

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    Glasairs, GlaStars and Sportsman Aircraft use VE. I’m far from an expert, but have some experience.

    Good choice. How much cobalt you use to promote it, and DMA for lower temperature work greatly influence pot life, as does amount of MEKP.

    The yellow plastic squeeges work better for me, but I use a brush for most things. I’ll check my gloves, but I’m not aware of any problem there.

    Use cabosil if the resin is flowing. Use a quality peel ply otherwise. I use the (expensive) blue stuff.

    Only in rare instances where access is difficult (example, inside of leading edge of vertical stabilizer) have I used a carrier film. I place some resin, then the laminate, wet it, let it soak for a minute or to, then work it with a brush. In some instances I place the glass dry, use little pieces of masking tape on the edges to hold it in place, then apply resin. The masking tape is easily removed arter the glass has been wetted out. Bigger brushes work better than smaller brushes. Leave the first laminate (of two, or more) resin rich, place the next layer of cloth, work with brush, and repeat. Top with peel ply, and work excess resin out, blotting the peel ply as required. Note that there is a sizing for glass that makes it accept the VE much better than does bare glass. I don’t have any name or technical data. Don’t know about CF.

    Can’t help you much there. Multiple layers of mold release wax allowed easy release in some applications.

    The Glasair header tank, about 7 gallons capacity, uses 1/2” foam for the bottom, 1/4” for the sides and back, each with two layers of glass, with the inside surfaces extra rich with resin. Fittings are either potted in, or screwed to an aluminum insert. The top of the tank is the fuselage immediately aft of the firewall.

    Similar to a pilot who learned to fly with the third wheel up front, you were spoiled by starting with epoxy.


    BJC
     
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  3. Dec 13, 2019 #3

    jonlaury

    jonlaury

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    Hi Bill,
    I built a Glasair and a ton of custom parts- all with 411-350 & MEKP. I chose the Glasair over a Lancair because I was quite comfortable with polyester resin from patching and building surfboards as a kid.

    I like VE because you can make it kick really fast if you want, with more MEKP and or heat guns, lamps, or you can slow it way down for more working time, then kick it with heat or place in the sun (esp when using carbon). It's also practically bullet proof regarding other fuels and solvents once cured. I put samples of cured laminate into auto gas of all the major producers (about 7 or 8 at the time) and pulled them out after 7 years and compared to the parent laminate that had been sitting on a shelf. No difference in peel or shear strength that I could detect, no surface gumminess or other changes. I've also worked with it for going on 30 years, not always wearing protective gloves or vapor masks, (not recommended), without experiencing allergic reactions. Nitrile snug fitting gloves worked well for me. Planning proved to be the key to avoiding the worst sticky problems, but some are unavoidable.

    Hope this helps,
    John

    When I needed a carrier, I used plastic wrap like Saran, but most of the time I would mask and cut cloth to fit and trim with a razor when it reached green cure, careful not to score the substrate, then .

    In making molds, I used plaster (too hard), drywall mud, bondo, PU foam, cardboard/packing tape, 1/8" door skin/tape and anything else that seemed suitable. Polystyrene packaging foams were too much grief and the stuff I used didn't sand well. It was prone to tear-out and I had some tremendous fails because the styrene in VE is a very strong solvent and would make a mess if it found it's way in to the PS. I had good success using epoxy surface coating on substrate with multiple polished carnauba wax layers. But PU foam is the best for shaping and tolerating styrene.

    Vacuum bagging is great for larger more resin-rich wet outs and saving weight, but for small parts I used stippling with a brush and white rubber squeegees when the part would allow.

    Not sure what you mean about "lifting" from substrates. Sounds like surface contamination. But if it's a contaminated surface or even one that's been unattended for some time,I would always use an acetone wipe and then 80 grit to abrade. Some think that wiping again with acetone makes it a "live" surface that will chemically bond with the new lam, but I don't remember any experienced composite people agreeing with that. VE does make hellacious strong mechanical bonds to the abraded surface.
     
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  4. Dec 13, 2019 #4

    cheapracer

    cheapracer

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    Over 40 years I have made heaps of things with VE.

    I am no expert, I don't claim to be able to make anything structural other than simple external bodywork, dashboards, covers ect. and the molds for them. Like Jon, I make all my own bucks out of anything, from wire, rope, wood, junk laying around, it's just a shape for a single use ..

    I use almost nothing but paint brushes 90% of the time - hard, fast dabbing action. I never use rollers or similar tools as the brushes get all the air out 99% of the time, just occasionally pricking a bubble or 2. Sometimes I'll run a squeegee to get excess resin off if I've stuffed up my guesstimate of resin.

    I use a line of paper cups with resin with the hardener/s waiting to go for which I have a few syringes on standby (sometimes they don't like the hardener and jam, so have a few ready to go), grab a cup throw the hardener in, stir and straight onto the job.

    I usually lay the first mat down and over-wet it, then apply the next layer as an absorbant layer for the overly wet first layer working the resin through - repeat for thickness required. This has always worked very well for me.

    It is messy sticky stuff, I always use rubber dishwashing gloves.

    The paint brushes wash out successfully with boiling water and clothes washing powder worked into the bristles.

    I concur with Jon above, you can change the setting times dramatically, but on the other hand, always run samples first, times can change wildly depending on temps and humidity etc.

    If you haven't enough hardener, you'll soon know, like 1 or 2 hours later even with lamps, and I make up a small batch of fast setting resin and apply it rapidly all over (you have no choice!).

    I don't think about it much, maybe that's the secret and that's all I got.
     
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  5. Dec 13, 2019 #5

    jonlaury

    jonlaury

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    One thing I was religious about is eye protection before opening any MEKP container. One errant drop in an eye is "hello, Cyclops"
     
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  6. Dec 13, 2019 #6

    wsimpso1

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    OK, looks like lots of good advice. Time to go make some more forms, practice on a couple of small pieces, and try to come to peace with the stuff.

    Bill
     
  7. Dec 14, 2019 #7

    wsimpso1

    wsimpso1

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    Maybe you do not call it lifting, but you have seen it. Cloth "lifting" from where it was applied is the term I learned 30 year ago.This usually happens near corners or bends in the surfaces the cloth is applied to. If I had a sharp corner or a substantial amount of cloth overhanging the edge of an underlying part, the cloth is trying to straighten out and it lifts off of the underlying surface before it cures. I am accustomed to making glass cloth go where I want it by using generous outside radii and applying fillets on inside corners to allow viscosity to hold the cloth in place while it cures. Instead of a good looking part staying stuck and curing, the cloth near the bend separates from the underlying material, and now we have a bubble or worse to deal with after it cures.

    My technique has been to wet out plies between pieces of visqueen, cut to size for application, and after getting it in place, is smoothed out and stuck to the substrate everywhere. This works like a dream with even thin epoxies, but fails miserably with vinylester. And having a ply or two lift off in places is a real surprise. I have even stayed with parts until resin has begun to gel with nice bubble free laminations, and still found one or more plies had lifted away from the layer below after I left the part to finish curing.

    I will try some cabosil to thicken my resin. I really do not think that I can be getting behaviour out of this resin that nobody else has... And since so many folks have worked with this stuff, there just have to be techniques and methods already established for getting good parts out of it.

    Billski
     
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  8. Dec 14, 2019 #8

    BBerson

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    Just a guess, but maybe that glass has a binder that dissolves in epoxy but not with vinyl ester.
     
  9. Dec 14, 2019 #9

    jonlaury

    jonlaury

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    There's got to be something on your substrate, or in your cloth that doesn't agree with VE. I've never encountered what you're describing in building a whole plane with different brands/weaves/types of cloth and different sources of 411-350. If you're trying to fit lams into a 3D corner, how you cut the cloth can have a large effect on the tension placed on the fibers. Possibly what you are doing unknowingly is putting a preload on the lam by the cloth being unable to conform the shape you want and as it cures it could be pulling ("lifiting") an edge or a spot in the field. This isn't "a thing" that's known... just brainstorming.
    Glasair supplied 7781 cloth and in the build manual, most of the lams are called out to be cut on a 45 deg bias, which makes them very conforming and reduces edge fraying. I was able to lam into a 3D corner, go up and over the rib (one face of the corner)and down into the 3D corner on the back side and spread out in 2 dimensions on the floor without wrinkles or experiencing what you describe. Worst case was if I didn't like what it looked like, I peeled it off the lam and replaced it. It always seemed like the first lam was the most problematic. Once it was wetted out and massaged into place, the other lams would kind of glide over it by dabbing (stippling) with a brush. It's an effective method for equally distributing tension within the lam to conform to the shape you want and you can easily see where the cloth is pulling and how to massage it to alleviate the tension. If it was too wet after completing the prescribed # of lams, I draped the lam with Saran wrap, used resin as a lubricant for my gloved fingers to squeegee out the excess. This was very effective for scavenging excess resin from thick laminations by being able to apply much more pressure than when using a brush. One caveat, as the lam gets drier, overzealous scavenging can cause delamination. Use the stippling brush with a little resin to get it to lie back down.

    FYI, different cloth manufacturers do use differing amounts and types of sizing. I had one batch that would not wet out with the resin I was using. But it was obvious by the cloth never going 100% translucent after application of resin; lots of white strands. And off the roll, it was somewhat stiff, like paper, instead of the soft drape of all the other 7781. Have you tried another cloth mfgr same spec product? Most will send you a sample free.

    FWIW
    Questions on Aircraft Spruce:
    Q: My glasair kit came with 50 wide, 9 oz, style 7781 bidirectional fiberglass cloth. Glasair states that the cloth is chemically treated (chemical sizing) for better strength with vinylester resin. Is the fiberglass cloth on your website also chemically treated?
    Yes, Hexcel uses an F16 sizing which works with structural epoxy, polyester, and vinyl-ester resins.

    Q: Is this bidirectional?
    No, it is not. (See above on cutting)
     
  10. Dec 31, 2019 #10

    wsimpso1

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    Ok, I have come to peace with vinylester resin. The stuff is not epoxy and many of your epoxy techniques will not be applicable. The advice given above has panned out, plus a few other details I figured out on my own.

    Processing details for my work with this stuff:

    Make sure that you really want this part in vinylester before starting;
    Have EVERYTHING laid out ahead of time, with all possible steps that can precede mixing already done;
    Raise viscosity by adding some cab-o-sil in the resin before catalyst;
    Slow down your mixed resin - MEKP at about 0.60-0.70%;
    Mix no more than you will use in the next 10-15 minutes, less is even better;
    One ply at a time;
    Moisten at least some of the surface with resin before applying the first ply;
    Where you place the cloth is pretty much where it will end up;
    Wet fast and move on - neaten up only after the entire ply is where you want it;
    Do not touch wet cloth with your gloves unless you are removing it;
    Work almost exclusively with brushes;
    Change gloves and clean scissors whenever you have gotten resin on them;
    Leave edges dry until after scissors trim;
    Stay with an open layup until the first hint of gelling;
    Have your process for vacuum bag application and sealing squared away for quick clean draw down.

    If I have missed anything, let me know and I will edit this list.

    Thanks for the help guys!

    Billski
     
    Last edited: Dec 31, 2019
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  11. Dec 31, 2019 #11

    cheapracer

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    /\ This man now knows!
     
  12. Dec 31, 2019 #12

    BJC

    BJC

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    Bill:

    One more: Promote with cobalt and DMA for the ambient conditions. If you buy already promoted, know the amount of cobalt and DMA (if any) to ensure that your chosen catalyst percentage will both fully cure the resin and not severely shorten pot life.

    I’ve never used less than 0.75% MEKP.

    Use VE long enough, and you will learn to savor the aroma.


    BJC
     

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