edges of panel under vac

Discussion in 'Fiberglass and Composite Boat Building' started by fallguy, Sep 6, 2017.

  1. fallguy
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    fallguy Senior Member

    For panel edges when wet bagging or laminating flat panels on a table, how do you keep the resin from flowing around the edges of the part where the vac bag has trouble making the 90 degree angle?

    Do you leave a void in the bagging operation to allow some bag stretch?

    Do you avoid or prefer breather over the panel edges?

    Other?

    Thanks.
     
  2. AndrewK
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    AndrewK Senior Member

    Sounds like you need more pleats in the bag, especially in line with the core edges. Also apply the vacuum in stages so that you can push the bag around the core to avoid the bridging.
    The breather should be bigger than the job.
    For wet bagging some bridging is not a problem unlike infusion.
    Are you displacing too much resin from your laminate into these voids?
     
  3. fallguy
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    fallguy Senior Member

    I think we are okay on the laminate. For awhile I was concerned with discoloration and a whitish appearance, but I weighed one of the parts and had 47% resin to glass, with a higher content assumed on the table side and less on the peelply side. And now I'm going much higher on the resin content prevac, so very confident in my wetout. Triax does NOT look the same after curing as 6 ounce fabric turns out. And I did some destructive testing too early in the cure. And the destructive testing showed failure, guess where? In the 90 degree delta between the 45s where the laminate even appeared a bit dry. This was unnerving enough to scrap my first two large 3'x33' panels which I did.

    We changed a number of things on the approach.

    The rebates form a pond. Almost all the table side resin is going into the pond over surfacing veil now. We even out the resin in the pond, then I am wetting out bottoms up. I am getting resin into the part voids at the edges, but it is probably good excess resin lost.

    I also added to the corecell wetout and we are now at about 3 ounces per pound of fabric. I really can't get a lot more resin into the part without losing it to the vacuum at this point. I increased my resin wetout rate from 110% and lots of extra small batches here and there to 150% on the table side with the veil and 110% on the top. The top is much easier to wetout in general. So, the losses on the edges are totally okay. Keep in mind my posting on this question was about 2 weeks ago. I did try running a sample at 200% resin to glass and it was pretty much a sloppy mess. I didn't weigh it yet, but that was one of the parts where the 0 fabric strand was on the corecell side and it looked perfect.

    Thanks for the reply. I never realized how artsy this business was until the last few weeks. While I see the benefit to infusion, I also realize the downside. For the panel edges, you obviously can't flow vac/resin through that area.

    We have been unable to get the bag edges down onto the part edges, but the parts are 33' long, so that is the real story. I think you'd almost need to put lead shotbaggs onto the edges before you turned the vac on to keep those edges sharper. I am spending about 3 hours trimming panel edges today and prepping the rebates for tape (easier on the table). gotta go
     
  4. AndrewK
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    AndrewK Senior Member

    Are you using perforated foam and if so at what spacing?
    If the laminates are not translucent the whiteishnes could be due to moisture in the fabric, too high a vacuum, entrapped air.
    Why no peelply on the table side? economics?

    When calculating resin requirement calculate resin required to fill the core surface and perforations separately, usually 200-300gsm each side depending on the core, then 100% glass weight will be right.
    Why and what type of veil on the table side?

    Rebates on the table side I think we discussed in your early stages of information gathering, they are done by placing smooth plastic strips in position. Dont bother to rebate first as the core will bend around this, there will be a slight resin rich area at the edge of the plastic unless you chamfer the plastic but not a problem if the plastic is no more than ~2mm. There will be a bump on the topside but most dont compensate as this becomes the inside where fairing is not so high a priority.

    For infusion you really do need to concentrate on the details to get great results but as this is all done at the dry stage with no time pressure it is not a big deal.
     
  5. fallguy
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    fallguy Senior Member

     
  6. fallguy
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    fallguy Senior Member

    I sanded for like 3 hours yesterday on 2 large panels. If I can peelply the table side, I'll buy you a bottle of scotch. I already owe Halliday some Bombay.
     
  7. fallguy
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    fallguy Senior Member

    I did not give you permission to sleep on the job !!! ;) Many thanks. I just checked the Aussie time zones!
     
  8. AndrewK
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    AndrewK Senior Member

    As you discovered the time spent on sanding easily covers the cost of peel ply, silly not to use it in my opinion. No it will not stick to the laminate any more than to the top side.
    I am just about to head off for four days so will reply to the other points when back.

    There should be no reason to use the veil you should not be trapping air between fibres.
    Go back to the resin calculator spreadsheet I posted earlier to see the quantities I use.
     
  9. fallguy
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    fallguy Senior Member

    We did the bow join today. It was really difficult due to the fine entry of this boat, my inexperience, the 90 degree outside heat that I mistakenly wore a t-shirt, the tons of fiberglass shards on my parts that ended up on my arms from gazoodles of sanding yesterday. The panels are hooked to the ribbands and the bow is joined and it is time to tie the sides to the bottom.

    I will continue to use the veil (I spent $500 usd on it), but I'm curious and plan to do some sampling of peelply on the table side with and without veil. Thank you Andrew. You have no idea how glad I am to hear peelply can go on the table.
     
  10. fallguy
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    fallguy Senior Member

    I made some changes to the process, but am still getting some air into my part surface. We still used veil, but we also peelplied the bottom.

    It is a combination of factors causing air.

    We used 216 ounces of epoxy for a 10.1# part for the wetout of the peelply, veil, and 22 ounce triax. I had to mix another 24 ounce batch for a few spots that were dry at the end. Wet poured the epoxy onto the veil and peeply this time. Last time we poured epoxy onto the table and laid the veil overtop. We did have a little more areas of veil that were dry this way.

    I mixed 42 ounces of epoxy for the initial wetout of the corecell. We wetted it right away and rewetted it a second time. This I will not do anymore. I will wet it once just before flipping it. If you wet it early, it seems to get a dry appearance.

    While laminating, I noticed a few areas where the glass was wetting out differently. I believe my laminating rollers are creating some foaming if we overwork a drier looking area. The rebates are higher than the rest of the part and require some effort to push resin up to, and the taped edge that forms the pond is a good place for some air bubbles, but easy to see and repair with a sander (area gets faired later anyhow).

    When we flip the core onto the wetted epoxy, any air is entrapped by the rebates. The reason I am not seeing any air near the perforations is that air has left. It is only not near perforations where we have any entrapped air. I am 2" square perfed.

    I never ran above 14" HG. Due to the high amount of resin used, I did get quite a bit of resin (as expected) into my breather fabric through the breather film.

    My only thoughts are that I could use even more resin for the bottom and somehow try to squeegee it into a bucket for the top. This would avoid any foaming as the topside laminate gets the air pulled out by vac, but I would still end up with some bubbles when we flip the core. The idea of putting more holes in the corecell is oppressive. The last part was roughly 8 yards or 72 square feet. I think that'd be 72 more holes per square foot or 4900 holes to drill?

    Perhaps I am just winning arguments for infusion and polyester resins.

    Is there a different way to manage the vacuum that would help? I just took it up and as soon as it hit 14", I was at the relief valve taking it down to 14". If you run the vacuum higher quicker, it seems like you could get more air out, or vice versa, lower longer might work as well, but the air is trapped, so maybe nothing you can do. This last time I was not as careful to walk down the part and relied on my crew for the bubble removal. I will need to make sure and do one final solo walk. There is also a bubble buster roller, would that help any? I am using aluminum laminating rollers 6".
     
  11. fallguy
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    fallguy Senior Member

    The relief valve is just near the pump, so when I go to relieve the pressure, I am basically creating a path of least resistance right to the pump. And I think that is also a factor. If I put a relief valve on the part, I would be doing the same thing.
     
  12. AndrewK
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    AndrewK Senior Member

    Still not sure what is causing the trapped air in the laminate, some photos may help.
    2" spacing for core perforations is sufficient.
    Have you made any small panels, if so are these any better?
    If not I suggest you do this, make a bunk top and see how this works out, dont use the veil. You need to solve this rather than compensating with extra resin.
    I havent converted your weights to grams, as long as you are using 1:1by weight resin:glass plus the 350g resin m2 for each side of foam you will be right ( I find 300g is enough but stick to what you have been told). If using only a thin peel ply then dont need extra resin for this.
    Put the peel ply down on to the table and the glass dry then pour the calculated resin on to the job and spread around with a squeegee working the air out with the squeegee. If you wish you can also give it a light roll (dont over work) with the consolidator but should not be required. I personally prefer not to use rollers to apply the resin.
    Wet out the core and press down into the wet laminate and then repeat for the top laminate.

    Also suggest you put the vacuum gauge on to the job, off to the side of the panel. Leave the relief valve at the pump, how steady is your final setting?
     
  13. fallguy
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    fallguy Senior Member

    I am running at 150% and you are suggesting 146% with the 350g rate. At 150% we had one area that was a bit drier in the middle, and I made 24 ounces of extra resin for areas that were drier on the edges, so we actually ran at 167%, but allowed nothing for peeply or the veil. I think I probably needed to run higher than that, but my breather fabric was saturated by the time the epoxy gelled.

    This bag was new and we had no detectable leaks or any areas of concern after about 2 minutes into the vac.

    The first panels I did I ran with the resin on top, same story.
    The last panels I ran with the resin underneath the glass, but above the veil and peelply. The veil has no weight on the scale. It is that light. However, it is probably using some resin.

    In this particular run, even the veil had a couple areas that were dry. Those were directly under the 0 fabric strands on the crew end. Some people are not systematic and probably pressed not as hard. When I run my laminating roller, I run up and down and overlap, but my buddy was sort of all over the place. This would be great if problems were just on the crew end, but the end I did had some air pockets as well.

    If I used another layer of breather film, can I turn the pressure up? I ran at 14" HG and I'm concerned that rate is not enough to force out any air.

    I think a good experiment would be to build a 30", 8' panel with a rebate, and use double breather film and double fabric and crank up the pressure. I could also set a timer and not turn on the vac until say at 90% of the cure time, which is 108 minutes I think and crank it up higher than 14" HG. One of my vendors has a customer who always vacuum bags all his parts at max pressure. Not sure how he can keep the resin from coming through and saturating everything. Maybe he doesn't care?

    To replicate the job during a small sample is very difficult because it takes quite a bit of time to get the larger panel wetted out. My open time is supposed to be 120 minutes, but I am really only treating it as 100 minutes.
     
  14. rxcomposite
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    rxcomposite Senior Member

    Still having problem? This was the same problem we had before.

    I attached the diagram of the bag lay up which I could not do in our conversation mode. It worked for us with a high degree of repeatabilty.

    The main cause of our problem was entrapped air. When full vac is applied, the entrapped air has nowhere to go. It just increases in size creating a larger void. To release the entrapped air, we drilled holes in our caul plate to facilitate path for the air to evacuate. If no caul plate is used, the combination of perforated release film, peel ply, and breather cloth should do it.

    The goal is to release all air so that the resin can fill the void. There are other cause of void which I will post later.
     

    Attached Files:

    Dejay likes this.

  15. rxcomposite
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    rxcomposite Senior Member

    Another possible cause of void is the fabric architecture and the vacuum. Uni tends to have lesser void as it provides a pathway for the resin to flow along the direction of the fibers. However, with woven, there transverse fibers which trip the resin flow. The solution is to increase vacuum. There is a caveat to this when using Chopped Strand Mat. At very high vacuum it compresses and causes turbulence and voids as the fibers are randomly oriented. It is primarily intended as a flow medium to facilitate resin flow and should be at low vacuum. CSM and veil cloth belong to the category.

    Last to look at is the entrapped air in the resin during mixing. We usually degass the resin whenever we do vac set up. Attached is the diagram of the void formation and an excerpt from the same article by By Jonathan E. Kenerson, B.S. University of Maine, Orono, 2007

    "For low resin velocity infusions (corresponding to a lower Ca) as in (a) in Figure
    2.9 the driving force is from capillary action, a wicking of the resin into the tow. This
    results in the interior of the tow being saturated with resin while the inter-tow region
    contains voids that are on the order of millimeters. For high velocity infusions
    (corresponding to a higher Ca) as in (b) in Figure 2.9 the driving force is a viscous force,
    a resistance of the resin to be drawn into the tow. This results in the inter-tow region
    being saturated with resin while the region within the tow contains voids on the order of
    microns. Inter-tow voids (a) resulting from slow infusions can exceed 15% of the volume
    of the laminate, while intra-tow voids (b) resulting from fast infusions will be less than
    2%. This means that erring on the side of a rapid infusion is preferable; however Leclerc
    and Ruiz (2008) emphasize the importance of determining the optimum resin infusion
    velocity for different types of fabric to minimize void content. For any fabric there exists
    an optimum capillary number which will correspond to minimization of both the intertow
    voids and the intra-tow voids.
    Leclerc and Ruiz (2008) conducted experiments on two woven fabrics (a multiaxial
    non-crimped LIBA stitch bonded fabric and a woven fabric consisting of single end
    23
    glass rovings) to determine optimal infusion velocities. They varied infusion velocities
    and tested void content for the infusions. They found that for the optimal infusion
    velocities for the multi-axial non-crimped fabric and for the woven fabric was 7.5mm/s
    (0.3in/s) and 20mm/s (0.8in/s). Leclerc and Ruiz (2008) did not vary viscosity in their
    experiments, but do cite this as important factor to control when determining optimal
    infusion velocities."
     

    Attached Files:

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