Peel ply directly on the mold surface?

Discussion in 'Fiberglass and Composite Boat Building' started by benglish300, Jul 17, 2013.

  1. benglish300
    Joined: Jan 2012
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    benglish300 Junior Member

    Hi all, a co-worker and I were discussing why in some cases peel ply is applied directly to the mold? I've seen reps from sp gurit do infusion demos on a thoroughly waxed part and apply peel ply before loading the reenforcments. Is this to simply protect the un-coated mold surface (no gel coat nor skin coat on demo) from harm, or is it more complex, such as pinholes, or a better bonding surface for coatings?
     
  2. Herman
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    Herman Senior Member

    Reasons can be many. It gives a good surface for bonding, coating and fairing. It can also help reducing pinholes. You just never get a shiny finish.

    The mould should be able to cope with resin, so that is not an issue.
     
  3. SamSam
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    SamSam Senior Member

    How would putting it on the mold reduce pinholes?
     
  4. tunnels

    tunnels Previous Member

    ok what makes pinholes ??
    where does the air come from to make pinholes and also porosity ??
    Take a guess !!:confused:
     
  5. groper
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    groper Senior Member

    I put peel ply on the mold all the time... and infuse with epoxy so when it's de molded I have a surface which is protected from contamination and peel it off when im ready for secondary bonding or go straight to paint prep etc...
     
  6. benglish300
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    benglish300 Junior Member

    I see I see. Does it help with pin holes though?
     
  7. SamSam
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    SamSam Senior Member

    So...how does putting it on the mold reduce pinholes?
     
  8. groper
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    groper Senior Member

    I don't have a problem with pinholes either way... It's more to do with the quality of the infusion, if I have leaks or other problems, like too fast flow speed etc, I get pinholes. If ii have a tight vacuum, and dont stuff anything up, there is none. The type of reinforcement also would make a difference. If you have a very open weave, you would be more prone to pinholes. I only use stitched reinforcements and they work well for me...
     
  9. tunnels

    tunnels Previous Member

    surfaced that has peel ply ,then peeled just before secondary bonding if its structural and will take a lot of loads always should be sanded or ground with a 16 grit disc to expose the glass fibres , if you don't sand then its a cured resin bond join on one side and wet resin and becomes a non etching into join and just resin to resin only !! non of the resins actually etch to each other !! take a look at a join up under a high powered microscope some time one not sanded of ground and the other ground and or sanded !! there's a distinct resin line between so easy to see which isn't sanded or ground as the peel ply breaks away from the resin there is a very small amount of glass fibres exposed but is minimal , the grinder with a course disc will really roughen the surface and tears and exposes a lot of fibres that will give a much better surface to grip to !!
    !! :eek:
     
  10. groper
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    groper Senior Member

    This again has nothing to do with original thread, but true, ground surfaces always bond better than peel ply only prep. The relevant point is, how much adhesion do you need for the joint in question? When using epoxy - as i already said - the lap shear strength of a peel ply prep secondary bond, is nearly 3 times as strong as a grinding prep with polyester resin.

    But dont take my word for it, heres the proof, all ISO controlled test procedures;

    Epoxy lap shear with peel ply only prep = 16Mpa
    http://www.atlcomposites.com.au/files2/epoxy_products.adhesives/techniglue-hp_r15-eng.data.pdf

    Polyester lap shear with grinding prep = 6.5Mpa
    http://www.duflex.com.au/duflex2/professional/performance_data/secondary_bonding
     
  11. fcfc
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    fcfc Senior Member

    I do not see the point, because the duflex link you posted show 4 test cases.
    2 are peel ply, 2 are sanded.

    And they all show about the same shear strengh ...
     
  12. waikikin
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    waikikin Senior Member

    The common link is the use of polyester tabbing in those tests, not sure why thy didn't throw a pair of epoxy examples in to the table though?
    So.... to keep on topic, this peel plying of mold surfaces only seems appropriate on creation of flat panels.
    Jeff
     
  13. groper
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    groper Senior Member

    I would say that peel ply application on a molded part is more appropriate to epoxy and or weight sensitive structures. If it were laminated with a syrenated resin - you would just gelcoat it and have your surface finish done. With epoxy, cant gelcoat without VE tie coat etc... so after demolding, pull the peel ply off and you can go straight to paint without sanding the whole thing. Painting is lighter, and of course can have more colour choice, effects etc.

    Yes, the results showed not a great deal of difference in the bonding effectiveness of ground VS peel ply, but none the less, there IS a difference of more than 10%, this could make a difference depending on the load a joint/bond is exposed to, especially using PE resin... If its a low strength joint, or anything not structural, you may not need the 6.5Mpa, in which case you might choose the peel ply option in order to save creating a heap of dust everytime you wanted to secondary bond something... the possibilities are endless really...

    You also need to remember, that if not gelcoating etc and the laminate goes onto teh mold. some of teh mold release will stay on the cured laminate. By using peel ply, all of this contamination is removed, no washing, no solvents, no sanding etc... Like i said, i leave it on for months, even years after curing, before removing it only when im ready to do something with the laminate - it protects it from spills, dirt and grease etc. When you peel it off, it takes the dust and everything else off with it, and you have a perfectly clean surface that looks like the day you laminated it - no vacuuming, wiping etc...
     
  14. rwatson
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    rwatson Senior Member

    I wonder how peelply would work if the parts weren't develop-able. Its a bugger to keep flat on compound curves.
     

  15. groper
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    groper Senior Member

    Yes it is... easy fix, strips...
     
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