Working Time, Pot Life, Open Time, Gel Time... Huh?!

Discussion in 'Materials' started by CatBuilder, Jul 21, 2010.

  1. hoytedow
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    hoytedow Wood Butcher

    If you want the hull to run true, you must first remove the dog.:)
     
  2. CatBuilder

    CatBuilder Previous Member

    Oh no! More confusion! :D
     
  3. hoytedow
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    hoytedow Wood Butcher

    This is because the cup holds the heat more than the glass, increasing speed of set-up.
     
  4. Charly
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    Charly Senior Member

    Catbuilder,
    I used the Raka slow hardner with their medium resin, and had good results in summer heat. We worked two of the hulls in the am, starting about 07:30 (hey its asking a lot to get some helpers to show up before breakfast;-0). and two in the evening, about sundown ~20:30 or so. It was hot as hell every time! my guess is about 82 degrees F on average. We worked out of the sun, with fans running and i had previously cooled the resin down by storing it in airconditioned room on a tile floor. I was afraid to make it too cool that it might attract moisture and "sweat".

    We mixed three gallons at the time, RAKA uses two resin to one hardner, so measuring was a "no brainer" In the heat you don't want to have to think too much :) using a milwaukee "hole hog" with a stirring rod attachment we mixed for five minutes, poured into another fivegallon bucket, swished it around a few more times with stick and quickly poured it ALL out into flat trays. (see photos in my KH 36 thread) The folks at RAKA stressed the importance of thorough mixing, and so we mixed the cowboy dogsh*t out of it! And it performed just as they said. It never gelled up on us.

    For my project, the 36, it takes fifteen panels, 8x7. We used nine gallons each time, with about half a gallon left over each time. We had one guy mixing (duct taped the trigger on the hole hog, so you dont have to stand there and hold it.), and trouble shooting, and two guys rolling and placing the panels. If you have everything in order, and work presto, it takes about an hour, a little longer for you since your boat will be bigger. But stack your panels on top of each other, in order, on a long, long set of sawhorses , close to the forms, and you can do it. If I can do it anyone can do it ;-)
    Just don't give out any beer until the bag is on and the vac is running.

    I took the leftovers each session, that had hardened in the trays and whacked them with a hammer. I am not a scientist, so I could not measure the whacking force necessary to break the chunks up, but I can tell you I whacked them good and hard before they broke :)
     
  5. AndrewK
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    AndrewK Senior Member

    CatBuilder, there are many curing agents that will give you a very long open time but as I said generally anything with the standard 100g at 22'C gel time over 2hrs must be post cured. See attached data sheets as an example, I do not use these resins but have attached them as they are global brands.

    I assumed you were spreading epoxy glue on to the ply sheets rather than laminating resin. Unlike resorcinol when gluing with epoxy too thin a glue line is not the best. I imagined that the viscosity of laminating epoxy would be too low (especially at your temperatures) to get a thick enough coating without draining out.
    What is the viscosity of the rake resin/hardenr that Charlie used. Could the low viscosity be the cause of the voids he had?

    Knowing now that you are resin coating only I would look for a high viscosity resin and hardener. No point in paying for a laminating resin that has been diluted with reactive diluents. Epoxy coatings suppliers may be a better source for you. What does Kurt say?

    Andrew
     

    Attached Files:

  6. apex1

    apex1 Guest

    Pot life and gel time are the same. You don´t leave the resin in a pot, you pour it in a shallow tray before laminating / applying.

    Open time is a term often used to describe the max. time window you have to apply a next coat and still have a safe chemical bond to the former.

    And Andrew made a good point. Be sure you don´t squeeze out the resin when bagging.

    Regards
    Richard
     
  7. CatBuilder

    CatBuilder Previous Member

    Wow, things are finally starting to "gel" for me. :p :D

    I understand what you are saying, Andrew. Thank you. The Raka was a "medium" viscosity resin, which means nothing quantitatively, but qualitatively says it was thicker than their thinnest. It was also the hardener with the longest open time they have available. This is the same combination I am looking at using from them.

    Very good thinking, regarding the viscosity of the resin and the voids Charly got. I think by the 2nd or 3rd panel, he had figured out that by pressing down on a spot during vacuum bagging, he was able to correct the void. I've read so much lately though, I can't be sure if that was true.

    Post Curing: I looked at the attached PDF documents. I have no problem reaching 50 deg C for about 12 hours per day, possibly longer, in my building location. Can I post cure to an acceptable, but not perfect state by heating the final boat to 50 deg C for 12 hours per day for a week straight? At night, it would come back down, but not down very far. Possibly, I could use electric heaters at night to maintain the 50 deg C...


    Raka vs. West System vs. System Three vs. ?: Elongation is as follows - 8% for Raka, 11% for System Three and 4.5% with West System Tropical. Don't I want an epoxy with as little elongation as possible in my hulls to produce nice, stiff hulls, or is this not a concern because I'm just laminating plywood?

    The bulkheads and structural items are specified in the plans to be very stiff epoxy (West System specified). I know everyone on here says, "epoxy is epoxy", but doesn't the elongation figure make a difference?
     
  8. AndrewK
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    AndrewK Senior Member

    CatBuider
    Yes elongation is a very important resin property the higher the better.
    For reinforced laminates the matrix (resin) should have a larger elongation than the reinforcement, for glass this means >5%.
    West 105, System Three (dont know about Raka) are formulated to have good elongation to match the timber/epoxy construction.

    Tensile elongation for the west 105/209 that I have is 13% and HDT 44'C at ambient cure which increases to 16% and 57'C HDT with 8hr at 60'C post cure. Personally I would only use this hardener for sealing the timber if one is restricted to ambient cure.

    West 105/206 has 9% elongation & 51'C HDT for ambient cure which increase to 21% elongation & 52'C HDT with 8hr at 60'C post cure. While the HDT is just acceptable the high elongation is what makes this a popular choice for timber epoxy construction.

    Same goes for System Three, dont know anything about Raka.
    Hexion is one of a few epoxy manufacturers rather than just a formulator/reseller and have a extensive range of resins and curing agents. I think you should chase up your local distributor.

    As mentioned before I strongly recommend you draw up a table or a spreadsheet with all of the strength, elongation, HDT properties as well as processing conditions for the candidate resins. As you have to look at all of the parameters at once.

    Charly, sorry for miss spelling your name earlier.

    cheers
    Andrew
     
  9. apex1

    apex1 Guest

    No to your "post curing" plan. 5 weeks at 50°C are not as good as 12hrs. at 75°C which should be easy to achieve in FL.

    Don´t mix up the elongation rate and the stiffnes / hardness of the resin once cured. All of the systems mentioned will provide what your plans specify.

    Regards
    Richard
     
  10. Herman
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    Herman Senior Member

    At 50 degrees C postcure you will end up (roughly) at 65 degrees C Tg (in general)

    At 75 degrees C postcure you will end up (roughly) at 85-90 degrees C Tg (in general).

    Of course the epoxy must be capable of reaching the Tg given.
    Numbers are in the rough, every epoxy is different, although this kind of properties does not vary much.
     
  11. hoytedow
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    hoytedow Wood Butcher

    75.8* F is average daily temp. in October here. EP will get a good cure.
     
    Last edited: Jul 25, 2010
  12. Herman
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    Herman Senior Member

    I hope not. I think it is 75 degrees Fahrenheit, not Celcius, in Florida.
     
  13. hoytedow
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    hoytedow Wood Butcher

    :eek: Oops, sorry.:eek:
     
  14. Herman
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    Herman Senior Member

    75 degrees C = 167 degrees F. (at that temperature you can still enter the oven, if needed, but wear gloves, the air is bearable, but things are hot!)
     

  15. hoytedow
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    hoytedow Wood Butcher

    Yeah, I already knew that, but was sloppy in my posting. Please don't rub it in.:eek:
     
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