infusing with contour balsa

Discussion in 'Fiberglass and Composite Boat Building' started by Steve W, Jan 9, 2014.

  1. AndrewK
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    AndrewK Senior Member

    Forgot to say have not used or seen the MTI hose, sounds great.
    If there are no leaks then there is no issue with very long gel time resins, other than the electricity used.
    If you have a big enough resin break with only peel ply and do not put excess resin into the job you can not suck resin out. Resin will only come out if you had more than enough that was required or you have air leaks that flush the resin out.
     
  2. Steve W
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    Steve W Senior Member

    Thanks guys, we probably have time for one more test panel before we have to do the job, the long gel time is kicking our *** as where we are working we don't feel comfortable leaving heat or mechanical stuff on unattended for the long periods needed, the boat is in a huge heated (55 degrees f) storage building with probably 50 large boats, so, many millions of $$$ so we cant risk something of ours causing a fire.
    We bagged the boat last night to see if we could hold vacuum and couldn't even though we couldn't locate any leaks so tonite we will coat the whole repair area with west 105 epoxy and squeegee it in, then we have to wash off the blush and sand it and hopefully that will fix it. We have isolated every part of the vacuum system, both of my pumps themselves leak down, but I don't think that is a problem as the pump will be running continuously, we have a very large resin trap which we can isolate from the pump and it does not leak down at all, ever.
    We are about 600ft above sea level and the pump model shows a max of 29.3hg, last nights test showed a max of about 25"hg on the brand new liquid filled gauge on the resin trap while the dry gauges on both pumps read close to full vacuum which we should not be able to achieve at our altitude so im inclined to believe the new gauge, so we will reduce down to perhaps 80% of that after infusion. Im still concerned about continuing to remove resin as in our last test we had a bag that was able to hold vacuum for 16 hours after we shut off the pump, we had clamped off the 3 feed lines and then plugged the ends as well yet we still sucked resin out. We are now going to valve the feed lines at the buckets and then clamp them off as well close to the bag. I don't think we are going to be able to try the MTI hose this time but will soon or perhaps make our own with tyvek. I believe we now have enough info to accuratlly calculate how much resin to introduce but IF we continue to draw resin out I don't know how to stop it when the gel time is so long. I like the idea of doing my own tests on the resin as you suggest Andrew but I don't think we have time this time around.

    Steve.
     
  3. Steve W
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    Steve W Senior Member

    Andrew, how far from the edge of the part would you suggest for placing the vacuum lines? it seems just about anything works and we have been setting them up at about 3" but as you say, a longer resin break should help keep the resin from reaching the lines. Another factor that may or may not influence this is that we will be drawing uphill, ie, the vacuum lines will be higher up the hull about 24 to 30" out from center on a typical fin keel boat while the resin buckets will be well below this level, im not sure if this makes a difference but I know the height of the resin bucket affects the flow.

    Steve.
     
  4. groper
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    groper Senior Member

    Controlling resin content is about controlling the vacuum pressure, and therefore the compaction pressure and thus laminate thickness - it has nothing to do with "sucking resin out of the job" - this is still thinking like wet bagging.

    When you see resin migrating across your resin brake and then up your vacuum lines and eventually ends up in your resin trap - its not because your "sucking it out" and reducing resin %... its purely because you put too much in, in the first place! A good infusion strategy involves very accurately calculating the required resin for the job before you begin. The calculation involves specifying the resin weight %, based on the vacuum pressure after filling.

    So after its filled, the reduction in vac guage pressure to say 80%, mean less compaction and a higher resin content in the cured laminate because the entire laminate is resin rich whilst the resin is flowing. This occurs because the laminate springs back once its wet, increases in volume, and therefore has a high resin to fibre ratio.

    After the job is filled, the atmospheric pressure presses down on the laminate whilst the vacuum scavenges any excess - this part of the process evens out the pressure gradient and resin content gradient, from the resin rich inlet to the vac line. If you reduce the vacuum guage pressure at this time, you reduce the pressure gradient and the entire laminate will reach equilibrium at a higher resin content.
     
  5. Steve W
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    Steve W Senior Member

    Thank you Groper, that is about the clearest explanation for the not so physics inclined that I have seen thus far and just what i need right now.

    Steve.
     
  6. jorgepease
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    jorgepease Senior Member

    I found this out the hard way on one of my infusions when I had to shut the pump down after my resin trap over filled ... I was a faulty infusion strategy but at least the whole part was infused.

    Once vac was off the laminate uncompressed and the upper layers became essentially starved.
     
  7. groper
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    groper Senior Member

    Steve, you need to know the following;

    Resin absorbed by the flow media;
    Resin absorbed by the peel ply;
    Resin absorbed by any core materials and their surface porosity;
    Resin absorbed by any core material perforations or grooves;
    Resin to fill the volume of the feed lines and under bag feed runners;
    And lastly the glass or carbon fabric reinforcement - which will vary dependant vacuum pressure.

    So once you know how much your stack will consume, multiply by the unit area, and you will know exactly how much resin to mix with zero wastage and no excess to clean out of your vac lines and catch pot. I reuse my vac lines over and over....

    It's no use me or anyone else giving you values to use because our materials are no doubt going to be different. But just to give you an idea, my stack consumes the following;

    Peel ply - 80 grams per square meter,
    Flow media - 320gsm,
    80kg/m3 divinycell foam surface porosity - 300gsm per side - 600gsm for a double sided sandwich infusion,
    Stitched Dbias e-glass - 30% of the tex fabric weight @ 100% vac @ 10m elevation above sea level. Goes up to about 38% resin weight @ 80% guage pressure.
    Resin line volume depends on the cross sectional area of your hose x hose length.

    Once you add up all that, you can weigh out your resin based on your total area and begin. Highly recommend automating the calculation via an excel spreadsheet. You may have to do some small weight samples to determine your consumables resin consumption and get accurate numbers for the type and brand materials your using.
     
  8. AndrewK
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    AndrewK Senior Member

    Steve, most important rule is if you have any leaks then do not infuse.

    How big a resin break to have? as big as you can.
    I try to have at least 6" peel ply only break. But have infused right up to the edge with no resin break when I had no option, in a case like this you can not avoid some resin in the catchpot without the use of MTI hose.

    Groper, Peter and I calculate our resin requirement for each job fairly precisely so get the benefit of reusing the vacuum lines and also more iportantly eliminate the potential of decompression of the job if the vacuum lines gel up and isolate the pump before the thin laminates gel. Of course if you have a perfect seal even this is not an issue.

    I have posted this spreadsheet on previous infusion threads, here it is again to give you an idea how I do it. But as Groper said you have to know the resin uptake of your materials at the absolute pressure/pressures that you use.
     

    Attached Files:

  9. Steve W
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    Steve W Senior Member

    Thanks again guys, I do know the resin weights retained in the various consumables and don't have any core to figure in this time, this is the first time with solid glass, 25 plies in total tapering out at about a 20:1 ratio, we have set it all up on the boat and have a pretty good bag, not perfect though but we have quite a bit more work to do at low vacuum to manipulate the glass a bit better in the bag, it is quite difficult to get all those layers to lay just right. Ive got to say its a lot more difficult assembling everything with gravity against you, makes you really appreciate working on the table. So we are only able to achieve about 25.5 HG on the gauge on the brand new liquid filled gauge on the resin trap, while the old dry gauges on both pumps are reading close to 29.9, (I don't have a digital absolute pressure gauge yet, its about the last thing I need to get) but I am more likely to believe the new one on the trap because the new pump is only capable of 29.3 plus we are at 600ft above sea level. So, if I go by that one I would be backing off my pressure to 80% of that reading, to 20.4hg, correct? We have incorporated a 6" peel ply resin break. I know that the goal is an absolutely leak free bag but as groper mentioned on another thread, it is very difficult to achieve, we couldn't even come close on this repair until we pre sealed the whole repair area. So, what would be an minimum acceptable drop test?

    Steve.
     
  10. groper
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    groper Senior Member

    Don't do it Steve!

    Hand lay the first layer so you can get a better seal. When not using good molds or tables, you would not believe how porous some things can be... assuming you've checked everything that you have access to without disassembling the stack...

    And no, just because you have altitude does not mean you should scale the vacuum lower to get the 80%. This is why talking in absolute vac pressure is better as it'd always consistent no matter where in the world you are. So shoot for 200 mbar absolute - whatever that may be at your altitude and equivalent Guage pressure... This is after the part has filled , still infuse at full vac.
     
  11. AndrewK
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    AndrewK Senior Member

    If the gauges are at least reasonably accurate then this is a major leak, I would not attemt the infusion. This is a personal standard that you make, I have seen what I consider terible infused laminates due to air leaks what others consider OK.

    First check your gauges, reverse them. Or as mentioned earlier I monitor the pump output to see how big the leaks are.

    As far as the vacumm level to target so far we have discussed two tifferent things.
    One is to target the resin wt% in the laminate, we do this by the compression pressure. So in places at high altitude you need higher vacuum levels not less to achieve the same clamping pressure at sea level.
    The other one was minimising micro voids, also can be done by reducing vacuum level after impregnation that I and Groper use at times. I think this is the only thing Peter differs on to Groper and I.
     
  12. jorgepease
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    jorgepease Senior Member

    I had some really tough leaks to find. If I could not hear the leak with the detector and my bag dropped off quickly, it usually meant lot's of little leaks.

    On almost every infusion I did my bag would drop a bit, say down to 28, over 10 minutes and then hold there for at least 30 minutes. How fast is your bag dropping? My gauge was likely inaccurate, I would worry more about drop test.

    You can deal with pinholes that develop pretty easy but if it's a big leak that could be ugly. Your 20 cfm pump will be able to hold vacuum but you will drag air through the part and resin out.

    As a last resort, probably even wrong to suggest it, but I would have a spare vacuum line connected to a pouch holding some mti hose wrapped in flow media so you could pierce your bag in the location of the leak and at least keep air from dragging across part for 18 hours.

    Good luck, I wouldn't do it if your bag is dropping any faster than I mentioned above.
     
  13. Steve W
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    Steve W Senior Member

    Well, we did the infusion on sunday and im pleased to say, all went well, as I had said before i sealed the repair area with west 105 epoxy and that made the world of difference and then we spent a lot of time chasing down the leaks until we got it down to just over a 1"hg drop in 5 minutes. The fill took just under an hour. I am ordering a digital absolute pressure gauge tonight along with some MTI hose from German composites, the gauges i have are just too inaccurate. Im really interested in trying the mti hose, if it performs anything like advertised it will be a great product.

    Steve.
     
  14. Steve W
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    Steve W Senior Member

    Jorge, i also find that I get a drop in the first couple of minutes and then it holds, this is true of almost every bag, unless of course we have big leaks. We had a guy helping chase down the leaks and he was very patient with the leak detector, we are finally getting used to the thing. We have also found a stethoscope without the end piece to be very useful.

    Steve.
     

  15. jorgepease
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    jorgepease Senior Member

    That's great! I was getting nervous just reading about it here lol ))
     
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