Infusion Plan

Discussion in 'Fiberglass and Composite Boat Building' started by jorgepease, Jun 4, 2012.

  1. groper
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    groper Senior Member

    Nice one mate,

    Illl just reaffirm what peter said, those dry lines you had, suggest a leak in that area and a loss in vacuum. The resin would have flowed past that area in the runners and kept going, once the resin had filled between the runners on the vacuum side, the leaky area is sealed off by the resin and things continue normally from there.

    Im guessing the dry spot on the vacuum line, would have filled in after you stopped filming?

    When i stop the flow media short of the vac line, the last little bits can take upto an hour or more to fully infuse, long after ive clamped off and walked away...
     
  2. jorgepease
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    jorgepease Senior Member

    Yeah you guys are right I believe ... I can't believe I could not find that leak with the detector ... I did notice though that when the leak is in a fold of the bag, it's not possible to hear with this detector. The few leaks I did find where after repositioning the folds in the bag.

    The dry spot was filling in when we left .... and I noticed the air bubbles had moved toward the mti hose so seems that was working as claimed. I will see on Monday :)
     
  3. petereng
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    petereng Senior Member

    Hi Jorge - I wouldn't get too hooked into the MTI hose. I read their product data and it seems to me that all it does is encourage you to set up your bag incorrectly. It must be a relatively expensive material as the membrane will be goretex or a derivative eg tyvek. Once the bag is filled the bubbles can't "move" towards the MTI unless the resin is still moving. This is called transport. 1) The bubbles should not be there in the first place 2) once the transport stops (bag is filled) then the only force on the bubbles is bouyancy. So they should rise into your media (generally speaking). Your vacuum system and your resin system should be considered as two seperate systems. Its interface is the resin flow front. To make life easier always design your fill system so you only have one flow front. If you have more than one you open the chance of having close outs ands dry spots. (keep that syringe handy) Its been years since I've had a drop of resin come out of a bag. By only running the media to say 50mm from the edge of a part you brake the flow. Have string or peel ply connect your job to your vacuum pump. Ensure there are no leaks by doing pressure drop tests and if your doing a lot of VIP buy an absolute pressure gauge. You will learn alot about your bagging (poor) skills. Once you have an absolute gage ensure you have pulled the bag down to its bottom pressure before proceeding every time. This ensures all steam and outgassing has finished before you fill . If no gauge then let the bag vacuum soak for at least an hour before you start. Some of my jobs take two hours to pull down especially if the humidity is high and the fabric has absorbed atmospheric moisture while being stacked. This illiminates considerable variability in the results. ie if everything is correct and there is a dry spot it could be moisture boiling off the cloth etc not a "dry" spot or a vacuum spot at all. Cheers Peter S
     
  4. jorgepease
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    jorgepease Senior Member

    Good advice, thanks. I will work with the MTI hose till I use it up but at the same time trying to set up the bag as if I was using regular spiral wrap.

    I will have the better pictures tomorrow and hopefully that will show what happened on the dry spot. It's as if the resin ran into a dam in that area but in the end it appears to have been filling in.

    One good thing, nothing really race-tracked to the vac line, that was a small victory :)
     
  5. jorgepease
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    jorgepease Senior Member

    Here is the still photo sequence - The pump is located at midpoint of boat on far side, check out how much faster that side infused. We should have opened the valves to the side farthest from the boat first!

    0 Minutes
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    3 Minutes - Notice how much faster bow is infusing compared to stern??
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    6 Minutes
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    9 Minutes
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    12 Minutes
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    15 Minutes
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    18 Minutes
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    21 Minutes
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    24 Minutes
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    27 Minutes
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    30 Minutes
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    33 Minutes - Looks like we sprung a leak in the bow? Looks okay this morning
    [​IMG]

    The dry spot appears to have mostly filled in. I notice that in the future I would switch infusion lines to be vacuum lines to suck out extra resin ... It wasn't terrible but there was a little extra resin in areas.
     
  6. petereng
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    petereng Senior Member

    Hi Jorge - The position of the pump should not matter. The pump is not pumping the resin. The pump is creating a pressure difference and the atmosphere is pushing down on the resin in the bucket and pushes the resin into the job. The difference in the resin flow from side to side means there was a presssure difference. This means the bag was not pumped down fully or there is a "communication" problem from side to side. Plus you have converging flow fronts. Remember I said to have one flow front? So fill from transom to bow as the bow is a natural small area. Or feed all around the edge so it flows as a ring into the middle. Place a vacuum guage on the resin feedline before you fill to ensure your pumped down at the feedline. Also place a vacuum guage at the furthest point from the vac pump. Remember to clamp these off and remove before you do the infusion!! Or use the same guage and move it around. You do not need to suck out resin, you just need to stop the mesh short of the edges and use a peel ply or string to connect to your vacuum ring line. If the bag is pumped down correctly and there is a high resin resistance path to the vac line the fill will stop at the brake and no resin will get into the vacuum lines. I suggest you stop using spiral for the vac line and use something like hessian tape that is used to hold trees to stakes. Its flat, cheap and air/vac travels through it easily but resin does not. Congrats again, it worked which is the main thing. Extra resin means you had a higher pressure in that area. Work on checking vac levels next time to get a feel for pressure differential in the bag. Its surprising how much it differs around the bag when you measure it. Peter S
     
  7. jorgepease
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    jorgepease Senior Member

    My bad, I meant position of resin bucket. The bucket is located midpoint on the starboard side of boat and you can see the difference it made, just an extra 7' of hose. Had I given the far side a 3 minute head start the sides would have infused more evenly.

    Yes I did the above. Stopped infusion flow media early and only connected with peel ply to the vacuum hose. This worked very well. The excess resin is under the resin line where the bag did not completely compress around, its a small amount. The bag I am using is super thick, I switched to it because I needed the larger size, it does not stretch very much at all.

    You mean stop using the MTI hose right? and use spiral wrap with tape? Wait can you explain that a bit LOL :)

    Thanks very much for that overview. I pulled some of the bag off already and it looks good. The dry spot I was worried about disappeared. The boat is stiff, I could walk on it and it feels strong.
     
  8. groper
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    groper Senior Member

    The pic @ 9 mins tells the story...

    Along that dry line you can see in the above pic, directly under this line i bet there was a join in the foam core??? which is why its showing as such a neat line... and also there must be a poor part of laminate on the hull bottom to let the air in which is going to need attention when you flip it over or your boat will leak...

    As peter said, it was slow on that side because of the reduced vacuum pressure due to the air leak...

    You would have picked this up in the drop test, but couldnt find anymore leaks as the ones under the job are the most difficult to hear... you thought stuff it, we will just shoot it anyway because your sick of mucking around with this damn thing... been there done that :p - sometimes a small repair in a non critical area is alot less work than pulling the entire thing to peices and chasing leaks.

    In future, you will adopt methods that are less likely to leak in the first place so sealing the bag and finding leaks becomes much less painful... the last job i did was a 20ft X 8ft panel and it took 5 hours from applying the mold release, to opening the resin lines.... everything went perfect.... this is why they say start small because with infusion theres little choice but to learn the hard way.... :D
     
  9. jorgepease
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    jorgepease Senior Member

    Hmmm my core joins run in the opposite direction of that perfect line, though the dry spot does just manage to touch a join at the extreme end and its only leaked in one direction from the join.

    I did do a drop test for 30 minutes with a one inch drop in pressure the day before. That line is just about where my peelply, release and infusion media film splices are. I bet I had a small leak in the fold of the bag that wasn't leaking till the bag relaxed and then the drop in pressure along with the extra resistance of the seams caused the resin to flow around that area. I found several leaks in the bag by easing off the pressure and repositioning the folds, I thought I had got them all though.

    Anyway bottom line is I have to continue to improve. Also I think this bag material is full of pin holes but the boat looks great now so I am not going to worry about it, just keep pushing forward with a little more skill each time.
     
  10. petereng
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    petereng Senior Member

    Hi Gorge -
    1) If you had the bag pulled down proper the resin would have shot across 7ft in a split second. It moves so fast that it makes a hammer noise when it stops at the other end!!

    2) OK thats good. If the bag has leaks then you may have to use it in double. So you build a bag, check it then put a some cheap netting over it then put another bag over that. The netting is connected to the pump as well. In this way the leaks in the outer bag go to vacuum and the leaks from inner bag go to vacuum. You can reuse the outer bag. "Proper" infusion bags are slightly stretchy and laminated. film is "blown" and blown film has microholes as its stretched to shape and thickness. Stretching produces holes.
    3) I don't like spiral or hoses for resin feeds on the job. They leave a hugh mark and resin pools around them. I use flat resin lines such as plastic infusion mesh cut into strips. If you have a core you can cut grooves in the core and use a 6mm or 8mm spiral placed in the groove then place the skin over the top and leave the spiral in. You can also place the spiral in a pleat and wrap mesh around the spiral and connect to the job. This leaves no mark but is hard to set up on big jobs holding hoses and pleats up in the air while the vac comes on. My current best strategy is to feed from the edges as it fills nicely into the middle, travels further as the flow front length gets smaller as it progresses vs a linear flow front or your fishbone type filling or the worst is where the flowfront gets longer.

    Starting to talk about small technical differences now. You could have used a bucket both sides. Theres many many ways to do it, you are well on your way!! I've been doing it for over 13 years and I'm still learning. Cheers peter s
     
  11. petereng
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    petereng Senior Member

    Hi Jorge - pressure drop test. When I set up a bag it takes hours to see a drop on a normal mechanical vacuum gauge. So just keep aiming for better and better starting vac pressure. If you went to a shop and bought something in a vac sealed bag you'd expect it to be sealed a year, 2 years after it was made. Thats the attitude and result you have to strive for. Some people say the vac pressure decreases during infusion, not so. It should stay static at same pressure or even get a bit better. If the vac pressure decreases ie absolute pressure increases then the bag volume is gaining which means you have a leak.

    The evacuation rate should be greater then your micro leak rate. If this is the case then the bag pulls down better as the infusion proceeds as the volume decreases and the pump improves performance. If you use styrenated resins this is not the case as styrenes outgases and reduces the pumps performance. stick with epoxy you will not be disappointed. Peter
     
  12. jorgepease
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    jorgepease Senior Member

    We definitely did not hear any sound and we didn't even see the resin flow in the hose, we actually thought it was not flowing till we saw the wet spot.

    I suspect the bag more than the core. It had lots of gashes and wrinkles straight out of the box. I just don't get how I am supposed to find a leak that I can not hear even with a detector and can not see (except as dry spot) when the resin is flowing.

    I think the concern was that if the resin front had not hit the edge where the sides and bottom connect evenly, then the resin could have race tracked along that line and left lots of dry spots in the sides. Are you saying that you would have put the resin lines all the way around the flange and just let it pull all the way to the center of boat? How far do you pull resin?

    Funny, Darko was saying we could do that too. I am just baffled that if such a huge pressure loss existed, how could I not find it.
     
  13. jorgepease
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    jorgepease Senior Member

    Yeah, I have to do a better bag. The next components I have to infuse are small, I am going to wrap the bag entirely around them so there is no question as to where the leak is from.

    Also my pressure gauge did not go down when I started pulling resin, it was like a hair under 30 and then pegged 30 as resin filled but the bag was not tight like before the resin. You could grab a pleat and lift slightly. This was the case anywhere on the boat.
     
  14. petereng
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    petereng Senior Member

    Lifting a pleat slightly is no problem. Just means the inside pressure and outside pressure is the same. But usually the pleats should stay hard in a good infusion. Its possible to infuse at 50% vacuum but the result is not quite as good. The point is the vacuum has to be connected to the flow front at all times, the vac pressure has to remain the same or improve through the fill and off course no leaks. Was your guage at the pump or at the furthest spot from the vac inlet? If at the pump its not much good, needs to be way away from the pump. Cheers Peter S
     

  15. petereng
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    petereng Senior Member

    resin flow length - using grooved core and styrenated resins up to 1500mm. Epoxy up to 850mm. These are linear distances if you edge feed it flows further. Some of the rtm mats flow up to 2000mm. Using airtech green mesh say 700-900mm depends on the laminate. I usually do a flow test with a new laminate. I lay out a 300mm wide strip by 2000mm long. I mark the flowfront every minute. Then once it stops I meausre the marks and graph the flow. It usually asymptotes in shape. This tells you how far it flows and when it becomes uneconomic to try to go further. Flow front speed ranges from 50mm per min to 200mm per min. I think over 100mm per min is too fast, easy to get dry spots and if the resin is a bit bubbly the bubbles will get stuck in the resin. If slow the bubbles will disperse into the flowfront and to the pump. cheers peter s
     
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