Infusion Plan

Yes core is one side of the bag. That has been done before here - http://www.fram.nl/workshop/controlled_vacuum_infusion/cvi.htm

I have been pretty careful to make a perfectly sealed core. I will skim coat the flange so the sealant tape can adhere well and make a good seal. I don't think the core itself will leak but I will test a small panel first to see if it holds.

Pulling up or down that is what I need to know If I pull up it might be easier with less vac lines. I would only have 3 instead of 6.

 

leak detector

Jorge,

Are you using a leak detector? They are certainly worth the investment.


Allan

 

I am waiting to see if I can find one used on ebay or elsewhere. At the moment I am hoping I can put together a leak free bag because of the pretty simple and small shape.

 

Take great care in installing the sealant tape in pleats and corners. Do a decent drop test, and chase leaks by the ear. Also run your thumb over the sealant tape a couple of times, and squeeze the pleats. Corners and overlaps are places where leaks occur.

Other leak paths:
-fiber under the tape
-pinhole in bag (is usually found reasonably quickly as it causes bubbling in the resin)
-pinhole in foam or seam (hard to find)

I supplied all materials to Henny (www.fram.nl) and can confirm that it is perfectly possible to get an air tight foam structure. However, closing the seams is quite some work.

As for infusion strategy, I am a big fan of the "dutch" way, which is a fishbone. I am not too fond of infusing "up side down" as infusing downwards can cause some more bubbling.

Depending on the width of the boat, your resin, infusion mesh used (or not), infusion consumables available, and your ability to perfectly seal the edges with sealant tape, there are several strategies possible:

-parallel lines:
easy for the mind
cumbersome to operate all valves.
lot of imprint of the spirals

-fishbone outward (downwards in this case)
if a leak occurs in the bag seam, it is not disastrous for the part
easy infusion: open a valve, and weight (and keep an eye on resin level)
downwards is not pretty, but it is only a small amount.
lot of imprint from the spiral runners.

-fishbone inward
technically more correct
lot of imprint from spirals
leak in the sealant tape makes life more difficult
slight resin loss due to some resin coming upwards in centre vacuum line, unless a more advanced material is used (MTI hose, Dahltexx, or similar. These solutions allow air to escape, but do not let resin through)

-feed on sides, vacuum in middle, use infusion mesh
small amount of imprint from spiral (when using the flat airtech Dahltexx material, no imprint at all)
simple
leak in sealant tape can still be awkward.

Personally I would opt for the latter system in this case, using a slow epoxy. This said I have the advantage that I have available all thinkable infusion materials (Airtech distributor, and have our own line of materials as well) as well as a variety of resins.

 

I must have Dutch mentality from my father living in the Hague for many years because the fishbone method really appeals to me

You have a lot more resin flowing so it would seem infusion can happen very quickly and the imprint does not bother me so much because I believe I am going to have to apply a skim coat to fair the hull anyway ... though maybe a couple of extra runners of infusion flow material would help diminish the imprint.

I like this Dahltexx or MTI material for vacuum, that would take a load off my mind.

The latter method you mention, you say needs slow epoxy and I have 3 kits, 2 with slow hardener and one with fast because I felt the slow gave me too much time so I was going to blend the hardener to make it set a little faster.

On the flange I was planning on adding a little shelf (just a narrow piece of foam glued to the flange and stick my sealing tape on top of that keeping it up from the resin line. It's more work, I know, never worked with sealant tape so don't know how well it sticks and if it can come loose around resin.

 

Oh, forgot: as a runner, you can use plastic spiral wrap. Just make sure you get a thicker walled one. I am having 1/16" wall thickness specially made. (I buy 5 miles of this every time)

Forget about the shelf. First of all you will be sticking it to a dry flange, not a dripping wet one, and second, the stuff sticks like crazy.

 

glad to hear about the tape. I will get the runner from an infusion supplier, don't know where else I would get it.

 

Jorge,

What is to stop the joint between the added foam flange and your mold from leaking? The adhesive used to attach the two together? I would suggest making the flange very rigid so it doesn't fail after your infusion has started.
It might be worthwhile for you to post a sketch of your flange detail to enable the forum members to vet the idea.

Most HVAC (heating and air conditioning) contractors have and use ultra sonic leak detectors. Do you have any HVAC friends that would lend you one? or maybe rent one from a HVAC contractor for a day or two?


Herman is totally on the mark as always. Applying the tape at the pleats is a pain and needs to be done with great care. He also mentioned the importance of doing a "drop test". My interpretation of a "drop test" is, after you have sealed everything to the best of your ability, shut off the vac pump. If you loose full vac within than 15 minutes you have a leak that needs to be found and fixed prior to infusion.


I hope this helps


Allan

 

The flange is supported by the jig. I screw the flange from below and then add a fillet. As this is an inside joint I will just create a rounded fillet, I don't think I have to route a groove. The flange is not just for the resin hose, it will be for the hull to deck connection and bolt through cleats etc ...

The engineer at work may have a leak detector now that you mention it, I will ask him, that would be great. If not I will do the bag test like you say. I read somewhere to do that test below ??? 95% ??? vacuum as above that outgassing occurs and can give a false indication of a leak. Does that sound right?

I am doing all this Saturday, I will post a picture of that then.

 

"Some water vapour will be present in almost every vacuum situation, but there will be a large increase in volume when liquid water starts to boil. Water will boil at reducing temperatures as the vacuum level increases. Any combination of temperature and vacuum above the boiling point curve will generate large volumes of water vapour until all of the water has boiled away. A slowdown in vacuum pump performance should also be expected until the vacuum pump has removed the water vapour and discharged it from the pump exhaust.

Another source of vapour may be resin solvents. Particularly polyesters and vinylesters will outgas under vacuum. The level of vacuum for this effect to take place is dependent on the vapor pressure of the solvents present in these resins. Resin suppliers will be able to advice these vapor pressure and the correct level of vacuum to be applied at the end of an infusion to avoid unnecessary out-gassing of the solvents required for the curing process."

from

http://www.fram.nl/workshop/vacuum/index.htm

indicates yes.

 

Thanks, that explains the wide range from 10" to Full Vacuum that I have been reading in these forums

 

RWatson,

I was recently reading a Du Pont Tech sheet about Kelvar and noticed that their Kevlar 29 as a typical moisture content of 7.5 %

http://www2.dupont.com/Kevlar/en_US/assets/downloads/KEVLAR_Technical_Guide.pdf

Do you know if any Builders pre-dry their their materials prior to installation, to lessen the boil off issue?


I can imagine that it would be problematic on large boats, but it would be pretty simple to do for my canoes.


llan

 

Some interesting point in the current thread

http://www.boatdesign.net/forums/fi...-building/what-caused-any-one-know-43457.html

about high vac issues.

Tunnels controlled the vapour issue by lowering the vac, Groper cut grooves to ensure proper gas relief.

I have read 2 or 3 articles about drying fg products prior to layup, as much for weight reduction as any infusion problems.

 

I think dropping the vacuum makes sense, my only problem is I don't think my two stage pumps can run for very long like that. I was wondering if I could put a valve between the pump regulator and the catch-pot and keep that valve almost closed and then but another regulator on the catch pot, I could bleed vacuum off the resin trap yet keep the pump pulling hard by limiting air flow??

Does that make sense?

 

You're working at definition cross purposes here, I think. Tunnels solved the problem of vapor by lessening the vacumm , not increasing it.