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wetting the lower side in VIP

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blup
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wetting the lower side in VIP

Postby blup » Mon Apr 01, 2013 8:47 pm

hi,


I tried already two times, but i still have a problem wetting the fibers on the underside of the foam core. Here is my stack from bottom to top:

rocker table, Mylar sheet, 3 layer of fiber, corecell foam, 3 layer combined with UD carbon, peel ply, plastic infusion mesh, vacuum bag.

I use vacuum infusion, which works well, I drill holes throught the foam every 4-5 cm, but I always have a few areas where the resin hasn't wetted the fibers.

Now I was wondering, has somebody used an infusion mesh and peel ply on the underside. Between the mylar sheet and the fiber layers.

Thanks for your help.

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Re: wetting the lower side in VIP

Postby plummet » Mon Apr 01, 2013 9:27 pm

never done infusion. why not do a wet layup? or partial wet layup with the rest infused?
channels in the core?
heat to make the resin thinner?
double the number of holes drilled in the core?
use a longer cure time hardener?
higher vacuum for longer?
different resin inlet, vacuum outlet locations?


personally i don't see an advantage of resin infusion for kiteboard construction apart from the obvious less mess during layup.

I have successfully vac bagged and mechanically pressed top and bottom skins with breather and peal ply on both sides. so I don't see why you can't use breather on both sides for infusion.

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Re: wetting the lower side in VIP

Postby everding5792 » Tue Apr 02, 2013 3:12 am

No experience to share but I wonder why the holes in the core does the resin flow side to side or top to bottom if side to side I would not have holes in the core. I thought the resin should flow freely on a controlled path over a set time period. If you have holes in the core it would seem to obstruct the guided path.

Sorry no answers just questions

Jim

plummet
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Re: wetting the lower side in VIP

Postby plummet » Tue Apr 02, 2013 3:40 am

you need the holes to allow resin to flow through and trapped air to be sucked out.

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Re: wetting the lower side in VIP

Postby FrederikS » Tue Apr 02, 2013 10:37 am

Where in the mold is it trapping the air? It could be several things. Is it possible you could do a quick sketch or perhaps an image of what is happing with clearly marked inlets and outlets?


This is just one typical scenario: mold side and top side flow speed is mismatched allowing for trapped air, here you could stop the flow media before the trouble zone effectively slowing down the flow.

You might also want to get a lower viscosity resin system that has always helped here.

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Re: wetting the lower side in VIP

Postby Bigdog » Tue Apr 02, 2013 2:27 pm

I have played with small tests but never did a full board so I am curious about this.

Are you 100% sure you have a vacuum tight system? My understanding is that if you have a good vacuum everywhere then the reason must fill those "empty" spaces. Maybe there is some sort of outgassing happening creating a gas pocket that the resin cannot fill. Could be a resin problem I suppose. If you pull a good vacuum it should stay like that for overnight with pump off and the valve closed. Not easy to achieve in my experience.

Let us know how it goes.

Cheers
Stan

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Re: wetting the lower side in VIP

Postby blup » Tue Apr 02, 2013 8:58 pm

Well,

I will try to answer all questions. The problem is that with the distribution mesh on the top side, the resin is flowing faster on the top side. On the bottom side it's going a bit slower. At the end of the infusion proces, the resin reaches the suction vacuum tube, and is sucked in to the cache pot. Sucking more resin through the board, is all flowing on the top side, while on the bottom side, some areas, more in the corners, are still not wetted.

Next time I will use two suction tubes, to try to avoid the dry corners. But I was just wondering if somebody has already tried to use a distribution mesh on the bottom side, to get the resin flowing about equal speed on both sides.

I have used vacuum infusion for other products, and that works very well, it's that core, what makes it difficult.

thanks for al reactions

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Re: wetting the lower side in VIP

Postby plummet » Tue Apr 02, 2013 9:50 pm

how about this for a left field idea.
set you inlet on the bottom? then the resin has to flow through the core to the top? probably difficult but not impossible.

anyway. breather cloth top and bottom will work. your just have to do separate finish coats on top and bottom.

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Re: wetting the lower side in VIP

Postby Johnny Rotten » Wed Apr 03, 2013 4:24 am

A bunch of options many mentioned
+ 1 for frederiks advice. Stopping the infusion mesh earlier can act as a "resin brake" slowing down the flow on the top side and forcing the bottom to pull more. Running mesh to the edge of the part can result in resin "shooting" off the edge. Different meshes can be used to control the speed as well.

Also unsure of your resin viscosity and temperature at which your using it.....these are important.

+1 for big dog, if you're bags got a leak you'll NEVER pull resin into an area that's already breathing to atmosphere.

More holes might help too, 1" x 1" grid is what I've successfully run test panels with but haven't tried much with other spacing. Given you indicate it's the corners and not the center this is not likely the true cause but may help nonetheless.

Everding: the holes are there to allow air to be pulled through the core from bottom to top. The idea behind infusion is that the air goes out of all voids and resin replaces the air. If there we no holes, the bottom center of the board would be pretty much sealed and the air would not be able to migrate out easily.... If air can't get out, resin can't get in.

Blup:
I would not bother with mesh on the bottom, then you end up with 2 B grade surface finishes and a fair bit of work to fix em. Infusion is best used to get an A grade finish without having to sand. if getting B surfaces, infusion is not worth the hassle or increased disposable cost IMHO. Initial Vf will be better but likely not enough to save significant weight after you resin the crap out of it to get back a presentable surface finish.

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Re: wetting the lower side in VIP

Postby FrederikS » Wed Apr 03, 2013 4:59 pm

One of the main advantages for VIP besides the low volume fraction of porosities is that the surface quality on the mold side will be as good as that of the mold assuming no print trough. The low amount of post processing is also very nice it the mold system is done right.

Most hobby resin systems for infusion work best from 20 degree C to around 30 (read limits on your stuff first not all systems work the same). Due to the exothermic reaction above 30 is generally not recommendable as some might reach boiling point while mixing in the pot. If possible use heated molds with a decent thermal mass and diffusivity.

Going under 20 might lead to stagnation and the epoxy not being able to cure. Also the viscosity is temperature dependent so low temperatures is a no go.


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