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how mutch vac to use ?

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mattthieu
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how mutch vac to use ?

Postby mattthieu » Mon Jun 24, 2013 3:09 am

hi

simple question, how mutch vac to use ?

let me explain: jsut did the top of a bord ( my third ) and, despite the vac ( witch is good to get the rail wraped ) i could not get all the bubbles away ( some little ones i could not push away ). but, i'm using only polythene film over the laminate, no release no breather.

the next board i'm going to go with release ( perforated and breather ) and then polythene !

my concern, once the breather is on, no way to see anything so no wayto see if they are some bubbles !

i woul dbe tempted to get full vac ( in my case, minus 25 inch is the max my pump does ) but i'm concerned this would dry out the laminate and transfer all resin into the breather !

i'm concerned if i set the vac ton low bubbles might not get out !

any ideas, anyone already done it ?

thanks

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Re: how mutch vac to use ?

Postby plummet » Mon Jun 24, 2013 7:38 am

Do it at 25hg.

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Re: how mutch vac to use ?

Postby sijandy » Mon Jun 24, 2013 7:56 am

I'm interested to see what responses this gets, i run mine at 29inhg but also got bubbles and dry spots. there are many factors than can cause this but have wondered if there is an optimum vacuum laying up boards. I've been under the impression that the higher the vac the more bubbles are drawn to the surface and break?

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Re: how mutch vac to use ?

Postby Larse » Mon Jun 24, 2013 12:53 pm

As much vac as possible... I use an inustrial vac pump, which sucks to almost total vacuum. I have a good connection at Danfoss and got one they use to test high pressure systems with. No other vac pump in the world can suck as much as that :)

But my first board was made with 2 powerfull vacuum clearners and that ok as well. I use plypeel and a layer to suck up ledt over resin. That doesn't leave bubbles or anything...

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Re: how mutch vac to use ?

Postby FrederikS » Mon Jun 24, 2013 1:21 pm

Bubbles can be caused by a lot of things.

Primary causes: mixing base and hardener without letting it settle or not degassing, moisture content in the mats, viscosity of the resin is too high.

You could also be pulling to much vacuum getting the resin to boil, but I doubt that is the cause.

Usual procedure is that you pull it to max vacuum the pump is capable of for some time like for instance 10 min (experiment) or close to max if you want to be able to reproduce it at all time, and then reduce it by 20-25% after that. This is not ideal in terms of volume fraction of fibers but it allows for some of the trapped bubbles to be squashed together.

mattthieu
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Re: how mutch vac to use ?

Postby mattthieu » Mon Jun 24, 2013 2:05 pm

thanks everyone !

my concern is, IF i put it to max vac ( mine at least ) wont it dry the fabric to mutch ? that would be worst the heaving few air bubbles !

it's not even the money waisted ( of course it is also money !) but, it's the hours of shping the wooden core that will go to waist if the fabrik is to dry !

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Re: how mutch vac to use ?

Postby FrederikS » Mon Jun 24, 2013 2:25 pm

mattthieu wrote:thanks everyone !

my concern is, IF i put it to max vac ( mine at least ) wont it dry the fabric to mutch ? that would be worst the heaving few air bubbles !

it's not even the money waisted ( of course it is also money !) but, it's the hours of shping the wooden core that will go to waist if the fabrik is to dry !


If I were you I would test the setup first to see what gives the best results. Like 3 small layups, three slightly different procedures. That way you do not waste as much material and you learn what works faster.

mattthieu
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Re: how mutch vac to use ?

Postby mattthieu » Mon Jun 24, 2013 2:36 pm

i shure will test, i ws just wondering if someone had a vac level to sujest to test with.

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Re: how mutch vac to use ?

Postby FrederikS » Mon Jun 24, 2013 3:17 pm

mattthieu wrote:i shure will test, i ws just wondering if someone had a vac level to sujest to test with.


I would test with a lower level than what you used when it failed. Like maybe 10% less. Also maybe test the procedure where you turn down the vacuum about 20% once the bag has compacted and the bleeder has absorbed some resin.

It is all about finding out what works with your resin system, pump and procedure. Normal vac gauges are not that precise anyhow so saying a certain pressure will not help that much I am afraid :P

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Re: how mutch vac to use ?

Postby zfennell » Mon Jun 24, 2013 5:53 pm

mattthieu wrote:hi

simple question, how mutch vac to use ?

......my concern, once the breather is on, no way to see anything so no wayto see if they are some bubbles !

....... but i'm concerned this would dry out the laminate and transfer all resin into the breather !

any ideas, anyone already done it ?

thanks



regardless of vac setting, everything in the bag is supposedly at the same pressure.
The perforated film or peel ply is mechanically forced against the glass cloth.
The resin does not really move much, Its more a function of the release film moving from top of resin to top of the glass.
the only other forces involved that may move excess resin out of the cloth would be
1) gravity (nothing)
2) diffusion (a little)
3) maybe capillary action
4) a leak in your bag ( potentially big effect on transport)
5) slow leak from core (timing issue)


a good test you can do quickly.

wet out 1 square inch of glass and put down on plastic sheet.
add 1 square inch of peel ply
add 1 sqaure inch of breather
add plastic sheet on top
put 15 lb weight (1x1 base) on top of everything

come back in 8 hours to see what happens.


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