what caused this !! any one know ??

hi
This is a photo i had taken about 10 years ago . vac 20 mm core down onto core bond so this was the underside that could not be seen till the panel was released from the bench and turned over to be greated with this from one end to the other.
any one want to have a guess at what the cause was ??

 

forgot the picture so here it is !!

 

improper preping of the surface the core bonded to and was allowed to let water in?? did it delaminate? was it wet with water/ was the core coated with resin when it was bonded?? or it may have been that it had trapped styrene under it!

 

its brand new straigh off the bench !! everything by the book !!

Sorry you are not even close !!

Was really quite funny we had made lots panels some really big and had been using 50mm core on everything had also done some 30 mm thick panels always we had prided our selves on a perfect job 100 % of the time !! then this happened and everyone paniced . what the hell had we done wrong going through our check list and with all the guys present we mulled this over . before the day was done we had lectures from the university engineering department , guys from every notable resin company and a few boat builders all speculation and pointing the finger and no one , not one person came up with any thing inteigent at all and never comeing up with a answer . when they had all gone the problem still remained a mystery to our resin chemist wandered in a in a very short quick demo showed what had caused it .
i have asked the question a few times on this post and no one ever has come up with the answer yet we all use vacumn every day but do we really and truely understand it?? if you had seen this on one of your panels where would you point the finger and who could you blame or lay the cause of the problem at there feet ??
product ? catalyst ? the equipment ? the proceedure ? what ?? everything was the same as everytime before ,just this was our first 2o mm thick panel
I made a point and was always present when they were cutting panels and collected off cuts and cut outs and tearing into them and always 100% ok never any problems at all .

rawleyjerel@yah i am impressed with some of your posts and never want to tread on toes . friends !!!

Going to wait for a few more answers before i reveal the cause and the answer my astound a few people. specially some die hards !!

 

How much vacumn do we really need ??

Well this was the result of the vac being to high!! After a demonstration by a friend /chemist from the resin company that supplied all our resin .
so i asked the question how much vac do we actually need ?? lots head scratching and a log jamb at the door with professers and chemical experts running for cover . no one had ever been asked such a thing and obviously no one had the answers either .
So was left up to us to crawl out on the skinny limb again !!
"we'd love to know your findings but have to go Bye !!"
so exsperiment time .
I will refer to things in percentage of total vac as the gauges we used went to 100 from 0 !!
Lets make some samples and see what we get . lots a 600 mm X600 mm X 20mm foam squares and planted in a line along the bench each one exactly the same, borebond ,bags and all the bits i had 2 vac regulators and 2 gauges so did them 2 at a time .
1@ 50% vac same as before bubbles
2@ 25% vac a little better but bubbles .
3 @10% now we were getting some where
4 @ 5 % vac and hello just very small bubbles !!!
I asked again how low can we or should we go No replies the silence was deafining . so lets halve that
5@ 2,5% and almost no bubbles at all like really had to look hard to find !!
6@ 2% and there was no differance that anyone could find between the two panels
We repeated the 2.5% thing on a bigger panel always doing what we had done on every other panel same core bond same catalyst, same trowel ,same bag etc etc . when it cam off the bench it was 99% perfect i ground a part of the core off slowly layer by layer all way to the glass on the other side and only found tiny little bubbles that you could find in any laminate any where .
so what do you think ??
Some one will ask !! yes the foam was perfirated straight from the box we always pre-resin coated !!
now thats another interesting thing as well how much resin would you use to pre wet foam going down onto Core bond ??
We had a spray saturator gun so life was simple . but we also rolled the resin to make sure it really got into those pores of the foam plus resin coated edges ! it was left to stand for a few minutes before being laid face down always from one edge and rolled into the core bond from one side . always making as best job was possible to make !!,
So if you have a system that works why change it !!.

 

Vacuum too high ? this flies in the face of everything I have read over the years. how do you have too high a vacuum ?

The percentages quoted could be misleading - you really need to specifying the actual figures.

 

Dont you own a calculater ??

And its why i have given my figures in % of unltimate vacuum . which is ??

atmospheric pressure (1 Atm.)
--------------------------------------------------------------------------------
= 1.013 bar, =1013 millibars (mbar), = 101325 Pascal (Pa); =101 kPa
= 760 millimeters of mercury absolute (mmHgA) = 760 Torr (1 Torr = 1 mm HgA)
= 29.92 inches of mercury absolute ("HgA), = 14.7 pounds per square inch absolute (lb/in², PSIA)

what is written and what can be used can be two completely differant things .
Tell me why do you use vac to put down a core on to core bond ??
one you suck the air out completely and run the risk of squashing out the core bond till theres almost nothig left OR
simply use enough vac to hold the core in place while the core bond goes hard and sticks it in place ??
which one do you choose and why

Funny had some strange looks from guys when i ask how much vac you going to use to do what ever the job is they going to do know one knows its all hit and miss and suck till theres nothing more to suck . .

This flies in the face of everything I have read over the years!, Yes and just about everyone will agree with you !!
BUT
You asked how do you have too high a vacuum ?
When what you see in the photo happens ,thats when !!
From the time i did my own exsperimanting to the end of the next project i will be using just enough vacuum to do the job of sticking Balsa core sheets to the sides of our hull and all over the deck and the small flybridge of the 90 footer we are doing !!
Did the same in Korea when we did 8 racing yachts and all the hulls used foam core from Gunwhale to gunwhale and all the decks every where were foam core amd never use more than 50% at the most of vacuum any where .
My reasoning was to make sure there was a good film of resin left under the core to bond and cure properly .
Man did it stick !!.
Had to chisel out one square foot of core off a hull and it had stuck like i never seen foam stick before !
Just used 450 csm and vinylester resin thats all !!. That was 2007/8 and boats are still going strong !!.

 

IF that's what the 0 - 100 meant, which I doubt.

For a start, there is no such thing as ultimate vacuum ever pulled in an industrial environment,

and, there is a lot of other things those numbers can mean, and even the geographical location can alter the readings. Even then, gauges can be very approximate depending on their age and usage condition.

"Vacuum gauges are calibrated in inches of mercury (in-Hg), just as barometric (ambient atmospheric) pressure is expressed. This brings up a couple of points.

First, that scale is mainly of interest in the U.S. So vacuum gauges usually have an additional (metric) scale, expressed in centimeters of mercury (cm-Hg) or millimeters of mercury (mm-Hg). Some are also calibrated in kilopascals (kPa).

Secondly, barometric pressure varies with altitude. You should expect to see somewhere around 18 to 22 inches of vacuum at sea level. Although your Vig's "ability to suck air" will remain constant, it'll vary relative to the barometric pressure at the altitude where you live. If you live in Death Valley, your reading will be higher. If you live in the Alps, your reading will be lower. The gauge is reading the difference between manifold pressure and ambient air pressure. Here's a chart that'll give you rough offsets above sea level.

Altitude Inches of Vacuum

Sea Level - 1000 ft. 18 - 22

1000 - 2000 ft 17 - 21

2000 - 3000 ft 16 - 20

3000 - 4000 ft 15 - 19

4000 - 5000 ft 14 - 18

5000 - 6000 ft 13 - 17"

As far as 'too much vacuum', maybe the reason that all the 'experts' looked at you strangely, because the problem of voids has so many other potential causes...

You may like to consider this excerpt.

"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"

from this site, amongst others

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

So rather than merely 'too much vacuum', you are better off considering what formula's of resin will outgas under what actual pressures.

 

What do you do for a living ??

 

What does it matter ?

Have I supplied any bad info ?

 

the resin volatiles (styrene etc) wont boil off till about 93% absolute... so i doubt this is the reason - however i wouldnt go so far as to say it wasnt the level of vacuum that did this.

Ill put this to you, if when you lay the core onto the corebond, you enevitably trap air under it... if you increase the vacuum, the entrapped air expands - which is contrary to what you might think as the core is crushed down more and more with increasing vacuum, a paradigm if you will...

However, the dark blobs in the photo do not look like air bubbles? they look like resin? so little pools of resin trapped? did you cut them open and see what was in them?

 

Get your point and yes i cut open and ground the top layer completely off was all bubbles .
The method, the materials, and every thing was the same as we had been doing for the 6 months previous !!, just the thickness of the core had dropped from 40 mm down to 20 mm .
Was the first 20mm panel we made , lucky was only small !! had others to do after and they were quite big but the vac pressure we kept it at 2,5 % and perfect each and every time . Because the pressure was so low i sat and watched it till gel time . could always tell when had gelled the pressure went up a little . Next time i get back to nz i must try and find the disc with all my hundreds of pictures about the same time i know there should be at least another 4 or 5 pictures .

 

Yes, very true

http://www.lightweight-structures.c...g-of-resins-before-vacuum-infusion/index.html

states

" For an epoxy resin, Wood and Bader (reference 9) measured the equilibrium gas concentration of nitrogen at atmospheric pressure to approx. 1.7 % by volume. These 1.7 % of dissolved gas may not seem like a considerable amount of gas, but at a vacuum pressure of 20 mbar, which is commonly used in vacuum injection, this would expand 50 times if brought out of solution."

But its not just the volatiles- its just plain air entrapped during mixing.

 

i used a vac process similar to this, with vinylester resin on a 15mm core... i had to cut grooves in the bottom of the foam (about 2mm deep) which would let all the air escape out to edge of the panel from underneath it. I used 90% vacuum and no problems... (after i figured out the grooves)

I used a high vacuum as i wanted to compress the laminate at the same time. many way to skin the same cat ...

 

no just wondered what line of work you were into thats all !!:idea: