I placed three very wet layers of kevlar into the mould applied peel ply, perferated film, breather and then my vac bag. I started the vac and managed to get it to maximum.
Alot of resin was soaked up by the breather so much that many areas were completely soaked with resin and not the usual poka dots that you get.
When I de-moulded I found that I had some completely dry areas on the cloth and also some pits, almost like craters (about 2mm to 3mm).
Can anyone tell me if this is usual with Kevlar and how and if this can be avoided?
I would like to do the next one with the first layer being carbon fiber and the last 2/3 layers being kevlar but with the price and availability of carbon am scared to do so if I get the same results!
Could someone please help, I will answer anything further you may need to know.
To avoid over wetting your cloth do this: Weigh the cloth, then weigh out the exact same amount of resin using a digital scale. I bought mine for $40 at office depot. Your bleeding will be minimized quite a bit.
Another thing you will never read about is breather cloth weight. If you use to little breather you will saturate the breather which will then cut off all vacuum to the wetted out areas. Just because your vacuum guage (at the pump) says 20" doesnt mean your part is under 20" of vacuum (or whatever vacuum your using). 3oz breather, which seems to be the standard, sucks if your going to use it as your breather AND bleeder layer.
If your not going to use a separate layer to bleed, and a separate layer to allow the vacuum to breath (and thus supply continuous vacuum pressure) then go with a heavier breather. Like 4 oz or double up on the 3 oz breather.
To ensure full vacuum you can use a separater layer, or, a second perferated layer on top of your bleeder.
So the layers would go like this:
X layers of glass
perferated release film
bleeder (same material as breather, or, low weight csm)
perferated release film, or, same material as the bag
breather (3 oz is fine if your only using it as breather)
and your bag.
Once everything is bagged and under vacuum you will need to make sure the bag fits tightly into all tight corners. And whats equally important is rolling the bubbles out of the layup while its under vacuum. Most people think just because its under vacuum that the bubbles will find their way out of the layup. Never will happen unless you are producing some serious pressure.
A technique you might find usefull is when you lay your release film over the wet layup. Roll any visible air out of the layup at that point. So roll a roller on top of the release film towards the sides of the layup. Air can get out, but, it wont be able to get back in.
Also resin viscosity plays a key part into how much air will be allowed to move once the part is under vacuum. The faster the resin, the slower the air.
One more thing…Peel ply can cause a LOT of problems. If you definitly need it, then use it. If not save it for a better day.
Ill bet all the money in my pocket peel ply cuased your “dry looking” areas. Not all peel plys are created equal. Some will leave your part extremely dry for secondary bonding (like what happend on your part). And the finer peel plys will leave your part looking like wrinkle paint, but, fully saturated.
Thanks for your post. The dry areas were on the finished side of the product not on the inside where the peel ply was, is this what you mean? Will the peel ply cause dry spots on the finished side (good side layed against the mould?
oh don’t be mean!! we all know you only have 23 lintballs, and a half eatten wooden nickle in your pocket!
hee…sorry.
long morning…
I was left with a mess, a confusion, and a 200lbs 74"x43" mold to move myself into the oven on teh other side of the building through 2 normal doors…
On the PeelPly issue… Wet out the peelply before you put it on or at least wet it out after it is on. The stuff will suck up resin and you want there to be a clean resin rich area there for secondary bonding or smooth finish. It is best for flat areas and not curves and radius, too much cutting and it doesnt stretch. Not too much resin or it will be difficult to remove.
