Trying Hard

General Composites Discussions Composites Talk
#1

Hey guys. Ive been laying up my molds for a very long time now and i got the technic perfect. my parts come out great! but, then at the end i always have to spend a lot of time filling in the pinholes =(

So, i desided to move onto Vacuum bagging.

I dont have much money to work with, so i started researching. Well i got to a point where the joenveneer wood something website where they use a compressor -> vacuum.
Then i researched some more and some people have been very successful using vinyl bags about 4 mil from home depot and sealing the outside with a heat unit + piece of paper. leaving 1 side open it works very well (i think so far). after inserting 1 of my parts, and turned on the system, and closing the 1 side… i noticed a couple of things

  1. i need a breather (i only put one around the nozzle of the vacuum. what was happeneing? well… the far end it wasnt moving much and i still saw some spaces.

Plan on wht i think i should do and here is where i need your help guys.

Sol ? 1) Put 1 layer of 2-3 mil plastic in the inside on top of the mold after its layed up, (should i put tiny holes on that sheet?) and then paper towels or some sort of breather on top of that. then vacuum

then, i noticed i also had a tiny leak somewhere. i think its b/c i bought the 4 mil pack that looks like they folded this thing out on the floor and stepped all over it =(
So today i bought the small pack and it looks like it came straight from the machine and rolled. no holes.

hope i could get some inside tips. oh yeah, doing this process, will it eliminate the pinholes??

#2

get some proper vac bagging kit,film,tape.peelply and breather,its not very expensive.if you can get a perfect and full vacuum you will be ok but you need a vacuum gauge really.unfortunately making carbon parts on the cheap doesnt really work/pay.

#3

What Gtfour said.

Vacuum bagging carbon without high pressure (autoclaved) or pre preg is really not worth it.

Tiny erratic pinholes (worm holes) are caused by having insufficient pressure while the part is curing. What happens is the epoxy shrinks/recededs the dryer it gets. If the part was under a larger amount of vacuum your chances of worm holes developing gets lower. Letting you breather cloth get fully saturated can cause them.

Micro bubbles, are ok. They wont effect the strength of the part and most manufacturers dont list them as defects.

You need to cover the entire layup with breather. Any area of the part not covered by breather cloth is getting little to no vacuum/pressure. Home depot drop cloths will almost always make for bad bags. Buy some nylon bagging film, or, strechlon. You wont regret it.

Make sure you get rid of ALL of you vacuum leaks. If you have one it will cause a lot of surface bubbles on your part. The air will travel from the leak to the vacuum outlet and leave plenty of bubbles along the way.

#4

the biggest thing i have learnt over the last 2 years is that if you cant seal a bag,pull vacuum,switch the vac off and the bag stays under full vacuum for 10 minutes on its own then FORGET IT,you will never make a succesful part if you cant achieve this fundamental part of the process,practise on an empty mold.