I apply the fabric to the mold by first brushing the surface of the mold quite liberally with resin. It may even pool in the low spots. Then I insert the fabric into the mold and work the fabric into the resin and position with a brush. Most of the fabric gets fully saturated with the painted in resin. I then apply more resin to any area that isn’t fully saturated. You can be rather liberal again with the resin. The next layer will just soak it up. Then apply the next layer and add more resin to areas that need it. You want to use light brush pressure through the entire process. If you push too hard you will compact the fibers, squeeze out the resin, then the fibers will rebound and suck air back in. If the last layer looks really wet you can either absorb the excess pooled resin with a paper towel of just brush on a layer of peel-ply.
Are you then bagging the part? If so at what level of vacuum, are you using perf film and breather? The method you describe is basically how I did it the first couple of times. When I did it that way, I had surface pin holes and dry spots between tows. I was doing it at 24" vac until cured. I then started to gel coat and that solved the surface problem but I still have the between the tow problem. I will keep trying but I sure would like to get this resolved before I move on to the larger body pieces and blow through more CF. I realize infusion may solve this but these are small parts and will be one-off pieces. It seem there must be a solution.
Re-asking my last post.
Most polyesters and vinyl esters “boil” at 20" of mercury or anything over.
What most people think of when they see porosity is “trapped air” when actually it is styrene “boiling off”.
Try to keep your mercury gauge as low as you can and still get good compaction, say in the 14" to 18" range. Too much vacuum can be a bad thing. You can suck too much resin out.
If you are making cosmetic parts you may have to eat a few parts to dial in the process and create a methodology. I have two parts that are virtually identical, except one goes on the right side and one on the left. The left processes best at 16" and the right at 17.5". Go figure. The engineer says that this is impossible, as the molds are CNC cut, with the file being flipped to make the opposite side. When I make these parts I get a good left and a good right one…when anyone else makes them they always loose one side or the other. When the plant manager wanted to know why I always get a good set and others can only get one side or the other…I just smiled politely and told him the engineer said that’s impossible.
The point being, each mold may have it’s own individual nuances, you have to dial in and create a methodology that works.
I have some other tricks that are much more complicated, if this doesn’t help you, but this is the most common cause of porosity being misdiagnosed.
Interesting data. I am using epoxy resin. I have tried at various levels of vacuum without complete success. Some inprovement however when done at 15". I am adding to my flanges and serching for a better vacuum pump so I can give infusion a go. Worst case I’d have to get my parts painted. Somewhat defeats the purpose though.
I have tested the styrene boil-off thing: put a mixing cup with styrene in the vacuum degasser.
Guess what? I did not manage to get the styrene to boil. I did try with water as well, and that boiled at some 20 mbar or so (as expected)
I also made plenty of perfect parts (using infusion) with polyester resin, using about as full a vacuum as you can get (in the 1-5 mbar range).
Most voids can be contributed to moisture, or in the case of polyester the choice of catalyst. (type and quality)
When wet bagging it is also about technique. You laminate at ambient pressure. You create a void. Then the bag goes over it, and you pull a vacuum. Now the void increases in size. When the void becomes so big that it reaches a perforation in the release film, the air escapes into the breather, and out through the pump. At the same time the resin should be moving in again. This not only depends on pressure, but also on viscosity (which is dependant on type, time and temperature)
Also the growing void pushes more resin into the breather, as well as the general compaction of the laminate.
All these variables do not make wet bagging ultra high quality parts an easy job.
mbar= inHg 1= 0.0295300, 2= 0.0590600, 3= 0.0885899, 4= 0.118120, 5= 0.147650,
677= 19.9918, 678= 20.0213, 679== 20.0509, 680= 20.0804, 681= 20.1099, 682= 20.1394
and yes moisture can be a problem also