What vacuum pressure?

General Composites Discussions Equipment Talk
#1

I have been doing some experimental lay up and find that I am getting voids in the carbon? One friend suggested that I was creating to much vacuum. I always thought the more vac the better? The gauge on my pump set up reads 25 in Hg when everything is sealed up but I still get the voids? Both examples below were layed up wet on a piece of melamine with peel ply breather and then wrap and gummy tape to seal to the melamine. Ultimate goal is to make some wing uprights for our race car and they need to be void free and smooth on both sides. This just isn’t cutting it.

First shot is two layers of 3k twill with a 3mm piece of “coremat” and a 3k top layer

This is a a piece of 3/8" foam with the same 3k twill, one layer on both sides.

#2

Try a test part with much less vac like around 8-10,less vac=less resin being pulled out.Other things you can do are,smaller perf film,allow resin to kick a little before vac.

Theres a few other threads here with the same problem,have a look.

#3

Wet layup will have voids… it’s mostly dependent on your technique. Wet lay can be one of the hardest to use because it takes practice and even then it’s known to be the most resin rich and have the highest void content. Id say that in your examples here, it’s probably just a dry laminate on the bottom. Looks very rich on top though. Remember resin is very brittle and weak. More resin will make a much weaker part. It’s good to weigh out your resin, weigh your dry materials, then weigh final part and calculate how much resin is in the part.

For the strongest parts you want a good resin ratio (60/40 is ideal) and low void content. Strong doesn’t mean pretty necessarily. A rich laminate will look smoother and glossier but might not be strongest. If you want a strong part, infusion will give you better results once you figure out your process and setup.

And more vacuum is better. The more vacuum you can muster, the close you will get to max atmospheric pressure pushing down and compacting the laminate and thus the voids. There are always voids, but if you can crush them down, they become smaller and smaller.

Wing uprights should be fairly simple parts to make and a good project to learn from.

#4

Thanks guys. Got some good advice from a fellow racer who theorized that I was not getting a complete seal and therefor the air leaking in was providing an escape path for the resin. I think this is what is happening because the resin is traveling to the vac port instead of just being compressed where it lies.

#5

If you have an air leak, that means that air is infiltrating your panel and moving across the laminate. Some resin will flow but, air is the real enemy. You’d see a pulsing of the air coming through flowing to the vacuum line.

Did you take another try at it?

#6

I have pulled air through melamine under vacuum. That was back around 2001 in my early days with infusion, and the melamine had particle board in the middle rather than the MDF I get now. So it may depend on the quality of the melamine. Having said that, I haven’t applied vacuum directly to the surface of melamine since then.

#7

I have pulled air through melamine under vacuum. That was back around 2001 in my early days with infusion, and the melamine had particle board in the middle rather than the MDF I get now. So it may depend on the quality of the melamine. Having said that, I haven’t applied vacuum directly to the surface of melamine since then.

Ugh! I never even considered that. I give it a test.