Wet laying Carbon Fibre

Talk Composites - The Forum for Advanced Composites

Back

Wet laying Carbon Fibre

Author	Message
dilligaf76	dilligaf76 posted 5 Years Ago HOT Post Details
Group: Forum Members Posts: 49, Visits: 115	Prepreg, now that’s another one I’ve heard of but again I’ve never used Prepreg Carbon Fibre, hopefully it will open up the discussion for Vacuum levels now you’ve mentioned it Steve. Another thing that came to mind is when mixing the resin do I have to wait or degas it before I start slapping it on or will the vacuum take all the air and bubble out?
	Reply Like 3
Steve Broad	Steve Broad posted 5 Years Ago HOT Post Details
Group: Forum Members Posts: 408, Visits: 4.1K	+x dilligaf76 - 6/14/2020 9:21:27 AM Prepreg, now that’s another one I’ve heard of but again I’ve never used Prepreg Carbon Fibre, hopefully it will open up the discussion for Vacuum levels now you’ve mentioned it Steve. Another thing that came to mind is when mixing the resin do I have to wait or degas it before I start slapping it on or will the vacuum take all the air and bubble out? Didn't have any issues with bubbles. Stir gently, don't whisk! :-) IMO the action of applying the resin will remove any bubbles and the vacuum will get rid of any that remain. Again, this is just my experience and that is all I can comment on. Prepreg: No mess No rush Much quicker to cure. Prepreg is probably not suitable for all projects, but I have yet to find one :-) Love the stuff. Need a bracket? From making aluminium former to debagging in less than 3 hours (with two of those hours in the oven).
	Reply Like 3
Hanaldo	Hanaldo posted 5 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	+x Steve Broad - 6/14/2020 9:12:38 AM +x Chris Rogers - 6/14/2020 2:35:24 AM I have a bunch of laminate sample videos and some use this bagged wet layup method - you can see the whole process though the bagging is not the focus. I agree with what Steve says - but the vacuum level depends on the situation. If you aren't using core, full vacuum will probably be fine but less would be better if you have only two plies. And you will probably use too much resin at first - but better too much than too little! Here are two videos that might be useful: https://youtu.be/cDZ4GBIjcp4 https://youtu.be/06-0Vxs_9nY The discussion regarding vacuum levels is interesting as I have always striven for the best vacuum I can achieve as I am looking for minimum weight on my project car. I did not encounter any issues and the panels came out pretty light with a close to ideal carbon:resin ratio for wet lay. However, I can see the argument for not running a full vacuum in some situations. Having moved on to prepreg there is no discussion regarding levels of vacuum :-) The reason you don't want to pull full vacuum with wet-lay is more to do with void content. Excessive resin bleed is a consideration, but a lot of the time people slap the resin on way too heavy and there is plenty to bleed away, so that is really only a concern if you have calculated your resin for the reinforcement weight and don't have a lot of excess. The trouble with going more than 80% vacuum is that is when the air in the resin really starts to expand. Wet-lay by nature traps a lot of air in the laminate, that's where the skill of it is. If you can avoid entrapping air you will get better quality laminates, if your technique traps air then you will get poor quality laminates. But you exasperate the problem when you pull a high vacuum, expanding that trapped air and causing very high void content; leading to a laminate that is actually structurally weaker than if you had only pulled 50% vacuum. 50% vacuum is enough to get compaction into the laminate and squeeze out some excess resin. I like to go to about 60-65% vacuum for a bit of extra compaction, but I try not to go above that. it is better to get rid of excess resin before bagging, so that air isn't trapped in the laminate to begin with, and that's where your technique matters more.
	Reply Like 3
dilligaf76	dilligaf76 posted 5 Years Ago HOT Post Details
Group: Forum Members Posts: 49, Visits: 115	So what is 50% vacuum, if you have a powerful vacuum pump that can be a lot compared to a less powerful one? I might be missing something but then that does happen to me lol
	Reply Like 2
Hanaldo	Hanaldo posted 5 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	Yeh pumps are only on or off, you can't control the vacuum with the pump. You need a vacuum regulator. This can be as fancy as dedicated composites vacuum regulator, or as cheap and simple as a fish tank air valve. It is essentially just introducing a leak in a controlled manner, so you leak away half of your vacuum or whatever your target is. Or, if you know what you're doing and you have a perfectly sealed bag, you can just pull roughly half vacuum and shut off the pump. But this is very reliant on your bag, if you have any leaks at all then all bets are off. To confuse you even more: The absolute best method is actually quite similar to pre-preg, where you want to work out the viscosity of the resin system in relation to its cure cycle. If you can hold the vacuum level at quite a low vacuum while it is at its lowest viscosity, and then ramp up the vacuum as the resin viscosity goes up, then you can time it so that you reach a full vacuum just before the resin cures. By doing that, you minimise how much the air can expand with the vacuum but you still get full compaction. Very tricky to pull off.
	Reply Like 3
dilligaf76	dilligaf76 posted 5 Years Ago HOT Post Details
Group: Forum Members Posts: 49, Visits: 115	+x Hanaldo - 6/14/2020 1:53:02 PM Yeh pumps are only on or off, you can't control the vacuum with the pump. You need a vacuum regulator. This can be as fancy as dedicated composites vacuum regulator, or as cheap and simple as a fish tank air valve. It is essentially just introducing a leak in a controlled manner, so you leak away half of your vacuum or whatever your target is. Or, if you know what you're doing and you have a perfectly sealed bag, you can just pull roughly half vacuum and shut off the pump. But this is very reliant on your bag, if you have any leaks at all then all bets are off. To confuse you even more: The absolute best method is actually quite similar to pre-preg, where you want to work out the viscosity of the resin system in relation to its cure cycle. If you can hold the vacuum level at quite a low vacuum while it is at its lowest viscosity, and then ramp up the vacuum as the resin viscosity goes up, then you can time it so that you reach a full vacuum just before the resin cures. By doing that, you minimise how much the air can expand with the vacuum but you still get full compaction. Very tricky to pull off. I'm still not sure what for instance 50% vacuum is, I mean I know its half way but half way could be 15HG or 100HG. The fish pond air control valve soundlike a great idea if you haven't got money to burn, I like it.
	Reply Like 3