I had my first try with resin infusion.
My vacuum bag was sealed 100%, pump sucked up to -0,95bar
But…the flat sheet I made , has some resin-empty spaces, especially where the fibers of carbon crossing. These are not airbubbles, but simply looks like voids cause its regular on element.I used 3 layers of carbon fiber then , peel-ply next flow mesh green from airtech and typicall vacuum bag + spiral hose.
Why have those voids? I heard it might be because of too quick resin flow through part, but how to decrease the speed? my pump is 100litres/minute.
One thing that might cause this. Did you degass your resin? What resin did you use? Viscosity? What was you laminate schedule? I found degassing helps and MTI vacumn hose helps too.
Hey, I didnt degass the resin, as I know its only for minimizing air bubbles in product ( BTW i left resin for 10minutes before laminating), but as you can see these are not airbubles but resin-voids.
Schedule was:
release wax
2 layers of CF
2 layers of glass fibers
peel-ply
green flow mesh airtech
vacuum bag
What about perforated film? Maybe it will decrease the speed of resin flow? Cause a flat sheet like 40x40 cm’s was filled in about 1 minute.
I recommend that you degass your resin and use the MTI-hose. The problem with the spiral hose is that resin can escape the mould cavity which can causes voids in your laminate. Also, each possible embedded air bubble is able to grow to its maximum size within the remaining vacuum atmosphere. The MTI-hose works like a valve. When it is once covered completely with resin it shuts the door to the vacuum pump which means that you get ambient pressure in your closed system. This in turns leads to a collapse of embedded air bubbles and furthermore the resin can not escape the mould cavity - no pinholes arises. Your vacuum level should reach below 10 mbar (absolute pressure).
How only a hose could remove pinholes… I cannot understand it, you mean while the vacuum is on the mti will still suck air but wont suck resin? If yes then it would be better to leave pump on for a while even though the resin reach MTI hose, am I correct understanding?
Also only Hose probably wont resolve my problem with fast resin flow…
1: leave the pump on until the part is cured. if you shut it off, and the vacuum pressure changes, it can cause dissolved bubbles to expand.
2: the pump flow rate does not matter much in infusion. If the resin is infusing too fast, YES…clamp the tube slightly, until the flow is as slow as you want it. Obviously fast enough so it doesn’t cure while infusing. Remember, carbon is a very small fiber, and it is packed well in a fabric. It takes time to get the resin INSIDE the carbon tow. If you only allow resin to flow over the tow, you risk some pressure in the fabric to escape to the surface.
3: make sure you do a leak check. Shut off the vacuum supply, and look at your vacuum level. It should NOT change in 5-10min. if you loose vacuum, you have a leak!!!
As my pump is 100l/minute and hoses were 8mm , the flow of resin was quick, so I changed the mesh into slower one and use 6mm hoses.
It helps alot, I also degassed resin , the effect was nice looking surface, but there were still very very little randomly placed holes. I could say these holes are “micro holes” visible only when you look at specific angle.
Any suggestions? or this is just a standard? Maybe in-mould coating would help here ?
I used gelcoat on first layer it didnt help, as I only close those little voids between gelcat and first layer of cf.
I still have voids where the fibers crossing grr
Your pump CFM has no bearing on the infusion speed, the vacuum PRESSURE is the driving force. The only thing a high CFM pump will give you is it allows you to initially pull the excess air from the bag quicker, after that its just the ultimate vacuum pressure that does the work.
So in order to help, you need to provide more detail on your process.
What vacuum pressure are you acheiving?
Are you boiling off the moisture prior to infusion?
Are you drop testing to ensure no leaks? If so, how long?
When you degas are you using a a bubble seeding device in the resin such as a scotchbrite pad?
Are you burping the resin line before allowing the infusion to commece?
What is the temperature of the resin, tool, and room?
How fast is the resin front moving where the voids are occuring? (distance per time)
Im acheiving about -0,97bar ,
What do you mean “boiling off moisture”?
Im testing for leaks for about 20 minutes
I dont know what is bubble seeding device… I simply degass in catch pot.
What do you mean by burping the resin?
Temperature is around 22* celcius
Resin travel at the start very quick, last time I infused 3 layer flat sheet 30x30cm about 2 minutes like so
Did you use MTI hose the last time? If not, bring back the vacuum to about 0,9 or even lower (0,8, 0,7) after the infusion. During the infusion the pressure should be as low as possible, preferably -0,99 or more.
Ok, first your vacuum is not strong enough. -0.97bar @ 22C will not boil off the moisture in your layup. All of your layup absorbs moisture from the humidity in the air. Most of this will be in your fibre reinforcements due to their hydroscopic nature. When you put liquids into a reduced pressure environment, the boiling temperature of the liquid also reduces with the reduced pressure. As you know, Water will boil (turn to vapour) at 100C @ std atmospheric pressure of 1 bar. Under reduced pressure (vacuum) water will boil at a room temperature of ~ 25C at around -98.5bar. So when you vac out your layup, the moisutre will boil off and be sucked out of the bag as a vapour and ejected through the exhaust of your vac pump thus leaving you with a dry layup when its had time to clear. Failure to do this will leave you with blemishes in your layup.
Secondly, at -0.97bar, there is still a significant amount of air in the bag aswell. This air has to end up somewhere and a large portion of it will remain in your cured laminate. If you begin with no air in your bag (-100bar or very close to it) then air bubbles can not be left in your laminate by this mechanism.
So where does your voids come from? Well if you had no air in the bag to start with (or moisture reactions), and no leaks in your bag, and then you degassed your resin, there is no mechanism for air to get into your layup - so you will not have any voids.
Bubble seeding can be done many ways. But the idea is that if you can start a small bubble, more air will come out of solution as the bubbles grow - hence the name. Using materials/fabric in the resin that have a high surface area and cavities to trap micro bubbles will help to seed more bubbles and get rid of more air in your resin in a shorter period of time - as you know you have be quick or risk your resin going off early. Another method is to deliberately bubble air through the resin like a fish tank air stone, although this is not practical for most people. Next time you degas, try throwing a scotchbrite pad into your resin before you degas and leave it in there during degassing. Watch how effective it is (if you have a window in your degassing pot).
Lastly, burping the resin feed lines is simply letting the resin go past the clamp and then clamping off again to get rid of the air lock that exists in the resin line between your bucket of resin and the clamp. So you let that air be evacuated out the pump for a minnute or 2 before letting the resin hit the job - again its just removing every possible tiny bit of air from the layup to minimize any voids.
So, no air in the job before you begin, none in the resin, and no leaks during- its impossible to have voids…
Refer to your state that"Under reduced pressure (vacuum) water will boil at a room temperature of ~ 25C at around -98.5bar."
My room temperature is more than 25c which is around 27-32c.the water will biol at vacuum -0.97 which is lower vacuum, does’n it?
Ok groper, nw I understood much more what is really happens there , thanks.
And one thing about this scotchbrite, I should put it in resin bucket while degassing and I guess leave there while infusing right?
