Does the viscosity of the resin affect its ability to wet out the cloth correctly.I have tried a much higher viscosity resin than i normally use (500 cps vs 180 cps for the old resin).It takes a lot longer to infuse a part with the 500cps resin and sometimes leaves minute parts of the carbon not wet out correctly if you look very close.This could be 20 -30 small dry parts on something the size of a bonnet/hood.I thought with the resin moving so slowly it should infuse the cloth perfectly and not leave any dry spots.I have perfect vacuum and no leaks.I can infuse parts perfectly 95% of the time but sometimes I have this problem with dry spots.
When do you stop the infusion?
I usually have the flow mesh finishing about 1"- 2" after the end of the part.I stop the infusion when the resin has reached this point.I try to time the infusion so that the resin is starting to go off about 5 mins after the part is fully infused.I noticed with very small parts it is possible to get dry spots because of the very short infusion time so I let the resin run on a few inches past the part and that seems to get the cloth wet out perfectly.
what size are the dry spots? are they all clustered together?
I have had small dry spots but usually it was from air being trapped in the laminate.
I’m not sure if this is proper technique but sometimes I would use my hand to push the resin to the dry area while it is infusing… when the resin flow line has moved past an area that is dry.
I have infused with 650cps resin. Also are you using the green or red flow medium or another type? I think the red works well.
Do you have peel ply underneath the resin flow medium? I’ve heard of people leaving the flow netting on the part and just paint it after.
The dry spots are all over the part but just one here and there.The air sems to move out of the part well during infusion with no visable dry spots.I noticed that all the dry parts are on the same direction in the cloth.Eg the warp and weft of the 2x2 twill cloth.in the part of the weave with the tow running in the direction of the flow it is all perfect but in the tow running 90 degrees to the resin flow that is where the dry spots are?.Hope you can understand this.They are so tiny I cannot get a good photo to show them but I wouldnt be happy with the part unless it is perfect.I am using a knitted flow mesh which I have found to better than the green or red airtech mesh.I think it is the same as greenflow 185 from airtech.I have peelply below the flow mesh
Without giving too much away, just because the resin looks like it has traveled all the way across the flow media, doesn’t mean it’s the same on the tool side. Resin mainly travels across the flow media, and then down through the thickness of the laminate. This is a very important concept to understand.
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So how do you make sure the resin has wet out the cloth below the flow media then?.What can change this eg,type of flow media,number or size of resin feed lines etc.Even on something the size of a hood I will only have one resin feed line in the middle of the part.Is this not letting enough resin on to the laminate to wet it out correctly.So fustrated that I cant get perfect parts all the time and its always this same problem of a few tiny dry spots.
thats why they dont have flow media across the whole part,maybe a bit more than half the part, to slow down the process and give the resin time to fill up everything, and air bubbles to travel faster than the resin and get out through the vacuum line.
No. Put flow media anywhere you want resin to reach. Not doing so is a big mistake, unless the reinforcements are specifically made to flow resin on their own. Do not count on resin flowing through fabric and wetting out completely.
I was just doing some consulting work at a large sub-contractor for Boeing last week, and this was one of the biggest problems they were having. They are infusing 3" thick 10’x30’ pieces and couldn’t get perfect results. I found some very simple corrections and even though their resin is about 600cps at @ 72*, no problem infusing the parts with perfect results. Just a note, aerospace standards usually require a void content of less than 2%, and we achieved that easily.
So Tet what changes did you make to their infusion to make the parts perfect.Thats a serious thickness of laminate to infuse.I have been doing some trial infusions lately with 3mm lantor soric and 4 layers of carbon for parts with cores.Thats the thickest I have tried and they have been perfect so far.
The soric flows the resin really well.aga the part would never infuse without the resin flow media going all over it with the 600cps resin although I could of done it with the lower viscosity resin I used to use.
The most annoying thing is I can infuse 10 parts exactly the same and without aparently changing anything and get one of the batch with the dry spots
I have same problem. I use high viscosity epoxy resin (about 500cps) and Enkafusion flow media. Enkafusion is really quick flow media even with high viscosity resins, so I tune the speed with inlet tube diameter. and I also tried to clamp inlet tube a little bit to make infusion slower. But always same problem with tiny voids in fabric. I think that maybe there is a problem with micro voids in mixed resin. They are not so visible on free air, but they expand under vacuum. Next time I’m going to degas resin at first, then use it for infusion. I don’t have any idea whats going on…
This is where infusion gets tricky. Some poeple think it’s easy because they can vacuum bag with no leaks and find a good resin. Not so simple. 
The setup and materials used have a big influence on the results. Things like exact location of feed and vac line ends, flow media edges, peel ply size, etc. all have an influence.
dont forget about racetracking and degassing the resin!!!
yep I can attest to having the vacuum and inlet lines in the right places. I have seen one or two of my infusions leave an area totally dry… the resin just bypassed 24sq inches of area and flowed around it.
You may have a vacuum line that is too large in diameter… it wants to suck so fast it leaves some dry spots.
If you are doing a hood size part you probably should have spiral wrap vacuum line around the entire perimeter and three inlets spaced evenly toward the center area of the mold.
‘Racetracking’?
He means that resin will find a free channel to quickly flow from inlet to outlet. For example bridging can do that.