help with interlaminar flow media

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#1

I have been researching interlaminar flow media for some time now and am at a dead end.

What I need is a very thin flow media what I can put inbetween carbon fibre laminate layups in closed moulds to produce a double sided glossy finish. I also want to infuse double sided glossy panels in one hit. These are generally turned into machined items so I cant have an obvious discolouration or bits along the machined edge.

The usual airtech flow media works great BUT unfortunately has no strength characteristics when used like this and delaminates.

spoke to all the major players and no luck, incredible that no one seems to have a solution for this.

is there anything glass fabric based that would do the trick? someone mentioned a dissolvable flow media but was very hush hush. Even the RTM boys dont have anything special to use.

#2

I highly doubt you will find an interlaminar flow media that provides any strength to the laminate. It will be a weak spot, and should generally be avoided. I’ve never seen a structural part that needs to have a Class A finish on both sides, straight from the mold.
And then good luck with not having it show on the edges, as they all have a color. Black is a color, but at least it would blend in with the carbon fibers.

#3

Uh yeeeah. I really don’t think you are going to find anything. I have not heard of anything like this. Normally when close molded systems are used, pressure or vacuum is used to inject the resin into the part. After modeling, or testing, one can see how long it takes to fully infuse the part. I know someone around here is doing RTM experiments and finding out the flow pattern. All it is, is glass preform, between 2 clear plates,and injected with resin.
The fibers themselves are the flow medium.
Normal plastic flow medium is just a helpful and faster way to do it without.

#4

what about using a layer or more of fiberglass uni? I know that resin is somewhat channeled through uni, I however, don’t have enough experience to comment more than just a suggestion.

#5

I don’t think that will work very well, unless several layers are used. It would increase panel stiffness a bit though if it works.
We use only unidirectional for fiberglass, and while it does infuse faster, I wouldn’t count on it to distribute resin across the whole part.
Flow medias are generally stiff materials that don’t fully compress (which would block flow) under vaccum.

#6

CSM may work I have never used it they way you intend too, but I have used it as flow media and worked well. You can separate the layers of the CSM by hand and make it very thin(something you will have to try to see what I’m getting at)and put it every 2 layers or so… I would experiment a bit with it.

I was going to order more CSM (continuous strand mat)some time ago but the place I got it no longer had any and I didn’t look into where to get more.

#7

we do tons of structural stuff which requires A1 finish on both sides. At the moment we press mould them out of prepreg carbon which is very expensive. Something I am trying to move away from. I may try the continuous strand mat, however I dont want obvious layers of the stuff throughout the carbon sheets/parts.

Someone please invent something :smiley:

#8

Structural parts that require a Class A finish on both sides? Sounds strange, I’ve never come across that on single components. They’re generally multiple pieces bonded together.
What type of application is this for?

#9

we do a lot of racing car adjustable wing mounts solid 6mm thick(obviously cant have a peel ply finish on one side) light aerospace parts, moulded flanges which require double sided press moulding, double sided boat components ie small structural hatches literally there are a multitude of applications that we have that would benifit from this kind of thing.

I am interested mostly to start in developing a method for this to infuse carbon sheet in one hit and then develop more complex mouldings, really surprised no-one else is doing something similar in the industry. Think I need to look at RTM type processes.

#10

What do you mean by that? Make thick parts with Class A on both surfaces? I’m sure that is done quite a bit. I have already infused .5" panels like that (table, layup of glass, aluminum plate, bag) with no flow medium besides the inlet.
Either way, RTM is a good way to go, or even SCRIM, etc…
The problem is tooling costs for small businesses/hobbists.

#11

class A finish being gelcoated moulded finish on both sides of the component instead of the usual peel ply finsih on one., so closed mould with two halves dry stack inbetween and then infuse all that. I have tried a carbon layup panel between 2 sheets of glass and infused that without much success. Even the thinnest resin fails to flow any great distance without any help from a distribution media.

What kind of glass did you do the panels with?

#12

carbon fiber honeycomb… there i invented something lol:D

#13

Riff, i thought with RTM there was an airspace for the resin to flow thru, like a very thin gap? If there is no gap then that method would be as strong as an infused laminate, no? From what i’ve heard from you guys is RTM is resin rich? Just asking.

#14

THere are different styles of RTM as a whole. Some have the mold halves apart, inject the resin, then compress the resin into the preform, letting excess gas/resin escape through vents.
RTM standard, where you inject, obviously a thin resin into the mold, at around 85psi. RTM lite is the same thing, but has a vacuum at the vent, along with a more comformable mold half, like silicone.
I would imagine that RTM can be resin rich, but it also is for mass production, due to the high-tool costs.
However, as long as you are compressing the preform enough, the resin is control by how much you put into the mold.
Hell, there are also RTM methods that also use film adhesive to speed up the infusion, that melts during mold heating.

unfortunatly, I don’t have m y processing book anymore, so I can’t go into too much more depth without some research.

If one needs a good surface on both sides, one has to do some sort of compression molding, beit from a press, or 2 mold halves with resin injection. If one can deal with tooling costs, RTM lite would be a good way.

#15

what pressure where you using?
I’ve seen mostly 24oz woven roving, both E and S glass.

#16

I was using full 29" Hg off vacuum pump and the thiiiiinest slowest epoxy resin I can get. No good for 2metre sqaure sheets :smiley:

Riff a couple of points you make seem very familiar.
Firstly I once pon a time tried experimenting with resin film infusion, (a little known process) like you mention with the film adhesive. Basically a film of prepreg type resin like you use to bond nomex cores to laminate is stacked inbetween dry laminate layers, vacuum pulled and then put in the oven. (didnt work perfectly and gave up but in theory the answer to my prayers). might have another go, was such a clean way of doing things.

Also today I had a rep in who was explaining a local company making grp canopies via closed mould process just layed up fibreglass on mould halves, poured a certain amount of resin in female mould and pulled a vacuum until excess resin and air came out of a vent and then closed the vent. MMnnn but they were using white gelcoat so I dont know if there would be any voids/air trapped under the surface.

#17

AH…29" of vacuum. RTM is using pressure to put the resin into the mold. VARTM is using vacuum. RTMlite is using a lower pressure and vacuum. All basiclly the same, just different methods and tooling issues.
Yeah, pouring resin in mold halves and compression is definitely one way. Problem is, you don’t have much control on whether or not the resin goes into all the areas.
But the whole point of this topic of composites is to have good part surfaces by adding resin in a preform somehow. I think the ways are endless, but it all depends on which one works for what you want to do in the end!

#18

Regarding the original question of interlaminar flow media, we’ve used Soric (http://www.lantor.nl/composites/fr_comp/frame_comp.html?../soric.html) successfully in the past to enhance flow within RTM laminates. May not meet your requirements for being invisible on the edges, but might be worth a try anyway. Rovicore (http://www.chomarat.com/Pages_anglais/start.htm) or Polymat (http://www.scott-fyfe.com/en/products/composite/polymat.htm) are good interlaminar flow media for RTM of thicker laminates.