3K vs 6K

General Composites Discussions Composites Talk
#1

I’ve always used 3K carbon fiber fabric but I’m thinking of making a switch to 6K because 1. Its almost twice as many strands of carbon than 3K for only a few extra bucks a yard, and 2. It will save me time.

I know all the up sides… But are there any down sides? For example…

If I use two layers of 11oz 6K carbon fiber instead of four layers of 5.7oz 3K carbon fiber, would I have a stronger part since there are just about the same amount of strands in less layers?

The only idea I’m trying to get over is now a simple interior part is made of only two layers of material vs four. It sounds bad but I might just be over thinking that idea?

Also could I be risking more pin holes? Or could that be fixed by backing the composite up with a layer of E-Glass or a layer of 5.7oz 3K?

It sounds like a no brainer really. More fabric for only about 20% more money, but am I missing any down sides?

#2

This is purely subjective but in my experience lesser tow fabrics stay together better. I like the tightness of weave of 3k fiber vs the 12k I have but it might be other factors such as the sizing or surface treatment.

#3

I found it very tricky infusing 6k.

6k lOoks wicked!!! More so than 3k in my opinion. I absolutely prefer to build tooling with 6k and when I can pre impregnate with wet lay up. Much faster and cheaper. It doesn’t like corners well.

#4

If it is for cosmetic parts, I would stick with 3k, or if the parts are relatively flat, you could use spread tow fabric.

Why not looking into other backing materials, including 6K and 12K fabrics, but also multiaxials, which are also cheap. Or even using glass with black resin, or basalt.

Oh, one other thing: a shortage of carbon fibers is expected again, mostly in the 3K and 12K region, as the airplane manufacturers are scaling up now (A380 and 787). Shortage according to some supposedly knowlingly customers will be “in a few months, probably before 2012”. If you can afford to generate some stock, I would do so.

#5

Weavers told me that 6K is better for cosmetic parts for two reasons. Less gapage, and its harder to mess up the weave because of the thicker build. Any body have the experience to back this up? Or is that a misconception? I make my parts to be strong and look good. With patience shouldn’t 6K be just as easy to put in the molds as 3K? I might just use 3K for interior parts and 6K for exterior parts. Hoods, spoilers, trunks, etc. Any extra input?

Maybe does anybody have a yard of 6K they can sell me at their cost price so that way I can give it a try? I tried asking other distributors but most want to sell me several yards. Those who sell single yards are not interested in helping…

Thanks!

#6

P.S Whats spread tow fabric?

Lastly… I’d rather use a fabric that already has the weave where the tows have very little gapage or spacing in between the neighboring tows. All my parts are pure cf so its not like I have problems with seeing light through the part or whatnot, but I just don’t like how you can see that the tows are spaced apart. Like this…

In this image below you can see vertical gray lines. Those gray lines indicates spacing between the vertical tows.

#7

I do really like the look of 6K and 12K and as long as the part doesn’t have very sharp corners (like roof and doors) I have had good success in using it but most of the time I use 3k so that the parts will match existing carbon parts on the car. I also typically use 8 harness satin weave for backing material, it has a very dense weave and will usually block any light.

#8

Some of my parts have lots of detail… Thats why I’m thinking to use 6K on exterior panels and 3K on interior. I was told by Solar Composites, (I highly recommend them to anybody who buys a few rolls or less of carbon at a time) that if I wanted a 3K with more threads per tow I could have a weaver custom make it for me for only a few dollars more a yard, (which is a very good price) but I’d have to buy one roll at a time. Right now I want to keep my budget at $700 or less… A full roll of a tighter weave + more threads per tow fabric in 2x2 would be roughly $25 a yard at a full roll price. I think… Give or take. But it will be right around there I was told. Great price! Just out of my reach for the time being :-/…

I’m thinking with enough patience I should be able to do anything with 6K that I do with 3K?

#9

Ask Jon soller to give you half yard of 6k and 12k so you can play with it. He will hook you up I’m sure. He has a good reputation for a reason.

#10

Good idea! I forgot that he sells everything by the foot. After I purchased my first yard from him two years ago or so, I have not gone anywhere else.

Would one layer of 12K be just as strong as four layers of 3K? Say if I were to make a small panel out of one layer of 12K… Is that recommended? Or should I at least back it up with a layer of 3K?

What if I made a quarter panel out of two layers of 12K?

#11

Spread tow for 2tall:

#12

6K and 12K are used for bulking up thickness quickly and economically. just because you use a 6k or 12k doesnt give it 2-4 times more fiber per area. 6k twill doesnt weigh 400gsm, but usually 370gsm, nor does 12k twill weigh 800gsm, usually 670gsm. Its all about the fiber type and how its wooven. IM7 6k weighs the same as AS4 3k (~200gsm). also a lot has to do with fiber nesting and the fiber volume you get from this, 6k and 12k can effect this. It really depends on what your making, that would determine your laminate schedule.

#13

Ahh I see. Thanks guys! Looks like I have some figuring out to do… I probably will just stick with 3K then and use the 6 - 12K to build up the composite quicker like suggested.

#14

Did you ever switch to 6k?

#15

I like those look of 6k a lot better. I have been testing out different cf on panels and the 6k just looks much larger and far more of a beautiful detail than the 3k.

#16

There are different weaves of 6K twill. I usually like to buy the 11x11 per inch thread count… it looks most similar to 3k twill. Last time I ordered 6K i messed up and they sent me some 8x8 thread count.

2talljohn… try the 6K… it certainly does conform to corners better than 3K, in that the weave does not distort as bad as 3K.