CF sizing?

General Composites Discussions Composites Talk
#1

I was reading this thread:

http://www.compositescentral.net/showthread.php?t=8614

and came upon the notion of sizing. Just when I think I have a handle on basic CF fabrication, some new concept rears up.

So, I need the ninety second rundown on sizing, because a general search wasn’t too helpful.

Are fabrics sized by weavers?

If so, and if the bond between the CF and whatever resin system is being used can be affected by the size, why aren’t fabrics designated as being sized or unsized by CF dealers?

For ultimate strength, do I need to find out if my fabric has been sized with something before doing a wet layup?

#2

Aw, man. I didn’t know about this either. So that makes at least two people that would like this explained further. Noob problems.

#3

The fiber is usually sized by the manufacturer. As a weaver, you buy the fiber with 3 main specs determined:

bundle size (1K, 3K, 6K, 12K, etc)
fiber type (Toray T300, T700, Toho Tenax UTS, STS)
sizing type

There are many types of sizing. For Toray, see the list in the PDF attached. This also shows all options.

As an end user in low volumes it is hard to demand a specific type. You basicly have to live with what is offered.

#4

At face value, that Toray PDF suggests that virtually all carbon fiber is compatible with epoxy regardless of sizing.

#5

Yes, that is true. By far most carbon is epoxy compatible.

#6

Yes, as herman noted almost all carbon fiber you see will have been sized by the fiber manufacturer. Also, what sizing they use will depend on what fiber it is as well (example: T700S from Toray will only use type 5, 6, and F sizes).

Unsized fiber can be rare (i.e. special order), and is typically used in niche high temperature composites (thermoplastics, carbon-carbon, etc.).

I wouldn’t worry too much about what fiber sizing is used as long as you are using a high grade resin system (preferrably epoxy, but full vinyl esters can work). I would not recommend using carbon with polyester (Ortho, Iso, DCPD, or blends) systems unless the composite had been fully characterized and you know what you are getting.

I always look at it this way, if you are going to spend the money on carbon fiber, why skimp on the resin system?

#7

I am using Aeropoxy PR2032 with PH3665 hardener. I was going to use West System, and in fact bought some, but a salesman at a composite store told me there were better choices. After looking at the numbers, overall strength and particularly glass transition temperature, Aeropoxy was the clear winner for my application.