Techniques for constructing carbon fiber tubes for intakes

[Christopher Chow]

Looking for some advice on tubular engine intake runners made from fiber/epoxy composite. In the past, we have created intakes using a "lost foam" using a polystyrene foam coated in plastic wrap. The plastic wrap was a attempt to get a smooth inside surface. Well, after lots of acetone, the plastic still got stuck in some spots and it wasn't that smooth anyways.
Im our next design, we want to have 4 curved tubes going into a box. (i think ohio state has these). Curved tubes, smooth inside, hows it dun?
Also, I do have access to a SLA machine that uses powderd plastic and liquid binder.

Thanks!
Chris

[Christopher Chow]

Looking for some advice on tubular engine intake runners made from fiber/epoxy composite. In the past, we have created intakes using a "lost foam" using a polystyrene foam coated in plastic wrap. The plastic wrap was a attempt to get a smooth inside surface. Well, after lots of acetone, the plastic still got stuck in some spots and it wasn't that smooth anyways.
Im our next design, we want to have 4 curved tubes going into a box. (i think ohio state has these). Curved tubes, smooth inside, hows it dun?
Also, I do have access to a SLA machine that uses powderd plastic and liquid binder.

Thanks!
Chris

[alfordda]

Ok, It is not super simple to do, we probably have 20 runners that were soft, leaked, or stuck to the sla mold, or didn't confrom to the mold. So it will take a little bit of work to get it right. But if you have some composites experience, it probably won't be that difficult. The guys working on it last year were 1'st timeres, so they had the learning curve to deal with.

There is a company here in Cincinnati called A & P Technology. They make the carbon braid that we used for the runners.

www.braider.com (http://www.braider.com)

Basically, the process goes like this. Make SLA female mold, make something that will contort to the shape of the runner (ballon, bicyclye tube, etc.), cut braid to length, standard wet layup use of epoxy and mold release, inflate ballon, wait til cured.

What is your email address? I'll send you the contact info.

[Christopher Chow]

cool, thanks for the tip, I PM'ed you with my email.

Do you use any special release agents or does the rubber release well on its own?

-Chris

[alfordda]

I wasn't closely involved with it, so I don't know what they had the best results with. I know they tried a few differnt things, mold release, vasolene, silicone, saran wrap. I think the biggest problem was the radius was too small, so it was hard to get the ballon and braid to expand into the corner.

[Travis Garrison]

Bladder molding might be a bit of a challenge for the inexperienced...plus there are lots of ways to screw up the inner surface of the runner...

You might have a much easier time building male tooling and laying up the runners in halves. You could use a flange on the edges of the runner halves to join them...provided you built in a locating feature or two, a series of small dimples for example...The big advantage to male tooling is that it would be much harder to screw up the surface that counts...which means your first set of layups would be more likely to give you useful parts.

Travis Garrison
UW FSAE

[BeaverGuy]

Our runners have been made using a "lost wax" process. A plastic mold is made in two halves then wax is melted into the mold. Then the carbon fiber is layed up over the molds. This last year not enough resin was used so the insides were a little rough. The year before they came out very smooth.