Carbon Fiber Tube Construction (Funnel Shape) 1

[carboncopy001]

Ref: thread711-9949


I have read some of the earlier threads written on this subject, but was unable to add my $0.02 since they were already “closed.” So I am starting this thread with the hopes of getting some new suggestions.

Project:
I am making CF tube that is approximately 18” long and has a 3” opening on one end with a 5” opening on the other and has compound contours. In order to give you a better visual simply imagine a funnel that is 18” tall…the bottom opening is 3”, while the top is 5”…in addition, both the bottom and top of the funnel are bent in different directions at 45 degree angles (ohh, I am looking for a smooth surface inside and out)…sound like a fun project? You betcha!

I have already made one and it looks like &*^$! I made a plug out of plaster and wrapped it with packing tape and waxed it a couple of times. I then slipped a CF sleeve over the plug and coated it with resin using a mini roller. After the sleeve was wetted, I slid a LARGE heat shrink tube over the entire thing and started to heat the tube with a heat gun. This process was suppose to squeeze out all the excess resin and give me a nice smooth surface. Well, the tube did not shrink well in the bends of the compound contours and I ended up with some “bunching” which gave me resin puddles in my final product…in addition, I think I may have been pushing the limits of the heat shrink tubing by expecting it to shrink adequately from 5” down to 3”.

I am getting ready to make another attempt at this and I am leaning towards the use of an inflatable bladder.

Has anyone done a similar shaped item in this manner? I am really unsure about how to adequately infuse the CF sleeve…I have read about some who use a bladder and infuse using a vacuum…but how is this done? Will a vacuum pull the resin through 18” of CF sleeve? Is a “Resin Distribution Medium” required? How do I insure that the entire CF sleeve is infused adequately? What about compound contours using a bladder ..any issues?

Any suggestions?

 

[MacGyverS2000]

I would go with the inflatable bladder idea, myself... and they make some heat shrink tubing that has a high shrink ratio (standard is like 2:1, the high shrink stuff is 4:1+). Consider, though, you may be running into an issue of the shrink's compression ability (or lack thereof).

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Pud]

You could also try pre-preg matting. Less resin, more CF. Needs heating to cure though.

H

http://www.tynevalleyplastics.co.uk

 

[MikeHalloran]

Heat shrink tube is too thick, and hard to control.

Heat shrink tape might work. As might regular vinyl tape, the stuff used for crowd control. McMaster stocks plain (bright) yellow, no adhesive. The drawback of tape is that you always get some bleed into the seams, which hardens into nasty sharp fragments that you have to sand off.

I have seen a geometrically similar part (a prosthetic leg) made by pulling a custom tapered PVA tube (bond PVA film into a cone using alcohol as a solvent cement), pulled axially over a wet layup of polyester and knitted cotton sock tubing. The PVA film is stretchy, and in this case the generally conical geometry makes axial assembly easier.



Mike Halloran
Pembroke Pines, FL, USA

 

[carboncopy001]

I for got to mention that I want to be able to reproduce this part with minimal deviations.

In addition, since I am a poorly funded novice (lol) I prefer to stay away from prepreg since it requires refrigeration and an oven for curing.

I think that the heat shrink tape would have given me better results than the heat shrink tube, (and I agree, the tube is THICK and hard to control) but this would be very time consuming in a production environment (small scale) as there would be alot manual effort to smooth out the seams (inside and out).

Has anyone tried to manually wet CF sleeves (brush or roller) and then expand it with a bladder? How does it come out? Do the fibers separate excessively when the bladder is inflated?

I think that the bladder and female mold approach will give me the best chance at getting a smooth surface (inside and out)...but I am not sure about getting enough resin into the fibers...

 

[MikeHalloran]

Now it sounds like Yet Another Cold Air Inlet Tube.

Which means that nobody will ever know how well or if it works, but it has to look good.

You won't get that with prepreg, or even fabric, because of the difficulty of neatly wrapping a cone with fabric. Hard enough from the outside, worse from the inside. Worst, you can't see if the part is acceptable until it's cured, and then it's scrap.

You need to wet-wrap the part on a spinning mandrel using yarn or tow or unidirectional tape, with a CNC applicator to work around the elbows, ensure consistency and generate interesting patterns.

No worries, such machines pay for themselves pretty quickly.
How many tubes can you sell per day?




Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Mike

;-)

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[carboncopy001]

Mike...you are "on the money!"

Another intake tube project! Boys and their toys..we never outgrow certain things.

You mentioned several different things in your post that I am not familiar with such as:

1) spinning mandrel using yarn (is this CF yarn?)
2) or TOW or unidirectional tape witha CNC applicator?

Item 1 sounds expensive and item 2 sounds VERY EXSPENSIVE. But I really have no idea what they are or how they work. Can you direct me to some links that would expand on these topics/items...

Thanks

 

[MikeHalloran]

Google is your friend.

Think filament winding, with more than one filament at once.

Aerospace guys have been doing it for decades.

If you're feeling ambitious, you could make the machine yourself. First you need a lathe... but it doesn't have to be a particularly good one, and it doesn't have to run fast.

Then you find a way to unroll a reel of tape, etc, dip it in goo, squeeze it a bit, and wrap it onto a spinning preform, while manipulating the roll/ dipper/ squeezer in 3 dimensions so the tape wraps nice around the workpiece. You could do it with cams, but electronics, i.e. CNC controls, make it easier, and especially, easier to change.

The good news is that homebrew CNC stuff is getting better and cheaper all the time.

The bad news is that it's cheaper relative to where it started, but nobody gives it away. You might be able to do it for a few tens of thousands of dollars, and a lot of sweat equity.

You'll learn a lot.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

Oh. Almost forgot.

You'll get sticky, too. Don't start in the living room.



Mike Halloran
Pembroke Pines, FL, USA

 

[carboncopy001]

Mike,

Thanks for the post...I am not sure about going that route, but it sure is making me think about different approaches...the whole spinning mandrel thing I mean.