carbon fiber tube

[mechpins]

Hello,

I have been looking for an off the shelf carbon fiber tube and can not seem to find one in a size that would work for me. Does anyone know of a COTS supplier for a thin walled tube in the 3 to 6 inch diameter range that is 30 inches or longer?

Thanks in advance for all the help.

 

[Compositepro]

You will not find such a thing. Carbon fiber tubes are made for specific applications. There is an infinite variety of inside and ouside diameters and fiber orientations and constructions. The best you can hope for is that you can find a tube already made for a specific application that is close enough for your needs. Or you can have a tube made.
Having someone make one tube for you is never cheap.

Or you can make your own which is not easy if you don't have experience already.

If you want to find a possible supplier you need to tell us what you want the tube for and the important specs. and someone may suggest a company that makes something close.

 

[mechpins]

I would like to use it as a boom to hold on to a part that is roughly one meter away from the test stand. The part mass is negligible and the boom diameter is still somewhat negotiable. I would like it to have a diameter around three or four inches. This tube will only be used a couple of times and then go into my parts bin, so I would really like to find something at a fair price rather then something that is the exact size.

 

[cmrini]

May I ask why it needs to be made out of carbon fiber?

 

[litebike]

You could try Maclean Composites. Not sure if it will suit but worth a look.

http://www.macqc.com/items.php

They the following in stock:
Part# 45285 3.0-70-FABR ID(in.) - 3 OD(in.) - 3.125
Wall(in.) - 0.062
Weight(lbs./ft) - 0.4
Length(in.) - 70 stock rw deco cello-wrap
Price 1-10 - $290.19
11-49 - $267.29
50+ - $240.96

 

[mechpins]

CMRINI,

It will be supporting a high voltage RF experiment. So we want to try and have a volatage gradient as it moves away from the test device. The hope is that the carbon fiber tube with have enough resistance through the length of the tube to smoth it out a little.

litebike,

that might work I will try to contact them today.

Thanks everyone

 

[MechanicalChef]

For a structural member which is also an insulator (and possibly electromagnetically transparent), why not a GFRP tube instead? Fiberglass is used rather exclusively for this purpose in the role of aircraft radomes and MRI equipment.

 

[Higgler]

Carbon fiber is pretty conductive, 3 ohms per square is a common number. I wouldn't call that resistive.

Don't you want an insulator with a slight amount of conductivity instead of a metal with a slight amount of loss?

You don't use carbon fiber as a radome, rf won't pass thru it. Aircraft radomes are often simple plastic and coated with a resistive paint that dissipates static.

What levels of voltage are you planning on?

kch

 

[mechpins]

Higgler is there a source where I can look up the resistance of carbon fiber based on the voltage level? As a mechanical engineer I have a very limited knowledge on this sort of thing. Most of what I know is based on what I have been told by some of my EE friends and co-workers. I know that rf work is a large field and I will likely never do design work in the area but I would love it if I could find a couple of good book sources to look for answers when I have rf questions.
I was not aware that carbon fiber would block rf.
For my current application if rf will not pass thru that is ok. We are looking at a 30kV max for this test.

 

[40818]

Higgler, dont assume that just because RF frequencies have difficulty passing through carbon fibre means that radomes are made from plastic.
I have never seen a plastic radome for any commercial or military aircraft i have worked on.
Its all a black art when it comes to military transmission stuff, and specific distances, thicknesses, coatings and angles are important, as is the ability to pass through the "dome", but plastic is something i've neve seen used.

 

[Higgler]

40818, I use plastic as a generic placeholder, not a specific product. Any plastic material can be used as a radome, just depends on it's loss.

I've done alot of radome design and one of the most common types is to pick a material that's physically tough and use a sheet of it that's 1/4 wavelength electrically thick. The reflection from the front face cancels the reflection from the back face and the thru loss is minimal. Two wrongs make a right in rf.

Usually this is done at X band, wavelength is one inch, quarter wavelength is 1/4 inch, material dielectric of 4 is typical, hence the 1/4 wave electrical length ends up 1/8 inch thick. Many radomes can be simple, especially if you only need to transmit through them straight on and don't need to go far out in angle. The most difficult is far out in angle and circular polarization and very wide bandwidth.

mechpins, I'd suggest some type of FR4/G10 tube.
Why do you need to have a resistance on the standoff?
If you're just trying to insulate your product, visit the power company and borrow an insulator used on the power poles.


kch

 

[Compositepro]

Most commercial aircraft radomes are made from e-glass/epoxy composite. The best and most expensive radomes use quartz fiber and cyanate resins. They are also often sandwich structures.

Even one filament of carbon fiber contamination in a radome can destroy it. The fiber will vaporize and char the resin which then will fry in microwaves.

 

[mechpins]

I found a fiberglass tube that will work. It has a 4 inch OD and the price is fair. The reason that I was looking to use a material with a higher resistance was to get a voltage gradient. One of the science guys working for us wanted the structure to affect the rf field as little as possible because the support will not be in the final product.

Thanks for all the help guys!