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composite tubes

Unread postPosted: Wed Mar 13, 2019 10:11 pm
Author: Anatine Duo
Here is something I've been working on for a long time. Access to smooth tubing is easy, but access to strong smooth-inside tubing is not always. My options are to order seamless steel (I shall when the time comes) or work with commonly available materials.
kevlar tube close.JPG

In another life I hand lay-up composites, so I thought to reinforce commonly available tubes made of pvc, abs, copper... I already have a launcher with this technology (the Bullshark)
kevlar tube in progress.JPG

The trick was building a jig to maintain some tension on the fabric as it is being wetted with epoxy, and then to hold the seam flat while the epoxy cures. I gave up using vacuum as it was just too tricky to keep the wrinkles and blisters out on this type of lay-up.
kevlar tube in progress 2.JPG


So far I have used Kevlar and fiberglass. Barlow's formula can be used to calculate pressure ratings. The strength of a home composite can be very roughly found by dividing the fiber strength by 2 (because the matrix doesn't really give much strength but takes up volume) and again by 2 (because half the fibers have a different orientation). I think 0/90 degree fiber orientation is ideal to give hoop and axial strength at the cost of torsional (torsional not necessary in this application)

I think that's a 3/4 copper pipe wrapped with enough Kevlar to give a burst strength of 21000 psi (not including the copper) and probably lighter than mild steel.

A more advanced pressure tube might have unidirectional fibers inside wrapping the liner to provide hoop strength and then unidirectional axial fibers on the outside for both axial strength and optimum beam strength.

Re: composite tubes

Unread postPosted: Thu Mar 14, 2019 10:45 am
Author: jackssmirkingrevenge
Nice work!

Carbon fiber wrapped tanks for paintball are rated for 4500 psi, still quite a bit of aluminum in them when you look at a sectioned one:

Image

It's definitely a messy and time consuming but lower cost option for those who want to play with higher pressures but cannot afford off-the-shelf rated components, especially parts more complex than a straight tube. That being said, it's important to know how to do it correctly and use the right materials.

I came across this tutorial for wrapping a stock in CF recently, something I'd like to try eventually.


Re: composite tubes

Unread postPosted: Thu Mar 14, 2019 12:30 pm
Author: wyz2285
So you don't have the weight advantage of CF nor the beauty of wood...? That doesn't make sense :lol:
Now if you make a foam mold then dissolve it after... That would be cool and worth the effort.

Re: composite tubes

Unread postPosted: Fri Mar 15, 2019 9:14 am
Author: jackssmirkingrevenge
wyz2285 wrote:So you don't have the weight advantage of CF nor the beauty of wood...?


What about the beauty of carbon fiber?

Re: composite tubes

Unread postPosted: Fri Mar 15, 2019 9:33 am
Author: wyz2285
"This ultra-light multi-purpose hunting rifle is the lightest Sako rifle ever made"
I'd say looks are the side effect, weight is the main objective. Same reason I never fancied these carbon fiber vinil wrapped car hoods :p

Re: composite tubes

Unread postPosted: Fri Mar 15, 2019 10:26 am
Author: jackssmirkingrevenge
I think it's pretty, de gustibus non disputandum est ;)

Re: composite tubes

Unread postPosted: Sat Mar 16, 2019 12:47 pm
Author: Anatine Duo
composite tubes.JPG


The largish Kevlar tube was my first try. It's on some very thin walled PVC (central vac tube maybe?) Note the finished edge didn't stay square but at least the fibers are all locked down. Also shown is ABS with fine glass before trimming. I can't even find the seam on that one.

To pretty these up I would use carbon fiber sleeving. Most times the seam can be down in a stock or something anyway. There's nothing wrong with paint either.

It is time consuming and messy and wasteful, but cool to know it works and possibly practical if big brother decides to ban strong smooth pipe. One day they might ban round pipe... hard to thread that square stuff though.

I added 12 kilos of carbon fiber to my car and it didn't get any lighter!

Re: composite tubes

Unread postPosted: Sat Mar 16, 2019 2:05 pm
Author: wyz2285
I added 12 kilos of carbon fiber to my car and it didn't get any lighter!
:lol: :lol:
Things must be priced very differently there than here; the amount of fiber and resin used for these two barrels I could buy a dozen meters of seamless aluminium tube with sufficient wall thickness for our applications.

Re: composite tubes

Unread postPosted: Sun Mar 17, 2019 6:24 am
Author: jackssmirkingrevenge
Anatine Duo wrote:It is time consuming and messy and wasteful, but cool to know it works and possibly practical if big brother decides to ban strong smooth pipe. One day they might ban round pipe... hard to thread that square stuff though.


That sounds a little far-fetched, don't you think? Though I wouldn't be surprised if someone in the UK is contemplating it...

It sounds like a good way to add strength to 3D printed components...

Re: composite tubes

Unread postPosted: Sun Mar 17, 2019 1:22 pm
Author: Anatine Duo
lol Yes it's far-fetched! It's part of my argument against bizarre firearms laws... pipe, closed at one end, can be a firearm. Ban pipe now!

If someone ( I think you already know this) is contemplating strengthening a 3d print, always keep in mind the print might flow under pressure. I would certainly expect creep.

I started this just to see how difficult it is, and it has possible practical applications for very high pressure tubes (more than 6000 psi for example), but it is not cheap unless one has the materials on hand. I guess it's not cheap to turn a decent size 20 000 psi tube though on a lathe... or 100 000 psi, but that's not a topic for this forum ;)

Re: composite tubes

Unread postPosted: Mon Mar 18, 2019 4:57 am
Author: jackssmirkingrevenge
Anatine Duo wrote:If someone ( I think you already know this) is contemplating strengthening a 3d print, always keep in mind the print might flow under pressure. I would certainly expect creep.


I'm thinking that a pressure bearing component (like say and elbow) printed very thin and substantially covered with fiber and resin would do the job, with the print merely serving as a "frame" for the wrap and not expected to add any strength.

I started this just to see how difficult it is, and it has possible practical applications for very high pressure tubes (more than 6000 psi for example), but it is not cheap unless one has the materials on hand. I guess it's not cheap to turn a decent size 20 000 psi tube though on a lathe... or 100 000 psi, but that's not a topic for this forum ;)


Those pressures are certainly beyond the realm of spudfiles projects, but I think the practical application for our purposes would be more conventional pressure levels in larger parts, for example a large bore PVC launcher that can be taken beyond what would normally be acceptable.