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barrel material - Garolite / Nylon?

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LAN_403

Quantum Singularity

Thu Jun 01 2006, 05:42AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

I was just doing some thinking today about my future coilgun desing (reluctance) and did some research on barrel materials. One thing that is sort of set-in-stone is that my projectiles will be 5/16" diameter. What I am not 100% sure is how well these will slide down a barrel with the same 5/16" inside diameter? At worst I may have to sand down the projectiles slightly. So I did a search for some 5/16" ID plastic tubing on ebay, and other then flexible tubing found nothing. I did a quick google search and didnt find much either. So I went to mcmaster-carr and found some options. In 5/16" ID they had both nylon (3/8"OD and $1.99/5') and Garolite (3/8"OD $7.23/40"). I havent ever worked with thinwall plastics and not sure how rigid these will be? I can go slightly thicker but I want to keep the material as thin as possible. If I am not mistaken Garolite is very rigid. Not sure how smooth the interior of the tubing is though? Or do I need to go thicker? I am guessing the end result will be around a couple hundred joules per stage. Thanks for any advice.

Desmogod

Thu Jun 01 2006, 06:07AM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

I think you'll find you will have the same problems as people who have used glass for barrels, the coil will flex and snap it.

GODSFUSION

Thu Jun 01 2006, 07:49AM

Registered Member #157 Joined: Sun Feb 12 2006, 08:00PM
Location:
Posts: 76

I dont know how well it will work but couldent you soak your barrels in a poly bath and let it harden, then the coils wont flex...as much.

- wayne -

Sulaiman

Thu Jun 01 2006, 10:10AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Just did a quick google on garolite
seems to be woven fabric in phrnolic resin
here in uk it's brand name/manufacturer is Tufnol
which I'm familiar with.
I'd expect it to make a quite good barrel
Nylon is too soft for a thin-walled barrel in my opinion.

Quantum Singularity

Thu Jun 01 2006, 04:17PM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Thanks for the reply's. I wasnt sure about how rigid nylon is, the only priece of solid nylon have have held in my hand was larger than your common cutting board and thicker. Here is mcmaster-carr's basic description of the Garolite:

Grade CE Garolite: Compared to Grade XX Garolite, Grade CE offers higher impact strength. It's a cotton-cloth laminate with a phenolic resin binder.
Grade LE Garolite: Similar to Grade XX and CE Garolite, Grade LE is lightweight and strong. It offers lower water absorption than Grade CE so it can hold its shape better for tighter tolerances. It's a fine weave cotton fabric with a phenolic resin binder.
Grade XX Garolite: Like all Garolite, Grade XX is lighter than metals but dense and strong. It's a paper-based laminate with a phenolic resin binder that absorbs less moisture than Grade CE or LE Garolite. Good for use as a template board or for gasketing and gears.

There are a few more grades not available in ths size I was looking at, like G-10. I beleive this is the material alot of people have used on disks in rotary spark gaps. I beleive it might also go under the name phenolic but I am not a plastic expert.

Cesiumsponge

Fri Jun 02 2006, 12:41AM

Registered Member #397 Joined: Wed Apr 19 2006, 12:56AM
Location: Western Washington
Posts: 125

I believe Garolite is a brand name for any standardized types of paper/canvas/cotton/glass fiber phenolic/resin type thermosetting plastics...much like Lexan is a (GE?) brand name for generic polycarbonate. You can actually find a lot of phenolics for a tad cheaper than the Garolite brand if you know what type you are looking for specifically.

Also if you want a tight fit, find out the outer dimension of your projectile, the inner dimension of the tubing you are looking for, and the tolerance limits to see if they are compatible. I will assume it isn't super critical because the measurements you are making are in fractionals and not decimals. McMaster has a tolerance limit listed on most of their products but worst-come-worst, you can sand/grind/polish down your projectiles a bit. The only thing to watch out for if you want a very tight fit is that the wall thickness might vary a bit and it might pose a problem. Also your clamping forces on the barrel might deform it enough to pinch the projectile but it doesn't really need to be torqued down.

Phenolics or fiberglasses are probably the most rigid insulative materials you'll regularly come across without getting into exotic ceramics. I've seen the G-10 material label used interchangably with FR-4 grade fiberglass and it seems to be popular for amplifier and transmitting circuit boards, along with the brown phenolics. Its higher grade than the generic red fiberglass stuff also available (forgot it's specific designation) from McMaster. I don't believe it's too critical at your power levels so any type should do fairly well as they all have reasonable material ratings. The tubes are usually spiral wound with the laminate material so there should be homogenous strength radially, unlike sheets/plates which have a more critical orientation. If you want the ultimate, G-10 should be plenty good. G-7 is ungodly expensive only because of the resin binder. The CE/LE/XX and similar phenolics are a tad cheaper if price is pinnacle and they're still very rigid thermosetting materials.

Stuff like nylon and acetal (even polyethylenes and polypropylenes) are nice if you can stand a tad bit of flex because they have specific versions with increased lubricity (due to oil impregnation, teflon fill, etc) and they have lower friction coefficients but they aren't as stiff obviously. If you do plan to order from McMaster, you could try out a few different materials since they aren't terribly expensive (except the phenolics). I don't think too much has been done in the way of material testing on coilguns to show ultimately if a phenolic is required or you can squeak by with softer materials.

FastMHz

Sat Jun 03 2006, 06:00PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

I've successfully fired CGs with 3.5kj that were made with 1/8" thick PVC pipe with a 1/2" ID. But my projectile didn't fit very tight, so even if the coil compressed it a bit, it wasn't enough to grip the projectile. I also made a CG using copper tubing, slotted to prevent eddies, and was successful until I upped the power too much and crushed it. I'll be interested in your results with these other materials as I'm looking for something better than PVC.

Maz

Sat Jun 03 2006, 07:55PM

Registered Member #111 Joined: Fri Feb 10 2006, 01:04AM
Location: Menasha,Wisconsin
Posts: 65

Im not trying to hijack the thread, but isnt model aircraft fuel lines hard? i know they are a type of plastic or ceramic to withsand the heat. anybody know more about this than i do, because it might be worth looking into for a CG barrel.

Yohan

Sun Jun 04 2006, 08:36PM

Registered Member #194 Joined: Fri Feb 17 2006, 07:52PM
Location:
Posts: 19

Polycarbonate.

EDIT:

Quantum Singularity

Tue Jun 06 2006, 01:24AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

I checked out that link above... looks like some of their polycarb tubing is cheaper than mcmaster... unfortunately I still havent seen 5/16" ID in polycarb anywhere yet. Might have to alter my plans and ditch the 5/16" but before I do that I think its worth trying the Garolite.

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