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Aluminum Joints

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Aluminum Joints

Unread postAuthor: kjjohn » Wed Nov 11, 2009 9:48 pm

How can I "connect" together aluminum pipe fittings without threads without welding them? I know that welding aluminum pipe will lose its strength if welded, and I need it to be able to withstand up to 700psi in my hybrid. I was thinking metal-filled epoxies might work, but would the high pressure/temperatures render them useless?
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Unread postAuthor: rp181 » Wed Nov 11, 2009 11:30 pm

for large diameters, screws it basically your only option. for small diameters, there are flared fittings. check mcmaster-carr.
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Unread postAuthor: turner » Thu Nov 12, 2009 12:35 am

Many comrpressiom fittings would work.
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Unread postAuthor: iknowmy3tables » Thu Nov 12, 2009 1:42 am

soder? it works with copper
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Unread postAuthor: SpudBlaster15 » Thu Nov 12, 2009 2:14 am

Welding will be your best bet. Welding a tempered aluminum alloy does bring the area around the joint back to a 0 temper, but it's easy enough to regain the strength by having the entire structure post-weld annealed and then artificially age hardened.
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Unread postAuthor: Moonbogg » Thu Nov 12, 2009 4:23 pm

What size pipe or tubes are you thinking of using?
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Unread postAuthor: kjjohn » Thu Nov 12, 2009 5:30 pm

I am going to be using 2" and 3" sch 40 pipe and fittings. The reason that I am not just using threaded is that mcmaster is the only place that I can find that sells threaded pipe, but it is ridiculously expensive there.
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Unread postAuthor: Moonbogg » Thu Nov 12, 2009 6:21 pm

Yeah I understand. Aluminum pipe isn't cheap, not from McMaster at least. I looked all over and couldn't find threaded pipe for much cheaper to be honest. One thing is for sure, welding and heat treating won't be any cheaper unless you do it all yourself.
I would not be comfortable with epoxy at all. If you want it to be cheaper you can always use regular iron fittings right? Or maybe steel.
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Unread postAuthor: kjjohn » Thu Nov 12, 2009 6:49 pm

How do I heat treat aluminum myself? I want to use aluminum instead of steel because I want this cannon to be shoulder fired and weigh under 20 lbs (steel would make it 40+lbs). If not, would a combination of screws and epoxy work?
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Unread postAuthor: Gippeto » Thu Nov 12, 2009 7:04 pm

Can you sleeve one pipe into another, or fabricate sleeves to fit inside the joints?

If yes, then using the screws in shear, and epoxy/loctite or preferably...o-rings for a seal would be my recommendation.

Keep the holes for the screws at least 1 1/2 times the hole diameter from the edges.
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Unread postAuthor: kjjohn » Thu Nov 12, 2009 7:11 pm

I was actually thinking of doing something like that. I will be using regular sch 40 pipe and fittings, so I was thinking that I could first put o-ring at the end of the fitting, use epoxy to hold the pipe inside the fitting and tight against the o-ring, then drill several holes and put in screws around the diameter of the fitting.

The irony is, McMaster is so expensive that their iron pipe is more expensive than Speedymetal's aluminum pipe.

edit:
I was recently looking over the specs for Speedymetals aluminum pipe/tube, and I have some questions. First of all, is Speedymetal's pipe/tube treated or anodized? And second of all, it says that there is no way that the pipes will be able to telescope into each other because the sizes are not consistent, and because there is a weld inside the pipe. I am making a piston valve. Will this weld inside the pipe prevent my piston from making a tight seal/or fitting at all?
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Unread postAuthor: kjjohn » Mon Nov 16, 2009 8:46 pm

I was recently looking over the specs for Speedymetals aluminum pipe/tube, and I have some questions. First of all, is Speedymetal's pipe/tube treated or anodized? And second of all, it says that there is no way that the pipes will be able to telescope into each other because the sizes are not consistent, and because there is a weld inside the pipe. I am making a piston valve. Will this weld inside the pipe prevent my piston from making a tight seal/or fitting at all?
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Unread postAuthor: Moonbogg » Mon Nov 16, 2009 9:49 pm

You would have to email speedymetals to get those answers really. I bought aluminum pipe and tube from onlinemetals.com and the insides are totally smooth with no noticeable welds or anything.
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Unread postAuthor: inonickname » Mon Nov 16, 2009 10:01 pm

That weld is called a seam, and is an excellent idea to avoid completely.
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Unread postAuthor: kjjohn » Mon Nov 16, 2009 11:26 pm

The telescoping pipe page also said that DOM steel was the only metal they sell that is seamless, but if aluminum from onlinemetals doesn't have seems, i guess that'll work.

@Moonbogg - Also, since you've used these tubes before I thought I'd ask you this question: Are the diameters fairly consistent (accurate), for example, if a got a 1" ID by 2" OD tube (not pipe), could I sleeve it inside of a 2" ID tube?

Also, this may be getting off topic, but I was reading up a bit on different types of casting compounds, and I found that it is possible to buy aluminum urethane, which is basically an epoxy filled with aluminum powder. It says that once it is molded and hardens it is fully machinable and has a tensile strength of 4000psi. Would it be possibly to make a mold and create a whole cannon out of this, or would it not be able to withstand high pressures? I don't exactly know enough about material strength to know if that 4000psi of tensile strength will convert to 4000psi of pressure in a chamber.
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