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Thanks Ken!
Ken and I were having an email conversation, and I asked him to post it on the forums so that everybody could join in and help us all learn! PLEASE chime in with any ideas/help/methods. I certainly don't know it all, and usually learn as much as I give on these types of threads.
Here's a few things about canisters.....
1. IN GENERAL, when powder is used in any form in a "can", that overall can is going to require 50% OR MORE in reduction to ensure everything is solid/welded/no voids. So what that means is that you have to be cognisant of the size (mostly the width) of bar or blade you want to end up with...and start with the right size tubing that will get you there AFTER it's been reduced at least 50%, keeping in mind you will want a tad extra for the can walls, which will need to be removed. (either ground or milled away).
2. The wall thickness you choose goes back to the "give-n-take" again. 1/16" wall will certainly hold, you just have to be more gentle with how much you press at a time.... in terms of how deep you allow the press dies to press/bite into the can. The other side of using 1/16" wall, is that there is less to remove, and it will be easier to remove less "can" wall thickness. Typically I use between .080-.120 wall tubing... but because I start with such large size (often 4x4" or 5x5" square X 12+" long), by the time I have it forged to my desired end size, the can wall are just paper thin, and as long as I make sure I've kept to reasonably square while forging, after annealing, it's just a couple of passes with a face mill and the "can" is gone.
3. THE MOST IMPORTANT PART OF ANY CANISTER.....IS THE THICKNESS OF MATERIAL YOU USE FOR THE "LIDS", AND HOW YOU PLACE IT. OK, all caps should have grabbed your attention. my advice is to make your "lids" out of AT LEAST 3/8" thick plate, and then cut so it fits INSIDE the can, very tightly. Leave enough pace unfilled inside the "can" so that you can place the lid inside. and there is about the same "lip" left around the top of the "can" as the actual lid is thick..... in other words, push the "lid" down, pressing the can contents until there is about 3/8" or more of the "can", sticking up above the lid. Weld the lid on. If you do it that way, the weld will not break open before you have the contents solid enough to remain in place.
4. Now...onto forging. Next VERY IMPORTANT thing... BEFORE you weld the final lid on your canister (I also weld on a heavy section of rebar or pipe for a handle). Have your forge running, and up to the correct temp. Here's why..... if you weld the final lid on your canister, and the can is not fully/completely sealed (which they never are), as that weld cools, somewhere WILL suck in the surrounding atmosphere. If you allow that to occur, there is a very high probability that you will get a void or only partially welded area where the atmosphere got sucked into your canister. As soon as the final lid is welded in place, straight into the forge. There is always tons of scale, so I never concern myself with that. When it comes to heating/soaking, even the smallest canister I would ever make, gets at least 45mins of soak, AFTER it appears to be at welding temp. (I try to maintain 2370F or so for any "can" welding/forging)
Now, onto talking about how big a bite to take..... you always want to do your best to forge a can down as evenly as possible. That is what maintains any pattern you've built into the can. "Bites" or how much you press.... the very first weld is the biggest bites I take during the entire forging process... and those are never more than 1/4"....that means from the top AND the bottom, so neither dies bite in more then about 1/8". Rotate 90, do it again, then move down the length a die's width, do it again, repeat, repeat, repeat. You will "feel" the can stiffening at things weld. NEVER EVER try to take too big of a "bite"....that just distorts/wrecks things, and then you can never recover.
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