how they make it?

the recent "how it's made" post and 4140 post reminded me, what i'd REALLY like to see is how they draw 4140 tubing. i've seen cross sectional views of the machinery... and read about the process, but would really like to see it in person, and if not in person at least on video. thing that puzzles me is, how or why does the tube not thin off center, why does the tube never(?) thin, thinner on one side and thicker on the other, and if it does how can they detect it in the middle of a 20' long tube. i realize they have a mandrel inside the tube, but i'm imagining it's got to be relatively long, and therefore not rigid enough to resist any tendency of the tube to thin out more on one side than the other. also, 4140 is DAMN hard stuff, there must be TREMENDOUS pressures when they're drawing it. wonder how many break. maybe that's why it's so expensive?

another thing. once a while ago a guy i know said "i wonder how they make aluminum cans?!" since then i've seen episodes on tv about it and there's even a guy i know who services can making machinery and he had in his house a series of in-process examples, was pretty cool. what i said to this old guy i know (who was wondering about the aluminum cans) "*I* wonder how they make oxygen cylinders!" that must be some hairy incredible process, making oxy cylinders, i mean, making something that you've got to draw THAT deep and is guaranteed to hold all that pressure. and last that long. i had a oxy cylinder that had lots of hydro test stamps on it, i think the first was "23". it blows my mind that that tank has been around since (before!) 1923 and still tested good in the late 90's. would like to see that process on "how it's made", how they draw oxygen cylinders.


Reply to
William Wixon
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"*I* wonder how they

Actually they showed exactly that last week. Very interesting. Paul

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In australia, tubing made in this way is called 'seamless' or DOM meaning Drawn Over Mandrel as opposed to the other popular type of tubing which is commonly referred to as CREW (Cold Rolled Electric Welded). While i havent had anything to do with the actual process of making DOM pipe, Ive used a fair bit of it and i can tell you there pretty often is variation in wall thickness.

Ive used mandrel benders a fair bit, and they can be a bit tricky... I find any of that work is really quite hands on, and as much of an art as a science; bending, pressing, rolling etc. This is really getting down to the nitty gritty and intangible properties of the materials... most guys who are doing it develop their own ways of handing the machinery, and they know that the relative 'spring' of materials changes from one batch to the other, and even more so with aluminum. Whether its the metalurgy, or the heat treating process, things do have a fair bit of variation in it. This makes it really hard to produce consistent results in a production environment, and a really high art to produce a desired result in one-off custom fabrication.


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Shaun Van Poecke

Seen a film how they made hypodermic needles. They started with a tube of maybe 30mm OD and a length of something around 1m. They were welded, but that weld completely disappeared after some draws. Draw, temper, draw, temper, ... They had to cut the tube from time to time because it got longer and longer. They worked initially with a mandrel, but in the end only put some wire in (that was pulled out and replaced with a thinner one for the next pass).

Why the wall doesn't get unequal? Maybe it is because of work-hardening. Where it would get thinner, it also gets harder and resists more. So the thicker part will give in more until it is in balance again.

Measuring the wall-thickness somewhere in the middle: They either don't care (because their process works), or with ultrasonic.


Reply to
Nick Mueller

We used to see the odd Oxygen bottle go through our rotation, that had German Luftwaffe markings, circa 1940's. They get tested, pass, and keep getting used!

Cheers Trevor Jones

Reply to
Trevor Jones

Actually there are 3 types (for this discussion) of tubing: welded(ERW), welded and drawn (DOM), and seamless. Lots more types but this is a start.

The seamless starts as a large (several times the desired final diameter) solid rod, it's put through some angle rollers that cause the middle of the tube to get a stress fracture, poke a mandrel through the center to get a rough tube, then send it to the draw bench.

The draw bench is used on both ERW and seamless, has an die that is smaller than the incoming tube plus a mandrel plug on a cable that is set to be just ahead of the die. Grip tube, pull it though the combo. A

20' piece of thick wall larger tube becomes a smaller diameter and thinner wall. Once the piece gets too long or gets too work hardened, it is cut to a shorter length and may get a trip to the anealing oven. A typical pull bench runs 80' long, some are longer.

1026 DOM is a very uniform product. It is left in a work hardened state, typically has a tensile about 30% higher than standard 1026. For bending purposes you can depend on uniform springback, set it up, it just runs. Downside is that the ductility is lower, tends to fracture if you try tight radius bends.

Seamless is not very uniform: the process of mak>

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I think Ive still got an acethy bottle with the German eagle on the neck ring with a "42" on it. Ill have to check to see if Ive swapped it yet or not.


"Liberalism is a philosophy of consolation for Western civilization as it commits suicide"

- James Burnham

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