I need some tubing for a spacer. The outer diameter the same as a
608 bearing, and the inner diameter no greater than 1/4 inch. As
light as possible, hopefully no heavier than aluminum. It would be
cut to about 1 inch length.
What is a spacer like that called? I could use some keywords.
To get tubing without a seam, search for "DOM" or "Drawn Over Mandrel"
tubing as it is not welded or cast. It is essentially... well... Drawn
over a mandrel or precision extruded.
It's what they use when they need the strongest option as well as there are
no hard spots created while welding the seam.
Joe Agro, Jr.
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Oh contraire! DOM IS welded! I toured Trent Tube in WI and was
amazed at the process. It all starts out as coil stock then it goes
through a series of rolls that form it into a tube then it's TiG or
laser welded, cut to length then drawn over a mandrel in lengths equal
to the length of the mandrel.
FWIW. I had ordered some from McMaster Carr for another purpose, they
call aluminum seamless tubing "single-line". Their description is
"Formed from a pierced cylinder of material, creating a uniform tube
without a weld or seam."
Seamless steel is not actually drawn at all--it's spun between two
rollers and pressed over a mandrel, with the opening in the center
actually resulting from the rolling process and the mandrel being there
to provide a smooth inner surface with consistent (more or less)
Seamless aluminum tubing may be extruded or rolled.
I think you're speaking of the Mannesmann process, which is fairly recent.
But even there, they pierce the tube before the cavity opens up. The
conventional process, dating back to the 1920s, starts with actual
Aha! Here's a very succinct description of the Mannesmann process:
Essentially, they work the steel with rollers until the core is about to
rupture from overworking, but then they run the bar over a cone pierce
before it actually opens up.
Yeah, seamless tube is "drawn over mandrel" of necessity but, drawn
over mandrel is not necessarily seamless tube or pipe.
If you are in this racket it helps to know the ASTM specs!
"Drawn" is more likely to be extruded over a mandrel.
Ever wonder why doctors, dentists and lawyers have to Practice so much? Ever
wonder why you let them Practice on You?
DOM usually is first resistance-welded -- often submerged-arc welded -- and
then drawn over a mandrel to flatten the weld and to produce a fairly
uniform strength, hardness, and diameter. DOM may be shrunk from its
original diameter by extruding it through a die while it's being drawn over
Plain ERW, like EMT and common tubing of various types, may be sort of drawn
or rolled over a mandrel to flatten the weld, but it's not fully reformed
over a mandrel.
Seamless is pierced from solid bar and drawn over a mandrel. Once upon a
time it was the best tubing, but DOM made from flat sheet is so good today
that the performance is nearly identical. And DOM made from flat sheet
generally has more uniform thickness.
Some German tubing company had a miniature DOM machine at IMTS one year --
either '78 or '80 -- that was about six feet long and produced
soda-straw-sized tube from a flat strip of steel. I would love to have one
of those toys. It was really fun to watch.
In terms of pricing, ERW is the cheapest and seamless is the most expensive.
There also are some other methods used to make tubing today, including a
spinning method that produces a friction lap-weld. These came after my time
covering materials so I don't know anything about them.
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