"Ed Huntress" <[email protected]> wrote in message news:...
>
> "J. Clarke" <[email protected]> wrote in message
> news:[email protected]...
>> In article <[email protected]>, [email protected] says...
>>>
>>> > 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.
>>>
>>> Wow... Very interesting. Never would have thought that is the way it
>>> is
>>> done.
>>
>> If you want seamless, you specify "seamless", which is made by a rolling
>> process.
>>
>>
>
> 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 the mandrel.
>
> 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.
I should have added that it's generally rolled after piercing, too.
--
Ed Huntress
> 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.
>
> --
> Ed Huntress
>