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Fri Mar 12, 2010 9:05 am

There seem to be a lot of opinions of what DOM tubing actually is. I work for a tubing company that was founded in 1890 as the first seamless tube manufacting company in the US. We are still in business making seamless tubing up to 8.125 OD with a wall as heavy as 1.750. We also make welded tubing up to 12.500 with a wall up to .685. The welded tubing is formed cold and welded with high frequency welders. The flash is removed from the ID as well as the OD. Both seamless and welded tubing are cold drawn, which denotes the DOM. The welded tubing is normalized in a furnace at 1700 degrees, with an atmosphere, to keep the tube from scaling. From there it is pickled in a 8% sulphuric acid bath, rinsed and cold drawn in a draw bench. The tubes are pulled cold, not hot. After they are drawn, they are put thru a stress relief furnace at 900- 1200 degrees, depending on the grade of steel. From there they run thru a rotary straightener, amalog tested, and cut to length. So the bottom line is seamless and welded tubing is commonly cold drawn, thus making is DOM.

Fri Mar 12, 2010 9:14 am

So, what you are saying is that DOM can be had in both seamless and seamed?

Can you tell us what the strength difference between the two is (using the same size tubing and same wall thickness for comparrison of course)?

Fri Mar 12, 2010 9:23 am

Not without knowing what grade of steel the tube is made of. We weld many differant types of steel from 1018, 1020, 1026, 1028, 520, 620 4130 and so on. When it is drawn over the mandrel, it changes the properties, and it is a tougher tube. A comment was made that welded tubing splits easily, but that is not always true. Much of our DOM tubing is used in hydraulic cylinders with great results.

Fri Mar 12, 2010 9:28 am

When the welded tubing is drawn, is it twisted during the process? My recent purchase of 1 5/8 0.120 looks to have a inheirant twisting pattern to the tubing.

Fri Mar 12, 2010 9:41 am

forkzilla wrote: ..... From there they run thru a rotary straightener, amalog tested, and cut to length. .....

The DOM I use also has spiral patterning on outside, but looking on inside it proves not to be twisted and "seam" runs true (straight) whole length of tube.....

Dale

Fri Mar 12, 2010 11:08 am

The DOM I use also has spiral patterning on outside, but looking on inside it proThe DOM I use also has spiral patterning on outside, but looking on inside it proves not to be twisted and "seam" runs true (straight) whole length of tube.....

If you can see a seam on the inside, it is a welded tube that has been cold drawn. The rotory straightener can leave what we call "straightener rings" on the surface of the tube. Seamless tubing will have a tighter spiraling on the surface, but with no weld seam.

Fri Mar 12, 2010 11:13 am

I looked at a scrap piece of my DOM and it is the seamless varity.

Thanks forkzilla for the schooling!

Fri Mar 12, 2010 11:30 am

I have been at my job 36 years, since the day after high school, and it is not very often that tubing is the topic of conversation.
I posted a few pictures yesterday of our piercer, one of our draw benches and a picture with a few of the shapes we have made over the years.

http://www.thesamba.com/vw/forum/viewtopic.php?t=403625

Fri Mar 12, 2010 12:01 pm

http://images.thesamba.com/vw/gallery/pix/655815.jpg
http://images.thesamba.com/vw/gallery/pix/655816.jpg

Here are a few pics of one of our five shipping bays and our 8 inch weld mill.

Fri Mar 12, 2010 12:22 pm

I'm still unclear how a tube is made seamless. Is it an extrusion? What is the process starting from raw flat? material to a seamless tube? Does a seamless tube actually have a seam but is undetectable? :?

Fri Mar 12, 2010 12:33 pm

I know a little bit about metal as I was an aviation structural mechanic for several years but when it comes down to roll cages I just ask for DOM or 4130 and include the wall thickness and that is about it.

Fri Mar 12, 2010 12:57 pm

Here is a cutaway of the piercing process. The billet comes from the left and is driven over the point on the right. The billet is heated to 2300 degrees and is pretty soft at that temp. A 2500hp motor powers the mill.
After the tube is pierced, the bar is pulled out from the right and the tube kicks out of the mill. The piercer bar is put back near the piercer rolls and the process starts again.

Fri Mar 12, 2010 1:21 pm

How long of a stick can you make that way?

Fri Mar 12, 2010 1:32 pm

We can pierce up to 24 feet, as large as 8.125 X 1.750, a very heavy tube. The next step in the process is thru an "assel mill" which is smaller rolls, powered by a 1000hp motor. The tube is still red hot at this point, and an "assel bar" of the finish ID size is inserted into the pierced shell and the whole thing is run thru the assel mill. When it exits the assel, the bar is pulled back out and the process is started over.

Fri Mar 12, 2010 1:34 pm

I'm sorry, I forgot to mention that out of the assel mill, the tube can be up to 30 feet long. We slangly call the asel mill, the elongator. Our draw benches can draw up to 54 foot tubes. that is about the max that can be shipped on a truck.

Fri Mar 12, 2010 3:16 pm

One more clarification please, You mention in your initial post that "both seamless and welded tubing are cold drawn." In the illustrations above it stated the material is heated to 2300 deg. What did I miss?

Fri Mar 12, 2010 5:17 pm

forkzilla wrote: I'm sorry, I forgot to mention that out of the assel mill, the tube can be up to 30 feet long. We slangly call the asel mill, the elongator. Our draw benches can draw up to 54 foot tubes. that is about the max that can be shipped on a truck.

I used to drive a truck in my 20's and I hauled rebar steel up to 60' from the ports and rail hubs.

Fri Mar 12, 2010 9:26 pm

Both seamless and welded tube can be cold drawn. The process I explained where the steel is heated was for seamless. The welded tube is formed cold into a tube and welded. We can cold draw tubes to 56 feet, true, but our billets are cut to length at 5 to 8 feet, and then pierced, elongated, and cold drawn to our max of 56 feet, simply because of the max length that a semi can haul legally. The photo posted is our 8 inch mill, cold forming and welding tubing.

Fri Mar 12, 2010 11:18 pm

We did a lot of deep draw of stainless. The fuel tubes you see on fuel filters, the fuel filter cans, and a few reverse draw for one GMC Truck filter where the can is a double wall can. All done from flat strip stock.

Tue Mar 16, 2010 11:03 am

This is a picture of our 12.500 inch mill at the pressure rolls while it is being welded. The ID flash is removed from inside the tube just after the welding process as is the OD flash is being cut from the OD of the tube.

This cutaway shows how a tube is cold drawn to become DOM. The "pliars" on the left (blue in color) grip the pointed end of the tube, which is "push pointed" to a diameter small enough to fit thru the die (also blue). The right side of the die is tapered down to the finish size of the die. As the tube is drawn thru the die, the mandrel inside the tube reduces the wall size at the same time the die reduces the OD of the tube.
After the tube is drawn all the way thru the die, it drops off, rolls out of the draw bench and another tube is placed over the mandrel to start the process again.