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Old 12-29-2009, 01:15 AM
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What is DOM tubing?

I have seen a lot of fabrication done with this sort of material, but I do not know what grade of steel it is. We probably have it down under in Australia, but it has probably got a different name. Any info would be greatly appreciated.

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Old 12-29-2009, 01:34 AM
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Quote:
Originally Posted by mi chael
I have seen a lot of fabrication done with this sort of material, but I do not know what grade of steel it is. We probably have it down under in Australia, but it has probably got a different name. Any info would be greatly appreciated.
Do a search for "drawn over mandrel".
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Old 12-29-2009, 01:56 AM
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DOM tubing

Thanyou cobalt327 for the info. It is the same as we call it down under as "mild steel". The only difference is that it is black in colour, not bright. Thanks again.
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Old 12-29-2009, 07:53 AM
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DOM tubing is basically extruded.

The red hot steel is forced over a mandrel and through a die, of a set diameter , this results in a tube that has no seam.

Alot of tubing has a welded seam on the inside of the tube, this leads to an weak spot, DOM does not have this weakness. If you see a seem inside it is not DOM.
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Old 12-29-2009, 09:13 AM
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Some DOM tube has a line - ridge inside the tube. It is not a seam ,it is a ridge from the process of DOM manufacture .. there are different levels of DOM tube
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Old 12-29-2009, 09:30 AM
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From what I just read, the manufacturing process for DOM tubing involves a welded seam. Apparently this seam is made less noticeable (indiscernible, in some cases?) from the process of cold drawing the tubing.

From HERE:

"DOM
Drawn Over Mandrel (DOM) refers to high-strength, electrically-welded tubing that has been further processed by cold drawing through dies and over mandrels to improve its uniformity, mechanical properties and surface finish.

*snip*

The manufacturing process for DOM tubing begins with coils of steel, which are slit to the proper width for the desired tube size. The strip is cold formed and passed through an electric resistance welder which joins the edges together, under pressure, to complete the tubular shape. After testing the weld's integrity, the tubing is cut to length for further processing.

The cold-drawing process creates a uniform, precision product with substantially improved tolerances, surface finish and tensile strength, increased hardness and good machinability. In this process, the tube is cleaned and annealed, and one end of each length is squeezed to a point so it can be gripped by the drawing mechanism. The tube is then drawn through one or more dies and over mandrels (see drawing).

This reduces the diameter of the tube and thins its walls to the required dimensions in a controlled fashion to provide the qualities desired in the finished product. Metallurgically, drawing improves the tube's concentricity, tensile strength, hardness and machinability. Close dimensional accuracy is achieved through tight control of both outside and inside diameters."
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Old 12-29-2009, 11:24 AM
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Well, I guess I am better informed now.

When I think of DOM , I refer to Hyd. tubing. It is my understanding that it is seamless to withstand the high internal pressures. Has a very high tensile strength. When I am making suspension components, ie 4 links , panhard bars etc, I use hyd. tubing.

Here is the definition that I have found. I guess seamless / welded seam is dependant on application.

From www.stockcarracing.com

"The other method is extrusion. The metal is drawn over an appropriately sized mandrel--a process known as drawn-over-mandrel (DOM) tubing. This process yields a product that is more uniform in size from tube to tube. Also, both the inside and outside are smooth, without the seam from the weld process that is present on the tubes that are butt-welded together. Generally, welded-seam tubing is available only in the less-expensive and lower-strength steels.
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Old 12-29-2009, 11:32 AM
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Quote:
Originally Posted by ExcessiveRodder
When I think of DOM , I refer to Hyd. tubing. It is my understanding that it is seamless to withstand the high internal pressures.
I'm thinking that you're still correct to say seamless. For all intents and purposes it would seem that the seam is removed on at least some 'grades' during the processing. It's just that initially, there was a weld.

My post wasn't meant to contradict anyone, in any event.
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Old 12-29-2009, 12:09 PM
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Hey , nothing wrong with different and new information
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Old 12-29-2009, 11:22 PM
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From what I have gathered, DOM is a term used by the hot rod / racing communities to designate welded mild steel tubing which has been drawn over mandrel.
Seamless tubing is made by drawing the billet over mandrel, so I think this leads to confusion.
On one hand you have the material grade. This designates the chemical composition (% carbon, chrome, moly, silicon, nickle, etc.) and the physical properties (UTS, yield strength, percent elongation, etc.).
Then you have the manufacturing process. Rolled and welded. Rolled and welded and subsequently drawn over mandrel. Seamless (which is drawn over mandrel).
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Old 12-29-2009, 11:46 PM
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DOM tubing

A big thanks to all who gave me alot of useful info about DOM tubing.
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Old 12-30-2009, 01:16 AM
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DOM tubing is neither seamless nor extruded. As posted above, its welded tube that's been sized via drawing over a mandrel and thru a die. The drawing process also strengthens the tube via strain hardening. Normal grades of mild steel DOM are 1020 in smaller sizes and 1026 in larger ones. In the US, DOM tubing will be produced to meet ASTM A513 Type 5, and the exterior of the tube will carry that marking.

Hydraulic tubing can be either welded or seamless. Regardless of the method of manufacture, its probably the worst tubing you could use for anything structural. It will be the weakest of all types of tube for a given diameter and wall thickness because it has been annealled to a dead soft condition after manufacture to increase its ability to be flared, swaged, and bent. The strength of any mild steel is directly related to its hardness, so when tubing is annealled it goes to its softest and weakest state.

Seamless tubing is not extruded. It is produced by piercing a solid piece of round stock, and drawn over successively larger mandrels and thru dies until it reaches the proper size. Timken makes inner and outer race blanks for tapered roller bearings by piercing solid bearing material stock, making it into seamless tube, roll forming the blank shapes, and pinching them off the tube once they're formed. The bar is hot when its initially pierced, but no further heat is applied thru the rest of the manufacturing steps. The energy input from the various forming processes keeps the stock in the red heat range.

One of the main uses for seamless tube today is in material with very heavy wall thickness. There's a limit to the practical ratio of wall thickness to diameter for welded tube, but not nearly so much of a limit in seamless production. Seamless tubing is very expensive in relation to DOM or standard welded tube, so its rare to see it used in applications where a corresponding size of DOM is available.
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Old 12-30-2009, 01:42 AM
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Great info.

Is ERW basically a 'non-DOM' type of seamed tube?

Edit: I did a search and found: "ERW stands for Electric Resistance Welded. This is a mild steel tubing that started out as a flat sheet of steel, formed into tubing and welded. DOM stands for Drawn Over Mandrel and it is actually ERW tubing that has gone through a second process that shapes and smoothes the tubing so that the walls are more uniform. This in turn makes the tubing stronger than the original tubing. Chrome-Moly is an alloy of steel which incorporates both Chromium and Molybdenum in the process. Please don't confuse Chrome-Moly with Chrome finish."

Carry on, carry on now.

Last edited by C-10; 12-30-2009 at 02:25 AM. Reason: searched the web for ERW
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