How Tube Is Made
A tube mill never makes a tube from a tube. It starts with a flat strip of steel and bends it, a little at a time, until the edges meet and can be welded.
The Six Stations
Slit Strip
We slit each coil in house to a strip about as wide as the finished tube's perimeter, measured through the middle of the wall. A 2 x 2 tube starts as a strip about 7.6 inches wide.
Breakdown
The first stands of rolls turn the strip's edges up. Each stand bends it only a few degrees, so the steel never kinks.
Fin Pass
Rolls with a thin fin between them close the strip into an open round and line the two edges up face to face.
Weld
A high-frequency current heats just the edges to welding heat, and squeeze rolls press them into one seam. A blade trims the outside bead flush.
Sizing
The round passes through sizing rolls that bring it to its exact outside diameter and straighten it.
Shaping and Cutoff
For square and rectangle, shaping rolls push the round flat on four sides. A flying cold saw, with a circular blade that travels with the tube, cuts lengths without stopping the mill and leaves a clean end with little burr. The line then bundles and tags them.
Why It Matters When You Order.
Square tube is made from round, so its corners are rounded, not sharp: the outside corner is about twice the wall. If your part fits tight into a corner, allow for that radius.
Rectangles with the same perimeter come from the same strip, which is why a 3 x 1 and a 2 x 2 weigh the same per foot.
Before and After the Mill.
The forming and welding take seconds. Most of what decides the finished tube happens before the strip enters the first rolls.
The Coil Sets the Finish
Tube is formed from flat-rolled coil, so its surface is the coil's surface: hot rolled with mill scale, pickled and oiled, or galvanized. Our coil arrives already pickled or galvanized from Heidtman sister plants, and the steel grade comes from the coil too. See Finishes and Specs.
The Weld Uses No Filler
ERW stands for electric resistance welded. Current heats the strip edges, and squeeze rolls press them together. No wire or rod is added, so the seam is the same steel as the rest of the tube.
Flash Is Trimmed
Squeezing the edges pushes out a bead of steel called flash. The outside bead is cut off flush right after the weld; the inside bead is usually left in place.
Cut, Mark, Bundle, Tag
All three of our mills cut with flying cold saws. Lengths can be stenciled with the marking your order calls for, then stacked into bundles, banded and tagged with the heat number. See How Tube Is Bundled and Shipped and the Cut-Length Yield Calculator.
Questions.
To check a finished tube against its spec, see How to Measure Tube.
How is ERW tube made?
A coil is slit to a strip, and rows of rolls bend the strip into a round until its edges meet. A high-frequency current heats the edges, squeeze rolls weld them, the outside flash is trimmed, and sizing rolls bring the tube to size before it is cut to length.
What does ERW mean?
Electric resistance welded. The seam is joined by heating the strip edges with electric current and pressing them together, without filler metal.
Is ERW tube the same as seamless tube?
No. ERW tube is formed from flat strip and has a welded seam. Seamless tube is made by piercing a solid bar, and is mostly used for high-pressure and other special work.
Is square tube made from round tube?
On most tube mills, yes. The tube is welded as a round, then shaping rolls push it square or rectangular, which is why the corners are rounded.
What is weld flash on steel tube?
The bead of steel pushed out of the seam as the hot edges are squeezed together. The outside flash is cut off flush; the inside flash is usually left on.
More Lessons
Put it to use: Size Finder
Tell Us the Size,
Wall and Footage.
One size or a whole program, in mill lengths or cut to your length. The quote form takes about two minutes.