The short answer
Rollers are the tooling of a tube mill: shaped rings on the stand shafts that bend the strip into a tube, guide and squeeze the weld, and size and straighten the finished tube. Each finished size needs its own roller set, designed for its outside diameter, wall thickness and material. A square or rectangular tube can share the forming rollers of the round tube with the same perimeter, its "mother tube", and needs only one more set of sizing rollers, often called a half set. Rollers are not included in the line price: they are quoted for each size and invoiced on actual weight.
Buyers often call them tube mill rolls; in our documents the mill tooling is called rollers.
Where the rollers are on a tube mill
Following the strip, an ERW tube mill has rollers in these places:
- Breakdown (open) passes: driven horizontal stands with convex upper rollers and concave lower rollers start bending the strip.
- Side roller cluster: non-driven side rollers guide the open tube between the breakdown and fin passes.
- Fin (closed) passes: the upper rollers carry a fin that controls the two edges and keeps the seam in place.
- Welding area: seam guide rollers, the squeeze rollers that forge the weld, and ironing rollers after the outside scarfer.
- Sizing section: horizontal and vertical stands bring the tube to its final size and, for square and rectangular tube, shape it.
- Turk's heads: four-roller heads straighten the tube and finish square and rectangular sections.
A standard layout is "7+6": seven horizontal stands for forming and six for sizing, plus two Turk's heads. Each stage is described in ERW Pipe Making Process: From Steel Coil to Finished Tube.
One roller set for each size
A roller set is designed for one finished size. Stand by stand, the roller profiles take the strip through a planned sequence of shapes from flat strip to round tube. The roller design also sets the actual strip width, which is usually slightly less than the theoretical value from the tube's perimeter; the first coil of a new size is trial-run to confirm it. The perimeter estimate is explained in ERW Tube Mill Calculations: Strip Width and Weight per Meter.
For one outside diameter, a roller set covers a range of wall thickness. When the same diameter is made in very thin and very heavy walls, some stands may need different rollers; this is checked against your size list.
So, to count the roller sets you need, list every finished size: one full set for each round size, and one sizing set for each square or rectangular size whose mother tube you already make.
Sharing rollers between round, square and rectangular tube
Square and rectangular tubes are usually made by round-to-square forming. The tube is welded round, as its mother tube, and then shaped square or rectangular in the sizing section. Because the forming and welding work is the same as for the mother tube, the square or rectangular size shares the mother tube's forming rollers and adds only its own sizing rollers. Several square and rectangular sizes with the same perimeter can share one set of mother-tube forming rollers, each with its own sizing set.
Direct square forming, in which the strip is formed toward the square shape from the start, is a different process route. It needs the corresponding mill and tooling configuration, so do not assume it uses the same rollers.
Plan the tooling around your actual product list rather than the full range of the mill model: which sizes you run every week, which only now and then, and how often you change.
Changing rollers
Our forming and sizing stands are gantry-type with side roller change: the rollers come off the shafts from the side of the stand. Each size change also needs a matching set of roller bearings. After the new rollers are in, the mill is set up for the size and the first coil is trial-run.
Roller changes take production time, so plants that change size often should say so when they specify the mill; see Selecting a tube mill: start with your production mix. The time a change takes depends on the mill size, the number of stands and the crew's experience, so we do not give one figure for it.
Ordering rollers
- Rollers are quoted separately for the sizes you will produce and invoiced on actual weight: any overpayment is refunded and any shortfall is collected.
- For trial production, order the rollers for the trial sizes in advance, together with the line.
- For new sizes later, send the outside diameter or side lengths, the wall thickness, the material and the mill model. We keep supplying rollers and spare parts after delivery.
- We supply rollers only for mills we built ourselves, not for mills from other builders.
How rollers appear in a quotation is explained in Tube Mill Quotation Checklist: What Information We Need.
Roller material and wear
Tube mill rollers are made from hardened alloy tool steel, such as Cr12 or Cr12MoV. They wear with use, most in the passes that do the most work, and worn rollers show up as size drift, surface marks or an unstable weld. Worn rollers can often be re-machined to restore their profile, within the limits of the design. Keep unused sets clean, protected from rust and marked by size and stand, so that a size change starts with the right rollers.
What to send
- Every finished size: round outside diameter, or square and rectangular side lengths, with the wall thickness
- Material grade with yield and tensile strength, and the product standard
- Which sizes you run regularly and how often you change size
- Whether square and rectangular tubes are made round-to-square or by direct square forming
- For an existing mill: maker, model and the size range it runs now
Frequently asked questions
Prepared by the InGen Engineering Team. Values are reference values and are confirmed in the technical proposal and technical agreement.
- What are tube mill rollers? The shaped rollers on a tube mill's forming, welding, sizing and straightening stands. Each finished size needs its own set.
- How many roller sets do I need? One full set for each round size, plus one sizing set for each square or rectangular size whose mother tube you make. Your size list decides the count.
- Can square and round tube share rollers? Yes. A square or rectangular tube shares the forming rollers of the round tube with the same perimeter and needs one more set of sizing rollers, a half set.
- Are rollers included in the tube mill price? No. They are quoted separately for each size and invoiced on actual weight.
- Can I order rollers for new sizes later? Yes. Send the size, wall thickness, material and mill model.
- What are the rollers made of? Hardened alloy tool steel, such as Cr12 or Cr12MoV.
- How long does a roller change take? It depends on the mill size, the number of stands and the crew; we do not give one figure.
About this article
Prepared by the InGen Engineering Team. This is a general technical guide, not a specification or performance guarantee for any project. Roller design is done for each project; final parameters are set in the technical proposal and technical agreement.