The short answer
On an ERW tube mill, the entry-section leveler, also called a leveling machine or straightening machine, is installed after the uncoiler and before the shear & butt welder. During threading, two pinch rolls pull the strip head in, and the head is bent back and forth between staggered upper and lower leveling rolls. This takes out the coil set and delivers a flat strip head to the shear & butt welder, so that coil ends can be sheared square and butt-welded.
It is not a precision leveler. Final flattening before forming is done by the non-driven flattening rolls at the tube mill entry and by the forming section itself. That is why an entry leveler has relatively few leveling rolls (usually 5 to 8) and a modest motor. InGen MillTek's current main design is a 6-roll leveler: 2 pinch rolls plus 6 leveling rolls, 3 upper and 3 lower, staggered and adjusted hydraulically in 3 groups.
Where the leveler sits in the entry section
A typical tube mill entry section runs in this order: coil car, uncoiler, leveler, shear & butt welder, flat support stand, adjustable twist stand, feeder, spiral accumulator, high turnover stand, then the tube mill. The leveler follows the uncoiler directly. Its job is to straighten the strip head peeled from the coil and hand it on to the shear & butt welder.
Built-in devices: peeler, powered hold-down and head straightener
When you compare proposals, check whether the leveler includes these devices.
- Peeler: swings up and down and extends or retracts to lift the strip head off the outer wrap of the coil and guide it toward the pinch rolls.
- Powered hold-down: an arm presses on the outer wrap, and its rubber-covered roll turns the coil slowly to bring out the strip head. It also keeps the coil from loosening.
- Head straightener: a hydraulic cylinder presses the bent strip head flat so it can enter the pinch rolls.
- Entry vertical guide rollers: guide and center the strip.
How leveling works: repeated bending that gets smaller toward the exit
During threading, the strip head passes between staggered rolls and is bent in the opposite direction at every roll. By the general principle of roller leveling, the bending is larger at the entry, so the strip yields and its original coil set is wiped out. Toward the exit the bending gets smaller and the remaining curvature cancels out, so the strip leaves with very little residual curvature.
To bend steel plastically, the bend radius must be smaller than its elastic-limit radius. From basic strength of materials, the surface of the strip starts to yield at a bend radius of about R ≈ E × t ÷ (2 × σy), where E is the elastic modulus (about 206 GPa for steel), t is thickness and σy is yield strength. Example (to show the trend only): with σy = 235 MPa, a 3 mm strip gives R ≈ 206,000 × 3 ÷ 470 ≈ 1.3 m; a 6 mm strip gives about 2.6 m.
The bending moment needed to yield the whole cross-section is about M ≈ σy × b × t² ÷ 4, where b is strip width. Double the thickness and the moment goes up four times; double the width and it only doubles. So thin strip needs small roll diameters and close roll spacing to be bent enough, while thick strip yields at a gentler bend but needs larger rolls, wider spacing and more torque. This is why the roll set is chosen mainly by thickness.
Inside the 6-roll leveler
Key features of InGen MillTek's current 6-roll leveler (summary level; exact dimensions and configuration are given in the technical proposal):
- Pinch rolls: 2. The lower roll is driven; the upper roll is pressed down by hydraulic cylinders.
- Leveling rolls: 6, arranged 3 upper and 3 lower in a staggered pattern.
- Adjustment: the leveling rolls are adjusted hydraulically in 3 groups, so the entry, middle and exit are set separately, with more bending at the entry and less at the exit.
- Drive: the driven rolls are in the lower row, powered by a motor through a reducer and a pneumatically operated jaw clutch. The pinch rolls and the driven leveling rolls run at the same surface speed.
- Roll face length: based on the maximum strip width; quotations typically state nominal width plus 100 mm (reference value).
- Accessories: peeler, powered hold-down, head straightener and entry vertical guide rollers.
Counting rolls: what 5-roll and 7-roll can mean
Besides the 6-roll design, there are machines with 2 pinch rolls plus 5 leveling rolls and other layouts, chosen per project. The same kind of machine may be called a 5-roll or a 7-roll leveler in different documents, depending on whether only the leveling rolls or all rolls are counted. When you compare proposals, check the number of pinch rolls and the number of leveling rolls separately instead of relying on the name.
Threading and normal running: how the clutch is used
During threading the clutch is engaged and the pinch and leveling rolls are driven, pushing the strip head into the shear & butt welder. Once the head is inside the welder, the operator opens the pinch and leveling rolls and disengages the clutch, as set out in the operating instructions. From then on the accumulator feeder pulls the strip and the uncoiler pays off passively. The threading sequence is repeated for each new coil.
Choosing the roll set: thickness first, not width
The 6-roll leveler comes with a small-diameter roll set and a large-diameter roll set, plus an intermediate option. The main deciding factor is strip thickness. Wide, thin strip can run on the small-diameter roll set, so a wider strip does not automatically need larger rolls, while thick strip needs the large-diameter roll set and a stronger drive. High-strength strip is reviewed by grade and strength instead of by a simple width or strength rule. When strength or thickness moves up a step, leveler power moves up a step as well. Roll diameters, motor and roll set are set by our engineers in the technical proposal. To size a leveler, we need:
- Strip width range (widest and narrowest)
- Thickness range
- Material grade with yield and tensile strength
- Coil set and strip shape condition of your coils
- For a single machine or a replacement: strip center height of the existing line
- Whether you need the peeler, powered hold-down and head straightener
When does a tube mill need a separate leveler?
The tube mill entry has its own non-driven flattening rolls, so small mills running ordinary strip usually do not need a separate leveler. Whether one is needed is assessed by our engineers from material strength, thickness and strip shape. If it is not needed, it does not appear in the quotation or the technical proposal.
Frequently asked questions
Prepared by the InGen Engineering Team. All values are reference values; they depend on configuration and are confirmed in the technical proposal and technical agreement.
- Is a leveler the same as a leveling machine or straightening machine? In a tube mill entry section, yes, these names describe the same equipment. The non-driven flattening rolls at the tube mill entry belong to the mill, not to this leveler.
- How many rolls does a 6-roll leveler have? 2 pinch rolls plus 6 leveling rolls, 3 upper and 3 lower.
- Does wider strip always need larger rolls? No. The roll set is chosen mainly by thickness; wide, thin strip can run on the small-diameter roll set.
- Can an entry leveler replace a precision leveler? No. Its job is to flatten the strip head during threading, taking out coil set so the coil ends can be sheared and butt-welded. Products with special flatness requirements need a separate review.
- Can I buy a leveler on its own? Yes, it can be supplied as a single machine. Tell us the strip width, thickness, material strength and the strip center height of your line.
- What does a leveler cost? It is configured to strip width, thickness, material and accessories, and quoted individually.