Sheet Metal Leveler Sizing: How to Read a Straightening Capacity Chart
A leveler rated for 7 mm and 1,600 mm usually cannot flatten 7 mm strip 1,600 mm wide. Its capacity chart shows what it can do. Learn to read the chart's three zones, see why stronger steel shrinks it, and size a machine from three material data points.
Leveler specifications usually come as two ranges, for example 0.5โ6.0 mm thick and up to 1,600 mm wide. Read together, they suggest that the machine flattens 6 mm strip 1,600 mm wide. In most cases it does not, and it was never designed to. Each number comes from a different limit: the thinnest strip from the roll system and the flatness grade, the widest strip from the length of the rolls, and the thickest strip from the straightening force, which on most machines is enough for heavy strip only on narrow widths.
The straightening capacity chart joins these limits in one picture. It is one of the most useful documents a leveler maker can give you, and one of the least used. This guide reads the chart of one example machine, shows how it is calculated, and lets you change the yield strength, the rolls and the force to see how the chart moves.
Size a sheet metal leveler from its straightening capacity chart, not from its maximum thickness or its maximum width. For each yield strength, the chart gives the widest strip the machine can flatten at every thickness, and it has three zones. Below a minimum thickness, the flatness grade cannot be reached. In the middle, the machine handles its full width. Above the rated thickness, the straightening force is used up and the allowable width falls with the square of the thickness. Stronger material shrinks all three zones. To size a machine, check your thinnest strip, your widest strip and your hardest strip (yield strength, thickness and width) against the chart, then confirm the flatness target and the line speed.
01How it works
A leveler bends the strip until one small curvature is left
A roller leveler passes the strip between two staggered rows of work rolls. Each roll bends it the other way: hard at the entry, less and less towards the exit.
The first bends are strong enough to yield the outer layers of the strip, so the curvature it brought from the coil, the slitter or the press is replaced by curvature that the machine controls. Each following roll bends it less. The strip leaves with one small, even curvature and springs back flat.
That only works on material that is both elastic and plastic. A spring is fully elastic and recovers from every bend; putty is fully plastic and keeps every dent. Material with an elongation below about 5% is very hard to level, and heavy local waves, camber or twist need more than a parallel-roll leveler can give. The roller leveling guide explains each shape defect and how it is corrected.
02The capacity chart
One chart shows what a leveler can flatten
A capacity chart plots strip width against strip thickness for one yield strength. The shaded area is everything the machine can flatten to its flatness grade.
The chart is drawn for one reference material, here steel with a yield strength of 245 MPa (25 kgf/mmยฒ), a common reference value for ordinary low-carbon steel such as Q235. Some makers use 235 MPa. The difference is small, but check which value a table is based on.
The example machine
Used for every chart and number in this guide. It is a design example, not the specification of a particular model.
- Work rolls
- 9 rolls, ร80 mm
- Roll pitch
- 100 mm
- Maximum width
- 1,600 mm (63 in)
- Straightening force
- 200 kN
- Reference material
- 245 MPa yield (35.5 ksi)
- Thickness range
- 1.0โ7.0 mm (0.039โ0.276 in)
- Elastic modulus
- 210 GPa (steel)
- Your own material
- Chart explorer in chapter 03
- 1Flatness limit, t0 to t1Below t1, the flatness grade cannot be reached at full width. Narrower strip can be thinner, down to t0: 1.0 mm on narrow strip, 1.3 mm at the full 1,600 mm.
- 2Full width, t1 to t2From 1.3 mm to about 2.7 mm, the machine flattens any width it can take.
- 3Strength limit, t2 to t3Above about 2.7 mm, the straightening force is used up. The allowable width falls with thickness, to about 240 mm (w0) at 7.0 mm.
The three thickness numbers on a spec sheet
The three zones explain the three thickness values a leveler is quoted with.
The thinnest strip that still reaches the flatness grade: t1 at full width, t0 on narrow strip.
The thickest strip the machine flattens at its full width: t2. Below it, width does not matter, which makes it the most useful single number on the sheet.
The thickest strip it can flatten at all, which is possible only on narrow strip: t3. Makers rate it at different widths, such as 10 times the roll diameter, 200 mm or 400 mm, so ask which width it refers to.
For the standards, test materials and flatness grades behind these terms, see leveler specifications and standards explained.
The full-width zone is smaller than most buyers expect. On the example machine it covers 1.3โ2.7 mm of a 1.0โ7.0 mm range. Above the rated thickness, check the width of every strip you plan to run: forcing an over-wide, over-thick strip through the machine overloads the rolls, the bearings and the frame.
03Yield strength
Why stronger steel is harder to level
Yield strength moves both edges of the chart. Stronger material has to be bent more tightly before it yields, so the minimum thickness rises roughly in proportion to the yield strength. It also needs more force for the same bend, so the strength edge pulls in. The full-width zone shrinks from both sides.
On the example machine the full-width zone covers 1.3โ2.7 mm at 245 MPa, but only 1.8โ2.2 mm at 368 MPa. At a little over 400 MPa it disappears: from there on, no thickness can be flattened across the full 1,600 mm.
A leveler flattens 3 mm ร 1,000 mm strip in 245 MPa steel. Will it flatten the same strip in a 368 MPa steel?
Show the answer
No. At 368 MPa the example machine allows only about 860 mm at 3 mm. The force needed to bend the strip grows in proportion to its yield strength, so at the same thickness the allowable width shrinks in proportion.
Use the yield strength, not the tensile strength, and use the value of the coil you actually buy: mill certificates often show more than the standard minimum. For stainless steel, high-strength steel and hard aluminium tempers, the yield strength, rather than the thickness, usually decides the machine.
Reading a maker's table for stronger material
Published tables are stated for one reference strength. HENLI's TL coil straightener and BTL heavy-duty leveler tables, for example, give the maximum strip width at each thickness for material up to 235 N/mmยฒ. For stronger material at the same thickness, a first estimate is:
04One rating, whole edge
One rating point gives you the whole strength edge
Along the strength edge, yield strength ร width ร thicknessยฒ stays the same. Know one point on the edge, and you can calculate all the others.
Bending a strip until it yields through its section takes a bending moment proportional to ฯ ร b ร hยฒ. The rolls deliver that moment through the straightening force, with the roll pitch as the lever arm, so for a given roll system and force the product is fixed. It is the machine's maximum load characteristic, and it is why the right-hand edge of every capacity chart is the same smooth curve.
A plate leveler is rated for 10 mm at 1,250 mm wide in 245 MPa steel: 245 ร 1.25 ร 10ยฒ = 30,625. At 400 mm wide, the same edge allows โ(30,625 รท (245 ร 0.4)) = 17.7 mm, and at 200 mm wide, 25 mm. In 400 MPa steel, the width at 10 mm falls to 1,250 ร 245 รท 400 โ 770 mm.
| Thickness | 245 MPa | 400 MPa |
|---|---|---|
| 6.0 mm | 1,250 full | 1,250 full |
| 8.0 mm | 1,250 full | 1,200 |
| 10.0 mm | 1,250 full | 770 |
| 12.0 mm | 870 | 530 |
| 15.0 mm | 560 | 340 |
| 20.0 mm | 310 | 190 |
| 25.0 mm | 200 | 120 |
What the edge does not tell you. It describes the force limit and nothing else. A published table for a specific model also includes margins and other limits, such as drive power, roll and bearing load and the opening between the rolls, so at some thicknesses it sits inside the edge. Use the edge to understand a table and to compare materials; use the model's own table for the limit.
05Rolls and force
Bigger rolls, more rolls, more force: what each one moves
The roll system and the straightening force are the designer's levers. Each one moves a different edge of the chart, and none of them moves every edge the right way.
A tighter bend yields thinner strip: the minimum thickness falls roughly with the square of the pitch. With a shorter lever arm, the same force handles less thick strip.
The whole chart moves towards thicker material: more capacity for thick, wide strip and poorer results on thin strip.
Thinner strip and better flatness, but thick strip needs more force. In one design calculation, a 13-roll version of a 9-roll machine needed about 35 t instead of 20 t of force to match the original on thick strip.
Extends the thick, wide side of the chart and leaves the thin side as it is, as long as the rolls, bearings and frame can carry it. Each roll diameter has a force limit.
This is why a leveler range uses several roll diameters instead of one machine for every thickness. HENLI's SSL precision levelers, for example, use ร20 mm work rolls for 0.1โ0.6 mm and ร54 mm rolls for 0.5โ6.0 mm. A wide range of thicknesses is covered by machines whose charts overlap. For how the diameter is chosen, see how to choose the roller diameter.
06Power and speed
Straightening power: enough is enough
Straightening power follows the force and the speed. It has to be sufficient; beyond that, it adds nothing.
In one design calculation for the example machine at 50 m/min, the drive power behaved like this:
Too little power, and the machine cannot reach the capacity its rolls and force allow. The chart shrinks sharply.
Enough power to use the whole chart that the roll system and the straightening force provide.
Exactly the same chart as 15 kW. Power above what the force can use is wasted.
- Speed sets the power. Doubling the leveling speed roughly doubles the power, and halving it roughly halves it. Ordinary sheet leveling rarely needs more than 10โ15 m/min.
- Friction is often half of it. Roll and bearing friction often take half or more of the straightening power, so drive efficiency and bearing type matter.
- Bad shape costs power. Heavy coil set and waves take more force and power than the reference material behind the chart.
- Start-stop lines run faster. In a 3-in-1 straightener feeder, the straightening section runs at about two to three times the average line speed so that it keeps up with start-stop feeding. See how to select a 3-in-1 feeder.
07Sizing steps
Size a leveler in five steps
Name the jobCut sheets and parts, coil strip ahead of a press, or rough straightening inside a 3-in-1 feed line. Each uses a different roll system and handling: an SSL precision leveler for sheets and parts, a TL or BTL leveler for coil strip, or a 3-in-1 straightener feeder. See coil straightener vs sheet leveler.
Convert the flatness target to mm/mA tolerance only means something together with the length it is measured over. For a single curvature, the deviation grows with the square of the length, so 0.2 mm over 400 mm is about 1.25 mm/m. See flatness units explained.
Give three material pointsYour thinnest strip, your widest strip, and your hardest strip as yield strength, thickness and width, for example 400 MPa, 5.0 mm and 600 mm. Everything else you run should lie between them.
Choose the rolls, then the force and powerThe smallest roll diameter that can carry the force for your hardest strip, enough rolls for the flatness grade, then the straightening force and the power with margin.
Confirm the speed and the lineLeveling speed, coil or sheet size, the shortest part length, and the feeder, press or shear after the leveler. A speed you do not need costs power.
What to send for a leveler sizing check
- Job: cut sheets or parts, coil strip, or a 3-in-1 line, and what happens before and after the leveler.
- Flatness: the target, the length or sheet size it applies to, and how it will be measured.
- Three material points: thinnest, widest and hardest strip, the last one as yield strength, thickness and width.
- Material: grade and condition, yield strength from the mill certificate, elongation, coating and surface sensitivity.
- Incoming shape: coil set, crossbow, edge wave, center buckle, camber or twist. Photos or a short video help.
- Line: speed, coil ID, OD and weight or sheet size, the shortest part length, and the voltage.
- Acceptance: the sample lots, and how the result will be checked at the factory acceptance test.
Scope of this guide: the charts and calculators show how capacity is calculated on an example machine. The roll system, force and power for a real project are confirmed for the specific model and material.
HENLI levelers
Find the leveler for your material
Each HENLI family covers its own part of the thickness range. Open a product page for its capacity table, configurations and quotation checklist.
08Cheat sheet
Leveler capacity on one page
| Question | What decides it | Rule | Example machine |
|---|---|---|---|
| Thinnest strip | Roll pitch, flatness grade, yield strength | t_min โ pitchยฒ ร ฯ | 1.0 mm narrow, 1.3 mm at 1,600 mm |
| Rated thickness | Straightening force, pitch, machine width | ฯ ร b ร hยฒ = constant | About 2.7 mm at 245 MPa |
| Width above it | Straightening force | b โ 1 รท hยฒ | 1.5ร thicker โ 56% narrower |
| Stronger material | Yield strength | b โ 1 รท ฯ, t_min โ ฯ | At 3 mm: 1,300 โ 860 mm from 245 to 368 MPa |
| Bigger rolls | Roll diameter and pitch | Chart moves to thicker strip | ร80 โ ร100 mm: thinnest 1.0 โ 1.6 mm, rated 2.7 โ 3.0 mm |
| More rolls | Number of rolls | Thinner and flatter; needs more force | 9 โ 13 rolls: about 35 t instead of 20 t |
| More force | Rolls, bearings, frame | Thick, wide side only | 200 โ 300 kN: rated 2.7 โ 3.3 mm |
| Speed and power | Speed, friction, incoming shape | P โ v; spare power adds nothing | 2ร speed โ 2ร power |
| Shortest part | Roll diameter | About 1.8 ร roll diameter | ร80 mm โ about 150 mm |
?FAQ
Leveler sizing questions
How do you choose a sheet metal leveler?
Start from the machine's straightening capacity chart rather than its maximum thickness. Check three points against it: your thinnest strip, your widest strip, and your hardest strip as yield strength, thickness and width. Then confirm the flatness target in mm/m, the line speed and the incoming shape of the material.
Why can't a leveler flatten its maximum thickness at its maximum width?
The maximum width is set by the length of the rolls and the maximum thickness by the straightening force. Bending strip until it yields takes a moment proportional to yield strength ร width ร thicknessยฒ, so above the rated thickness the allowable width falls with the square of the thickness. The maximum thickness is reached only on narrow strip.
How does yield strength affect leveler capacity?
At the same thickness, the allowable width falls in proportion to the yield strength: double the strength, half the width. The minimum thickness also rises roughly in proportion to the yield strength, so the full-width zone shrinks from both sides and disappears for high-strength material.
What is the rated thickness of a leveler?
The thickest strip the leveler can flatten across its full width. Below it, width does not limit the machine; above it, every strip has to be checked against the capacity chart. It differs from the minimum thickness, the thinnest strip that reaches the flatness grade, and from the maximum thickness, the thickest strip it can flatten at all, on narrow strip.
Why do levelers use small rolls for thin sheet and large rolls for thick plate?
Thin strip only yields when it is bent around a tight radius, which needs small, closely spaced rolls: the minimum thickness rises with the square of the roll pitch. Thick strip needs a large bending moment, which small rolls cannot carry. Larger rolls move the whole chart towards thicker material, so one roll diameter cannot cover every thickness.
Does a bigger motor increase leveler capacity?
Only until the power is sufficient for the force and the speed. Power rises roughly in proportion to the leveling speed, and power beyond what the roll system and the force can use adds nothing. Too little power, however, shrinks the capacity chart sharply.
Need a Leveler Sized for Your Material?
Send your thinnest, widest and hardest strip, the flatness target and the line speed. HENLI will check them against the capacity charts of suitable models and recommend a roll system and configuration.
