Skip to content

Crowning of 4-Roll Steel Plate Rolling Machine’s Roll

  • by
Guide to Determining the Bending Capacity of a Plate Roller

Although both the steel plate rolling machine and the profile bending machine are roll bending equipment, due to the different forms of materials for roll circles, the technical points of attention of the two types of sheet metal rolling equipment are also different.

Elastic deformation of the roll

The biggest difference between the two is that the length of the rolls of the steel plate rolling machine is much longer than that of the angle roller (profile bending machine).
The aim of sheet metal roll bending is to maintain a parallel line of pressure wherever the sheet metal rolling machine’s roll contact the workpiece. Unfortunately, physics works against this ideal, resulting in deflection. The plate rolling machine has crowning methods that account for machine deflection. When the machine deflects, the forming pressure it exerts isn’t constant from one end of the machine to the other.

The sheet metal rolling machine is most rigid at its side frames and least rigid in the middle. If a steel plate rolling machine had no method of crowning, the workpiece would force the middle of the bending area to bow.
Thus two problems arise that must be resolved. One is that the elastic deformation of the roll requires the shape of the roll to compensate. The other is that the parallelism between the rolls needs to be guaranteed.

Crowning of the sheet metal rolling machine’s roll

In the steel plate rolling machine, the crowning is in the rolls. A crowned roll has a diameter that’s slightly larger in the middle, and that subtle “bulge” counteracts the deflection.

As shown in the figure below, the pre-designed crowning of the roll becomes a straight line after the roll is clamped, so that the contact between the sheet and the roll becomes a straight line, this is ideal.

Crowning Of 4-Roll Steel Plate Rolling Machine’s Roll

Notes of crowning

Because crowning is built into the rolls themselves, steel plate rolling machines are designed for optimal crowning for a specific thickness range, usually about 75% of the machine’s nominal capacity.

Excessive crowning squeezes the workpiece too hard in the middle and can produce an hourglass shape.
Conversely, insufficient crowning can lead to barreling, where the cylinder diameter is greater in the middle than on the ends.
The same effect can form radius parts with a canoe shape, bulging in the center and tighter on the ends.

As shown in the figure below, if the crowning is too large, the rolled cylinder will have a thin waist; if the drum shape is too small, the rolled cylinder will have a bulging phenomenon.

Crowning Of 4-Roll Steel Plate Rolling Machine’s Roll

To correct this, certain plate rollers now offer dynamic crowning systems that use sensors to detect the pressure and apply the needed compensation. On plate bending machines, dynamic crowning systems allow for either the manual or automatic adjustment of roll pressure.

The parallelism between the rolls is critical to the dimensional consistency of both ends of the rolled cylinder. That is to say, the big and small head phenomenon of the cylinder is caused by the poor parallelism of the rollers. In the case that the position adjustment at both ends of the roller is hydraulically adjusted, the adjustment system with a more reasonable design and a more sensitive response can better maintain the parallelism during the rolling plate process.

Final words

Therefore, equipment (such as plate rolls or angle rolls) design capability and drum size are closely related. The design and manufacturing experience of equipment manufacturers is crucial. The rigidity of the frame and rollers designed by high-quality manufacturers is perfect, and the rolling effect obtained is better.

Works Cited: Don’t get flattened by the wrong plate roll