A parabolic leaf is not a flat bar with tapered ends. Its thickness is rolled to a designed profile along the length, so that the leaf carries its load with fewer leaves and less steel. That makes every millimetre of the profile, and every part of the surface, count.
Whatever is on the leaf in the roll gap is rolled into the spring. Scale must come off before parabolic rolling, not after it.
What scale does in the roll gap
The leaf leaves the furnace with an oxide layer on it. If that scale is still there when the leaf enters the rollers:
- The profile is rolled with the scale on it. The rollers size the leaf including the scale. When the scale comes off later, in heat treatment or shot blasting, the steel underneath is thinner than the profile you designed. In our experience the scale layer can reach up to 1 mm per side, depending on heating temperature, time and process.
- The surface is marked along the whole taper. Rolled-in scale leaves pits and indentations. A parabolic leaf works hard along its whole length, not only at the centre, so a pit anywhere on the taper can become a fatigue-crack initiation site.
- The rollers pay for it. Scale is hard and abrasive. Rolled through the roll gap, it wears and marks the roller surface, and a marked roller prints its marks onto every leaf that follows.
- Peening cannot undo it. Shot or stress peening adds compressive stress to the surface, but pits and residual scale reduce how consistent and effective it is, and they stay in the spring as fatigue-critical imperfections.
Descale immediately before rolling
Steel keeps oxidising while it is hot, so a fresh layer starts to form as soon as the leaf is cleaned. The shorter the gap between descaling and the roll bite, the less scale reaches the rollers. That is why the R-Tech rolling-cell descaler sits right before the parabolic rolling machine.
- 300 bar water-jet descaling, with imported tungsten carbide nozzles, and water alone: no chemicals.
- Intermittent descaling to suit the rolling rhythm: high-pressure water is delivered only while a leaf is being descaled.
- Scale removal is confirmed in trials on your own leaves. This machine is R-Tech's own development.
Protect the rollers as well as the leaf
A clean leaf protects the roller, and a good roller protects the next leaf. R-Tech rollers for parabolic rolling are a two-piece design: a hard sleeve on a tough, reusable shaft, in imported steels, vacuum heat treated, for hot rolling at 900 °C or below. When the sleeve is worn, replace the sleeve and keep the shaft.
Roll the steel, not the scale
Planning a parabolic rolling cell, or chasing undersize or marked leaves in an existing one? Send us your leaf section, rolling temperature and line rhythm, and we will engineer the descaler into the cell.
Images for pictorial purpose only; actual machine may vary. The roller image is a 3D render.
