Name the defect before changing rolls
Edge wave — also called edge wrinkle — is a repeating buckle along the strip edge after the section has been formed. On C, Z and U purlins it often appears on the flange tip or at the lip. Photographs without a scale do not establish severity. Mark a sample with coil heat, mill configuration and measurement points, then compare body and cut ends. The C/Z/U/Sigma purlin line is the usual equipment family for this discussion.
Check the strip before the mill
A correctly aligned mill can still wave if the incoming strip is already strained at the edge. Review:
- Slitting-edge burr, smear or work-hardened lip from the upstream slitter.
- Camber and crossbow on the decoiled strip, measured before the first pass.
- Thickness variation across the width, especially on structural-grade coil.
If a known-good coil of the same specification runs clean, the mill is not the first place to recut. Coil preparation is covered in the slitting and leveling planning note and the coil processing line.
Entry guides and early passes
Over-tight entry guides, mis-set side rolls or an aggressive first-pass bite put extra longitudinal strain into the edge before the web has been supported. Loosening a guide without recording the previous setting is not a trial method. Write down gap, height and which station was moved.
Flower pattern and shared C/Z stations
Combined C/Z mills share early passes. A flower pattern that is acceptable for one section can over-strain the edge of the other. Do not assume a simulation package is included in a tooling review. Agree whether the review is a drawing check, a station-by-station gap sheet, or a loaded trial on the intended coil. Related forming defects such as twist and end flare are discussed in the springback planning guide and the end-flare and cutoff note.
What to send for a review
A useful pack is: profile revision, material ticket with thickness in millimetres (not gauge alone), photos of the wave with a scale, and which mill configuration was running. Use the project enquiry form rather than an unmarked video. This article is diagnosis planning, not a promised correction angle or a machine rating.