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Stop-Cut, Flying Shear, and Twist-Break on Purlin Lines
Table of Contents
- Definition
- Common cut-off variants
- When each variant fits
- Speed reading rule
- Front vs rear shear
- Boundaries
- Buyer FAQ
- References
1. Definition
Cut-off type is a configuration choice on the same C / Z / U purlin product family. It affects achievable production speed, noise, blade change practice, and auxiliary motors. One shear variant is not the only public standard.
2. Common cut-off variants
| Variant | How it works | What changes on the quote |
|---|---|---|
| Stop-cut / hydraulic cut-to-length | Line stops or slows; hydraulic shear cuts the formed section | Common on standard Automatic-class packages; simpler mechanics, throughput limited by stop/start |
| Flying shear / flying saw | Cut carriage synchronizes with the moving profile (non-stop or near-continuous) | Higher speed tiers; adds saw/shear motor power — e.g. flying-saw motor about 15 kW on some C/U references |
| Twist-break (twist shear) | Hydraulic twist-style cut on the formed purlin; tight blade spacing for clean ends on some heavy/structural packages | Alternate cut package; size changes may require blade attention unless an “infinite” companion shear is fitted |
Industry literature also separates pre-cut (flat strip before the mill) from post-cut (after forming). Pre-cut can share one flat blade across sizes; post-cut favors end geometry. Flying systems are usually post-cut implementations.
3. When each variant fits
- Moderate cuts/hour, longer lengths, simpler maintenance → stop-cut often enough
- Continuous speed and high cuts/hour → flying shear / flying saw
- Heavy structural packages needing tight end quality → twist-break (confirm with named proposal)
4. Speed reading rule
Compare production speed only when punch method and shear type match. A flying-shear tier is not interchangeable with a stop-cut tier without re-quoting. Example: gearbox + flying-saw packages on C or U lines may cite about 30 m/min, while flying-shear U references sit around 8–10 m/min — different packages.
5. Front vs rear shear
Z-purlin packages document both front (pre) shear and rear stop-cut layouts. State which is quoted. Some lines carry both pre-cut and post-cut stations for threading and final length.
6. Boundaries
- Shear variants are configuration options on the same C/Z/U family — not new product-line IDs by default
- Do not paste flying-shear speed onto a stop-cut quote
- Process spine overview → purlin process-flow encyclopedia entry
7. Buyer FAQ
Is flying shear always better?
Not always. For moderate cut frequency and long lengths, stop-cut can be simpler and sufficient. Flying systems pay off when cuts/hour and continuous speed dominate.
Is twist-break the same as flying saw?
No. Twist-break is a distinct cut mechanism; flying saw is a synchronized moving cut. Ask for the named package.
Do I need a new product line ID for each shear?
No — they are configuration variants on the same C/Z/U family, confirmed in the technical proposal.
Pre-cut or post-cut — which should I pick?
Pre-cut favors multi-size flat-blade sharing; post-cut favors formed-end geometry. Flying systems are usually post-cut. Match the drawing and mix of sizes.
Final ratings follow the confirmed technical proposal for the named cut package. Price and lead time are out of scope.
References
- Technical FAQs for C purlin, Z purlin, and U channel lines (shear / cut-off configuration notes)
- FAQ — flying vs stop-cut: Hydraulic flying cut-off vs stop-and-cut
- FAQ — twist shear package: Flying-cut twist shear and infinite shear on CZ purlin packages
- FAQ — variants on same family: Flying / pre-cut / post-cut on CZ purlin machines
- FAQ — pre-cut vs post-cut: Pre-cut versus post-cut rollforming lines